Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A High Fraction of Mergers in the cluster MS1054-03 at z=0.83   We used the Hubble Space Telescope to take a wide field, multicolor image of
the high redshift cluster MS1054-03 at z=0.83. The Keck telescope was used to
take 200 redshifts in the field. We have a total of 81 spectroscopically
confirmed cluster members with deep WFPC2 imaging. A surprisingly large number
of these cluster members are mergers: 13 out of 77 galaxies are classified as
merger remnants, or mergers in progress. Most of these are red, and massive.
Their restframe B luminosities are amongst the brightest in the cluster: we
find that 5 out of the brightest 16 are mergers. No such bright mergers were
found in a lower redshift cluster with similar wide field coverage. The mergers
in MS1054-03 are preferentially found in the outskirts of the cluster. The
distribution of pairs in the outskirts of the cluster shows an excess of
galaxies with separation < 10 h^-1 kpc, which is independent confirmation of
the enhanced interaction rate. The fraction of mergers (17 %) is comparable to
the fraction of ellipticals (22 %). Hence up to 50 % of low redshift
ellipticals may have formed through mergers since z=1. There is no evidence for
strong star formation in most of the mergers. The mean stellar ages of the
mergers may therefore be much older than the ``assembly age'', i.e., the age
since the time the system was put together. These new results are qualitatively
consistent with predictions from hierarchical galaxy formation, and are
inconsistent with an early collapse for all early type galaxies.

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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: funct-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: cond-mat
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol