Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multiwavelength study of massive galaxies at z~2. II. Widespread Compton
  thick AGN and the concurrent growth of black holes and bulges   Approximately 20-30% of 1.4<z<2.5 galaxies with K<22 (Vega) detected with
Spitzer MIPS at 24um show excess mid-IR emission relative to that expected
based on the rates of star formation measured from other multiwavelength
data.These galaxies also display some near-IR excess in Spitzer IRAC data, with
a spectral energy distribution peaking longward of 1.6um in the rest frame,
indicating the presence of warm-dust emission usually absent in star forming
galaxies. Stacking Chandra data for the mid-IR excess galaxies yields a
significant hard X-ray detection at rest-frame energies >6.2 keV. The stacked
X-ray spectrum rises steeply at >10 keV, suggesting that these sources host
Compton-thick Active Galactic Nuclei (AGNs) with column densities N_H~10^{24}
cm^-2 and an average, unobscured X-ray luminosity L_{2-8 keV}~(1-4)x10^43
erg/s. Their sky density(~3200 deg^-2) and space density (~2.6x10^-4 Mpc^-3)
are twice those of X-ray detected AGNs at z~2, and much larger than those of
previously-known Compton thick sources at similar redshifts. The mid-IR excess
galaxies are part of the long sought-after population of distant heavily
obscured AGNs predicted by synthesis models of the X-ray background. The
fraction of mid-IR excess objects increases with galaxy mass, reaching ~50-60%
for M~10^11 M_sun, an effect likely connected with downsizing in galaxy
formation. The ratio of theinferred black hole growth rate from these
Compton-thick sources to the global star formation rate at z=2 is similar to
the mass ratio of black holes to stars inlocal spheroids, implying concurrent
growth of both within the precursors oftoday's massive galaxies.

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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc
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The categories of this paper are: cs
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The categories of this paper are: physics
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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex
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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: solv-int
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ex