An Ultraluminous Lyman Alpha Emitter with a Blue Wing at z=6.6

TL;DR

This paper reports the discovery of the most luminous high-redshift Lyman Alpha Emitting galaxy, COLA1, which exhibits a unique multi-component line profile with a blue wing, providing insights into the ionization state of the early universe.

Contribution

It presents the first detection of a highly luminous LAE at z=6.6 with a blue wing in its Lyman alpha profile, indicating a highly ionized environment and potential infall.

Findings

COLA1 is the most luminous LAE at z=6.6.

It shows a multi-component Lyman alpha line with a blue wing.

The galaxy may reside in a highly ionized region of the intergalactic medium.

Abstract

We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized region of the intergalactic medium and could have significant infall. If this interpretation is correct, then ultra-luminous LAEs like COLA1 offer a unique opportunity to determine the properties of the HII regions around these galaxies which will help in understanding the ionization of the z ~ 7 intergalactic medium.