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

TL;DR

This study reports the detection of the [CII] line in a gravitationally lensed galaxy at redshift 7, providing insights into its metallicity, feedback processes, and ionizing photon escape, with implications for early galaxy evolution.

Contribution

First detection of [CII] emission in a z=7 galaxy behind a lens, revealing lower luminosity and potential feedback effects compared to local galaxies.

Findings

[CII] luminosity is about 5 times fainter than other z~7 galaxies.

Small velocity offset suggests possible ionizing photon escape.

Low [CII] luminosity may be due to low metallicity or feedback effects.

Abstract

We present the results of ALMA spectroscopic follow-up of a $z=6.765$ Lyman-$\alpha$ emitting galaxy behind the cluster RXJ1347-1145. We report the detection of [CII]158$\mu$m line fully consistent with the Lyman-$\alpha$ redshift and with the peak of the optical emission. Given the magnification of $\mu=5.0 \pm 0.3$ the intrinsic (corrected for lensing) luminosity of the [CII] line is $L_{[CII]} =1.4^{+0.2}_{-0.3} \times 10^7L_{\odot}$, 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 ($\Delta v = 20_{-40}^{+140} \rm km/s$) between the Lyman-$\alpha$ and [CII] line is unusual, and may be indicative of ionizing photons escaping.