Interacting galaxies in the IllustrisTNG simulations - V. Comparing the influence of star-forming versus passive companions

We study interacting galaxy pairs in the TNG100-1 and TNG300-1 cosmological simulations using previously generated closest companion samples. We study the specific star-formation rates (sSFRs) of massive (1010 M-circle star < M*< 1012 M-circle star) galaxies at z = 0.2 as a function of separation from the closest companion galaxy. We split our sample based on whether the companion galaxy is star-forming or passive. We find that galaxies with close star-forming companions have sSFRs that are enhanced (on average) by a factor of 2.9 +/- 0.3 in TNG100-1 and 2.27 +/- 0.06 in TNG300-1 compared to controls, with enhancements present out to separations of similar to 300 kpc. Galaxies with passive companions in TNG300-1 exhibit mild sSFR suppression (similar to 12 per cent) at 100-300 kpc and small sSFR enhancements at separations below 50 kpc. sSFR suppression is strongest in pairs where the galaxy's stellar mass is more than 2 times that of its passive companion. By generating a stellar mass-matched (`twinned') sample in TNG300-1, we show that differences in sSFR trends between companion types are not a result of intrinsic stellar mass differences in star-forming versus passive galaxies. We compare with an analogous sample of galaxy pairs from SDSS, finding consistent results between observations and simulations. Overall, we find that star-forming galaxies show enhanced sSFRs regardless of companion type, but that galaxies with close passive companions are more likely to be passive themselves.