Abstract
Subaru/SuprimeCam narrowband photometry of the SSA22 field reveals the
presence of four Lyman continuum (LyC) candidates among a sample of 14 AGN. Two
show offsets and likely have stellar LyC in nature or are foreground
contaminants. The remaining two LyC candidates are Type I AGN. We argue that
the average LyC escape fraction of high redshift quasars is not likely to be
unity, as often assumed in the literature. From direct measurement we obtain
the average LyC-to-UV flux density ratio and ionizing emissivity for a number
of AGN classes and find it at least a factor of two lower than values obtained
assuming f_esc = 1. Comparing to recent Ly\alpha forest measurements, AGNs at
redshift z\sim3 make up at most \sim20% and as little as 3% of the total
ionizing budget. Our results suggest that AGNs are unlikely to dominate the
ionization budget of the Universe at high redshifts.
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