Solving the conundrum of intervening strong Mgii absorbers towards gamma-ray bursts and quasars

L. Christensen, S. D. Vergani, S. Schulze, N. Annau, J. Selsing, J. P.U. Fynbo, A. De Ugarte Postigo, R. Cañameras, S. Lopez, D. Passi, P. Cortés-Zuleta, S. L. Ellison, V. D'Odorico, G. Becker, T. A.M. Berg, Z. Cano, S. Covino, G. Cupani, V. D'Elia, P. GoldoniA. Gomboc, F. Hammer, K. E. Heintz, P. Jakobsson, J. Japelj, L. Kaper, D. Malesani, P. Møller, P. Petitjean, V. Pugliese, R. Sánchez-Ramírez, N. R. Tanvir, C. C. Thöne, M. Vestergaard, K. Wiersema, G. Worseck

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6 Citations (Scopus)


Previous studies have shown that the incidence rate of intervening strong Mgii absorbers towards gamma-ray bursts (GRBs) were a factor of 2-4 higher than towards quasars. Exploring the similar sized and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong Mgii absorbers with rest-frame equivalent widths Wλ2796 r > 1 Å towards GRBs and quasars in the redshift range 0:1 . z . 5. With large and similar sample sizes, and path length coverages of Δz = 57:8 and 254.4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1σ uncertainty levels at all redshifts. For absorbers at z < 2:3; the incidence towards GRBs is a factor of 1.5± 0.4 higher than the expected number of strong Mgii absorbers in Sloan Digital Sky Survey (SDSS) quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4 ± 0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high-spectralresolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS Mgii catalogues and high-spectral-resolution studies. The rest-frame equivalent-width distribution also agrees to within 1σ uncertainty levels between the GRB and quasar samples. Intervening strong Mgii absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.

Original languageEnglish
Article numberA84
JournalAstronomy and Astrophysics
Publication statusPublished - 1 Dec 2017

Bibliographical note

Funding Information:
We acknowledge valuable comments from an anonymous referee. L.C. and R.C. are supported by YDUN grant DFF 4090-00079. S.D.V. is supported by the French National Research Agency (ANR) under contract ANR- 16-CE31-0003 BEaPro. S.L. has been supported by FONDECYT grant number 1140838 and partially by PFB-06 CATA. A.d.U.P. and C.T. acknowledge support from Ramón y Cajal fellowships, and with RSR a BBVA Foundation Grant for Researchers and Cultural Creators, and the Spanish Ministry of Economy and Competitiveness through project AYA2014-58381-P. G.B. acknowledges support from the National Science Foundation through grant AST-1615814. Z.C. acknowledges support from the Juan de la Cierva Incorporación fellowship IJCI- 2014-21669 and from the Spanish research project AYA 2014-58381-P. P.J. and K.E.H. acknowledge support by a Project Grant (162948-051) from The Icelandic Research Fund. J.J. acknowledges support from NOVA and NWOFAPESP grant for advanced instrumentation in astronomy. R.S.R. acknowledges support from ASI (Italian Space Agency) through the Contract No. 2015-046- R.0 and from European Union Horizon 2020 Programme under the AHEAD project (grant agreement No. 654215). M.V. gratefully acknowledges financial support from the Danish Council for Independent Research via grant no. DFF 4002-00275.

Publisher Copyright:
© ESO 2017.

Other keywords

  • Galaxies: halos
  • Gamma rays: general
  • Quasars: Absorption lines


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