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ONSALA RYMDOBSERVATORIUM CHALMERS TEKNISKA HÖGSKOLA ONSALA SPACE OBSERVATORY CHALMERS UNIVERSITY OF TECHNOLOGY

STRATEGIC PLAN 2012 – 2016

Onsala Space Observatory The Swedish National Facility for Radio Astronomy

The Onsala site with the radome-enclosed 20m telescope in the centre, the 25 m telescope to the left, and the LOFAR station to the right.

This report presents the Strategic Plan of the Onsala Space Observatory (OSO) for the years 2012 to 2016, with a view towards the years that follow. It was approved by the OSO Steering Committee on its meeting May 3, 2012. At the end of this period the APEX project is probably nearing its lifetime, which will release operations resources. This period also coincides in time with the pre-construction phase of the SKA project. Therefore, 2016 is a timely date for a revision of the strategic plan. Onsala, August 14, 2012

Hans Olofsson Director, Onsala Space Observatory

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The Content 1. Onsala Space Observatory and its mission p. 2 2. Astronomy and geoscience p. 3 3. Brief description of the present situation p. 5 4. Considerations for the future p. 12 5. Investments and operations costs p. 18 6. The strategic plan p. 22 Appendix A. Science cases p. 31 1. Onsala Space Observatory and Its Mission Onsala Space Observatory (OSO) is the Swedish National Facility for Radio Astronomy. The Swedish Research Council (VR) evaluates and finances the activities of the Facility, which is operated by Chalmers University of Technology (Gothenburg). Organisationally, it is part of the Department of Earth and Space Sciences. The operation costs are covered by VR, Chalmers, and a TransNational Access grant through the EU-financed RadioNet3 project. External funding for R&D and construction are sought separately. Presently, OSO is involved in four EU-financed projects: ALMA Enhancement Programme (FP6), NEXPReS (FP7), PrepSKA (FP7), and RadioNet3 (FP7). Chalmers and VR jointly select a Steering Committee for the National Facility.

OSO’s mission is to support high-quality research within the areas of radio astronomy and geoscience through its activities at the Onsala site and through international collaborations. The instrumentation offered builds on the technology and methods developed for radio astronomical research. The activities are briefly outlined in Sect. 3. The long-term strategic planning is guided by scientific questions that are central to contemporary astronomy and geoscience as described in Sect. 2.

OSO’s headquarter is located on the Onsala peninsula about 45 km south of Gothenburg, where it operates three radio astronomical telescopes and geoscience instrumentation. It is also involved in a number of international projects, including being a partner in a collaboration operating a telescope in Chile.

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2. Astronomy and Geoscience In this section we briefly present the main science drivers within astronomy and geoscience. Electromagnetic radiation at radio wavelengths originate in high-energy phenomena (compact binary systems, supernovae, pulsars, active galactic nuclei, etc.), in the cold phases of our Universe (the circumstellar medium, the diffuse interstellar medium, and the denser regions where stars and planetary systems form), and it carries the oldest observational information on the young universe, the cosmic microwave background. In this way radio astronomical observations contribute to essentially all aspects of astronomical research. The information is complementary to that obtained at other wavelengths, and quite often unique.

The geoscience activities are based on the measurements of a number of crucial parameters of the Earth, e.g., its rotation and the crustal motion, combined with measurements of the atmosphere and the hydrosphere. Such observations are of great importance for the understanding of processes of the solid Earth, its oceans, and its atmosphere. Hence, they are important for monitoring and understanding changes in the climate of the Earth. In addition, they are crucial for the determination of the terrestrial and celestial reference frames and their relation. 2.1 Astronomy The goals of modern astronomy are particularly well described in the Science Vision document (http://www.astronet-eu.org/spip.php?article149) of Astronet (a project supported by the European Commission, and the funding agencies within Europe, aimed at identifying the most important questions within contemporary astronomy and suggesting a technological roadmap for infrastructures required to answer these). They are summarised under four headings, and exemplified by a number of sub-questions: i) Do we understand the extremes of the Universe? - How did the Universe begin? - What is dark matter and dark energy? - Can we observe strong gravity in action? - How do supernovae and gamma-ray bursts work? - How do black hole accretion, jets and outflows operate? - What do we learn from energetic radiation and particles? ii) How do galaxies form and evolve? - How do the first stars and galaxies form after the Dark Ages? - What are the dominant sources for re-ionization of the Universe? - How did the structure of the cosmic web of galaxies and intergalactic gas evolve? - What are the histories of the production of the metals in the Universe? - How was the present-day Hubble sequence of galaxies assembled? - What is the detailed history of the formation and evolution of our own Galaxy? iii) What is the origin and evolution of stars and planets? - How do stars form? - Do we understand stellar structure and evolution? - What is the life cycle of the interstellar medium and stars? - How do planetary systems form and evolve? - Is there evidence for life on exoplanets? iv) How do we fit in? - What can the Solar System teach us about astrophysical processes? - What drives Solar variability on all scales?

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- What is the impact of Solar activity on life on Earth? - What is the dynamical history of the Solar System? - Where should we look for life in the Solar System? These questions embrace essentially all of astronomy. It is the aim of OSO to provide, or facilitate the use of, radio astronomical instrumentation which can be used to successfully unravel the answers to many, if not all, of these questions. This is outlined in more detail in Appendix A, where a number of science cases are presented. 2.2 Geoscience OSO operates geoscience instrumentation with the goal to provide the national and international geoscience research community with observations that allow studies of the complex system Earth. The system Earth with its atmosphere, oceans, cryosphere, land surfaces, and its interior is subject to a multitude of dynamical processes, which cover a broad variety of spatial and temporal scales, all affecting our life and the life of future generations. In modern times there are man-made influences on these processes, and their impact is still to a large extent unknown. Major decisions that human society has to take in the near future depend on a much deeper understanding of the complex system Earth.

This requires large international efforts. The international geoscience community has started collaborations that strive to achieve this goal. One example is the international geodetic community that currently builds up the Global Geodetic Observing System (GGOS). GGOS aims at providing global-scale observations and models for spatial and temporal changes of the shape of our planet, of the oceans, the cryosphere, and the land surfaces. Additionally, it will provide Earth rotation data and information on mass transport and mass exchange in the Earth system. The backbone for GGOS is the international network of fundamental geodetic stations that provide observations of the three major components of geodesy, i.e., Earth rotation, geometry, and gravity.

The National Facility is the only Fundamental Geodetic Station in Sweden and operates instrumentation to observe Earth rotation – primarily with a radio telescope for geodetic Very Long Baseline Interferometry (VLBI), geometry – primarily with VLBI and instrumentation for Global Navigation Satellite System (GNSS) measurements, and gravity – with a superconducting gravimeter. Additionally, it operates geoscience sensors such as a tide gauge, a seismometer, and several microwave radiometers for atmospheric studies.

The integration of the three components of geodesy is essential for global-change research and will allow studies of deformation processes, mass anomalies and transport inside individual parts of the Earth system, mass exchange between different parts of the Earth system, and the exchange of angular momentum in the Earth system. Complex phenomena like glacial isostatic adjustment, sea-level rise, the hydrological cycle, transport in the oceans, and the dynamics of the troposphere and ionosphere can thus be studied. For example, there is evidence that geodetic VLBI is the most accurate method available today to measure the water vapour content of the atmosphere over long time scales. As water vapour is an effective greenhouse gas, and its saturation pressure is strongly dependent on the temperature, VLBI may provide the ultimate calibration to denser networks of radiosonde stations and GNSS sites used in climate research.

It is of major importance for global change studies that the original observations – provided by the international network of fundamental geodetic stations – are consistent in space and time having a reproducibility for baseline measurements on the global scale of as high as 1 part-per-billion over decades.

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3. Brief Description of the Present Situation 3.1 Activities OSO operates a 25 m cm-wave telescope, a radome-enclosed 20 m mm-wave telescope, and a LOFAR (Low Frequency Array) station for m-wave studies at Onsala, Fig. 1. The 25 m telescope is used for astronomical VLBI observations, the 20 m telescope is used for single-dish, astronomical VLBI, and geodetic VLBI observations, and the LOFAR station is part of a European network (see below).

Fig. 1. The 25 m telescope (left), the 20 m telescope (middle), and the LOFAR station (right) at Onsala.

OSO is also involved in a number of international radio astronomical projects. It is one of three partners that operate APEX (Atacama Pathfinder Experiment; a 12 m sub-mm telescope) at 5100 m of altitude on Llano Chajnantor in northern Chile, Fig. 2. The other partners are the Max-Planck-Institute for Radio Astronomy (MPIfR) and the European Southern Observatory (ESO). In addition to the telescope, an observing base (with dormitories, restaurant, offices, laboratories, and control room) is operated in Sequitor (on the outskirts of the city San Pedro de Atacama) at an altitude of 2500 m.

Fig. 2. The APEX 12 m sub-mm telescope on Llano Chajnantor (at 5100 m altitude) in the northern part of the Atacama desert in Chile.

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OSO is involved in astronomical very long baseline interferometry (VLBI) as a

partner of the European VLBI Network (EVN; http://www.evlbi.org/), which regularly connects about 20 radio telescopes within Europe (and China, Russia, South Africa, and the US), Fig. 3, and as a partner of global VLBI. OSO is also a paying member of the Joint Institute for VLBI in Europe (JIVE, a Dutch foundation; http://www.jive.nl/), the EVN correlator and support centre in the Netherlands.

Fig. 3. The European VLBI Network (EVN) of radio telescopes spread over the globe. The LOFAR activities are channelled via the International LOFAR Telescope

(ILT; a Dutch foundation; see http://www.lofar.org/), but LOFAR is operated by ASTRON (Netherlands Institute for Radio Astronomy), Fig. 4. OSO contributes to the central operation cost of the ILT. A 10 Gb/s dedicated light path to Stockholm has been installed to accommodate activities within LOFAR (and VLBI), and OSO pays the data transfer to Amsterdam.

Fig. 4. The present composition of the International LOFAR Telescope.

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OSO is involved in the Atacama Large Millimeter/submillimeter Array (ALMA;

http://www.almaobservatory.org/), an international project which is currently installing the world’s largest mm- and sub-mm-wave radio interferometer on Llano Chajnantor, Fig. 5. OSO has designed and built six heterodyne receiver cartridges for the ALMA Band 5 (covering the range 163 – 211 GHz), and it hosts the Nordic ALMA Regional Centre (ARC) node to support the use of ALMA in the Nordic (and also the Baltic) countries. OSO also designed and tested the prototype of the ALMA water vapour radiometer, as well as designed the layout of the telescope locations (the configurations). Early science (cycle 0) observations started in autumn 2011 with at least 16 telescopes in operation.

Fig. 5. ALMA at Llano Chajnantor in mid autumn 2011 with 19 telescopes on the high site.

OSO has in the last few years begun a significant involvement in the Square

Kilometre Array (SKA; http://www.skatelescope.org/), an international project with the aim to build the world’s largest m- and cm-wave radio interferometer (a project on the ESFRI list, and top-ranked on the Astronet technological roadmap for astronomical infrastructure) to be located in Australia and South Africa with neighbouring countries. OSO represents Sweden on the SKA Organisation Board, which is presently in charge of the project. It is a member of the European SKA Consortium (ESKAC), a consortium with the aim to support the SKA as a global project with considerable European involvement.

Another essential part of the OSO activities is the development of high-sensitive radiometers to be used for radio astronomical research. The Group for Advanced Receiver Development (GARD), located at Chalmers, is well established internationally, in particular through its cryogenically-cooled, low-noise, heterodyne receivers (Fig. 6), and is known for its research and technological innovations. It has developed frontends for the two Onsala telescopes, developed the APEX heterodyne facility receiver (four bands in the range from 210 GHz to 1.4 THz), and it has developed and built six receiver cartridges for ALMA Band 5.

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Fig. 6. Fabrication of SIS devices (the critical element of mixers that utilizes a quantum mechanical effect to reach high sensitivity) in the clean room facility at Chalmers.

The geoscience activities are centred on geodetic VLBI. OSO is a partner in the International VLBI Service for Geodesy and Astrometry (IVS; http://ivscc.gsfc.nasa.gov/), a network of about 35 radio telescopes around the world, Fig. 7, which contributes to the International Earth Rotation and Reference Frame Service (IERS). OSO operates the most accurate site in the national ground-based GPS/GNSS network SWEPOS (operated by the Swedish Lantmäteriet; GNSS = Global Navigational Satellite Systems), and it is one of the fundamental sites in the EUREF Permanent Network (EPN), and in the International GNSS Service (IGS). Absolute and relative gravimeter measurements are also supported by OSO and they contribute e.g. to the Global Geodynamics Project (GGP). In this way, OSO has the status of a Fundamental Geodetic Station (FGS) in the sense of GGOS, i.e., it contributes to the three pillars of geodesy: geokinematics, Earth rotation, and the gravity field of the Earth.

Fig. 7. IVS stations contributing to geodetic VLBI. Stations with a white dot are recognized Fundamental Geodetic Stations in the sense of GGOS, i.e. they contribute to the three pillars of geodesy: geokinematics, Earth rotation, and the gravity field of the Earth. Complementary measurements are provided with tide-level gauges (which

measure the water level in the sea outside Onsala), and a seismograph (operated in collaboration with Uppsala University). An aeronomy station measures the

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atmospheric content of H2O, CO, and O3 at Onsala as part of the Network for the Detection of Atmospheric Composition Change (NDACC).

A time and frequency laboratory, based on two hydrogen masers, is operated in collaboration with the SP Technical Research Institute of Sweden. Among other things this contributes to the determination of TAI (International Atomic Time), and participates in the Swedish time-distribution system.

Outreach activities include e.g. guided tours of the Observatory (about 2500 people, of all ages, per year), popular talks at a variety of occasions, participation in science festivals, and a student radio telescope system that can be used by students visiting the Onsala site or via the web, Fig. 8. An exhibition describing astronomy in general, radio astronomy and its techniques in general, and the history of the observatory, is installed in the old control building of the 25 m telescope. Press releases are regularly released.

Fig. 8. Two student radio telescopes, SALSA on the Onsala site, equipped to observe cosmic hydrogen. OSO is represented in the following international boards/committees: - Atacama Pathfinder Experiment (APEX) Board - ESF Committee on Radio Astronomy Frequencies (CRAF) - European SKA Consortium (ESKAC) Board - European VLBI Network (EVN) Board - GGOS Inter Agency Committee (GIAC) - International Earth Rotation and Reference Frame Service (IERS) Directing Board - International LOFAR Telescope Board - International VLBI Service (IVS) Directing Board - Joint Institute for VLBI in Europe (JIVE) Board - NEXPReS (Novel Explorations Pushing Robust e-VLBI Services) Board - Nordic Geodetic Commission (NKG) Working Group on Infrastructure - PrepSKA (Preparatory Phase Project for the Square Kilometre Array) Board - RadioNet3 (Advanced Radio Astronomy in Europe) Board - SKA Board of Directors Astronomical observing time is distributed via peer-review systems, and OSO endorses the open-sky policy. A Time Allocation Committee (TAC) exists for astronomical programmes on the Onsala 20 m and APEX telescopes, while astronomical VLBI programmes are allocated via the EVN TAC, and observing time on LOFAR is allocated by the ILT TAC. The geodetic VLBI observing programme is handled by the IVS. The observations are performed by the scientists themselves or in service mode. The GNSS, gravimeter, and aeronomy station data are made available via public archives.

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3.2 Economy 3.2.1 Revenues in 2012 The total operations costs are covered by three sources: VR ≈ 36 Mkr Chalmers ≈ 14 Mkr RadioNet3 TNA ≈ 1 Mkr Income for infrastructure and R&D comes from various sources: ALMA, ALMA Band 5 Full Production ≈ 50 Mkr (2012–2016) EU, ALMA Enhancement Programme ≈ 50 Mkr (2006–2012) KAW, Twin-telescope System ≈ 30 Mkr (2013–2019) NEXPReS ≈ 2.7 Mkr (2010–2013) PrepSKA ≈ 0.5 Mkr (2012) RadioNet3, AETHER ≈ 1.1 Mkr (2012–2015) RadioNet3, DIVA ≈ 2.2 Mkr (2012–2015) 3.2.2 Expenditures in 2012 The operations costs of the individual activities have been identified. To this has been added the costs for facility management and administration, rent, electricity, etc., in proportion to the specific cost of each activity. The figures are: - 20 m mm-wave single dish observations ≈ 6.6 Mkr - VLBI, EVN ≈ 9.2 Mkr - LOFAR ≈ 4.3 Mkr - APEX ≈ 14.6 Mkr - ALMA, Nordic ARC node ≈ 3.4 Mkr - Geoscience activities ≈ 5.2 Mkr - Outreach ≈ 1.7 Mkr The operations cost of the 20 m telescopes has been divided among the single dish, astronomical VLBI, and geodetic VLBI activities in proportion to the time used for these activities. In addition to this we have R&D and construction costs for the following activities: ALMA Band 5 cartridge production, AETHER and DIVA, NEXPReS, 3mm receiver upgrade, ultra-wide-band feeds (VLBI2010 & SKA), and SKA: - R&D and construction ≈ 15 Mkr 3.3 Staff in 2012 The personal per activity is difficult to give in exact terms, since a fair fraction of the staff members work in more than one activity. Therefore, the staffing situation is given in two ways, per group and per activity. In rough terms the situation looks like this (in terms of full time equivalent, FTE) in 2012:

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i) Group: - Facility management 2 FTE - Administration and economy 2 FTE - Electronics laboratory 6 FTE - Advanced receiver development (GARD) 10 FTE - Mechanical workshop, buildings, … 4.5 FTE - Computers, network, … 4 FTE - Support astronomers (excl. ARC) 3.5 FTE - Nordic ARC node 2.5 FTE + 1 ESO fellow - SKA R&D 1.3 FTE - Support geoscience 1.7 FTE - Outreach 1.4 FTE Total 39 FTE ii) Activity: - 20 m mm-wave single dish observations 6.3 FTE - VLBI, EVN 7.0 FTE - LOFAR 1.5 FTE - APEX 4.0 FTE - ALMA, Nordic ARC node 3.2 FTE + 1 ESO fellow - Geoscience activities 4.4 FTE - Outreach 2.0 FTE - R&D 10.7 FTE For each activity the FTEs on management and administration are added in proportion to the specific cost of the activities.

