The Dawn of the Red: Star formation histories of group galaxies over the past 5 billion years

TL;DR

This study compares star formation histories of group and field galaxies over the past 5 billion years, revealing environment and mass-dependent evolution and suggesting long timescales for environmental effects.

Contribution

It provides a detailed analysis of star formation rate evolution in group versus field galaxies using multi-wavelength data and models, highlighting mass and environment dependencies.

Findings

Star formation rates decrease over time in all environments.

Passive galaxy fraction is higher in groups at both redshifts.

Environmental effects on galaxies occur over approximately 3 Gyrs.

Abstract

We examine the star formation properties of group and field galaxies in two surveys, the Sloan Digital Sky Survey (SDSS; at z ~ 0.08) and the Group Environment and Evolution Collaboration (GEEC; at z ~ 0.4). Using UV imaging from the GALEX space telescope, along with optical and, for GEEC, near infrared photometry, we compare the observed spectral energy distributions to large suites of stellar population synthesis models. This allows us to accurately determine star formation rates and stellar masses. We find that star forming galaxies of all environments undergo a systematic lowering of their star formation rate between z=0.4 and z=0.08 regardless of mass. Nonetheless, the fraction of passive galaxies is higher in groups than the field at both redshifts. Moreover, the difference between the group and field grows with time and is mass-dependent, in the sense the the difference is larger at low masses. However, the star formation properties of star forming galaxies, as measured by their average specific star formation rates, are consistent within the errors in the group and field environment at fixed redshift. The evolution of passive fraction in groups between z=0.4 and z=0 is consistent with a simple accretion model, in which galaxies are environmentally affected 3 Gyrs after falling into a ~ 10E13 Msun group. This long timescale appears to be inconsistent with the need to transform galaxies quickly enough to ensure that star forming galaxies appear similar in both the group and field, as observed.