The Proximity Effect and the UV Radiation Background
Session 28 -- QSO Absorption-Line Studies with HST and Keck
Oral presentation, Tuesday, June 13, 1995, 2:00pm - 5:30pm

## [28.03] The Proximity Effect and the UV Radiation Background

Limin Lu (Caltech)

The level of the metagalactic UV ionizing radiation background is of interest for many astrophysical problems. The UV radiation background affects the ionization state of the intergalactic medium. It also has effects on the formation process of galaxies through photoionization heating. The origin of the UV radiation background is also interesting: Is the background dominated by the UV fluxes from quasars and active galactic nuclei? Do galaxies contribute appreciably to this background? How does the UV radiation background change with redshift? Direct estimates of the UV radiation background upto the redshift of $\sim 4$ can now be made using the so-called proximity effect, i.e., the depopulation of Ly$\alpha$ forest clouds in the vicinity of quasars due to the enhanced ionization from the nearby quasars. In this talk, I will review recent progresses made in the determinations of the UV radiation background at \$0 Tuesday program listing