1. Luminosity and Mass functions in spectroscopically-selected groups at z~0.5 George Hau, Durham University Dave Wilman (MPE) Mike Balogh (Waterloo) Richard Bower (Durham) John Mulchaey, Gus Oemler (Carnegie) Ray Carlberg (Toronto)

2. Plan of talk Motivation CNOC2 Groups at 0.3 < z < 0.55 survey Preliminary LFs for individual groups Mass function Summary

3. Motivation Kodama & Bower 2004: Little evolution in stellar mass of cluster galaxies since z~1 Decline of volume- averaged SFR by fact of ~5 from z~1-2 to present. Poorer environments such as groups must drive the evolution of field galaxy population since z~1. Little evolution in clusters since z~1 Kodama & Bower 2004

4. Motivation > 50% of present day galaxies in groups. Groups = typical environment of galaxies. Understanding "cosmic downsizing”: Active star formation shifts to lower and lower mass galaxies as the Universe evolves. But… Groups have low density contrast against background-- hard to build large samples (Eke review. See also works by Mulchaey, Zabludoff, Ponman etc) Compact Groups (eg. Hickson et al 1989) X-ray luminous (e.g. Mulchaey et al 2003) Radio selected (e.g. Allington-Smith et al 1993) Our approach: Select groups based on redshifts and positions

5. CNOC2 Groups at 0.3≤z≤0.55: Based on CNOC2 redshift survey (Yee et al 2000): 4x10 4 galaxies with UBVRI photometry + 6000 redshifts Groups detection by –Friends-of-friends algorithm –Spatial (1.5*r200) + velocity (3σ) trimming + iteration. 200 Groups 0.12 < z < 0.55 identified (Carlberg et al 2001).

6. Magellan followup spectroscopy (Wilman et al 2004) Extended spectroscopic sample to R C =22.0 Final sample contains (0.3 < z < 0.55): –282 members in 26 groups. –334 serendipitous field galaxies. Selection function is well understood and sample is representative. [OII] emission infers presence of star formation (EW≥5Ǻ). SED fitting -> rest-frame luminosities. Groups range in σ v from < 100 km/s to ~800 km/s (~poor cluster) [OII]

7. Wilman et al 2004 groups Wilman et al 2004 Galaxy properties and evolution in groups -- see Dave Wilman’s talk

8. Additional data GALEX UV imaging (current) –star formation NIR imaging: SOFI, Spitzer GTO Chandra observations scheduled

9. HST Morphologies Observations of 20 groups for 1 orbit each in F775W filter. Visual classification by Gus Oemler of all 0.3 ≤ z ≤ 0.55 galaxies in the 16 fields Classification possible to R~23.9, according to the MORPHS scheme. Preliminary results for 16 ACS fields. 158 classified group galaxies & 124 classified field galaxies.

10. New FORS2 spectroscopy: probing z~0.5 counterparts of local post-starburst population Kauffmann et al 2003 stellar age indicator for SDSS galaxies

11. New VLT FORS spectroscopy FORS2 Followup spectroscopy: Targeting faint galaxies down to R~23 to improve completeness & probe star forming population –June 2005: 3 nights, 6 groups -- preliminary results presented here –~240 new redshifts, >27 new group members –Sep 2005: 10.4 hrs, 4 groups. Data not reduced yet

12. FORS2 mask

13. Galaxy selection function Old LDSS2 data + new FORS2 data After correction Survey limit R Fraction of galaxies with z

14. Luminosity function of individual groups (preliminary) z=0.359 z=0.536z=0.471 z=0.361 z=0.510z=0.372 M*M* New data Old data

15. Morphological segregation Group 37 dec r’ 0 dv (km/s) RA

16. Morphological segregation Group 38 dec r’ 0 dv (km/s) RA

17. Mass function of CNOC2 groups (Balogh et al in prep) Spitzer GTO data in sub area of survey Chose groups with >60% IR spatial coverage Matched IR data (IRAC 3.6µm) to CNOC2 groups catalogue. Mass from stellar M/L ratios calculated using population synthesis models Total stellar mass M stellar for all gals within R200.

18. Mass Functions as function of z and σ σ z

19. Combined Mass Function Local MF, α=-0.6 Combined MF, z~0.3 More IR data will help--Valentine take note! :)

20. Summary New FORS2 spectroscopy down to R~23.2 Presented LF functions for 6 groups Presented mass functions using SPITZER imaging No evidence for trends in Mass Functions -- in concordance with idea that group stellar mass in place by z~1. (cf. Conselice’s talk) Future Plan: Combined LF & MS & comparison with local functions Investigation of SFH with [OII] Serendipitous groups & filaments. Improving mass function using SOFI data

21. See Dave Wilman’s talk Galaxy properties and evolution in groups

22. Group members OldWith FORS2 G241115 G251922 G2868 G371926 G381923 G391522

23. Baryonic Matter

24. CNOC2 Groups at 0.3≤z≤0.55: Based on CNOC2 redshift survey (Yee et al 2000): 4x10^4 galaxies with UBVRI photometry + ~6000 redshifts 200 Groups 0.12 < z < 0.55 identified (Carlberg et al 2001). Kinematically selected from the CNOC2 redshift survey. Group detection described in Carlberg et al. (2001)

25. Groups at z=0.4 Øfollow-up observations with Magellan to gain higher completeness and depth ØAim of comparing star formation rates in groups at z~0.4 and locally ØAlso infrared data from WHT; HST ACS imaging being analysed now. • “LDSS-2 Distant Group Survey”: Based on the CNOC2 redshift survey aimed at z~0.5. Group selection and inital look at properties described in Carlberg et al. (2001)

26. Magellan Spectroscopy Extended spectroscopic sample to R C =22.0 Combined sample contains: –282 0.3 ≤ z ≤ 0.55 group members in 26 groups. –334 0.3 ≤ z ≤ 0.55 serendipitous field galaxies. (= everything in FOV – targetted groups) Selection function is well understood and sample is representative. (see paper I !) [OII] emission infers presence of star formation (EW≥5Ǻ). SED fitting -> rest-frame luminosities. Groups range in σ v from <100km/s to ~800km/s (~poor cluster) [OII]