Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Galaxy evolution in a complex environment: a multi-wavelength study of
  HCG 7   [Abridged] The environment where galaxies are found heavily influences their
evolution. Close groupings, like the cores of galaxy clusters or compact
groups, evolve in ways far more dramatic than their isolated counterparts. We
have conducted a multiwavelength study of HCG7, consisting of four giant
galaxies: 3 spirals and 1 lenticular. We use Hubble Space Telescope (HST)
imaging to identify and characterize the young and old star cluster
populations. We find young massive clusters (YMC) mostly in the three spirals,
while the lenticular features a large, unimodal population of globular clusters
(GC) but no detectable clusters with ages less than ~Gyr. The spatial and
approximate age distributions of the ~300 YMCs and ~150 GCs thus hint at a
regular star formation history in the group over a Hubble time. While at first
glance the HST data show the galaxies as undisturbed, our deep ground-based,
wide-field imaging that extends the HST coverage reveals faint signatures of
stellar material in the intra-group medium. We do not detect the intra-group
medium in HI or Chandra X-ray observations, signatures that would be expected
to arise from major mergers. We find that the HI gas content of the individual
galaxies and the group as a whole are a third of the expected abundance. The
appearance of quiescence is challenged by spectroscopy that reveals an intense
ionization continuum in one galaxy nucleus, and post-burst characteristics in
another. Our spectroscopic survey of dwarf galaxy members yields one dwarf
elliptical in an apparent tidal feature. We therefore suggest an evolutionary
scenario for HCG7, whereby the galaxies convert most of their available gas
into stars without major mergers and result in a dry merger. As the conditions
governing compact groups are reminiscent of galaxies at intermediate redshift,
we propose that HCGs are appropriate for studying galaxy evolution at z~1-2.

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The categories of this paper are: math
21
The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: nucl-ex
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: nlin
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The categories of this paper are: cond-mat
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The categories of this paper are: chem-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