High Redshift Galaxies Richard Ellis (Caltech) Plan Motivation for studies of high z galaxies Methods for finding them, connections between various populations, recent progress (3 < z < 7) Cosmic reionization (z >7): when, what and how? - direct & indirect probes of role of SF galaxies Future observational prospects

Importance of High z Data Our understanding of the local population of galaxies is largely confined to its spatial distribution and (perhaps) some environmental trends in the broadest sense Standard model needs major `additional ingredients’ to reconcile local color and luminosity distributions: such effects have major implications for assembly and SF histories; this motivates studies of sources with z > 1 Census of earliest objects (z > 7) addresses issues related to cosmic reionization and feedback in low mass halos - areas where theoretical predictions are very uncertain Introduce four key galaxy populations whose studies are relevant I: Lyman break galaxies: color-selected star forming galaxies z > 2 II: Sub-mm galaxies located via redshifted dust emission III: Various passively-evolving sources selected via deep IR data IV: Lyman alpha emitters: sources selected via narrow-band imaging or spectroscopy

The Lyman continuum discontinuity is particularly powerful for isolating star- forming high redshift galaxies. From the ground, we have access to the redshift range z=2.5-6 in the micron range. Steidel et al 1999 Ap J 462, L17 Steidel et al 1999 Ap J 519, 1 Steidel et al 2003 Ap J Lyman Break Galaxies Effect of neutral hydrogen

Expectations Real Data (10’ field) Spectral energy distributions allow us to predict where distant SF galaxies lie in color-color diagrams such as (U-G vs G-R) (Steidel et al 1996) Photometric Cuts: Predictions and Practice

Spectroscopic Confirmation at Keck

Sub-mm Star Forming Sources SCUBA array15m JCMT SCUBA: 850  m array detects dusty star forming sources: - behind lensing clusters (Smail et al Ap J 490, L5, 1997) - in blind surveys (Hughes et al Nature 394, 211, 1998) Source density implies 3 dex excess over no evolution model based on density of local IRAS sources: Key question is what is the typical redshift, luminosity and SF rate? Sub-mm astronomers

Negative k-correction for sub-mm sources Blain et al (2002) Phys. Rept, 369,111 K-correction is the dimming due to the (1+z) shifting of the wavelength band (and its width) for a filter with response S( ) In the Rayleigh-Jeans tail of the dust blackbody spectrum, galaxies get brighter as they are redshifted to greater distance

Radio Identification of Sub-mm Sources SCUBA sources often have no clear optical counterpart, so search with VLA & OVRO L ~ L  if z~2 Could be as important as the UV Lyman break population Frayer et al (2000) AJ 120, 1668

VLA positions for 70% of f(850  m) > 5 mJy (20% b/g) Slits placed on radio positions (22 < I < 26.5) with Keck 10-fold increase in number of SCUBA redshifts (LRIS-B) Chapman et al (2003) Nature 422, 695 Chapman et al (2005) Ap J 622, 722 Spectra of Radio-Detected SCUBA Sources

50% completeness with LRIS-B and radio selection limits Radio-selected sub-mm sources  20% of background Most sub-mm sources have z < 4 Peak z = 2.4 – comparable to that for AGN Although  (LBG)  10  (SCUBA), luminosity/SF densities comparable Sub-mm and Lyman Break Galaxies are Co-eval

for z ~ 1-2: select on I-H colour for z > 2: select on J-K colour Such objects would not be seen in the Lyman break samples LBGs and sub-mm are both star forming sources Arrival of panoramic IR cameras opens possibility of locating non-SF (or dusty) galaxies at high z Termed variously: Extremely Red Objects Distant Red Galaxies depending on selection criterion. Passively-Evolving Galaxies

Surprisingly high surface density: –~0.8/arcmin to K=21 (two fields) –~2/arcmin to K=22 (HDF-S) –~3/arcmin to K=23 (HDF-S) 2 2 van Dokkum,Franx, Rix et al Objects with J-K > 2.3

Z=2.43 Z=2.71 Z=3.52 Keck Spectroscopy (van Dokkum et al)

Absorption Line Spectroscopy (Gemini GNIRS) Now practical (but slow) to secure redshifts for K-limited samples using low resolution JHK GNIRS spectrograph 20 z > 2 massive galaxies of which ~half are quiescent (Kriek et al 2006)

Complementary techniques (z>6): - narrow band (f  < cgs, SFR~3 M  yr -1, V~ Mpc 3 ) - lensed spectra (f  < , SFR~0.1 M  yr -1, V <50 Mpc 3 ) Origin: ionizing flux absorbed by H gas  Ly  photons (as in Galactic HII regions) Efficient: < 6-7% of total radiation may emerge in Ly  depending on IMF, metallicity etc; better contrast against sky background 1 M  yr -1 = ergs sec -1 (Kennicutt 1998) Lyman Alpha Emitters

