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)

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

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

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

CNOC2 Groups at 0.3≤z≤0.55: Based on CNOC2 redshift survey (Yee et al 2000): 4x10 4 galaxies with UBVRI photometry 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).

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]

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

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

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.

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

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

FORS2 mask

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

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

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

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

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.

Mass Functions as function of z and σ σ z

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

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

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

Group members OldWith FORS2 G G G2868 G G G391522

Baryonic Matter

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)

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)

Magellan Spectroscopy Extended spectroscopic sample to R C =22.0 Combined sample contains: – ≤ z ≤ 0.55 group members in 26 groups. – ≤ 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]