Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High Resolution Optical/Near-Infrared Imaging of Cool Ultraluminous
  Infrared Galaxies   We present high spatial resolution (FWHM 0.3-0.8") BIHK'-band imaging of a
sample of ultraluminous infrared galaxies with "cool" mid-infrared colors
(f25/f60 < 0.2) which select against AGN-like systems and which form a
complementary sample to the "warm" ULIGs of Surace et al. (1998). We find that
all of the cool ULIGs are either advanced mergers or are pre-mergers with
evidence for still-separate nuclei with separations greater than 600 pc.
Extended tidal features such as tails and loops as well as clustered star
formation are observed in most systems. This extended tidal structure suggests
a common progenitor geometry for most of the ULIGs: a plunging disk collision
where the disks are highly inclined with respect to each other. The underlying
host galaxies have H-band luminosities of 1-2.5 L*, very similar to that found
in the "warm" ULIGs. The nuclear regions of these galaxies have morphologies
and colors characteristic of a recent burst of star formation mixed with hot
dust and mildly extinguished by A_v=2-5 magnitudes; only in o ne case (IRAS
22491-1808) is there evidence for a compact emission region with colors similar
to an extinguished QSO. Most of the observed star-forming knots appear to have
very young (10 Myr) ages based on their optical/near-infrared colors. These
star-forming knots are insufficiently luminous to typically provide more than
10% of the high bolometric luminosity of the systems.

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The categories of this paper are: gr-qc
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The categories of this paper are: eess
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The categories of this paper are: math
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The categories of this paper are: atom-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-ex
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The categories of this paper are: nlin
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The categories of this paper are: cs
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The categories of this paper are: bayes-an
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: q-bio