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. 2003Papovich et al. 2002

Dickinson et al (HDFN) Fontana et al (K20) Glazebrook et al (GDDS) ; Brinchmann & Ellis 2000; Cohen et al. 2000; Rudnick et al (FIRES); Drory et al (MUNICS); van Dokkum, et al stellar mass massive galaxies (both old/evolved and dusty/star forming) are being discovered in significant numbers at redshifts as high as z=2…

local galaxies m*>2.5E10 M sun m*>1.0E11 M sun EROs sub-mm K20 SDSS QSOs LBGs Do massive galaxies at high redshift pose a crisis for CDM? these kinds of observations could refute CDM, but so far they do not pose a problem. n.b. all theorists agree on this

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

Glazebrook et al Fontana et al Stellar mass assembly history: comparison with LCDM models

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) IMF=Kroupa Tecza et al (SMG’s)

SAMs vs. N-body+hydro omost hydro simulations overpredict  * today because feedback is relatively ineffective owhen strong outflows included, results agree well with SAMs (e.g. Springel & Hernquist, Nagamine et al.) semi-analytic models N-body+hydro Springel & Hernquist Nagamine et al.

SPH SAM We use stellar populations to trace the star formation history… omodels do well at reproducing optically identified star forming populations at z ~ 3-6 (LBGs) & global SFR odifference between SAM and SPH (Springel & Hernquist) at z>3 is due to small mass galaxies

why do galaxies come in two basic types? thin disk dynamically cold supported by rotation blue colors strong emission lines broad range of stellar ages, ongoing star formation spheroidal, dynamically hot red colors strong absorption lines predominantly old stars little recent star formation

Baldry et al color blue red luminosity bright faint SDSS galaxy colors (and many other properties) are strongly bimodal

Baldry et al color 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 ~3x10 10 M sun old young Kauffmann et al. 2003

Balogh et al increasing density--> decreasing luminosity--> u-r what is the role of environment? (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

rest U-V color rest V magnitude (luminosity) the red sequence & color bimodality seen at z=1! Bell et al also seen in the DEEP2 redshift 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 black: SDSS purple: SAM

rest U-V color rest V magnitude (luminosity) model prediction: color-magnitude relation at high redshift colored points meet R<24 COMBO-17 selection criterion

rest U-V color rest V magnitude (luminosity)Bell et al. 2003

red: B/T>0.5 blue: B/T<0.5 cyan: t mrg < 0.5 Gyr red: E/S0 blue: S/Irr cyan: merger GEMS models produce enough bright/massive/bulge dominated galaxies -- but they are too blue

K AB < rss et al GOODS ApJL GOODS not enough EROs

Bell et al 2003 Results from state-of-the-art numerical hydrodynamic simulations are very similar Dave et al., see also Nagamine et al.

Why are red galaxies red? oCDM models produce enough old, massive galaxies. the problem is a continuous ‘trickle’ of star formation othere must be some process that shuts off star formation after galaxies have become massive othis process must be rapid, and seems to be connected with the presence of a spheroid omust 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 M h >M crit 3.shut off star formation when M * >M crit 4.shut off star formation when M *,bulge >M crit

toy models 1.remove all remaining gas after major mergers –has almost no effect (fresh gas gets accreted) 2.shut off cooling/SF when M h >M crit –kills massive galaxies entirely; does not produce bimodality oshut off star formation when M * >M crit –kills massive galaxies entirely; does not produce bimodality shut off star formation when M *,bulge >M crit

Color-magnitude distribution SDSS SAM: gas ejected after major merger

Color-magnitude distribution SDSS SAM: SF shut off when M h >M crit

SF quenched when M h >M crit M r < (purple=SAM black=SDSS)

Color-magnitude distribution SDSS SAM: SF shut off when M bulge >M crit

Metallicity normalization increased by a factor of 2 SDSS SAM: SF shut off when M bulge >M crit

SF quenched when M bulge >M crit M r < (purple=SAM black=SDSS)

when do galaxies become ‘quenched’? SF quenched when M bulge >M crit

M bulge quenched model GEMS dry mergers?

AGN: the missing link? otight observed relation between M bulge and M BH oenergy emitted expected to be proportional to M BH Di Matteo, Springel & Hernquist 2005

AGN feedback by momentum-driven winds Murray, Quataert & Thompson 2004 BH bulge SDSS ‘transition mass’ f g =0.1 f g =0.05 observed M BH -  rln

caveats oradiation pressure only one of many physical mechanisms whereby AGN can couple to gas ospherical symmetry assumed -- unrealistic? oconstant opacity assumed -- in reality, a function of metallicity oconstant relationship between M bulge & M BH assumed at all redshifts

‘momentum wind’ model cold gas ejected (and never re-accreted) if M bulge >M crit (  ) still have a ‘cooling flow’ problem!

‘momentum wind’ model cold gas ejected (and never re-accreted) if M bulge >M crit (  ) still have a ‘cooling flow’ problem!

AGN ‘momentum wind’ model red sequence improved, and bimodality appears in the right place, but too many intermediate luminosity blues… still have a ‘cooling flow’ problem

‘momentum wind’ model cold gas ejected (and never re-accreted) if M bulge >M crit (  ) cooling shut off in halos with V c >350 km/s ‘standard’ merging prescription still have a ‘cooling flow’ problem!

AGN feedback, cooling cutoff, merging

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 orecent work suggests even columnated jets can heat a large filling factor of ICM oresulting bubbles look similar to those seen in Chandra images of some clusters oEffective in cluster or perhaps group environments Bruggen, Ruszkowski & Hallen 2005

‘runaway’ QSO growth Bromley, rss & Fabian 2004, 2005 onumber density of bright QSO’s does not turn over at low redshift unless an adhoc scaling in accretion efficiency is applied, or M BH -  relation enforced ‘by hand’ (e.g. Kauffmann & Haehnelt; Volonteri et al.; Wyithe & Loeb)

Stellar Populations as fossil relics of star formation 10 realizations of a ‘Coma’ cluster

actual light-weighted ageactual metallicity age from grids Z from grids ‘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

Summary oCDM-based models of galaxy formation that produce reasonable agreement with the z=0 stellar mass function form enough massive galaxies at high z<2 oBut 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 omomentum-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!