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4. Considerations for the Future 4.1 Astronomy The astronomical observational activities within OSO today can be summarized as follows in terms of wavelength range: m-waves: LOFAR cm-waves: EVN (20 m and 25 m telescopes) mm/sub-mm-waves: 20 m telescope APEX ALMA The future astronomical activities will consist of a subgroup of the following: m waves: LOFAR – 2020:ies (or longer) SKA 2020 – 2050:ies cm waves: EVN – 2020:ies (or longer) SKA 2020 – 2050:ies eMERLIN 2013 – mm/sub-mm waves: 20 m telescope APEX 2015 (– 2017 or longer) ALMA – 2030:ies (or longer) CCAT 2018 – NOEMA 2015 – These various activities will be described in some detail below, while the science cases for SKA, astronomical VLBI, mm-wave observing at the 20 m telescope, APEX continuation, and CCAT are given in Appendix A. 4.1.1 m and cm waves: At metre and centimetre wavelengths the OSO activities come primarily via our participation in interferometer projects. Present operational activities are LOFAR (at m wavelengths) and VLBI (at cm wavelengths). Technical development is ongoing in preparation for the future SKA instrument which will operate at both m and cm wavelengths.

The Onsala LOFAR station, which was officially opened on Sept 26th 2011 by the Swedish minister of education, is now integrated into the European LOFAR network, the International LOFAR Telescope (ILT). It is fully involved in the ongoing ‘Multi-wavelength Sky Survey’ observations. Additionally, a single-station mode is being implemented to observe pulsars and fast transients and to allow experiments with radar astronomy of solar system objects. A national consortium of astronomers (LOFAR-Sweden) has been organised to distribute the national observing time that Sweden receives in return for its involvement in the ILT. LOFAR is recognized as an SKA pathfinder. OSO will remain committed to the LOFAR collaboration well into the 2020:ies.

Centimetre wavelength observations at Onsala are almost entirely via using the 25 m and 20 m telescopes within European and Global VLBI arrays. VLBI has a unique and irreplaceable role as the highest-resolution imaging and astrometric method in astronomy, and it will be further developed in the coming decades. The real-time mode of VLBI (e-VLBI) is a recognized SKA pathfinder. The US Very Long Baseline Array

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(VLBA) will most likely decrease its availability for VLBI, greatly increasing the dominance of the EVN (which despite its name includes stations in Russia, China, South Africa, and Puerto Rico). In the coming years the EVN may also be complemented by the African VLBI Network (AVN; a proposed telescope network in Africa for VLBI based on available satellite communication dishes) with which it will co-observe. The OSO VLBI activity includes an operational contribution to JIVE, the organisation that operates the EVN correlator and supports the EVN operation in general.

The EVN has a bright future as the dominant instrument for VLBI in the coming decade and through the SKA era, in particular at the shorter wavelengths not covered by the SKA. This was amply accentuated in the recent evaluation of JIVE and the capabilities of European astronomical VLBI. We quote from the report “The Review Committee was very impressed indeed by the effectiveness of JIVE and its achievements.”, “In our view, JIVE has a major role to play in the future development of precision astronomy and astrometry.”, “The Committee strongly recommends the continuation of the present programme with all the planned enhancements of the facilities.”, and “The EVN and JIVE teams should grasp the opportunities for innovative science which will be of great interest outside the traditional VLBI community. There is great potential for expanding the scope of VLBI observations to much wider areas of astrophysics than in the past and this should be proactively supported by the staff of EVN/JIVE.”

Furthermore, the VLBI activities at OSO over more than 40 years have laid the base for OSO’s involvement in ALMA, LOFAR, and SKA. We envision that astronomical cm (and mm) VLBI will remain a core activity of OSO, but in the future the 20 m telescope will increasingly replace the 25 m as our workhorse for VLBI. Although one of the smaller dishes of the EVN, it is one of a few telescopes that also does mm-wavelength VLBI – its accurate surface gives it an high aperture efficiency also at the highest frequencies used for VLBI. As the achievable bit rate of VLBI increases continuum observations will be forced to ever higher frequencies just to accommodate the high spanned bandwidth – making high-frequency-capable antennas of increasing importance within the EVN. However, in order to serve a role in VLBI the radome of the 20 m telescope, which is rapidly ageing and is well beyond the guaranteed lifetime, must be replaced.

We are presently in the design phase of moving the VLBI observations at C-band (i.e., 4.5 – 7 GHz) to the 20 m telescope from the 25 m telescope, where the efficiency and pointing accuracy only marginally allow observations. The lowest VLBI frequency band (L-band, 1.2 – 1.8 GHz) cannot be practically moved to the 20 m telescope and so this frequency will remain at the 25 m telescope. However, the 25 m telescope is old (almost 50 years) and even though it is well maintained there is always a risk that a fatal problem can arise. An interesting possibility to consider for the longer term would be to replace the 25 m with a small array of cheap telescopes developed for the SKA project. This approach could also give a larger collecting area (equivalent at least to a 30 m diameter dish).

Another possibility, related to the VLBI activities, is that the Onsala telescopes join the eMERLIN cm-wave radio interferometer in the UK to increase its sensitivity and angular resolution (http://www.e-merlin.ac.uk/).

SKA is the next major global project within radio astronomy and is driven by a number of internationally-recognised high-priority scientific questions. SKA will be built on the same overall design as LOFAR, stations displaced by baselines up to 3000 km connected via a fibre link network (Fig. 9). A dual-site solution with telescopes in both Australia and South Africa has been adopted. SKA will be implemented in (at least) two phases, with SKA phase 1 (SKA1) focussing on the longer wavelengths and having only part of the final collecting area, while SKA2 completes the full collecting area and adds shorter wavelengths. There are very strong arguments for Swedish participation in this project, both scientifically and technologically.

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SKA has in 2012 just entered its pre-construction phase that will last four years until 2015. During this phase the agreed Project Execution Plan (PEP) will be implemented by the SKA Project Office (SPO); the estimated total funding requirement for this phase is 91 M€ over 4 years. A legal entity in the form of a Brittish company, the SKA Organisation Ltd, was established in December 2011 to lead the SKA project through this phase. The following countries have signed the MoU which establishes the company, Australia, Canada, China, Italy, the Netherlands, New Zealand, South Africa, Sweden (represented by OSO), and the United Kingdom, and India has become an associated member. Germany is expected to sign in the near future. Aspiring countries (which may be invited as guests to SKA Organisation Board meetings) include Brazil, France, Japan, Korea, and Spain. The pre-construction phase will be followed by the SKA1 construction phase starting in 2016, and the SKA2 construction phase starting in 2020. SKA1 science operations are projected to start in 2020 and SKA2 science operations in 2024.

OSOs involvement within the SKA has ramped up considerably during the last years. Within the PrepSKA project OSO is involved both with studies of aperture array calibration and single-pixel ultra-wideband feed (UWBF) development for dishes, the latter development being partly funded by a contract with the SKA Project Development Office (SPDO). The latter work is being done in close collaboration with the Chalmers Antenna group. Jointly with this group Master and PhD students are involved in examining the performance of UWBFs in dishes, phased array feeds (FAPs), and receiver noise modelling. The latter as part of an exchange programme with South Africa, one of the SKA siting countries.

Fig. 9. Three types of “telescopes” will be used in the SKA stations, sparse aperture arrays for the longest wavelengths (left), dense aperture arrays for the mid-wavelength range (middle), and parabolas for the shorter wavelengths (right) (artist’s impressions). 4.1.2 mm- and sub-mm waves: OSO has a strong tradition and a significant technology heritage in this area. The Onsala 20 m telescope was the world’s largest mm-wave telescope for about a decade. It lead eventually to the very successful Swedish ESO Submillimetre Telescope (SEST) collaboration with the European Southern Observatory (ESO), the subsequent APEX collaboration with ESO and the MPIfR, and to the involvement at an early stage in the ALMA project. The receiver developments within OSO are performed by GARD, and they are focussed on heterodyne receivers for the mm and sub-mm wavelength ranges. Considering this glorious history within radio astronomy at short wavelengths one must seriously consider how these activities can be continued in the future.

Astronomical research using the ‘single-dish’ capability of the Onsala 20 m telescope has suffered from the lack of funding to keep its mm-wave instrumentation at the top level at the same time as SEST and later APEX required investments in manpower and money. At the same time, there are few telescopes in the world capable of doing mm-wave observations, and the telescope is well maintained. Onsala is not a perfect site for mm-wave observations, but the scarcity of mm-wave telescopes makes it fairly easy to identify niches where very important astronomical observations can be pursued with the 20 m telescope, e.g. using broad-band receivers for spectral line

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surveys and radio cameras for mapping projects. The major problem is the radome, which has passed well beyond the guaranteed lifetime, shows definite signs of aging, and must be replaced.

APEX is undoubtedly the flagship in this area for the moment, but the present agreement to operate the telescope ends at the end of 2015. However, all parties have opened up for an extension until, at least, 2017 provided that an evaluation of the project in 2013 strongly recommends continued operation. This is a sufficiently long time of operation to consider the possibility of new receiver investments, e.g., in the form of heterodyne receiver arrays or new single-pixel receivers at frequencies not covered by ALMA (e.g., THz frequencies). Array receivers are expensive, but can be done in collaboration with other partners (even outside the APEX partners).

A large part of the mm/sub-mm activities will also be focussed on ALMA. The Nordic ARC node will continue and expand its role in supporting Nordic ALMA users in making observing time applications and reducing both their own and archive data. Another long-term role of the ARC node will be to develop new advanced methods of observing, of data reduction, and to contribute data-reduction algorithms and software to the ALMA project. The full production of ALMA Band 5 receiver cartridges has recently been approved by the ALMA Board. NOVA (NL) and OSO/GARD will together with NRAO (US) build 67 receiver cartridges. The full cost of ALMA is ≈ 1.3 B$, and the Swedish share of ALMA investments and operations is covered via its ESO contribution.

Given this strong expertise of OSO, continued activity on the sub-mm-wave arena beyond APEX should be a part of the OSO strategic plan. There are two obvious possibilities discussed briefly here. The Caltech-Cornell Atacama Telescope (CCAT; http://www.submm.org/ccat.html) is a very ambitious project aimed at installing and operating an enclosed 25 m sub-mm telescope on Cerro Chajnantor (i.e., on a mountain summit above the APEX and ALMA plateau), Fig. 10. It will have a surface accuracy of 10 µm (rms) allowing observations up to 2 THz. The field of view will be as large as 20’. This project was very highly rated in the US decadal astronomy review Astro2010 ‘New Worlds, New Horizons in Astronomy and Astrophysics’ carried out by the National Research Council of the National Academies. The expected spending profile extends over 6 years, and regular observations are presently expected to commence in 2018. There are interested parties in the US, Canada, Germany, and the UK, but the project is not yet fully funded. The THz activities of OSO’s receiver group GARD would fit nicely into such a project, and the Swedish scientific interest is strong. The CCAT collaboration has shown an interest to involve OSO in its work.

Fig. 10. The proposed radome-enclosed 25 m Caltech Cornell Atacama Telescope (CCAT) on Cerro Chajnantor (5600 m of altitude; artist impression).

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Another potential project is the extension of the Plateau de Bure Interferometer (Northern Extended Millimeter Array, NOEMA) located outside Grenoble and operated by the German-French-Spanish consortium IRAM (Institute Radioastronomie Millimetrique; http://www.iram-institute.org/). Through almost doubling the collecting area (from 6 to 10 telescopes), increasing the baseline lengths, and adding more sensitive receivers with broad band performance, it will make NOEMA almost comparable in sensitivity to ALMA for continuum observations in the 1 – 3 mm range, but with a poorer uv-coverage (10 telescopes compared to ALMA’s 66). NOEMA will cover the parts of the northern hemisphere not reachable by ALMA. This project has a lower attractiveness considering that Swedish astronomers already have the possibility to use ALMA, and it is questionable whether there will be any technological collaborations suitable for OSO in this project. For these reasons, this project is not further considered in the strategic plan. 4.2 Geoscience OSO has the status of a Fundamental Geodetic Station (FGS) in the sense of GGOS, i.e., it contributes to the three pillars of geodesy: geokinematics, Earth rotation, and the gravity field of the Earth. Recently, OSO applied, together with Lantmäteriet, to be recognized as a GGOS Core Site. The international network of FGSs forms the backbone of the Global Earth Observation System of Systems (GEOSS), which is an international initiative by governments and international organizations to exploit global Earth observations to support decision making. These activities support the national networks SWEPOS and the Swedish National Seismic Network (SNSN), and the collaborations with the SP Technical Research Institute of Sweden and the Swedish Meteorological and Hydrological Institute (SMHI).

Any foreseeable major infrastructure investments will come in the area of geodetic VLBI. IVS, which is organising the international geodetic VLBI activities of the 35 IVS-stations, has adopted a technological roadmap, VLBI2010, which outlines a scenario where the IVS-stations have one or more telescopes that can switch fast from source to source, and that are equipped with state-of-the-art VLBI equipment (for data storage or real-time data transfer at rates of about 8 Gb/s) and broad band receivers for observations in the 2 – 14 GHz range, a twin-telescope system. Recently, the Knut and Alice Wallenberg Foundation decided to contribute funding, about 30 Mkr, to the realisation of such a system in Onsala, Fig. 11. Geodetic VLBI at OSO today is performed with the Onsala 20 m telescope. Continuing operations for geodesy with this telescope is desirable even when the new geodetic telescopes are available, both for continuity with historical data and as a backup in the case of bad weather or instrument failure. OSO’s activity in this area is top ranked. It was the most reliable IVS-station during 2008 and 2009.

In addition, necessary investments to maintain and operate the other existing geoscientific sensors are expected, both in terms of techniques and staff competence. The goal is to operate a reliable park of measurement sensors for geoscience applications at the Fundamental Geodetic Station OSO. We aim at synergy with our partners, Lantmäteriet, Swedish Meteorological and Hydrological Institute (SMHI), Swedish National Seismic Network (SNSN), and SP Swedish Technical Research Institute. For the near future, the plan is to install a super tide-gauge station at OSO in collaboration with SMHI.

Finally, it is important to mention in this context that OSO, together with the Antenna group at Chalmers, has developed a cryogenically cooled broad-band feed for VLBI2010 that is now being commercialized by a Swedish company (Omnisys Instruments AB).

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Fig. 11 An artist impression of the Twin-telescope System for geodetic VLBI at Onsala.

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5. Investments and Operations Costs In this section we give estimates of the investments and operations costs of the activities discussed in the previous sections. This forms an important base of a realistic strategic plan, and the investment and operations costs to be covered within the prioritized activities are given in Sect. 6. 5.1 Astronomy 5.1.1 The Onsala Site Continued operation of the Onsala 20 m telescope for astronomical and geodetic VLBI, and single-dish observations can only be performed if a new radome is purchased. Otherwise, the radome and the telescope must be dismantled. The estimated remaining lifetime of the radome is about five years. A quotation for the cost of a new radome has been obtained from the ESSCO company. This should, in principle, be regarded as maintenance rather than an infrastructure investment.

The investment cost of an upgraded broad-band 4/3 mm receiver for the 20 m telescope is estimated based on the experience with the APEX and ALMA receivers (this is also the reason why this relatively complex receiver can be built at such a low cost). A new C-band receiver must be built to operate 6 cm VLBI at the 20 m telescope. Finally, new VLBI equipment, e.g., hydrogen maser, digital base band converters, etc., must be purchased. Investment cost of new radome ≥ 15 Mkr Investment cost of upgrade 4/3 mm receiver ≈ 5 Mkr Investment cost VLBI (C-band, equipment) ≈ 5 Mkr In the longer term (toward the end of this decade) a possible replacement for the 25 m telescope could consist of a small array of, say seven, cheap 12–15 m diameter dishes (e.g., those to be developed in the SKA project). Such a telescope cluster, corresponding to the collecting area of that if a 32–40 m diameter dish) can be used as an interferometer (with a suitable software correlator) and as a phased-up array for VLBI. It is estimated that the total cost per dish (i.e., including receivers) will be ≈ 300 k€. Investment cost of telescope cluster ≈ 20 Mkr It is estimated that none of these investments will seriously change the operations costs for the activities at the Onsala site. 5.1.2 APEX Receivers Utilising the full capacity of APEX until 2017 (and perhaps beyond) will require investment in new array receivers; bolometer cameras as well as heterodyne arrays. The costs of such receivers are difficult to give at this point, and will depend on discussions with the APEX partners during the years to come. Any new receiver will most likely be a multi-partner project because of the costs associated with it. As outlined in Appendix A4 participation in the construction of a 7 pixel 350 GHz and 19 pixel 450 GHz heterodyne arrays receiver (LAsMA) could be of interest to OSO. The cost of such a receiver is most likely of the order 50 M€, and the Swedish share could be 30%, i.e., 15 Mkr. Investment cost of new APEX receiver ≥ 15 Mkr

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5.1.3 ALMA The Nordic ARC node will continue its work to support Nordic (and Baltic) use of ALMA. It is presently staffed with 2.5 FTE which is considered to be adequate also in the future. The investment costs are mainly in the form of computers and they are estimated to be moderate. No hiring of new staff is foreseen.

