Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A New Observational Upper Limit to the Low Redshift Ionizing Background
  Radiation   We report a new Fabry-Perot search for Halpha emission from the intergalactic
cloud HI 1225+01 in an attempt to measure the low redshift ionizing background
radiation. We set a new 2 sigma upper limit on Halpha emission of 8 mR (5 x
10^{-20} ergs cm^{-2} s^{-1} arcsec^{-2}). Conversion of this limit to limits
on the strength of the ionizing background requires knowledge of the ratio of
the projected to total surface area of this cloud, which is uncertain. We
discuss the plausible range of this ratio, and within this range find that the
strength of the ionizing backround is in the lower range of, but consistent
with, previous observational and theoretical estimates.

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The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
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The categories of this paper are: hep-th