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 (SFR) 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 deg² 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 Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their restframe FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). 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 mag in FUV - r and -0.075 ±0.038 mag in NUV -r, corresponding to an ∼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 ≤ 30h^-1 kpc pair galaxies, for which the average color offsets are -0.193 ± 0.065 mag in FUV - r and -0.159 ± 0.048 mag in NUV - r, corresponding to an ∼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 SFR density across this redshift range.