Lyman continuum leaking AGN in the SSA22 field
  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 low luminosity AGN 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~3 make up at most ~12% and as little as ~5% of
the total ionizing budget. Our results suggest that AGNs are unlikely to
dominate the ionization budget of the Universe at high redshifts.