The production of 67 ALMA Band 5 cartridges is financed within the ALMA Development Program. The OSO/GARD costs for salaries and hardware amount to ≈ 50 Mkr over five years. No hiring of new staff is foreseen. 5.1.4 SKA The total cost of participating in the SKA project is uncertain, but the fee for membership in the SKA Organisation Ltd amounts to a total of 1 M€ spread over 4 years. Sweden is now a member of the SKA Organisation, and it is represented by OSO, which also provides the membership fee. The cost of participating in the development programme during the pre-construction phase depends on the ambition, but an investment at the same level as the membership fee must be regarded as a minimum. Several countries have already committed themselves to 5 M€ or more. This is regarded as the most efficient way to secure industrial involvement once the construction phase starts. The operations and investment costs during the SKA1 and SKA2 phases are estimated based on their accepted costs of 350 M€ for SKA1 and 1.5 B€ for the full SKA, assuming that the host country takes 30% of the cost and Europe 1/3 of the rest, and the Swedish GDP in comparison with the other European partners. The investment costs are estimated to be: Investment cost during 2016 – 2019 (SKA1) ≈ 40 Mkr Investment cost during 2020 – 2024 (SKA2) ≈ 100 Mkr The operations costs are estimated to be: SKA Organisation during 2012 – 2015 ≈ 10 Mkr Development programme during 2012 – 2015 ≈ 20 Mkr Operation cost during 2016 – 2019 (SKA1) ≈ 4 Mkr/yr Operation cost during 2020 – (SKA2) ≈ 15 Mkr/yr Decisions on financial contributions towards construction of SKA1 and SKA2 will come around 2014 and 2018, respectively. 5.1.5 CCAT The minimum share for entering the CCAT project is 5% of the total development and construction costs. The current estimates of the costs of the telescope and associated facilities are based on the analysis carried out in the course of the feasibility study of 2004 – 2006. Including a contingency of 25%, the estimated cost is 110 M$ (including 20 M$ for first-light instruments). The operations cost is divided into two parts, one for technical operation and one for carrying out the surveys. The former is estimated to be 6 M$/yr. It will take considerable effort to design and plan the surveys, to schedule and carry out the observations, to calibrate and process the data, and to produce and release catalogues and other data products to the community in a timely manner and through robust access tools. The present cost estimate for this is 6 M$/yr. We estimate the contribution to these operating costs as 5%. The results are:

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Investment costs during 2014 – 18 ≈ 40 Mkr Operations costs during 2018 – ≈ 5 Mkr/yr 5.2 Geoscience The investment cost for continued participation in the IVS network is determined by the requirements listed in the technological roadmap VLBI2010. It envisions that each IVS station shall have a two-telescope system where each telescope is equipped with a broadband receiver system and a VLBI backend, and that there is fibre link connection for up to 8 Gb/s data rate transfer. The full cost of such a system, based on two low-cost telescopes, and its installation has been estimated to be: Investment cost for geodetic VLBI ≈ 35 Mkr An application to the Knut and Alice Wallenberg foundation for ≈ 30 Mkr was recently approved. The remaining cost (the depreciation cost of the telescopes beyond the five years financed by KAW) will be covered by OSO since the IVS observations are a service activity and user fees are not an option. The operational cost will not differ much from the present one, but we note that minor investments must be done to maintain and operate the other existing geoscience sensors, both in terms of techniques and staff competence. The goal is to operate a reliable park of measurement sensors for geoscience applications at the Fundamental Geodetic Station OSO. 5.3 Summary of Investments and Operation Costs Here we summarize the estimated investments and operations costs described above. These form part of the base for the strategic plan since clearly priorities must be set.

Table 1. Summary of investments costs of the activities discussed in the previous sections.

Table 2. Summary of operations costs of the new activities discussed in the previous sections.

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6. The Strategic Plan 6.1 Introduction It is clear from the previous sections that OSO has considerable expertise in radio astronomical science and technology from m to sub-mm wavelengths, and that the geoscience activities have now matured around a suite of instruments with geodetic VLBI as the centre activity. The strategic plan must consider the appropriate position of the National Facility in an era where ALMA and potentially the SKA will, to a large extent, dominate radio astronomy. In this context, we argue strongly that OSO should fulfil the following roles in the future:

• OSO should act as a support centre for the large, and complicated, international facilities in order to strongly promote the Swedish use of such facilities (the ALMA Nordic ARC node is an excellent example). This support includes both expert staff and optimized large computer resources and software for reduction of radio astronomy data, which are increasing well beyond that which is easily provided at university departments,

• OSO should contribute with technical developments for the large international

facilities, and as such also stimulate industrial involvement (OSO has successfully done so in the case of ALMA; almost 200 Mkr in terms of contracts to OSO and a Swedish company),

• OSO should pursue activities not covered by the large international facilities, but

are deemed important for scientific or technological reasons (e.g., VLBI, and THz observations).

In addition to the pure technical and scientific considerations one must also

consider the value of having an active observatory as a home base. This is something that over the years has played an important role for fostering generations of Swedish radio astronomers capable of playing important roles in radio astronomical infrastructures around the world (e.g., SEST, James Clerk Maxwell Telescope on Hawaii, APEX, and ALMA) and in space (e.g., the Swedish-led satellite Odin and Herschel Space Observatory).

The path forward in the geoscience arena is, for the moment, relatively straightforward:

• OSO will continue develop the Fundamental Geodetic Station.

This means to operate, maintain, and upgrade the existing park of geoscientific

sensors, and to be open for considerations for future additional complementary sensors. The goal is to provide reliable and highly-accurate-measurement data for the national and international geoscience communities. This is to be implemented in collaboration with our partners Lantmäteriet, SMHI, SNSN and SP. A major infrastructure investment for OSO in the near future is coming within geodetic VLBI, and the technological road map is defined and accepted among all partners. The investment cost is, in comparison, relatively modest, and only a limited increase in the operational cost is required.

Financially, the base for the strategic plan discussion is given in Sect. 4 and in Sect. 5, where also estimated time scales for the spending profiles are given (summarised in Tables 1 and 2), and the scientific cases for future activities are given in Appendix A.

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6.2 SKA Among the possible activities listed above the SKA project is a very special case. Its sheer size means that it must be a national project and hence should eventually be handled by VR in the same way as other major infrastructures such as CERN, ESO (e.g., ALMA and, recently, E-ELT), FAIR, and XFEL. Indeed, the SKA Organisation Ltd has, except for OSO, only national funding agencies as members. It cannot be expected that OSO should contribute significantly financially to the operations and investments of such a large project. What OSO has done so far is to invest in scientific and technological know-how relevant for the SKA, e.g., through LOFAR and various recruitments, and it represents Sweden in the SKA Organisation (including providing the membership fee). In the future it is prepared to contribute expertise to various aspects of the project, including technical development and user support after completion, in much the same way as it did (and does) for ALMA. In this way the SKA project will of course affect the priorities within OSO. Due to the magnitude of the project it, as well as the OSO involvement, will be described in some detail below.

The SKA is a project where there is great potential for Swedish industrial involvement, an involvement that should start as early as possible during the pre-construction phase. Developments during this phase will be organised within Work Packages (WPs). There will be calls for tenders for these WPs which consortia of research organisations and companies can bid for (with WP assignments for the first half od the pre-construction phase being decided on by the SKA Organisation board by early 2013). Bidding organisations must be able to guarantee their own national funding; there will not be any central funding from the SKA Project Office for the WPs. In Sweden we have expertise in several important areas of technology and in end-to-end modelling of interferometric imaging. Formally, since Sweden is one of the SKA member states, OSO can lead a WP. The funding level for membership during the next four years is relatively modest, while a decision on a commitment to provide more substantial construction and operations funding for SKA1 need only be made toward the end of the pre-construction phase. OSO personnel are involved in the development of the Work Breakdown Structure (WBS) and the Statement of Work (SOW) against which potential WP consortia can provide bids. This SBS/SOW for stage 1 of the pre-construction phase will be released in October 2012. OSO is also in negotiation with other partners as potential member of a European consortium bidding for WPs in the Dish domain.

In conclusion, the SKA project is heading into a crucial period and through the work of OSO Sweden has a strong foothold in the project. OSO is prepared to invest manpower to further promote Sweden’s position within the SKA, but a firm commitment, also in terms of funding, from Sweden is required in the not so distant future. 6.2.1 SKA Development Work at OSO In the last two years there has been a significant expansion in the OSO involvement in SKA development work, with two new staff members beginning work on SKA modelling issues, and significant work done on developing ultra-wide-band feeds. There is increasingly close and valuable collaboration with members of the Antenna Group at Chalmers. The main areas of SKA development work at OSO/Chalmers are described below.

Ultra wide-band feeds: A vital component of any radio telescope is the feed system that channels radio waves at the focus of the telescope to the low-noise amplifiers where radio waves are converted to electrical signals. Conventional feed systems only span an octave of frequency, consequently it follows that a large suite of such feeds is required to span the full frequency range of an instrument. Ultra-

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wideband feeds (UWBFs) which can span up to a decade in frequency are an active area of research within antenna engineering. Given the thousands of antennas that will be needed for the SKA the prospect of employing UWBFs combined with wide-band receivers offers the prospect of greatly reducing the number of feed-receiver packages, resulting in significant reductions in cost, power consumption, and maintenance load. Additionally, using UWBFs wider range of frequencies can be observed simultaneously improving the sensitivity of continuum observations and the accuracy of astrometry observations. The challenge for UWBFs is to ensure that sensitivity performance stays comparable to conventional feeds over a much wider band.

One of the leading designs of UWBFs for the SKA is the Eleven-feed, which originated with prof. Per-Simon Kildal of the Antenna Group at Chalmers. Compared to other UWBF designs it is simple, extremely compact and has a constant phase centre irrespective of frequency. Over the last few years this design has been jointly developed by OSO, the Chalmers Antenna Group, and the Omnisys Instruments AB (Gothenburg). A version spanning 2 –14 GHz has been developed for geodetic VLBI-use to fit the VLBI2010 specification, and a second version specifically for the SKA has been developed under contract between OSO and the SKA Project Development Office over the last two years. This version is optimised to operate over the 1.2 – 4 GHz frequency range, the goal being to develop a system with equivalent sensitivity to octave feeds, but over this much wider frequency range. Electronic interface circuits for connecting the feed to different types of wide-band low-noise amplifiers have been developed. A complete system model incorporating EM modelling of the feed and noise/gain/matching of receiver components has been developed (including work of joint South-Africa/Chalmers, SIDA funded, PhD student). The predicted final noise performance versus frequency closely matches the results of on-sky measurements.

Work on UWBFs has been identified by the SKA project as one of the components of the Advanced Instrumentation Plan within the SKA pre-construction phase 2012 - 2015. Technologies developed within this program will be used within SKA1 as demonstrators, and, if successful, will beome part of SKA2. OSO plans to lead the work package on UWBFs. Additionally, as part of a possible European prototype antenna consortium OSO intends to be part of the group developing eleven-feeds/amplifier/cooling systems covering the 0.4 – 1.4 GHz and 1.2 – 4 GHz bands, respectively.

Antenna Optics: An important decision within SKA is whether the dish array will use a conventional symmetrical parabola or an offset Gregorian antenna geometry. Work on evaluating the performance of these alternatives, including the effects of different feed designs, has been done by OSO. The resulting simulations allowed estimates of total sensitivity performance to be made including spillover (pickup of noise from the ground). The work on symmetric dishes was incorporated into the design document for the European dish consortium submitted to the SKA Dish Design Review held in Calgary in July 2011. More recently, work on simulations of the performance of UWBFs, in particular the Eleven-feed, as a component of reflector antennas has been done.

Array modelling: Modelling the electromagnetic performance of arrays is important both in the context of the aperture arrays that will be used for the SKA at low frequencies (similar to LOFAR) and of array receivers at the focus of a dish, used to improve field of view, so-called Phased Array Feeds (PAFs). Work in the former area has been conducted by OSO as part of the Aperture Array Verification Programme (AAVP) of the EU-funded programme PrepSKA. Of general application to both areas is a new method of simulating arrays using physics-based basis-functions developed by members of the Chalmers Antenna Group. A VR-funded PhD student will further develop this work incorporating the effects of array calibration using these basis functions to dramatically reduce the number of unknowns that must be solved for. Related work, including the modelling and calibration of non-planar PAFs, will be conducted through a South-African/Chalmers collaboration.

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SKA specifications and end-to-end performance: OSO staff has worked on relating the SKA instrumental polarization specifications to the accuracy of pulsar timing (a major SKA astrophysical goal for detecting gravity waves and testing the equation of state of neutron stars). This specification includes the effects of using observations of astronomical sources to calibrate and correct for instrumental polarisation effects. Additionally, work has started on estimating the impact of the properties of different dish designs (such as symmetric and offset Gregorian) on achievable imaging dynamic range, again after incorporating astronomical calibration.

Work on PEP phase Work Breakdown Structure: An OSO staff member was at the end of 2011 chosen to be a member of the 15-member group of world experts on dishes to define the work breakdown substructure for the next four year Project Execution Plan (PEP) phase of the SKA. This breakdown structure, which was recently finalised, will form the technical basis of bids for work by consortia in the dish area during the next four-year long SKA pre-construction phase. 6.3 The Strategic Plan, 2012 – 2016 The strategic plan for the OSO activities in the period 2012 – 2016, with a view towards the years that follow, is summarised below. At the end of this period the APEX project is probably nearing its lifetime, which will release operations resources. This period also coincides in time with the pre-construction phase of the SKA project. Therefore, 2016 is a timely date for a revision of the strategic plan. Apart from the costs for participation in an SKA Work Package Consortium, and the possible participation in an APEX receiver project, the investment costs are moderate for the coming five years. Also the operations costs are expected to be only marginally increased during this period. In addition to the operations and technical developments, the promotion of the use of radio astronomical facilities by Swedish scientists is a key activity for OSO. Through the Nordic ARC node and the Swedish LOFAR Consortium we have established platforms through which such an activity can be efficiently operated. The former has, as one of its prime roles, the promotion of the use of ALMA, but it is used also to run schools and workshops on radio astronomical techniques and science in general. As examples, OSO has together with the Nordic Optical Telescope (NOT) arranged three successful summer schools, which included active use of the Onsala 20 m telescope and the NOT, and a number of workshops/schools have been arranged around ALMA. Since, in particular, ALMA is such a unique instrument with applications in essentially all fields of modern astronomy, the prognosis for the Swedish use of radio astronomical facilities is very good. There is a second aspect on this. By being operators of state-of-the-art instruments over the years OSO has produced a large number of highly qualified radio astronomers that have played important roles in radio astronomical infrastructures around the world and in space. 6.3.1 Activities Astronomical VLBI: It is an important, and in may respects unique, observing method, which has a strong complementary nature to e.g. LOFAR and SKA, see Appendix A2. OSO also has strong standing, technologically and methodologically, in this global activity. OSO therefore aim for moderate investments in this area.

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• Astronomical VLBI observations will continue on the Onsala 20 m and 25 m telescopes.

• OSO will continue its funding of JIVE, and also supports its ambition to become an European Research Infrastructure Consortium (ERIC).

• The C-band system will be moved to the 20 m telescope to improve performance and decrease the sensitivity to weather conditions.

• The 3 mm receiver system on the 20 m telescope will be upgraded to allow double-polarisation VLBI observations.

• Upgrades following decisions within EVN will be done. • A new radome must be installed at an estimated cost of 1.5 – 2 Mkr/yr over 10

years. • The investment costs for new receivers and VLBI equipment are estimated to be

modest, 5 Mkr over the five-year period. • Eventually, the 25 m telescope must be replaced if VLBI observations at λ >

15 cm are still worth pursuing (today they comprise about 50% of the EVN observing time). This becomes an issue at the end of the decade.

LOFAR: The International LOFAR Telescope collaboration has just started. The first regular call for proposals has just been released with a deadline September 17th 2012. Over the period of this strategic plan we foresee no major changes in our LOFAR activities, and only very modest investments.

• OSO will remain a partner of the ILT within the coming decade. • Only minor investment costs are foreseen.

SKA: This project is of great strategic interest to OSO since it will dominate m- and cm-wave radio astronomy for decades, and the science case is very strong, Appendix A1. The developments within the project will have a strong influence on the boundary conditions for the strategic plan, and hence adds some uncertainty to it.

• OSO contributes the 1 M€ (over 4 years) which makes Sweden (represented by OSO) a member of the SKA Organisation Ltd. This gives a seat in the SKA Board of Directors and in the Members Committee.

• Further funding for R&D and industrial involvement during the pre-construction phase (2012 – 2015) must come from other sources.

• A decision on whether Sweden will join the SKA1 must come at the end of the period.

Single-dish observations at the 20 m telescope: There are a number of interesting observing programmes that can be pursued on this telescope at a modest cost, Appendix A3, since the telescope is well maintained for continued use in astronomical and geodetic VLBI. The mm-receiver investments are also important for VLBI observations. Yet, the priority set on this activity has decreased over the years, and the observing is now done by the visiting astronomers with some

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support but without operators. Thus, this activity will continue during the period, but it will have the lowest priority should resources become strained.

• Single-dish astronomical observations at a moderate level will continue on the 20 m telescope.

• Upgraded receivers (in particular at 3 mm, but maybe also at 4 mm) based on APEX and ALMA technology can be built at a moderate cost, and are nevertheless required by mm VLBI.

• A new radome must be installed at an estimated cost of 1.5 – 2 Mkr/yr over 10 years.

• The investment costs are moderate, ≈ 5 Mkr over the five-year period. APEX: OSO will continue its partnership until the end of 2015. An extension until the end of 2017 (or longer) is to be expected if the suite of receivers continues to deliver high-quality data of sufficient demand, but this will have to be prioritized in competition with e.g. SKA activities in the next period.

• New array receivers will add ALMA-complementary features, Appendix A4. OSO is interested to become a partner in the LAsMA project, two heterodyne arrays for large-scale mappings.

• The estimated investment cost amounts to about 15 Mkr. ALMA: The Joint ALMA Observatory will soon release its Cycle 1 Call for Proposals and full science operation is expected to start in 2013. ALMA will remain a frontline instrument for several decades. The Nordic ARC node will continue its mission to stimulate and support the use of this large infrastructure investment in Sweden and the Nordic area.

