2014ApJ...789L..31W

We identify a strong lensing galaxy in the cluster IRC 0218 (also known as XMM-LSS J02182-05102) 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 z_S= 2.26. Using HST imaging in ACS/F475W, ACS/F814W, WFC3/F125W, and WFC3/F160W, 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 θ_E = 0.38_–0.0^+0.02 arcsec (3.2_–0.1^+0.2 kpc) and the total enclosed mass is M_tot(<θ_E) = 1.8_–0.1^+0.2x10¹¹ M_☉ . We estimate that the cluster environment contributes ∼10% of this total mass. Assuming a Chabrier initial mass function (IMF), the dark matter fraction within θ_E is ∫_DM^Chab = 0.3_–0.3^+0.1, while a Salpeter IMF is marginally inconsistent with the enclosed mass (∫_DM^Salp = -0.3_–0.5^+0.2). The total magnification of the source is µ_tot = 2.1_–0.3^+0.4. The source has at least one bright compact region offset from the source center. Emission from Lyα and [O III] are likely to probe different regions in the source.