The First Positive Detection of Molecular Gas in a GRB Host Galaxy - Astrophysics > High Energy Astrophysical PhenomenaReport as inadecuate




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Abstract: We report on strong H2 and CO absorption from gas within the host galaxy ofgamma-ray burst GRB 080607. Analysis of our Keck-LRIS afterglow spectrumreveals a very large HI column density NHI = 10^22.70 cm^-2 and strongmetal-line absorption at z GRB = 3.0363 with a roughly solar metallicity. Wedetect a series of A-X bandheads from CO and estimate NCO = 10^16.5 cm^-2 andT ex^CO > 100K. We argue that the high excitation temperature results from UVpumping of the CO gas by the GRB afterglow. Similarly, we observe H2 absorptionvia the Lyman-Werner bands and estimate NH2 = 10^21.2 cm^-2 with T ex^H2 =10-300K. The afterglow photometry suggests an extinction law with R V=4 andA V=3.2 mag and requires the presence of a modest 2175A bump. Additionally,modeling of the Swift-XRT X-ray spectrum confirms a large column density withNH = 10^22.58 cm^-2. Remarkably, this molecular gas has extinctionproperties, metallicity, and a CO-H2 ratio comparable to those of translucentmolecular clouds of the Milky Way, suggesting that star formation at high zproceeds in similar environments as today. However, the integrateddust-to-metals ratio is sub-Galactic, suggesting the dust is primarilyassociated with the molecular phase while the atomic gas has a much lowerdust-to-gas ratio. Sightlines like GRB 080607 serve as powerful probes ofnucleosynthesis and star-forming regions in the young universe and contributeto the population of -dark- GRB afterglows.



Author: J. X. Prochaska 1,2, Y. Sheffer 3, D.A. Perley 4, J. S. Bloom 4, L. A. Lopez 2, M. Dessauges-Zavadsky 5, H.-W. Chen 6, A. V. Fili

Source: https://arxiv.org/







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