Molecular Hydrogen in the Damped Lyman-alpha System towards GRB 120815A at z=2.36
Abstract
We present the discovery of molecular hydrogen (H_2), including the presence of vibrationally-excited H_2^* in the optical spectrum of the afterglow of GRB 120815A at z=2.36 obtained with X-shooter at the VLT. Simultaneous photometric broad-band data from GROND and X-ray observations by Swift/XRT place further constraints on the amount and nature of dust along the sightline. The galactic environment of GRB 120815A is characterized by a strong DLA with log(N(H)/cm^-2) = 21.95 +/- 0.10, prominent H_2 absorption in the Lyman-Werner bands (log(N(H_2)/cm^-2) = 20.53 +/- 0.13) and thus a molecular gas fraction log f(H_2)=-1.14 +/- 0.15. The distance d between the absorbing neutral gas and GRB 120815A is constrained via photo-excitation modeling of fine-structure and meta-stable transitions of FeII and NiII to d = 0.5 +/- 0.1 kpc. The DLA metallicity ([Zn/H] = -1.15 +/- 0.12), visual extinction (A_V < 0.15 mag) and dust depletion ([Zn/Fe] = 1.01 +/- 0.10) are intermediate between the values of well-studied, H_2-deficient GRB-DLAs observed at high spectral resolution, and the approximately solar metallicity, highly-obscured and H_2-rich GRB 080607 sightline. With respect to N(H), metallicity, as well as dust-extinction and depletion, GRB 120815A is fairly representative of the average properties of GRB-DLAs. This demonstrates that molecular hydrogen is present in at least a fraction of the more typical GRB-DLAs, and H_2 and H_2^* are probably more wide-spread among GRB-selected systems than the few examples of previous detections would suggest.
Keywords
Cite
@article{arxiv.1304.7003,
title = {Molecular Hydrogen in the Damped Lyman-alpha System towards GRB 120815A at z=2.36},
author = {T. Krühler and C. Ledoux and J. P. U. Fynbo and P. M. Vreeswijk and S. Schmidl and D. Malesani and L. Christensen and A. De Cia and J. Hjorth and P. Jakobsson and D. A. Kann and L. Kaper and S. D. Vergani and P. M. J. Afonso and S. Covino and A. de Ugarte Postigo and V. D'Elia and R. Filgas and P. Goldoni and J. Greiner and O. E. Hartoog and B. Milvang-Jensen and M. Nardini and S. Piranomonte and A. Rossi and R. Sánchez-Ramírez and P. Schady and S. Schulze and V. Sudilovsky and N. R. Tanvir and G. Tagliaferri and D. J. Watson and K. Wiersema and R. A. M. J. Wijers and D. Xu},
journal= {arXiv preprint arXiv:1304.7003},
year = {2013}
}
Comments
21 pages, 14 figures, accepted for publication in A&A