1. The Complex Web of Galaxy Formation Richard Bower Andreea Font, Ian McCarthy, Andrew Benson & the GALFORM team Using semi-analytic models to create a holistic approach to galaxy ecology.

2. Galaxy Ecology Galaxy Ecology - modeling how galaxies interact with their environment Galaxy Ecology - modeling how galaxies interact with their environment Role in shaping the star formation history of the universe Role in shaping the star formation history of the universe Talk overview Talk overview Mechanisms Mechanisms Observations…the challenges Observations…the challenges Problems with semi- analytic models Problems with semi- analytic models Towards a model that works Towards a model that works The need for a holistic model The need for a holistic model

3. Nature vs Nuture 1.Are the differences due to evolutionary processes? (nurture) 2.Or due to intrinsic differences in progenitors mass? (nature) All most everyone focuses on (1) All most everyone focuses on (1) The universe is hierarchical The universe is hierarchical Clusters are formed out of smaller systems Clusters are formed out of smaller systems 3. A new twist - central vs satellite galaxies

4. z = 0.0 The taxonomy of ecological models The classical view Galaxies contain lots of cold gas They must fight to retain their cold gas The modern view Galaxies rapidly deplete their cold gas They must continually be refueled The post-modern view: Properties only depend on mass and central/satellite Springel et al 2005 Larson, Tinsley & Caldwell 1984 Gunn & Gott, 1972 Van den Bosch et al 2008

5. Post-modern: "of, relating to, or being a theory that involves a radical reappraisal of modern assumptions about culture, identity, history, or language (merriam-webster on-line dictionary)

6. Mechanisms Mechanisms Why should galaxy properties depend on the environment? Ram-pressure Ram-pressure Collisions / harassment Collisions / harassment "Strangulation" "Strangulation" Removal of cold disk gas Removal of hot gas halo

7. Current thinking (circa 2007): Ram-pressure: Ram-pressure: only densest regions – most galaxies have lost their gas before this becomes important only densest regions – most galaxies have lost their gas before this becomes important Collisions / harassment: Collisions / harassment: important in shaping morphology, but not so important in using up gas important in shaping morphology, but not so important in using up gas Strangulation: Strangulation: the most important mechanism. In fact its often too strong. the most important mechanism. In fact its often too strong.

8. What the data say…

9. Constraining models: The Colour-Magnitude diagram CMR - a good tool for studying clusters CMR - a good tool for studying clusters Simple, integrated colours Simple, integrated colours …but dust obscurred and metal dependent …but dust obscurred and metal dependent …or SFR directly? …or SFR directly? Direct comparison of physical quantities Direct comparison of physical quantities Needs high quality spectra and/or UV data Needs high quality spectra and/or UV data This is a theory talk, so I wont make an issue of this. This is a theory talk, so I wont make an issue of this. Baldry et al. 2003 (see also Hogg et al. 2003)

10. Baldry et al. 2003 (u-r) For a better analysis, take slices through the CMR: Colour distribution in 0.5 mag bins can be fit with two Gaussians Mean and dispersion of each distribution depends strongly on luminosity Dispersion includes variation in dust, metallicity, SF history, and photometric errors Bright Faint (u-r)

11. Fraction of star forming galaxies suppressed in dense environments – but its a continuous trend Fraction of star forming galaxies suppressed in dense environments – but its a continuous trend Local density is more important than halo mass Local density is more important than halo mass Luminosity is more important than environment Luminosity is more important than environment isolated galaxies isolated galaxies Even isolated regions contain passive galaxies Even isolated regions contain passive galaxies Balogh et al. 2004 The colour-magnitude diagram

12. The post-modern view: satellite colours depend weakly on halo Van den Bosch 2008 But clearly the details do depend on stellar mass. Even at fixed mass, there are more red-sequence galaxies in higher mass haloes Radial gradients within systems (Smith et al 2008) Can this be explained by tidal stripping, or reduced or more extended suppression ? Mean and spread depend only weakly on stellar mass. Stellar mass halo mass

13. Back to the the modern view Weinmann et al 2006; same data as Van dev Bosch et al 2008 ???…but the differences between panels are largely due to the properties of central galaxies

