Galaxy evolution as a function of environment and luminosity

TL;DR

This study analyzes how galaxy star formation and nuclear activity depend on environment and luminosity, revealing that dense regions have mostly passive galaxies regardless of brightness, while in less dense areas, luminosity strongly influences galaxy activity.

Contribution

It provides a detailed analysis of galaxy activity as a function of environment and luminosity, highlighting the role of AGN feedback and merger history in galaxy evolution.

Findings

70% of galaxies in high-density regions are passively evolving.

In low-density regions, passive galaxy fraction drops with luminosity.

AGN activity decreases with decreasing luminosity, mirroring passive galaxy trends.

Abstract

We present an analysis of star formation and nuclear activity of about 28000 galaxies in a volume-limited sample taken from SDSS DR4 low-redshift catalogue (LRC) taken from the New York University Value Added Galaxy Catalogue (NYU-VAGC) of Blanton et al. 2005, with 0.005<z<0.037, ~90\% complete to M_r=-18.0. We find that in high-density regions ~70 per cent of galaxies are passively evolving independent of luminosity. In the rarefied field, however, the fraction of passively evolving galaxies is a strong function of luminosity, dropping from 50 per cent for Mr <~ -21 to zero by Mr ~ -18. Moreover the few passively evolving dwarf galaxies in field regions appear as satellites to bright (>~ L*) galaxies. Moreover the fraction of galaxies with the optical signatures of an active galactic nucleus (AGN) decreases steadily from ~50\% at Mr~-21 to ~0 per cent by Mr~-18 closely mirroring the luminosity dependence of the passive galaxy fraction in low-density environments (see fig. 1 continuous lines). This result reflects the increasing importance of AGN feedback with galaxy mass for their evolution, such that the star formation histories of massive galaxies are primarily determined by their past merger history.