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

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

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

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

  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. New stellar population model • 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 Calibration: Maraston, Greggio, Renzini et al. 2003, A&A

  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 Mg/Fe ratio Age-Metallicity 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. Cluster Cluster Field Field Monte Carlo approach Field galaxies 1-2 Gyr younger /Fe identical in cluster and field

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

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

  15. Star formation histories α/Fe- [α/Fe] ≈ 1/5 – 1/6 log Δt log Δt ≈ 3.88 – 1.78 log σ Age- Chem. evolution: Thomas et al. 1998, 1999

  16. Stellar mass density at z~1 >> 50 per cent 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 History of mass assembly • Anti-hierarchical formation of baryons • Galaxy formation is delayed in the field • Early mass assembly • Massive SF in massive objects at high z Thomas et al. 2004, ApJ, submitted

  17. A converging picture 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., … 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

  18. Star formation in massive objects • Early • No late } • QSO  SF Granato et al. 2001, 2004; Cattaneo & Bernardi 2003 • Shield of hot gas prevents further SF Binney 2004 Challenges for hierarchical modelsHydro (R. Dave) and semi-analytic (R. Somerville) Astro-archaeology andhigh-z surveys

  19. Summary • 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) • Similar share between Z/H and /Fe • Formation epochs around z~2-5 • Baryons form anti-hierarchically • Massive Field Es delayed by 1-2 Gyr

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

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