• OSO will continue its support for ALMA observations through the Nordic ARC node at roughly the present level in the next 5 years.

• The approved full production of ALMA Band 5 cartridges will secure funding for a large fraction of GARD over the coming five years.

• Only minor investment costs are foreseen. CCAT: It will be impossible to find resources, manpower as well as financial, for OSO to engage also in this large infrastructure project. However, it remains a strategically interesting project, Appendix A5, should e.g. the time scale of the SKA project change, and OSO will follow its development. Any actions will depend on the developments within the APEX and SKA projects. Geoscience: OSO has recently reached the status of a Fundamental Geodetic Station, and a suite of complementary equipment to geodetic VLBI is being installed.

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• Geodetic VLBI will continue on the 20 m telescope, Appendix A6. • A twin-telescope system for geodetic VLBI will be installed at Onsala. • The investment cost is estimated to be about 5 Mkr (in the period 2020 – 2024),

the rest is covered by a Wallenberg grant. • Upgrades of the other geoscience sensors will be done, as well as a possible

installation of a tide-level gauge instrument in collaboration with SMHI. For this only minor investment costs are foreseen.

6.3.2 Risks There are of course uncertainties and risks associated with this plan. We list and discuss the major ones below. Astronomical VLBI: - This activity is crucially dependent on the existence of JIVE. However, JIVE funding, at least at the present level, is at threat in some member states. A not too optimistic estimate is though that sufficient funding will be available to allow JIVE to continue to provide the base support for the operation of the EVN. - The 25 m telescope is close to 50 years old, and the risk for a major failure must be considered high. This will affect only L-band VLBI once the C-band has been moved to the 20 m telescope. - The major risk for the 20 m telescope is a radome failure. This can, in the worst case, have dramatic consequences since this telescope is not built for being exposed to the open air. Therefore, a replacement of the radome is of high priority to assure that at least one of the major radio telescope parabolas is operational at Onsala. SKA: - This is a very complex project, both technically and governance/funding wise, and substantial changes in time scales cannot be excluded. - Should this happen, OSO can compensate by e.g. becoming involved in the South-African MeerKAT project (part of SKA1), which has a number of interesting complementary features to LOFAR and VLBI. The proposed African VLBI Network is another interesting partner. - A lack of extra funding during the pre-construction phase will severely limit OSO’s technical involvement in the SKA, and therefore most likely any industrial return from the project. APEX: - Operation beyond 2015 is dependent on decisions by the two other partners. In addition, Swedish participation depends crucially on the developments within the SKA project. 20 m telescope single-dish observing: - This is to a large extent piggybacked on the VLBI activities on the telescope and therefore is exposed to the same risks. On the other hand, this is not a high-priority activity. ALMA and LOFAR: The risks associated with these activities are regarded to be minor. Geoscience: The risks are estimated to be small here, assuming that the installation and commissioning of the twin-telescope system for geodetic VLBI are successful.

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The exchange rate of the krona: A considerable uncertainty in the OSO spending is the exchange rate of the Swedish crown with respect to the euro and the US dollar. The yearly contributions to various international projects amount to ≈ 1.1 M€, i.e., a 10% change amounts to 1 Mkr/yr. To this should be added costs of equipment where prices are often given in euro or US dollar. Staff: The risk in terms of lacking qualified staff is regarded to be small. OSO has gone through a period where the operations staff from the 60:ies and 70:ies has been successfully replaced. In addition, recruitments within interferometry, antenna optics, aperture array, and network techniques have been made. The increased use of complex digital electronics at all levels of the radio astronomical systems may in the future require staff with new qualifications. 6.3.3 Economy The financial effects of this strategic plan are summarised below, Table 3 and Fig. 12. A number of assumptions go into the expenditures. The Band 5 Full Production project will cover about 50% of the GARD salaries during this period. The operations can be covered with the existing staff and the costs will increase by 3% per year. The APEX operation continues in 2016. The cost of a new radome is seen as maintenance and it is covered by the operations budget and depreciated over 10 years. The investments in astronomical VLBI, and an upgraded 3 mm reciver for the 20 m telescope are seen as minor investments and they are covered by the operations budget. Likewise, a number of assumptions go into the revenues. It is assumed that the VR operations grant will increase by 3% after the present contract between Chalmers and VR expires at the end of 2013. It is also assumed that the Chalmers operations grant will reach a level corresponding to 50% of the VR operations grant at the end of this period. The investment in a twin-telescope system for geodetic VLBI is covered by the grant from the Knut and Alice Wallenberg Foundation. In addition, the revenues do not contain the income from RadioNet3 (in particular TNA, AETHER and DIVA projects) and the Band 5 Full Production projects (overheads). In summary, the expenditures and the revenues have a small negative balance over the five-year period, but there are additional revenues, due to RadioNet3 and ALMA Band 5, that are not accounted for.

Table 3. Summary of expenditures and revenues in the period 2012 – 2016

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Fig. 12. Summary of expenditures (left) and revenues (right; including the cumulative balance in orange) in the period 2012 – 2016. Finally, investements in a new receiver for the APEX telescope and involvement in the SKA Work Package Consortia must come from other resources. In the former case through the VR grants for expensive equipment, and in the latter case through ear-marked funding for Swedish SKA involvement. Should the difference between revenues and expenditures develop negatively priorities must be made. The mm-wave observations on the 20 m telescope are currently the weakest spot. In Sect. 3.2.2 its operations cost is estimated to be 6.4 Mkr/yr, this figure is arrived at by dividing the total 20 m operations cost by the time spend on its various activities. Terminating only single-dish operations would only release a fraction of this amount because the telescope and the receivers (including that at 3 mm) must be maintained for astronomical and geodetic VLBI. Closing down the astronomical VLBI activities at the 25 m telescope is the next option. Moving the C-band (≈ 5 GHz) operation to the 20 m telescope is one step in this direction, but still L-band (≈ 1.4 GHz) constitutes about 50% of the astronomical VLBI observations, and hence if the 25 m is closed OSO will not be able to participate in VLBI at this frequency. Finally, about 6 Mkr/yr is released should APEX be closed down at the end of 2015. In summary, it is difficult to estimate exactly the resources that become available should these activities be closed down, but it is reasonable to assume that it will be possible to cover any deficits in the budget for the 2012 – 2016 period.

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Appendix A. Science Cases We present below the science cases for the SKA (A1), astronomical VLBI (A2), mm-wave observations at the Onsala 20 m telescope (A3), continued APEX operation (A4) , CCAT (A5), and geodetic VLBI (A6). A.1 Science Case for SKA The Square Kilometre Array (SKA) will be one of the ‘Great Observatories’ of the 21st century, being the equivalent in radio to the optical 40 m-diameter-class optical European Extremely Large Telescope (E-ELT) to be built by ESO. The SKA will have a collecting area of approximately one million square metres and the final design goal is that it will operate between the frequencies 70 MHz to 25 GHz. At these frequencies SKA will have a sensitivity 50 times that of the largest existing radio interferometer array and a survey speed which is 10 000 times faster. The SKA is a global project supported by a consortium of countries with European nations taking a leading role. It has recently been decided that both South Africa and Australia will host elements of the SKA with the low-frequency part going to Australia and most of the high-frequency dishes to South Africa.

The full SKA science case was developed and published in a book ‘Science with the Square Kilometre Array’ (2004) which is available online (http://www.skatelescope.org/media-outreach/books/science-book/). This science case has been extensively studied by expert astronomer panels within the European Astronet consortium (formed on the initiative of European science research councils) which have reviewed future European science and infrastructure requirements for Astronomy. SKA features prominently in both the Astronet ‘Science Vision’ report of 2007 and its infrastructure roadmap of 2009 (documents at http://www. www.astronet-eu.org). In the latter document the SKA and the E-ELT were identified as the two flagship ground-based astronomy projects of the future. The SKA is also identified as a priority for European infrastructure investments within the ESFRI roadmaps, the latest strategy report of which was issued in 2010. Swedish astronomers have top-ranked the project through the National Committee for Astronomy. Finally the SKA is highlighted in the latest 2012 VR guide to infrastructure as an important future infrastructure for astronomy.

One of the key aspects of an interferometer array like the SKA is that it can begin conducting scientifically useful observations well before it reaches its full capabilities. An important staging point in the development of this growing telescope is defined as SKA1, which represents crudely when the SKA has reached approximately 10% of its full capability. SKA1 will be equipped to cover the frequency range 70MHz- 3GHz (although the dishes will be specified to reach 10GHz) and will have baselines out to 100km. For a planned construction start in 2016, SKA1 will be operational around 2020. SKA2 will complete the full SKA collecting area for the frequency range 70 MHz to 10 GHz, and is planned to be operational by 2024. SKA3 will add the highest frequencies, its time-scale is uncertain. All phases of SKA development are planned in accordance with five key science projects (KSPs) described in the book ‘Science with the Square Kilometre Array’. In addition, flexibility is being built into the system to allow for the discovery of the unknown. It should be noted that while these KSPs are the most important questions that SKA will address, and it is these that drive the design of SKA, they are not a complete description of the SKA science capabilities, in fact virtually all astronomy presently being done at radio frequencies will be enormously impacted and enhanced by the SKA.

Below we briefly describe the SKA KSPs while in Sect. A.1.7 we specifically describe the specific science goals of SKA1.

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A.1.1 Probing the Dark Ages and the Epoch of Reionisation The ionising ultraviolet radiation from the first stars and galaxies produced a fundamental change in the surrounding intergalactic medium, from a nearly completely neutral state to the nearly completely ionised Universe in which we live today. The most direct probe of this Epoch of Re-ionisation (EoR), and of the first large-scale structure formation, will be obtained by imaging warm neutral hydrogen and tracking the transition of the intergalactic medium from a neutral to an ionized state, Fig. A.1.1. Moreover, as the first galaxies and AGN form, the SKA will provide an un-obscured view of their gas content and dynamics via observations of highly redshifted emission from low-lying molecular transitions (e.g., from CO).

Fig. A.1.1. Epoch of Reionisation observations.Top figure shows a cartoon illustrating how as a function of redshift the first stars and galaxies form (yellow dots) producing surrounding regions of warm atomic hydrogen (red) and then ionized regions(black) (J.Pritchard, Univ. of Oxford). Bottom figure (from Garrelt Mellema, Univ of Stockholm) shows a SKA simulation of the radio emission from atomic hydrogen as a function of increasing redshift (i.e. decreasing frequency) from z = 8 to 10. A.1.2 Galaxy Evolution, Cosmology, and Dark Energy Hydrogen is the fundamental baryonic component of the Universe. The SKA will have sufficient sensitivity to the 21 cm hyperfine line of atomic hydrogen (HI) to detect galaxies such as our own out to redshifts z > 1. One of the key questions for 21st century astronomy is the assembly of galaxies; the SKA will probe how galaxies convert their gas into stars over a significant fraction of cosmic time, and how the environment of

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galaxies affects their properties. Simultaneously, by mapping the 3D distribution of galaxies SKA will be able to trace the effects of baryonic acoustic oscillations (BAOs), the remnants of early density fluctuations in the Universe. The SKA will assemble a large enough sample (at least 109) of galaxies that it will be possible to measure the BAO signal as a function of redshift to constrain the equation of state of dark energy.

Fig. A.1.2. The above figure shows the result of VLA observations of atomic hydrogen in a sample of 34 galaxies ranging from giant spirals to dwarves (THINGS sample, Walter et al. 2008). These observations allow the derivation of galactic total mass distributions (baryonic plus dark matter) out to large radii and the distribution/kinematic of galactic atomic gas. The latter gas phase, accreted from the cosmic web in the intergalactic medium, likely provides the ultimate fuel source for star formation in spirals. The SKA will allow such detailed imaging studies for tens of thousands of galaxies over a range of redshift, and the work can start already with SKA1. A.1.3 The Origin and Evolution of Cosmic Magnetism Magnetic fields play an important role throughout astrophysics, including in particle acceleration, cosmic ray propagation, and galaxy and star formation. Radio observations have a unique role in studying the magnetic universe via observations of polarised synchrotron emission, Faraday rotation and Zeeman splitting of spectral lines. Unlike gravity, which has always been present in the Universe, magnetic fields have likely been built up through cosmic history, enhanced from very small primordial seed fields. By measuring the Faraday rotation toward large numbers of background sources, the SKA will track the evolution of magnetic fields in galaxies, galaxy clusters and the intergalactic medium over a large fraction of cosmic time.

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A.1.4 Strong-field Tests of Gravity using Pulsars and Black Holes With magnetic field strengths as large as 1015 G, rotation rates approaching 1000 Hz, central densities exceeding 1014 g cm−3, and normalized gravitational strengths of order 0.4, neutron stars, many of them being pulsars, represent extreme laboratories. Pulsars are also compact objects suitable for high accuracy kinematical studies via pulse timing or astrometry. The utility of pulsars as physical probes has already been demonstrated by the award of two separate Nobel Prizes in Physics involving pulsars. The SKA will enormously expand known samples of both normal and millisecond pulsars. Via high-precision timing of these pulsars it will be possible to construct a Pulsar Timing Array (see Fig A.1.3) for the detection of nano-Hz gravitational waves, theoretically expected to be generated in the early universe. SKA will also use pulsars to probe the space-time environment around black holes via observing both ultra-relativistic binaries (e.g., pulsar-black hole binaries) and pulsars orbiting the central super-massive black hole in the centre of the Milky Way. Via timing analysis of pulsars SKA will also probe the equation of state of the nuclear matter within neutron starts testing standard models of sub-atomic physics.

Fig. A.1.3. SKA detection of gravitational waves using the pulsar timing array. The passage of very-long-wavelength gravitational waves through our region of the galaxy causes slight variations in the regular ‘ticking’ of the lighthouse-like radio beams from rotating pulsars. These variations can be detected using SKA pulsar timing observations. A.1.5 The Cradle of Life The existence of life elsewhere in the Universe has been a topic of speculation for millennia. In the latter half of the 20th Century these speculations began to be informed by observational data, including the detection of organic molecules in interstellar space, and the discovery of both proto-planetary disks and planets orbiting nearby stars. With its sensitivity and resolution, the SKA will be able to observe the cm-wavelength thermal radiation from dust (see Fig A.1.4) in the inner regions of nearby proto-planetary disks thereby probing a key regime in the planetary formation process. On larger scales in molecular clouds, the SKA will search for complex pre-biotic molecules. Finally, detection of radio transmissions from another civilization would provide immediate and direct evidence of life elsewhere in the Universe. SKA will provide sufficient sensitivity to enable, for the first time, searches for unintentional emissions or ‘leakage’ from samples of nearby stellar systems.

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A.1.6 Exploration of the Unknown In addition to the Key Science Projects listed above, and recognising the long history of discovery at radio wavelengths (pulsars, cosmic microwave background, quasars, masers, the first extrasolar planets around pulsars etc.), the international science community has also recommended that the design and development of SKA have “Exploration of the Unknown” as a philosophy. Wherever possible, the design of the telescope is being developed in a manner to allow maximum flexibility and evolution of its capabilities to probe new parameter space (e.g., time-variable phenomena that current radio telescopes are not well-equipped to detect). This philosophy is essential as many of the outstanding questions of the 2020 – 2050 era, when the SKA will be in its most productive years, are likely not even known today.

Fig. A.1.4 Dust evolution and planet formation in circumstellar discs. Left: Artistic view of the formation of pebbles in circumstellar discs (Bill Saxton, NRAO/AUI/NSF). Right: Simulation of the formation of a gap in a disc around a young star due to the gravitational effect of a newly formed giant planet (Geoff Bryden). A.1.7 Specific Science Goals of SKA1 SKA1 will already be an enormous advance in radio astronomy capabilities, increasing sensitivity compared to current instruments by a factor of 10. Such a large sensitivity increase will facilitate advances in virtually all of the many areas of astrophysics presently explored by radio observations. A full description of the science goals achievable with phase 1 is given in the SKA Phase 1 Design Reference document (follow links in http://www.skatelescope.org/public/) The largest impacts of SKA1 will likely be in three Key Science projects, namely – 1) Epoch of Reionisation, 2) Cosmic Evolution of Galaxies, and 4) Strong Field Tests of Gravity. SKA1 will for instance very likely be able to make the first images of HI in emission at the epoch of reionisation (as opposed to LOFAR which will only be able to make statistical detections if it is fortunate). SKA1 will be able to study the HI (21cm) absorption forest toward the first quasars and it will also be possible to image in HI thousands of galaxies in the nearby universe (closer than 60 Mpc). It will be possible in detail to study the relations between galaxies and the intergalactic medium (IGM) and possible continuing accretion from the ‘intergalactic web’ of gas filaments. HI

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observations of galaxies will also be used to understand internal galaxy dynamics, galaxy mass distributions, and the role of atomic gas as a reservoir for ongoing star formation in galaxies. The pulsar survey of SKA1 will increase the total number of known pulsars by at least a factor of ten, provide a large sample for the proposed physical tests and hopefully detect several ‘holy grail’ pulsar-black hole binaries, which will be especially useful for testing General Relativity. The timing analysis observations should allow the detection and characterisation of the cosmological background of gravitational waves and also constrain the equation of state of neutron star matter in tight binaries. The latter observations will test the properties of extremely dense matter against the predictions of standard particle models. In addition to the above highlights, the Design Reference Mission document for SKA1 lists another 25 areas of science impact for the proposed SKA1. These areas include the mapping of our own galaxy's magnetic field as both an observational goal in itself and a pre-requisite for the studies of the magnetic fields in nearby galaxies and the intergalactic medium that will be accomplished by SKA2. Additionally, SKA1 should be able to conduct important work in the ‘Cradle of Life’ KSP especially if it is technically possible, using Ultra-Wideband Feeds (see Section 6.2.1), to give SKA1 a capability above 3 GHz in order to image forming planetary systems.

