2004MNRAS.349..518F

We present deep wide-field K_s-band observations of six Hyperluminous Infrared Galaxies (HLIRGs) spanning a redshift range 0.44 < z < 1.55. The sample resides in a wide variety of environments, from the field to Abell 2 clusters, with a mean galaxy-HLIRG clustering amplitude of <B_gh≥ 190 ±45 Mpc^1.77. The range in environments, and the mean clustering level, are both greater than those seen in local IR-luminous galaxies, from which we infer that the range of galaxy evolution processes driving IR-luminous galaxy evolution at z > 0.5 is greater than locally, and includes mergers between gas-rich spiral galaxies in the field, but also includes encounters in clusters and hierarchical build-up. The similarity in the range of environments and mean clustering amplitude between our sample and QSOs over a similar redshift range is consistent with the interpretation where evolutionary connections between IR-luminous galaxies and QSOs are stronger at z > 0.5 than locally, and that, at these redshifts, the processes that drive QSO evolution are similar to those that drive IR-luminous galaxy evolution. From comparison of the HLIRG and QSO host galaxies we further postulate that a larger fraction of IR-luminous galaxies pass through an optical QSO stage at z > 0.5 than locally.