The epochs of early-type galaxy formation in clusters and in the

field

D. Thomas, C. Maraston, R. Bender, C. Mendes de OliveiraMax-Planck-Institut für extraterrestrische Physik, Garching

Universitäts-Sternwarte München

Unresolved stellar populations Population synthesis Data sample Ages and Mg/Fe ratios of early-type galaxies

Star formation histories and epochs Conclusions

Comparison with high-z universe Challenges for galaxy formation models

Epoch of galaxy formation

Redshift surveyRedshift surveyAstro-archeology Astro-archeology

Age-Z degeneracy

Direct link to local sample

Comparison with models

Time evolution resolved

Progenitor bias

Source identification

ConsistencyConsistency

prediction

Ages

Resolved Stellar Populations

Age + Metallicity

Element ratios

Unresolved Stellar Populations

Population Synthesis Models

Model Grid

Mgb yields younger ages and higher metallicities

Calibration: Maraston, Greggio, Renzini et al. 2003, A&A

Thomas, Maraston, Bender, 2003a, MNRAS, 339, 897

Based on Maraston (1998) Fuel consumption theorem (Renzini & Buzzoni 1986) Stellar atmosphere calculations (Tripicco & Bell 1995; Korn, Maraston, Thomas in prep.) Extension of method introduced by Trager et al. (2000) Abundance ratio effect “semi-theoretically” included www.mpe.mpg.de/~dthomas

New stellar population model

Stellar model atmosphere calculations

Cou

rtesy

: A

. K

orn

Model atmospheres from Tripicco & Bell 1995; Korn, Maraston, Thomas, in preparation

α/Fe matters…also for Balmer line indices

Thomas, Maraston, Korn, 2004

MNRAS, 351, L19

Data: Kuntschner (2000)

Data Sample

Data: González 1993; Beuing et al. 2002; Mehlert et al. 2003

Data and Models

Age-Metallicity Mg/Fe ratio

ClusterField

▲ Lenticular ● Elliptical

Effects of correlated errors

Correlated errors canmimik wrong trends(e.g., Trager et al. 2000; Kuntschner et al. 2001)

Monte Carlosimulations

Cluster

FieldCluster

Field

Monte Carlo approach

Field galaxies 1-2 Gyr younger/Fe identical in cluster and field

Relations with

Field is younger + more metal rich

α/Fe low in hierarchical models(Thomas 1999)

Metallicity

Age

α/FeKauffmann & Charlot ‘98

Independent of environment

α/Fe bias at high metallicities?

Bensby et al. 2004

Proctor et al. 2004

Bensby et al. 2003

E galaxies

?

α/Fe-

Age-

Star formation histories

Chem. evolution: Thomas et al. 1998, 1999

[α/Fe] ≈ 1/5 – 1/6 log Δt

log Δt ≈ 3.88 – 1.78 log σ

History of mass assembly

Thomas et al. 2004, ApJ, submitted

Anti-hierarchical formation of baryons

Galaxy formation is delayed in the field

Early mass assembly

Massive SF in massive objects at high z

Cohen 2002Dickinson et al. 2003

Fontana et al. 2003Rudnick et al 2003

Fontana et al. 2004Glazebrook et al. 2004

Bell et al. 2003

Stellar mass densityat z~1 >> 50 per cent

A converging picture

Passive evolution up to z~1: Aragón-Salamanca et al. 1993;

Bender et al. 1996; Stanford et al. 1998; Kodama et al. 1999;Kelson et al. 2000; Rusin et al. 2003 ; Pozzetti et al.

2003EROs at redshift z~1: Daddi et al. 2000; Saracco et al. 2003; Moustakas et al. 2004; Väisänen & Johansson 2004; Pierini et al. 2004Evolved galaxies at z~2: van Dokkum et al. 2003;

Franx et al. 2003; Labbé et al. 2003; Chen & Marzke 2004

Massive star forming objects at z~3 (Scuba):Smail et al. 2002; Genzel et al. 2003; Tecza et al. 2004

Galaxies in formation at z~2-5: Totani et al. 2001; Lehnert & Bremer 2003; de Mello et al. 2004

Astro-archaeology: Bower et al. 1992; Renzini & Ciotti 1993; Bender et al. 1993; Trager et al. 2000; Kuntschner 2000; Poggianti et al. 2001; Terlevich & Forbes 2001; Proctor et al. 2002; Thomas et al. 2002; Vazdekis et al. 2003; Strader et

al.; Sanchez-Blazquez et al., …

Challenges for hierarchical modelsHydro (R. Dave) and semi-analytic (R. Somerville)

Astro-archaeology and high-z surveys

• QSO SF Granato et al. 2001, 2004; Cattaneo & Bernardi 2003

• Shield of hot gas prevents further SF Binney 2004

• Early• No late } Star formation

in massive objects

Astro-archeology z-Surveys

Origin of the Mg- relation

Star formation histories of ellipticals

SSP models with variable /Fe Monte Carlo approach

(t,Z/H,/Fe)

Summary

Formation epochs around z~2-5 Baryons form anti-hierarchically Massive Field Es delayed by 1-2

Gyr

Similar share between Z/H and /Fe

Calibration

Horizontal branchMorphology

(Maraston & Thomas 2000)