Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Detection of Lyman-alpha Absorption from Nine Nearby Galaxies   We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in
the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs
and AGN as probes. The foreground galaxies are intercepted between 26 and 199
h-1 kpc from their centers, and in all cases we detect Lya within +/-500 km/s
of the galaxies' systemic velocities. The intervening galaxies have a wide
range of luminosities, from M_B = -17.1 to -20.0, and reside in various
environments: half the galaxies are relatively isolated, the remainder form
parts of groups or clusters of varying richness. The equivalent widths of the
Lya lines range from 0.08 - 0.68 A and, with the notable exception of
absorption from one pair, crudely correlate with sightline separation in a way
consistent with previously published data, though the column densities derived
from the lines do not. The lack of correlation between line strength and galaxy
luminosity or, in particular, the environment of the galaxy, suggests that the
absorption is not related to any individual galaxy, but arises in gas which
follows the same dark-matter structures that the galaxies inhabit.

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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-ex