What powers hyperluminous infrared galaxies at z ~ 1-2?

Abstract

We investigate what powers hyperluminous infrared galaxies (HyLIRGs; LIR,8-1000μm > 1013 L⊙) at z ~ 1-2, by examining the behaviour of the infrared luminosity function of active galactic nuclei (AGN) in relation to the infrared galaxy luminosity function. The former corresponds to emission fromAGN-heated dust only, whereas the latter includes emission from dust heated by stars and AGN. Our results show that the two luminosity functions are substantially different below 1013 L⊙ but converge in the HyLIRG regime.We find that the fraction of AGN-dominated sources increases with the total infrared luminosity and at LIR > 1013.5 L⊙ AGN can account for the entire infrared emission. We conclude that the bright end of the 1 < z < 2 infrared galaxy luminosity function is shaped by AGN rather than star-forming galaxies.