Megacam Suprime-Cam Suprime Cam: 10 CCDs, 34  27 arcmin FOV (upgraded to deep depletion devices in 2008) Coming soon.. HyperSuprime Cam: 1.5 deg FOV Panoramic Imaging Camera on Subaru 8 meter

Narrow Bands in `Quiet’ Windows in Sky Spectrum z(L  ) = NB: Requires panoramic imaging as  z range is small Airglow spectrum

Selection & Spectroscopic Verification Hu et al (2003) z=5.7 survey Compare signal in nb filter with broad- band signal using Subaru bb-nb Spectroscopic follow- up of candidates with Keck 5007Å 3727Å 1216Å

Hopkins & Beacom Ap J 651, 142 (2006) GALEX, SDSS UV Spitzer FIR ACS dropouts Standardize observations (cosmology, extinction, incompleteness) Fit parametric form to star formation history and integrate Predicts local stellar mass density  * (z=0) in absolute units from 2dF Cole et al 2dF 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 historyMass assembly history Cosmic Star Formation History

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, LAEs). 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: van Dokkum et al Ap J 638, L59 (2006); Papovich et al Ap J 640, 92 (2006); Reddy et al Ap J 644, 792 (2006); Gawiser et al Ap J 642, L13 (2006) Grazian et al (astro-ph/ ) Unified View of the Various Populations

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) Clustering of Lyman Break Galaxies

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) Luminosity Function at 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 Properties of Lyman Break Galaxies (z~3)

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 Composite Spectra: Young versus Old Shapley et al 2001 Ap J 562, 95

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 Q: How is this LBG-submm connection viewed from the sub-mm point of view? Q: Where do massive red galaxies fit into the picture? Lyman Break Galaxies: Summary

Blain et al 2004 Ap J 611, 725 Angular correlation functionCorrelation length r 0 Tentative evidence for stronger clustering than LBGs (but N=73 cf. N>1000 LBGs!) suggesting more massive subset in dense structures Clustering of Sub-mm Galaxies

Massive Red Galaxies at z~2 Glazebrook et al Nature 430, 181 (2004) R-K Redshift Coadded spectrum of z~1.5 red galaxies 20 red galaxies z~1.5, age Gyr, z F = Progenitors have SFRs ~ M  yr -1 (sub-mm gals?) McCarthy et al Ap J 614, L9 (2004)

Key question for z>5 studies is relationship between Lyman break & Ly  emitters: do the techniques find similar or different types of sources? Gawiser et al (2006) study of 40 z~3 LAE c.f. various subsamples in larger Shapley et al (2001) LBG study Suggest LAEs are lower mass and less dusty than comparably young LBGs Kashikawa et al (2006) and Overzier et al (2006) provide contrasting views of the clustering of LBGs and LAEs at z~6 consistent with LAEs being in lower mass halos Composite SED of z~3 LAE Distinguishing Between LBGs and LAEs

Evolution 3 < z < 7: What to Believe? How effective are the various high z selection methods? - L*(z=6)  i~26 where spectroscopy is hard - spectroscopic samples biased to include strong L  - great reliance on photometric redshifts Is there a decline in the UV luminosity density 3<z<6? - results are in some disagreement - differing trends in continuum drops & L  emitters Is the observed  UV at z>6 sufficient for reionization? - contribution from (unobserved) faint end of LF? - unusual pop ns : intense EW(L  ), steep UV continua? Significant stellar masses for post-burst z~6 galaxies - how reliable are the stellar masses? - inconsistent with declining SF observed 6<z<10? - does this imply an early intense period of activity?

Lyman breaks or `dropouts’ at higher z z-dropout Traditional dropout technique poorly-suited for z > 6 galaxies: - significant contamination (cool stars, z~2 passive galaxies) - spectroscopic verification impractical below ~few L* i-drop volumes : UDF ( ), GOODS-N/S ( ), Subaru (10 6 ) Mpc 3 flux limits: UDF z<28.5, GOODS z<25.6, Subaru z<25.4 Stanway et al (2003)

z~2 passive galaxies Addition of a precise optical-infrared color (z - J) can, in addition to the (i - z) dropout cut, assist in rejecting z~2 passive galaxy contaminants. (Stanway et al 2004) (z – J) (i – z) 5.7 < z < 6.5 This contamination is ~10% at z~25.6 but is negligible at UDF limit (z~28.5) Contamination from z~2 Passive Galaxies

