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

Jerusalem 2004Hans-Walter Rix - MPIA

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– Are all relevant sources included

• Faint• Obscured


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!


A current “UV-based” versionGiavalisco et al 2003 (GOODS)

=0.3 =0.7 H0=70from measured UV density

after dust correction


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)


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


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


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


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


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


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)


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?


Example: Red Galaxies in the Hubble Deep Field


SUBARU Deep Field Ouchi et al 2002


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


S.A.M prediction

Kauffmann et al 99

Baugh et al 99

Corr

ela

tion L

ength

Bia

s

Ouchi et al 2003


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

??


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


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?


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


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


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


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


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


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*)


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 The Evolution of the High-z Galaxy Populations.

Documents

hanswalter rix mpia

hanswalter rix mpia

redshift slide

dust correction slide

baugh et

steidel et

lilly et

madau et