A Lyman Alpha Galaxy at Redshift z=6.944 in the COSMOS Field

TL;DR

This paper reports the discovery of a faint Lyman-alpha emitting galaxy at redshift 6.944 in the COSMOS field, providing insights into the state of the intergalactic medium during reionization.

Contribution

It presents the identification and spectroscopic confirmation of a new high-redshift Lyman-alpha galaxy, the third such galaxy confirmed at redshift seven, expanding the sample of known early universe galaxies.

Findings

The galaxy is at redshift 6.944, close to the epoch of reionization.

It is 2-3 times fainter than previously confirmed galaxies at similar redshift.

Current data are consistent with a wide range of IGM neutral fractions at redshift seven.

Abstract

Lyman-alpha emitting galaxies can be used to study cosmological reionization, because a neutral intergalactic medium scatters Lyman-alpha photons into diffuse halos whose surface brightness falls below typical survey detection limits. Here we present the Lyman-alpha emitting galaxy LAE J095950.99+021219.1, identified at redshift z=6.944 in the COSMOS field using narrowband imaging and followup spectroscopy with the IMACS instrument on the Magellan I Baade telescope. With a single object spectroscopically confirmed so far, our survey remains consistent with a wide range of IGM neutral fraction at redshift seven, but further observations are planned and will help clarify the situation. Meantime, the object we present here is only the third Lyman-alpha selected galaxy to be spectroscopically confirmed at redshift seven, and is 2--3 times fainter than the previously confirmed redshift seven Lyman alpha galaxies.