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massive galaxies at
high redshift:
models confront observations
rachel somerville
STScI
GIRLS; Leiden, September 2008
 shock heating &
radiative cooling
 photoionization
squelching
 merging
 star formation
(quiescent &
burst)
 SN heating & SNdriven winds
 chemical
evolution
 stellar populations
& dust
z=5.7 (t=1.0 Gyr)
z=1.4 (t=4.7 Gyr)
z=0 (t=13.6 Gyr)
Springel et al. 2006
Wechsler et al. 2002
fairly broad consensus:
 SN-driven winds remove baryons in small-mass halos
 some process(es) prevent(s) cooling in large-mass
halos (radio jets, clumps, conduction, cosmic ray
pressure?)
rss, Hopkins, Cox, Robertson & Hernquist 2008, MN in press
quenching of massive galaxies
(note the slope is wrong for
low mass galaxies.
this is not due to AGN FB, &
cannot be easily solved by
‘tweaking’)
stellar mass
rss, Hopkins, Cox, Robertson & Hernquist 2008, MN in press
hot vs. cold flows
 halos with primarily “cold” vs.
“hot” flows separated by a
critical mass of few x 1012 Msun
at low redshift (e.g. Birnboim
& Dekel 2003; Keres et al.
2004);
 heating processes only
effective when a quasi-static
hot gas halo is present (i.e. in
large mass halos)
simulations:
A. Kravtsov
dense cold filaments can penetrate the hot medium
in large-mass halos at high redshift
1014
1013
Mvir
[Mʘ]
all hot
1012
cold filaments
in hot medium
Mshock~M
Mshock>>M*
*
all cold
1011
1010
109
Mshock
Dekel,
Birnboim,
Zinger,
Kravtsov
M*
0
1
2
3
redshift z
4
5
QSO/bright mode
 associated with optical/Xray luminous AGN/QSO
 triggered/fed by mergers
or secular (bar) instabilities
 high accretion rates (0.1-1
LEdd), fueled by cold gas
via thin accretion disk
 may drive winds that can
shut off further accretion
onto the BH and sweep
the ISM out of the galaxy
Radio Mode
 radio galaxies (classical FR
I and FR II type sources);
generally no optical
emission lines
 ‘low accretion state’ (low
Eddington ratio, <10-3
Bondi accretion or ADAF?)
 jets may heat gas in a
hydrostatic hot halo,
offsetting or quenching
cooling flow
time-dependent IMF?
SFR at high-z overestimated?
star formation history
blue: fiducial model
(cLCDM 8=0.9)
red: WMAP3
orange: no cooling if
Mh<1011 Msun
stellar mass build-up
all stars
star formation
in bursts
stellar mass function evolution
Fontanot, de Lucia, Monaco & rss
in prep
“raw” model predictions
solid: MORGANA
dash: Munich Mill.
dot-dash: rss08
with convolved errors
stellar mass assembly
without mass errors
with errors (0.25 dex)
solid: MORGANA
dash: Munich Mill.
dot-dash: rss08
data:
red: Conselice et al.
blue: composite MF
Fontanot et al. in prep
star formation rate density as
function of galaxy mass
solid: MORGANA
dash: Munich Mill.
dot-dash: rss08
green: GOODS; blue: Zheng et al. (COMBO-17)
red: Conselice et al.; cyan: Mobasher et al. 2008
Fontanot et al. in prep
evolution of the SF ‘main sequence’
data:
red square: Drory et al. 2008
blue: Bell et al. 2007
cyan: Martin et al. 2007
green: Grazian et al. 2006
magenta: Noeske et al. 2007
red x: Chen et al. 2008
blue diamond: Dunne et al. 2008
Fontanot et al. in prep
archeological downsizing
data: Panter et al. 2007
data: Gallazzi et al. 2007
Fontanot et al. in prep
when did the red
sequence emerge?
 the red sequence is still clearly identifiable
in the field & clusters up to z~1 (Bell et al.
2005; Faber et al. 2007)
 recently, a population of massive red
galaxies detected in the field at 2<z<3
(Kriek et al. 2008; Taylor et al. 2008)
 very red populations discovered in
clusters up to z~2, but absent by z~3 (Zirm
et al. 2008; Kodama et al. 2008)
Kriek et al. 2008
field
population
Zirm et al. 2008
color-magnitude
relation for coma
black points: SDSS
red points: SAM
Trager & rss 2008
rest-frame u-r for proto-clusters (M>1014 Msun)
z~0
SDSS
RS
Millennium
z=2 clusters
‘field’ RS
from Taylor
et al. ECDFS
observed frame J-H for proto-clusters (M>1014 Msun)
z=2
Zirm et al.
data
H(AB)
Testing physical parameter extraction
from broad-band photometry
 created SAM mock catalogs (including
dust & IGM) and extracted U-, B-, and Vdropouts using GOODS selection criteria
 added photometric errors by
bootstrapping from GOODS data
 ran a fairly standard BC03-based SEDfitting code on ACS+ISAAC+IRAC
photometry (extract stellar mass, stellar
population age, and SFR)
S. Lee, R. Idzi, H. Ferguson, rss, T. Wikland, M. Giavalisco
-19%
-65%
x2
U-drops (z~3); redshift fixed
-25%
-58%
x2
B-drops (z~4); redshift fixed
B-drops; redshift fit
U-drops with largest mass errors
U-drops with smallest mass errors
z~0.4-1.4
DEEP+Palomar photometry
fixed redshift
bootstrapped photometric
errors
Bundy et al. (2006) mass
estimation method
no significant offset or
mass trend
--> scatter ~0.15 dex
Stringer et al. 2008
parameter estimation summary
 sources of error:
 mismatch between assumed “tau” SFHs and
SAM predicted SFH
 ‘hiding’ of mass beneath young stellar
population
 ‘conspiracy’ of overestimated age (-->
higher mass estimate) + ‘youth bias’
(lowers mass estimate) actually reduces
mass errors
 two-component models (with ‘maximally
old’ component or secondary burst)
produce improved age & SFR estimates,
but poorer mass estimates!
summary
 differences between observational datasets much
larger than differences between models!
 number/mass density of massive galaxies is
reproduced fairly well by models (when mass errors
convolved) to z~2
 SFR of massive galaxies at z~1-2 underestimated by
factor of ~few in models if observational estimates
taken at face value (IMF, AGN contamination,
large errors in SED-fit based estimates?)
 low mass galaxies form too early in models --> mass
assembly “upsizes” rather than “downsizes”
 massive galaxies in large mass halos are being
quenched too late in models (RS emerges late)
 errors in stellar masses, SFR, and ages derived from
SED fitting to broad-band photometry at high
redshift may be larger than we think...
bias in line-strength
derived ages
mass weighted age
LS derived age
for 20 realizations of
a Coma-sized halo
stellar mass
Trager & rss 2008
star formation histories of early type galaxies
as a function of stellar mass
 SF histories of E’s in hierarchical models show
qualitatively correct ‘downsizing’ behavior
 but, probably not strong enough (new evidence
from /Fe ratios -- Arrigoni, Trager & rss in prep)
the original downsizing plot
~SSFR
~stellar mass
Cowie et al. 1996
the many manifestations
of ‘downsizing’
 SF history from lookback studies (original Cowie
definition): star formation activity shifts to lower
mass galaxies over time
 mass assembly histories: high mass galaxies
assembled early, low mass galaxies assembled
later
 archeological downsizing: stellar ages are
younger in low mass galaxies, indicating a later
epoch of SF
 chemo-archeological downsizing: higher [/Fe]
ratios in more massive galaxies indicate a shorter
epoch of formation