1301.5903 (D. A. Perley et al.)

A Population of Massive, Luminous Galaxies Hosting Heavily Dust-Obscured Gamma-Ray Bursts: Implications for the Use of GRBs as Tracers of Cosmic Star Formation    [PDF]

D. A. Perley, A. J. Levan, N. R. Tanvir, S. B. Cenko, J. S. Bloom, J. Hjorth, T. Kruehler, A. V. Filippenko, A. Fruchter, J. P. U. Fynbo, P. Jakobsson, J. Kalirai, B. Milvang-Jensen, A. N. Morgan, J. X. Prochaska, J. M. Silverman

We present observations and analysis of the host galaxies of 23 heavily dust-obscured gamma-ray bursts (GRBs) observed by the Swift satellite between the years 2005-2009, a sample representing all GRBs during this period with an unambiguous host-frame extinction of at least A_V>1 mag. Deep observations with Keck, Gemini, VLT, HST, and Spitzer successfully detect the host galaxies and establish redshifts for all 23 events, enabling us to provide measurements of the host stellar masses, star-formation rates (SFRs), and mean extinctions. Compared to the hosts of unobscured GRBs at similar redshifts, we find that the hosts of dust-obscured GRBs are (on average) more massive by about an order of magnitude and are also significantly more rapidly star-forming and more dust-obscured. However, while the inclusion of this population of dust-obscured hosts shows that GRBs populate all types of star-forming galaxies including the most massive, luminous systems at z~2, at redshifts below z<1.5 the overall GRB population continues to show a highly significant aversion away from massive galaxies and a corresponding preference for low-mass systems relative to would be expected given a purely SFR-selected galaxy sample. This supports the notion that the GRB rate is strongly dependent on metallicity, and may suggest that the most massive galaxies in the universe underwent an significant transition in their chemical properties approximately 9 Gyr ago. We also conclude that, based on the absence of unobscured GRBs in massive galaxies and the absence of obscured GRBs in low-mass galaxies, the dust distributions of both the lowest-mass and the highest-mass galaxies are relatively homogeneous, while intermediate-mass galaxies (~10^9 M_sun) have much more diverse internal dust properties.

View original: http://arxiv.org/abs/1301.5903