Yun, Reddy & Condon (2001). The entire population was evolved with pure luminosity evolution (1+z)$^{3.1}$ out to z=1.5 (defined in an Einstein-de Sitter cosmology but adapted to the flat-$\Lambda$ cosmology used for the simulation). The default post-processing option consists of negative space density evolution of the form $(1+z)^{-7.9}$ above $z=4.8$. We stress that the terms ‘normal galaxy’ and ‘starburst’ are merely convenient labels for these two components of the local luminosity function in our phenomenological model. Physically speaking, the terms may not necessarily offer an accurate description of the nature of the star formation in these populations, especially beyond the local Universe.

The first step in assigning an infrared SED is to use the far-infrared–radio correlation for star-forming galaxies (eqn. 5 of Yun, Reddy & Condon 2001) in order to derive the rest-frame far-infrared luminosity, L(FIR), given the rest-frame 1.4 GHz luminosity, L$_{\rm{1.4 GHz}}$. The relation is characterised by the “q” parameter:

$$q = \rm{ log [L(FIR,W)}/3.75 \times 10^{12} Hz] - log [\rm{L_{\rm{1.4 GHz}} (W Hz^{-1})}],$$

for which we assume a gaussian distribution with $\mu = 2.34$ and $\sigma = 0.26$ (Yun, Reddy & Condon). There is evidence that this relation holds out to redshift $z > 1$ (e.g. Appleton 