CASTING LIGHT ON THE 'ANOMALOUS' STATISTICS OF Mg II ABSORBERS TOWARD GAMMA-RAY BURST AFTERGLOWS: THE INCIDENCE OF WEAK SYSTEMS
- Departamento de AstronomIa, Universidad de Chile, Casilla 36-D, Santiago (Chile)
- Department of Astronomy, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720-3411 (United States)
- Department of Astronomy, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 (United States)
- Geneva Observatory, University of Geneva, 51, Ch. des Maillettes, 1290 Sauverny (Switzerland)
We revisit echelle spectra (spectral resolution R approx 40,000) of eight gamma-ray burst (GRB) afterglows to obtain the incidence (dN/dz) of weak intervening Mg II systems at a mean redshift of (z) = 1.5. We show that dN/dz of systems having rest-frame equivalent widths 0.07 A <=W{sub r}{sup Mg}{sub I}{sub I}<1 A toward GRBs is statistically consistent with the incidence toward quasi-stellar objects (QSOs). Our result is in contrast to the results for Mg II systems having W{sub r} >= 1 A, where dN/dz toward GRBs has been found to be larger than toward QSOs by a factor of approx4. We confirm the overdensity albeit at a factor of approx3 only. This suggests that any explanation for the GRB/QSO discrepancy, be it intrinsic to the absorbers or a selection effect, should be inherent only to the galaxies that host strong absorbers in the line of sight to GRBs. We argue that, of all scenarios that have been proposed, lensing amplification is the one that could explain the strong Mg II enhancement while allowing for no significant enhancement in the weak absorbers.
- OSTI ID:
- 21378090
- Journal Information:
- Astrophysical Journal, Vol. 706, Issue 2; Other Information: DOI: 10.1088/0004-637X/706/2/1309; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
THE REDSHIFT DISTRIBUTION OF INTERVENING WEAK Mg II QUASAR ABSORBERS AND A CURIOUS DEPENDENCE ON QUASAR LUMINOSITY
AN INDEPENDENT MEASUREMENT OF THE INCIDENCE OF Mg II ABSORBERS ALONG GAMMA-RAY BURST SIGHT LINES: THE END OF THE MYSTERY?