The effect of galaxy interactions on star formation rates in the COLIBRE simulations

Abstract

Observations and theory indicate that galaxy interactions enhance star formation rates (SFRs). However, the degree of enhancement and its dependence on the properties of the interacting galaxies vary across different studies. In this work, we use the COLIBRE simulations of galaxy formation to investigate the effect of interactions on the SFRs of star-forming galaxies at redshift $z\approx 0$. The COLIBRE simulations capture the multiphase nature of the interstellar medium and have volumes up to $200^3$ and $400^3$ cMpc${}^3$ at m6 (gas and dark-matter particle mass $\sim 10^6{\mathrm{M}}_{\odot }$) and m7 ($\sim 10^7{\mathrm{M}}_{\odot }$) resolutions, respectively. After constructing samples of interacting galaxies (with mass ratios $>0.1$) and isolated controls, matched in stellar mass, large- and small-scale environment, and redshift, we show that the average specific SFR (sSFR) of interacting galaxies is enhanced by up to a factor of $\approx 2$ for separations of $\approx 10$ kpc. The enhancement decreases with pair separation but remains significant out to $\approx 200$ kpc. The enhancement increases with increasing numerical resolution, is more pronounced in the central regions of galaxies, and decreases with increasing stellar mass at fixed separation. Mergers with higher mass ratios induce stronger sSFR enhancement. We compare our results with observational data from the SDSS, finding good agreement in the dependence of the mean sSFR enhancement on separation, but underpredicting its normalisation by a factor of $\approx 2$. Finally, we show that the pre-merger sSFR enhancement of resolved interactions accounts for $\approx 2$ per cent of the $z\approx 0$ cosmic SFR density.

21 pages, 20 figures; submitted to MNRAS