Galaxy Evolution: Internally or Externally Driven?

1. Galaxy Evolution: Internally or Externally Driven? Michael Balogh University of Durham

3. Why Does Star Formation Stop? 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)

4. Hierarchical Evolution? • Star formation history of Milky Way is approximately constant(e.g. Rocha-Pinto et al. 2000) • Seems very likely that clusters inhibit star formation (e.g. Balogh et al. 1998; 2002) • But clusters are very rare, so is this • sufficient?

5. Groups Poor Clusters Rich Clusters SFR vs. Environment 1. Externally Driven Evolution Star Formation Rate 0 Redshift

6. Groups Poor Clusters Rich Clusters SFR vs. Environment 2. Internally Driven Evolution Star Formation Rate 0 Redshift

7. 2dFGRS (Lewis et al. 2002, MNRAS in press) Ha in 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, in prep.) volume-limited sample of 8600 galaxies from the EDR, MR<-20.5 SFR-density relation independent of proximity to a cluster The Local Universe

8. SFR-Environment Relation in the 2dFGRS Field SFR-Radius Relation Field Field Lewis et al. 2002 MNRAS, in press

9. 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, in press

10. SFR-Environment relation in the SDSS Gomez et al. (2002, in prep) Field 75th percentile Star Formation Rate (Mo/yr) 75th percentile Median Field median Galaxy Surface Density (Mpc-2)

11. 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 AAT-WFI and Magellan LDSS-2 study of cluster wide fields (~10 Mpc) at z=0.45 Clusters and Groups at z=0.2-0.5

12. Star Formation in Low-Lx Clusters Balogh et al. 1997

13. CNOC2 Groups at z~0.45

14. [OII] [OII] CNOC2 Groups at z=0.45

15. [OII] [OII] CNOC2 Groups at z~0.45

16. CNOC2 Groups at z~0.45 CNOC2 groups from Carlberg et al. 2001 ApJ 552, 427 Balogh et al. 1997

17. CNOC2 Groups CNOC1 Field Low-Lx Clusters SDSSField 2dF Clusters CNOC1 Clusters Working toward the Answer! 10 Mean EW [OII] (Angstroms) 5 0.5 0 0.3 Redshift

18. 2dFGRS and SDSS: SFR-density relation shows critical density at 1 Mpc-2 SFR suppressed in all dense regions, in structures more massive than large groups Lack of strong evolution in clusters + abundance of structure above the critical threshold, suggests environmental processes are important to global evolution. Conclusions

19. Conclusions Good conference!