A Galaxy at z = 6.545 and Constraints on the Epoch of Reionization

Research paper by Daniel Stern, Sarah A. Yost, Megan E. Eckart, Fiona A. Harrison, David J. Helfand, S. G. Djorgovski, Sangeeta Malhotra, James E. Rhoads

Indexed on: 19 Jul '04Published on: 19 Jul '04Published in: Astrophysics


We report the discovery of a Lyman-alpha-emitting galaxy at redshift z=6.545 serendipitously identified in the course of spectroscopic follow-up of hard X-ray sources on behalf of the Serendipitous Extragalactic X-Ray Source Identification (SEXSI) survey. The line flux of the galaxy, 2.1e-17 erg/cm2/s, is similar to line fluxes probed by narrow-band imaging surveys; the 5.2 square-arcminutes surveyed implies a surface density of z~6.5 Lyman-alpha emitters somewhat higher than that inferred from narrow-band surveys. This source marks the sixth Lyman-alpha-emitting galaxy identified at z~6.5, a redshift putatively beyond the epoch of reionization when the damping wings of the neutral hydrogen of the intergalactic medium is capable of severely attenuating Lyman-alpha emission. By comparing the Lyman-alpha emitter luminosity functions at z~5.7 and z~6.5, we infer that the intergalactic medium may remain largely reionized from the local universe out to z~6.5.