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A.2 Science Case for Astronomical VLBI OSO is involved in both cm wavelength VLBI by our participation in the European VLBI Network (EVN, encompassing telescopes also in Africa, Asia, and the US) and in mm VLBI via the Global Millimetre VLBI Array (GMVA). OSO was a pioneer in developing the VLBI technique, and over the last 40 years it has laid the base for OSO’s involvement in ALMA, LOFAR, and SKA. Recently, the VLBI-interested scientific staff at OSO has been expanded, e.g., by the recruitment of two new permanent staff members.

Improvement of the European and global VLBI arrays is continuously ongoing, including expansion to higher bandwidth, new correlator capabilities, and new telescopes. The latter include the new 64 m VLBI telescope in Sardinia, and Russian and Chinese telescopes. In the near future an Africa Array is being formed from old satellite-communication dishes; combined EVN observations with this will improve uv coverage in the north-south direction for low-declination sources. The steady improvement in VLBI capability over the last decade or so has resulted in increased proposal pressure for EVN observing time (see Fig A.2.1). Since, because of budget constraints in the US, the Very Long Baseline Array (VLBA) will be much less available for users in the coming years the pressure on the EVN is likely to grow further.

Fig. A.2.1. Number of proposals for the European VLBI network versus time over the last five years.

Presently, most VLBI observations are done at a data rate of 1 Gb/s, but 16 Gb/s has recently been demonstrated, and this is predicted to increase to 128 Gb/s by the end of the decade. As bandwidths increase the importance of high-frequency telescopes like the Onsala 20 m telescope for VLBI arrays increases, since only at high frequency is it possible to get enough bandwidth to make use of the high bit rates. The projected improvements within the next decade will allow for increases in sensitivity for continuum observations of between 5 and 10, allowing VLBI observations of whole new classes of objects. Finally, there is expected to be a significant synergy between LOFAR and the EVN with the former operating as survey telescope and discovering many targets that can later be studied in detail at high resolution with cm VLBI.

While there is some overlap between VLBI science and the science to be done with the SKA, the two instruments are complementary. The future global VLBI array centred in the Northern hemisphere (with likely extensions into equatorial and southern Africa) has baselines out to 10 000 km (and a total collecting area just in existing telescopes of 0.15 square km). Such an array offers much higher resolution than

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the SKA due to the longer baselines (100 km and 3000 km for SKA1 and SKA2, respectively) and also has much better uv coverage due to the larger Northern hemisphere landmass. VLBI also goes to much higher frequency (86 GHz and higher, compared to 3 GHz/10 GHz for SKA1/SKA2, respectively). Finally, the much larger Northern hemisphere optical network capacity will make economic a larger bandwidth on long baselines compared to that available to the SKA. The detailed science case for future cm wavelength VLBI has been outlined in the ‘EVN2015’ vision document (http://www.evlbi.org/publications/EVN2015FinalV2.pdf). This document demonstrates that the present and future science undertaken using VLBI is extremely varied. Below we summarise what we consider are some of the main areas of high impact of future VLBI involving OSO. A.2.1 Evolution of Galaxies and Active Galactic Nuclei A major goal of extragalactic astronomy today is to understand the processes by which galaxies and supermassive black holes have evolved through cosmic time. A unique obscuration-free tracer of star formation in galaxies is radio continuum emission. While large EVLA and eMERLIN survey observations are best suited for observing the stellar-powered radio emission itself, VLBI observations have a vital role in detecting and removing contaminating emission from Active Galactic Nuclei (AGNs, generated from accreting black holes at the centres of galaxies). Studying the statistics of AGN-related radio emission in galaxies is also crucial in its own right. It has become clear that AGN activity exists at a low level in nearly all galaxies, and in addition that most galaxies go through at least one period of intense AGN activity during their lifetime. The mechanical feedback from AGN jets likely sets the upper limit on galaxy mass; such feedback is an important ingredient of models which seek to explain the mass spectrum of galaxies in the universe. A close connection between star-formation and the growth of super-massive black holes is also required to explain the tight correlation found between the mass of the central black hole and the mass of the galaxy spheroid. VLBI observations provide a way to observe jets within AGN both in continuum and via atomic and molecular absorption studies their interaction with gas; and so observe the mechanical feedback process in action.

As well as powerful AGNs, VLBI can also study the more common 'dormant' mode of AGNs. For the majority of supermassive black holes (SMBHs) in the nuclei of galaxies, accretion rates (dm/dt) are low and radiation is produced inefficiently (luminosity proportional to (dm/dt)2), resulting in undetectably low optical through X-ray luminosities. However, radio emission from jets scales as a lower power of accretion rate and hence is more easily detectable. The projected µ-Jansky sensitivity of future VLBI arrays will make it possible to measure accurate black hole accretion rates as a function of galaxy type for all large-bulge (mostly elliptical) galaxies closer than 20 Mpc (http://www.e-merlin.ac.uk/legacy/proposals//eMERLIN_Legacy_LeMMINGs.pdf). Understanding how this low luminosity ‘maintainence’ AGN mode operates is important for understanding how elliptical galaxies stay ‘red and dead’ despite the likely continuous accretion of matter from the intergalactic medium.

Another important area of potential future LOFAR/VLBI synergy is the detection of the highest redshift galaxies. It is of great interest to determine the highest redshift at which super-massive black holes exist, since this constrains their formation processes. It has been argued that the first jets from some super-massive black holes will terminate within their host galaxies, giving sources with a characteristic low-frequency-peaking synchrotron self-absorption radio spectrum (Falcke 2004, New Astronomy Reviews 48, 1157). Sources with such spectra can be detected initially with LOFAR, but confirming their identity and determining their properties (linear size, mechanical energy input, etc.) requires the (better than) 10 milliarcsecond resolution that is provided by cm wavelength VLBI observations.

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A.2.2 Testing Dark Matter Distributions and Measuring Cosmological Parameters VLBI observations of gravitational lenses provide interesting ways to study dark matter distributions around massive galaxies and in clusters. To first order 1/r2 isothermal density profiles seem favoured by present observations although future larger samples will be able to study this in more detail. An exciting prospect is to measure or set limits to micro-lensing effects due to the sub-galactic clumps of dark matter predicted by Cold Dark Matter (CDM) structure-formation scenarios. Although a large abundance of such sub-halos is predicted under CDM there is no evidence from optical observations for dwarf galaxies in the numbers expected, suggesting that they may consist purely of dark matter. Such dark sub-halos are however potentially detectable via the predicted sub-millarcsecond level kinks and bends they induce within multiple images of strong gravitational lenses. Gravitational-lensing effects on such scales can only be studied with VLBI (Zackrisson & Riehm 2010, Advances in Astronomy, ID 478910). An important synergy exists here with LOFAR which in its ten-million-source northern hemisphere survey should find thousands of strong radio gravitational lenses, which can be studied at high resolution in follow-up VLBI observations to search for microlensing effects.

VLBI gravitational lens observations can also be used to make direct measurements of Hubble’s constant (H0). Because of their high resolution VLBI observations of radio gravitational lenses can very accurately constrain the lens magnification field and hence the lensing mass distribution. Combined with time-delay measurements of the background sources such mass modelling gives H0. A complementary method of measuring Hubble's constant, and potentially other cosmological parameters, is provided by VLBI observations of water ‘mega-maser’ emission in AGNs (Kuo et al. 2011, ApJ 727, 20). These masers form sub-parsec scale disks around the supermassive black holes at the centres of AGNs. Measuring acceleration of radio spots and the disk-rotation rate gives the linear radius where the emission occurs, which, when compared to the angular radius of the maser disk from VLBI, gives the distance. Such observations also give very accurate black hole masses. A.2.3 Star Formation and Death in Galaxies VLBI has an important role to play in understanding star-formation processes within galaxies and the internal feedback processes that regulate this star formation. Of particular interest is star formation within nearby starburst galaxies which (compared to normal galactic disk star formation) occurs in regions with very high gas densities and temperatures. The most extreme starbursts observed within 200 Mpc have star-formation rates per unit area which are comparable to those in proto-galaxies at redshift z ≈ 6 (Walter et al. 2006, Nature 457, 699). Important questions include whether star formation in regions with such extreme density and temperature proceed by the same route, and follow the same scaling laws, as galactic disk star formation. Specifically, does the same stellar Initial Mass Function (IMF) apply, and does star formation intensity follow the same scaling with gas surface density? If the above quantities vary what are then the implications for using radio emission as a tracer of star formation at high z?

An obscuration-independent way to measure star-formation rates in starburst galaxies is via the VLBI detection and imaging of radio supernovae (SNe); existing observations of the starbursts Arp220 (Parra et al. 2007, ApJ 659, 314; Batejat et al. 2011, ApJ 740, 95, Fig A.2.2) and Arp299 (Bondi et al. 2012, ApJ 539, 134) suggest rates of occurrence of powerful radio SNe in powerful starbursts which are much larger than those expected assuming Milky-Way-like star formation. This observed discrepancy seems to be consistent with having a top-heavy stellar IMF, as predicted by many theoretical models for the hot gas environment of starbursts. VLBI also makes possible

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detailed studies of the structure and evolution of individual radio SNe (e.g., SN1993J, see Fig. A.2.3; Marti-Vidal et al. 2011, A&A 526, 143). These observations constrain models of diffusive particle acceleration in strong supernovae shocks and allow the study of mass-loss processes in the progenitor star in the tens of thousands of years prior to its explosion. The subsequent phase of Supernova Remnant (SNR) evolution when the supernova ejecta interacts with the interstellar medium (ISM) can also be studied using VLBI and these observation can be used to constrain ISM density and pressure. Since SNRs are the sites where relativistic particles, which produce star-formation-related radio emission, are accelerated, detailed studies are required of SNR to reach a full understanding of the physical mechanisms underlying the radio to star formation correlation (a major tool which instruments like the SKA are being built to exploit).

Fig. A.2.2. Deep global VLBI image of the Western nucleus of Arp220 (Batejat et al 2012, A&A, in press). The image is approximately 100 pc across. The detected point sources are mostly a mixture of radio supernovae and supernova remnants. The ellipse marks the approximate size of a hot dust feature observed with mm-interferometers, the green symbols give estimates of the centroid position of this feature and the red symbol the mean position of these estimates.

Spectral-line VLBI observations can also study the dynamics of gas in starburst

galaxies via observations of atomic hydrogen absorption or OH absorption/maser line emission. Since the total mass in such systems is usually gas dominated, estimates of gas surface density on very small scales (smaller than those observable with ALMA) can be obtained and compared with the star-formation rate (inferred from FIR or radio continuum emission) to test the so-called Schmidt-Kennicutt star-formation law. Magnetic field strengths can be measured via Zeeman splitting and rotation measures (across the spectral profile) of OH mega-masers. Other potential VLBI targets associated with the end points of stellar evolution in galaxies are radio observations of gamma-ray bursts, relativistic expansion in some types of Type Ib/c SNe, and the possibility if detecting radio emission from ultra-luminous X-ray sources.

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Fig. A.2.3. VLBI images of the expanding radio supernova SN1993J in the galaxy M81. Combined analysis of spatial and spectral properties allows constraints on the mass-loss history of the pre-explosion wind and mechanisms of particle acceleration and magnetic field enhancement (Marti-Vidal et al. 2011, ApJ 526, 143). A.2.4 Large-scale Structure of the Milky Way Within our own galaxy, VLBI has an important vital role to play in determining its mass distribution and internal spiral structure via astrometric observations. While the upcoming GAIA mission will measure proper motions and distances for over a billion stars this optical instrument cannot make measurements in regions of our galaxy obscured by dust. This will limit its observations in the Galactic plane to a range of 1 to 2 kpc in directions inward from the Sun. VLBI observations have no such limitations. The methanol maser line at 6.7 GHz provides the best tracer of dynamics, and is bright enough that it can be observed even on the far side of the galaxy. While such observations constrain the Milky Way’s mass distribution, its large-scale magnetic field distribution can be studied by observing pulsar rotation measures and dispersion measures combined with VLBI parallax observations to determine their distances. Such pulsar astrometry observations also give their proper motions which can be used to constrain models of the formation of different classes of pulsars. A.2.5 Galactic Star Formation and Stellar Observations Theoretical star-formation models have made important strides in recent years, with theories providing detailed predictions ready to be tested by new instruments. Important unsolved issues include the mechanisms that determine the stellar IMF and whether high-mass stars are formed by similar accretion processes as low-mass stars or

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via a different mechanism, e.g., via the coalescence of smaller proto-stars. Another issue is the influence on star formation of the feedback from massive young stellar objects which can severely disrupt their environment. Nearly all VLBI observational work in star formation at present (and likely in the near future) relates to massive star formation, since the environment around massive proto-stars most easily produces detectable radio continuum and maser emission. Within this area of high-mass star formation, VLBI observations play a vital role since they can penetrate the obscuring dust which is always present in high-mass star-forming regions. Furthermore, VLBI observations are often the only observations with high enough angular resolution to study small spatial scales, given that the nearest high-mass-star-forming regions are many kiloparsecs distant.

Various maser features occur within massive star-forming envelopes at different combinations of density and temperature. The presence or absence of these masing species also depends on the evolutionary state of the massive proto-star region, and therefore can be used to determine the stage of development of the proto-star. VLBI observations of different maser species can be used to measure the dynamics at different radii. Since both radial motions and proper motions of maser spots can be measured, in total 5 out of 6 of their space-velocity components can be constrained. These observations can be used to distinguish between different competing geometries, e.g., infall, outflow, and rotation, which are linked to the different physical theories of massive star formation. Importantly, maser observations are also at present the only probes of the magnetic field strength and structure in the densest proto-stellar regions. Linear and circular polarization (i.e., Zeeman splitting) has been detected for all four major maser species (OH, H2O, CH3OH, and SiO), and in particular the recent EVN observations of 6.7 GHz methanol maser polarization have opened a new window into the magnetic field around massive proto-stars (Fig. A.2.4; Surcis et al. 2010, ISKAF Science Meeting 2010; Surcis et al. 2011, A&A 533, 47).

Fig. A.2.4. EVN observations of the magnetic field in the massive star-forming region W75N (Surcis et al. 2010, ISKAF Science Meeting 2010). The large-scale magnetic field is derived from linear polarization (red line segments) of 6.7 GHz methanol masers detected (indicated by the red circles). The blue triangles are the VLBI detections of 22 GHz water masers.

At the other end of the stellar lifetime, VLBI observations can be used to trace the matter that is recycled back from stars into the ISM via stellar winds. Stars of the sun's mass and larger go through a red giant phase in which the relatively weak gravity at

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the stellar surface can be overcome by radiation pressure on dust grains formed in the cool stellar atmosphere, these grains then drag the gas outward. Understanding this mass-loss process is important for understanding mass-exchange processes between the stellar population and the gas component of galaxies. Within individual stars stellar outflows can be studied by observations of various maser species including OH (1.6 GHz), H2O (22 GHz) and SiO (43 and 86 GHz). VLBI observations of the polarization of the masers in circumstellar envelopes can also indicate the presence of dynamically important magnetic fields that potentially contribute to driving the stellar mass loss (Vlemmings et al. 2005, A&A 434, 1029). In some cases (e.g., W43A, see Fig. A.2.5) highly collimated axisymmetric outflows are observed (Vlemmings et al. 2006, Nature 440, 58). These flows are thought to be magnetically confined. Precessing collimated outflows of this type, the so-called ‘water fountains’, can explain the complex structures seen in proto-planetary nebulae. The study of the outflows of these rare objects, that likely represent a crucial phase in the formation of planetary nebulae, can only be performed using VLBI.

Fig. A.2.5. The magnetically collimated 'water fountain' in the evolved star W43A (Vlemmings et al. 2006, Nature 440, 58). A.2.6 Detailed Jet Physics in AGNs and Micro-quasars The generation of bipolar jets is a ubiquitous phenomenon in nearly all known types of accreting objects in the universe, yet how such jets are produced is unclear. Jets can carry substantial mechanical energies and the less collimated versions can also carry substantial angular momentum. Most spectacular are the relativistic jets produced in extragalactic AGNs and in so called ‘micro-quasars’ within our own galaxy. The latter objects are powered by accreting stellar-mass black holes or neutron stars. Remarkably, micro-quasar and AGN properties fit scaling relations linking mass, radio and x-ray luminosity that extend over ten orders of magnitude (Fender et al. 2007, 6:th Microquasar Workshop). This fundamental plane relationship points to a common physical process linking all these objects. Micro-quasars have the advantage that they switch over short times scales (days) between different x-ray and radio states, whereas the corresponding time scales for AGNs are millions of years. The wide diversity of AGN ‘types’ could therefore plausibly be explained by different accretion disc states. Studying in detail the processes of jet formation and propagation in micro-quasars is therefore of the highest importance for understanding the relativistic jet phenomena in general; important questions are to determine the relationship between the weak steady radio jets (Rushton et al. 2012, MNRAS 419, 319), episodic powerful jets, and x-ray emission properties. Also of great interest is to determine what source properties

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determine the jet velocity. To date only a few micro-quasars have been studied in detail by VLBI, this is however changing rapidly due to the advent of real-time e-VLBI and the increasing EVN array sensitivity. In the next few years a larger population of micro-quasars and other galactic radio transients is expected to be detected with LOFAR (and later APERITIF operating on the Westerbork array in the Netherlands). These can then be followed up at cm wavelengths using e-VLBI.

