Аннотация
We presents results from a spectroscopic survey of $z\sim5$ quasars in the
CFHT Legacy Survey (CFHTLS). Using both optical color selection and a
likelihood method we select 97 candidates over an area of 105 deg$^2$ to a
limit of $i_AB < 23.2$, and 7 candidates in the range $23.2 < i_AB
< 23.7$ over an area of 18.5 deg$^2$. Spectroscopic observations for 43
candidates were obtained with Gemini, MMT, and LBT, of which 37 are $z>4$
quasars. This sample extends measurements of the quasar luminosity function
$\sim$1.5 mag fainter than our previous work in SDSS Stripe 82. The resulting
luminosity function is in good agreement with our previous results, and
suggests that the faint end slope is not steep. We perform a detailed
examination of our survey completeness, particularly the impact of the
Ly$\alpha$ emission assumed in our quasar spectral models, and find hints that
the observed Ly$\alpha$ emission from faint $z\sim5$ quasars is weaker than for
$z\sim3$ quasars at a similar luminosity. Our results strongly disfavor a
significant contribution of faint quasars to the hydrogen-ionizing background
at $z=5$.
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