2013MNRAS.432L...6B

Lyman α emitters (LAEs) are usually thought to be powered by star formation. It has been recently reported that a fraction of LAEs at redshift z ∼ 3-4 host an active galactic nuclei (AGNs). If an AGN is present, it could be obscured and undetectable in X-rays, but yet dominate the Lyα luminosity. We examine the properties of these AGN-powered LAEs at high redshift (z ≥ 6) using radiative transfer cosmological simulations and obtain a reliable criterion to identify them from their observed Lyα line and surface brightness. We find that these sources should have (a) negative line weighted skewness, Sw < 0, and (b) surface brightness profile full width at half-maximum ≥ 1.5arcsec. This parameter space cannot be populated by starburst LAEs. Thus, LAEs satisfying this criterion would be strong candidates for the presence of a hidden AGN powering their luminosity.