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 .