1. Models & Observations galaxy clusters Gabriella De Lucia Max-Planck Institut für Astrophysik Ringberg - October 28, 2005

2. Outline: Semi-analytic models -- substructures & galaxies -- hybrid models – methods, limits & aims -- applications The ESO Distant Cluster Survey (EDisCS) -- the colour-magnitude relation -- cluster structure

3. Mathis H. et al., 2002  CDM  CDM The SAM – the hybrid models : Halo galaxy Central galaxy Satellite galaxy Springel et al. (2001) De Lucia et al., MNRAS, 2004

4. The SAM – the physics: Hot GasCold Gas cooling Ejected Gas feedback star formation recycling Stars re-incorporation Metallicity dependence (Sutherland & Dopita 1993) It is important!! (Tissera & Scannapieco 2003) DLG, Kauffmann & White, 2004

5. 4 Mpc DM density map Cluster galaxies A simulated cluster (M ~ 10 15 M  ) B-V > 0.8 B-V < 0.8 Gabriella De Lucia, PhD Thesis

6. Luminosity function Colour-magnitude Tully-Fisher Metallicity- mass Gas fraction- luminosity DLG, Kauffmann & White, 2004

7. The field metal budget ej. slowwind slow 1+redshift Mass metals / Y * Mstar gas stars hot gas ejected retentionej. fast Observational signature of different feedback models #2: DLG, Kauffmann & White, 2004 Differences between different models become more dramatic at high redshifts

8. EDisCS clusters White et al., A&A, in press A wide range of masses and structural properties

9. The CM of 2 EDisCS clusters 55 33 spec. conf. members single burst z=3 exp. s.f.r. z=3 De Lucia et al., ApJL, 2004

10. deficit De Propris et al.(2003) V Composite EDisCS @z=0.75 Coma I-obs V-rest Number of galaxies The red-sequence LF Robust result – also present in the full photometric catalogue! De Lucia et al., ApJL, 2004 De Lucia et al., ApJL, 2004 (see also Kodama et al. 2004)

11. #lum/#faint redshift Coma A496 EDisCS clusters There is a clear increase in the luminous-to-faint ratio with increasing redshift De Lucia et al., in prep. The build-up of the CM relation A “cosmic down-sizing” (Cowie, 1996). A problem for the hierarchical paradigm?

12. Ellipticals in our hierarchical model Three channels to make bulges: In a ‘minor’ merger the stellar mass of the merged galaxy is transferred to the bulge of the central galaxies + burst of a fraction of the combined cold gas A ‘major’ merger completely destroys the disc of the central galaxy + burst of a fraction of the remaining gas Disk instability (Mo, Mao & White 1998) 1,031,049 (810,486 ) Es with Mstar > 4x10 9 (1x10 10 ) Msun 16% Es / 66% Sp / 18 % S0 (MV < -18) (13%, 67%, 20% Loveday et al., 1996) AGN model for suppression of the cooling-flows (Croton et al., 2005) De Lucia et al., astro-ph/0509725

13. increasing Z increasing age Brighter ellipticals are older AND more metal rich The origin of the colour-magnitude De Lucia et al., in preparation Gallazzi et al., in preparation

14. Elliptical galaxies also have a shorter formation timescale! This is “anti-hierarchical”!!! The star formation histories: mass De Lucia et al., astro-ph/0509725 cluster ellipticals field ellipticals redshift Lookback time (Gyr) M star = 10 12 M sun M star = 10 9 M sun clusters field 10 10 M  10 11 M  10 12 M  cluster field Lookback time (Gyr)

15. redshift M 200 = 10 15 M sun M 200 = 10 12 M sun Elliptical galaxies in denser environment are older The “double-downsizing” (see talk by T. Treu) De Lucia et al., astro-ph/0509725 A natural expectation in the hierarchical scenario

16. Ellipticals: formation & assembly 50 % stars formed 80 % redshift Fraction of galaxies 50 % stars in a single object 80 % redshift De Lucia et al., astro-ph/0509725

17. 1 Mpc Simulation z=0.398 cl1018-1211 z=0.472 cl1216-1201 z=0.795 Simulation z=0.783 1’ Simulated and real clusters Full information about the spatial and redshift distribution of model galaxies construction of simulated catalogues of galaxies including luminosity, colour, bulge-to-disc ratio etc.

18. Observing a simulated cluster Model results can be treated with exactly the same methods used for the observational data

19. cl1216-1201 @ z= 0.8 a simulated cl @ z=0.8 Structure comparison De Lucia et al., in preparation

20. Conclusions: Semi-analytic models are a technique for studying galaxy formation - they are not meant to be definitive! The ever more detailed picture of our Universe also requires a more complex modelling An apparent “down-sizing” in the formation of elliptical galaxies is not in contradiction with the hierarchical paradigm A self-consistent approach that takes into account the spectro- photometric AND chemical evolution is necessary Comparison with observational results (expecially at high redshifts) will provide important constraints on physical processes and missing physics. CM of EDisCS clusters: a clear increase of the Lum/Faint ratio for passive red galaxies as a function of redshift