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Galaxy properties in different environments: Observations

Galaxy properties in different environments: Observations. Michael Balogh. University 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.

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Galaxy properties in different environments: Observations

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  1. Galaxy properties in different environments: Observations Michael Balogh University of Waterloo, Canada (Look for 3 new job postings on AAS soon)

  2. Outline • Morphology • Evolution of early and late types • Colours • Star formation rates, HI • E+A galaxies

  3. Galaxy morphology

  4. Morphology-Density Relation • Morphological mix correlates best with local galaxy density • Possibly additional effects in innermost regions (Whitmore et al. 1995; Dominguez et al. 2001) Coma cluster E S0 Clusters Spirals Field Dressler 1980 Also: Oemler 1974; Melnick & Sargent 1977

  5. Morphology-density: evolution Low redshift NS0/NE Number of galaxies Z~0.5 Redshift Dressler et al. 1997; Couch et al. 1994; 1998 Fasano et al. 2000 Wide field HST: Treu et al. 2003 Log surface density

  6. S to S0 transformation? Kenney et al. 2003 Vollmer et al. 2004 • 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) Non-SF spiral galaxies from SDSS (Goto et al. 2003) First noted by Poggianti et al. (1999) in z~0.5 clusters

  7. 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) Bulge size Dressler 1980

  8. Arguments against ram pressure stripping: 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) Spiral fraction Local galaxy density (3d)

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

  10. Early type galaxies Tight colour-magnitude relation (Faber 1973; Visvanathan & Sandage 1977; Terlevich et al. 2001) E S0 Bower, Lucey & Ellis 1992 Kuntschner & Davies 1998 (also Poggianti et al. 2001) see also Bernardi et al. 2003 for results based on SDSS data Field early-types ~2-3 Gyr younger than clusters (Kuntschner et al. 2002)

  11. Early-type galaxies van Dokkum & Franx 1996: M/L evolution consistent with high formation redshift Zform= ∞ Zform=1 • Disappearance of faint red galaxies by z~1 Kodama et al. 2004 (also Bell et al. 2003) De Lucia et al. 2004

  12. 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

  13. 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 (u-r) Baldry et al. 2003

  14. 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)

  15. Butcher-Oemler effect • Concentrated clusters at high redshift have more blue galaxies than concentrated clusters at low redshift Butcher & Oemler (1984)

  16. Butcher-Oemler Effect Margoniner et al. 2000 • 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) Andreon, Lobo & Iovino 2004 Blue fraction Radius (Mpc) Blue fraction Blue fraction Margoniner et al. 2001 Redshift

  17. Kodama & Bower (2000) model: clusters inhibit star formation, but recent infall maintains a high blue fraction at higher redshift. • Leads to steeper colour gradients in higher redshift clusters Ellingson et al. (2001)

  18. Tully-Fisher relation at z~1 Milvang-Jensen et al. 2004 • Spiral galaxies at z~1 (both cluster and field) are brighter in B than at low redshift • Z~1 cluster spirals brighter at fixed s than field spirals (?) • See poster by Milvang-Jensen et al.

  19. Star formation and gas

  20. HI deficiency Mark I and II imaging of Virgo galaxies Davies & Lewis 1973 VLA imaging of Coma spirals Bravo-Alfaro et al. 2000 18 nearby clusters: Solanes et al. 2001

  21. Emission lines • Cluster galaxies of given morphological type show less nebular emission than field galaxies • suggests star formation is suppressed in cluster galaxies Emission line fraction Dressler, Thompson & Shectman 1985; Also Gisler 1978

  22. Star formation • 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 Cluster infall regions Emission line fraction in SDSS and 2dFGRS (Balogh et al. 2004) A901/902 supercluster (Gray et al. 2004) correlation with dark matter density

  23. Ha distribution Virgo spirals • Cluster galaxies often show peculiar distribution of Ha emission: usually truncated, or globally suppressed • In some cases, star formation is centrally enhanced (Moss & Whittle 1993; 2000) Ha for Virgo galaxy Ha for normal galaxy Koopmann & Kenney 2004 also: Vogt et al. 2004

  24. Cluster galaxy evolution z~0.3 Kodama et al. 2004 z~0.5 Field Field Complete Ha studies: Even at z=0.5, total SFR in clusters lower than in surrounding field Tresse et al. 2002 Couch et al. 2001 Balogh et al. 2002 Fujita et al. 2003 SDSS/2dFGRS: Emission-line galaxies only: Ha distribution does not depend strongly on environment (Balogh et al. 2004) [OII] luminosity functions: Lotz et al. 2003 Martin et al. 2000

  25. Emission lines at z~0.5 Dressler et al. 1997 Balogh et al. 1998

  26. Nakata et al., in prep Field Postman, Lubin & Oke 2001 van Dokkum et al. 2000 2dF Fisher et al. 1998 Czoske et al. 2001 Clusters Cluster galaxy evolution

  27. Cluster galaxy evolution • Complete Ha 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 Finn et al. 2003 Finn et al. 2003 Kodama et al. 2004

  28. Cluster galaxy evolution • Complete Ha 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 Finn et al. 2003 Kodama et al. 2004 Finn et al. in prep

  29. E+A galaxies • Aka: k+a, a+k, PSG, PSB, HDS, e(a)…

  30. Butcher-Oemler effect SDSS: Goto et al. (2003) • 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 E+A galaxies Couch & Sharples 1987 Balogh et al. in prep.

  31. 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. UKIRT imaging emission Poggianti et al. 2004 E+A Balogh et al. in prep.

  32. 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

  33. The future: • Higher redshift clusters (e.g. RCS2, CFHTLS, HIROCS) • HI and Ha 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

  34. Time run out? References to your figure here

  35. Ha distribution • Ha distribution shows a bimodality: mean/median of whole distribution can be misleading Balogh et al. 2004

  36. 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

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