Galaxy properties in different Galaxy properties in different environments: Observationsenvironments: Observations

Michael BaloghUniversity of Waterloo, Canada(Look for 3 new job postings on AAS soon)

Outline

• Morphology– Evolution of early and late types

• Colours• Star formation rates, HI• E+A galaxies

Galaxy morphology

E

ClustersF

ield

S0Spirals

Morphology-Density Relation

Dressler 1980Also: Oemler 1974; Melnick & Sargent 1977

Coma cluster • Morphological mix correlates best with local galaxy density

• Possibly additional effects in innermost regions (Whitmore et al. 1995; Dominguez et al. 2001)

Morphology-density: evolution

Dressler et al. 1997; Couch et al. 1994; 1998Fasano et al. 2000Wide field HST: Treu et al. 2003

Log surface density

Nu

mb

er

of

gala

xies

RedshiftN

S0/N

E

Low redshift

Z~0.5

• Ram pressure stripping of the disk could transform a spiral into a S0 (Gunn & Gott 1972; Solanes & Salvador-Solé 2001)

• Another possibility: gradual decline in SFR due to loss of gas halo (Larson, Tinsley & Caldwell 1980; Balogh et al. 2000)

• May lead to anemic or passive spiral galaxies (Shiyoa et al. 2002)

S to S0 transformation?Kenney et al. 2003Vollmer et al. 2004

Non-SF spiral galaxies from SDSS (Goto et al. 2003)First noted by Poggianti et al. (1999) in z~0.5 clusters

S to S0 transformation?• But bulges of S0 galaxies

larger than those of spirals (Dressler 1980; Christlein & Zabludoff 2004)

• Requires S0 formation preferentially from spirals with large bulges (Larson, Tinsley & Caldwell 1980) perhaps due to extended merger history in dense regions (Balogh et al. 2002)

Dressler 1980

Bulge size

1. S0 galaxies found far from the cluster core

– Galaxies well beyond Rvirial may have already been through cluster core (e.g. Balogh et al. 2000; Mamon et al. 2004; Gill et al. 2004)

2. Morphology-density relation holds equally well for irregular clusters, centrally-concentrated clusters, and groups

- but may be able to induce bursts strong enough to consume the gas (see Mayer et al. poster)

Gill et al. 2004

Groups (Postman & Geller 1984)

Local galaxy density (3d)

Sp

iral

fract

ion

Arguments against ram pressure stripping:

Galaxy colours• Easier to measure than morphology (lower quality data)• Easier to quantify• Can be directly related to stellar population models

Early type galaxies

Bower, Lucey & Ellis 1992

Tight colour-magnitude relation (Faber 1973; Visvanathan & Sandage 1977; Terlevich et al. 2001)

ES0

Kuntschner & Davies 1998 (also Poggianti et al. 2001)see also Bernardi et al. 2003 for results based on SDSS dataField early-types ~2-3 Gyr younger than clusters (Kuntschner et al. 2002)

Early-type galaxiesvan Dokkum & Franx 1996:M/L evolution consistent with high formation redshift

Zform= ∞

Zform=1

De Lucia et al. 2004Kodama et al. 2004(also Bell et al. 2003)

• Disappearance of faint red galaxies by z~1

Colour-magnitude relation

CMR for spiral galaxies also observed (e.g. Chester & Roberts 1964; Visvanathan 1981; Tully, Mould & Aaronson 1982)

SDSS allows full distribution to be quantified with high precision ( Baldry et al. 2003; Hogg et al. 2003;Blanton et al. 2003)

Sloan DSS data

Baldry et al. 2003(u-r)

Analysis of colours in SDSS data:

• 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

• Bimodality exists out to z~1 (Bell et al. 2004)

Bright

Faint

• Fraction of red galaxies depends strongly on density. This is the primary influence of environment on the colour distribution.

• Mean colours depend weakly on environment: transitions between two populations must be rapid (or rare at the present day)

Butcher-Oemler effect

• Concentrated clusters at high redshift have more blue galaxies than concentrated clusters at low redshift

Butcher & Oemler (1984)

Butcher-Oemler Effect

Andreon, Lobo & Iovino 2004

• Blue fraction depends strongly on luminosity and radius• Great care needs to be taken to evaluate blue fraction at same luminosity limit, and within same (appropriate) radius. • Increase in blue fraction is not just restricted to clusters (e.g. Lilly et al. 1996)

Margoniner et al. 2000

Margoniner et al. 2001

Redshift

Blu

e f

ract

ion

Radius (Mpc)

Blu

e f

ract

ion

Blu

e f

ract

ion

• Kodama & Bower (2000) model: clusters inhibit star formation, but recent infall maintains a high blue fraction at higher redshift.

