PRIMUS: Enhanced Specific Star Formation Rates In Close Galaxy Pairs
  Tidal interactions between galaxies can trigger star formation, which
contributes to the global star formation rate density of the universe and could
be a factor in the transformation of blue, star-forming galaxies to red,
quiescent galaxies over cosmic time. We investigate tidally-triggered star
formation in isolated close galaxy pairs drawn from the Prism Multi-Object
Survey (PRIMUS), a low-dispersion prism redshift survey that has measured
~120,000 robust galaxy redshifts over 9.1 deg^2 out to z ~ 1. We select a
sample of galaxies in isolated galaxy pairs at redshifts 0.25 < z < 0.75, with
no other objects within a projected separation of 300 h^-1 kpc and dz/(1+z) =
0.01, and compare them to a control sample of isolated galaxies to test for
systematic differences in their rest-frame FUV-r and NUV-r colors as a proxy
for relative specific SFR. We find that galaxies in r_p < 50 h^-1 kpc pairs
have bluer dust-corrected UV-r colors on average than the control galaxies by
-0.134 +/- 0.045 magnitudes in FUV-r and -0.075 +/- 0.038 magnitudes in NUV-r,
corresponding to a ~15-20% increase in SSFR. This indicates an enhancement in
SSFR due to tidal interactions. We also find that this relative enhancement is
greater for a subset of r_p < 30 h^-1 kpc pair galaxies, for which the average
colors offsets are -0.193 +/- 0.065 magnitudes in FUV-r and -0.159 +/- 0.048
magnitudes in NUV-r, corresponding to a ~25-30% increase in SSFR. We test for
evolution in the enhancement of tidally-triggered star formation with redshift
across our sample redshift range and find marginal evidence for a decrease in
SSFR enhancement from 0.25 < z < 0.5 to 0.5 < z < 0.75. This indicates that a
change in enhanced star formation triggered by tidal interactions in low
density environments is not a contributor to the decline in the global star
formation rate density across this redshift range.
