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Galaxy Groups

Galaxy Groups. Michael Balogh University of Durham. Galaxy Groups. z=0: Richard Bower, Vince Eke (Durham) Warrick Couch, Ian Lewis and the 2dF team Bob Nichol, Chris Miller (CMU) z=0.5: Dave Wilman, Richard Bower (Durham)

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Galaxy Groups

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  1. Galaxy Groups Michael Balogh University of Durham

  2. Galaxy Groups z=0: Richard Bower, Vince Eke (Durham) Warrick Couch, Ian Lewis and the 2dF team Bob Nichol, Chris Miller (CMU) z=0.5: Dave Wilman, Richard Bower (Durham) John Mulchaey, Gus Oemler (Carnegie) Ray Carlberg (Toronto) z=1: Fumiaki Nakata, Mark Sullivan, Dave Gilbank, Ian Smail, Richard Bower (Durham) Taddy Kodama, Ichi Tanaka (Tokyo)

  3. Number evolution of Groups Groups Clusters

  4. Z=0 : The 2dFGRS and SDSS

  5. Combined volume-limited sample from both surveys. Final catalogue of ~15000 galaxies Mr<-20.6, 0.05<z<0.1 Group catalogues from V. Eke (2dFgrs) and C. Miller (SDSS Early data release) Measure star formation rates from Ha emission Z=0 : The SDSS and 2dFGRS

  6. Group Finder 2dFgrs Based on a friends-of- friends algorithm (Eke et al., in prep) Effective at finding small groups with s«500 km/s SDSS Different algorithm, includes colour information (Miller et al. in prep). Effective at finding more massive groups

  7. Star formation in groups Preliminary results: Average Ha equivalent width within Rvir is lower than the global average, for s>200 km/s Mean SFR is suppressed in all bound galaxy associations at z=0 Field Balogh et al. in prep

  8. SFR-Density Relation in the 2dFGRS Lewis et al. (2002) identified a critical density of ~1 Mpc-2, where environmental effects become important This relation is independent of group velocity dispersion Field Lewis, Balogh et al. 2002 MNRAS 334, 673

  9. X-ray properties of 2dF groups • Mass-selected sample of 21 groups from 2dFgrs catalogue, s>500 km/s • XMM proposal to observe 9 of the lowest X-ray luminosity groups, for which good data does not already exist P. Mazzotta, PI

  10. Z=0.5 : The CNOC2 survey

  11. Groups at Z=0.5 • Based on the CNOC2 redshift survey. Group selection and inital look at properties described in Carlberg et al. (2001) • Durham involvement: follow-up observations with Magellan to gain higher completeness and depth • Also infrared data from WHT Wilman, Balogh, Bower Mulchaey, Oemler Carlberg

  12. CNOC2 groups at z~0.5 Velocity dispersions range from ~200 km/s to ~650 km/s Wilman et al. in prep

  13. CNOC2 groups at z~0.5 Preliminary result for 7 groups Within ~1 Mpc of group centre, galaxy SFR is low relative to surrounding field Compare with z=0 data to establish evolution of the “critial” density Mean EW [OII] (Å) 0 5 10 15 20 25 30 0 0.5 1.0 1.5 2.0 2.5 Distance from centre (Mpc) Wilman et al. in prep.

  14. Z > 1 : The Future

  15. Deep multicolour (VRi′z′JKs) images of Lynx and Q1335+28 (z=1.2). Proposals to observe high redshift radio galaxies and radio-loud quasars: known to reside in dense environments IRIS2 narrow band Ha and [OIII] at z=2.3 GMOS/FORS2 narrow band filter + grism Ha and [OII] spectroscopy at z=1.4, 1.47, 2.3 Groups at z > 1

  16. Lynx clusters: z=1.2 Subaru VRi’z’ INGRID JKs Identified 7 groups around the clusters from photometric redshifts. GMOS spectroscopy pending Y (arcmin) Nakata et al. (2002) X (arcmin)

  17. Groups around the Lynx clusters Group at z=1.27, ~3 Mpc from main cluster CMR is present, perhaps with more scatter and fewer bright galaxies GR3 CL1 CL2 Nakata et al. in prep

  18. Groups around the Lynx clusters M*clus ~ 20.13 M*group ~ 21.80 Nakata et al. in prep

  19. The goal… Steidel et al. 1999 What does the “Madau” plot look like for galaxy groups? This will distinguish evolution driven by large scale structure from evolution driven by local physics

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