THE EDDINGTON RATIO OF ACTIVE GALACTIC NUCLEI IN ACCRETION-DISK AND DYNAMIC-MODELS

The UV continuum spectrum is used to estimate the mass (and the Eddington ratio) of quasars and AGN, assuming the UV is dominated by thermal emission from a thin accretion disk. This is done by fitting the observed UV luminosity and spectral slope by an accretion disk model spectrum calculated numerically accretion rate). An analytic approximation to this calculation is given as well. An independent estimate of the mass is obtained from the broad emission-lines, assuming that the velocity dispersion implied by the Doppler line width is induced by the gravitational potential of the central compact object. For a sample of 36 quasars and Seyfert 1 galaxies, for which both data, the UV spectrum and the H-beta line width are available, the masses calculated with the two independent methods are in good agreement (within a factor of 2 for 75% of the sample) and highly correlated. Over three orders of magnitude in luminosity, the mass is found to increase less than linearly with luminosity, being in the range 10(8) < M < 10(10) M., with L(1450 A)/L(Edd) ranging from 0.001 for Seyferts to 0.03 for bright quasars.