Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The extinction by dust in the outer parts of spiral galaxies   To investigate the distribution of dust in Sb and Sc galaxies we have
analyzed near-infrared and optical surface photometry for an unbiased sample of
37 galaxies. Since light in the $K$-band is very little affected by extinction
by dust, the $B-K$ colour is a good indicator of the amount of extinction, and
using the colour-inclination relation we can statistically determine the
extinction for an average Sb/Sc galaxy. We find in general a considerable
amount of extinction in spiral galaxies in the central regions, all the way out
to their effective radii. In the outer parts, at D$_{K,21}$, or at 3 times the
typical exponential scale lengths of the stellar distribution , we find a
maximum optical depth of 0.5 in $B$ for a face-on galaxy. If we impose the
condition that the dust is distributed in the same way as the stars, this upper
limit would go down to 0.1.

18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
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The categories of this paper are: eess
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The categories of this paper are: stat
31
The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn