ALMA Lensing Cluster Survey: A spectral stacking analysis of [C II] in lensed z similar to 6 galaxies Jolly, Jean-Baptiste Espada Fernández, Daniel Galaxies: formation Galaxies: statistics Galaxies: high-redshift Radio lines: galaxies Galaxies: evolution Galaxies: star formation We thank the anonymous referee for their helpful comments. This paper makes use of the ALMA data: ALMA #2018.1.00035.L, #2013.1.00999.S, and #2015.1.01425.S. ALMA is a partnership of the ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, AUI/NRAO, and NAOJ. K. K. acknowledges support from the Swedish Research Council (2015-05580), and the Knut and Alice Wallenberg Foundation. K. Kohno acknowledges the JSPS KAKENHI Grant Number JP17H06130 and the NAOJ ALMA Scientific Research Grant Number 2017-06B. F.E.B. acknowledges support from ANID grants CATA-Basal AFB-170002, FONDECYT Regular 1190818, 1200495 and Millennium Science Initiative ICN12_009. D. E. acknowledges support from a Beatriz Galindo senior fellowship (BG20/00224) from the Ministry of Science and Innovation. G. E. M. and F. V. acknowledge the Villum Fonden research grant 13160 "Gas to stars, stars to dust: tracing star formation across cosmic time"? and the Cosmic Dawn Center of Excellence funded by the Danish National Research Foundation under then grant No. 140. F. V. acknowledges support from the Carlsberg Foundation Research Grant CF18-0388 "Galaxies: Rise and Death". A.Z. acknowledges support from the Ministry of Science and Technology, Israel. Context. 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 [C II] 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. Aims. With the aim to study the interstellar medium properties of gravitationally lensed galaxies at z>6, we search for [C II] and thermal dust emission in a sample of 52 > 6 galaxies observed by the ALMA Lensing Cluster Survey. Methods. We perform our analysis using LINESTACKER, stacking both [C II] 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)<0.02) in nine galaxy clusters. Source properties of the target galaxies are either extracted from the literature or computed using spectral energy distribution fitting. Both weighted-average and median stacking are used, on both the full sample and three sub-samples. Results. Our analyses find no detection of either [C II] or continuum. An upper limit on L-[CII] is derived, implying that [C II] remains marginally consistent for low-SFR z>6 galaxies but likely is under-luminous compared to the local L-[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. 2021-11-11T09:22:34Z 2021-11-11T09:22:34Z 2021-08-23 journal article Jolly, J-B... [et al.]. ALMA Lensing Cluster Survey: A spectral stacking analysis of [C II] in lensed z similar to 6 galaxies. A&A 652, A128 (2021) [https://doi.org/10.1051/0004-6361/202140878] http://hdl.handle.net/10481/71434 10.1051/0004-6361/202140878 eng http://creativecommons.org/licenses/by-nc-nd/3.0/es/ open access Atribución-NoComercial-SinDerivadas 3.0 España EDP Sciences