Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local
  Universe   We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies
in the local universe. Herein, we compare GALEX UV and visible--NIR images of
189 nearby (D$<$40 Mpc) S0--Sm galaxies included in the GALEX Atlas of Nearby
Galaxies and present the first catalogue of XUV-disk galaxies. We find that
XUV-disk galaxies are surprisingly common but have varied relative (UV/optical)
extent and morphology. Type~1 objects ($\ga$20% incidence) have structured,
UV-bright/optically-faint emission features in the outer disk, beyond the
traditional star formation threshold. Type~2 XUV-disk galaxies ($\sim$10%
incidence) exhibit an exceptionally large,
UV-bright/optically-low-surface-brightness (LSB) zone having blue $UV-K_s$
outside the effective extent of the inner, older stellar population, but not
reaching extreme galactocentric distance. If the activity occuring in XUV-disks
is episodic, a higher fraction of present-day spirals could be influenced by
such outer disk star formation. Type~1 disks are associated with spirals of all
types, whereas Type~2 XUV-disks are predominantly found in late-type spirals.
Type~2 XUV-disks are forming stars quickly enough to double their [presently
low] stellar mass in the next Gyr (assuming a constant SF rate). XUV-disk
galaxies of both types are systematically more gas-rich than the general galaxy
population. Minor external perturbation may stimulate XUV-disk incidence, at
least for Type~1 objects. XUV-disks are the most actively evolving galaxies
growing via inside-out disk formation in the current epoch, and may constitute
a segment of the galaxy population experiencing significant, continued gas
accretion from the intergalactic medium or neighboring objects.

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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: econ
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The categories of this paper are: patt-sol
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th