Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-05-06
Astronomy and Astrophysics
Astrophysics
6 pages, 4 figures, uses iauc.cls. To appear in IAU 199 conf. proc.: "Probing Galaxies through Quasar Absorption Lines," eds.
Scientific paper
10.1017/S1743921305002498
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 $W_0^{\lambda2796} \lesssim 0.3$\AA) systems relative to the exponential dN/dW 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'' ($W_0^{\lambda2796} \ge 4.0$\AA) MgII absorbers.
Nestor Daniel. B.
Rao Someswara M.
Turnshek David A.
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