A Lyman-Alpha Galaxy at Redshift z=6.944

Searching for high redshift galaxies is one of the most active fields of observational cosmology and is essential to characterizing and understanding the formation and evolution of galaxies. Galaxies at redshift 6 are routinely found. Detection of z≈7 galaxies is however still rare. From z=6.5 to z=7 light dimming due to luminosity distance is 17% and the age of the Universe differs by 172 Myr. At these redshifts, the Universe is thought to be undergoing re-ionization. Lyman-α-emitting galaxies can be used to study cosmological reionization, because resonant scattering of Lyman-α photons should effectively hide them from view in a neutral universe.

We here present a Lyman-α emitting galaxy identified at redshift z = 6.944 in the COSMOS field, based on a combination of narrowband imaging and follow-up 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 Inter-Galactic Medium (IGM) neutral fraction at z ≈ 7, but further observations are planned and will help clarify the situation. Meantime, the object we present here is only the second Lyman-α-selected galaxy to be spectroscopically confirmed at z ≈7, and is considerably fainter than the previously known z ≈ 7 LAE (Iye et al. 2006).