HST half-light radius R h more effective than broad-band colors Contamination at bright end (z<25.6) is significant (30-40%) L dwarfs E/S0 UDF z<25.6 (Stanway et al 2004) Contamination by Galactic dwarfs - more worrisome

L-dwarfs contaminate at bright end z=5.83 L  Keck spectroscopy of i-drops: 10.5 hrs z AB < 25.6

Bunker, Stanway, Ellis & McMahon MNRAS 355, 374 (2004) GOODS/UDF data to z AB =28.5 consistent with z=3 LBG LF but  6  6 from z~3 UDFGOODS Spec limit Counts for i-band drops (GOODS+UDF)

Declining UV luminosity density of dropouts Rapid decline in UV luminosity density 3<z<7 Increased fraction of low luminosity galaxies at high z Bouwens & Illingworth (2006) Bouwens et al (astro-ph/ )

What is Physical Cause of this Evolution? Bouwens et al (astro-ph/ ) claim: - primary evolution is a shift in M* (0.7 mag in 0.7 Gyr over 4<z<6) - change in shape of LF less secure (but  =-1.7 is very steep) - evolution explained by various semi-analytic models driven by halo mergers z = 4,5,6,7 Stark, Loeb & Ellis (astro-ph/ )

HST offers superior photometry & resolution (important for stellar contamination) but SuPrimeCam has much bigger field (each pointing = 2  GOODS-N+S) Additional photometric bands developed to sort stellar contamination Shioya et al (2005): used intermediate band 709nm, 826nm to estimate stellar contamination in z~5 and z~6 samples respectively Shimasaku et al (2005) split z-band into two intermediate filters z B, z R to measure UV continuum slope Yoshida et al (2006): comprehensive survey of B, V and R drops in Subaru Deep Field These studies confirm LBG trends indicated via HST studies Confirmation from Subaru

Evolution of Lyman Break Galaxy LF (Subaru) Yoshida et al 2006 Ap J 653, 988 Subaru deep field (875 arcmin 2 ) - not as sensitive to faint end but supports steep  - primary evolution over 4<z<6 is in M*

Independent Confirmation from Spitzer Verma et al (astro-ph/ ): 21 V-drops with clean IRAC detections enabling ages and stellar masses for comparison with samples at z~3

For similarly-luminous LBGs, those at z~5 are younger and less massive than at z~2 Verma et al (astro-ph/ ) Stellar Masses & Ages: Comparing z~5 & z~3 LBGs z~5 z~3

Ouchi et al 2005 Ap J 620 L1 Subaru Rules the Waves for Ly  Emitters! Large scale structure from 515 Ly  emitters at z=5.7

Nature 443, 186 (2006)

Ouchi et al astro-ph/ Latest Subaru Results: 3.1 < z < LAEs over 1 deg 2 84 spectroscopically- confirmed No evolution in L* or  Contrasts with LBG evolution suggests LAEs are a more dominant population at early times

Lyman Alpha Emission and the IGM Lyman alpha emission: n=2  1, E=10.199eV, 1216Å Resonant transition: foreground H gas cloud scatters away Ly  photons in direction and frequency in partly ionized IGM, scattering is maximum at 1216Å in rest- frame of gas cloud - affects blue side of observed line in fully neutral IGM, scattering far from resonance can occur - damping wings As a result many workers have stressed the importance of monitoring evolution in the Ly  LF and the line profile Miralda-Escude 1998 Ap J 501, 15 Haiman 2002 Ap J 576, L1 Barkana & Loeb 2004 Ap J 601, 64 Santos 2004 MNRAS 349, 1137

Ly  damping wing is absorbed by HI and thus valuable tracer of x HI (Miralda-Escude 1998) In weaker systems, such as those found via strong lensing, Ly  may be a sensitive probe of reionisation Might expect to see abrupt change in LF at the time when reionization ends NB-limit Lensed limit Ly  LF: Effective Indicator of Reionization?

No Evolution in Ly  LF 5.7 < z < 6.5? No evolution suggests x HI < 0.3 (Malhotra & Rhoads 2004 Ap J 617, L5), but: small dynamic range of data limits utility of test realistic models of ionized spheres suggest weaker constraint (Furlanetto et al 2005) indicating strong emitters will persist until x HI ~ 0.5 lensed emitters no data

Kashikawa et al (2006) Sudden decline seen in the LF of Ly  over a surprisingly small redshift interval! Result remains controversial. Although originally claimed a signature of reionization, most likely due to growth of halo mass function or affected by cosmic variance (Dijkstra et al 2006) Subaru View of Ly  Emitters 5.7 < z < 6.5

