ALMA Lensing Cluster Survey: A spectral stacking analysis of [CII] in lensed $z\sim6$ galaxies

The properties of galaxies at redshift $z>6$ hold the key to our understanding of the early stages of galaxy evolution and can potentially identify the sources of the ultraviolet radiation that give rise to the epoch of reionisation. The far-infrared cooling line of [CII] at 158$\mu$m is known to be bright and correlate with the star formation rate (SFR) of low-redshift galaxies, and hence is also suggested to be an important tracer of star formation and interstellar medium properties for very high-redshift galaxies. With the aim to study the interstellar medium properties of gravitationally lensed galaxies at $z>6$, we search for [CII] and thermal dust emission in a sample of 52 $z\sim6$ galaxies observed by the ALMA Lensing Cluster Survey (ALCS). We perform our analysis using \textsc{LineStacker}, stacking both [CII] and continuum emission. The target sample is selected from multiple catalogues, and the sample galaxies have spectroscopic redshift or low-uncertainty photometric redshifts ($\sigma_z 6$ galaxies but likely is under-luminous compared to the local $L_{\rm [CII]}$-SFR relationship. We discuss potential biases and possible physical effects that may be the cause of the non-detection. Further, the upper limit on the dust continuum implies that less than half of the star formation is obscured.