The distance scale and Eddington efficiency of luminous quasars

The relation between the central mass and quasar luminosity (MBH ∝ L α FHWM ) links a given Eddington ratio with a value of H0, within a cosmology with fixed (Ωm,ΩΛ). We point out that because the relation is calibrated at low z using distance independent reverberation mapping to get the BLR size, the derived MBH interestingly does not depend on H0, while L/LEdd is sensitive to H0, but rather robust to changes of ΩΛ in the standard flat model. This means, e.g., that enough of extragalactic objects radiating at the Eddington limit could be used to study the global Hubble constant in a new way, bypassing the local distance ladder. The method could become practical when systematic errors in derived MBH are understood and objects with L <∼ LEdd can be independently identified. As an illustration, if we take a sample of tranquil very luminous quasars in the redshift range 0.5 < z < 1.6, and assume that they are radiating with Lbol ≤ LEdd, then the usual numerical factors used for calculating MBH and Lbol would lead to the result that the Hubble constant must be larger than 45 km/s/Mpc.