IPAC Astronomy Lunch Seminar

If gamma-ray bursts trace the cosmic star-formation rate, a significant fraction of these events should occur in luminous and dusty galaxies, but such galaxies are extremely rare among known GRB hosts. I will describe results from a campaign targeting GRBs (ranging in redshift from 0.8 to 3.1) whose optical afterglows were highly dust-obscured and whose hosts were difficult to study until recently. The host population of this class, which comprises about a quarter of all GRBs, turns out to be very diverse and includes a significant number of red, dusty, luminous galaxies previously unknown among GRB hosts. Faint radio and submillimeter fluxes suggest that these galaxies are LIRGs typical of average galaxies found in Spitzer flux-limited samples; none (to date) are bright ULIRGs. GRBs may therefore trace cosmic star-formation better than previously believed, although they still appear to avoid the most extreme high-redshift systems.