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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