Neutral hydrogen in the archetype post-merger : dual active galactic nucleus system NGC 6240

Abstract

NGC 6240 is a prototypical merger system in the nearby universe hosting a dual active galactic nucleus. It is a well studied object and has been observed across the electromagnetic spectrum using most major ground- and space-based observatories over several decades. In this thesis, we report on the first detection of H I emission in this system. We find that there are two planes of H I emission, one aligned with the galactic dust plane and the other in line with a neighbouring galaxy at a projected separation of ∼90 kpc. This interacting neighbour has extended ultravio let and compact x-ray emission, indicating active star formation and active nuclear black hole accretion, respectively. As far as we are aware, this is the first evidence of an interaction between NGC 6240 and this neighbouring galaxy. Overall, the H I emission is predominately found to the south of the dual AGN, including some tidal debris to the south-west. The previously reported H I absorption is shown to have the same orientation as the galaxy disk, based on the high-imaging fidelity and sensitivity, which enable high relative astrometry of the absorption line. Combining the above, we are able to compare and contrast the H I emission and absorption view, providing a richer picture of this prototypical local-universe merger system. Detailed H I studies such as this will improve our understanding of H I at galaxy formation and evolution in higher redshift systems, where the galaxy merger rate, AGN prevalence, and cosmic star formation rate density all show a dramatic increas