ALMA [CII] detection of a redshift 7 lensed galaxy behind RXJ1347.1-1145

Abstract

We present the results of ALMA spectroscopic follow-up of a $z=6.765$ Lyman-$\hat{I}\pm$ emitting galaxy behind the cluster RXJ1347-1145. We report the detection of [CII]158$\hat{I}¼$m line fully consistent with the Lyman-$\hat{I}\pm$ redshift and with the peak of the optical emission. Given the magnification of $\hat{I}¼=5.0\pm 0.3$ the intrinsic (corrected for lensing) luminosity of the [CII] line is $L_{[CII]}=1.4_{-0.3}^{+0.2}\times 10^7{L}_{\odot }$, which is $\sim 5$ times fainter than other detections of $z\sim 7$ galaxies. The result indicates that low $L_{[CII]}$ in $z\sim 7$ galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity off-set ($\hat{I}”v=20_{-40}^{+140}km/s$) between the Lyman-$\hat{I}\pm$ and [CII] line is unusual, and may be indicative of ionizing photons escaping.

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