Correlation between the virial product and luminosity of the Hα emission line. The apparent correlation between mass and luminosity is due to selection effects. Sources in the lower right (high luminosity, low mass) are generally excluded by the Eddington limit. Sources in the upper left (low luminosity, high mass) are scarce (a) because high mass objects are rare and therefore mostly at large distances, and thus faint, and (b) because their accretion rates are so low that they do not manifest themselves as AGNs.