1. “Nature” and “nurture” a theoretical perspective Gabriella De Lucia INAF – Astronomical Observatory of Trieste

2. Gabriella De Lucia, November 5, Bologna The morphology-density relation projected density R [Mpc] Dressler 1980 “There are some indications of a correlation between characteristic type and compactness, the density of the cluster diminishing as the most frequent type advances along the sequence of classification” Hubble, “The Realm of the Nebulae”, 1936 Heredity or Nature against Nurture or Environment

3. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna ✔ Techniques we use to model galaxy formation in a cosmological framework (limits & aims) ✔ Overview of the most relevant physical processes, and of their relative importance at different masses, times, and environments ✔ Critical review of recent progress and open issues. ✔ The role of “heredity” ✔ A brief presentation of the project(s) ongoing in a new group recently formed in Trieste Outline

4. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna A premise ✔ Theoretical (and observational) studies trying to assess the influence of the environment on galaxy evolution have mostly focused on galaxy clusters (“good laboratories”, “easy” to find, etc)

5. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna A premise ✔ Theoretical (and observational) studies trying to assess the influence of the environment on galaxy evolution have mostly focused on galaxy clusters (“good laboratories”, “easy” to find, etc) ✔ Clusters are biased environments and represent rare objects. In addition, in order to really establish if some cluster-dependent physics is playing a role, one would need to establish a difference between the evolution of galaxies in clusters and that of identical galaxies in the field.

6. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna A premise ✔ Theoretical (and observational) studies trying to assess the influence of the environment on galaxy evolution have mostly focused on galaxy clusters (“good laboratories”, “easy” to find, etc) ✔ Clusters are biased environments and represent rare objects. In addition, in order to really establish if some cluster-dependent physics is playing a role, one would need to establish a difference between the evolution of galaxies in clusters and that of identical galaxies in the field. ✔ If we live in a hierarchical Universe, then structure grows hierarchically. In this framework, a simple distinction between “nature” and “nurture” is difficult to accommodate and both are likely playing a role in determining the observed environmental dependences

7. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna GALAXY FORMATION Cooling (metallicity, halo structure, conductivity) Star formation (threshold, efficiency, initial mass function) Dust (formation,distribution, heating and cooling) Mergers and Galaxy interactions (morphological transformations, induced star formation) SN Feedback (IGM heating, IGM enrichment, efficiency, winds) Stellar evolution (spectro-photometric evolution, yields,feedback) BHs and AGNs (BH growth, quasar winds, radio bubbles)

8. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna ✔ Halo occupation models (bypass modeling of physical processes, provide a statistical characterization of the link between DM and galaxies) P(N|M) + spatial distribution Dark matter haloes & galaxies #1 Berlind et al. 2002

9. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna ✔ Hydrodynamical simulations (explicit description of gas dynamics, limited mass and spatial resolution, computational time, “sub-grid” physics) z = 0.8 Dark matter haloes & galaxies #2 Courtesy: Volker Springel Roediger & Brueggen (2007)

10. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna ✔ Semi-analytic models (simple but physically and observationally motivated prescriptions, large dynamic range, fast) feedback star formation Hot Gas Cold Gas cooling Ejected Gas Stars re-incorporation - AGN heating z=3. z=1. z=0. Dark matter haloes & galaxies #3 Kauffmann et al. 1999 De Lucia et al. 2004, De Lucia & Blaizot 2007 Croton et al. 2006

11. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Physical mechanisms e.g. Negroponte & White ‘82, Barnes & Hernquist ‘91, ‘96 Mihos & Hernquist ‘94, ‘96, WHERE : field + low velocity dispersion groups WHAT : strong internal dynamical response Galaxy mergers:

12. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna M51 Galaxy mergers Mihos 2004 Cox, PhD thesis, 2004 Barnes & Hernquist, 1996 Toomre & Toomre, 1972 Springel, PhD Thesis, 1999

13. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Galaxy mergers in SAMs Observational evidence for dry mergers (e.g. van Dokkum 2005) but mergers rates are not accurately measured fraction redshift formation time assembly time Mstar [M  h -1 ] Effective # of mergers De Lucia et al. 2006

14. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Physical mechanisms e.g. Negroponte & White ‘82, Barnes & Hernquist ‘91, ‘96 Mihos & Hernquist ‘94, ‘96, WHERE : field + low velocity dispersion groups WHAT : strong internal dynamical response Galaxy mergers: e.g. Spitzer & Baade ‘51, Richstone ‘76, Farouky & Shapiro ‘81, Moore et al. ‘96, Moore et al. ‘98 WHERE : in massive clusters WHAT : some damage but less than mergers – at least on luminous members Harassment:

15. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Harassment Mastropietro et al, 2005

16. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Physical mechanisms e.g. Negroponte & White ‘82, Barnes & Hernquist ‘91, ‘96 Mihos & Hernquist ‘94, ‘96, WHERE : field + low velocity dispersion groups WHAT : strong internal dynamical response Galaxy mergers: e.g. Spitzer & Baade ‘51, Richstone ‘76, Farouky & Shapiro ‘81, Moore et al. ‘96, Moore et al. ‘98 WHERE : in massive clusters WHAT : some damage but less than mergers – at least on luminous members Harassment: e.g. Gunn & Gott ‘72, Cowie & Songaila ‘77, Nulsen ‘82, Quilis et al. ‘00 WHERE : in the central regions of clusters WHAT : suppression of star formation and indirect effect on morphology Gas stripping:

17. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Ram-pressure in SAMs Okamoto & Nagashima 2003 Lanzoni et al. 2005 “we find that ram-pressure stripping is not important for colours and star formation rates of galaxies in the cluster core” “including or neglecting ram-pressure stripping in the model, galaxy properties only show mild variations” B-V r/R 200

18. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Physical mechanisms e.g. Negroponte & White ‘82, Barnes & Hernquist ‘91, ‘96 Mihos & Hernquist ‘94, ‘96, WHERE : field + low velocity dispersion groups WHAT : strong internal dynamical response Galaxy mergers: e.g. Spitzer & Baade ‘51, Richstone ‘76, Farouky & Shapiro ‘81, Moore et al. ‘96, Moore et al. ‘98 WHERE : in massive clusters WHAT : some damage but less than mergers – at least on luminous members Harassment: e.g. Gunn & Gott ‘72, Cowie & Songaila ‘77, Nulsen ‘82, Quilis et al. ‘00 WHERE : in the central regions of clusters WHAT : suppression of star formation and indirect effect on morphology Gas stripping: e.g. Larson, Tinsley & Caldwell ’80, Balogh, Navarro & Morris ‘00 WHERE : anytime the galaxy falls in a larger system WHAT : suppression of star formation and indirect effect on morphology Strangulation:

19. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna The colour-magnitude bimodality ✔ Tail of blue bright object (despite a “strong” AGN feedback – a “dust” problem?) ✔ Excess of faint red satellites ✔ Transition region not as well populated as in the observational data Quantitatively, the CM bimodality is not well reproduced (see discussion in De Lucia 2007)

20. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna The stripping of the hot reservoir Strangulation is usually assumed to be instantaneous. Transition from blue cloud to red sequence occurs on very short time-scales (because there is also an efficient feedback from supernovae) Recent numerical studies suggest that the stripping of hot gas occurs on longer time-scales. This can potentially help keeping satellite galaxies active for longer times McCarthy et al. 2008 gas dark matter

21. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Font et al. 2008 The colours of satellites Assume a non- instantaneous stripping of hot material + this material can cool on satellite galaxies Central galaxies are basically unaffected but a larger fraction of satellites become now bluer (qualitative agreement with obs. data) See also Kang et al. 2008

22. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Physical mechanisms - continued e.g. Tabor & Binney 1993, Churazov et al. ‘01, Brueggen et al. ’02, Sijacki & Springel ’06, +++++++ WHERE : centre of massive groups/clusters WHAT : suppression of “cooling flows” AGN heating: McNamara et al. 2005 Croton et al. 2006 Bower et al. 2006

23. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Physical mechanisms - continued e.g. Tabor & Binney 1993, Churazov et al. ‘01, Brueggen et al. ’02, Sijacki & Springel ’06, +++++++ WHERE : centre of massive groups/clusters WHAT : suppression of “cooling flows” AGN heating: e.g. Ostriker & Tremaine ‘75, White, ‘76, Makumuth & Richstone ‘84, Merritt ‘85 WHERE : groups and clusters WHAT : formation of BCGs? Cannibalism:

24. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna The merger tree of a BCG De Lucia & Blaizot 2007

25. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna The role of “heredity” Halo properties do depend on the “environment”: ✔ Present day haloes in clusters are on average more concentrated, more spherical, and rotate slower than haloes in the field (e.g. Avila- Reese et al. 2005, Wechsler et al. 2006) ✔ Haloes in high-density environments form earlier and a higher fraction of their mass is assembled during major mergers, compared to haloes in low density environments (e.g. Sheth & Tormen 2004, Maulbetsch et al. 2007) This is bound to leave an “imprint” on galaxies that inhabit different regions today

26. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna The role of “heredity” De Lucia et al. 2006 Gao et al. 2004

27. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna M = 1.4x10 11 M  M V = -22.15 B - V = 0.77 Cluster “Field” M = 1.3x10 11 M  M V = -22.11 B - V = 0.79 Symbols: objects with M > 10 10 M  Color-coding: B - V The role of “heredity”

28. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna 1 VVDS mock Masses from SED fitting The agreement with the observed mass functions is quite good. No significant deficit - rather an excess of faint and intermediate mass galaxies Courtesy: Lucia Pozzetti (see also Stringer et al. 2008)

29. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna ✔ Unsurprisingly, both heredity and environment affect galaxy evolution, but what is their relative importance? ✔ Little attention has been devoted so far in “quantifying explicitly the importance of conditions at formation (nature rather than nurture). Not surprising either… this is difficult… ✔ We need to have gain a better understanding about physical processes at the group scale. This is the most common galaxy environment ✔ We also need to improve (and better understand) our definitions of environment Conclusions

30. INAF – Astronomical Observatory of Trieste Gabriella De Lucia, November 5, Bologna Lookback time [Gyr] Stellar Mass [10 10 Msun/h] Tidal stripping of stars (stellar halo, intra- cluster light) Obs measurements are, unfortunately, very uncertain (from few % to more than 50%!!!) Tidal stripping is not the main channel for the production of ICL ( Rudick et al. 2006, Murante et al. 2007 ). Unfortunately, results do not converge. Saro et al. submitted Tidal stripping of stars