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Towards an understanding of the physical nature of MgII absorption systems

Published online by Cambridge University Press:  06 October 2005

D. B. Nestor
Affiliation:
Department of Astronomy, University of Florida, Gainesville, FL 32611, USA email: dbn@astro.ufl.edu
D. A. Turnshek
Affiliation:
Department of Physics & Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA email: turnshek@quasar.astro.pitt.edu, rao@everest.phyast.pitt.edu
S. M. Rao
Affiliation:
Department of Physics & Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA email: turnshek@quasar.astro.pitt.edu, rao@everest.phyast.pitt.edu
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Abstract

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We discuss issues concerning the physical nature of intervening MgII quasar absorption systems in light of results from our recent surveys using SDSS EDR QSO spectra and data obtained at the MMT. These surveys indicate an excess of weak ($W_0^{\lambda2796} \lesssim 0.3$Å) systems relative to the exponential $\partial N/\partial W_0$ distribution of stronger systems. The incidence of intermediate-strength lines shows remarkably little evolution with redshift, thereby constraining models for the nature of the clouds comprising these absorbers. The total distribution does evolve, with the incidence decreasing with decreasing redshift in a $W_0^{\lambda2796}$-dependent rate (the strongest systems evolve the fastest). This suggests that multiple populations that evolve at different rates contribute to the incidence in a $W_0^{\lambda2796}$-dependent manner. We also present two images of fields containing unprecedented “ultra-strong” ($W_0^{\lambda2796} \ge 4.0$Å) MgII absorbers.

Type
Contributed Papers
Copyright
© 2005 International Astronomical Union