Interpreting stellar populations in a cosmological context
description
Transcript of Interpreting stellar populations in a cosmological context
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
Dickinson et al. 2003 (HDFN)
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 Dokkum, et al. 2004
stel
lar
mas
s
massive galaxies (both old/evolved and dusty/star forming) are being discovered in significant numbers at redshifts as high as z=2…
local galaxiesm*>2.5E10 Msun
m*>1.0E11 Msun
EROs
sub-mm
K20
SDSS QSOs
LBGs
Do massive galaxies at high redshift pose a crisis for CDM?
these kinds of observations couldrefute CDM, butso far they do notpose a problem.n.b. all theoristsagree on this
the overcooling problemhalo mass functioncooling+SF…+squelching…+SN FB…+ merging suppressed
in clusters
need to suppress coolingand/or star formation inmassive halos to fit z=0 stellar mass functionand luminosity functions
Glazebrook et al. 2004 Fontana et al. 2004
Stellar mass assembly history: comparison with
LCDM models
stellar mass assembly history
good agreement withobservational 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)
IMF=Kroupa
Tecza et al. 2003(SMG’s)
why do galaxies come in two basic types?
thin diskdynamically cold supported by rotation blue colorsstrong emission linesbroad range of stellar ages,ongoing star formation
spheroidal, dynamically hotred colorsstrong absorption lines predominantly old stars little recent star formation
Baldry et al. 2003
colo
r
blue
red
luminosity
bright faint
SDSS
galaxy colors (and manyother properties) are strongly bimodal
Baldry et al. 2003
colo
r
blue
red
luminosity
bright faint
SDSS
old, no recent star formation, high concentration/surface brightness
The two types are divided by a critical mass
young, recent star formation, low concentration/surface brightness
~3x1010 Msun
old
young
Kauffmann et al. 2003
Balogh et al. 2004
increasing density-->
decreasing luminosity-->
u-r
what is the role of environment?
(u-r)
the color of the redsequence is almostindependent ofenvironment…but the fraction ofgalaxies in the redsequence vs. theblue cloud is a strong function oflocal density
rest
U-V
col
or
rest V magnitude (luminosity)
the red sequence & color bimodality seen at z=1!
Bell et al. 2003
also seen in the DEEP2redshift survey(Willmer et al.in prep)
cluster of galaxies
‘Milky Way’ galaxy
in hierarchical models, merger history determines galaxy morphology
Color-magnitude distribution
SDSS SAM
predicted color distributions are not bimodal
-22.5 -21.5 -20.5
-19.5 -18.5black: SDSSpurple: SAM
rest
U-V
col
or
rest V magnitude (luminosity)
model prediction: color-magnitude relation at high redshift
colored pointsmeet R<24 COMBO-17selection criterion
rest
U-V
col
or
rest V magnitude (luminosity)Bell et al. 2003
red: B/T>0.5blue: B/T<0.5cyan: tmrg < 0.5 Gyr
red: E/S0blue: S/Irrcyan: merger
GEMS
models produce enough bright/massive/bulgedominated galaxies -- but they are too blue
KAB<22
13.55.83.21.00.50.1
rss et al. 2004 GOODS ApJLGOODS
not enough EROs
Bell et al 2003Results from state-of-the-artnumerical hydrodynamic simulations are very similar
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. remove all remaining gas after major mergers
2. shut off cooling/SF when Mh>Mcrit
3. shut off star formation when M*>Mcrit
4. shut off star formation when M*,bulge>Mcrit
toy models
1. remove all remaining gas after major mergers
– has almost no effect (fresh gas gets accreted)
2. shut off cooling/SF when Mh>Mcrit
– kills massive galaxies entirely; does not produce bimodality
o shut off star formation when M*>Mcrit
– kills massive galaxies entirely; does not produce bimodality
1. 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 2SDSS SAM: SF shut off when Mbulge>Mcrit
SF quenched whenMbulge>Mcrit Mr<-22.75
-21.75
-20.75
-19.75
-18.75
(purple=SAMblack=SDSS)
when do galaxies become ‘quenched’?
SF quenched when Mbulge>Mcrit
Mbulge quenched model
GEMS
dry mergers?
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 fgc
Gσ 4
€
M•,crit / Msun = 0.12η Edd−1 fg
0.1
⎛
⎝ ⎜
⎞
⎠ ⎟
σ
km /s
⎛
⎝ ⎜
⎞
⎠ ⎟
4
Murray, Quataert & Thompson 2004
€
L• = η Edd LEdd BH
bulge
SDSS ‘transition mass’
fg=0.1fg=0.05
observed MBH- rln
‘momentum wind’ modelcold gas ejected (and never re-accreted) if Mbulge>Mcrit()
still have a ‘cooling flow’problem!
AGN‘momentum wind’
model
-22.75
-18.75
red sequence improved, and bimodality appears in the right place, but too many intermediate luminosity blues…still have a ‘cooling flow’ problem
AGN-feedback model
too much scatter in red sequence at highredshift…formation time too late or toospread out
AGN feedback model
too much scatter in red sequence at highredshift…formation time too late or toospread 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
formation10 realizations of a ‘Coma’ cluster
actual light-weighted age actual metallicity
age
from
gri
ds
Z f
rom
gri
ds
‘real’ vs. ‘grid-derived’ age and 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
Summaryo 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!