Galaxy main sequence and brightness temperatures for the CGG-z4 galaxies. (a) SFR vs. stellar mass. The solid lines indicate the star-forming main sequence (MS) at z = 4.3, with the shaded area being the 1σ scatter (Speagle et al. 2014; Schreiber et al. 2015). CGG-z4.a and CGG-z4.b are shown as magenta diamonds, while other galaxies in CGG-z4 are shown as blue circles. (b) The brightness temperature relationship between [CI](1–0) and CO(4–3). CGG-z4.a and CGG-z4.b are shown as magenta diamonds. Linear fits are from Lee et al. (2021), with the data used being z = 2.5 protocluster galaxies from Lee et al. (2021) (L21). Cold dusty galaxies at z = 3.5 − 6 from Jin et al. (2019, 2022) (J19+22), a mix of local LIRGs (including AGNs), z = 1 main sequence galaxies, and DSFGs from Valentino et al. (2020) (V20), main sequence star-forming galaxies at z ∼ 1 from Boogaard et al. (2020) (B20), and the SPT DSFG average from Spilker et al. (2014) (S14). The remaining data comprise SMGs from Daddi et al. (2009), Cox et al. (2011), Lestrade et al. (2011), Alaghband-Zadeh et al. (2013), Aravena et al. (2013), Bothwell et al. (2013), Bothwell et al. (2017), Omont et al. (2013), Cañameras et al. (2015), Harrington et al. (2016), Yang et al. (2017), Valentino et al. (2020).