Lyman continuum leaking AGN in the SSA22 field

TL;DR

This study investigates the Lyman continuum leakage from AGN in the SSA22 field, finding that the average escape fraction is likely below unity and AGNs contribute a small fraction to the universe's ionizing budget at high redshift.

Contribution

It provides direct measurements of LyC escape fractions for AGN, challenging the assumption of unity escape fraction and quantifying AGN contribution to cosmic reionization.

Findings

Only two of four LyC candidates are likely genuine AGN LyC emitters.

The average LyC escape fraction for AGN is significantly less than 100%.

AGN contribute at most 12%, possibly as little as 5%, to the ionizing background at z~3.

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 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.