Galaxy Ecology The role of galaxy environment in determining the star formation history of the universe Michael Balogh ICC, University of Durham Plus: Richard Bower, Ian Smail, Simon Morris, Vince Eke (Durham) Ian Lewis and the 2df team Bob Nichol, Percy Gomez, Chris Miller, Tomo Goto (CMU) Ann Zabludoff (Arizona) John Mulchaey, Gus Oemler (Carnegie) Ray Carlberg (Toronto) Warrick Couch (UNSW) Galaxy Ecology The role of galaxy environment in determining the star formation history of the universe Michael Balogh ICC, University of Durham Motivation: cosmological context of observations Clusters at intermediate redshift The local universe: 2dF galaxy redshift survey, and Sloan digital sky survey Low mass clusters and groups at intermediate redshift Why Does Star Formation Stop? Steidel et al. 1999 SFR ~ (1+z)1.7 (Wilson, Cowie et al. 2002) A) Internal? i.e. gas consumption and “normal” aging B) External? Hierarchical build-up of structure inhibits star formation A Press-Schechter plot showing the growth of the mass structure of the universe LCDM cosmology Growth of structure still rapid But how should curves be normalised? Groups Clusters Renormalised relative to 1011 Msol Galaxy clusters: the end of star formation? 30 AC114 (z=0.31) (Couch et al. 2001) 200 Butcher-Oemler effect? 100 Does star formation take place in clusters at z>0 ? DRA 0 -100 -200 -300 -200 -100 0 100 200 Abell 2390 (z~0.23) 3.6 arcmin R image from CNOC survey (Yee et al. 1996) Ha in Abell 2390 Balogh & Morris 2000 3.6 arcmin Nod & Shuffle: LDSS++ (AAT) band-limiting filter + microslit = ~800 galaxies per 7’ field Ha in Rich Clusters at z~0.3 LDSS++ with nod and shuffle sky subtraction, on AAT (Field) Couch et al. 2001 ApJ 549, 820 Balogh et al. 2002 MNRAS, 335, 110 Fine for clusters – but what about groups? Groups Clusters Mechanisms Ram-pressure stripping – Needs dense ICM and high velocities - clusters Collisions / harassment – Groups are preferred place! "Strangulation" – Removal of the gas halo – Similar to ram-pressure stripping but much easier! Ram pressure - simulations from Quilis et al. 2000 Gunn & Gott, 1972 Examples of galaxy collisions in the real universe and in a simulation (Moore et al 1995) Strangulation ? Use numerical model of infall to estimate timescale for disruption of SFR Radial gradients in CNOC clusters suggest t ~2 Gyr (Balogh, Navarro & Morris 2000) Strangulation - removal of the gas halo Could occur in groups First suggested by Larson, Tinsley & Caldwell, 1984 Where do environmental effects become important? The Local Universe 2dFGRS (Lewis et al. 2002, MNRAS 334, 673) – Ha in 11000 galaxies within 20 Mpc of 17 clusters, down to MB=-19 – SFR-density, SFR-radius relations in clusters with s>400 km/s SDSS (Gomez et al. 2002, ApJ in press) – volume-limited sample of 8600 galaxies from the EDR, MR<-20.5 – SFR-density relation independent of proximity to a cluster Galaxy Transformation in the 2DF survey Data for 17 Abell-like clusters A1620 Covers velocity dispersions 500 km/s - 1100 km/s Rvir Region out to > 20 Rvir extracted from the survey Major advantages: ● Star formation rate measured from Ha ● Complete redshift information - no need to subtract background! ● Compare with surrounding field directly 1 degree (data extracted over ~7 deg field) SFR-Environment Relation in the 2dFGRS Field SFR-Radius Relation Field Field Lewis et al. 2002 MNRAS 334, 673 SFR-Environment Relation in the 2dFGRS Field SFR-Density Relation Field Field Lewis et al. 2002 MNRAS 334, 673 SFR-Environment Relation in the 2dFGRS Field SFR-Density Relation c.f. Morphology-Density Relation R>2 Rvirial Field Field Lewis et al. 2002 MNRAS 334, 673 SFR-Environment relation in the SDSS Star Formation Rate (Mo/yr) Gomez et al. (2002) Field 75th percentile 75th percentile Median Field median Galaxy Surface Density (Mpc-2) What You Must Remember! Galaxy Transformation does not occur in clusters! => ram-pressure