Galaxy Evolution in Groups and Clusters Michael Balogh Department of Physics and Astronomy University of Waterloo

Outline 1.Established correlations at z=0. Correlations and insight from the SDSS What do we mean by environment? What are the important tracers of galaxy population? 2.Evolution Importance and predictions 3.Direct evidence for transforming galaxies Where are the smoking guns? 4.Our surveys: CLUE, GEEC and ROLES Targeting the low-mass galaxies 5.Outstanding questions

The SFR sequence McGee et al. (2010) Population of star-forming and passively-evolving galaxies are generally well-separated SFR and proportion of passive galaxies depend strongly on stellar mass.

Separation of mass and environment Baldry et al. (2006) Passive fraction depends on both stellar mass and environment By comparing with galaxies at the lowest density, it is possible to determine what fraction of galaxies, at a given mass, must have been “quenched” by processes related to environment alone (Peng et al. 2010)

Environmental “quenching” Peng et al. (2011) Remarkably, this quenching fraction is nearly independent of stellar mass It affects only satellite galaxies, and depends only on local overdensity There is no clear interpretation of this “quenching efficiency” though.

Halo mass dependence Kimm et al. (2009) Fraction of passive galaxies is larger for satellite galaxies in massive haloes Is there a weak dependence on halo mass? Peng et al. (2011)

Halo mass dependence Balogh & McGee (2009) Clusters are homogeneous, with little measurable scatter between them.

Evolution Evolution in the quenched fraction is sensitive to the timescale of transformation McGee et al. (2009) Increasing Redshift Quenching efficiency Increasing Timescale Infall rate is strongly redshift dependent Short timescales lead to little evolution while, with long timescales, environmental effects should disappear by z>1.5. In all cases, dependence on halo mass is weak.

Evolution - zCOSMOS Quenching efficiency appears roughly constant with epoch, though this is not tightly constrained Measurement in a wide bin Worth revisiting older studies of massive clusters in this context? Peng et al. (2010)

Transforming Galaxies Results here are considerably more controversial and in apparent conflict. – Some studies find colour or SFR distribution of SF-galaxies shows little or no dependence on environment. Balogh et al. (2004); McGee et al. (2010); Greene et al. (in prep) McGee et al. (2010)

Results here are considerably more controversial and in apparent conflict. – Others claim to detect a population of low-SFR, intermediate colour galaxies in groups or clusters. Wolf et al. (2009); Vulcani et al. (2010); Balogh et al. (2010); Lu et al. (2011) Vulcani et al. (2010) Transforming Galaxies

Results here are considerably more controversial and in apparent conflict. – Still others claim an increase in SFR for at least some SF-galaxies in dense environments. e.g. Elbaz et al. (2007); Li et al. (2010) Li et al. (2010) Transforming Galaxies

Results here are considerably more controversial and in apparent conflict. – Some studies find colour or SFR distribution of SF-galaxies shows little or no dependence on environment. Balogh et al. (2004); McGee et al. (2010); Greene et al. (in prep) – Others claim to detect a population of low-SFR, intermediate colour galaxies in groups or clusters. Wolf et al. (2009); Vulcani et al. (2009); Balogh et al. (2010); Lu et al. (2011) – Still others claim an increase in SFR for at least some SF-galaxies in dense environments. e.g. Elbaz et al. (2007); Li et al. (2010) Post-starburst galaxies can be fairly easily identified spectroscopically, but have to take care to control for stellar mass, and have a fair low- density comparison sample. Of course there are clear examples of ram pressure stripping in some Virgo spiral galaxies. Transforming Galaxies

New data: CLUE The CFHTLS Ultraviolet Extension, using GALEX NUV imaging Part of Ting Lu’s thesis, based on ~100 massive clusters at z<0.3 – Deep, wide photometry allows us to probe low-mass galaxies, far from cluster cores faint end of red-sequence LF has increased dramatically over the past 2.5 Gyr – see also Rudnick et al. (2010), Bolzonella et al. (2010), Bell et al. (2004) Lu et al. (2009)

Dense environments in CLUE Lu et al. (submitted) Only ~10-20% of blue galaxies in dense environments show SFR>0.7 Msun/year, compared with % in the field.

