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 Lyα emission at 7204 Å, 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 04 from the knot. The effective radius of the bright knot is 0022 or 130 h⁻¹₅₀ 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 × 10¹¹ L_☉. This can be produced by a star formation rate of 36 h⁻²₅₀ M_☉ yr^-1 (q₀ = 0.5) or by an instantaneous starburst of 3 × 10⁸ 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 Lyα emission, and the Lyα 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 Lyα 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.