Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Intergalactic Medium and the Energy Distribution of Quasars   The ionizing spectral energy distribution of quasars is known to exhibit a
steepening of the distribution short-ward of 1050\AA. It has been assumed that
this change of power-law index from -1 to -2 is intrinsic to the quasars. We
study an alternative interpretation, in which a tenuous absorption screen is
responsible for the change of index. A successful spectral fit is obtained
using a total hydrogen density distribution decreasing with redshift as $\sim
(1+z)^{\xi}$ with $\xi$ of the order -3.5 if we suppose that the ionization
state of the intervening gas is controlled by the line-of-sight quasar. This
interpretation is not compatible, however, with the relative weakness of the
observed quasar intensities with respect to that of the local background
metagalactic radiation. Therefore, our interpretation in its present form
cannot be sustained.

9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org