Heavily reddened type 1 quasars at z > 2 – I. Evidence for significant obscured black hole growth at the highest quasar luminosities

We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ≲ E(B − V) ≲ 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS (European Southern Observatory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>10¹³ L⊙), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Hα equivalent widths relative to unobscured quasars. The average black hole masses (∼10⁹–10¹⁰ M⊙) and bolometric luminosities (∼10⁴⁷ erg s⁻¹) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ∼10⁴⁸erg s⁻¹. 66 per cent of the reddened quasars are detected at >3σ at 22 μm by WISE. The average 6-μm rest-frame luminosity is log10(L6 μm/ erg s⁻¹) = 47.1 ± 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (−30 < Mi < −27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2–3. At the brightest magnitudes, Mi ≲ −29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation.