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The Evolution of the High-z Galaxy Populations

The Evolution of the High-z Galaxy Populations. The Evolution of the Cosmic Star Formation Rate. When did it start / ramp up? When were half of the stars formed? Are we at the end of star-formation? Estimating the “cosmic star-formation rate” Estimating the SFRs in individual objects

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The Evolution of the High-z Galaxy Populations

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  1. The Evolution of the High-z Galaxy Populations Jerusalem 2004 Hans-Walter Rix - MPIA

  2. The Evolution of the Cosmic Star Formation Rate • When did it start / ramp up? • When were half of the stars formed? • Are we at the end of star-formation? • Estimating the “cosmic star-formation rate” • Estimating the SFRs in individual objects • Are all relevant sources included • Faint • Obscured Jerusalem 2004 Hans-Walter Rix - MPIA

  3. The impact of LSS! Steidel et al HDF (too “empty”) First (1996-1997) estimates of the cosmic star-formation history W=1!! HDF Lilly et al 1995 after Madau et al 1996 Warning: historical plots. Do not use for research!! Jerusalem 2004 Hans-Walter Rix - MPIA

  4. A current “UV-based” versionGiavalisco et al 2003 (GOODS) after dust correction from measured UVdensity W=0.3 L=0.7 H0=70 Jerusalem 2004 Hans-Walter Rix - MPIA

  5. Dust corrected UV (Giavalisco et al 03) And from the perspective of sub-mm (thermal dust emission) Completeness corrected x 11 (undetected sources) thermal IR observed in sources W=1 Barger et al 2000 Jerusalem 2004 Hans-Walter Rix - MPIA

  6. Detected sources are likely to have luminosities ~ 5x Arp 220 SFR from ULIRGS now The Evolution of Intense Starbursts • SFR from ULIRGs has dropped by > 100 since ~3! • NB: many high-z QSO’s also show enormous thermal dust emission  phases of intense SFR Jerusalem 2004 Hans-Walter Rix - MPIA

  7. Cosmic Star-Formation History: Upshot • <SFR> has risen by 5-7 x from z~0 to z~1.2 • UV based estimates (after correction by 10) and sub-mm/thermal IR (after different correction of 10) give consistent <SFR> estimates 2<z<5 • 1.5<z<5 <SFR> approximately constant (~2) (Note: there is some evidence for a drop beyond 5) • ULIRG (>few 100Msun/yr) mode of star-formation has dropped by >100 since z~3 Jerusalem 2004 Hans-Walter Rix - MPIA

  8. Brief, but important aside • Galaxies with low SFR exist at 1<z<3.5 • they can be found in IR-selected samples • They seem to make up ½ of the stellar mass (see below) at z~2-3 FIRES: van Dokkum et al 2003 with Spectra Jerusalem 2004 Hans-Walter Rix - MPIA

  9. The Build-Up of the Stellar MassStep 1 The mean color of galaxies as function of redshift (Rudnick et al 2003): • Optical colors  M/LB as long as star-formation history is not too “bursty” (Bell and de Jong 2001) • Individual galaxies may have bursts, but an ensemble of galaxies at a given epoch (say Dz~0.5) should not have their bursts all at the same time •  Look at the mean color of the galaxies as a function of Jerusalem 2004 Hans-Walter Rix - MPIA

  10. SFR ~ e-t/7Gyr since z~4-5 Mean Color of the Galaxy Population as a Function of Redshift • On average, galaxies were much bluer in the past • <M/L> was 10 x lower at z~3  redshift K-band selected sample (lrest>5000A) x10 in M/L! Jerusalem 2004 Hans-Walter Rix - MPIA

  11. The Build-Up of Stellar MassRudnick et al 2003 • Take IR-selected sample • Multiply jV with <M/L>V to get <r*> • ½ of stars since z~1.4 • 50% between 2>z>1 • 10% before z~3 Integrated SFR estimates (e.g. Giavalisco 03) Big Bang Now Jerusalem 2004 Hans-Walter Rix - MPIA

  12. Galaxy Clustering and its Evolution • Generic prediction of hierarchical CDM models: • More massive halos (=more luminous galaxies?) are more strongly clustered • (Luminous) Galaxies at early epochs are increasingly “biased”  their clustering remains high • Present epoch: redder galaxies are more clustered than blue ones • Has that always been true? Jerusalem 2004 Hans-Walter Rix - MPIA

