et al. 2011; Bethermin et al. 2012; Viero et al. 2013a). The large-scale cross-correlation signal of quasars and star-forming galaxies is determined by the effective linear bias (or equivalently, the effective host halo mass) of both sets of tracers of the underlying large-scale structure. The small-scale cross-correlation signal constrains the halo occupation distributions (HODs) of star-forming galaxies in quasar-hosting dark matter halos and the HODs of quasars in halos hosting star-forming galaxies. In contrast, the auto-correlation function constrains the HODs of each population independently, not the HODs of one population in the presence of the other. Therefore, the cross-correlation function is arguably more suited to studying the co-evolution of the quasars and the star-forming galaxies[^1].

Quasars are very luminous active galactic nuclei (AGN) and hence can be seen out to great distances. They are great tracers of the large-scale structure. To measure their clustering properties reliably, large-volume surveys are required, due to the low spatial density of quasars. The Sloan Digital Sky Survey (SDSS; York et al. 2000) has produced some of the largest quasar samples to date and that is what we use in this paper.

FIR and sub-mm observations are critical for studying star-forming galaxies, as dust absorbs 