Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The shallow slope of the z~6 quasar luminosity function: limits from the
  lack of multiple image gravitational lenses   We place a limit on the logarithmic slope of the luminous quasar luminosity
function at z~6 of beta>-3.0 (90%) using gravitational lensing constraints to
build on the limit of beta>-3.3 (90%) derived from an analysis of the
luminosity distribution (Fan et al. 2003). This tight constraint is obtained by
noting that of the two quasars which are lensed by foreground galaxies, neither
are multiply imaged. These observations are surprising if the luminosity
function is steep because magnification bias results in an overabundance of
multiply imaged relative to singly imaged lensed quasars. Our Bayesian analysis
uses the a-posteriori information regarding alignments with foreground galaxies
of the two lensed quasars, and provides a constraint on beta that is nearly
independent of the uncertain evolution in the lens population. The results
suggest that the bright end of the quasar luminosity function continues to
flatten out to z~6, as is observed between z~3 and z~5 (Fan et al. 2001).
Provided that SDSS J1148-5251 at z=6.37 is magnified by an intervening lens
galaxy at z~5 (White et al. 2003), we also show that the high lens redshift in
this system implies a co-moving density of massive galaxies that is close to
constant out to high redshift. This is in agreement with the lack of redshift
evolution in the velocity function of dark-matter halos with velocity
dispersions near 200 km/sec as predicted by the Press-Schechter formalism. The
combination of constraints on the quasar luminosity function and lens galaxy
evolution are used to compute an improved estimate for the z~6 multiple image
lens fraction of ~1-3%.

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The categories of this paper are: hep-lat
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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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: ao-sci
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph