Galaxy counterparts of intervening high-z sub-DLAs/DLAs and Mg ii absorbers towards gamma-ray bursts

Creators: Schulze, S.; Fynbo, J. P. U.; Milvang-Jensen, B.; Rossi, A.; Jakobsson, P.; Ledoux, C.; De Cia, A.; Krühler, T.; Mehner, A.; Björnsson, G.; Chen, H.-W.; Vreeswijk, P. M.; Perley, D. A.; Hjorth, J.; Levan, A. J.; Tanvir, N. R.; Ellison, S.; Møller, P.; Worseck, G.; Chapman, R.; Dall'Aglio, A.; Letawe, G.

Abstract

We present the first search for galaxy counterparts of intervening high-z (2 < z < 3.6) sub-damped Lyα absorbers (sub-DLAs) and DLAs towards gamma-ray bursts (GRBs). Our final sample comprises five intervening sub-DLAs and DLAs in four GRB fields. To identify candidate galaxy counterparts of the absorbers we used deep optical- and near-infrared imaging, and low-, mid- and high-resolution spectroscopy acquired with 6-m to 10-m class telescopes, the Hubble and the Spitzer Space Telescopes. Furthermore, we used the spectroscopic information and spectral-energy-distribution fitting techniques to study them in detail. Our main result is the detection and spectroscopic confirmation of the galaxy counterpart of the intervening DLA at z = 3.096 in the field of GRB 070721B (z_GRB = 3.6298) as proposed by other authors. We also identify good candidates for the galaxy counterparts of the two strong Mg ii absorbers at z = 0.6915 and 1.4288 towards GRB 050820A (z_GRB = 2.615). The properties of the detected DLA galaxy are typical for Lyman-break galaxies (LBGs) at similar redshifts; a young, highly star-forming galaxy that shows evidence for a galactic outflow. This supports thehypothesis that a DLA can be the gaseous halo of an LBG. In addition, we report a redshift coincidence of different objects associated with metal lines in the same field, separated by 130–161 kpc. The high detection rate of three correlated structures on a length scale as short as ~150 kpc in two pairs of lines of sight is intriguing. The absorbers in each of these are most likely not part of the same gravitationally bound structure. They more likely represent groups of galaxies.

Additional Information

© 2012 ESO. Article Published by EDP Sciences. Received 14 December 2011; Accepted 24 July 2012. Published online 01 October 2012. Based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of the programs 075.A-0603, 075.A-0385, 077.A-0312, 084.A-0303, 177.A-0591 and 275.D-5022. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a co-operative agreement with the NSF on behalf of the Gemini partnership. We thank the referee for a careful reading of the manuscript and for helpful comments that improved this paper. S.S., A.D.C. and P.J. acknowledge support by a Grant of Excellence from the Icelandic Research Fund. J.P.U.F. acknowledges support form the ERC-StG grant EGGS-278202. A.R. acknowledges support by the Thüringer Landessternwarte Tautenburg and by the Graduierten-Akademie Jena, Germany. S.S. thanks D. Malesani (Dark Cosmology Centre, Copenhagen) for many productive and valuable discussions and D. A. Kann (Thüringer Landessternwarte Tautenburg, Germany) for corrections and comments on the manuscript.

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