A statistical study of multiply imaged systems in the lensing cluster Abell 68

We have carried out an extensive spectroscopic survey with the Keck and VLT telescopes, targeting lensed galaxies in the background of the massive cluster Abell 68. Spectroscopic measurements are obtained for 26 lensed images, including a distant galaxy at z = 5.4. Redshifts have been determined for 5 out of 7 multiple-image systems. Through a careful modeling of the mass distribution in the strongly lensed regime, we derive a mass estimate of 5:3 x 10(14) M-circle dot within 500 kpc. Our mass model is then used to constrain the redshift distribution of the remaining multiply imaged and singly imaged sources. This enables us to examine the physical properties for a subsample of 7 Ly alpha emitters at 1.7 less than or similar to z less than or similar to 5.5, whose unlensed luminosities of similar or equal to 10(41) ergs s(-1) are fainter than similar objects found in blank fields. Of particular interest is an extended Ly alpha emission region surrounding a highly magnified source at z = 2.6, detected in VIMOS integral field spectroscopy data. The physical scale of the most distant lensed source at z = 5.4 is very small (< 300 pc), similar to the lensed z similar to 5.6 emitter reported by Ellis et al. in Abell 2218. New photometric data available for Abell 2218 allow for a direct comparison between these two unique objects. Our survey illustrates the practicality of using lensing clusters to probe the faint end of the z similar to 2-5 Ly alpha luminosity function in a manner that is complementary to blank-field narrowband surveys.