Detection of Lyman-α-emitting galaxies at redshift 4.55

STUDIESof the formation and early history of galaxies have been hampered by the difficulties inherent in detecting faint galaxy populations at high redshift. As a consequence, observations at the highest redshifts (z = 3.5–5) have been restricted to objects that are intrinsically bright. These include quasars, radio galaxies, and some Lyman-α-emitting objects1–3 that are very close to (within ∼10kpc)—and appear to be physically associated with—quasars. But the extremely energetic processes which make these objects easy to detect also make them unrepresentative of normal (field) galaxies. Here we report the discovery of two Lyman-α-emitting galaxies at redshift z = 4.55, which are sufficiently far from the nearest quasar (∼700kpc) that radiation from the quasar is unlikely to provide the excitation source of the Lyman-α emission. Instead, these galaxies appear to be undergoing their first burst of star formation, at a time when the Universe was less than one billion years old.