# The XXL Survey: XXXVII. The role of the environment in shaping the stellar population properties of galaxies at 0.1<z<0.5

## TL;DR

This study analyzes how different definitions of galaxy environment influence stellar population properties and star formation activity in galaxies at 0.1<z<0.5, revealing environment-dependent variations in galaxy evolution.

## Contribution

It compares global and local environment parametrizations, demonstrating their different physical implications and effects on galaxy star formation and transition populations.

## Key findings

- Blue/star-forming fraction highest in low-density regions.
- Star-forming fraction exceeds blue galaxy fraction across environments.
- Environment parametrization affects the observed galaxy transition populations.

## Abstract

Exploiting a sample of galaxies drawn from the XXL-N 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/outer members and field galaxies. When considering the "local" environment, we take into account the projected number density of galaxies in a fixed aperture of 1Mpc in the sky. We find that regardless of the environmental definition adopted, the fraction of blue/star-forming galaxies is the highest in the field/least dense regions and the lowest in the virial regions of clusters/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.