Dusty MgII Absorbers: Implications for the GRB/Quasar Incidence Discrepancy

Abstract

There is nearly a factor of four difference in the number density of intervening MgII absorbers as determined from gamma-ray burst (GRB) and quasar lines of sight. We use a Monte-Carlo simulation to test if a dust extinction bias can account for this discrepancy. We apply an empirically determined relationship between dust column density and MgII rest equivalent width to simulated quasar sight-lines and model the underlying number of quasars that must be present to explain the published magnitude distribution of SDSS quasars. We find that an input MgII number density dn/dz of 0.273 +- 0.002 over the range 0.4 <= z <= 2.0 and with MgII equivalent width W_0 >= 1.0 angstroms accurately reproduces observed distributions. From this value, we conclude that a dust obstruction bias cannot be the sole cause of the observed discrepancy between GRB and quasar sight-lines: this bias is likely to reduce the discrepancy only by ~10%.

11 pages (including 4 figures). ApJ Accepted Revision: Corrected author list

References in corpus (7)

• The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy
• Lensing, reddening and extinction effects of MgII absorbers from z=0.4 to z=2
• High-Redshift Starbursting Dwarf Galaxies Revealed by GRB Afterglows
• Intervening Metal Systems in GRB and QSO sight-lines: The Mgii and Civ Question
• Disparate MgII Absorption Statistics towards Quasars and Gamma-Ray Bursts : A Possible Explanation
• On the Incidence of C IV Absorbers Along the Sightlines to Gamma-Ray Bursts
• Direct Observational Test Rules Out Small MgII Absorbers

Cited by in corpus (11)

• The Host Galaxies of Swift Dark Gamma-Ray Bursts: Observational Constraints on Highly Obscured and Very High-Redshift GRBs
• Casting light on the 'anomalous' statistics of Mg II absorbers toward Gamma-Ray Burst afterglows: the incidence of weak systems
• Dusty MgII absorbers: population statistics, extinction curves and gamma-ray burst sightlines
• Incidence of MgII absorbers towards Blazars and the GRB/QSO puzzle
• A gravitational lensing explanation for the excess of strong Mg-II absorbers in GRB afterglow spectra
• The Redshift Distribution of Intervening Weak MgII Quasar Absorbers and a Curious Dependence on Quasar Luminosity
• Constraints on the relative sizes of intervening Mg II-absorbing clouds and quasar emitting regions
• Non variability of intervening absorbers observed in the UVES spectra of the "naked-eye" GRB080319
• On the significance of the excess number of strong MgII absorbers observed towards Gamma-ray bursts
• Clustering of galaxies around GRB sight-lines
• GRBs as Probes of the IGM