Observing the effects of galaxy interactions on the circumgalactic medium

We continue our empirical study of the emission line flux originating in the cool (T ∼ 10⁴ K) gas that populates the halos of galaxies and their environments. Specifically, we present results obtained for a sample of galaxy pairs with a range of projected separations,, and mass ratios <1:5, intersected by 5443 Sloan Digital Sky Survey lines of sight at projected radii of 10-50 kpc from either or both of the two galaxies. We find significant enhancement in Hα emission and a moderate enhancement in [N ii]6583 emission for low-mass pairs (mean stellar mass per galaxy M*, <10^10.4M⊙), relative to the results from a control sample. This enhanced Hα emission comes almost entirely from sight lines located between the galaxies, consistent with a short-term, interaction-driven origin for the enhancement. We find no enhancement in Hα emission, but significant enhancement in [N ii]6583 emission for high-mass M*, >10^10.4M⊙) pairs. Furthermore, we find a dependence of the emission line properties on the galaxy pair mass ratio such that those with a mass ratio below 1:2.5 have enhanced [N ii]6583 and those with a mass ratio between 1:2.5 and 1:5 do not. In all cases, departures from the control sample are only detected for close pairs (S _p < 100 kpc). Attributing an elevated [N ii]6583/Hα ratio to shocks, we infer that shocks play a role in determining the circumgalactic medium properties for close pairs that are among the more massive and have mass ratios closer to 1:1.