Submm-bright X-ray-absorbed QSOs at z ∼ 2: insights into the coevolution of AGN and star formation

Abstract

We have assembled a sample of five X-ray-absorbed and submm-luminous type 1 QSOs at z ∼ 2 which are simultaneously growing their central black holes through accretion and forming stars copiously. We present here the analysis of their rest-frame UV-to-submm spectral energy distributions (SEDs), including new Herschel data. Both AGN (direct and reprocessed) and star formation (SF) emission are needed to model their SEDs. From the SEDs and their UV–optical spectra we have estimated the masses of their black holes MBH ∼ 109–1010 M⊙, their intrinsic AGN bolometric luminosities LBOL ∼ (0.8–20) × 1013 L⊙, Eddington ratios LBOL/LEdd ∼ 0.1–1.1 and bolometric corrections LBOL/LX,2−10∼30−500LBOL/LX,2−10∼30−500. These values are common among optically and X-ray-selected type 1 QSOs (except for RX J1249), except for the bolometric corrections, which are higher. These objects show very high far-infrared luminosities LFIR ∼ (2–8) × 1012 M⊙ and star formation rates SFR ∼1000 M⊙ yr−1. From their LFIR and the shape of their FIR–submm emission we have estimated star-forming dust masses of MDUST ∼ 109 M⊙. We have found evidence of a tentative correlation between the gas column densities of the ionized absorbers detected in X-ray (NHionNHion) and SFR. Our computed black hole masses are amongst the most massive known.