Galaxy mergers are a major evolutionary transformation whose effects areborne out by a plethora of observations and numerical simulations. However,most previous simulations have used idealised, isolated, binary mergers andthere has not been significant progress on studying statistical samples ofgalaxy mergers in large cosmological simulations. We present a sample of 27,691post-merger (PM) galaxies ($0\le z \le 1$) identified from IllustrisTNG: acosmological, large box, magneto-hydrodynamical simulation suite. The PM samplespans a wide range of merger and galaxy properties ($M_\star$, $\mu$,$f_\mathrm{gas}$). We demonstrate that star forming (SF) PMs exhibit enhancedstar formation rates (SFRs) on average by a factor of $\sim 2$, while thepassive PMs show no statistical enhancement. We find that the SFR enhancements:(1) show no dependence on redshift, (2) anti-correlate with the PM's stellarmass, and (3) correlate with the gas fraction of the PM's progenitors. However,SF PMs show stronger enhancements which may indicate other processes being atplay (e.g., gas phase, feedback efficiency). Although the SFR enhancementcorrelates mildly with the merger mass ratio, the more abundant minor mergers($0.1 \le \mu < 0.3 $) still contribute $\sim 50\%$ of the total SFRenhancement. By tracing the PM sample forward in time, we find that galaxymergers can drive significant SFR enhancements which decay over $\sim 0.5$ Gyrindependent of the merger mass ratio, although the decay timescale is dependenton the simulation resolution. The strongest merger-driven starburst galaxiesevolve to be passive/quenched on faster timescales than their controls.

We use data from the GAMA and GALEX surveys to demonstrate that the UVupturn, an unexpected excess of ultraviolet flux from a hot stellar component,seen in the spectra of many early-type galaxies, arises from processes internalto individual galaxies with no measurable influence from the galaxies' largerenvironment. We first define a clean sample of passive galaxies without asignificant contribution to their UV flux from low-level star formation. Weconfirm that galaxies with the optical colours of red sequence galaxies oftenhave signs of residual star formation, which, without other information, wouldprevent a convincing demonstration of the presence of UV upturns. However, byincluding (NUV$-u$) and {\it WISE} (W2-W3) colours, and FUV data where itexists, we can convincingly constrain samples to be composed ofnon-star-forming objects. Using such a sample, we examine GALEX photometry oflow redshift GAMA galaxies in a range of low-density environments, from groupsto the general field, searching for UV upturns. We find a wide range of(NUV$-r$) colours, entirely consistent with the range seen -- and attributed tothe UV upturn -- in low-redshift red sequence cluster galaxies. The range ofcolours is independent of group multiplicity or velocity dispersion, withisolated passive galaxies just as likely to have blue UV-to-optical colours,implying significant upturn components, as those in richer groups and in theprevious data on clusters. This is supported by equivalent results for(FUV$-r$) colours which are clear indicators of upturn components.