Parameters of active galaxy nuclei, and the approach to critical luminosity

Although active nuclei of galaxies can be described by diversified empirical parameters, they all depend on a single dimensionless quantity: the ratio of the observed nucleus luminosity L to the critical Eddington luminosity L/sub E/dd for the corresponding mass. Parameters are analyzed for a sample of roughly-equal100 Seyfert 1, 2 galaxies and nearby quasars. As L ..-->.. L/sub E/dd: a) the proportion of active-nucleus radiation increases relative to the underlying background of the parent galaxy; b) beginning at some critical velocity a gas outflow develops, producing the broad permitted-line emission wings; c) the nucleus continuum ''hardens.'' Quasars and Seyfert 1 nuclei have near-critical luminosities, whereas Seyfert 2 nuclei have L<