FIRST LIGHT IN THE UNIVERSE Richard Ellis, Caltech 1.Role of Observations in Cosmology & Galaxy Formation 2.Galaxies & the Hubble Sequence 3.Cosmic Star Formation Histories 4.Stellar Mass Assembly 5.Witnessing the End of Cosmic Reionization 6.Into the Dark Ages: Lyman Drop Outs 7.Gravitational Lensing & Lyman Alpha Emitters 8.Cosmic Infrared Background 9.Future Observational Prospects Saas-Fee, April 2006

When Did Galaxies Form? In the ’s, astronomers sought for a distinct era of galaxy formation Synthesis models suggested E/S0s formed a high z via luminous `initial burst’ These searches for `primeval galaxies’ were unsuccessful In 1990’s gradual assembly was deduced via studies of cosmic SF history Shown to be consistent with CDM

Early Searches for Primeval Galaxies What would they look like? Partridge & Peebles (1967, Ap J 147, 868): free-fall collapse L* systems at z~10-30, large diffuse & red, possible L  Meier (1976, Ap J 207, 343): compact stellar systems, possibly QSOs Tinsley (1980, Ap J 241, 41): MS brightening goes as dM/dt  x leading to observed excess in blue galaxy counts Bruzual (1983, Ap J 241, 41): updated synthesis models Pritchet 1994 PASP 106, 1052: Comprehensive review of a decade of searching! Spectral evolutionHubble diagram look-back time SF history log F m B (z) log z

Local Inventory of Stars Relevant papers: Fukugita et al 1998 Ap J 503, 518 Fukugita & Peebles 2004 Ap J 616, 643 Survey data: Cole et al 2001 MNRAS 326, 255 (2dF+2MASS) Kauffmann et al 2003 MNRAS 341, 33 (SDSS) Stellar density: derives from local infrared LF,  (LK) scaled by a mean mass/light ratio (M/L K ) which depends on initial mass function Useful stellar density is that corrected for fractional loss R of stellar material due to winds & SNe: this should be integral of past SF history (e.g. R~0.28 for Salpeter IMF) Cole et al find  stars h = ± ; M/L K = 0.73 (Miller-Scalo)  stars h = ± ; M/L K = 1.32 (Salpeter) Fukugita & Peebles:  stars h = ± (5% in brown dwarfs)  gas = ± (H I, He I, H 2 ) NB: only 6% of baryons are in stars!

Some Initial Mass Functions Mass (M  ) Mass fraction per log mass bin Salpeter > 1 M  reproduces colors and H  properties of spirals IMF < 1 M  makes minor contribution to light but is very important for mass inventory

Stellar Mass Function at z=0 17,000 K-band selected galaxies with K<13.0 2dFGRS redshifts & 2MASS photometry K Stellar mass

Cosmic Star Formation History Various probes of the global SF rate:  * (z) M  yr -1 comoving Mpc -3 UV continuum (GALEX, LBGs) H  and [O II] emission in spectroscopic surveys mid-IR dust emission 1.4GHz radio emission No simple `best method’: each has pros and cons (dust extinction, sample depth, z range and physical calibration uncertainties) Each has different time-sensitivity to main sequence activity so if SFR not uniform do not expect same answers for the same sources Would expect the integral of the past activity to agree with locally- determined stellar density (Fukugita & Peebles 2004) Can also determine the stellar growth rate for comparison with the stellar mass assembly history (next lecture) Recent review: Hopkins 2004 Ap 615, 209

Time-Dependence of Various SF Diagnostics Each SF diagnostic arises from a component of the stellar population whose lifetime is different, e.g. in a situation where the SF is erratic. So there is no single “best” one Radio continuum is thought to arise from SN remnants and offers the potential of a dust-free diagnostic Burst model

Comparison of UV and Hα for same local galaxies Sullivan et al (2000) MNRAS 312, Myr; 10-30% mass UV(2000Å) c.f. H  (corrected for extinction via Balmer line ratio) Scatter cannot be explained with a dispersion in IMFs and metallicities Suggests evidence for non-uniform SF histories &/or significant dust complications

Cosmic SFH: Calibration Kennicutt 1998 Ann Rev A&A 36, 189 (Salpeter IMF) 1.UV continuum ( Å) : Pro: Extensive datasets over 0 5M , timescales >10 8 yr, calibration largely independent of l Con: dust! (A < 3 mag); IMF-dependent 2. Line emission (H , [O II] : Pro: Very sensitive probe, available to z~2: M>10M  timescales <10 6 yr, Con: uncertain fesc of ionizing photons; strong IMF-dependence (  3), excitation uncertainties [OII] 3. Far IR emission (  m) : Pro: Independent method, available for obscured sources to high z: Con: uncertain source of dust heating (AGN/SF?); age of stellar popn, primarily applicable in starbursts, bolometric FIR flux required

