1. The epochs of early-type galaxy formation in clusters and in the field D. Thomas, C. Maraston, R. Bender, C. Mendes de Oliveira Max-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

2. Epoch of galaxy formation Redshift survey Astro-archeology Age-Z degeneracy Direct link to local sample Comparison with models Time evolution resolved Progenitor bias Source identification Consistency prediction Ages

3. Resolved Stellar Populations Age + Metallicity Element ratios

4. Unresolved Stellar Populations Population Synthesis Models

5. Model Grid Mgb yields younger ages and higher metallicities

6. 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

7. Stellar model atmosphere calculations Courtesy: A. Korn Model atmospheres from Tripicco & Bell 1995; Korn, Maraston, Thomas, in preparation

8. α/Fe matters…also for Balmer line indices Thomas, Maraston, Korn, 2004 MNRAS, 351, L19 Data: Kuntschner (2000)

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

10. Data and Models Age-Metallicity Mg/Fe ratio Cluster Field ▲ Lenticular ● Elliptical

11. Effects of correlated errors Correlated errors can mimik wrong trends (e.g., Trager et al. 2000; Kuntschner et al. 2001) Monte Carlo simulations

12. ClusterFieldClusterField Monte Carlo approach Field galaxies 1-2 Gyr younger  /Fe identical in cluster and field

13. Relations with  Field is younger + more metal rich α/Fe low in hierarchical models (Thomas 1999) Metallicity Age α/Fe Kauffmann & Charlot ‘98 Independent of environment

14. α/Fe bias at high metallicities? Bensby et al. 2004 Proctor et al. 2004 Bensby et al. 2003 E galaxies ?

15. 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

16. 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 2002 Dickinson et al. 2003 Fontana et al. 2003 Rudnick et al 2003 Fontana et al. 2004 Glazebrook et al. 2004 Bell et al. 2003 Stellar mass density at z~1 >> 50 per cent

17. 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. 2003 EROs at redshift z~1: Daddi et al. 2000; Saracco et al. 2003; Moustakas et al. 2004; Väisänen & Johansson 2004; Pierini et al. 2004 Evolved 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., …

18. Challenges for hierarchical models Hydro (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

19. 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

20. Calibration Horizontal branch Morphology (Maraston & Thomas 2000)