Exploring the Host Galaxies of Unusual Astrophysical Transients

Most astrophysical transients arise from one of two sources - the accretion of material onto a compact source, releasing its gravitational potential, or the sudden release of energy when a star reaches the end of its life and merges with its neighbour or collapses under its own weight. In both cases, but particularly the latter, the study of the transient's host galaxy and its stellar populations can lend insights into the progenitor and environment that shape the event. Core collapse gamma-ray bursts (GRBs) are the most energetic explosions in the Universe, with some reaching isotropic energies as high as 1054 ergs s-1. GRBs have a range of luminosities and different spectral and temporal profiles. The handful of nearby bursts offer the best opportunities to study the hosts of GRBs. It is possible that these correspond in position to the small number of GRB hosts detected in the WISE IR survey. We have data in hand, including VLT/X-Shooter spectra, WHT data and ATCA radio observations, exploring these objects, and these will form the initial focus of this project. The nature of the WISE objects will be determined - are they chance alignments, nearby star forming galaxies, or more distant dusty galaxies? Work will be done to characterise potential GRB host galaxies, using to determine the star formation rates and chemical compositions of the galaxies. Do they have the expected properties, given that they produced a GRB?
This study will then be extended to the host galaxies of further classes of unusual astrophysical transients (potentially including gravitational wave sources, or more exotic transients such as FRBs or TDEs). Such transients reveal structures and stellar populations that are very challenging to observe directly. Hence they may be critical for estimating the fraction of obscured star formation in the Universe, constraining the conditions under which GRB and other transient progenitors can form, and even placing limits on stellar interactions and the end of stellar life - a particularly salient point in this new era of gravitational wave astronomy.