Title:Galaxy evolution in the post-merger regime. IV -- The long-term effect of mergers on galactic stellar mass growth and distribution

Abstract:Galaxy mergers are known to trigger bursts of central star formation, which should therefore lead to stellar mass growth in their inner regions. However, observational measurements of this `burst mass fraction' are scant. Here, we assemble a large sample of ~14,000 post-coalescence galaxies that have recently completed their merger-induced star formation, and compare various measurements of central stellar mass with a matched control sample. Specifically, we quantify (at fixed redshift, star formation rate and total stellar mass) the stellar mass enhancement within a fixed angular aperture (Delta M_{star,fibre}) and in the galactic bulge (Delta M_{star,bulge}), finding burst mass fractions of 10 -- 20%. 61 galaxies in our sample are at z<0.05 and have integral field unit data from the Mapping Galaxies at Apache Point (MaNGA) survey, allowing further kpc-scale assessment of excess stellar mass and radial gradients. When assessed within apertures defined in units of kpc we again find a ~ 15 -- 20% excess of stellar mass in the central regions of the post-mergers compared with matched controls. However, within apertures defined in units of effective radius this stellar mass enhancement increases to 40%, suggesting that the relative structure/size of the galaxy is important for regulating the location of the merger induced star formation. Moreover, we find that these stellar mass enhancements are spatially extended, out to ~7 kpc or around 1 R/R_e, although the small sample size of the MaNGA overlap limits our radial sampling. Our work represents the first direct measurement of merger-induced stellar mass growth that is independent of stellar population modelling, or fitting light profiles, demonstrating significant and extended mass build-up in late stage post-mergers.