The evolution of star formation activity in galaxy groups

G Erfanianfar,P Popesso,F Ziparo,O Ilbert,R M Bielby,S Berta,M Mirkazemi,K Nandra,A Cimatti,A Biviano,F E Bauer ,Jeffrey A Newman ,B Altiéri ,A Finoguenov,H Aussel,D Lutz,Michael L Balogh ,D Fadda,John S Mulchaey ,Michael C Cooper ,R Nordon,D Elbaz,A Poglitsch,Niel Brandt ,Masayuki Tanaka ,Stijn Wuyts ,F Pozzi,David J Wilman ,N Cappelluti,E Le Floc’h ,M Salvato,B Magnelli,Mark Dickinson

doi:10.1093/mnras/stu1883

Abstract

We study the evolution of the total star formation (SF) activity, total stellar mass and halo occupation distribution in massive halos by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of SFR for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from SED fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high redshift groups (0.5<z<1.1) is higher with respect to the low redshift (0.15<z<0.5) sample at any mass by 0.8+/-0.12 dex. A milder difference (0.35+/-0.1 dex) is observed between the low redshift bin and the groups at z~0. We show that the level of SF activity is declining more rapidly in the more massive halos than in the more common lower mass halos. We do not observe any evolution in the halo occupation distribution and total stellar mass- halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass halos, consistently with a "halo downsizing" scenario.

Highlights

One of the most fundamental correlations between the properties of galaxies in the local Universe is the so-called morphology-density relation (Dressler 1980; Davis & Geller 1976)
We study the evolution of the total star formation (SF) activity, total stellar mass and halo occupation distribution in massive halos by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, Chandra Deep Field North (CDFN), Cosmic Evolution Survey (COSMOS), All-wavelength Extended Groth strip International Survey (AEGIS))
Since LX and σv are the only independent measurments and they exhibit a relation with a tight scatter (Figure 1), we discuss in particular only the ΣSFR−M200 relation to relate the evolution of the star formation activity of the group population to the total DM halo mass

Summary

Introduction

One of the most fundamental correlations between the properties of galaxies in the local Universe is the so-called morphology-density relation (Dressler 1980; Davis & Geller 1976). Galaxy groups have at any epoch a volume density orders of magnitude higher than those of massive clusters, which represents the rare and extreme specimen at the high mass end of the dark halo mass function (Jenkins et al 2001). This is confirmed by the observational evidence that groups are the most common environment of galaxies in the present day universe, containing 50%-70% of the galaxy population (Geller & Huchra 1983; Eke et al 2005). This naturally implies that processes taking place in the group environment can have a significant impact on the evolution of the galaxy population as a whole

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Conclusion