Transcript How do the most massive galaxies constrain theories of

Interpreting stellar populations in a
cosmological context
rachel somerville
MPIA
with thanks to the GOODS & GEMS teams, S. Faber, B. Allgood, J.
Primack, A. Dekel, & R. Wechsler
Stellar populations can be used to
‘weigh’ galaxies
Bell et al. 2003
Papovich et al. 2002
massive galaxies (both
old/evolved and dusty/star
forming) are being
discovered in significant
numbers at redshifts as
high as z=2…
Fontana et al. 2004 (K20)
Glazebrook et al. 2004 (GDDS); Brinchmann &
Ellis 2000; Cohen et al. 2000; Rudnick et al. 2004
(FIRES); Drory et al. 2004 (MUNICS); van
Dickinson et al. 2003 (HDFN)
Dokkum, et al. 2004
Do massive galaxies at high redshift
pose a crisis for CDM?
local galaxies
m*>2.5E10 Msun
m*>1.0E11 Msun
LBGs
K20
EROs
sub-mm
these kinds of
observations could
refute CDM, but
so far they do not
pose a problem.
n.b. all theorists
agree on this
SDSS
QSOs
the overcooling problem
halo mass function
cooling+SF
…+squelching
…+SN FB
…+ merging suppressed
in clusters
need to suppress cooling
and/or star formation in
massive halos to fit
z=0 stellar mass function
and luminosity functions
Stellar mass assembly history:
comparison with LCDM models
Glazebrook et al. 2004
Fontana et al. 2004
stellar mass
assembly
history
good agreement with
observational estimates
Glazebrook et al. (GDDS)
Rudnick et al. (FIRES)
Dickinson et al. (HDFN)
Fontana et al. (K20)
Borch et al. (COMBO-17)
Somerville et al. (GOODS)
Tecza et al. 2003
(SMG’s)
IMF=Kroupa
why do galaxies come in two basic types?
spheroidal, dynamically hot
red colors
strong absorption lines
predominantly old stars
little recent star formation
thin disk
dynamically cold
supported by rotation
blue colors
strong emission lines
broad range of stellar ages,
ongoing star formation
galaxy colors (and many
other properties) are
strongly bimodal
color
red
blue
bright
faint
luminosity
SDSS
Baldry et al. 2003
color
red
blue
bright
faint
luminosity
SDSS
Baldry et al. 2003
The two types are divided by a critical mass
~3x1010 Msun old, no recent star formation,
high concentration/surface brightness
old
young
young, recent star formation,
low concentration/surface brightness
Kauffmann et al. 2003
what is the role of environment?
increasing density-->
decreasing luminosity-->
(u-r)
the color of the red
sequence is almost
independent of
environment…
but the fraction of
galaxies in the red
sequence vs. the
blue cloud is a
strong function of
local density
u-r
Balogh et al. 2004
the red sequence & color bimodality seen at z=1!
also seen in
the DEEP2
redshift survey
(Willmer et al.
in prep)
Bell et al. 2003
rest V magnitude (luminosity)
in hierarchical models, merger
history determines galaxy
morphology
cluster
of galaxies
‘Milky Way’
galaxy
Color-magnitude distribution
SDSS
SAM
predicted color distributions are not bimodal
-22.5
-19.5
-21.5
-20.5
-18.5
black: SDSS
purple: SAM
model prediction: color-magnitude relation at high redshift
colored points
meet R<24
COMBO-17
selection
criterion
rest V magnitude (luminosity)
Bell et al. 2003
rest V magnitude (luminosity)
models produce enough bright/massive/bulge
dominated galaxies -- but they are too blue
red: E/S0
blue: S/Irr
cyan: merger
GEMS
red: B/T>0.5
blue: B/T<0.5
cyan: tmrg < 0.5 Gyr
not enough EROs
13.5
5.8
3.2
1.0
0.5
0.1
GOODS
KAB<22
rss et al. 2004 GOODS ApJL
Results from state-of-the-art
numerical hydrodynamic
simulations are very similar
Bell et al 2003
Dave et al., see also Nagamine et al.
Why are red galaxies red?
o CDM models produce enough old, massive
galaxies. the problem is a continuous ‘trickle’ of
star formation
o there must be some process that shuts off star
formation after galaxies have become massive
o this process must be rapid, and seems to be
connected with the presence of a spheroid
o must work in all environments, but happen to a
larger fraction of galaxies in dense places
toy models
1.
2.
3.
4.
remove all remaining gas after major mergers
shut off cooling/SF when Mh>Mcrit
shut off star formation when M*>Mcrit
shut off star formation when M*,bulge>Mcrit
toy models
1.
2.
o
–
–
–
remove all remaining gas after major mergers
has almost no effect (fresh gas gets accreted)
shut off cooling/SF when Mh>Mcrit
kills massive galaxies entirely; does not produce bimodality
shut off star formation when M*>Mcrit
kills massive galaxies entirely; does not produce bimodality
 shut off star formation when M*,bulge>Mcrit
Color-magnitude distribution
SDSS
SAM: SF shut off when Mh>Mcrit
Color-magnitude distribution
SDSS
SAM: SF shut off when Mbulge>Mcrit
Metallicity normalization increased
by a factor of 2
SDSS
SAM: SF shut off when Mbulge>Mcrit
SF quenched when
Mbulge>Mcrit
(purple=SAM
black=SDSS)
Mr<-22.75
-21.75
-20.75
-19.75
-18.75
when do galaxies become ‘quenched’?
SF quenched when Mbulge>Mcrit
Mbulge quenched model
dry mergers?
GEMS
AGN: the missing link?
o tight observed relation
between Mbulge and MBH
o energy emitted expected to
be proportional to MBH
Di Matteo, Springel &
Hernquist 2005
AGN feedback by momentum-driven winds
Lcrit 
4 f gc
G
4
Murray, Quataert &
Thompson 2004
L  Edd LEdd
M,crit / M sun
4




