Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Redshift Evolution of the 2-8 keV X-ray Luminosity Function   The high angular resolution and sensitivity of the Chandra X-ray Observatory
has yielded large numbers of faint X-ray sources with measured redshifts in the
soft (0.5-2 keV) and hard (2-8 keV) energy bands. Many of these sources show
few obvious optical signatures of active galactic nuclei (AGN). We use Chandra
observations of the Hubble Deep Field North region, A370, and the Hawaii Survey
Fields SSA13 and SSA22, together with the ROSAT Ultra Deep Survey soft sample
and the ASCA Large Sky Survey hard sample, to construct rest-frame 2-8 keV
luminosity functions versus redshift for all the X-ray sources, regardless of
their optical AGN characteristics. At z=0.1-1 most of the 2-8 keV light density
arises in sources with luminosities in the 10^42 erg/s to 10^44 erg/s range. We
show that the number density of sources in this luminosity range is rising, or
is at least constant, with decreasing redshift. Broad-line AGN are the dominant
population at higher luminosities, and these sources show the well-known rapid
positive evolution with increasing redshift to z~3. We argue that the dominant
supermassive black hole formation has occurred at recent times in objects with
low accretion mass flow rates rather than at earlier times in more X-ray
luminous objects with high accretion mass flow rates.

35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
34
The categories of this paper are: chem-ph