Schematic showing how different galaxy populations affect IGM and LIM observables. Top: SHMR panels from Figure 5, where we set our galaxy scaling relations to be consistent with either the SERRA or Astrid cosmological simulations. Middle: resulting 21cm brightness temperature and CII surface brightness density lightcones in the range 6 < z < 16. Bottom: auto power spectra from both fields, as well as their cross power spectrum at the midpoint of reionisation $⟨x_{\mathrm{H}\mathrm{I}}⟩=0.5$. Each galaxy population produces a starkly different CD scenario, easily distinguished by the power spectra of the 21cm and/or CII fields.