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Conference Summary

Conference Summary. Richard Ellis (Caltech). 51 talks × 30 slides = 1530 slides AND 54 posters All carefully digested, rationalized, inter-compared with results in the literature to give a “lucid, crisp, holistic view of the role of the environment in the formation of galaxies…..”.

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Conference Summary

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  1. Conference Summary Richard Ellis (Caltech) 51 talks × 30 slides = 1530 slides AND 54 posters All carefully digested, rationalized, inter-compared with results in the literature to give a “lucid, crisp, holistic view of the role of the environment in the formation of galaxies…..”

  2. `Environmental processes’ as `astronomical weather’ • Everyone knows it happens • Theorists don’t think it’s important in the `big picture’ • Numerical predictions of it are often famously wrong • …and we all know it does have an important effect! Totally soaked!

  3. The Environmental Revolution Dressler 1980 Butcher et al 1984 • Key ingredients governing `environmental revolution’ • Morphology – density relation (T – Σ) • Rising blue fraction fB(z) • Gas stripping as likely mechanism (Gunn & Gott 1972)

  4. But also strong evolution in the field 0<z<1.. Redshift  Huang et al B-K K UV, [O II],H,mid-IR Hopkins (2004), Hopkins & Beacom (2006)

  5. Mass fn:  (M, ) f() Fraction in red light Importance of Environment:  (Mpc-2) ~25% of all stars at z~0 are in ellipticals (75% in spheroids) Most are in massive galaxies whose mass function is correlated with 25% of stellar mass is in dense environments (lg  > 0.4) Baldry, Balogh, Bower et al MNRAS 373, 469 (2006)

  6. Evolution of Morphology Density Relation Smith et al Ap J 620, 78 (2005) fE/S0 fE/S0 Environmental density  plays key role in governing morphological mix: - Continued growth in high  but delay for lower  regions - Slower conversion of spirals to S0s with only Es at z > 1?

  7. Changing Paradigms of Galaxy Formation • Classical paradigm (1963-1985): galaxies evolve in isolation present-day properties governed by SF history ellipticals: prompt conversion of gas stars spirals: gradual consumption of gas, continuous SF • DM paradigm (1985-): grav. instability governs merging of halos low mass halos collapse first (bottom up formation) mergers transform morphologies (ellipticals form late) dense environments evolve faster (clusters older than field) • “Enhanced” DM paradigm (2003-): feedback solves all finally match the galaxy LF (after 20 years of trying) reverse assembly history (a.k.a downsizing, initially disputed) now enthusiastically embraced via AGN heating externally-driven processes not so important Have we come full circle?

  8. Why Question Importance of the Environment? • It’s hard to distinguish between effects of mass (which depends on ) and external processes expected due to the environment (accelerated evolution vs environmental evolution) • It’s hard to find correlations between some of the finer properties of galaxies and  (but this depends on scale/epoch) • Evolutionary trends (T- ) may reflect global trends in the field or subtle biases • Theorists are happy `fiddling with feedback’ as it does so well it matching data BEWARE OF ANY THEORY THAT “EXPLAINS ALL KNOWN DATA”!

  9. Profound statements by some of our pundits • This slide will self-destruct after the meeting, so don’t worry.. • `Nature’ is beating `nurture’ (Bower) but I don’t think he meant it! • `Halo mass is king’ (Croton) • It’s all compatible with hierarchical assembly (Croton) • Environment just buys you more time in mass assembly (Lilly) • I have nothing to say about clusters (Lilly) • Field L* galaxies are the most important objects (Cooper) • Possible explanation: • environmental effects are relevant but at a level below that for which the above pundits are interested (i.e. secondary) • the data is good enough to warrant much more detailed physical considerations, so numerical simulations particularly important `Gene-expression is influenced by environment which in turn is shaped by gene-expression’ (Babul)

  10. Environment is equivalent to > 2 Gyr retardation NB: Cosmos field does not probe full range of cosmic densities Cross-over mass for early types Lilly/Tasca A mere delay in gas exhaustion or two different processes?

