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

DOI: 
10.1051/0004-6361/201731382
Publication date: 
01/12/2017
Main author: 
Christensen L.
IAA authors: 
De Ugarte Postigo, A.;Cano, Z.;Sánchez-Ramírez, R.;Thöne, C.C.
Authors: 
Christensen L., Vergani S.D., Schulze S., Annau N., Selsing J., Fynbo J.P.U., De Ugarte Postigo A., Cañameras R., Lopez S., Passi D., Cortés-Zuleta P., Ellison S.L., D'Odorico V., Becker G., Berg T.A.M., Cano Z., Covino S., Cupani G., D'Elia V., Goldoni P., Gomboc A., Hammer F., Heintz K.E., Jakobsson P., Japelj J., Kaper L., Malesani D., Møller P., Petitjean P., Pugliese V., Sánchez-Ramírez R., Tanvir N.R., Thöne C.C., Vestergaard M., Wiersema K., Worseck G.
Journal: 
Astronomy and Astrophysics
Refereed: 
Yes
Publication type: 
Article
Volume: 
608
Pages: 
A84
Number: 
A84
Abstract: 
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. © ESO 2017.
Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85038215597&doi=10.1051%2f0004-6361%2f201731382&partnerID=40&md5=a41b6b640350e0b4b6064057855d6dc9
ADS Bibcode: 
2017A&A...608A..84C
Keywords: 
Galaxies: halos; Gamma rays: general; Quasars: Absorption lines