The XXL Survey

V Guglielmo,C Adami,J Fritz,S Fotopoulou,M Pierre,B Vulcani,M Bolzonella,S Maurogordato,B M Poggianti

doi:10.1051/0004-6361/201834970

Abstract

Exploiting a sample of galaxies drawn from the XXL-North multiwavelength survey, we present an analysis of the stellar population properties of galaxies at 0.1 ≤ z ≤ 0.5, by studying galaxy fractions and the star formation rate (SFR)–stellar mass (M⋆) relation. Furthermore, we exploit and compare two parametrisations of environment. When adopting a definition of “global” environment, we consider separately cluster virial (r ≤ 1r200) and outer (1r200 < r ≤ 3r200) members and field galaxies. We also distinguish between galaxies that belong or do not belong to superclusters, but never find systematic differences between the two subgroups. When considering the “local” environment, we take into account the projected number density of galaxies in a fixed aperture of 1 Mpc in the sky. We find that regardless of the environmental definition adopted, the fraction of blue or star-forming galaxies is the highest in the field or least dense regions and the lowest in the virial regions of clusters or highest densities. Furthermore, the fraction of star-forming galaxies is higher than the fraction of blue galaxies, regardless of the environment. This result is particularly evident in the virial cluster regions, most likely reflecting the different star formation histories of galaxies in different environments. Also the overall SFR–M⋆ relation does not seem to depend on the parametrisation adopted. Nonetheless, the two definitions of environment lead to different results as far as the fraction of galaxies in transition between the star-forming main sequence and the quenched regime is concerned. In fact, using the local environment the fraction of galaxies below the main sequence is similar at low and high densities, whereas in clusters (and especially within the virial radii) a population with reduced SFR with respect to the field is observed. Our results show that the two parametrisations adopted to describe the environment have different physical meanings, i.e. are intrinsically related to different physical processes acting on galaxy populations and are able to probe different physical scales.

Highlights

Observational studies aiming at understanding the processes that affect galaxy properties and determining the evolution of galaxies have been focussing more and more on the role played by both the environment in which a galaxy was formed and that in which it is embedded for most of its lifetime (Oemler 1974; Dressler 1980; Balogh et al 2004a; Kauffmann et al 2004; Baldry et al 2006; Poggianti et al 2009)
Exploiting a sample of galaxies drawn from the XXL-North multiwavelength survey, we present an analysis of the stellar population properties of galaxies at 0.1 ≤ z ≤ 0.5, by studying galaxy fractions and the star formation rate (SFR)–stellar mass (M ) relation
Our results show that the two parametrisations adopted to describe the environment have different physical meanings, i.e. are intrinsically related to different physical processes acting on galaxy populations and are able to probe different physical scales

Summary

Introduction

Observational studies aiming at understanding the processes that affect galaxy properties and determining the evolution of galaxies have been focussing more and more on the role played by both the environment in which a galaxy was formed and that in which it is embedded for most of its lifetime (Oemler 1974; Dressler 1980; Balogh et al 2004a; Kauffmann et al 2004; Baldry et al 2006; Poggianti et al 2009). Galaxies that are gathered together and/or hosted in the potential well of dark matter haloes, together with those accreted from the cosmic web into bigger structures, undergo a variety of physical processes that may influence the timescale of star formation and stellar mass assembly. The first approach is based on the potential well of dark matter haloes, and relies on physical properties of the cosmic structures such as the virial masses and radii, X-ray luminosity, and dynamical masses According to this definition, which is commonly referred to as “global” environment, going from the largest scale (i.e. the most massive haloes) in the cosmic web down to the scales of single

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