The dependence of galaxy group star formation rates and metallicities on
  large scale environment
  We construct a sample of 75,863 star forming galaxies with robust metallicity
and star formation rate measurements from the Sloan Digital Sky Survey Data
Release 7 (SDSS DR7), from which we select a clean sample of compact group (CG)
galaxies. The CGs are defined to be close configurations of at least 4 galaxies
that are otherwise apparently isolated. Our selection results in a sample of
112 spectroscopically identified compact group galaxies, which can be further
divided into groups that are either embedded within a larger structure, such as
a cluster or large group, or truly isolated systems. The compact groups then
serve as a probe into the influence of large scale environment on a galaxy's
evolution, while keeping the local density fixed at high values. We find that
the star formation rates (SFRs) of star forming galaxies in compact groups are
significantly different between isolated and embedded systems. Galaxies in
isolated systems show significantly enhanced SFR, relative to a control sample
matched in mass and redshift, a trend not seen in the embedded systems.
Galaxies in isolated systems exhibit a median SFR enhancement at fixed stellar
mass of +0.07 \pm 0.03 dex. These dependences on large scale environment are
small in magnitude relative to the apparent influence of local scale effects
found in previous studies, but the significance of the difference in SFRs
between our two samples constrains the effect of large scale environment to be
non-zero. We find no significant change in the gas-phase interstellar
metallicity for either the isolated or embedded compact group sample relative
to their controls. However, simulated samples that include artificial offsets
indicate that we are only sensitive to metallicity changes of log O/H >0.13 dex
(at 99% confidence), which is considerably larger than the typical metallicity
differences seen in previous environmental studies.