Another approach to understanding jet formation processes is via detailed imaging of individual objects. Here global 86 GHz VLBI imaging is starting to resolve the regions in which jets are formed. Millimetre-wave VLBI observations of the jet base in the giant elliptical galaxy M87 (using as one element the Onsala 20 m telescope) constrain this region to be smaller than 15 x 56 Schwartzschild radii (Krichbaum et al. 2008, in Extragalactic Jets, ASP Conf. Series, Fig A.2.6). These results already rule out some proposed jet formation mechanisms such as that of Blandford & Payne (1982, MNRAS 199, 883) which requires that jets be anchored to larger-scale accretion disk magnetic fields. Coming improvements in VLBI bandwidth are likely to make a huge impact on mm-VLBI allowing such studies to be done on more sources. At the very short sub-mm wavelengths accessible to VLBI using APEX (and ALMA when it is phased up) it should be possible to detect general relativity effects in the inner regions around super-massive black holes. Such effects distort the radio emission coming from the accretion disk or inner jets. Detailed VLBI imaging can then constrain the spin of the black hole. Such observations are feasible in the coming years toward M87 and in Sgr A* by using global VLBI arrays operating at 345 GHz, the so-called ‘Event Horizon Telescope’. Another approach to obtaining extremely high resolution in AGN nuclei is to use space-VLBI to an orbiting satellite (i.e., to the recently launched Russian satellite RadioAstron).

Fig. A.2.6. The jet-collimation region in the nucleus of the giant elliptical galaxy M87 as seen through 86 GHz VLBI images by Krichbaum et al (2008). The region in which the jet collimation occurs is constrained to less than 15 x 56 Schwartzschild radii in size.

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A.3. Science Case for Onsala 20 m Millimeter-wave Observations A.3.1 Introduction The strategies for instrumentation and operations at other mm-wave facilities open some important areas for the Onsala 20 m telescope. For example, a considerable fraction of the 4 mm band (70 – 87 GHz) is not available to European astronomers and barely covered anywhere else in the world, despite being spectroscopically rich for studies of interstellar and circumstellar matter. Also, the availability of a 4 mm band opens up extragalactic observations of the CO(J=1–0) line at redshifts around 0.5. At present, it appears that a 4 mm receiver is operating occasionally only at the Arizona Radio Observatory 12 m telescope in the USA. In fact, even in the more competitive 3 mm regime will a broad-band receiver at the 20 m telescope be very valuable, since e.g. the IRAM 30 m telescope will be under enormous pressure from observers, and interesting observing programmes requiring a lot of observing time, but not necessarily the highest sensitivity, may simply not be done. A.3.2 Spectral Scans in the 4 and 3 mm Bands The scientific justification for a 4 mm heterodyne receiver is straightforward: this wavelength band is remarkably rich in low-lying transitions of important interstellar and circumstellar molecules (Table A.3.1 and Fig. A.3.1), especially deuterated forms of several of the most common species: DCO+, DCN, DNC, N2D+, DC3N, HDO, C3HD, etc. Many of these lines have never been observed extensively, and it should be stressed that the low temperatures of interstellar clouds make the lowest-lying transition particularly observationally important. A new receiver could be the focal point for a new category of large programmes at the 20 m telescope to be undertaken by well-organized consortia. For example, there is a need for extensive surveys of the most common deuterium-bearing molecules in a large sample of molecular clouds of all types, to complement the continuing interest in the most extreme cases of enhanced deuteration levels and multiple deuteration (NHD2, ND3, D2CO, CD3OH, etc.) seen primarily in regions associated with low-mass protostars (Ceccarelli et al. 1998, A&A 338, L43; Saito et al. 2000, ApJ 535, 227; van der Tak et al. 2002, A&A 388, L53; Parise et al. 2006, A&A 453, 949). With a broad-band receiver, the frequency interval 70 – 86 GHz could be covered in as few as 3 local-oscillator settings with an 8 GHz spectrometer; therefore, such surveys could be envisioned as general-purpose spectral scans.

Between 1979 and 1982, the 20 m telescope was used to make spectral scans of Orion A and IRC+10216 in the frequency interval 72 – 91 GHz, with a sensitivity slightly better than 0.1 K at 1 MHz resolution (Johansson et al. A&A 130, 227, 1984; Johansson et al. A&AS 60, 135, 1985; in fact OSO pioneered this type of studies). With a modern, broad-band receiver, it would be possible to observe most of the 70 – 86 GHz band with a sensitivity of 0.01 K (rms) at 250 kHz resolution (1 km/s in Doppler velocity at 75 GHz) in about 60 hours of observing time. Thus, it would be feasible to carry out a long-term campaign to obtain such diagnostic spectral scans of some 50 sources over a period of a few years. A 3 mm receiver is also justified in this context because it provides the ability to measure the H-counterparts of the D-bearing molecules, cf Fig. A.3.1. Figure A.3.2 gives an example of a broad-band spectral survey. A.3.3 Extragalactic Spectroscopy Even extragalactic spectroscopy is now turning towards the regime of spectral scans, and new model techniques are being developed to handle multiple lines. Science goals

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include surveys of the astrochemistry of starburst and active galaxies to evaluate type and evolutionary status of the activity (in the 4 mm regime the deuterated species are of particular interest also for nearby galaxies). Furthermore, multiple transitions of H2CO, HC3N, and OCS have a particularly useful diagnostic value for luminous galaxies with deeply obscured nuclei, dense gas, and strong IR fields. The 20 m telescope can take on large projects of, for example, spectral scans and surveys of nearby galaxies. To date, spectral scans have only been carried out on a handful of objects – not in a statistically sound sample of galaxies. The importance of such a study to properly put luminous, active starburst galaxies – as well as high-redshift objects – into perspective cannot be overstated. In addition, the 4 mm band will enable us to study the cold molecular gas in galaxies with redshifts up to about 0.64 using the fundamental CO(J=1-0) line. Especially in the higher end, z = 0.4 – 0.6, only a few galaxies (the most luminous ones, so called ULIRGS) have been observed and detected so far due to lack of suitable receivers (e.g., Combes et al., in SF2A-2007: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics, p.312). With broad-band 4 and 3 mm receivers, combined with accurate pointing and reliable calibration, the 20 m telescope will continue to be competitive in extragalactic studies. This is a perfect area for the 20 m telescope and would be an invaluable service to the community.

The most sensitive extragalactic observations make use of absorption spectroscopy toward distant flat-spectrum quasars. These measurements are limited only by the S/N ratio that can be achieved on the background continuum source. It is not necessary to have the sensitivity to detect extremely faint emission lines in distant sources. The measurement of molecular absorption lines offers a lot of interesting astrophysics. The z = 0.89 absorption system toward PKS 1830-211, for example, shows lines from more than 30 different molecules in the rest-frame 4 mm wavelength-band alone (Muller et al. 2011, in preparation). The absorption measurements make possible accurate determinations of relative molecular abundances, which can be used to explore the general chemical evolution of galaxies out to high redshifts. Because there are so many low-excitation transitions of common molecules at wavelengths around 4 mm, this band is also valuable for Galactic absorption spectroscopy. Table A.3.1. Molecular lines in the 4 mm window. Most of the D-species have their H-counterparts in the 3 mm window. The lines below 70 GHz will be difficult to observe due to high atmospheric opacity.

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Figure A.3.1. Overview of the frequency coverage of the proposed receiver bands at 4 mm (70 – 87 GHz) and 3 mm (85 –116 GHz). Shown also are the atmospheric brightness temperature, Tatm, for a normal amount of precipitable water vapour of 9 mm, an estimated total system temperature in the zenith direction, including both receiver and atmospheric contributions, assuming the shown receiver temperature, Trec. Observations at frequencies above the CO(J=1-0) line are severly hampered by the atmospheric O2 rotational line at 118 GHz. Likewise, below 70 GHz the O2 spin-flip transitions around 60 GHz start to become the major obstacle for ground-based observations. The astrophysically most important spectral lines in this frequency regime are indicated with arrows. Note especially the deuterated pairs, HCO+/DCO+, DCN/HCN, and N2D+/N2H+, that will become observationally available with the proposed receiver system.

Figure A.3.2. As an example, a very broad-band spectrum, in the 2 mm band, obtained towards the starforming region Orion-KL, at a distance of about 1500 light years, is shown here. There is in total about 17000 spectral lines, of which only about two thirds have been identified so far, from interstellar molecules of varying complexity.

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A.3.5 Global 3mm VLBI Finally, the Global 3mm VLBI Array (GMVA; consists of a VLBI network of the large mm-wave telescopes in the world) provides resolution down to 40 µarcs, and hence VLBI at millimetre wavelengths provides a unique tool to probe the most central regions of compact Galactic and extragalactic radio sources that are unobservable at longer wavelengths. Sources such as the super-massive black hole in the centre of our Galaxy (Sgr A*), the even more massive black hole in M87, and similar other objects can be studied with an angular resolution high enough that the event horizon and the gravitational light bending near these black holes may in principle be detected in the near future. The main science drivers are tests of general relativity, accretion around black holes, and the genesis and evolution of jets. OSO will continue to take part in the international GMVA observations and the dual-polarisation capability of a new receiver would immediately improve our performance. Indeed, a significant number of proposals ask for dual circular polarisation. In addition, we foresee a demand for an increasing bandwidth at 86 GHz.

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A.4. Science Case for Continued APEX Operation A.4.1 Selected Science Highlights with APEX Over its first years of operation, APEX has significantly contributed to a wide variety of science areas. A total of 26 articles appeared in a special issue of Astronomy & Astrophysics (August 2006) with the telescope receiving title page prominence. Since 2006, ≈ 150 refereed papers have appeared in journals. This is especially remarkable since during the first years of operation, the telescope was operated without its full facility instrument complement, so we expect the publication rate to increase even further in the coming years. The science case for APEX is to a large extent the same as that for CCAT (see below), and instead of repeating it here we exemplify what can be done with a sub-mm telescope on an excellent site by providing a list of selected highlights, covering a breadth of science areas, from the first years of APEX operation: • Deep and wide-field 870 µm imaging of cosmological fields such as the ECDFS,

Cosmos, Akari Deep Field, lensing cluster fields and a Ly α proto-cluster at z = 2.38. In particular, the ECDFS project is the most uniform wide-field blank-field survey with a vast amount of supporting multi-wavelength data. Apart from a source list of over 130 securely detected sources, the uniformity of this LABOCA survey allows a detailed analysis of the sub-mm properties of many thousand sources using the stacking technique (Greve et al. 2010, ApJ 719, 483; Lutz et al. 2010, ApJ 712, 1287).

• The detection of sub-mm galaxies behind the Bullet cluster, which acts as a gravitational lens magnifying the background galaxies (Johansson et al. 2010, A&A 514, A77). In a LABOCA survey of sub-mm galaxies behind galaxy clusters, 37 sub-mm sources were detected, 14 have not been previously reported (Johansson et al. 2011, A&A 527, A117), Fig. A.4.1.

• The LABOCA (870 µm) and ASZCA (2 mm) bolometer cameras have been used to observe the hot gas in galaxy clusters via the Sunyaev-Zeldovich (SZ) effect. The SZ-effect was observed in the cluster Abell 2163 (Nord et al. 2009, A&A 506, 623) and the Bullet cluster (Halverson et al. 2009, ApJ 701, 42). A map at 2 mm wavelength of a 0.8 deg2 part of the sky was used to constrain the high-l power spectrum of mm-wave anisotropies (Reichardt et al. 2009, ApJ 201, 1958).

• The APEX Large Survey of the Galaxy, ATLASGAL, a sub-mm dust-continuum survey of the inner Galactic plane with LABOCA, has been completed, Fig. A.4.2. The survey has produced a large-scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, an extremely valuable preparation for ALMA and Herschel follow-up observations. Thanks to its location in the southern hemisphere, APEX has a much better visibility of the Galactic Centre region.

• The first detection of sub-mm flares in the Galactic Centre from coordinated APEX and VLT observations (Eckart et al. 2008, A&A 492, 337). The radiative counterpart of the super-massive black hole at the Galactic Center, Sgr A*, has been studied with concurrent X-ray, near-IR, sub-mm, and GeV gamma-ray observations. A strong sub-mm outburst 200 minutes after a bright NIR flare was detected with LABOCA, putting constraints on theoretical models of flares.

• Redshifted emission from the CII 157.74 µm line has been detected in three sources using SHFI. In the lensed galaxy BRI 0952-0115 at z = 4.43, the line is much stronger than previous CII detections at high-z, partly due to the lensing amplification (Maiolino et al. 2009, A&A 500, L1). The quasar BRI 1335-0417 at z = 4.41 is the most luminous unlensed C II line emitter known at high redshift (Wagg et al. 2010, A&A 519, L1). Observations of C II and CO in the z = 4.76 sub-mm galaxy LESS J033229.4-275619 suggest that the highest redshift star-forming

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galaxies may also be characterized by lower metallicities (De Breuck et al. 2011, A&A 530, L8).

• LABOCA observations of debris disks around stars, possible leftover planetesimal belts analogous to the asteroid and comet reservoirs of the Solar System, e.g., q1 Eridani, a solar type star with a planet and a dust belt (Liseau et al 2008), ten exo-Kuiper-Belt candidates (Nilsson et al. 2010, A&A 518, A40), and three infrared-excess stars (Nilsson et al. 2009, A&A 508, 1057).

• The first detections of a number of molecular ions: CF+, with APEX-2a, which is a ubiquitous component of the interstellar medium (Neufeld et al. 2006, A&A 454, L37), OH+, with CHAMP+ (Wyrowski et al. 2010, A&A 518, A26), and SH+ in absorption towards the strong Galactic Centre continuum source Sgr B2(M) (Menten et al. 2011, A&A 525, A77).

• Observations of the fragmenting comet 73P/Schwassmann-Wachmann (Biver et al. 2008, in Asteroids, Comets, Meteors, LPI Contribution No. 1405, paper id. 8149) and of the Venusian mesospheric winds using APEX-2a (Lellouche et al. 2008, P&SS 56, 1355).

• The first detection of hydrogen peroxide, HOOH, in the interstellar medium, made with SHFI towards the cloud core rho Ophiuchi A (Bergman et al. 2011, A&A 531, L8), Fig. A.4.3.

• SHFI observations of deuterated molecules, e.g., deuterated formaldehyde in rho Oph A (Bergman et al. 2011, A&A 527, A39), D2H+ in a prestellar core (Parise et al. 2011, A&A 526, A31), water deuterium fractionation in the low-mass protostar NGC1333-IRAS2A (Liu et al. 2011, A&A 527, A19), and deuterium fractionation and the degree of ionization in massive clumps within infrared dark clouds (Miettinen et al. 2011, A&A 534, A134).

• Emission lines from circumstellar envelopes observed with APEX were used as external calibrators in evaluations of the in-orbit performance of the HIFI instrument onboard the Herschel Space Observatory (HSO) (Roelfsema et al. 2011, A&A 537, A17).

Fig. A.4.1 Signal-to-noise maps of five galaxy cluster fields obtained with LABOCA. White circles represent the significant sources in the map (Johansson et al. 2011).

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Fig. A.4.2. Part of the galactic plane covered by the ATLASGAL project using LABOCA, and details of some massive star-forming regions (Schuller et al. 2009). A.4.2 Present Receiver Status Since its dedication in September 2005 the APEX telescope, equipped with state-of-the-art instrumentation, has been pioneering the southern sky at sub-mm wavelengths. It has produced major scientific results, summarized above, in virtually all fields of astronomy. These astronomical achievements were made possible by a number of ground-breaking technological innovations. APEX operate(d)

• as first telescope a heterodyne (SIS and HEB mixers) receiver suite, built by OSO and MPIfR, covering all the frequencies accessible from the ground from 200 GHz up to 1.4 THz,

• the first short-submillimetre-wavelength multi-pixel SIS array receiver CHAMP+, built by the MPIfR, with 7 pixels each covering the 350 and 450 µm atmospheric windows,

• wideband Fast Fourier Transform spectrometers (FFTSs) based on Field Programmable Gate Arrays,

• two submillimetre bolometer array cameras built by the MPIfR; LABOCA (850 µm) based on semi-conductor thermistors, and SABOCA (350 µm) based on superconducting Transition Edge Sensor (TES) technology,

• a UCal Berkeley-built bolometer camera employing TES technology at 2 mm wavelength (ASZCA),

• a UCol Boulder-built very broad-band spectrometer aimed for detections of highly redshifted CO lines (Z-Spec) and, finally

• an innovative operating system (APECS), based on advanced software tech-nology developed hand in hand with ALMA software, and complex data reduction packages were developed.

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Fig. A.4.3 The first interstellar detection of HOOH towards ρ Oph A (Bergman et al. 2011). A.4.3 Future Science Drivers The science drivers for continued APEX observations are essentially the same as for the CCAT project (with the limitations imposed by the slightly lower site and the smaller collecting area), and we refer to Sect. A.5 for a more detailed description of them. Here we merely summarize five areas where APEX will contribute significantly in the future:

• ALMA: APEX will provide ALMA with the necessary large-scale information, as well as the sources for which follow-up, high-angular-resolution observations will be made. Figure A.4.4. illustrates the large-scale complexity of the ISM, and it will be impossible to map with ALMA the very large areas covered by the HSO observations.

• HSO: There is a tremendous scientific synergy between the HSO and APEX, not least because of their similar beam sizes. HSO will trigger many complementary APEX science projects well beyond its estimated lifetime of 3.5 years (from 2009).

• VLBI: APEX can be part of an ‘Event Horizon Telescope’: this is based on the VLBI method and will provide the possibility to study super-massive black holes in unprecedented detail, in particular the one in the Galactic Centre.

• THz heterodyne receivers: After the end of HSO and before CCAT, APEX will provide the only way to THz observations (e.g., high-J CO lines). GARD has special expertize in this area.

• Technological testbed: APEX can be used for testing new exploratory sub-mm-

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wave instruments, which can subsequently be used on APEX, ALMA, or sub-mm telescopes to come.

In addition, APEX, being located in the southern hemisphere, is particularly well placed for studies of e.g. the centre of the Milky Way, the Magellanic Clouds, the most nearby starforming regions, and nearby Active Galactic Nuclei as Centaurus A.

