A pair of lensed galaxies at z = 4.92 in the field of CL 1358+62

The cluster CL 1358+62 displays a prominent red arc in WFPC2 images obtained with the Hubble Space Telescope. Keck spectra of the arc show Ly alpha emission at 7204 Angstrom, a continuum drop blueward of the line, and several absorption lines to the red. We identify the arc as a gravitationally lensed galaxy at a redshift of z = 4.92. It is the highest redshift object currently known. A gravitational lens model was used to reconstruct images of the high-redshift galaxy. The reconstructed image is asymmetric, containing a bright knot and a patch of extended emission 0''.4 from the knot. The effective radius of the bright knot is 0''.022 or 130 h(50)(-1) pc. The extended patch is partially resolved into compact regions of star formation. The reconstructed galaxy has I-AB = 24, giving a bolometric luminosity of about 3 x 10(11) L.. This can be produced by a star formation rate of 36 h(50)(-2) M. yr(-1) (q(0) = 0.5) or by an instantaneous starburst of 3 x 10(8) M.. The spectral lines show velocity variations on the order of 300 km s(-1) along the arc. The Si II line is blueshifted with respect to the Ly alpha emission, and the Ly alpha emission line is asymmetric with a red tail. These spectral features are naturally explained by an outflow model, in which the blue side of the Ly alpha line has been absorbed by outflowing neutral H I. Evidence from other sources indicates that outflows are common in starburst galaxies at high and low redshift, We have discovered a companion galaxy with a radial velocity only 450 km s(-1) different than that of the arc. The serendipitous discovery of these two galaxies suggests that systematic searches may uncover galaxies at even higher redshifts.