Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Broad-Line and Narrow-Line Regions of the LINER NGC 4579   We report the discovery of an extremely broad H-alpha emission line in the
LINER nucleus of NGC 4579. From ground-based observations, the galaxy was
previously known to contain a Type 1 nucleus with a broad H-alpha line of FWHM
= 2300 km/s and FWZI ~ 5000 km/s. New spectra obtained with the Hubble Space
Telescope and a 0.2 arcsec-wide slit reveal an H-alpha component with FWZI ~
18,000 km/s. The line is not obviously double-peaked, but it does possess
shoulders on the red and blue sides which resemble the H-alpha profiles of
double-peaked emitters such as NGC 4203 and NGC 4450. This similarity suggests
that the very broad H-alpha profile in NGC 4579 may represent emission from an
accretion disk. Three such objects have been found recently in two HST programs
which have targeted a total of 30 galaxies, demonstrating that double-peaked or
extremely broad-line emission in LINERs must be much more common than would be
inferred from ground-based surveys. The ratio of the narrow [S II] 6716, 6731
lines shows a pronounced gradient indicating a steep rise in density toward the
nucleus. The direct detection of a density gradient within the inner arcsecond
of the narrow-line region confirms expectations from previous observations of
linewidth-critical density correlations in several LINERs.

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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: math
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas
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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: hep-ph
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The categories of this paper are: ao-sci