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

  12. - Do AGNs really live in quenched/ing galaxies? Nandra et al. 2006

  13. Topics at the Meeting (..a selection) • Environmental processes in clusters (Bekki, Babul, Ma, Poggianti, Kodama, Tran) • Detailed studies of local clusters (Chung, Cote, Gallazzi, Ferrari, Smith) • Growth of red sequence galaxies and  dependences (Bower, Almaini, Rettura, Aragon-Salamanca, Lilly, Tasca, Cooper, Yee, Kaviraj) • Dynamical masses and ages of red galaxies (Hudson, Colless) • Groups vs clusters (Barton, Balogh, Rasmussen, V-Montenegro,Wilman) • HI/X-ray studies of galaxies and groups (Alighieri, Hau, Hughes, Mulchaey) • Role of mergers (Duc, Conselice, Robaina) • Dusty SF galaxies as tracers (Cirasuolo, Saintonge, Le Floc’h, Haines) • Nearby E and E+A galaxies (Bureau, Goto, Couch) • Mass - metallicity relations (Ellison)

  14. Clusters are excellent laboratories • They contain a significant fraction of red galaxies at high  • Physically-sound simulations indicating a range of important processes occur (stripping, starvation, tidal effects, harassment) (Bekki, Smith) • We see evidence of these processes: • - recent production of S0s (Just, Wilman) - in-situ evolution in selected clusters (Moran, Kodama) - intracluster stars (Coté, Tran) • Issues: • why is it hard to see environmental dependencies in local color-mag and FP (Bower, Colless) • could many of the evolutionary trends simply reflect processes occurring naturally in the field (Haines)?

  15. Recent Formation of S0s Dennis Just (award-winning poster!) see also Wilman Strong differential growth of S0s between field and cluster is clear evidence for importance of environmental processes

  16. Removal of gas in cluster environs (Bekki) (DM halo + bulge + disk stars/gas + halo gas+SF) Halo gas • More efficient stripping in clusters (Fstrip depends on Mcl, V, T etc). • Typically 70% of gas can be removed from galaxy halos. Disk gas Hot gas V=500 km/s T=107 K (Mcl=1014 Msun) Md=6*1010Msun,vc=220 km/s,B/D=0.2

  17. In Situ Evoln - I: Radial Trends in Cluster E/S0s E+A • Sharp onset of [OII] emitters at RVIRIAL~1.5Mpc • Subsequently enhanced Balmer absorption (H) • Recently-arrived field galaxies interact with ICM in cluster environs • Model illustration: 200 Myr burst at RVIRIAL involving 1% burst by mass • “Environmental rejuvenation” as important as mass-dependent trends H + H [OII] R (Mpc) Moran et al (2007)

  18. In Situ Evoln - II: Passive Spirals No optical emission (OII <5 Å) • lack of star formation Visible spiral structure • no major disruption to the structure of the galaxy (e.g. major merger) But strong FUV emission! Passive spirals caught in final decline in SFR in last 107-108 yr Sp E Moran et al Ap J 641, L97 (2006)

  19. Measuring the Quenching Timescale ~100Myr NUV-r ~1Gyr Dn4000

  20. Passive Spirals: Cl 0024 vs. MS 0451 Passive spirals less concentrated in MS0451 as expected for starvation Abundances  timescales sufficient for production of local S0s

  21. high med low Sharp colour transition in groups/outskirts 銀河の色は中間的な環境で急激に変化する RXJ1716 cluster (z=0.81) （赤い銀河の割合） high ～ cluster core med ～ group / filament low ～ field Koyama, TK,et al. (2008)

  22. Spatial Distribution of the 15μm sources A void of 15um sources at the center! X-ray (Chandra) map (Jeltema et al.) ○single /△blended 15μm sources Koyama, TK, et al. (2008)

  23. The S0 Bulge Problem: A Possible Resolution • Passive spirals are sufficiently abundant over 0<z<1 to be precursors of local cluster S0s • But local S0s have more prominent bulges than their spirals cohorts. So how can one be a faded version of the other? • Spitzer IRS data reveals a population of circumnuclear starburst galaxies which may precede the passive spiral stage, building up the bulge mass 12 cluster LIRGS in Cl0024 S24 < 0.6mJy Geach et al (2008)

  24. Diffuse Starlight in Virgo (Mihos et al)

  25. 6dF survey K<12.75 10,000g (Colless) Maybe environmental trends have been erased by z=0?

  26. Marginal Environmental Dependence of FP v Dokkum & vd Marel (2007) Treu et al Ap J 622, L5 (2005) clusters field SDSS log  Only marginal trends seen with density (including SDSS): - mass-dependent growth is a galactic-scale phenomenon? - age differential (field vs cluster) ~ 0.4 Gyr @ z~0 (4%)

  27. Radial Dependence of FP in One System Coma Radial dependence of FP: 71 spheroidals in Cl0024+16 (z=0.40) Spheroidals in core are passively evolving since zF > 2 Outermost spheroids have younger stellar popn (t > 0.6 Gyr) Moran et al Ap J 634,977 (2005)

  28. Are Mergers a key feature of galaxy assembly? • We all agree mergers happen • Simulations show they can destroy disks, remove/consume remaining gas and produce a red and dead product • Detailed studies of nearby spheroidals show evidence of past accretions • But what fraction of the mass growth in the red sequence comes from these events • [Speakers seemed more obsessed with comparing observations with Millenium Simulation rather than addressing this question!]

