“Nature” and “nurture” a theoretical perspective

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

2. projected density R [Mpc] The morphology-density relation “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 Dressler 1980

3. Outline • 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

4. 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. 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. 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. Star formation(threshold, efficiency, initial mass function) Cooling(metallicity, halo structure, conductivity) Mergers and Galaxy interactions(morphological transformations, induced star formation) Dust(formation,distribution, heating and cooling) GALAXY 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. Dark matter haloes & galaxies #1 • Halo occupation models • (bypass modeling of physical processes, provide a statistical characterization of the link between DM and galaxies) P(N|M) + spatial distribution Berlind et al. 2002

9. Dark matter haloes & galaxies #2 Roediger & Brueggen (2007) • Hydrodynamical simulations • (explicit description of gas dynamics, • limited mass and spatial resolution, • computational time, “sub-grid” physics) z = 0.8 Courtesy: Volker Springel

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

11. WHERE : field + low velocity dispersion groups WHAT : strong internal dynamical response Physical mechanisms Galaxy mergers: e.g. Negroponte & White ‘82, Barnes & Hernquist ‘91, ‘96 Mihos & Hernquist ‘94, ‘96,

12. M51 Galaxy mergers Toomre & Toomre, 1972 Mihos 2004 Springel, PhD Thesis, 1999 Cox, PhD thesis, 2004 Barnes & Hernquist, 1996

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

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

15. Harassment Mastropietro et al, 2005

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

17. Ram-pressure in SAMs “we find that ram-pressure stripping is not important for colours and star formation rates of galaxies in the cluster core” Okamoto & Nagashima 2003 B-V Lanzoni et al. 2005 “including or neglecting ram-pressure stripping in the model, galaxy properties only show mild variations” r/R200

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

19. 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. The stripping of the hot reservoir McCarthy et al. 2008 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 dark matter gas

21. 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 Font et al. 2008

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

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

24. The merger tree of a BCG De Lucia & Blaizot 2007

25. 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. The role of “heredity” Gao et al. 2004 De Lucia et al. 2006

27. M = 1.4x1011 M MV = -22.15 B - V = 0.77 The role of “heredity” M = 1.3x1011 M MV = -22.11 B - V = 0.79 Symbols: objects with M > 1010 M Cluster “Field” Color-coding: B - V

28. 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. Conclusions • 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

30. Tidal stripping of stars 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 Stellar Mass [1010 Msun/h] Lookback time [Gyr]