Spectroscopic confirmation of an ultra-faint galaxy at the epoch of reionization (original) (raw)

Within one billion years of the Big Bang, intergalactic hydrogen was ionized by sources emitting ultraviolet and higher energy photons. This was the final phenomenon to globally affect all the baryons (visible matter) in the Universe. It is referred to as cosmic reionization and is an integral component of cosmology. It is broadly expected that intrinsically faint galaxies were the primary ionizing sources due to their abundance in this epoch. However, at the highest redshifts (z > 7.5; lookback time 13.1 Gyr), all galaxies with spectroscopic confirmations to date are intrinsically bright and therefore not necessarily representative of the general population. Here we report the unequivocal spectroscopic detection of a low luminosity galaxy at z > 7.5. We detected the Lyman-alpha (Lyα) emission line at ∼ 10504Å in two separate observations 1