2002ApJ...566..229C

We present deep 2.2 µm imaging of 12 gamma-ray burst host galaxies. Template spectral energy distributions are fitted to the multiband photometry between visible and near-infrared wavelengths to derive a better constraint on the stellar mass of these galaxies. The internal extinction in the host galaxies is estimated using the rest-frame ultraviolet (UV) slope. We find that the extinction-corrected star formation rates (SFRs) of the galaxies are significantly larger than rates derived from emission lines in the visible or the UV continuum. The ratio between the extinction-corrected SFRs and stellar mass for seven of the host galaxies is high compared to local starbursts, and three of the hosts have derived far-infrared luminosities comparable to infrared luminous galaxies. In addition, existing observational data reveal that at least six of the 11 putative hosts seem to be disturbed or have companion galaxies within a projected angular separation of ∼2".5. If we assume that the host and the companion are at similar redshifts, this corresponds to a physical separation of less than 20 kpc, providing some evidence for an ongoing/recent tidal encounter. We conclude that tidally induced starbursts such as those found in infrared luminous galaxies might be popular birthplaces for gamma-ray bursts. The age of the stellar population in four out of six galaxies is rather young, of order 10 Myr. This favors models where gamma-ray bursts result from the core collapse of isolated, massive stars and explosion of the resultant black hole/accretion disk system.