Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical Spectroscopy of X-ray sources in the Extended Chandra Deep Field
  South   We present the first results of our optical spectroscopy program aimed to
provide redshifts and identifications for the X-ray sources in the Extended
Chandra Deep Field South. A total of 339 sources were targeted using the IMACS
spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT.
We measured redshifts for 186 X-ray sources, including archival data and a
literature search. We find that the AGN host galaxies have on average redder
rest-frame optical colors than non-active galaxies, and that they live mostly
in the "green valley". The dependence of the fraction of AGN that are obscured
on both luminosity and redshift is confirmed at high significance and the
observed AGN space density is compared with the expectations from existing
luminosity functions. These AGN show a significant difference in the mid-IR to
X-ray flux ratio for obscured and unobscured AGN, which can be explained by the
effects of dust self-absorption on the former. This difference is larger for
lower luminosity sources, which is consistent with the dust opening angle
depending on AGN luminosity.

19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
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The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
2
The categories of this paper are: math