AN IMPROVED MEASURE OF QUASAR ORIENTATION

Radio core dominance, usually measured by R, the rest frame ratio of c ore to lobe flux density, has been used as an indicator of Doppler boo sting of a quasar's radio jets and hence the inclination of the centra l engine's spin axis to the line of sight. The use of lobe flux densit y as a means of normalizing the boosted core flux density to the avail able intrinsic power of the central engine introduces scatter. This is because the emission from the radio lobes depends strongly on the int eraction of the jet with the environment at distances beyond several k iloparsecs from the nucleus. Total kinetic power in the extended radio emission is approximately proportional to emission-line luminosity, a nd emission-line luminosity is proportional to the luminosity of the f eatureless continua of active galactic nuclei-both over four orders of magnitude. Thus, a quasar's optical luminosity may be an excellent me asure of available intrinsic jet power. Therefore, we define a new cor e dominance parameter, R(V), the ratio of radio core to optical (rest frame Vband) continuum luminosity, that is not directly dependent on j et interactions with the super-kiloparsec-scale environment. We show t hat the use of R(V), rather than R, results in significantly improved inverse correlations with the beaming angle as deduced from apparent s uperluminal velocities and inverse-Compton-scattered X-ray emission an d with the FWHM of a quasar's broad H beta emission line. We discuss s ome implications and applications of the new parameter.