# A High Space Density of Luminous Lyman Alpha Emitters at z~6.5

## TL;DR

This study identifies a high density of luminous Lyman-alpha emitters at redshift around 6.5 using HST WISP data, revealing their potential role in cosmic reionization and the existence of large ionized regions in the early universe.

## Contribution

First systematic search for bright LAEs at z~6.5 with broad spectral coverage, providing new insights into their abundance and ionized environments.

## Key findings

- Detected two luminous LAEs at z=6.38 and 6.44.
- High number density of LAEs at this epoch.
- LAEs likely reside in large ionized bubbles.

## Abstract

We present the results of a systematic search for Lyman-alpha emitters (LAEs) at $6 \lesssim z \lesssim 7.6$ using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is $\sim 8 \times10^5$ Mpc$^3$, comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at $z=6.38$ and $6.44$ with line luminosities of L$_{\mathrm{Ly}\alpha} \sim 4.7 \times 10^{43}$ erg s$^{-1}$, putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of $7.7\times10^{-6}$ Mpc$^{-3}$. We argue that the LAEs reside in Mpc-scale ionized bubbles that allow the Lyman-alpha photons to redshift out of resonance before encountering the neutral IGM. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles.