the large synoptic survey telescope and precision studies of cosmology david l. burke slac c2cr07...
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The Large Synoptic Survey Telescopeand Precision Studies of Cosmology
David L. BurkeSLAC
C2CR07Granlibakken, California
February 26, 2007
Brookhaven National Laboratory
California Institute of Technology
Google Corporation
Harvard-Smithsonian Center for Astrophysics
Johns Hopkins University
Las Cumbres Observatory
Lawrence Livermore National Laboratory
National Optical Astronomy Observatory
Ohio State University
Pennsylvania State University
Princeton University
Research Corporation
Stanford Linear Accelerator Center
Stanford University
University of Arizona
University of California, Davis
University of Illinois
University of Pennsylvania
University of Washington
The LSST Collaboration
Outline
• The LSST Mission
• The LSST Telescope and Camera
• Precision Cosmology and Dark Energy
• Schedule and Plans
Concordance and Consternation
Is CDM all there is?
Is the universe really flat?
What is the dark matter? Is it just one thing?
What is driving the acceleration of the universe?
What is inflation?
Can general relativity be reconciled with quantum mechanics?
The LSST Mission
Photometric survey of half the sky ( 20,000 square degrees).
Multi-epoch data set with return to each point on the sky approximately every 4 nights for up to 10 years.
A new 10 square degree field every 40 seconds.
Prompt alerts (within 60 seconds of detection) to transients.
Deliverables
Archive over 3 billion galaxies with photometric redshifts to z = 3.
Detect 250,000 Type 1a supernovae per year (with photo-z < 0.8).
Telescope and Camera
8.4m Primary-TertiaryMonolithic Mirror
3.5° Photometric Camera
3.4m Secondary Meniscus Mirror
Aperture and Field of View
Primary mirror diameter
Field of view
KeckTelescope
0.2 degrees10 m
3.5 degrees
LSST
Optical Throughput – Eténdue AΩ
0
40
80
120
160
200
240
280
320
Ete
nd
ue
(m
2 de
g2 )
LSST PS4 PS1 Subaru CFHT SDSS MMT DES 4m VST VISTAIR
All facilities assumed operating100% in one survey
Telescope Optics
Polychromatic diffraction energy collection
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 80 160 240 320
Detector position ( mm )
Imag
e di
amet
er (
arc-
sec
)
U 80% G 80% R 80% I 80% Z 80% Y 80%
U 50% G 50% R 50% I 50% Z 50% Y 50%
PSF controlled over full FOV.
Paul-Baker Three-Mirror Optics
8.4 meter primary aperture.
3.5° FOV with f/1.23 beam and 0.20” plate scale.
Similar Optical Mirrors and Systems
Large Binocular Telescope
f/1.1 optics with two 8.4m primary mirrors.
SOAR 4.2m meniscus primary mirror
Camera and Focal Plane Array
Filters and Shutter
Focal Plane Array3.2 Giga pixels
~ 2mWavefront Sensors and
Fast Guide Sensors
“Raft” of nine 4kx4k CCDs.
0.65m Diameter
Focal Plane Metrology
Silicon Displacement:CCD Thickness (100m)
+10 m
0 m
-10 m
PSF
Assembly-stage adjustment to achieve tolerance of 10 microns peak-to-valley surface flatness.
Simulated LSST photon beam in silicon.
LSST Site
El Peñón
Cerro Pachón
Gemini South and SOAR
LSST Facility Sketch
LSST Cosmology Highlights
o Weak lensing of galaxies to z = 3. Tomographic shear correlations in linear and
non-linear gravitational regimes.
o Supernovae to z = 1. Lensed supernovae and time delays.
o Galaxies and cluster number densities as function of z. Power spectra on very large scales k ~ 10-3 h Mpc-1.
o Baryon acoustic oscillations. Power spectra on scales k ~ 10-1 h Mpc-1.
More
Propagation of Light Rays
Can be several (or even an infinite number of) geodesics along which light travels from the source to the observer.
Displaced and distorted images.
Multiple images.
Time delays in appearances of images.
Observables are sensitive to cosmic distances and to the structure of energy and matter (near) line-of-sight.
A complete Einstein ring.
Strong Lensing
Galaxy at z =1.7 multiply imaged by a cluster at z = 0.4.
Multiply imaged quasar (with time delays).
Distorted Image
Source
ξi
ξj
Convergence and Shear
“Convergence” and “shear” determine the magnification and shape (ellipticity) of the image.
Distortion matrix
with the co-moving coordinate along the geodesic, and a function of angular diameter distances.
( )
Simulation courtesy of S. Colombi (IAP, France).
Weak Lensing of Distant Galaxies
Sensitive to cosmological distances, large-scale structure of matter, and the nature of gravitation.
Source galaxies are also lenses for more distant galaxies.
Observables and Survey Strategy
Galaxies are not round!
g ~ 30%
The cosmic signal is 1%.
Must average a large number of source galaxies.
Signal is the gradient of , with zero curl.
“B-Mode” must be zero.
Weak Lensing Results
Discovery (2000 – 2003) 1 sq deg/survey 30,000 galaxies/survey
CFHT Legacy Survey (2006) 20 sq deg (“Wide”) 1,600,000 galaxies
“B-Mode”
Requires Dark Energy (w0 < -0.4 at 99.7% C.L.)
Shear Power Spectra Tomography
LSST designed to achieve 0.001 or better residual shear error.
0.01
0.001
Ne
ede
d S
he
ar Se
nsitivity
Linear regime Non-linear regime
CDM
LSST Postage Stamp(10-4 of Full LSST FOV)
Exposure of 20 minutes on 8 m Subaru telescope. Point spread width 0.52 arc-sec (FWHM). Depth r < 26 AB.
Field contains about 10 stars and 100 galaxies useful for analysis.
1 arc-minute
LSST will see each point on the sky in each optical filter this well every 6-12 months.
Multi-Epoch Data Archive
Average down instrumental and atmospheric statistical variations.
Large dataset allows systematic errors to be
addressed by subdivision.
Multi-Epoch Data Archive
Average down instrumental and atmospheric statistical variations.
Large dataset allows systematic errors to be
addressed by subdivision.
Residual Shear Correlations
CDM shear signal
Typical separation of reference stars in LSST exposures.
Data from Subaru.
Photometric Measurement of Redshifts “Photo-z’s”
Galaxy Spectral Energy Density (SED)
Moves right larger z.Moves left smaller z.
“Balmer Break”
Photo-z Calibration
Calibrate with 20,000 spectroscopic redshifts.
Need to calibrate bias and width to 10% accuracy to reach desired precision
Simulation of 6-band photo-z.
z 0.05 (1+z)
Simulation photo-z calibration.
z 0.03 (1+z)
Precision on Dark Energy Parameters
Measurements have different systematic limits.
Combination is significantly better than any individual measurement.
Project Schedule
2006 Site SelectionPrimary Mirror Contract (Arizona Mirror Lab)
Construction Proposals (NSF and DOE)
2007-2009 Complete Engineering and DesignLong-Lead Procurements
2010-2013 Construction and First Light
2014 Commissioning and Science
Done