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Session 96 - QSO Absorption Systems.
Oral session, Wednesday, January 17
Salon del Rey South, Hilton

[96.01] Physical Properties of Lyman-alpha Forest and Damped Lyman-alpha Systems

V. P. Kulkarni (STScI, U. Chicago), S. M. Fall (STScI)

We present a review of our results regarding various physical properties of quasar absorption line systems, in particular, the Lyman-alpha forest and the damped Lyman-alpha systems. We made the first detection of the quasar proximity effect at low redshifts, using HST Key Project data on the Ly-\alpha forest for z < 1. This allowed the first empirical estimate of the intensity of the ionizing UV background at \langle z \rangle \sim 0.5 and showed evidence for evolution of the ionizing UV background with redshift. We have also studied the implications of non-thermal motions inside Ly-\alpha forest clouds for the statistics of these clouds. We showed that the distributions in H I column densities f(N) for systems with saturated Ly-\alpha lines and the extent (and sign) of N-\sigma correlations could differ from previous estimates, if the clouds possessed non-Maxwellian velocity distributions. We also present results of a study of the chemical properties of several damped Lyman-\alpha systems, based on published high-sensitivity observations. In particular, we examine the total (gas + solid phase) metallicity and the dust content of these systems. Results will also be presented of an analysis of an 18 km s^-1 resolution spectrum of the Ly-\alpha forest of the z = 2.1 quasar Q1331+170, performed in collaboration with Dr. D. G. York, Dr. D. E. Welty (U. Chicago), Dr. R. F. Green, Dr. K. Huang (NOAO) and Dr. J. Bechtold (U. Arizona). One of the main results is some evidence for small-scale clustering among the Ly-\alpha forest clouds.

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