1. Galaxy Ecology The role of galaxy environment in determining the star formation history of the universe Michael Balogh ICC, University of Durham

2. 1.Motivation: cosmological context of observations 2. The local universe: 2dF and Sloan surveys 3. Low mass clusters and groups at intermediate redshift 4. Clusters and groups at z~1 and beyond Galaxy Ecology

3. 1. Motivation: cosmological context of observations 2. The local universe: 2dF and Sloan surveys Bob Nichol, Chris Miller, Percy Gomez (CMU), Ann Zabludoff (Arizona), Tomo Goto (CMU, Tokyo), Vince Eke, Richard Bower (Durham), Ian Lewis (Oxford) and many others… 3. Low mass clusters and groups at intermediate redshift 4. Clusters and groups at z~1 and beyond Galaxy Ecology

4. 1. Motivation: cosmological context of observations 2. The local universe: 2dF and Sloan surveys 3. Low mass clusters and groups at intermediate redshift Richard Bower, Roger Davies, Ian Smail, Simon Morris, Dave Wilman (Durham), John Mulchaey, Gus Oemler (Carnegie) 4. Clusters and groups at z~1 and beyond Galaxy Ecology

5. 1. Motivation: cosmological context of observations 2. The local universe: 2dF and Sloan surveys 3. Low mass clusters and groups at intermediate redshift 4. Clusters and groups at z~1 and beyond Fumiaki Nakata, Ian Smail, Richard Bower (Durham) Taddy Kodama, Ichi Tanaka, Toru Yamada (NAOJ) Galaxy Ecology

6. Motivation: Two questions: 1. Why does star formation decline? 2. What physical mechanisms operate in dense environments?

7. B) External? Hierarchical build-up of structure inhibits star formation A) Internal? i.e. gas consumption and “normal” aging Steidel et al. 1999 SFR ~ (1+z) 1.7 (Wilson, Cowie et al. 2002) Why Does Star Formation Stop?

8. Galaxy clusters: the end of star formation?

9. Abell 2390 (z~0.23) 3.6 arcmin R image from CNOC survey (Yee et al. 1996)

10. H  in Abell 2390 3.6 arcmin Balogh & Morris 2000

11. CNOC: Galaxy populations Balogh et al. 1997, ApJ 488, L75 Measurements of [OII] emission line for galaxies in 15 clusters and the surrounding field at z~0.3 [OII] closely related to star formation rate (SFR) Showed that average SFR within the virialised regions of clusters is much lower than in lower density regions

12. H  in Rich Clusters at z~0.3 Balogh et al. 2002 MNRAS, 335, 110 Couch et al. 2001 ApJ 549, 820 LDSS++ with nod and shuffle sky subtraction, on AAT Star formation rate is low in all clusters observed (Field)

13. CNOC: Galaxy populations Balogh et al. 1998, ApJ 504, L75 Showed presence of strong radial gradient in SFR. Always lower than the field Gradient much steeper than expected from morphology-density relation Observed relation Morph-density relation Field

14. Tying star formation to structure growth Groups Clusters Press-Schechter plot of dark matter mass evolution Normalised to 10 11 M o Clusters are negligible; but groups dominate and evolve strongly Thus, can environmental processes be responsible for SFR evolution?

15. Additional physics? 1.Ram-pressure stripping (Gunn & Gott 1972) 2.Collisions / harassment (Moore et al. 1995) 3.“Strangulation” (Larson et al. 1980; Balogh et al. 2000)

16. Additional physics? 1.Ram-pressure stripping (Gunn & Gott 1972) 2.Collisions / harassment (Moore et al. 1995) 3.“Strangulation” (Larson et al. 1980; Balogh et al. 2000) Quilis, Moore & Bower 2000 short timescale

17. Additional physics? 1.Ram-pressure stripping (Gunn & Gott 1972) 2.Collisions / harassment (Moore et al. 1995) 3.“Strangulation” (Larson et al. 1980; Balogh et al. 2000) important in groups?

