Depletion time as a function of IR surface brightness. The position of RV4 is indicated by the red cross. The depletion time is the one computed from the gas mass estimated from [CI] (Sect. 4.2). The blue square is HFLS3 (Riechers et al. 2013) at z = 6.34, the green triangle is ALESS73.1 at z = 4.76 (De Breuck et al. 2014), the purple diamond is HDF850.1 (Neri et al. 2014) at z = 5.19, and the pink downward triangle is the source of Yang et al. (2019b) at z = 6.5. The orange dots are the strongly lensed sample of SMG of Yang et al. (2017) spanning a redshift range between 2.09 and 4.24. The yellow pentagons are SPT sources from Spilker et al. (2016) and Aravena et al. (2016). The relation obtained for a sample of MS galaxies at z = 2 by Elbaz et al. (2018) is shown in black solid and dashed lines in the Σ_IR range probed by their data.