The HELLAS2XMM survey. X. The bolometric output of luminous obscured quasars: The Spitzer perspective

Aims:We aim at estimating the spectral energy distributions (SEDs) and the physical parameters related to the black holes harbored in eight high X-ray-to-optical ({F_X}/{F_R}>10) obscured quasars at z > 0.9 selected in the 2-10 keV band from the HELLAS2XMM survey.
Methods: We use IRAC and MIPS 24 μm observations, along with optical and K_s-band photometry, to obtain the SEDs of the sources. The observed SEDs are modeled using a combination of an elliptical template and torus emission (using the phenomenological templates of Silva et al. 2004) for six sources associated with passive galaxies; for two point-like sources, the empirical SEDs of red quasars are adopted. The bolometric luminosities and the M_BH-L_K relation are used to provide an estimate of the masses and Eddington ratios of the black holes residing in these AGN.
Results: All of our sources are detected in the IRAC and MIPS (at 24 μm) bands. The SED modeling described above is in good agreement with the observed near- and mid-infrared data. The derived bolometric luminosities are in the range ≈10⁴⁵-10⁴⁷ erg s^-1, and the median 2-10 keV bolometric correction is ≈25, consistent with the widely adopted value derived by Elvis et al. (1994). For the objects with elliptical-like profiles in the K_s band, we derive high stellar masses (0.8-6.2)×10¹¹ M_⊙, black hole masses in the range (0.2-2.5)×10⁹ M_⊙, and Eddington ratios L/L_Edd<0.1, suggesting a low-accretion phase.