A RADIO-QUIET GALAXY AT REDSHIFT Z=3.409

We report the discovery of an unresolved radio-quiet object with redshift z(em) = 3.409 and visual magnitude V congruent-to 24.3 +/- 0.5. The object was identified during an imaging search for Ly-alpha emission near the redshift of a z(abs) = 3.390 damped Ly-alpha absorption-line system which appears in the spectrum of the z(em) = 4.11 QSO 0000-2619. For H(o) = 50 km s-1 Mpc-1 and q(o) = 0.5, we find that the bulk of the object's Ly-alpha and continuum emission comes from an unresolved region less than 9 kpc (FWHM congruent-to 1".2), and its absolute magnitude in the rest-frame ultraviolet near Ly-alpha is approximately -21.2. A long-slit CCD spectrum at 500 km s-1 resolution shows that it has kinematically unresolved Ly-alpha emission with a rest equivalent width in the range approximately 10-20 angstrom. The object's properties are therefore consistent with those of a galaxy or a burst of star formation in a galaxy. Although a number of high-redshift objects have been identified as radio galaxies, these objects are clearly active, having QSO-like luminosities in the rest-frame optical and radio. This new object would be the highest redshift radio-quiet galaxy known. The object is observed to be approximately 135 kpc (19") in projection from the sight line to the QSO. Previously unidentified weak absorption lines due to low- and high-ionization metals are possibly present in the QSO spectrum at z(abs) = 3.409 (i.e., at a redshift consistent with the emission-line redshift). If present, they would indicate the existence of an extended, gaseous region associated with the optical object. The presence of metals in the extended gas would suggest that it has been enriched by star formation. However, if this absorption system proves not to be real, then this places an upper limit on the size/covering factor of any extended absorbing region surrounding the galaxy. No emission at the redshift of the damped Ly-alpha absorber is detected. The damped absorber has neutral hydrogen column density N(H I) congruent-to 3 x 10(21) cm-2 and it exhibits strong metal-line transitions due to low- and high-ionization species. The damped Ly-alpha absorbers may be the progenitors of present-day galactic H I disks. Since the velocity separation of the damped absorber and the proposed new galaxy is approximately 1300 km s-1, the observations indicate that these two high-redshift objects reside in the same cluster.