stripping not important It occurs in groups ... these might then end up in clusters. Groups at z=0.2-0.5 Low-Lx Clusters at z=0.25 – Factor ~10 less massive than CNOC clusters – HST imaging, extensive ground-based spectroscopy CNOC2 groups at z=0.45 – Spectroscopy with LDSS-2 on Magellan 6.5-m – Goal is complete group membership to M*+1 Low Lx Clusters at z~0.25 Cl0841 Cl0849 Cl1701 Cl1702 z=0.24 z=0.23 z=0.24 z=0.22 s=390 s=750 s=590 s=370 Cl0818 Cl0819 Cl1309 Cl1444 z=0.27 z=0.23 z=0.29 z=0.29 s=630 s=340 s=640 s=500 Lx ~ 1043 - 1044 ergs/s, ~ 10 X less massive than CNOC Morphologies in Low-Lx Clusters at z~0.25 Bulge/Total Fractions from GIM2D (Simard et al. 2002) Disks B/T<0.4 Intermediate Bulges B/T>0.6 Balogh et al. 2002, ApJ 566, 123 Low-Lx Disk Fractions (from Medium Deep Survey) High-Lx Clusters from the lensing sample of Smith et al. 2001 Balogh et al. 2002, ApJ 566, 123 Morphology-density relation at z~0.25 Balogh et al. 2002 ApJ 566, 123 Bulge Creation or Disk Destruction? Balogh et al. 2002, ApJ 566, 123 Disk Luminosity Functions (at fixed density) Bulge Creation or Disk Destruction? Balogh et al. 2002, ApJ 566, 123 Bulge Luminosity Functions (at fixed density) Star Formation in Low-Lx Clusters Spectroscopy for 172 cluster members Mr< -19 (h=1) Balogh et al. 1997 SFR from [OII] emission line Balogh et al. (2002) MNRAS, in press astro-ph/0207360 Disks Without Star Formation Cl 1309 id=83 [OII] z=0.2934 B/T = 0.39 Wo (OII)=-2.64.0 3” HST Image Wo (Hd)=3.8 2.1 Disks Without Star Formation [OII] Cl 1444 id=78 z=0.2899 B/T = 0.42 Wo (OII)=3.5 2.7 3” HST Image Wo (Hd)=4.9 1.3 Disks Without Star Formation Cl 0818 id=58 [OII] z=0.2667 B/T = 0.19 Wo (OII)=-9.6 7.8 Wo (Ha)=22.1 11.6 3” HST Image Wo (Hd)=2.0 3.6 Ha Disks Without Star Formation Cl 0841 id=20 [OII] z=0.2372 B/T = 0.42 Wo (OII)=-0.2 1.2 3” HST Image Wo (Ha)=-1.4 0.6 Wo (Hd)=0.0 0.6 Ha Low-Lx Clusters: Summary Bulge formation may be more efficient in more massive clusters but star formation in disks is suppressed in all clusters The CNOC2 groups project The CNOC2 redshift survey was aimed at measuring correlation strengths and star formation rates in the z=0.5 universe. Group selection and inital look at properties described in Carlberg et al 2001 Durham involvement: follow-up observations with Magellan to gain higher completeness confirming complete samples of group members using LDSS-2. Overall aim of comparing star formation rates in groups at z=0.5 and locally (Mulchaey & Zabludoff etc, 2dfgrs coming soon!) Bower, Mulchaey, Oemler, Carlberg et al - in prep. CNOC2 Groups at z~0.45 Deep spectroscopy with LDSS-2 Infrared (Ks) images from INGRID on Magellan 1 Combined with CNOC2 multicolour photometry and spectroscopy, we can determine group structure, dynamics, stellar mass, and star formation history. LDSS2 on Magellan [OII] [OII] CNOC2 Groups at z~0.45 Preliminary results based on only 12 Balogh et al. 1997 CNOC2 groups Have observed >30 groups to date Putting it all together… Wilson et al. 2002 20 Mean EW [OII] (Angstroms) ? 15 CNOC2 Groups ? CNOC1 Field 10 SDSS Field Low-Lx Clusters 5 Clusters CNOC1 Clusters SDSS 0 0.3 0.5 1.0 Redshift Local Groups in the 2dFGRS Based on friends-of-friends catalogue (V. Eke) Mean SFR appears to be suppressed in all galaxy associations at z=0! So where is star formation going on?? The Environmental-Madau plot Wilson et al. 2002 20 Mean EW [OII] (Angstroms) ? 15 CNOC2 Groups ? CNOC1 Field 10 SDSS Field Low-Lx Clusters 2dF Clusters 5 ? CNOC1 Clusters 0 0.3 0.5 1.0 Redshift Summary 2dFGRS and SDSS: SFR-density relation shows critical density at 1 Mpc-2 SFR suppressed in all dense regions, in structures more massive than groups Lack of strong evolution in clusters + abundance of structure above the critical threshold suggests environmental processes are important to global evolution. BUT: Strong evolution in group SFRs?
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