And the winner is: galaxy mass

TL;DR

This study investigates how environment influences early-type galaxy evolution, finding that galaxy mass predominantly drives properties like age and metallicity, with environment affecting only a minor rejuvenation fraction.

Contribution

It provides evidence that galaxy mass is the main factor in galaxy evolution, suggesting the morphology-density relationship may be mass-driven rather than environment-driven.

Findings

10% of early-type galaxies are rejuvenated by recent star formation

Rejuvenation fraction increases with decreasing galaxy mass and density

Galaxy properties scale with mass independently of environment

Abstract

The environment is known to affect the formation and evolution of galaxies considerably best visible through the well-known morphology-density relationship. We study the effect of environment on the evolution of early-type galaxies for a sample of 3,360 galaxies morphologically selected by visual inspection from the SDSS in the redshift range 0.05<z<0.06, and analyse luminosity-weighted age, metallicity, and alpha/Fe ratio as function of environment and galaxy mass. We find that on average 10 per cent of early-type galaxies are rejuvenated through minor recent star formation. This fraction increases with both decreasing galaxy mass and decreasing environmental density. However, the bulk of the population obeys a well-defined scaling of age, metallicity, and alpha/Fe ratio with galaxy mass that is independent of environment. Our results contribute to the growing evidence in the recent literature that galaxy mass is the major driver of galaxy formation. Even the morphology-density relationship may actually be mass-driven, as the consequence of an environment dependent characteristic galaxy mass coupled with the fact that late-type galaxy morphologies are more prevalent in low-mass galaxies.