Investigating evidence for different black hole accretion modes since redshift z ̃ 1
Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U-V versus V-J colours of X-ray AGN hosts in the redshift intervals 0.1 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≥10-3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies.We compare these results with the predictions of the GALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z < 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.