Relativistic beaming and the intrinsic properties of extragalactic radio jets

Relations between the observed quantities for a beamed radio jet, which are the apparent transverse speed and the apparent luminosity (beta(app), L), and the intrinsic quantities, which are the Lorentz factor and the intrinsic luminosity (gamma, L-0), are investigated. The inversion from measured to intrinsic values is not unique, but approximate limits to gamma and L-0 can be found using probability arguments. Roughly half the sources in a flux density-limited, beamed sample have a value of gamma close to the measured value of beta(app). The methods are applied to observations of 119 AGN jets made with the VLBA at 15 GHz during 1994-2002. The results strongly support the common relativistic beam model for an extragalactic radio jet. The (beta(app), L) data are closely bounded by a theoretical envelope, an ''aspect'' curve for gamma = 32 and L-0 10(25) W Hz(-1). This gives limits to the maximum values of gamma and L-0 in the sample: gamma(max) approximate to 32, and L-0,L-max similar to 10(26) W Hz(-1). No sources with both high values of beta(app) and low values of L are observed. This is not the result of selection effects due to the observing limits, which are a flux density of S > 0.5 Jy and an angular velocity of mu < 4 mas yr(-1). Many of the fastest quasars have a pattern Lorentz factor, gamma(p), that is close to that of the beam, gamma(b), but some of the slow quasars must have gamma(p)<< gamma(b). Three of the 10 galaxies in the sample have a superluminal feature, with speeds up to beta(app) approximate to 6. The others are at most mildly relativistic. The galaxies are not off-axis versions of the powerful quasars, but Cygnus A might be an exception.