Spectroscopic identification of a galaxy at a probable redshift of z = 6.68

Abstract

The detection and identification of distant galaxies is an important goal of observational cosmology, as such galaxies are seen at a time when the Universe was very young. The development of new techniques and instrumentation permits the search for ever-fainter galaxies, and so aids attempts to determine when the first stars and galaxies formed. Here we report the identification of a galaxy at a probable redshift of 6.68, the most distant object yet detected. The galaxy's spectrum is characterized by an abrupt discontinuity at a wavelength λ~ 9,300Å, which we interpret as arising from the absorption of light at shorter wavelengths by hydrogen gas along the line of sight (the Lyman-α decrement), and by an emission line at λ~ 9,334Å, which we interpret as the Lyman-α line at a redshift of 6.68. The galaxy is relatively bright: the ultraviolet luminosity density contributed by this one galaxy is almost ten times the value measured at z = 3.