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Solving the conundrum of intervening strong MgII absorbers towards GRBs and quasars

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posted on 2018-04-10, 15:33 authored by L. Christensen, S. D. Vergani, S. Schulze, N. Annau, J. Selsing, J. P. U. Fynbo, A. D. U. 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. Goldoni, A. 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
Previous studies have shown that the incidence rate of intervening strong Mg ii 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 Mg ii 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 ∆z = 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 Mg ii 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 Mg ii 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 Mg ii absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.



Astronomy and Astrophysics, 2017, 608, A84

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


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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 ANR16-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 IJCI2014-21669 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.



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