Thomas R. GreveMax-Planck Institute for Astronomy

Galaxy Formation and Evolution from the Epoch of Reionization to z=4

Purple Mountain Observatory, Nanjing, April 3rd 2009

1) Cosmic history: the Universe beyond z > 4- Identifying outstanding problems in galaxy formation and evolution and

key science drivers for the next decade

2) How do we find galaxies at z > 4?- Dust obscured star formation at z > 4- All-sky optical/near-IR surveys: hunting for z > 4 QSOs - Pristine galaxies at z > 4: Lyman-α Emitters

3) Understanding the interstellar medium in z > 4 galaxies?- How interstellar medium studies can help solve the key problems in galaxy

formation and evolution

4) Summary

Outline of this talk

1) Cosmic history: the Universe beyond z > 4

Identifying outstanding problems in galaxy formation and evolution and key science drivers for the next decade

Cosmic History

Galaxy (z=6.4)

Galaxy (z=2.5)

Galaxy (z=0)

Old StarsYoung star/ionized gas

Molecular gas

z=4

z=?

The new cosmic frontier

The new cosmic frontier: the epoch of reionization

Key questions to be addressed in the coming decade:

-When did the EoR start?

-How and when did the first galaxies form?

-How and when did the first supermassive black holes form?

-What was the inter-relationship between supermassive black hole and host galaxy growth at these early epochs?

This requires large, robust samples of z > 4 galaxies!

z=4

z=?

The new cosmic frontier

Dust obscured star formation at z > 4

2) How do we best observe the first galaxies at z > 4?

LIR = 1x1013L

The dust-obscured Universe

UVOB stars

IR/FIR

dust

Hughes et al. (1998)HDF-N

Far-IR luminosity

(Obscured) star formation rate

The submm probes the reionization epoch!

850μm

SCUBA

JCMT, Hawaii

~1 sq. degree of sky has been surveyed at submm wavelengths to date resulting in the detection of more than ~400 bright SMGs (>3mJy)

~20-30% of the (sub)mm background has been resolved by blank-field surveys. ~80% by galaxy cluster surveys but poor number statistics

Submm/FIR

Optical/UV

The submm Universe

Submillimetre/Millimetre SurveysHughes et al. (1998)

HDF-NBorys et al. (2005)Greve et al. (2008)

Submm surveys suffer from poor resolution (FWHM=11-15”)

Condon (1992)

The radio-FIR correlation

Chapman et al. (2005)

Radio inteferometry, however, offers <1” resolution

Optical spectroscopy of 90 radio-ID submm galaxies

Radio

?

Model prediction of the volume density of SCUBA galaxies

?

A significant population of z > 4 SMGs?

Extended Chandra Deep Field South

Weiss et al. (2009)

A significant population of z > 4 SMGs?

Discovery: a z=4.76 submm-selected source not associated with a QSO

SMMJ033229.5 (z=4.76 from optical spectrum)

Coppin et al. (2009)

870μm APEX/LABOCA Survey

z=4

Model prediction of the volume density of SCUBA galaxies

Student project!A multi-wavelength ‘hunt’ for submm-selected galaxies at z > 4

Quantify their abundance and intrinsic properties

A significant population of z > 4 SMGs?

The next submillimetre revolution

SCUBA-2 (first light 2009)

ALMA (first light 2012)

SCUBA-2 will deliver thousands of submm-selected sources

Sub-arcsecond submm/mm interferometry with ALMA:- immediate identification (no need for radio

identification)

A census of the z > 4 submm population

✔Dust obscured star formation at z > 4All-sky optical/near-IR surveys: hunting for z > 4 QSOs

Pristine galaxies at z > 4: Lyman-α Emitters

2) How do we best observe the first galaxies at z > 4?

z=4

Becker et al. (2006)

Gunn-Peterson trough

All-sky optical/near-IR surveys: hunting for z>4 QSOsAll-sky surveys such as the SLOAN have found numerous, extremely luminous z > 4 QSOs by means of drop-out techniques in the opticalThey represent massive, extremely rare, overdensities in the primordial density distribution.

