L_X,gal−SFR relationship arising from ULXs produced through CHE at two different metallicities, compared to the predicted metallicity-independent relationship from Grimm et al. (2003) for the luminosity in the 2−10 keV band. Systems at log  Z = −4 can also produce BHs above the pair instability gap, resulting in the slightly different structure at low SFR. For simplicity we assume all the luminosity from accretion is emitted as X-rays. For different values of the SFR modelled we constructed 10 000 synthetic galaxies, and the colour plot indicates the fraction of galaxies contained around the median (i.e. the 20% region is bounded by the fourth and sixth deciles).