Conference SummaryRichard 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…..”

`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!

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)

The Environmental Revolution

But also strong evolution in the field 0<z<1..

Redshift

UV, [O II], H, mid-IR

Hopkins (2004), Hopkins & Beacom (2006)

K

B-K

Huang et al

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)

Mass fn: (M, ) Fraction in red lightf()

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?

Smith et al Ap J 620, 78 (2005)

fE/S0 fE/S0

Evolution of Morphology Density Relation

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 starsspirals: gradual consumption of gas, continuous SF

• DM paradigm (1985-): grav. instability governs merging of haloslow 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 heatingexternally-driven processes not so important

Have we come full circle?

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”!

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)

Environment is equivalent to > 2 Gyr retardation

NB: Cosmos field does not probe full range of cosmic densities

A mere delay in gas exhaustion or two different processes?

Cross-over mass for early types

Lilly/Tasca

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” galaxiesBalogh et al. 2004

The colour-magnitude diagram

- Do AGNs really live in quenched/ing galaxies?

Nandra et al. 2006

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)

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)?

Recent Formation of S0sDennis Just (award-winning poster!) see also Wilman

Strong differential growth of S0s between field and cluster is clear evidence for importance of environmental processes

Hot gasDisk gas

Halo gas

V=500 km/s T=107 K (Mcl=1014 Msun) Md=6*1010Msun,vc=220 km/s,B/D=0.2

(DM halo + bulge + disk stars/gas + halo gas+SF)

Removal of gas in cluster environs (Bekki)

• More efficient stripping in clusters (Fstrip depends on Mcl, V, T etc).• Typically 70% of gas can be removed from galaxy halos.

• 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 [OII]

H + H

E+A

R (Mpc)

Moran et al (2007)

In Situ Evoln - I: Radial Trends in Cluster E/S0s

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

Moran et al Ap J 641, L97 (2006)

ESp

In Situ Evoln - II: Passive Spirals In Situ Evoln - II: Passive Spirals

Measuring the Quenching Timescale

~100Myr

~1Gyr

NUV-r

Dn4000

Passive spirals less concentrated in MS0451 as expected for starvation

Abundances timescales sufficient for production of local S0s

Passive Spirals: Cl 0024 vs. MS 0451Passive Spirals: Cl 0024 vs. MS 0451

銀河の色は中間的な環境で急激に変化する

hig

h

med

low

（

赤い銀河の割合

）

high ～ cluster core

med ～ group / filament

low ～ field

Sharp colour transition in groups/outskirts

RXJ1716 cluster (z=0.81)

Koyama, TK, et al. (2008)

Spatial Distribution of the 15μm sources

Koyama, TK, et al. (2008)

A void of 15um sources at the center!

○single /△ blended 15μm sources

X-ray (Chandra) map(Jeltema et al.)

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

Geach et al (2008)

12 cluster LIRGS in Cl0024 S24 < 0.6mJy

Diffuse Starlight in Virgo (Mihos et al)

6dF survey K<12.75 10,000g (Colless)

Maybe environmental trends have been erased by z=0?

Treu et al Ap J 622, L5 (2005) v Dokkum & vd Marel (2007)

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%)

clusters field

SDSS

log

Marginal Environmental Dependence of FP Marginal Environmental Dependence of FP

Radial Dependence of FP in One System

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)

Coma

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!]

Dichotomy in Local Early-Types

Martin Bureau

We Know the Growth Rate in Red Galaxies

• 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

Bundy et al (2006)

Downsizing: Red Growth

Mass

Increasing abundance butstrongly mass-dependent

Morphological spheroidals have a similar formation pattern. (Bundy et al. 2005)

Bundy et al. 2006

Mass Dependent Pair Fraction

Background field

correction

Redshift pair

correction.

Log M* ~ 11.3

Log M* ~ 10.3

Lin et al. Lin et al. 20082008DEEP2DEEP2

Bundy et al 2009

Volumetric Merger RateLog Merger Rate Density, Gyr-1 Mpc-3

Log M*

Too few mergers

to explain growth of early typesAND to

drive AGN activity!Bundy et al (2008)

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..)

The End of Downsizing?

(Smith et al 07, Allanson et al 09)

Hudson/Smith

Biases inherent in luminosity-selected samples?

1.5 < z < 1.75 1.75<z<2.251.25 < z < 1.5

1.0 < z < 1.250.75 < z < 1.00.25 < z < 0.75

(u-b

) rest

MK

Evolution in colour bimodality to KAB=23

Cirasuolo et al. (2009)Cirasuolo et al. (2009)c.f Kodama et al (2008)

Clustering evolution with redshift and luminosityClustering evolution with redshift and luminosity((passivepassive vs vs starformingstarforming))

Hartley et al. (in prep)

Almaini/Hartley

Some good things about Some good things about semi-analytic modelssemi-analytic models

Current models Current models seem to do seem to do reasonably well …. reasonably well …. (I’m sure someone will contradict (I’m sure someone will contradict me!)me!)

Present-day Present-day luminosity functionsluminosity functions

The transition massThe transition mass Galaxy down-sizingGalaxy down-sizing

The models achieve The models achieve this by suppressing this by suppressing cooling in high mass cooling in high mass haloeshaloes

See also Croton et al., De Lucia et al.; Kitzbichler et al., Somerville et al 2008

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!

We Spanned the Full Range of Environment!

Kuala Lumpur

log = 3.0

(excluding motorcycles!)

Kuala Selangor

log = 0.0

(discounting fireflies)

..and we had a great party!

Many thanks to..

Meghan, Frazer, Mike Merrifield, Duncan, Taddy, Jiasheng…and others!

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.

Halo Merger Rates from Millennium

Bundy et al. Ap J 665, L5 (2007)

Growth rate of halos seen in MS also fails to match production rate of halos hosting new spheroidals in GOODS