The extreme luminosities of z > 4 QSOs make them ideal laboratories to study galaxy formation and black hole growth at the high-mass-end

Submm/mm photometry: 1/3 of optically selected QSOs are IR hyper-luminous (LIR ≥ 1013L)

Wang et al. (2007)

The most distant QSO knownSDSSJ1148+5152 (z=6.42)

mm-emission/near-IR

Bertoldi et al. (2003)

1 arcmin

5 arcsec

Walter et al. (2003)

CO (3-2)

All-sky optical/near-IR surveys: hunting for z>4 QSOs

Extreme galaxy in place <1Gyr after the Big Bang!

The extreme luminosities of z > 4 QSOs make them ideal laboratories to study galaxy formation and black hole growth at the high-mass-end

Submm/mm photometry: 1/3 of optically selected QSOs are IR hyper-luminous (LIR ≥ 1013L)

Wang et al. (2007)

The most distant QSO knownSDSSJ1148+5152 (z=6.42)

mm-emission/near-IR

Bertoldi et al. (2003)

1 arcmin

LFIR ≈ 1013L

Mgas ≈ 7 x 1010M

Mdust ≈ 109M

All-sky optical/near-IR surveys: hunting for z>4 QSOs

Future large samples of distant QSOsFull UKIDSS Large Area Survey (4000 deg2, Y<19):

# 8.0 > z > 5.8 QSOs: 17

Full Pan-STARRS Survey (10,000 deg2, Y<20.5):

# 8.0 > z > 5.8 QSOs: 73

These samples of QSOs will be prime targets for multi-line molecular/atomic follow-up observations!

✔Dust obscured star formation at z > 4✔All-sky optical/near-IR surveys: hunting for z > 4 QSOsPristine galaxies at z > 4: Lyman-α Emitters

1) How do we best observe the first galaxies at z > 4?

z=4

Pristine galaxies at z > 4: Lyman-α Emitters

NBz’

i’

i’z’

NB

Kodaira et al. (2003)

z=6.541

z=6.578

In the absence of dust and strong optical continuum, the easiest way to find the first galaxies is via the Lyα recombination line: the strongest emission line produced by the hydrogen atom (Partridge & Peebles 1967)

Gawiser et al. (2007)

Pristine galaxies at z > 4: Lyman-α Emitters

Low stellar masses (<109M) and

star formation rates (<30M/yr).

No dust (very metal-poor)Small linear scales (<1kpc)

Lyman-α Emitters (LAEs) are likely to be pure starbursts – and representing the first building-blocks of galaxies

The large number of z > 6 LAEs (30 per 0.25 sq. deg) implies that they could play a dominant role in reionizing the Universe

There are currently several hundreds known LAEs at z > 4

JWST+ELT will be able to detect the smallest and most distant galaxies (z > 7), increasing the number of LAEs by order of magnitude

Future samples of distant Lyman-α emitters

James Webb space telescope 6.5m optical/near-IR/mid-IR telescope in space

Extremely Large Telescope30m optical/near-IR ground-based telescope

✔Dust obscured star formation at z > 4✔All-sky optical/near-IR surveys: hunting for z > 4 QSOs✔Pristine galaxies at z > 4: Lyman-α Emitters

1) How do we best observe the first galaxies at z > 4?

What is the most effective way of studying these first galaxies in order to maximize constraints on formation and evolution

models?

The gravitational hierarchical build-up of dark matter structures provides the framework for galaxy formation and evolution

z = 6.4 (t = 0.9 Gyr)

Springel et al. (2006), Nature

The interstellar medium (gas and dust) is a key ingredient in galaxy formation and evolution as it provides the ‘fuel’ for star formation and supermassive black hole accretion

z = 0 (t = 13.6 Gyr)z = 2.5 (t = 4.0 Gyr)

The role of gas in galaxy formation and evolution

Dark matter Dark matter Dark matter

GalaxyGalaxyGalaxy

…so understanding the physical properties of the interstellar medium (ISM) in distant galaxies is fundamental to our picture of galaxy formation and evolution

Observing the interstellar medium

Other important molecular gas tracers: HCN and HCO+

Atomic fine-structure lines: [CI] and [CII] (ν = 490-1900GHz)

Molecular hydrogen (H2) is by far the main component of the ISM – but its lack of a permanent dipole moment makes it virtually impossible to observe directly Instead the rotational lines of CO are mainly used to study the ISM

C

O

J=1-0 (ν = 115GHz)

J=2-1 (ν = 230GHz) . . .