18. Additional physics? 1.Ram-pressure stripping (Gunn & Gott 1972) 2.Collisions / harassment (Moore et al. 1995) 3.“Strangulation” (Larson et al. 1980; Balogh et al. 2000) long timescale

19. Timescales Numerical model of infall rate + assumed decay rate of star formation => radial gradient in SFR Radial gradients in CNOC clusters suggest  ~2 Gyr Suppressed star formation within several Mpc of cluster centre! What environment is responsible? Balogh, Navarro & Morris 2000 Diaferio et al. 2001

20. The local Universe: Going beyond cluster cores…

21. The 2dFGRS and SDSS 1.2dF Galaxy redshift survey: spectra and redshifts for 220 000 nearby galaxies only photographic plate photometry 2.Sloan digital sky survey: goal is spectra for 1 million galaxies, with digital photometry (ugriz) First data release contains 186 240 galaxies

22. 2dFGRS/SDSS Part I: 2dF clusters A1620 Rvir (data extracted over ~7 deg field) Data for 17 Abell-like clusters Covers velocity dispersions 500 km/s - 1100 km/s Region out to > 20 Rvir extracted from the survey  Star formation rate measured from H  1 degree Lewis, Balogh et al. 2002 MNRAS 334, 673

23. Lewis, Balogh et al. 2002 MNRAS 334, 673 Field Normalised star formation rate measured from H  in 17 nearby clusters Identified a critical density of ~1 Mpc -2, where environmental effects become important This corresponds to low density groups in the infall regions of clusters 2dFGRS/SDSS Part I: 2dF clusters Critical density: ~group scales

24. SFR-Density Relation Lewis et al. 2002 MNRAS 334, 673 Field 2dFGRS/SDSS Part I: 2dF clusters

25. Lewis et al. 2002 MNRAS 334, 673 R>2 R virial SFR-Density Relation c.f. Morphology-Density Relation Field 2dFGRS/SDSS Part I: 2dF clusters

26. 2dFGRS/SDSS Part II: SDSS Star Formation Rate (M o /yr) Galaxy Surface Density (Mpc -2 ) Median 75 th percentile Gomez et al. (2003) Field 75 th percentile Field median

27. 2dFGRS/SDSS Part III: Groups Compare groups with clusters and the field: does the large-scale environment play any role?

28. 2dFGRS/SDSS Part III: Groups 2dFgrs Based on a friends-of- friends algorithm (Eke et al., in prep) Effective at finding small groups with  « 500 km/s SDSS Different algorithm, includes colour information (Miller et al. in prep). Effective at finding more massive groups

29. SFR of galaxies as a function of group velocity dispersion ● 2dFGRS ● SDSS Mean SFR appears to be suppressed in all galaxy associations at z=0! There is a trend with group mass, but this is due to the different distributions of local densities… 2dFGRS/SDSS Part III: Groups Field Balogh et al., in prep

30. 2dFGRS/SDSS Part III: Groups Balogh et al., in prep Median 75 th %-tile Field Red hatched region: all galaxies (~30 000) White lines: groups with indicated 

31. Luminosity dependence Balogh et al., in prep

32. Does any environment enhance star formation?

33. Close pairs in the SDSS Balogh et al., in prep  v~100 km/s  r~50 kpc ds~(  v/250) 2 +(  r/100) 2

34. Close pairs in SDSS groups Balogh et al., in prep  v~100 km/s  r~50 kpc ds~(  v/250) 2 +(  r/100) 2

35. Groups at z~0.4

36. Outskirts of Clusters at z~0.4 Kodama et al. 2001 Subaru image Abell 851 at z=0.41 30 arcmin

37. Outskirts of Clusters at z~0.4 Kodama et al. 2001 Critical density where red sequence first appears.  crit ~4 Mpc -2 Corresponds to density of infalling groups, well outside of cluster

38. Star formation in groups at z=0.2-0.5 1.Low-Lx Clusters at z=0.25 Factor ~10 less massive than CNOC clusters HST imaging, extensive ground-based spectroscopy 2.CNOC2 groups at z=0.45 Spectroscopy with LDSS-2 on Magellan 6.5-m Goal is complete group membership to M*+1

39. Low L x Clusters at z~0.25 Cl0818 z=0.27  =630 Cl0819 z=0.23  =340 Cl0841 z=0.24  =390 Cl0849 z=0.23  =750 Cl1309 z=0.29  =640 Cl1444 z=0.29  =500 Cl1701 z=0.24  =590 Cl1702 z=0.22  =370 L x ~ 10 43 - 10 44 ergs/s, ~ 10 X less massive than CNOC

40. Morphology-density relation at z~0.25 Balogh et al. 2002 ApJ 566, 123 Some evidence that disk galaxies are more common in groups than clusters, for a given local density. The same is not true of star formation rates, however… Low L x (groups) High L x (clusters)

41. Star Formation in Low-Lx Clusters Balogh et al. 1997 Spectroscopy for 172 cluster members M r < -19 (h=1) SFR from [OII] emission line Distributions of massive and low-mass clusters are identical! Therefore, there must be a population of disk- dominated galaxies with low SFR… Balogh et al. (2002) MNRAS, 337, 256

42. [OII] 3” HST Image Disks Without Star Formation Cl 1309 id=83 z=0.2934 B/T = 0.39 W o (OII)=-2.6  4.0 W o (H  )=3.8  2.1

43. [OII] 3” HST Image Disks Without Star Formation Cl 1444 id=78 z=0.2899 B/T = 0.42 W o (OII)=3.5  2.7 W o (H  )=4.9  1.3

44. [OII] HH 3” HST Image Disks Without Star Formation Cl 0818 id=58 z=0.2667 B/T = 0.19 W o (OII)=-9.6  7.8 W o (H  )=22.1  11.6 W o (H  )=2.0  3.6

45. [OII] HH 3” HST Image Disks Without Star Formation Cl 0841 id=20 z=0.2372 B/T = 0.42 W o (OII)=-0.2  1.2 W o (H  )=-1.4  0.6 W o (H  )=0.0  0.6

46. CNOC2 Groups 1.Identified a sample of groups from original survey (Carlberg et al. 2001 ApJ 552, 427) 2.Properties of these groups can be directly compared with low redshift counterparts from 2dFgrs and SDSS 3.Durham involvement: follow-up observations with Magellan to gain higher completeness confirming complete samples of group members using LDSS-2

47. CNOC2 Groups at z~0.45 Deep spectroscopy with LDSS-2 on Magellan 1 (~30 groups) Infrared (Ks) images from INGRID Combined with CNOC2 multicolour photometry and spectroscopy, we can determine group structure, dynamics, stellar mass, and star formation history.

48. LDSS2 on Magellan [OII]

49. CNOC2 groups at z~0.45 Wilman et al. in prep. Distance from centre (Mpc) Mean EW [OII] (Å) 0 0.5 1.0 1.5 2.0 2.5 0 5 10 15 20 25 30 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

50. CNOC2 Groups at z~0.45 Preliminary results based on only 12 CNOC2 groups Have observed >30 groups to date Balogh et al. 1997 Preliminary results for 13 groups show excess star formation in groups, compared with rich clusters. But is this due to differences in density distributions? Wilman et al. in prep

51. Implications?

52. Implications: SFR Evolution  crit (z~0) ~ 1 Mpc -2 (Lewis et al. 2002)  crit (z~0.4) ~ 4 Mpc -2 (Kodama et al. 2001, corrected) Critical density 0.61.6-0.6

53. Implications: SFR Evolution Global SFR evolves as (1+z) 1.7 So increases by ~70% between z=0 and z=0.4 This is consistent with an unevolving SFR-density correlation if most of the mass in Universe at z~0.4 is below  crit However, nature of SF must be different at z~1

54. Implications: SFR Evolution Global SFR evolves as (1+z) 1.7 So increases by ~70% between z=0 and z=0.4 This is consistent with an unevolving SFR-density correlation if most of the mass in Universe at z~0.4 is below  crit However, nature of SF must be different at z~1 70% increase?

55. Implications: Physical mechanisms Ram-pressure stripping Strangulation Galaxy interactions

56. Implications: Physical mechanisms Ram-pressure stripping Strangulation Galaxy interactions not important in groups

57. Implications: Physical mechanisms Ram-pressure stripping Strangulation Galaxy interactions no dependence on 

58. Clusters and Groups at z~1

59. Groups at z > 1 1.Deep multicolour (VRi′z′JK s ) images of Lynx and Q1335+28 (z=1.2). 2.Proposals to observe high redshift radio galaxies and radio-loud quasars: known to reside in dense environments IRIS2 narrow band H  and [OIII] at z=2.3 GMOS/FORS2 narrow band filter + grism H  and [OII] spectroscopy at z=1.4, 1.47, 2.3

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

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

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

63. Overdensities around HizRG Best et al. 2003 z=1.59z=1.44

64. Conclusions 1. Clusters and groups have a large impact on galaxy star formation rates at the present day 2. Bright galaxies have little density dependence; trends driven by faintest galaxies 3.Observations just consistent with explanation of global SFR evolution to z~0.4 as due to growth of clustering 4.Most likely physical mechanism for transformation is galaxy-galaxy interactions.