Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and Infrared Properties of the 2 Ms Chandra Deep Field-North
  X-ray Sources   We present an optical and NIR catalog for the X-ray sources in the 2 Ms
Chandra observation of the Hubble Deep Field-North region. We have high-quality
multicolor images of all 503 X-ray point sources and reliable spectroscopic
redshifts for 284. We spectroscopically identify six z>1 type II quasars. Our
spectroscopic completeness for the R<24 sources is 87%. The spectroscopic
redshift distribution shows two broad redshift spikes that have clearly grown
over those originally seen in the 1 Ms exposure. The spectroscopically
identified extragalactic sources already comprise 75% of the measured 2-8 keV
light. Redshift slices versus 2-8 keV flux show that an impressive 54% of the
measured 2-8 keV light arises from sources at z<1 and 68% from sources at z<2.
We use seven broadband colors and a Bayesian photometric redshift estimation
code to obtain photometric redshifts. The photometric redshifts are within 25%
of the spectroscopic redshifts for 94% of the non-broad-line sources with both
photometric and spectroscopic measurements. We use our wide wavelength coverage
to determine rest-frame colors for the X-ray sources with spectroscopic or
photometric redshifts. Many of the X-ray sources have the rest-frame colors of
evolved red galaxies and there is very little evolution in these colors with
redshift. We also determine absolute magnitudes and find that many of the
non-broad-line sources are more luminous than Mstar, even at high redshifts. We
therefore infer that deep X-ray observations may provide an effective way of
locating Mstar galaxies with colors similar to present-day early-type galaxies
to high redshifts. (Abridged)

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The categories of this paper are: mtrl-th
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: eess
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The categories of this paper are: quant-ph
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The categories of this paper are: math
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: cs