Ratio of [C ii] 158 μm over FIR luminosity, L_[CII]/L_FIR, versus L_FIR for MACS J0451+0006 (large, black stars) and comparison samples, which are detected both in [C ii] and in the dust continuum. For MACS J0451+0006, the two points are meant to illustrate the uncertainties from L_FIR, μ, and the band 9 calibration. Small symbols show nearby galaxies and AGN, large symbols sources at z> 2 from the following papers: M01: Malhotra et al. (2001), S12: Sargsyan et al. (2012), S10: Stacey et al. (2010), B14: Brisbin et al. (2015), C10,14: Cormier et al. (2010), Cormier et al. (2014), M14: Magdis et al. (2014), R14: Rawle et al. (2014), and z4: individual z> 4 galaxies (cf. Casey et al. 2014, and references therein).