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Jerusalem 2004Hans-Walter Rix - MPIA
The Evolution of the High-z Galaxy Populations
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
First (1996-1997) estimates of the cosmic star-formation history
Warning: historical plots. Do not use for research!!
after Madau et al 1996
=1!!
Lilly et al 1995
HDF
HDF
(too “empty”)
Steidel et al
The impact of LSS!
Jerusalem 2004Hans-Walter Rix - MPIA
A current “UV-based” versionGiavalisco et al 2003 (GOODS)
=0.3 =0.7 H0=70from measured UV density
after dust correction
Jerusalem 2004Hans-Walter Rix - MPIA
And from the perspective of sub-mm (thermal dust emission)
Barger et al 2000
thermal IR observed in sources
Completeness corrected x 11 (undetected sources)
=1
Dust corrected UV (Giavalisco et al 03)
Jerusalem 2004Hans-Walter Rix - MPIA
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
Detected sources are likely to have luminosities ~ 5x Arp 220
SFR from ULIRGS now
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
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 z~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 2004Hans-Walter Rix - MPIA
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
K-band selected sample
(rest>5000A)
x10 in M/L!
SFR ~ e-t/7Gyr
since z~4-5
redshift
Jerusalem 2004Hans-Walter Rix - MPIA
The Build-Up of Stellar MassRudnick et al 2003
• Take IR-selected sample
• Multiply jV with <M/L>V to get <*>
• ½ of stars since z~1.4• 50% between 2>z>1• 10% before z~3
NowBig Bang
Integrated SFR estimates (e.g. Giavalisco 03)
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
Example: Red Galaxies in the Hubble Deep Field
Jerusalem 2004Hans-Walter Rix - MPIA
SUBARU Deep Field Ouchi et al 2002
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
S.A.M prediction
Kauffmann et al 99
Baugh et al 99
Corr
ela
tion L
ength
Bia
s
Ouchi et al 2003
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
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 parameteris universal• Size of galaxies reflects angular momentum of halo baryons have less ang. Mom. small galaxies
Jerusalem 2004Hans-Walter Rix - MPIA
Are there large (disk?) galaxies at high redshift?
(Labbe et al 2003; see also Lowenthal et al 1997)
M81 At the present, “normal” disk galaxies look completely different in the UV than in the optical
Zspec=2.
9
“peculiar”, or star-forming ring seen in the UV
Older / redder bulge / bar?
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
Size Evolutionfrom GOODS (Ferguson et al 2003)
UV size at a given UV luminosity was smaller in the past
Incre
asin
g re
dsh
ift
Apparent size [“]
Rest-frame 1500A Size
Constant size
Jerusalem 2004Hans-Walter Rix - MPIA
Can one map the evolution of size at a given (stellar) mass?
(FIRES; Trujillo et al 2003)
• What is the empirical null hypothesis?Size Luminosity Size Mass (stellar)
SDSS z~0
Shen et al 2003
Jerusalem 2004Hans-Walter Rix - MPIA
What if the SDSS Galaxies were
observed at 1<z<3 in FIRES?
Simulated distribution of sizes, assuming
•SDSS size distribution holds high-z
•same stellar mass as observed in FIRES
• all observational effects
Jerusalem 2004Hans-Walter Rix - MPIA
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 2004Hans-Walter Rix - MPIA
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)
• 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 2004Hans-Walter Rix - MPIA
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