Bright-End Excesses of the Lyα Luminosity Functions at z=5.7 and 6.6 Identified by Subaru/HSC Survey: Implications for the Faint AGN Contribution to Cosmic Reionization

Ryo Higuchi

We present number density excesses of bright-end luminosity functions (LFs) of Lyα emitters (LAEs) at z=5.7 and 6.6 identified by the narrowband imaging observations of Subaru/Hyper Suprime-Cam (HSC) SSP. We find the significant number density excesses made of 1 and 6 LAEs at z=5.7 and 6.6, respectively, at log L(Lyα)/[erg s^-1] > 43.7 beyond the extrapolation of the LFs from ~L*(Lyα). It is possible that the excesses of LAEs are made by AGN activities that brighten Lyα luminosities of the galaxies. In fact, Konno et al. (2016) find that all of z~2 LAEs with log L(Lyα)/[erg s^-1] >~ 43.5 show AGN activities based on their multiwavelength data analyses. Assuming that all of our z=5.7/6.6 LAEs at log L(Lyα)/[erg s^-1] >~ 43.7 are AGNs, we estimate the UV LFs of AGNs. Our UV LFs of AGNs are about 2-3 times lower than those derived by Giallongo et al. (2015) at z~6, including incompleteness corrections for Lyα faint AGNs. Our estimates infer that the ionizing photon contribution of faint AGNs to cosmic reionization would not be as large as those reported by Giallongo et al. (2015).