The Host Galaxies of Rapidly Evolving Transients in the Dark Energy Survey

TL;DR

This study analyzes the host galaxies of 106 rapidly evolving transients from the Dark Energy Survey, revealing their preference for star-forming, low-metallicity galaxies and suggesting a link to massive, young stars.

Contribution

It provides the largest sample and most comprehensive analysis of RET host galaxies, highlighting their unique properties compared to other explosive transients.

Findings

RETs occur exclusively in star-forming galaxies.

RETs prefer galaxies with high specific star-formation rates.

RET hosts show low metallicities similar to gamma-ray burst hosts.

Abstract

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.