Galaxy interactions in the local universe

(Brassington, Brinks)

Although it is now well accepted that galactic evolution and supermassive black-holes are intimately linked, the underlying causal mechanisms remain unknown. Indeed, the triggering and fuelling of active galactic nuclei, the co-evolution of their host galaxies and the role of environment remain key outstanding challenges in modern astrophysics.

We are addressing these issues by studying a large sample of interacting galaxies in the local Universe. From these observations we can quantify, in detail, the degree of nuclear and star-formation activity in these systems by analysing their mid-infrared emission (Spitzer IRAC, MIPS & IRS), as well as the X-ray properties of their nuclear emission (Chandra, XMM-Newton). These interacting galaxies have been selected on the basis of one or more close companions, instead of morphological peculiarities or infrared luminosities (e.g. ULIRGS), both of which are indicative of strong interactions. This selection criteria ensures that we include galaxies at early stages of interacting, which allows us to identify when and where star-formation is triggered in these systems. By observing a large sample of systems we are able to correlate the distribution and level of star-formation, as well as nuclear activity, with parameters of the interaction (e.g. galaxy gas content, mass-ratios, luminosities, interaction timescale). Further, we can identify whether there is a meaningful statistical evolutionary trend (e.g., do AGN trigger star-formation, and/or might star-formation activate or hide an AGN) during this process.