  29. Dichotomy in Local Early-Types Martin Bureau

  30. Using rest-frame U-B color as a discriminant, a threshold stellar mass is apparent above which there is no SF • Mass threshold increases from ~1011 M at z~0.3 to ~1012M at z >1 • Stable from field-to-field (V/bin~2.106 Mpc3) • Little change for high mass quiescent galaxies over z<1 We Know the Growth Rate in Red Galaxies Bundy et al (2006)

  31. Downsizing: Red Growth Increasing abundance but strongly mass-dependent Morphological spheroidals have a similar formation pattern. (Bundy et al. 2005) Mass Bundy et al. 2006

  32. Mass Dependent Pair Fraction Log M* ~ 11.3 Background field correction Log M* ~ 10.3 Lin et al. 2008 DEEP2 Redshift pair correction. Bundy et al 2009

  33. Volumetric Merger Rate Too few mergers to explain growth of early types AND to drive AGN activity! Log Merger Rate Density, Gyr-1 Mpc-3 Log M* Bundy et al (2008)

  34. Selected `Interesting Results’ • Stripping most efficient at the time when groups merge to form clusters (Bekki) • Extension of FP to very feeble galaxies suggest downsizing ends at 70 km/s dispersions (Hudson) • Serious selection effects in deriving color/T- relation in L-selected samples (Lilly/Tasca) • Incorporation of strangulation into semi-analytic models (Bower) • Evidence for environmental heating in clusters “galaxy stirring” (Babul) • Appearance of color-L relation at z > 2 in UKIDSS UDS (Almaini) • IFU spectroscopy of local E+A galaxies (Couch) • MIR B-O effect (Saintongue, Haines, Kodama) • Renewed interest in S0s (Wilman, Just, Bamford..)

  35. The End of Downsizing? (Smith et al 07, Allanson et al 09) Hudson/Smith

  36. Biases inherent in luminosity-selected samples?

  37. Evolution in colour bimodality to KAB=23 0.25 < z < 0.75 0.75 < z < 1.0 1.0 < z < 1.25 (u-b)rest 1.75<z<2.25 1.5 < z < 1.75 1.25 < z < 1.5 MK c.f Kodama et al (2008) Cirasuolo et al. (2009)

  38. Clustering evolution with redshift and luminosity (passivevs starforming) Hartley et al. (in prep) Almaini/Hartley

  39. Some good things about semi-analytic models • Current models seem to do reasonably well …. (I’m sure someone will contradict me!) • Present-day luminosity functions • The transition mass • Galaxy down-sizing • 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

  40. Where Next? • Multi-wavelength studies continue to drive the field • Detailed studies of individual systems (STAGES, A3921, 0024/0451) can be just as valuable as big surveys • High s/n spectroscopy can be very influential (also GALEX) • Resolved studies of distant galaxies is arriving (e.g. bulges, S0s) • Disentangling group processes from clusters is key - good progress • Attention to detail on biases in L/M-selected samples • Making semi-analytical models more realistic using physical simulations • Lots of work to keep us all happy and motivated!

  41. We Spanned the Full Range of Environment! Kuala Lumpur log  = 3.0 (excluding motorcycles!) Kuala Selangor log  = 0.0 (discounting fireflies)

  42. ..and we had a great party! Many thanks to.. Meghan, Frazer, Mike Merrifield, Duncan, Taddy, Jiasheng…and others!

  43. Conference Philosophy Just as a distinction between nature and nurture can prevent us from taking a holistic view of galaxy evolution, so divisions between observations at different wavelengths and redshifts, simulations and theory can inhibit a full understanding of galaxy evolution. The aim of this conference is to synthesize these diverse lines of research by dividing the programme into astrophysical rather than astronomical strands. The intention is that speakers should place their own contributions in a broader context, in order to develop understanding of the individual underlying physical processes that shape galaxy evolution.

  44. Halo Merger Rates from Millennium Growth rate of halos seen in MS also fails to match production rate of halos hosting new spheroidals in GOODS Bundy et al. Ap J 665, L5 (2007)

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