The CO J=1-0 line from a local galaxy falls within the 3mm atmospheric window,

…as does the (redshifted) CO J=5-4 line from a galaxy at z=4 (νobs = 575GHz/(1+z) = 115GHz)

Den

sity

Tem

pera

ture

1-0

Atmospheric transmission vs. frequency

2-1

3-2

CO

… 5-4

Observational status

This excitation-bias prevents a meaningful comparison between the molecular gas properties of local and high-z galaxies

Low-J CO linesDiffuse gas

High-J CO linesDense, warm gas

z > 4

CO 3-2 in SDSSJ1148+5152 (z=6.42)

Walter et al. (2003)

The highest CO detection to dateUniverse was 1/16 of its current age

Greve (2009)

The next five years will see a quantum leap in our ability to study the ISM in galaxies across the Cosmos - one that will take us from an epoch of merely detecting molecular lines at high-z to multi-line surveys capable of fully characterizing the ISM

Herschel, launch 2009

ALMA, first light 2012 EVLA, first light 2012

z = 0

A new golden era in ISM astronomy

Requires:An exhaustive inventory of the microscopic properties (e.g. chemistry, density, thermal balance) of the ISM in z > 4 galaxies, and their effect on macroscopic properties (e.g. star formation, luminosity, morphology)

Method:- Sampling of the spectral line distributions of CO, HCN and HCO+, [CII] 158μm and [CI] 369μm

- Spatially and kinematically resolved dust and molecular line observations

- For large samples of z > 4 objects (QSOs, SMGs, and LAEs)

A full understanding of galaxy formation and evolution at z > 4…

A new golden era in ISM astronomy

Key Questions:-When did the EoR start?

-How and when did the first galaxies form?

-How and when did the first supermassive black holes form?

-What was the inter-relationship between supermassive black hole and host galaxy growth at these early epochs?

High-z ISM studies at sub-kpc scales

High-resolution observations of the dust and molecular gas provide a direct image of the formation morphology, and can distinguish between several scenarios

i)A major merger between two gas-rich components (‘wet’ merger)

ii)Many minor bursts distributed within an extended potential and interspersed with periods of no star formation

iii)A single monolithic collapse

In addition, one obtains accuratedynamical masses, merger fractions etc.

Walter et al. (2003)

CO(3-2)

SDSSJ1148+5152 (z=6.42)

Submm galaxy at (z=2.49)

Tacconi et al. (2008)

Imaging galaxy formation

Black hole and galaxy host growth at z > 4

Häring & Rix (2004)

The local MBH-Mbulge relation (Magorrian et al. 1997)

Mbulge=0.002MBH

scatter < 0.30dex

High-z ISM studies at sub-kpc scales

An unusually tight relation between the mass of the supermassive black hole and that of its host spheriod has been established in the local Universe.

This relation connects a phenomenon ocuring on spatial scales of ≈10-5pc (black hole accretion) to the spheriod which is 8 orders of magnitude larger (≈103pc )

This suggest a deep, co-evolutionary link between the supermassive black hole and the galaxy spheriod.

What is the underlying physics?How does the relation evolve with redshift?

Local relation

Did the black holes start to grow first?

High-resolution CO studies can uniquely probe the MBH-Mbulge relation at high-z

Local relation

Walter et al. (2003)

CO(3-2)

SDSSJ1148+5152 (z=6.42)

QSOs

High-z ISM studies at sub-kpc scalesBlack hole and galaxy host growth at z > 4

CO-detected SMGs (Alexander et al. 2007)

Local relation

Or did the bulges grow first?