  13. Example: Red Galaxies in the Hubble Deep Field Jerusalem 2004 Hans-Walter Rix - MPIA

  14. Jerusalem 2004 Hans-Walter Rix - MPIA SUBARU Deep Field Ouchi et al 2002

  15. Ly-break galaxies are observed to be clustered(e.g. Giavalisco et al 1998; Ouchi et al 2003) Z~4 galaxies in the Subaru deep field Jerusalem 2004 Hans-Walter Rix - MPIA

  16. Correlation Length S.A.M prediction Kauffmann et al 99 Baugh et al 99 Bias Ouchi et al 2003 Jerusalem 2004 Hans-Walter Rix - MPIA

  17. How are galaxies and the IGM (=Ly-a forest) correlated? • Search for galaxies near the line of sight to a distant QSO • Is there an overabundance of neutral gas in the vicinity of galaxies at z~3? • Yes  Galaxies lived in large-scale overdense regions ??  more HI Distance LBG to Ly-a Absorption Jerusalem 2004 Hans-Walter Rix - MPIA

  18. Internal Structure of Early Galaxies • (Astro-)folklore: • High-z galaxies are compact • There are no big disks at high-z • Basis of that lore: • Observations (see below) • Theoretical expectation: • Halos that collapse early are denser • Spin parameter l is universal • Size of galaxies reflects angular momentum of halo  baryons have less ang. Mom.  small galaxies Jerusalem 2004 Hans-Walter Rix - MPIA

  19. At the present, “normal” disk galaxies look completely different in the UV than in the optical M81 “peculiar”, or star-forming ring seen in the UV Older / redder bulge / bar? Zspec=2.9 Are there large (disk?) galaxies at high redshift?(Labbe et al 2003; see also Lowenthal et al 1997) Jerusalem 2004 Hans-Walter Rix - MPIA

  20. Several examples in the HDF South • Can’t prove that these objects are disks, but they sure look like local examples • However, they are likely to be single entities that are not grossly disturbed Jerusalem 2004 Hans-Walter Rix - MPIA

  21. Rest-frame 1500A Size Constant size Increasing redshift  Apparent size [“] Size Evolutionfrom GOODS (Ferguson et al 2003) •  UV size at a given UV luminosity was smaller in the past Jerusalem 2004 Hans-Walter Rix - MPIA

  22. Size  Luminosity Size  Mass (stellar) SDSS z~0 Shen et al 2003 Can one map the evolution of size at a given (stellar) mass?(FIRES; Trujillo et al 2003) • What is the empirical null hypothesis? Jerusalem 2004 Hans-Walter Rix - MPIA

  23. Simulated distribution of sizes, assuming • SDSS size distribution holds high-z • same stellar mass as observed in FIRES • all observational effects What if the SDSS Galaxies were observed at 1<z<3 in FIRES? Jerusalem 2004 Hans-Walter Rix - MPIA

  24. What if the SDSS Galaxies were observed at 1<z<3 in FIRES? Actually observed in FIRES Note: rest-frame V-band sizes at all z’s Jerusalem 2004 Hans-Walter Rix - MPIA

  25. Describing (the lack of) size evolution with redshift • Let’s assume that the SDSS distribution holds in its functional form at all redshifts, but that re(M*)~(1+z)a • Fit a from the FIRES data… At a given stellar mass, galaxies have the same size at all (observed) redshifts! Re (z | Lv) Re (z | M*) Jerusalem 2004 Hans-Walter Rix - MPIA

  26. Summary • Different approaches to dM*/dt(z) and M*(z) give (surprisingly?) consistent answers, at the ~2 x level. • We live at the end of star/galaxy formation • The epoch where most, say 80%, of the stars form has been identified: 3>z>0.5 • No clear evidence for the “onset” of SF, yet. • Galaxies at high-z are observed to be highly clustered • They are “rarer” objects  bias • Galaxy sizes do not show the expected imprint of “formation epoch” • Re(M*)~ const. with z Jerusalem 2004 Hans-Walter Rix - MPIA

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