Star formation and AGN activity in interacting galaxies: a near-UV perspective

Abstract

We study nearby galaxies in close pairs to study the key factors affecting star formation and AGN activity triggered during galaxy interactions. Close pairs are selected from the Sloan Digital Sky Survey assuming a projected separation of $<$30kpc and recessional velocity difference $<$500km s$^{-1}$. Near-ultraviolet (NUV) fluxes from GALEX are used to estimate specific star formation rates (SSFRs). We find a factor of $\sim$5.3 increase in SSFR for low mass (10$^{8}-10^{11}$M$_{\odot}$) close pair galaxies and a factor of $\sim$2.1 increase in SSFR for high mass mass (10$^{11}-10^{13}$M$_{\odot}$) close pairs compared to the general galaxy population. Considering galaxies of all masses, we find a factor of $\sim$1.8 enhancement in SSFR for close pairs in field environments compared to non-pairs, with no significant increase for pairs in group and cluster environments. A modest decrease of a factor of $\sim$1.4 is found in the Seyfert fraction in close pair galaxies when compared to isolated galaxies, which suggests that mergers may not trigger AGN activity at the close-pair stage or may trigger a different class of AGN. This becomes a factor of $\sim$4.2 decrease when we restrict our analysis to high mass close pairs in group or cluster environments.