The first positive detection of molecular gas in a GRB host galaxy

Prochaska, JX, Sheffer, Y, Perley, DA, Bloom, JS, Lopez, LA, Dessauges-Zavadsky, M, Chen, HW, Filippenko, AV, Ganeshalingam, M, Li, W, Miller, AA and Starr, D (2009) The first positive detection of molecular gas in a GRB host galaxy. The Astrophysical Journal, 691 (1). L27-L32. ISSN 1538-4357

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Abstract

We report on strong H2 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 () 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 COex > 100 K. We argue that the high excitation temperature results from UV pumping of the CO gas by the GRB afterglow. Similarly, we observe H2 absorption via the Lyman-Werner bands and estimate with -300 K. The afterglow photometry suggests an extinction law with RV 4 and AV 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 = 1022.580.04 cm-2. Remarkably, this molecular gas has extinction properties, metallicity, and a CO/H2 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. © 2009. The American Astronomical Society. All rights reserved..

Item Type:	Article
Uncontrolled Keywords:	0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects:	Q Science > QB Astronomy Q Science > QC Physics Q Science > QD Chemistry
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	3 December 2008
Date of first compliant Open Access:	23 May 2017
Date Deposited:	23 May 2017 10:11
Last Modified:	20 Apr 2022 09:18
DOI or ID number:	10.1088/0004-637X/691/1/L27
URI:	https://researchonline.ljmu.ac.uk/id/eprint/6504

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