Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Imaging of the Host Galaxies of Three X-Ray Selected BL Lacertae Objects   Hubble Space Telescope (HST) WFPC-2 I-band (F814W) images of three X-ray
selected BL Lacertae objects (MS1221.8+2452, MS1407.9+5954, & MS2143.4+0704)
reveal that each of these BL Lac objects is well-centered in an extended
nebulosity that is consistent in brightness and morphology with being light
from an elliptical galaxy at the previously reported redshifts of these BL Lac
objects. Each of the detected host galaxies have radial surface brightness
profiles that are well fit by a DeVaucouleurs' law with effective radii of
between 3 to 12 kpc (H_0=50 km s^{-1} Mpc^{-1}, q_0 = 0). The absolute
magnitudes of the host galaxies fall in the range -24.7 < M_I < -23.5, in the
range of luminosities determined for other BL Lacertae object host galaxies. In
addition to allowing the measurement of the host galaxy magnitudes and radial
surface brightness profiles, the HST images allow a search for substructure in
the host galaxies and the presence of close companion galaxies at spatial
resolutions not yet achievable from the ground. While no evidence was found for
any ``bars'' or spiral arms, ``boxy'' isophotes are present in the host galaxy
of at least one of the three objects observed as part of this study
(MS2143.4+0704). The apparent magnitudes and image properties of the companions
of the BL Lac objects are catalogued as part of this work. The three BL Lacs
appear to occur in diverse environments, from being fairly isolated
(MS1221.8+2452) to possibly being a member of a rich group of galaxies
(MS1407.9+5954).

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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: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: math
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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: stat
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The categories of this paper are: gr-qc