Some Popular Dust Extinction Laws

How It Works: Early Estimate of Cosmic SFH Field redshift surveys to z~1 (Lilly et al 1996, Ellis et al 1996) Counts of LBGs z>2 (Madau et al 1996) Luminosity density  L (z) SFR(z) Madau et al (astro-ph/ ) Rapid rise in blue light to z~1 has its origins in galaxy count excesses back to 1980 Ellis 1997 Ann Rev A&A 35, 389

Cosmic SFH: Recent Compilation Hopkins 2004 Ap J 615, 209 (see also Hogg astro-ph/ ): - standardized all measures to same IMF, cosmology, extinction law - integrated LF over standardized range for each diagnostic (except at v high z)  *  (1+z) 3.1 (z<1) Fossil record decline? Star formation rate per unit comoving volume

Implications of Cosmic SFH Hopkins & Beacom (astro-ph/ ) GALEX, SDSS UV Spitzer FIR ACS dropouts Fitting parametric SFH can predict  * (z) in absolute units Cole et al 2dF Satisfactory agreement with local 2dF/2MASS mass density Data suggests half the local mass in stars is in place at z~2  0.2 Major uncertainties are IMF and luminosity-dependent extinction Star formation history Mass assembly history

Theoretical Estimates of Star Formation History: - I Baugh et al 2005 quiescent Baugh et al 1998, 2000 Extended SF histories was an early prediction of CDM models But considerable flexibility in matching changing datasets!! Energetic sub-mm sources posed a major challenge Invoke quiescent & burst modes of star formation Can only fit optical & thermal IR LFs if bursts have top-heavy IMF burst

Theoretical Estimates of Star Formation History: - II In same cosmology, hydrodynamic simulations predict more SF at high z - more than observed (even including the sub-mm sources!) - a “missing high redshift galaxies” problem! - z star (50%)  c.f. z star (50%)  1.3 for semi-analytic models Nagamine et al 2004

Towards a Unified View of the Various High z Populations Integrating to produce a comoving cosmic SFH dodges the important question of the physical relevance of the seemingly diverse categories of high z galaxies (e.g. LBGs, sub-mm, DRGs). Given they co-exist at 1<z<3 what is the relationship between these objects? Key variables: - basic physical properties (masses, SFRs, ages etc) - relative contributions to SF rate at a given redshift - degree of overlap (e.g. how many sub-mm sources are LBGs etc) - spatial clustering (relevant to bias) Some recent articles: Papovich et al (astro-ph/ ) Reddy et al (astro-ph/ )

Lyman Break Galaxies - Clustering UV bright galaxies at z~3 are clustered nearly as strongly as bright galaxies in the present Universe. Of what population are they the progenitors? What are the masses of these galaxies (both dark and stellar)? Adelberger et al (1998) demonstrated strong clustering of LBGs consistent with their hosting massive DM halos perhaps as progenitors of massive ellipticals (Baugh et al 1998)

V-band Luminosity Function at z~3 Local LF Shapley et al 2001 Ap J 562, 95 Key to physical nature of LBGs is origin of intense SF. Is it: - prolonged due to formation at z~3 (Baugh et al 1998) - temporary due to merger-induced star burst (Somerville et al 2001)

LBG Properties (z~3) = 320 z = 3 =0.15 A UV ~1.7  ~5 Shapley et al 2001 Ap J 562, 95 ~ 45 M  yr -1 = ~2 x M  Extinction correlates with age– young galaxies are much dustier SFR for youngest galaxies average 275 M  yr -1 ; oldest average 30 M  yr -1 Objects with the highest SFRs are the dustiest objects

Composite Spectra: Young vs. Old Young LBGs also have much weaker Ly  emission, stronger interstellar absorption lines and redder spectral continua Galaxy-scale outflows (“superwinds”), with velocities ~500 kms s -1, are present in essentially every case examined in sufficient detail

LBG Summary Period of elevated star formation (~100’s M  yr -1 ) for ~50 Myr with large dust opacity (sub-mm galaxy overlap) Superwinds drive out both gas and dust, resulting in more quiescent star formation (10’s M  yr -1 ) and smaller UV extinction Quiescent star formation phase lasts for at least a few hundred Myr; by end at least a few M  of stars have formed All phases are observable because of near-constant far-UV luminosity So how is this LBG-submm connection viewed from the sub-mm point of view?

