Spectroscopic Ultraluminous Lyα Luminosity Functions at z = 5.7 and z = 6.6 from HEROES: Evidence for Ionized Bubbles

We present spectroscopic Ly α luminosity functions (LFs) at z = 5.7 and z = 6.6 based on a large 209 source sample of Ly α emitter (LAE) candidates identified in Subaru/Hyper Suprime-Cam narrowband imaging and confirmed with Keck II/DEIMOS spectroscopy over a multiyear observing campaign. After applying photometric and spectroscopic cuts to produce homogeneous samples, we use the resulting samples of 49 z = 5.7 and 56 z = 6.6 LAEs to compute spectroscopic LAE LFs at each redshift. We correct our LFs for incompleteness using a source-injection simulation. We find excellent agreement with current spectroscopic and photometric LAE LFs from the literature. We look for evolution over the redshift range z = 5.7–6.6. We find a strong convergence of the LFs at L Lyα ≳ 10 43.4 erg s −1 . This convergence (noted in previous literature) provides strong evidence that the most luminous LAEs at z = 6.6 form ionized bubbles around themselves, allowing for greater Ly α transmission through the neutral intergalactic medium, which is measured as an increase in the bright end of the z = 6.6 LF over the expected evolution in the LF based on the faint end. We infer that ultraluminous LAEs may play a significant role in reionization.