Galaxy And Mass Assembly (GAMA): Galaxy environments and star formation
  rate variations
  We present a detailed investigation into the effects of galaxy environment on
their star formation rates (SFR) using galaxies observed in the Galaxy and Mass
Assembly Survey (GAMA). We use three independent volume-limited samples of
galaxies within z < 0.2 and Mr < -17.8. We investigate the known SFR-density
relationship and explore in detail the dependence of SFR on stellar mass and
density. We show that the SFR-density trend is only visible when we include the
passive galaxy population along with the star-forming population. This
SFR-density relation is absent when we consider only the star-forming
population of galaxies, consistent with previous work. While there is a strong
dependence of the EWH?a on density we find, as in previous studies, that these
trends are largely due to the passive galaxy population and this relationship
is absent when considering a "star-forming" sample of galaxies. We find that
stellar mass has the strongest influence on SFR and EWH?a with the environment
having no significant effect on the star-formation properties of the star
forming population. We also show that the SFR-density relationship is absent
for both early and late-type star-forming galaxies. We conclude that the
stellar mass has the largest impact on the current SFR of a galaxy, and any
environmental effect is not detectable. The observation that the trends with
density are due to the changing morphology fraction with density implies that
the timescales must be very short for any quenching of the SFR in infalling
galaxies. Alternatively galaxies may in fact undergo predominantly in-situ
evolution where the infall and quenching of galaxies from the field into dense
environments is not the dominant evolutionary mode.