Key Issue: Relationship between LBGs & LAEs Many papers with marginal datasets! Dow-Hygelund et al (astro-ph/ ); Finkelstein et al (astro-ph/ ); Kovac et al (astro-ph/ ); Pentericci et al (astro-ph/ ); Pirzkal et al (astro-ph/ ) Tentative conclusions so far: LAEs are younger, smaller, less massive, less clustered than LBGs and an increasing fraction of the SF density at higher z Other issues: Do LAE’s contain `pristene’ Pop III stars? - Claims for `anomalously high’ equivalent widths (marginal) - Searches for He II emission (high ionization line expected in populations with steep IMF) - none seen

Kovac et al (astro-ph/ ) Ouchi et al (astro-ph/ ) More on Ly  Emitters… LAEs less clustered than LBGs EW distributions r0r0 z

What About Passive Objects at z~5-6? IR arrays revealed significant new population of DRGs at z~2-3 Is our census at z~5-6 based on LBGs and LAEs complete? Spitzer is being used to locate potential passive populations at z~5-7 - Balmer break galaxies (Mobasher et al 2005 Ap J 635, 832) (Wiklind et al, in prep) - Color-selected samples (Rodighiero et al astro-ph/ ) Problem is lack of spectroscopic confirmation and confusion with lower z interlopers If many of the proposed candidates are really high z, life will become interesting! - short duty cycle of SF (expect many in `off’ state) - large amount of established stellar mass at z~5-6 (t=1 Gyr)

z = 7 t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr Balmer Break Galaxies (Mobasher, Wiklind et al) Idea: search for `double-break’ SEDs in IRAC-selected samples

H K 3.6  m J HK J dust-free post-starburst z ~ 7 dusty starburst z ~ 2.5 Dusty starburst at z ~ 2.5 Post starburst at z ~ 7 old Elliptical at z ~ 2.5 Dealing with Possible Interlopers

z =6.5; E B-V =0.0; Z=0.004, z F > 9; stellar mass: 2-7  M  Mobasher et al claim 25% chance of being at z ~ 2.5 High z interpretation challenged by Dunlop et al (marginal ACS detection) Chary et al (marginal 25  m detection) Extreme Example in UDF: JD2 (Mobasher et al 2005)

Massive Galaxies at High Redshift - Crisis for CDM?

z = 5.1 E B-V = 0.0 age = 0.9 Gyr  = 0.1 Gyr M * = M o z = 5.0 E B-V = 0.0 age = 0.8 Gyr  = 0.2 Gyr M * = M o Examples <11 candidates with M~10 11 M  in 160 arcmin 2 with 5<z<7

(Yan et al. 2006) Contribution to Stellar Mass Density from Yan et al IF CORRECT (!!): Dominant contribution from passive objects at z~5-6

We have seen tremendous observational progress in the redshift range 2 1 field galaxies and 10 years ago only the first U-dropouts. Now we have many distinct and independent probes of star-forming and quiescent galaxies in this era. Less progress in connecting the various populations: tentative links between (LBGs-submm-DRGs) and (LBGs-LAEs) but more reliable clustering signals required. A stunning development is the preponderance of passive galaxies even, perhaps, at z~5-6. Suggests we have underestimated the total stellar mass at high z and that the duty-cycle of SF is low. Fundamental limit to much of today’s lecture? Not stellar population modeling or dust, but absence of confirmatory spectroscopy. Summary of Lecture #1

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: passive galaxies (z-K) (B-z) How does this help?

Reddy et al 2005 Ap J 633, 248 Connecting the BzK, LBG and DRG Populations SF Density Contributions LBG Reddy et al (2005) - sBzK and LBGs are idential populations Kong et al (2006) - Clustering of sBzK and pBzK galaxies is identical, suggesting same population and SF is simply transient van Dokkum et al (2006) - LBGs constitute only 17% of massive galaxies! Distribution of M>10 11 M  galaxies LBG DRG van Dokkum et al 2006 Ap J 638, L59

f star = star formation efficiency  DC = star formation duty-cycle N  = ionizing photons per unit of star formation f Lya = escape fraction of Lya photons f ip = escape fraction of ionizing photons SFR(M halo ) = f star M halo  DC t H bb mm L 1500 = 8.0 x (SFR / 1 M  yr -1 ) erg s -1 Hz -1 L Lya = N  f Lya (1-f ip )SFR(M halo ) 2. Converting halo mass to star formation rate: 3. Converting SFR to luminosity of LBGs and Ly  emitters: 2 3 Stark, Loeb & Ellis (2007); see also Dijsktra & Wyithe, Mao et al 1. Assume SF driven by mergers according to Press-Schechter formalism Simple Analytical Model

Hu et al astro-ph/ No Obvious Change in Line Profiles