Abstract
We identify a strong lensing galaxy in the cluster IRC 0218 that is spectroscopically confirmed to be at z = 1.62, making it the highest-redshift strong lens galaxy known. The lens is one of the two brightest cluster galaxies and lenses a background source galaxy into an arc and a counterimage. With Hubble Space Telescope (HST) grism and Keck/LRIS spectroscopy, we measure the source redshift to be <TEX>$z_S=2.26$</TEX>. Using HST imaging, we model the lens mass distribution with an elliptical power-law profile and account for the effects of the cluster halo and nearby galaxies. The Einstein radius is <TEX>$^{\theta}E=0.38^{+0.02{\prime}{\prime}}_{-0.01}$</TEX> (<TEX>$3.2^{+0.2}_{-0.1}kpc$</TEX>) and the total enclosed mass is <TEX>$M_{tot}(</TEX><TEX><</TEX><TEX>^{\theta}_E)=1.8^{+0.2}_{-0.1}{\times}10^{11}M_{\odot}$</TEX>. We estimate that the cluster environment contributes ~ 10% of this total mass. Assuming a Chabrier IMF, the dark matter fraction within <TEX>$^{\theta}E$</TEX> is <TEX>$f^{Chab}_{DM}=0.3^{+0.1}_{-0.3}$</TEX>, while a Salpeter IMF is marginally inconsistent with the enclosed mass (<TEX>$f^{Salp}_{DM}=-0.3^{+0.2}_{-0.5}$</TEX>).
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