Gas flows and star formation as a consequence of galaxy interaction in compact groups

Abstract

The environment of galaxies is known to influence their evolution via a wide range of processes, such as tidal interactions, ram-pressure stripping, or galaxy harassment. However, the exact interconnectivity between the large scale environment-driven mechanisms and the other internal processes (starburst, star formation quenching, nuclear activity, and both outflows and inflows) remains poorly understood. This thesis describes the use of the WiFeS and MUSE integral field spectrographs to study gas flows and star formation activity inside two members of compact groups of galaxies: HCG 16c and HCG 91c. In particular, WiFeS and MUSE are used to resolve scales of 1 kpc at the distances of HCG 16c and HCG 91c - the size of giant molecular clouds and HII regions - in an effort to tie the environment to its impact within the disks of the galaxies. HCG 16c is found to host an asymmetric, bipolar, rotating galactic wind, powered by a nuclear starburst. Emission line ratio diagnostics indicate that photoionization is the dominant excitation mechanism at the base of the wind. The asymmetry of the wind is likely caused by one of the two lobes of the wind-blown bubble bursting out of its HI envelope. The characteristics of the wind suggest that it is caught early (a few Myr) in the wind evolution sequence. The wind is also quite different to the galactic wind in the partner galaxy HCG 16d which contains a symmetric, shock-excited wind. Given that both galaxies have (likely) similar interaction histories, the different wind characteristics must be a consequence of the intrinsic properties of HCG 16c and HCG 16d. In HCG 91c, WiFeS and MUSE reveal HII regions with kinematic and abundance offsets in this otherwise unremarkable star-forming spiral. Specifically, at least three HII regions harbor an oxygen abundance 0:15 dex lower than expected from their immediate surroundings and from the overall abundance gradient present in the disk of this galaxy. The same star forming regions are also associated with a small kinematic offset in the form of a lag of 5-10kms􀀀1 with respect to the local circular rotation of the gas. HI observations of HCG 91 from the VLA and broadband optical images from Pan-STARRS suggest that HCG 91c is caught early in its interaction with the compact group HCG 91. Altogether, evidence point towards infalling and collapsing extra-planar halo gas clouds at the disk-halo interface of the galaxy. As such, HCG 91c provides evidence that some of the perturbations possibly associated with the early phase of galaxy evolution in compact groups impact the star forming disk locally, and on sub-kpc scales. Finally, this thesis also describes a series of new tools developed for the processing, analysis and visualization of these integral field spectroscopy datasets. These comprise a new data reduction pipeline for the WiFeS instrument, interactive PDF & HTML documents for multi-dimensional data visualization and publication, 3-D printing of astrophysical datasets, the pyqz code to derive oxygen abundances & ionization parameters from strong emission line ratios, and 3-D line ratio diagnostic diagrams. Show more