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Infrared molecular hydrogen lines in GRB host galaxies

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posted on 2019-09-17, 15:34 authored by K Wiersema, A Togi, D Watson, L Christensen, JPU Fynbo, BP Gompertz, AB Higgins, AJ Levan, SR Oates, S Schulze, JDT Smith, ER Stanway, RLC Starling, D Steeghs, NR Tanvir
Molecular species, most frequently H2, are present in a small, but growing, number of gammaray burst (GRB) afterglow spectra at redshifts z ∼ 2−3, detected through their rest-frame UV absorption lines. In rare cases, lines of vibrationally excited states of H2 can be detected in the same spectra. The connection between afterglow line-of-sight absorption properties of molecular (and atomic) gas, and the observed behaviour in emission of similar sources at low redshift, is an important test of the suitability of GRB afterglows as general probes of conditions in star formation regions at high redshift. Recently, emission lines of carbon monoxide have been detected in a small sample of GRB host galaxies, at sub-mm wavelengths, but no searches for H2 in emission have been reported yet. In this paper we perform an exploratory search for rest-frame K band rotation-vibrational transitions of H2 in emission, observable only in the lowest redshift GRB hosts (z 0.22). Searching the data of four host galaxies, we detect a single significant rotation-vibrational H2 line candidate, in the host of GRB 031203. Reanalysis of Spitzer mid-infrared spectra of the same GRB host gives a single low significance rotational line candidate. The (limits on) line flux ratios are consistent with those of blue compact dwarf galaxies in the literature. New instrumentation, in particular on the JWST and the ELT, can facilitate a major increase in our understanding of the H2 properties of nearby GRB hosts, and the relation to H2 absorption in GRBs at higher redshift.


It is a pleasure to thank the staff at Isaac Newton Group of telescopes for their help in obtaining the LIRIS observations in this paper, and Jose Acosta Pulido for development of (and friendly assistance with) the LIRISDR software. We thank the anonymous referee for their constructive feedback. We acknowledge M. Michałowski and M. Arabsalmani for useful discussions. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 60.A-9022(C), 381.D-0723(C), and 084.A-0260(B). The William Herschel Telescope and its override programme (W/2015A/11 for observations in this paper) are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. AT is grateful for support from the National Science Foundation under grant no. 1616828. KW, NRT, and RLCS acknowledge funding from Science & Technology Facilities Council. The Cosmic Dawn center is funded by the Danish National Research Foundation.



Monthly Notices of the Royal Astronomical Society, 2018, 481 (1), pp. 1126-1132 (7)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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