14. the post-modern view Satellite vs central - important Satellite vs central - important Environment (aka halo mass) unimportant Environment (aka halo mass) unimportant No special processes No special processes Timescale for SF decay. Timescale for SF decay. less important! (updated) ( just one? stripping of halo gas?) (needs to be quite long compared to halo lifetime)

15. Qualitative explanation of the trends The strong dependence on galaxy mass The strong dependence on galaxy mass Nature? ie., the halo mass before accretion Nature? ie., the halo mass before accretion The subtle dependence on environment? The subtle dependence on environment? Immediately galaxies become satellites? Immediately galaxies become satellites? Or Pre-processing in groups? Or Pre-processing in groups? But what fraction of galaxies fall directly into clusters? ( But what fraction of galaxies fall directly into clusters? ( Berrier et al 2008; McGee et al 2009) A long timescale for suppression? A long timescale for suppression? …but not too long! Lets test the qualitative ideas with semi-analytic models

16. Semi-analytic models And what AGN feedback can do for you… Croton et al 2006, Bower et al 2006

17. Some good things about semi-analytic models Current models seem to do reasonably well …. (Im sure someone will contradict me!) Current models seem to do reasonably well …. (Im sure someone will contradict me!) Present-day luminosity functions Present-day luminosity functions The transition mass The transition mass Galaxy down-sizing Galaxy down-sizing The models achieve this by suppressing cooling in high mass haloes The models achieve this by suppressing cooling in high mass haloes See also Croton et al., De Lucia et al.; Kitzbichler et al., Somerville et al 2008

18. Semi-Analytic models: The state of the art AGN + semi-analytic galaxy formation provides a frame work for understanding the anti- hierarchical universe AGN + semi-analytic galaxy formation provides a frame work for understanding the anti- hierarchical universe B06 is by no means the only model to use AGN: eg., Hatton et al 2003, Granato et al 04, Croton et al. 06, De Lucia et al 07, Menci et al 07, Cattaneo 07, Summerville 08 - but be aware of the different flavours. B06 is by no means the only model to use AGN: eg., Hatton et al 2003, Granato et al 04, Croton et al. 06, De Lucia et al 07, Menci et al 07, Cattaneo 07, Summerville 08 - but be aware of the different flavours. The model seems to describe the properties of central galaxies reasonably well… The model seems to describe the properties of central galaxies reasonably well… But.. But.. …do they explain the environment-driven trends?

19. Problems with the standard model… Satellites are too red. Regardless of halo mass. Satellites are too red. Regardless of halo mass. The effect of strangulation is overestimated The effect of strangulation is overestimated A satellite galaxy orbiting within another halo is assumed to loose its own hot gas reservoir. A satellite galaxy orbiting within another halo is assumed to loose its own hot gas reservoir. This is far too simplistic This is far too simplistic Weinmann et al 2006; Baldry et al 2006.

20. Environmental Physics is not correctly handled All satellites are red! All Galaxies Satellite Galaxies No blue satellites!

21. Environmental Physics is not correctly handled Is this realistic? Mass ratio of haloes Gas atmosphere of the main halo Old Strangulation model Remove gas reservoir as galaxy orbits larger halo Hot gas reservoir SNe winds quickly exhaust disk gas Larson, Tinsley & Caldwell 1984 Strangulation = suffocation = starvation McCarthy et al 2007 – an improved model for halo stripping – depends on the orbit of the satellite and the gas content of the satellite and main halo. (Actually, Gunn & Gotts formulae re-calibrated for halo gas using numerical simulations)

22. McCarthy et al. 2007 Controlled SPH and FLASH simulations

23. - Hot gas: modelled with a beta- model / NFW Satellite velocities are sampled with a 2D distribution (Benson 2005): Implementation in GALFORM

24. Environmental Physics is not correctly handled New Strangulation Physics Old Strangulation model

25. Solving the problem by adjusting the environment physics Dramatic improvement in the environmental dependence of satellite properties from reducing the effects of starvation. Dramatic improvement in the environmental dependence of satellite properties from reducing the effects of starvation. Font et al 2008, also Kang & vdBosch 2008; Kimm et al 2009

26. A closer look at the colour distribution of galaxies The FieldThe Clusters Gilbank & Balogh 2008; Font, McGee, Balogh et al, in prep. (Distributions shifted to to agree with red-sequence colours) Too many intermediate colour galaxies, not enough blue objects Too many faint red galaxies