High-resolution CO studies can uniquely probe the MBH-Mbulge relation at high-z

High-resolution CO studies of submm galaxies

Tacconi et al. (2008)

Student project:

Spatially resolve (<1” FWHM) the gas-kinematics in a large sample of z>4 QSOs and SMGs in order to study the MBH-Mbulge relation in the early Universe

QSOs

SMGs

High-z ISM studies at sub-kpc scalesBlack hole and galaxy host growth at z > 4

Requires:An exhaustive inventory of the microscopic properties (e.g. chemistry, density, thermal balance) of the ISM in z > 4 galaxies, and their effect on macroscopic properties (e.g. star formation, luminosity, morphology)

Method:- Sampling of the spectral line distributions of CO, HCN and HCO+, [CII] 158μm and [CI] 369μm

- Spatially and kinematically resolved dust and molecular line observations

- For large samples of z > 4 objects (QSOs, SMGs, and LAEs)

A full understanding of galaxy formation and evolution at z > 4…

A new golden era in ISM astronomy

Key Questions:-When did the EoR start?

-How and when did the first galaxies form?

-How and when did the first supermassive black holes form?

-What was the inter-relationship between supermassive black hole and host galaxy growth at these early epochs?

The ISM conditions at z > 4: the density structure of the gas

Weiss et al. (2006)

The dense gas fraction of the ISM in a galaxy may govern its star formation efficiency and hence its evolutionary path. Determining the density structure of the ISM requires a very complete sampling of the CO rotational ladder

CO(4-3) CO(6-5) CO(9-8)

CO(10-9) CO(11-10)

APM0827 (z=3.9) Weiss et al. (2006)

Is the ISM in QSOs more excited than in submm-selected galaxies?

The ISM conditions at z > 4: the density structure of the gas

CO(4-3) CO(6-5) CO(9-8)

CO(10-9) CO(11-10) HCN(5-4)

APM0827 (z=3.9) Weiss et al. (2006)

HCO+(1-0) in the Cloverleaf (z=2.6)

Riechers et al. (2006)

Weiss et al. (2006)

Determining the density structure of the ISM requires a very complete sampling of the CO rotational ladder. As well as of dense gas tracers such as HCN and HCO+

Hailey-Dunsheath (2008)

The ISM conditions at z > 4: gas cooling

The [CII] 158μm line is the main cooling line in our Galaxy and in typical local starburst (L[CII]/LIR ≈ 5x10-3)

However, [CII] cools 10x less efficiently in the most IR-luminous galaxies (at low- and high-z)

High-z

Local ultra IR-luminous galaxies

Normal local galaxies

The first fully sampled CO spectrum (up to J=6-5) of a local IR-luminous galaxy (Papadopoulos et al. 2007)

Walter et al. (2009)

SDSSJ1148+5152 (z=6.42)

CO(6-5)

[CII]

Hailey-Dunsheath (2008)

The ISM conditions at z > 4: gas cooling

The [CII] 158μm line is the main cooling line in our Galaxy and in typical local starburst (L[CII]/LIR ≈ 5x10-3)

However, [CII] cools 10x less efficiently in the most IR-luminous galaxies (at low- and high-z)

High-z

Local ultra IR-luminous galaxies

Normal local galaxies

In metal-poor systems, however, we can have L[CII]/LIR ≈ 0.5-1x10-2

An z=7 LAE with LIR ≈ 2x1011L(SFR=30M/yr) will be detectable with ALMA!

SDSSJ1148+5152 (z=6.42)

Maiolino et al. (2005)

CO(6-5)

[CII]

Student project

Weiss et al. (2006)

Detecting the first objects at z > 7 with ALMA

The [CII] 158μm line may be the line of choice for z > 7 objects with ALMA

CO(8

-7)

[CII]

Maiolino et al. (2005)

CO(6-5)

[CII][CII] is 5x brighter than CO(6-5)

CO J > 8 no highly excited

Summary

Future surveys with PanSTARRS/UKIDSS, SCUBA-2, and JWST/ELT will drastically increase sample sizes of z > 4 galaxies

The next 5-10 years will see the advent of a number of new, ground-breaking cm/submm/far-IR facilities (e.g. ALMA, EVLA) allowing us to study such samples effectively

For the first time it will be possible to do a detailed characterization of the ISM in primeval galaxies during the epoch of reionization

This will revolutionize our understanding of galaxy formation and evolution at all cosmic epochs