Article

THE FIRST POSITIVE DETECTION OF MOLECULAR GAS IN A GRB HOST GALAXY

J. X. ProchaskaDepartment of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USAY. ShefferDepartment of Physics and Astronomy, University of Toledo, Toledo, OH 43606, USAD. A. PerleyDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USAJ. S. BloomDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USAL. A. LopezDepartment of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USAM. Dessauges-ZavadskyObservatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, SwitzerlandH.-W. ChenDepartment of Astronomy & Astrophysics, and Kavli Institute for Cosmological Physics, 5640 S. Ellis Ave, Chicago, IL 60637, USAA. V. FilippenkoDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USAM. GaneshalingamDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USAW. LiDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USAA. A. MillerDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USAD. StarrDepartment of Astronomy, University of California, Berkeley, CA 94720-3411, USA

2008en

ABI

Abstract

We report on strong H 2 and CO absorption from gas within the host galaxy of gamma-ray burst (GRB) 080607. Analysis of our Keck/LRIS afterglow spectrum reveals a very large H i column density (N H i = 10 22.700.15 cm -2 ) and strong metal-line absorption at z GRB = 3.0363 with a roughly solar metallicity. We detect a series of A -X bandheads from CO and estimate N (CO) = 10 16.50.3 cm -2 and T CO ex > 100 K. We argue that the high excitation temperature results from UV pumping of the CO gas by the GRB afterglow. Similarly, we observe H 2 absorption via the Lyman-Werner bands and estimate N H 2 = 10 21.20.2 cm -2 with T H 2 ex = 10-300 K. The afterglow photometry suggests an extinction law with R V 4 and A V 3.2 mag and requires the presence of a modest 2175 bump. Additionally, modeling of the Swift XRT X-ray spectrum confirms a large column density with N H = 10 22.580.04 cm -2 . Remarkably, this molecular gas has extinction properties, metallicity, and a CO/H 2 ratio comparable to those of translucent molecular clouds of the Milky Way, suggesting that star formation at high z proceeds in similar environments as today. However, the integrated dust-to-metals ratio is sub-Galactic, suggesting the dust is primarily associated with the molecular phase while the atomic gas has a much lower dust-to-gas ratio. Sightlines like GRB 080607 serve as powerful probes of nucleosynthesis and star-forming regions in the young universe and contribute to the population of "dark" GRB afterglows.

Identifiers

DOI: 10.1088/0004-637x/691/1/l27

Citations and references

Cited by 20 references

Metrics — AkademScholar