27. A closer look at the luminosity function

28. Towards a holistic model Model improvements: Model improvements: Including tidal stripping Including tidal stripping..needed to remove faint red galaxies..needed to remove faint red galaxies Towards an accurate model of the intra-group medium Towards an accurate model of the intra-group medium even the new stripping calculation is too aggressive even the new stripping calculation is too aggressive …needed to get ram pressure calculations right …needed to get ram pressure calculations right

29. X-ray Emission from Groups and Clusters L-T relation : well known that the self-similar relation fails L-T relation : well known that the self-similar relation fails AGN: standard model just prevents cooling… it doesnt affect the X-ray luminosity AGN: standard model just prevents cooling… it doesnt affect the X-ray luminosity Data from Horner et al. B06 Model Data from Osmond & Ponman

30. The AGN feedback loop (new version) Cooling AGN fuelling Hydrostatic ? Heating redistribute halo gas Based on the excess energy method (Wu et al 1999), plus the hydrostatic criterion radio mode P=min( L edd, M cool ) A note for pundits: This is in-situ heating theres no pre- heating its going to be expensive, but not prohibitively so.

31. X-ray Emission from Groups and Clusters L-T relation : well known that the self- similar relation fails L-T relation : well known that the self- similar relation fails AGN: standard model just prevents cooling AGN: standard model just prevents cooling Revised model, AGN feedback redistributes halo gas until the cooling rate drops and AGN power is cut off Revised model, AGN feedback redistributes halo gas until the cooling rate drops and AGN power is cut off AGN redistributes halo gas Scatter driven by diverse assembly history Voit & Bryan 2001; Bower et al 2008, MN, in press ( astro-ph/0808.2994) A huge step forward - Ive been trying to achieve this for ten years!

32. The baryon content of haloes - where are all those baryons? Stars and cold gas Hot X-ray emitting gas Ejected gas T (keV) Also Conroy & Ostriker 2008 ; Puchwein et al 2008; Dave et al 2008

33. Conclusions: what you should remember! The classical view: The classical view: Galaxies contain lots of cold gas and fight to retain their cold gas The modern view: The modern view: Galaxies rapidly deplete their cold gas and must continually be refueled Post-modern view: Post-modern view: central or satellite - thats all! Lengthens the timescale of starvation The properties of (faint) satellites are [somewhat] dependent on their parent halo nature wins (the mass of the halo before accretion)

34. Conclusions: what you should remember! Galaxy formation models: Galaxy formation models: 06 models: a reasonable description of centrals 06 models: a reasonable description of centrals need to be modified to calculate environmental effects properly need to be modified to calculate environmental effects properly 08 models match some satellite properties reasonably well 08 models match some satellite properties reasonably well …but the details still arent there yet… …but the details still arent there yet… Post-modern view is rather too easily accommodated! Post-modern view is rather too easily accommodated!

35. Improvements and challenges Model Improvements: Model Improvements: Tidal stripping - removing faint red galaxies; reproducing the intra-cluster light Tidal stripping - removing faint red galaxies; reproducing the intra-cluster light Better modeling the intra-group medium, understanding the X- ray haloes of groups and galaxies Better modeling the intra-group medium, understanding the X- ray haloes of groups and galaxies Observational challenges: Observational challenges: Pushing low-redshift measurements to fainter galaxies [GAMA, a wide-field redshift survey 2mag deeper than SDSS (pi Norberg) ] Pushing low-redshift measurements to fainter galaxies [GAMA, a wide-field redshift survey 2mag deeper than SDSS (pi Norberg) ] Establishing robust measurements for low mass galaxies at higher redshift. [ROLES, Gilbank et al 2009; zCOSMOS++?] Establishing robust measurements for low mass galaxies at higher redshift. [ROLES, Gilbank et al 2009; zCOSMOS++?]

36. Redshift One Emission Line Survey LDSS 3 on Magellan Gilbank, Davies, Li, Balogh, Glazebrook, Hau, Bower, Baldry, Savaglio, McCarthy

37. Thank you!

38. How many parameters do semi-analytic models have?

39. Post-modern view is rather too easy!

40. Beyond the modern view Weinmann et al 2006; Van dev Bosch et al 2008 …but the differences between panels are largely due to the properties of central galaxies