GEEC: Group Environment Evolution Collaboration Redshift:z<0.10.3<z<0.60.8<z<1 Number: > Selection: Redshift (SDSS) Redshift (CNOC2)X-ray (COSMOS) GEEC Follow-up: Magellan, HST, Spitzer, GALEX, Chandra, XMM Gemini (GMOS) Study evolution in a well-defined sample of groups, with high spectroscopic completeness With enough members in individual systems, look for trends and sources of scatter.

Z=0.4 SED-fitting (including GALEX UV) to get SFR and Stellar mass McGee et al. (2010)

Passive fraction Evolution in both field and groups. They appear to be much closer together by z=0.5. (See also zCOSMOS: Bolzonella et al. 2010) McGee et al. (2010)

Evolution in quenching efficiency But quenching efficiency is remarkably constant with mass and redshift This implies short transformation timescales, <2 Gyr or so

Z=0.9 We can recover a mass-limited sample from the R-selected data, an order of magnitude deeper than (e.g.) zCOSMOS. Balogh et al. (in prep) 16 Groups with X-ray detection selected from zCOSMOS at 0.8<z<1 Nod-and-shuffle, 2hour Gemini exposures allow us to go quite deep

Z=0.9 groups Balogh et al. (in prep) Preliminary results suggests these groups look very similar to z=0! – Implies an even higher quenching rate at z=0.9, which is hard to understand One possibility is that these groups sample denser (or at least different) environments from the groups at lower z. X-ray selection?

ROLES Deep, highly complete [OII] emission line survey to measure SFR in the lowest-mass galaxies possible, using LDSS3 on Magellan – See Gilbank et al. (2010) for the original z~1 survey details Targets CDFS and FIRES fields. At 0.7<z<0.8 both of these fields contain significant large scale structure. Greene et al. (in prep) At 0.7<z<0.8 we see no environmental dependence on sSFR for SF galaxies, at any masses At z=1, sSFR appears to be higher in dense environments (Li et al. 2010).

Outstanding questions 1.What is the relevant timescale of any transformation?

 >0 ? sSFR Weinmann et al. (2009) Quenched fraction is definitely not 100% in groups at z=0. Either transformation must not be instantaneous, or must not affect all galaxies equally. It is difficult to get models to match both this fraction, and the observed distribution of sSFR.

Outstanding questions 1.What is the relevant timescale of any transformation? 2.What is the primary environment variable that drives the correlations? Satellite vs central distinction, only? Halo mass? Local density? Large scale structure?

Outstanding questions 1.What is the relevant timescale of any transformation? 2.What is the primary environment variable that drives the correlations? 3.Is stellar mass the right “independent” quantity? Velocity dispersion (Smith et al. 2009) Surface mass density (Kauffmann et al. 2003)

Outstanding questions 1.What is the relevant timescale of any transformation? 2.What is the primary environment variable that drives the correlations? 3.Is stellar mass the right “independent” quantity? 4.Theory: What is the orbital dependence of stripping/strangulation processes? What happens in low mass haloes, M= , where galaxies first become satellites Do cosmological simulations capture the right physics? e.g. Cen et al. (2011) AMR simulations show a lot of blue, low SFR, satellite galaxies in clusters, with short but nonzero transformation timescales

Conclusions Environmental effects are rather subtle – Essential to consider mass-SFR plane, rather than colour-magnitude – Some care should be taken to ensure we are using consistent measures when comparing surveys. Be clear about how stellar mass and SFR are computed! Environmental effects should be most prominent for: a)low-mass galaxies: Not because they are more effectively quenched, but because more of them are more star-forming to begin with. b)Higher-redshift systems: where infall rates are higher, and systems are more gas-rich Will likely be hard to find direct evidence for the driving physics observationally, until we can see the gas – Rely on simulations and models to find plausible explanations – Require a careful treatment of observational selection (e.g. contamination)

Satellites in cosmological simulations Cen et al. (2011) Recent simulations seem to show a lot of blue, low SFR, satellite galaxies in clusters, with short but nonzero transformation timescales

Help: higher infall rates at z=0.9 From GEEC: Colour distribution of z=0.9 groups is heavily skewed to the red. Can be matched by a distribution in , with  ~1-2 Gyr. Balogh et al. (2010) Mok et al. (in prep)