DETECTION OF LYMAN-ALPHA-EMITTING GALAXIES AT REDSHIFT-4.55

STUDIES of the formation and early history of galaxies have been hampe red by the difficulties inherent in detecting faint galaxy populations at high redshift. As a consequence, observations at the highest redsh ifts (z = 3.5-5) have been restricted to objects that are Intrinsicall y bright, These include quasars, radio galaxies, and some Lyman-alpha- emitting objects(1-3) that are very close to (within similar to 10 kpc )-and appear to be physically associated with-quasars. But the extreme ly energetic processes which make these objects easy to detect also ma ke them unrepresentative of normal (field) galaxies. Here we report th e discovery of two Lyntan-alpha-emitting galaxies at redshift z = 4.55 , which are sufficiently far from the nearest quasar (similar to 700 k pc) that radiation from the quasar is unlikely to provide the excitati on source of the Lyman-alpha emission. Instead, these galaxies appear to be undergoing their first burst of star formation, at a time when t he Universe was less than one billion years old.