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

J. X. Prochaska, Y. Sheffer, D. A. Perley, J. S. Bloom, L. A. Lopez, M. Dessauges-Zavadsky, H. W. Chen, A. V. Filippenko, M. Ganeshalingam, W. Li, A. A. Miller, D. Starr

Research output: Contribution to journalArticlepeer-review

148 Scopus citations

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 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 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.

Original languageEnglish (US)
Pages (from-to)L27-L32
JournalAstrophysical Journal
Volume691
Issue number1
DOIs
StatePublished - 2009

Keywords

  • Gamma rays: bursts
  • ISM: molecules

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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