Comparison of the average SLED of BzK galaxies to the MW SLED (Fixsen et al. 1999), the average of SMGs (Bothwell et al. 2013; the SLED reported by Spilker et al. (2014) is similar, but higher at J> 5) and the average (U)LIRGs SLED derived in this paper using measurements from P12. All SLEDs are normalized to the CO[1–0] of the average BzK galaxy SLED, except the MW, which is normalized using CO[2–1]. The results from the toy model of P12 (see text) and the numerical simulations of B15 and Narayanan & Krumholz (2014) are also shown.