Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The proximity Effect on the Lyman alpha Forest due to a Foreground QSO   We present the results of our study on three close pairs of QSOs. Our results
are consistent with the existence of a proximity effect due to the foreground
QSO, but due to its weakness we can only reject the absence of such effect at
approx. 1 sigma level. By modelling this proximity effect in terms of a simple
photoionisation model, we find the best value for the UV ionizing background to
be approx. 10**(-20.5) erg cm**(-2) s**(-1) Hz**(-1) srad**(-1) at the Lyman
limit, and an absolute lower limit (95\% confidence) of 10**(-21.8) in the same
units. This lower limit rejects a number of models for the UV background where
it is mostly contributed by QSOs and absorption by Lyman limit systems is taken
into account.

28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat