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

TL;DR

This study measures Ly-alpha luminosity functions at redshifts 5.7 and 6.6, providing evidence that ultraluminous LAEs contribute significantly to cosmic reionization by forming ionized bubbles.

Contribution

First spectroscopic Ly-alpha luminosity functions at these redshifts derived from a large sample, revealing the role of ultraluminous LAEs in reionization.

Findings

Strong convergence of luminosity functions at high luminosities

Evidence for ionized bubbles around ultraluminous LAEs

Ultraluminous LAEs likely influence reionization

Abstract

We present spectroscopic Ly$\alpha$ luminosity functions (LFs) at z = 5.7 and z = 6.6 based on a large 209 source sample of Ly$\alpha$ emitter (LAE) candidates identified in Subaru/Hyper Suprime-Cam narrowband imaging and confirmed with Keck II/DEIMOS spectroscopy over a multi-year 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(Ly$\alpha$) > $10^{43.4}$ 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$\alpha$ 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.