The environmental dependence of the red galaxy sequence

TL;DR

This study investigates how the properties of the red galaxy sequence vary with environment, revealing that environment influences galaxy color and scatter, but bright red early types are similarly evolved across environments.

Contribution

It provides a detailed analysis of the environmental dependence of the red galaxy sequence's mean color and scatter, highlighting the roles of galaxy type and environment in galaxy evolution.

Findings

Field galaxies are bluer and have larger scatter than those in groups and clusters.

High mass systems have the reddest mean color and smallest scatter.

Red early type galaxies in different environments show similar evolutionary stages.

Abstract

The dependence of the sequence of red galaxies (RS) with the environment is investigated using field, group, and cluster galaxies drawn from the SDSS. Our work focuses in studying the mean colour ($\mu_R$) and the scatter ($\sigma_R$) of the RS as a function absolute magnitude in different environments characterised either by the mass of the system in which the galaxies are located or by the distance to the system's centre. The same analysis is carried out using red early type galaxies. For a given luminosity, $\mu_R$ of field galaxies is bluer and $\sigma_R$ is larger than their group and cluster counterparts irrespective of mass and position within the systems. Among systems of galaxies, high mass groups and clusters have the reddest $\mu_R$ and the smallest $\sigma_R$. These differences almost disappear when red early type galaxies alone are considered. Galaxies in the core and in the outskirts of groups have similar $\mu_R$, whereas galaxies in clusters show a strong dependence on cluster centric distance. Red early type galaxies in the outskirts of clusters have $\sigma_R$ values as large as field galaxies', while galaxies in the inner regions of clusters have lower values. We find that bright red early type galaxies have reached nearly the same evolutionary stage in all environments. Our results suggest that the cluster environment is not necessary to populate the RS. We propose a scenario in which the RS in massive systems is populated by two different star formation history galaxies: red early type galaxies that formed the bulk of their stars during the early stages of massive halo assembly, and red galaxies that passed most of their lives inhabiting poor groups or the field and fell into massive systems at lower redshifts.