Sub-mm Sources Sub-mm source counts Extragalactic background Source counts already provide bulk of the measured FIR background, so provided N(z) is unbiased, z~2-3 is where most of the sub-mm sources lie because of the negative k-term Blain et al 2002 Phys. Rep. 369, 111 COBE

What about clustering of sub-mm sources? Blain et al 2004 Ap J 611, 725 Angular correlation function Correlation length r 0 Clustering allows us to determine the typical halo mass in which different galaxy types live Tentative evidence for stronger clustering than LBGs (but N=73 cf. N>1000 LBGs!) suggesting more massive subset in dense structures

Passive Galaxies: The Classical Picture Passive Galaxies: The Classical Picture Homogeneity of Cluster E/S0 U-V Colors z  0.0z  0.5 (HST) Virgo & Coma:  (U-V) o < 0.05 (Bower, Lucey & Ellis 1990, Bower et al 1998) Morphs: = 0.5 sample:  (U-V) o < 0.07 (Ellis et al 1997)

Universal relation for Es and S0s (Sandage & Visvanathan 1978) Scatter dominated by observational errors (Bower et al 1990, Bower et al 1998)  (U-V) is sensitive probe of decline rate of MS component (Buzzoni 1989)  uniform star formation history: synchronisation of recent activity or old stellar population z F > 3 Tight color-luminosity relations: stars are old z  0 z  0.5 U-V (U-V) 0

Stellar Mass Assembly History (  CDM) CDM predicts recent growth in assembly of spheroids, slower growth in disks z=5,3,2,1,0.5,0 z=1 Evolution of stellar mass function time z=5,3,2,1,0.5,0 Merger trees time

Declining Red Sequence to z=1: Agreement with CDM? COMBO-17 data suggests  3 decline in `red sequence’ luminosity density to z=1: consistent with hierarchical predictions (Bell et al ApJ 608, ) Color-photometric z’s in COMBO-17Red luminosity density

Gemini Deep Deep Survey Glazebrook et al Nature 430, 181 (2004) By contrast, the Gemini DD Survey find an abundance of high mass old objects at redshifts z>1 - in seeming contradiction with the COMBO-17 results to z~1? (Can reconcile these contradictory observations if mass assembly is itself mass-dependent) R-K Redshift

McCarthy et al Ap J 614, L9 (2004) Gemini Deep Deep Survey: Spectroscopic Age-dating 20 red galaxies z~1.5, age Gyr, z F = Progenitors have SFRs ~ M  yr -1 (sub-mm gals?)

Daddi et al 2004 Ap J 617, 746 `BzK’ selection of passive and SF z>1.4 galaxies New apparently less-biased technique for finding all galaxies 1.4<z<2.5 sBzK: star forming galaxies pBzK: quiescent galaxies (z-K) (B-z) WHERE DO THESE FIT IN?

Reddy et al 2005 Ap J 633, 248 LBG & `BzK/SF’ z~2 populations are the same Fraction of BzK/SF galaxies selected as LBGs and v.v. (including X-ray AGN) (excluding X-ray AGN) Contribution to SF density LBG

Subaru/VLT Survey of K<20 `BzK’ Galaxies Large panoramic survey - but no spectroscopy Clustering of sBzK and pBzK galaxies is identical, suggesting they are the same massive population and SF is simply transient Space density of pBzKs with M>10 11 M  is ~ 20% local value Kong et al 2006 Ap J 638, 72 Source CountsClustering

Reddy et al 2005 Ap J 633, 248 Are SF and Passive z~2 populations distinct? Stellar mass distributions overlap indicating primary difference is current SF log stellar mass K Passive 1.6<z<2.9 LBG 1.5<z<2.9

Spitzer Studies of Massive Red Galaxies (J-K>2.3) Papovich et al astro-ph/ K-selected sample of 153 DRGs z M  ; 25% with AGN Specific SFR (including IR dust emission) ~2.4 Gyr -1 ; >> than for z<1 galaxies Witnessing bulk of SF in massive galaxies over 1.5<z<3 Stellar massSpecific SFR (/mass)

Summary of Lecture #3 Multi-wavelength (optical/UV, near-IR, Spitzer and sub-mm) observations have led to a revolution in tracking the history of star formation in the Universe We have a good understanding of the evolution of the co-moving density of SF since z~3 which accounts for the observed stellar mass density at z=0. Half the stars we see today were formed by z~2. Galaxy populations identified by various means (sub-mm, LBGs, BzK, DRG..) can be connected by their clustering, intermittent SF and dust content. The emerging picture has the bulk of the star formation in massive galaxies complete by z~1.5; subsequent evolution is largely occurring in the demise of activity in lower mass systems This `downsizing’ phenomenon (SF completed in massive galaxies earlier than in lower mass systems) is counter to simple hierarchical assembly and arises from feedback (Lecture #4).