Star formation and AGN activity in SDSS cluster galaxies

TL;DR

This study examines how star formation and AGN activity in SDSS cluster galaxies vary with distance from the cluster center, revealing environment-dependent quenching processes and the independence of star formation and AGN activity.

Contribution

It provides new insights into the environmental effects on galaxy evolution, showing that star formation is gradually quenched in clusters without significant influence from violent processes beyond 0.1 R_200.

Findings

Star formation is suppressed in cluster cores, especially for low-mass galaxies.

The fraction of AGN-hosting star-forming galaxies remains constant with radius.

Red galaxies with weak AGN decrease towards the cluster center.

Abstract

We investigate the recent and current star formation activity of galaxies as function of distance from the cluster center in a sample of 521 SDSS clusters at z<0.1. We show that when the BCGs are excluded from the galaxy sample, there is no evidence for mass segregation in the clusters, so that differences in cluster and field populations cannot simply be attributed to different mass functions. We find a marked star formation-radius relation in that almost all galaxies in the cluster core are quiescent, i.e. have terminated star formation a few Gyr ago. This star formation-radius relation is most pronounced for low-mass galaxies and is very weak or absent beyond the virial radius. The typical star formation rate of non-quiescent galaxies declines by approximately a factor of two towards the cluster center. However, the fraction of galaxies with young stellar populations indicating a recently completed starburst or a truncation of star formation does not vary significantly with radius. The fraction of star-forming galaxies which host a powerful optical AGN is also independent of clustercentric radius, indicating that the link between star formation and AGN in these galaxies operates independent of environment. The fraction of red galaxies which host a weak optical AGN decreases, however, towards the cluster center, with a similar timescale as the decline of star forming galaxies. Our results favor a scenario in which star formation is quenched slowly, on timescales similar to the cluster crossing time, and rule out significant contributions from more violent processes at least beyond cluster radii >0.1 R_200.