New constraints on the physical conditions in H$_2$-bearing GRB-host damped Lyman-$α$ absorbers

K. E. Heintz; J. Bolmer; C. Ledoux; P. Noterdaeme; J. -K. Krogager; J. P. U. Fynbo; P. Jakobsson; S. Covino; V. D'Elia; M. De Pasquale; D. H. Hartmann; L. Izzo; J. Japelj; D. A. Kann; L. Kaper; P. Petitjean; A. Rossi; R. Salvaterra; P. Schady; J. Selsing; R. Starling; N. R. Tanvir; C. C. Thöne; A. de Ugarte Postigo; S. D. Vergani; D. Watson; K. Wiersema; T. Zafar

doi:10.1051/0004-6361/201936250

paper

New constraints on the physical conditions in H $_{2}$ -bearing GRB-host damped Lyman- $α$ absorbers

arXiv:1908.02309 · doi:10.1051/0004-6361/201936250

Abstract

We report the detections of molecular hydrogen (H $_{2}$ ), vibrationally-excited H $_{2}$ (H $_{2}^{*}$ ), and neutral atomic carbon (CI), in two new afterglow spectra of GRBs\,181020A ( $z = 2.938$ ) and 190114A ( $z = 3.376$ ), observed with X-shooter at the Very Large Telescope (VLT). Both host-galaxy absorption systems are characterized by strong damped Lyman- $α$ absorbers (DLAs) and substantial amounts of molecular hydrogen with $lo g N$ (HI, H $_{2}$ ) = $22.20 \pm 0.05, 20.40 \pm 0.04$ (GRB\,181020A) and $lo g N$ (HI, H $_{2}$ ) = $22.15 \pm 0.05, 19.44 \pm 0.04$ (GRB\,190114A). The DLA metallicites, depletion levels and dust extinctions are [Zn/H] = $- 1.57 \pm 0.06$ , [Zn/Fe] = $0.67 \pm 0.03$ , and $A_{V} = 0.27 \pm 0.02$ \,mag (GRB\,181020A) and [Zn/H] = $- 1.23 \pm 0.07$ , [Zn/Fe] = $1.06 \pm 0.08$ , and $A_{V} = 0.36 \pm 0.02$ \,mag (GRB\,190114A). We then examine the molecular gas content of all known H $_{2}$ -bearing GRB-DLAs and explore the physical conditions and characteristics of these systems. We confirm that H $_{2}$ is detected in all CI- and H $_{2}^{*}$ -bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H $_{2}$ absorbers. We find that a large molecular fraction of $f_{H_{2}} ≳ 1 0^{- 3}$ is required for CI to be detected. The defining characteristic for H $_{2}^{*}$ to be present is less clear, though a large H $_{2}$ column density is an essential factor. We then derive the H $_{2}$ excitation temperatures of the molecular gas and find that they are relatively low with $T_{ex} \approx 100 - 300$ \,K, however, there could be evidence of warmer components populating the high- $J$ H $_{2}$ levels in GRBs\,181020A and 190114A. Finally, we demonstrate that the otherwise successful X-shooter GRB afterglow campaign is hampered by a significant dust bias excluding the most dust-obscured H $_{2}$ absorbers from identification [Abridged].

arXiv comment15 pages, 15 figures + Appendix. Accepted for publication in A&A

New constraints on the physical conditions in H $_{2}$ -bearing GRB-host damped Lyman- $α$ absorbers

Abstract

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Cited by in corpus (9)

New constraints on the physical conditions in H2​-bearing GRB-host damped Lyman-α absorbers

Abstract

References in corpus (87)

Cited by in corpus (9)

New constraints on the physical conditions in H $_{2}$ -bearing GRB-host damped Lyman- $α$ absorbers