A Pair of Lensed Galaxies at [CLC][ITAL]z[/ITAL][/CLC] = 4.92 in the Field of CL 1358+62

The cluster CL1358+62 displays a prominent red arc in WFPC2 images obtainedwith the Hubble Space Telescope. Keck spectra of the arc show Ly alpha emissionat 7204 Angstrom, a continuum drop blueward of the line, and several absorptionlines to the red. We identify the arc as a gravitationally lensed galaxy at aredshift of z=4.92. It is the highest redshift object currently known. Agravitational lens model was used to reconstruct images of the high-redshiftgalaxy. The reconstructed image is asymmetric, containing a bright knot and apatch of extended emission 0.4 arcsec from the knot. The effective radius ofthe bright knot is 0.022 arcsec or 130 h^-1 pc. The extended patch is partiallyresolved into compact regions of star formation. The reconstructed galaxy hasI_AB= 24, giving a bolometric luminosity of about 3e11 Lsun. This can beproduced by a star formation rate of 36 h^-2 Msun /yr (q0=0.5), or by aninstantaneous star burst of 3e8 Msun. The spectral lines show velocityvariations on the order of 300 km/s along the arc. The Si II line is blueshifted with respect to the Ly alpha emission, and the Ly alpha emission lineis asymmetric with a red tail. These spectral features are naturally explainedby an outflow model, in which the blue side of the Ly alpha line has beenabsorbed by outflowing neutral H I. Evidence from other sources indicates thatoutflows are common in starburst galaxies at high and low redshift. We havediscovered a companion galaxy with a radial velocity only 450 km/s differentthan the arc's. The serendipitous discovery of these two galaxies suggests thatsystematic searches may uncover galaxies at even higher redshifts.