Fig. A.4.4. An HSO image (false colour using 70, 160, and 250 µm data) from the Hi-GAL project showing the enormous complexity of the interstellar medium (image size is 2ox2o). A.4.4 Instrumentation Plan As explained above, APEX operates a full suite of very competitive bolometer and heterodyne receivers, some as facility instruments open to all APEX communities, others as PI instruments serving partner users, but also available to the wider community on a collaborative basis. The instrumentation programme for the coming years, recognizing the existence of the ALMA, aims at wider frequency coverage, more pixels, and improved sensitivity per pixel. In contrast to, e.g., optical technologies, heterodyne detectors at short sub-mm wavelengths do not yet operate at their quantum limit, and large improvements are still to be expected per pixel. For the bolometer cameras, there is a need for an increased field of view with more pixels to compete with SCUBA-2 (covering the northern sky from Mauna Kea Observatory, Hawaii). The number of pixels for the bolometer arrays (several thousand pixels for the next generation) and the increasing complexity of their read-out/data acquisition, as well as the considerably larger number of pixels for heterodyne arrays (as compared to the present situation) will make these instruments costly. In addition to this, the large interest in high-z galaxies requires specially designed very broad-band, coarse spectrometers to determine redshifts.

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New instruments that are on the verge to be installed on APEX are ArTeMiS (a 4096-channel bolometer array, which instantaneously fully sample the image in the focal plane, at 450, 350, and 200 µm, developed by CEA-Saclay in France) which will come as an ESO PI instrument in early 2013, and ZEUS-2 (a redshift spectrometer for the 350, 450, and 610 µm telluric windows) that will come as a collaboration with Cornell University. Both these receivers are in line with the future requirements of APEX receivers.

A new technique for building large bolometer arrays, MKID (Microwave Kinetic Inductance device), is investigated at a number of laboratories around the world and the APEX collaboration is following this. Large bolometer arrays can potentially be built much cheaper with this technique. Arrays at 350 and 850 GHz are being discussed. Heterodyne arrays are built around individual mixers with corrugated horns which limits the sampling of the image plane. Nevertheless, this is most likely the technique to be used in the foreseeable future. Present-day heterodyne arrays have around 10 pixels, but the ambitious programme for CCAT mentions arrays with more than 100 elements. It is not clear how realistic this is considering that the presently largest array, the 345 GHz Supercam of 64 elements, have taken a decade to build and it is still not commissioned on a telescope. It appears that the main interest for heterodyne arrays lie in the 300 to 500 GHz range, e.g., by covering the CI line at 492 GHz and the CO(J=4–3) line at 461 GHz simultaneously. A design of a 7 pixel 350 GHz and 19 pixel 450 GHz heterodyne arrays receiver (LAsMA) is underway.

Presently, there is no definite plan for new APEX facility instruments that has been approved by the APEX Board, but in summary we have the following situation in terms of new instruments:

• ArTeMiS bolometer arrays at at 450, 350, and 200 µm, 5000 pixels in total; installed 2013

• MKID bolometer arrays 350 (4000 pixels) and 850 GHz (24000 pixels); to be developed

• ZEUS-II, high-redshift spectrometer, installed 2012 • LAsMA, heterodyne arrays for 350 (7 pixels) and 450 GHz (19 pixels); to be

developed They will all be PI-instruments with different partners involved. From a technological point of view the LAsMA is most interesting for OSO.

An evaluation of the whole APEX project will be done in 2013, which, if successful, can lead to an extension until the end of 2017 (or possibly longer).

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A.5 Science Case for CCAT The Caltech-Cornell Atacama Telescope (CCAT) is a 25 m sub-mm radome-enclosed telescope to be placed at the Cerro Chajnantor summit at ≈ 5600 m of altitude, i.e., at about 600 m above the ALMA plateau. The optical design of CCAT foresees a compact Ritchey-Chrétien with f/0.4 hyperboloid (active) primary mirror, which allows for a relatively compact 40 m dome. It will have a surface accuracy of 10 µm (rms) allowing observations up to 2 THz. The field of view (FOV) will be as large as 20’.

The most recent sub-mm telescopes, Herschel Space Observatory (HSO; in orbit and scientifically operational since 2009) and APEX, have demonstrated the wealth of new knowledge which can be gained from the sub-mm and far-infrared part of the spectrum across many fields of astronomy. While APEX, HSO and CCAT share many scientific goals, CCAT will provide a long-term perspective that cannot be offered by HSO (expected to end operations in spring 2013), and an angular resolution that is 7 times better, and it will have a collecting area four times and a resolution twice that of APEX.

CCAT will act as a complementary facility to ALMA, as CCAT will provide the large scale view, through its ability to survey large parts of the sky (a sub-mm interferometer has a field of view limited to the primary beam). Indeed, with the large instantaneous field of view and the rapid mapping speed, CCAT is optimized for wide field sub-mm imaging. A prime science objective is conducting large-scale surveys, to which the consortium anticipates devoting about half of the available observing time. Multiple factors – the 25 m aperture, the improved atmospheric transparency of the higher site, the use of broad-band continuum detectors, the high aperture efficiency, and the possibility of achieving sensitivities limited by photon statistics – combine to give CCAT a continuum point-source flux sensitivity in the 350 and 450 µm atmospheric windows that is comparable to ALMA on a per-pixel basis, with ALMA gaining advantage at long wavelengths and CCAT gaining at shorter ones. Therefore, with the use of large array cameras, the mapping speed for CCAT will be many orders of magnitude faster than ALMA, enabling large-scale surveys and providing extraordinary complementarity with ALMA. The predicted sensitivity for CCAT is shown in Table A.5.1. Table. A.5.1. CCAT continuum sensitivities and confusion limits.

Figure 4: Left: CCAT continuum point-source sensitivity per pixel compared to other facilities,calculated for a 5! detection in one hour integration. Right: Optical layout and ray–tracing of theCCAT design, including overall dimensions for optical components in mm.

Table 2: CCAT Continuum Sensitivity! " PWV NEFDa CL fluxb CL timec CL densityd CL mappinge

(µm) (GHz) (mm) (mJy s1/2) (mJy) (min) 103 deg!2 deg2 yr!1

200 1500 0.3 151 0.36 116350 857 0.4 14.4 1.29 52 38 26450 667 0.5 13.8 1.45 38 23 60620 484 0.5 16.3 1.27 68 12 23865 347 1.0 5.83 0.92 17 6.2 3191180 254 1.0 1.74 0.61 3.4 3.3 23001400 214 1.5 2.93 0.45 18 2.4 4362000 150 1.5 2.30 0.20 58 1.2 803300 90.9 1.5 2.82 0.08 513 0.43 9a The NEFD is the 1 # flux sensitivity achieved for an integration time of one second,

calculated using the appropriate precipitable water vapor (PWV), as listed.b The source flux density level reached at the confusion limit (model prediction).c The time required to reach the confusion-limited flux, calculated for 5 # detection.d The source density at the confusion limit (CL), in units of 1000 sources, taken to

correspond to 30 beams per source. For reference, deep 24 µm imaging with Spitzer(Papovich et al. 2004, ApJS 154, 70) yields N(S24 µm > 30 µJy) ! 60, 000 deg!2.

e The confusion–limited mapping speed, taking into account PWV statistics (see Table 3),for a PWV-scheduled observing program utilizing instruments with 50, 000 detectors.

10

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For deep imaging, the raw sensitivity (NEFD) must be supplemented by estimates of the source confusion limit. Because CCAT’s sensitivity and angular resolution will allow probing much more deeply into the sub-mm galaxy population than current instruments, the confusion limit is not yet well known and must be predicted using models that extrapolate existing (shallower) measurements. At 350 µm, and using a very conservative value of 30 beams per source (i.e., 0.03 sources per beam), CCAT will yield a confusion-limited areal density of ≈ 40 000 sources per square degree, which is quite comparable to deep 24 µm counts with Spitzer. Relative to existing 10-15 m telescopes, CCAT will be well over an order of magnitude faster to reach a given flux level, and will have a deeper confusion limit.

Characteristic for most of the science goals is the requirement for a suit of instruments that can do both continuum and spectral line observations. The continuum is predominantly powered by thermal dust emission, where the continuum cameras will permit not only mapping out dusty regions, but also determine the temperature distribution across different environments. The focus of the spectral line observations is the detailed study of both atomic and molecular lines, which brings insight into the physical properties of the gas present in e.g. star-forming regions and starburst galaxies. For spectroscopy, line flux sensitivities (1σ, 1 s) lie in the range 2.2×10−18 W m−2 s1/2 at 350 µm to 1.6×10−19 W m−2 s1/2 at 1.2 mm. If CCAT is equipped with THz receivers it will also open a window that is not available through ALMA.

Below a number of specific areas are listed where CCAT will contribute significantly. A.5.1 Astrochemistry: Exploration of the Molecular Universe Molecules are a critical diagnostic of the chemical evolution of material as it cycles from diffuse clouds to the creation of stars and planetary systems and finally to dying stars that enrich the ISM. Wide-band spectroscopy in the sub-mm bands will yield a rich dataset to extract the properties of the gas along each step of this cycle. The resulting large line-survey data sets will contain a complete chemical inventory, the chemical history and evolutionary state, the line to continuum ratios, the excitation and cooling conditions, and a nearly complete dynamical picture of all objects surveyed. They will provide a foundation and an overall context for more detailed investigations of specific sources and processes with more limited spectral coverage. The fundamental questions to be addressed by these studies are: What is the life cycle of molecules in the Universe from the diffuse interstellar medium to planetary systems? What are the chemical pathways leading from simple atoms and diatomic molecules to complex organic species? What is the distribution and types of organics that seed the habitable zone around stars?

Since the inception of molecular astronomy, it was accepted that CO and its isotopologues are the best tracers of temperature and total column of molecular gas, while high-dipole moment molecules (e.g., H2CO and CS) best traced the dense star-forming core. Today we know that prior to star formation the dense gas is cold and these species are frozen onto grains. Star formation is thus viewed in the light of our growing understanding of the complex cloud core chemistry. While ALMA will study the heart of star formation, the area where collapse likely begins, a complete picture will ultimately require looking beyond the central condensation to explore the initial collapse dynamics from cloud to envelope and central core. This requires sensitivity to large scales that are accessible to CCAT, underscoring again its complementarity with ALMA.

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A.5.2 Star Formation Stars are formed in molecular clouds, and the process of star formation is fundamental in astronomy with impact on the properties of galaxies and their chemical evolution. Star formation is also closely linked with the formation of planetary systems, including our own. The molecular clouds hosting star formation can be as big as 50 pc and as massive as 106 M⊙. It is within their interiors, the densest regions, called ‘cloud cores’, that the youngest stars are found. This can be both isolated and multiple stellar systems with masses ranging from 0.3 to 3000 M⊙, and the stellar masses appear to follow (statistically) an Initial Mass Function (IMF) distribution. To make progress, we need data on molecular cloud cores as well as on young stars. Specifically, to understand the statistics of the overall problem as well as details of core structure, we need to have a large unbiased sample of cores in a variety of regions. In the Milky Way, the stellar IMF is remarkably consistent across a variety of environments. The origin of this uniformity is unknown. Among the physical processes that may lead to a seemingly invariant IMF are gravitational or turbulent fragmentation, feedback from stellar winds and outflows, competitive accretion, ejection of proto-stellar cores and stellar mergers. An intriguing possibility is that the mass function of dense clumps in molecular clouds, identified by their thermal dust emission, has a similar shape to the stellar IMF, suggesting that the clump mass function translates into the stellar IMF. CCAT observations will establish if the clump mass function follows the stellar IMF to the sub-stellar (brown dwarf) regime, and if the clump mass function is similar over a wide range of environments in the Galaxy. If the clump mass function is invariant, it will provide compelling evidence that the stellar IMF is imprinted in the fragmentation structure of molecular clouds. To make a definitive determination, observations specifically require:

• Sensitivity to clumps capable of forming a 0.01 M⊙ brown dwarf, an order of magnitude more sensitive than current surveys.

• Angular resolution < 5′′ to resolve 0.05 pc clumps to 1 kpc and to relieve the source confusion of imminent surveys with HSO and SCUBA-2 on the JCMT.

• Observations of both the dust continuum and molecular lines: dust emission probes dense regions where molecules may deplete onto grains; high spectral resolution observations of molecular lines yield the kinematic state (collapse, expansion, stability) of the clumps.

• Surveys over tens of square degrees to image molecular clouds, and of many fields in order to sample different environmental conditions.

• Multi-wavelength observations to measure dust temperatures and emissivity; because dust temperatures can range from ∼10 K to > 100 K, observations at λ ≤ 350 μm are needed.

The sensitivity, resolution, mapping speed and λ-coverage of CCAT will uniquely enable Galactic surveys that can link the stellar IMF to the physics and topology of the ISM. It is this data set that CCAT should be able to deliver, and it should have a major impact on unraveling the core-star connection in unprecedented detail. A.5.3 Circumstellar Disks The majority of the pre-Main-Sequence stars of low mass (M < 3 M⊙) are thought to have circumstellar disks of gas and dust. These are the precursors of planetary systems. Planets form in these disks, and the process is tightly related to the formation and evolution of dust. Circumstellar disks probably only last a few million years before

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dissipation, even though remnants remain visible for longer times in the form of debris disks. An understanding of the structure and evolution of disks is necessary to explain their ubiquity, as well as the processes and time scales associated with the formation of planets. Masses of circumstellar disks are uncertain — they are thought to be of the order of a few percent of the stellar mass, but the dispersion in that value is likely to be very large. With a similarly large dispersion, their sizes are on the order of a few hundred AU. Their temperatures are consistent with them being heated by the central star, most of their material glowing at temperatures of ~100 K or below. Thus, their dust emission falls mostly in the mid- and far-IR. Some disks are seen via the scattered starlight, as in the famous case of β Pic, and their gas content can be mapped with mm array telescopes.

A key observational component for the study of the physics of these structures is the measurement of the dust mass, which needs to be done by detecting their thermal emission, best observed in the sub-mm regime where it is thought to be optically thin. Spitzer and HSO have resulted in much progress in this area. However, these telescopes are severely resolution-limited. High resolution is not only important in detecting thermal gradients in disks and therefore allowing a more accurate estimate of the dust mass, but also in detecting the tidal distortions in the disk structure that may be produced by the assembly of planets. In addition, spatially and spectrally resolved line profiles of atomic and molecular species map out the physical and chemical conditions and the velocity fields in the disk. Successful theoretical models of these data provide tools to infer the dynamical state and age of the disk, which must match the age of the central stellar object and allowable time scales for planet formation.

The combination of angular resolution, operation at multiple sub-mm bands from 200 to 850 µm (thus allowing characterization of the temperature variations in the disk), continuum and line observations, and the large FOV of CCAT is the key to its extraordinary potential for work in this field. A.5.4 Star Formation and the ISM in Nearby galaxies To understand the strong evolution of star formation over cosmic time, nearby, spatially resolved galaxies must be studied to relate the astrophysical probes to high-z systems: Resolved sub-mm images will reveal the interplay between the star formation process and the natal interstellar medium (ISM), helping to understand the line emission from distant galaxies. Of particular interest are the most active regions in nearby normal and starburst galaxies because it is these regions that will provide the best templates for distant LIRG and ULIRG-class (bright and very bright in the IR) galaxies responsible for the bulk of the cosmic FIR background, Fig. A.5.1.

Multi-wavelength studies in concert with sub-mm observations will address fundamental questions about star formation in galaxies, such as: What are the relationships between the age (chemical abundances) of the ISM, the degree of star formation activity, galactic morphology, and the environment? What triggers galaxy-wide starbursts? Do starbursts burn themselves out by consuming all the available fuel or by disrupting the natal environment through stellar winds? Multi-band images can trace the process of gas compression in spiral density waves, the formation of stars in molecular cloud cores, and the disruption of the parent clouds by newly formed stars. Moreover, the FIR/sub-mm spectral regime provides a wide variety of extinction-free spectral line probes of both ambient radiation fields and the physical properties of interstellar gas (e.g., density, temperature, dynamics, radiation intensity and hardness). Most of those lines lie within a few hundred K of the ground state and have modest critical densities; the emitted radiation is nearly always optically thin. Therefore, these lines are important (often dominant) coolants for the phases of the ISM relevant to star formation processes.

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Nearby galaxies will make excellent targets for CCAT. With Fabry-Perot, Fourier transform, or waveguide-fed multi-object spectrometers, CCAT will be able to deliver spectroscopic images of galaxies in the NII 205 µm, CI 370 and 609 µm, mid-J CO (e.g., 4–3, 6–5, and 7–6) and 13CO(6–5 and 8–7) rotational lines at angular resolutions as fine as 2". In the nuclei of some galaxies (e.g., ULIRGs) it would detect CO emission up to J=13–12 (200 µm) arising from nuclear clouds highly excited by starbursts, or even CO emission from AGN-excited molecular tori, thus providing a link between stellar mass buildup and super-massive black hole growth.

Fig. A.5.1. The interacting galaxies NGC 4038/4039 at optical, IR, and sub-mm wavelengths. In the Hubble image on the left, light from hot, young stars is visible, as well as dark dust lanes. In the central panel from Spitzer, more sites of star formation become visible. In the right panel, 350 µm image from the Caltech Submillimeter Observatory shows that the bulk of the luminosity derives from star formation invisible at shorter wavelengths. At 350 µm, CCAT will have the same resolution as the Spitzer image. A.5.5 Distant Galaxies Among the potentially most important results of cosmology in the last decade is the realization that the star formation rate at redshifts z > 1 may have been higher than at present, and that much of the light produced by stars at high redshift reaches us in the far-IR, after having been reprocessed by dust.

Measuring the star formation history of galaxies across cosmic time is one of the most important problems of contemporary astronomy. Galaxies grow through mergers and accretion of intergalactic gas. The funneling of gas into nuclear regions stimulates bursts of star formation and presumably the growth of super-massive black holes at their centres. Sub-mm observations from 200 µm to 2 mm provide views of the epoch of galaxy formation, when stellar masses were being built up. Sub-mm spectral probes are keenly sensitive to physical conditions of the gas, thereby elucidating the context for star formation and providing a crucial observational link between the buildup of the stellar masses and central super-massive black holes.

