The Host Galaxies of Rapidly Evolving Transients in the Dark Energy
  Survey
  Rapidly evolving transients (RETs), also termed fast blue optical transients
(FBOTs), are a distinct class of astrophysical event. They are characterised by
lightcurves that decline much faster than common classes supernovae (SNe), span
vast ranges in peak luminosity and can be seen to redshifts greater than 1.
Their evolution on fast timescales has hindered high quality follow-up
observations, and thus their origin and explosion/emission mechanism remains
unexplained. In this paper we define the largest sample of RETs to date,
comprising 106 objects from the Dark Energy Survey, and perform the most
comprehensive analysis of RET host galaxies. Using deep-stacked photometry and
emission-lines from OzDES spectroscopy, we derive stellar masses and
star-formation rates (SFRs) for 49 host galaxies, and metallicities for 37. We
find that RETs explode exclusively in star-forming galaxies and are thus likely
associated with massive stars. Comparing RET hosts to samples of host galaxies
of other explosive transients as well as field galaxies, we find that RETs
prefer galaxies with high specific SFRs, indicating a link to young stellar
populations, similar to stripped-envelope SNe. RET hosts appear to show a lack
of chemical enrichment, their metallicities akin to long duration gamma-ray
bursts and superluminous SN host galaxies. There are no clear relationships
between properties of the host galaxies and the peak magnitudes or decline
rates of the transients themselves.
