Investigating a population of infrared-bright gamma-ray burst host galaxies

We identify and explore the properties of an infrared-bright gamma-ray burst (GRB) host population. Candidate hosts are selected by coincidence with sources in WISE, with matching to random coordinates and a false alarm probability analysis showing that the contamination fraction is ~0.5. This methodology has already identified the host galaxy of GRB080517. We combine survey photometry from Pan-STARRS, SDSS, APASS, 2MASS, GALEX, and WISE with our own WHT/ACAM and VLT/X-shooter observations to classify the candidates and identify interlopers. Galaxy SED fitting is performed using MAGPHYS, in addition to stellar template fitting, yielding 13 possible IR-bright hosts. A further seven candidates are identified from the previously published work. We report a candidate host for GRB061002, previously unidentified as such. The remainder of the galaxies have already been noted as potential hosts. Comparing the IR-bright population properties including redshift z, stellar mass M*, star formation rate SFR, and V-band attenuation A_V to GRB host catalogues in the literature, we find that the infrared-bright population is biased towards low z, high M*, and high A_V. This naturally arises from their initial selection - local and dusty galaxies are more likely to have the required IR flux to be detected in WISE. We conclude that while IR-bright GRB hosts are not a physically distinct class, they are useful for constraining existing GRB host populations, particularly for long GRBs.