The last decade has brought major advances in our knowledge of galaxies at high z. Among them is the understanding that the star formation rate per unit co-moving volume at 1 < z < 3 was 30 times the present rate. However, key questions about the galaxy formation process remain, such as: When did the earliest galaxies form? Can we identify high-redshift examples of the types of progenitors that grew to modern-day galaxies? What is the bolometric luminosity function of galaxies as a function of redshift? How are supermassive black hole and stellar mass growths related? Sub-mm observations with CCAT will help address each of these questions.

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To determine the amount of energy that has been released by galaxies, it is essential to measure their rest-frame far-IR radiation, which peaks at 50 – 200 µm and is redshifted into the sub-mm bands for z > 1. Dust emission comprises 50% of the total integrated luminosity of galaxies. That fraction is even larger for the most luminous galaxies and galaxies at high z. The amount of far-IR/sub-mm emission - and thus of star formation - from dusty galaxies is impossible to infer from the spectral properties of the escaping optical/UV light alone, Fig. A.5.2. Sub-mm observations have a strong advantage in searches for high-redshift galaxies. Because the slope of the product of the Planck function and the emissivity function of dust grains is so steep on the Rayleigh-Jeans side of the spectrum, the observed brightness of a galaxy is independent of z in the range 1 < z < 10, in that spectral regime. This has been referred to as a ‘negative-K-correction’. Thus, sub-mm surveys provide a natural mean for identifying high-redshift (z > 5) galaxy candidates within large-scale surveys: those with weak 200 – 700 µm emission and bright 800 µm to mm-wave emission.

Fig. A.5.2. Left: The sub-mm galaxy GOODS 850-5 (within the circle at the centre) in the optical (Hubble), IR (Hubble, Subaru, Spitzer), sub-mm (SMA) and radio (VLA). GOODS 850-5 has a FIR luminosity of 2×1013 L⊙, yet it is invisible at optical and near-IR wavelengths. Redshift estimates based on the far-IR/radio ratio and the stellar light observed by Spitzer suggest that z ≈ 4 − 6. Right: An example of redshift determination using a broadband spectrometer, a Z–Spec spectrum of the Cloverleaf quasar at z = 2.56 with CO rotational lines.

Existing observations of high z far-IR/sub-mm galaxies are currently limited to

the most luminous examples (i.e., > 1013 L⊙). They are known in small numbers. Redshifts and stellar masses for these galaxies can sometimes be determined from optical and near-IR observations, but total luminosities, gas and dynamical masses must be derived from far-IR/sub-mm observations of gas and dust. Without this information, far-IR/sub-mm-dominated high-redshift galaxies appear to be little different from optically-selected galaxies at the same redshifts, despite their much greater luminosity.

SCUBA-2 on the James Clerk Maxwell Telescope (JCMT, on Mauna Kea, Hawaii) and the HSO will have an important impact in this field in the next few years. However, both telescopes will be confusion limited at few to several mJy, while the confusion limit of CCAT will be ≈ 0.3 mJy or better, allowing it to reach substantially further down the luminosity function. SCUBA-2 will observe only at 450 and 850 µm - a much more restricted wavelength range than CCAT. Furthermore, HSO is a cryogenic mission which will be completed approximately when ALMA comes on line, precluding any opportunities for coordinated observations or surveys. On CCAT, a 10 square-degree survey, covering a cosmologically relevant volume, could be covered to a depth of 0.2 mJy (rms) at 350 µm in 2 000 hours, yielding of order a 100 mostly faint, distant galaxies. Moreover, CCAT will carry out a spectroscopic survey of sub-mm galaxies, using multi-object versions of broadband direct-detection grating spectrometers such as

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Z-Spec and ZEUS, now in use at the APEX and the Caltech Submillimeter Observatory (on Mauna Kea, Hawaii). Conceptual development indicates that spectrometers capable of observing 10 – 100 objects simultaneously, while spanning multiple atmospheric windows, will be feasible. Continuum surveys at CCAT will be paralleled by spectroscopic ones capable of determining redshifts via the CII and/or CO lines. A.5.6 The Solar System There are a number of interesting science areas in this context. Here we briefly mention a few. The sub-mm continuum from the sun is formed at an especially important region of steep temperature rise from the top of the photosphere through the chromosphere and into the corona. It is a crucial region for the control of the mechanical heating of the corona. In the case of comets studies of isotopic forms of water and related molecules (HDO, OH+, etc.) are particularly interesting. The Enceladus water torus in the Saturn system is extremely interesting and definitely observable from Earth at mm/sub-mm wavelengths. The outer Solar System offers an interesting example of the potential of CCAT as described here.

Over the last decade, several hundred solar system objects beyond Neptune have been discovered. Known as Kuiper Belt Objects (KBOs), they are believed to have formed very early on in the outer reaches of the proto-planetary disk around the Sun, and to have undergone very little evolution since then. The primitive nature of the material in this region holds important clues towards our understanding of the formation and evolution of the Solar System. These objects are small and very distant. The largest among them are Pluto and its moon Charon, 2400 and 1200 km in diameter, respectively; the third largest among KBOs is Varuna, with an estimated diameter of about 900 km. The measurement of the size of KBOs is an important goal, not only for determining the population properties, but also because a knowledge of the size allows estimates of the albedo and permits drawing inferences on the physical conditions of their surfaces. With angular diameters of, at best, a few tens of milli-arcseconds, they will appear unresolved in imaging surveys. To first order, size can be estimated from optical observations, the orbital parameters, and some value for the unknown albedo. This, however, gives no information on the physical properties of their surfaces as the value of the albedo needs to be assumed. A direct measurement of the size is possible from combined optical and IR measurements. At heliocentric distances on the order of 40 AU, KBOs have temperatures near 45 K, and their emissivity peaks near 70 µm. However, the Rayleigh-Jeans part of the KBOs' SED falls in the far-IR/sub-mm, and it is therefore possible to measure KBO sizes from the ground. Using that technique, the SCUBA bolometer on JCMT has been used at 850 µm to measure the diameter of Varuna and Quaor. Because of the faintness of KBOs’ far-IR emission and because of confusion with background sources, the far-IR/sub-mm technique is applicable to only the very brightest KBOs with existing telescopes. CCAT would change that, allowing the detection of KBOs to sizes of order 100 km, making possible a statistical investigation of both the size distribution and surface properties of these objects.

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A.6 Science Case for Geodetic VLBI A.6.1 Introduction The Earth as a system is difficult to fully understand in detail. In this perspective it is particularly worrisome that there is no longer any doubt that human activities are affecting its surface behaviour, not least the climate. In order to increase our understanding of system Earth and its evolution it is, among other things, necessary to observe and measure, often over long time scales, different parameters of paramount importance. Such activities are by necessity internationally organized, e.g., via the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), Fig. A.6.1. Geodetic Very Long Baseline Interferometry (VLBI), a technically very sophisticated method that uses a network of radio telescopes to measure e.g. the rotation and changes in the crust of the Earth, forms an important component of GGOS. Hence, it is of great importance for achieving a sustainable development and the survival of human society in an era of rapid environmental changes and risks due to natural and anthropogenic hazards.

OSO is the only geodetic VLBI station in Sweden. Worldwide there are about 35 similar geodetic VLBI stations. Only eight of these, incl. OSO, are equipped with VLBI, tracking stations for Global Navigational Satellite Systems (GNSS), and a superconducting gravimeter (SG), i.e., they are Fundamental Geodetic Stations in the sense of GGOS and as such particularly important for integrating and combining space geodetic techniques with physical measurements (e.g., gravity by SG). Geodetic VLBI is organised via The International VLBI Service for Geodesy and Astrometry (IVS).

Fig. A.6.1. The components of the Global Geodetic Observing System (GGOS).

OSO has played an important role for the development of global geodetic VLBI. The time is ripe to take the next step in the technical development of geodetic VLBI, as outlined in a well-defined international technological roadmap, VLBI2010 (see below), which will lead to an improvement in accuracy by one order of magnitude as compared to today’s VLBI system. The IVS has adopted VLBI2010 as its new standard (Schlüter et al., 2002, Adv Space Res, 30(2), 145; Schlüter & Behrend, 2007, J Geodesy, 81(6–8), 379),

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and OSO must follow this in order to remain a major partner within the IVS. The international goal is to equip all IVS stations with a twin-telescope solution. Of today's IVS stations, Wettzell (Germany), Ny-Ålesund (Spitzbergen, Norway) and OSO are in the building or planning phase. OSO has the goal to remain one of the leading IVS stations, both in terms of data quality and data reliability. With a dedicated twin-telescope system it can also become a leading station for the amount of data delivered to the international community. In addition, the OSO location far away from tectonic plate boundaries means that only small and rare episodic tectonic motions are expected, which is very beneficial for the purpose of maintaining e.g. the fundamental reference frames.

The proposed twin-telescope system for geodetic VLBI at OSO will be the Swedish contribution to the global geodetic VLBI network. The infrastructure will first of all provide observations to study the geodynamics of the Earth. The VLBI technique is unique and outstanding in providing the most accurate results for geodetic and astrometric reference systems, i.e., the International Terrestrial Reference Frame (ITRF) and the International Celestial Reference Frame (ICRF). Spin-off products are accurate estimates of the atmospheric water vapour content and synchronization of the atomic clocks used for the observations, relevant for climate research and accurate time-keeping applications, respectively. In summary, the measurement results, which are all archived and open to access, will be used by thousands of researchers spread over the world, working in research fields like:

• Atmosphere and climate • Earth rotation • Global geodynamics and plate tectonics • Space navigation • Terrestrial and celestial reference frames

Additionally, all applications that involve accurate reference systems, Earth

rotation, and/or global geodynamics rely on the results from geodetic VLBI. Therefore, the infrastructure results are indirectly used by millions of people everyday, e.g., every individual that uses a satellite-based navigation system (e.g., GPS) utilizes the reference frames that are created and maintained by geodetic VLBI. National collaborators for basic science and benefits to the society include: • Lantmäteriet (reference frames) • Swedish National Seismic Network (geodynamics) • SP Swedish Technical Research Institute (time keeping) • Swedish Meteorological and Hydrological Institute (climate research).

Finally, we emphasize that activities of this character are of great importance for

national education and science. Members of society of all ages are fascinated by the VLBI technique, which uses the most distant objects in our universe to measure space and time and derive the properties of our Earth. Geodetic VLBI also plays a significant role in OSO’s outreach activities. A.6.2 Geodetic VLBI at Onsala In the 60:es and 70:es the first models for plate motion were developed, based on geological records over millions of years (Minster & Jordan, 1978, J Geophys Res, 83, 5331). In parallel, space-geodetic techniques were applied to measure the actual plate motion. Among these techniques were laser ranging to artificial satellites and the moon, and the geodetic use of VLBI. Besides the primary goal of global geodetic measurements, further goals like the measurement of Earth rotation parameters and

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tidal phenomena were formulated already in the beginning of the development of the space-geodetic techniques.

The first VLBI experiment at OSO, and the first involving a European telescope, was performed in April 1968 as a combined geodesy and astronomy session. In the following ten years Mark–I data were acquired in many experiments. The observed reproducibility of estimates of baseline lengths (i.e., distance between two stations) was of the order of a few ten centimetres, and the estimates of the Earth orientation parameters were consistent with the models available at the time (Ryan et al., 1986, J Geophys Res, 91(B2), 1935). The Mark–I system was replaced by the dual-frequency Mark–III system, developed at Haystack Observatory and at NASA in the US, which allowed corrections for radio-wave delays caused by the ionosphere (Clark et al., 1985, IEEE Trans. Geoscience and Remote Sensing, GE-23, 438). The first successful Mark-III experiment was carried out in July 1980 and OSO was involved. The accuracy of baseline length estimates improved drastically, approaching cm accuracy. The first evidence for ongoing plate motion between North America and Europe was presented by Herring et al. (1986, J Geophys Res, 91, 8341).

Table A.6.1 lists geodetic milestones and major events related to the space-geodesy research, involving primarily VLBI and GPS activities, at OSO. OSO was the first European site active in geodetic VLBI. The long time series of intercontinental-baseline-length observations on the baseline Onsala–Westford clearly reveals present-day plate tectonic motion, Fig. A.6.2. Since long time series are of utmost importance for this type of studies, OSO is a very important partner of the geodetic VLBI network. The typical number of experiments per year has been rather constant around 15 – 25. Thanks to increasing recorded bandwidths, and improved sensitivities, the number of observed sources per experiment has significantly increased over the years. A typical number was 100–200 for the early Mark-III experiments whereas it now exceeds 400.

Since 2007, OSO is actively using e-VLBI for the determination of dUT1, the difference between Universal Time (UT1), which is directly connected to the rotational rate of the Earth, and Universal Time Coordinated (UTC), which is an atomic time, in almost real time. Earth rotation variations are not only of interest for geodynamical research but also for space navigations, since, e.g., an uncertainty in the knowledge of the Earth rotation angle of 0.1 millisecond corresponds to a few cm on the surface of the Earth (depending on latitude), but to an uncertainty of 1.5 km at the distance of Mars.

The OSO engagement has received several NASA Group Achievement Awards and the research has been graded as excellent by international evaluators several times. We note also that in the last years OSO has been recognized as one of the most reliable and productive IVS sites.

OSO is the only fundamental geodetic station in Sweden, hosting co-located equipment for a variety of techniques, e.g., geodetic VLBI, GNSS, a superconducting gravimeter, a seismometer, several ground-based microwave radiometers for atmospheric research, a GNSS-based tide gauge (Löfgren et al., 2011, Adv Space Res, 47(2), 213), and in the near future an independent pressure-sensor-based tide gauge. A.6.3 VLBI2010 – The Technological Roadmap The current geodetic VLBI system has reached its limit of performance. One important limiting factor is the severe man-made radio interference in one of the observed frequency bands (S-band, 2.1 – 2.4 GHz). Thus, the IVS started to develop a strategy for the next generation geodetic VLBI system that can fulfil the increasing accuracy requirements for space-geodetic results. This design was called VLBI2010 and a report on current and future requirements for such new geodetic VLBI systems was compiled

65 Table A.6.1. Geodetic milestones at Onsala Space Observatory. Year Event 1968 First transatlantic geodetic VLBI Onsala–Haystack (Mark–I, m accuracy) 1979 First observations with Mark-III system (dm to cm accuracy) 1985 Plate motion detected with VLBI Onsala–Westford 1987 Start of continuous GPS tracking at Onsala 1996 Detection of land uplift in Fennoscandia using GPS 2004 First intercontinental real-time VLBI Onsala–Westford 2008 Ultra-rapid Earth rotation observations Onsala–Tsukuba, < 4 min. time delay 2009 Superconducting gravimeter at Onsala; OSO a Fundamental Geodetic Station 2010 OSO recognized as one of the most reliable and productive IVS sites 2012 KAW funding of VLBI2010 Twin-telescope System

Fig. A.6.2. The increase of the Onsala – Westford (Massachusetts, US) distance with time due to continental drift. This was the first direct experimental evidence of plate tectonics. (http://ivscc.gsfc.nasa.gov/about/wg/wg3/IVS_WG3_report_050916.pdf). The overall goals of the VLBI2010 project are:

• 1 mm position and 0.1 mm/yr velocity accuracy on the Earth on global scales • Continuous time series of station positions and Earth orientation parameters • Turnaround time to initial geodetic results of less than 24 hours

An IVS committee was founded that presented detailed technical specifications

of the next generation VLBI system (Behrend et al., 2008, Proc. of the 2007 IAG General Assembly, Springer, 133 (Part 5), 833; Petrachenko et al., 2009, NASA/TM-2009-214180). The VLBI2010 system promises an improvement in accuracy by an order of magnitude. It will provide results with high temporal resolution and will lead to a significant improvement in the quality of the terrestrial and celestial reference frames. This in turn will allow studying e.g. the coupling mechanisms between large earthquakes and variations in Earth's rotation, the impact of modes of the Earth's inner core on Earth rotation, and will lead to more accurate measurements of global sea level.

One important aspect of the VLBI2010 system is the observed frequency range. In order to achieve higher accuracy of the final VLBI results, it is planned to observe a much broader frequency band than today. A simultaneous observation of the whole

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frequency range 2 – 14 GHz is proposed, in particular to avoid radio interference. The broadband observation scheme will also increase the accuracy of the observational data and the finally derived results.

Furthermore, smaller and faster radio telescopes are proposed that can perform more observations per time unit. Using fast telescopes, the local atmospheric conditions can be sensed much better and the handling of atmospheric influences on the VLBI observations can be improved. This promises to address atmospheric turbulence, the most important limiting factor for geodetic VLBI, in more detail than before (Nilsson et al., 2006, Proc. 9:th Specialist Meeting on Microwave Radiometry and Remote Sensing Applications, MicroRad, 2006, p. 270; Nilsson and Haas, 2008, Proc. 5th IVS General Meeting, p. 361), and might allow constraining numerical weather models (García-Espada et al., 2010, Proc. of the 6th IVS General Meeting, 232).

The VLBI2010 concept suggests having more than one telescope at each site, and to establish a twin-telescope facility. This means two identical, fast, 12 m diameter radio telescopes that can sense the local atmosphere and its inhomogeneities much better than a single telescope. Besides this, the dedicated twin-telescope concept will allow continuous operations, i.e., 24 hours per day, 7 days per week, and new innovative observing strategies, i.e. multi-directional observations, differential observations, space-craft and satellite tracking, etc. The VLBI2010 plan is also to increase the observational data rate to at least 8 Gb/s per station to achieve a high signal-to-noise ratio during the short observational time. The data will be sent via optical fibre lines to the correlator facilities for pre-processing using software correlator techniques (Deller et al., 2007, PASP, 119, 318).