Environmental Effects on Interacting Galaxy Pairs in the SDSS

Abstract

The cause of varying galaxy interaction outcomes in different environments is investigated using a sample of over 505,000 Sloan Digital Sky Survey Data Release 7 galaxies at $0.011$. For paired galaxies with mass ratio $<1$, this suppression is accompanied by a lack of mean asymmetry offset or enhancement at similar separations. Possible explanations of this result include suppression due to an earlier encounter whereby star bursts consume the star forming gas, and given sufficient time the galaxy settles into a symmetric shape. At close separations ($r_p<40$ \hkpc), reduced mean SFR enhancements in all environments are found together with increased asymmetry enhancement in comparison with paired galaxies with mass ratio $>1$. We hypothesize that the suppression in lower-mass paired galaxies is due to the depletion of their gas reservoirs prior to the interaction, and conclude that interactions in different environments produce various results due to assembly bias rather than differing interaction mechanisms in various environments.