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