Dr. Doron Chelouche
IAS

University of Florida Astronomy Colloquium - Apr. 18th, 2007

The Gaseous Halos of Galaxies and Quasars

It is well established that (strong) intervening metal absorption line systems in quasars spectra have their origin in large scale (~50kpc)  halos of galaxies. Nevertheless, little is known about the fundamental  physical properties of such gaseous halos. In this talk I will review  recent progress in the field and present new results from an ongoing  survey aimed at understanding the properties of cold gas in quasar  halos. A model for the  physical properties of cold gas in galaxy  halos will be outlined which is consistent with a large set of  observational constraints. New estimates for the total mass in cold gas around L* galaxies will be given and the implications for its origin  will be discussed. In addition, it will be shown that the same model  provides a natural explanation for the presence of absorbing and  emitting gaseous nebulae around quasars. This unification scheme  sheds light on old problems related to the physics of active galactic nuclei at present times, and in the early universe.