ALMA [C ii] 158 μm Detection of a Redshift 7 Lensed Galaxy behind RX J1347.1−1145*

We present the results of ALMA spectroscopic follow-up of a z = 6.766 Ly α emitting galaxy behind the cluster RX J1347.1−1145. We report the detection of [C ii ] 158 μ m line fully consistent with the Ly α redshift and with the peak of the optical emission. Given the magnification of μ = 5.0 ± 0.3, the intrinsic (corrected for lensing) luminosity of the [C ii ] line is L [C ii ] , roughly ∼5 times fainter than other detections of z ∼ 7 galaxies. The result indicates that low L [C ii ] in z ∼ 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset ( ) between the Ly α and [C ii ] line is unusual, and may be indicative of ionizing photons escaping.