Recent Star Formation and Evolution of Galaxies in Clusters: Observations and Hypotheses

1. VLT/ISAAC Lidman et al. 2004 Coma at z=1.24 Kodama&Arimoto 97 models ZF= 2,3,5 E S0 Late Piero Rosati -- Old galaxies at z=1-1.4 RDCS1252 (z = 1.24) C-M Relation with HST/ACS and VLT/ISAAC(Blakeslee et al. 03; Lidman et al. 03; Rosati et al . 04) HST/ACS The scatter and slope of the red sequence is very similar to low-z clusters, basically frozen over 65% of look-back times !

2. Alan Dressler -- Starburst galaxies and cluster suburbs only 2 k-type and no e(c)’s! 6 are e(a), 1 k+a The suburbs of A851: 7/9 are starbursts! ...a remarkable change in the amount and character of star formation in the recent past. In rich clusters of galaxies, but even in “the field,” the mode of star formation appears to shift to a much greater fraction which are starbursts (20-30%) Hypothesis: As gas-rich disk galaxies fall into these rich clusters, either individually or in small groups, they are severely jostled by tidal interactions. Alternate hypothesis: shocks from intracluster medium drive the starbursts. Dressler et al. 2004

3. Tommaso Treu: E+S0s: cluster induced bursts. GALEX view • Abundance of NUV detected E/S0 consistent with moderate amounts of recent star formation 10^7-10^8 Gyrs inside the virial radius. • Consistent with infall scenario and burst of starformation at ~ the virial radius CL0024 Moran et al. 2006 Also Adam Muzzin; Spitzer starbursts

4. Christian Wolf -- A population of dusty red galaxies 2-D Family: Age x Extinction

5. Michael Balogh -- Color trends at low-z • Fraction of red galaxies depends strongly on density. This is the primary influence of environment on the colour distribution. • Mean colours depend weakly on environment: transitions between two populations must be rapid (or rare at the present day) • Trend is not completely absent for fainter galaxies; but never dominant • Simple dependence of “late-type” fraction on environment characterizes much of observed trends (e.g. SFR-density, morphology-density, colour-density etc.). • Interpretation? • Two modes of formation. Within each peak is variance due to dust, metallicity (second-order effects). • Transitions: Where do S0, E+A fit in? Baloghet al. 2004

6. Anja von der Linden -- Local cluster samples from Sloan

7. Andrea Biviano -- Galaxy orbits

8. Paola Popesso -- The LF at low-z When measured within the physical size of the systems (given by r200), the Cluster LF isuniversal (Popesso et al. 2005) • bimodal behaviour of the cluster LF (steepening at the faint end) • the cluster LF is universal when measured with the virial radius • DGR increasing with the clustercentric distance

9. Vincent Eke -- 2PIGG LF vs mock catalogues from SA The way to do it! …but models don’t get it right

10. Veronica Strazzullo -- The LF at 1.1 < z < 1.3 --- The evolution of the NIR luminosity function of bright galaxies in X-ray luminous clusters at z~1.2 is consistent with passive evolution --- The redshift evolution of K* up to z=1.2 is compatible with passive evolution of a stellar population formed at z>2 --- The bright end of the LF appears to be dominated by galaxies already evolved both morphologically and spectrophotometrically Also Gabriella De Lucia, LF of red galaxies at z=0.8

11. Kim –V. Tran -- Red merging pairs also Marc Postman other high-z clusters: not universal phenomenon, but MS1054 not unique

12. Anthony Gonzales -- Supergroup (or supercluster?) Hierarchical Assembly: SG1120Ongoing mergers of massive galaxies • Detection: • Las Campanas Distant Cluster Survey (Gonzalez et al. 2001) • 4 candidates at z~0.4 within a 7’ diameter region • Confirmation: • Chandra + spectroscopy • 6 extended sources within a 13’ diameter region (~4 Mpc) Groups at z=0.37 (2,3,4,5) Cluster at z=0.48 (1) No redshift yet (6) • “Supergroup” SG1120-1202

13. Marc Postman - Morphologies Morphology - Density Relation • Cluster spirals are significantly redder their field counterparts • But, their quantitative morphologies (C,A,S) are indistinguishable • Sizes (R1/2 or disk scale height) of cluster and field galaxies are similar PG84 z~0 E+S0 Fraction D80/D97 z~0 E+S0 P2005 ACS z~1 E+S0 Smith et al2005 z~1 E+S0 P2005 ACS z ~ 1 Ellipticals PG84 z ~ 0 Ellipticals D80/D97 z ~ 0 Ellipticals • Blue cluster disk galaxies show evidence (97% C.L.) for “centralized” star formation. P2005 ACS z ~ 1 S0 Fraction PG84 z ~ 0 S0 Fraction D80/D97 z ~ 0 S0 Fraction Projected Density

14. Bianca Poggianti -- Evolution of the % of starforming galaxies as a function of environment EDisCS: z = 0.4-0.8 Sloan (Abell): z = 0.04-0.1 Direct link between the star formation activity in galaxies and the history of growth of clusters and groups? In a scenario in which the passive galaxy population has two components (primordial and quenched galaxies), only two informations needed: • fraction of mass/galaxies already in groups at z=2.5 • fraction of mass/galaxies that have experienced the cluster environment for a few Gyr

15. Current scenario (common to all of us?) • In clusters, some galaxies are very old (most massive, Es), both in SF and assembly. A significant % of the cluster galaxies have stopped forming stars at z<1 (from spirals to S0s) • Morphological evolution and evolution in the SF activity are taking place • Massive galaxies have on average shorter SF timescales than smaller ones (downsizing) • Dense environments quench star formation (dense environments?) • Environmental conditions act in two ways – New concept of “nature” vs “nurture”: “Today’s population is the result of different environments at different epochs”.“Primordial” environment & “proper” environmental effects (when galaxy experiences a “new” environment for the first time) – “Proper environmental effects” are second order effects? • Starbursts a more common mode of SF in the past than today • Well sinked in all of us: • clusters as part of a “web” – necessity of “cross-environmental” studies (wide-field studies, importance of the group environment) • history of the “environment” and galaxy history probably closely related

16. Results to be reconciled: • established scenario for Es and S0s form. & evolution • occurrence, consequences & timing of mergers • transformations of galaxy properties and variegated SFHs • apparent “simplicity” of color bimodality • dependence of SF properties on environment at high-z • no apparent dependence at low-z? • starbursts a more common mode of SF at higher z in all envrs. • environmentally-related enhancement of SF? • We still don’t know how the “proper” environmental effects really work to quench and/or enhance SF • To what extent are we observing “intrinsic” (field) galaxy evolution, and to what extent are field studies looking at environmentally-driven evolution?