Ellingson et al. (2001)

• Leads to steeper colour gradients in higher redshift clusters

Tully-Fisher relation at z~1

• Spiral galaxies at z~1 (both cluster and field) are brighter in B than at low redshift

• Z~1 cluster spirals brighter at fixed than field spirals (?)• See poster by Milvang-Jensen et al.

Milvang-Jensen et al. 2004

Star formation and gas

HI deficiency

Bravo-Alfaro et al. 2000

Davies & Lewis 1973

VLA imaging of Coma spirals

Mark I and II imaging of Virgo galaxies

18 nearby clusters: Solanes et al. 2001

Emission lines

Dressler, Thompson & Shectman 1985; Also Gisler 1978

• Cluster galaxies of given morphological type show less nebular emission than field galaxies

• suggests star formation is suppressed in cluster galaxies

Em

issi

on

lin

e f

ract

ion

Emission line fraction in SDSS and 2dFGRS (Balogh et al. 2004)

A901/902 supercluster (Gray et al. 2004) correlation with dark matter density

• Fraction of emission-line galaxies depends strongly on environment, on all scales

• Trend holds in groups, field, cluster outskirts (Lewis et al. 2002; Gomez et al. 2003)

• Fraction never reaches 100%, even at lowest densities

Star formation

Cluster infall regions

H distribution

Koopmann & Kenney 2004also: Vogt et al. 2004

• Cluster galaxies often show peculiar distribution of H emission: usually truncated, or globally suppressed

• In some cases, star formation is centrally enhanced (Moss & Whittle 1993; 2000)

Virgo spirals

H for Virgo galaxy

H for normal galaxy

Cluster galaxy evolution

Kodama et al. 2004

Couch et al. 2001Balogh et al. 2002Fujita et al. 2003

Tresse et al. 2002Complete H studies:Even at z=0.5, total SFR in clusters lower than in surrounding field

Field Field

z~0.3z~0.5

[OII] luminosity functions:Lotz et al. 2003Martin et al. 2000

SDSS/2dFGRS: Emission-line galaxies only: Ha distribution does not depend strongly on environment (Balogh et al. 2004)

Emission lines at z~0.5

Dressler et al. 1997 Balogh et al. 1998

Clusters

Field

2dF

Nakata et al., in prep

Postman, Lubin & Oke 2001van Dokkum et al. 2000

Fisher et al. 1998

Czoske et al. 2001

Cluster galaxy evolution

Cluster galaxy evolution

• Complete H based SFR estimates

• Evolution in total SFR per cluster not well constrained

• considerable scatter of unknown origin

• systematic uncertainties in mass estimates make scaling uncertain

Kodama et al. 2004

Finn et al. 2003Finn et al. 2003

Cluster galaxy evolution

• Complete H based SFR estimates

• Evolution in total SFR per cluster not well constrained

• considerable scatter of unknown origin

• systematic uncertainties in mass estimates make scaling uncertain

Kodama et al. 2004Finn et al. in prep

Finn et al. 2003

E+A galaxies

• Aka: k+a, a+k, PSG, PSB, HDS, e(a)…

Butcher-Oemler effect• Many of blue

galaxies turned out to have post-starburst spectra (Dressler & Gunn 1992; Couch & Sharples 1987)

• Also evidence for dust-obscured star formation from infrared (Fadda et al. 2000; Duc et al. 2002; Coia et al. 2004)

SDSS: Goto et al. (2003)

Couch & Sharples 1987Balogh et al. in prep.

SDSS E+A galaxies

Poggianti et al. 2004

• E+A galaxies in Coma may be correlated with X-ray emission• Strong luminosity evolution in E+A population (Tran et al. 2003)• Also found in the field (e.g.

Zabludoff et al. 1996; Balogh et al. 1999). But bright, field E+A galaxies locally may have different origin.

Balogh et al. in prep.

E+A

emission

UKIRT imaging

Consistent interpretation?

• Dense environments predominantly quench star formation, probably via a variety of mechanisms

• Butcher-Oemler effect:– Strength of trend in clusters still debatable– May arise from higher rate of infall of initially

bluer galaxies• Galaxy interactions and mergers:

– Build larger bulges in dense environments– Consume available gas in rapid starburst– Present in all environments, but more so at

higher densities– Establish red sequence in clusters at early

times

The future:

• Higher redshift clusters (e.g. RCS2, CFHTLS, HIROCS)

• HI and H distributions at higher redshift

• Galaxy groups, filaments etc. • Direct comparison with simulations.

Initial look shows current models get broad correlations correct, but details more difficult to understand

Time run out? References to your figure here

H distribution• H distribution shows a

bimodality: mean/median of whole distribution can be misleading

Balogh et al. 2004

Infared luminosity functions

• Balogh et al. (2001) evidence that MF does not vary strongly with environment.

• Also De Propris et al. (1998): find Coma LF consistent with the field