Thomas R. Greve Max-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 Stars Young 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?

L IR = 1x10 13 L  The dust-obscured Universe UV OB 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/FIROptical/UV The submm Universe

Submillimetre/Millimetre Surveys Hughes et al. (1998) HDF-N Borys 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 SMMJ (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 > 4 All-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 QSOs All-sky surveys such as the SLOAN have found numerous, extremely luminous z > 4 QSOs by means of drop-out techniques in the optical They 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 (L IR ≥ L  ) Wang et al. (2007) The most distant QSO known SDSSJ (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 (L IR ≥ L  ) Wang et al. (2007) The most distant QSO known SDSSJ (z=6.42) mm-emission/near-IR Bertoldi et al. (2003) 1 arcmin L FIR ≈ L  M gas ≈ 7 x M  M dust ≈ 10 9 M  All-sky optical/near-IR surveys: hunting for z>4 QSOs

Future large samples of distant QSOs Full UKIDSS Large Area Survey (4000 deg 2, Y<19): # 8.0 > z > 5.8 QSOs: 17 Full Pan-STARRS Survey (10,000 deg 2, 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 QSOs Pristine 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 NB z’ 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 (<10 9 M  ) 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 Telescope 30m 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 Galaxy …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 = GHz) Molecular hydrogen (H 2 ) 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 (ν obs = 575GHz/(1+z) = 115GHz) DensityTemperature 1-0 Atmospheric transmission vs. frequency 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 lines Diffuse gas High-J CO lines Dense, warm gas z > 4 CO 3-2 in SDSSJ (z=6.42) Walter et al. (2003) The highest CO detection to date Universe 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 2012EVLA, 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 accurate dynamical masses, merger fractions etc. Walter et al. (2003) CO(3-2) SDSSJ (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 M BH -M bulge relation (Magorrian et al. 1997) M bulge =0.002M BH 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 -5 pc (black hole accretion) to the spheriod which is 8 orders of magnitude larger (≈10 3 pc ) 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 M BH -M bulge relation at high-z Local relation Walter et al. (2003) CO(3-2) SDSSJ (z=6.42) QSOs High-z ISM studies at sub-kpc scales Black 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 M BH -M bulge relation at high-z High-resolution CO studies of submm galaxies Tacconi et al. (2008) Student project: Spatially resolve ( 4 QSOs and SMGs in order to study the M BH -M bulge relation in the early Universe QSOs SMGs High-z ISM studies at sub-kpc scales Black 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] /L IR ≈ 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) SDSSJ (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] /L IR ≈ 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] /L IR ≈ 0.5-1x10 -2 An z=7 LAE with L IR ≈ 2x10 11 L  (SFR=30M  /yr) will be detectable with ALMA! SDSSJ (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