f

g
 0.121


Edd 
0.1km /s 
SDSS
‘transition mass’
bulge
BH
fg=0.1
fg=0.05
observed MBH- rln
‘momentum wind’ model
cold gas ejected (and never re-accreted) if Mbulge>Mcrit()
still have a
‘cooling flow’
problem!
AGN
‘momentum wind’
model
-22.75
red sequence improved, and bimodality
appears in the right place, but too many
intermediate luminosity blues…
still have a ‘cooling flow’ problem
-18.75
AGN-feedback model
too much scatter in
red sequence at high
redshift…formation
time too late or too
spread out
AGN feedback
model
too much scatter in red sequence at high
redshift…formation time too late or too
spread out
‘Effervescent’ heating by giant radio jets
o recent work suggests even
columnated jets can heat a
large filling factor of ICM
o resulting bubbles look similar
to those seen in Chandra
images of some clusters
o Effective in cluster or
perhaps group environments
Bruggen, Ruszkowski & Hallen 2005
Stellar Populations as fossil
relics of star formation
10 realizations of a
‘Coma’ cluster
‘real’ vs. ‘grid-derived’
age and metallicity
actual light-weighted age
actual metallicity
SAM Coma
Trager et al.
Coma data
Dry mergers: simulations
Bell, Naab, McIntosh, rss et al.
Dry mergers: GEMS
Dry mergers
visible for ~250
Myr
every luminous
E has had ~0.5-1
dry merger since
z~1
in good
agreement with
expectations from
hierarchical
models
Summary
o CDM-based models of galaxy formation that produce
reasonable agreement with the z=0 stellar mass function form
enough massive galaxies at high z<2
o But default models do not produce enough massive red
galaxies, especially at high redshift, because of continuous low
level star formation. need a new process that quenches star
formation in massive, bulge-dominated galaxies
o momentum-driven winds powered by AGN a promising
mechanism…another process needed to solve ‘cooling flow’
problem -- but must make enough massive galaxies at high
redshift!