The jet-disk symbiosis II. Interpreting the Radio/UV correlations in quasars

Heino Falcke (1), Matthew A. Malkan (2) and Peter L. Biermann (1)

Astronomy and Astrophysics 298, 375 (1995)

Abstract:

We investigate the correlation between the accretion disk (UV) luminosity and the radio core emission of a quasar sample, containing all PG quasars, also deriving empirical conversion factors from emission line luminosities to disk luminosities. This method allows us to investigate the radio properties of AGN on the absolute scale set by the accretion power. In a radio vs. L_disk plot we find the quasars to be separated into four classes: core dominated quasars (CDQ), lobe dominated quasars (LDQ), radio-intermediate quasars (RIQ) and radio weak quasars. In general the radio core emission scales with the disk luminosity, especially in the radio weak quasars. This shows that radio and UV emission have a common energy source and that the difference between radio loud and radio weak is established already on the parsec scale. We investigate the possibility that radio jets are responsible for the rado core emission in radio loud and radio weak quasars. Comparing our data with a simple jet emission model that takes the limits imposed by energy and mass conservation in a coupled jet-disk system into account, we find that radio loud jets carry a total power Q_jet that is at least 1/3 of the observed disk luminosity L_disk. The strong radio core emission in radio loud quasars relative to L_disk is difficult to explain by normal acceleration of thermal electrons into a non-thermal powerlaw distribution. One rather is forced to postulate an efficient process producing a large number of pairs and/or injecting electrons with a distribution with low-energy cut-off around 50 MeV -- secondary pair production in hadronic cascades could be such a process. Width and shape of the UV-radio correlation of LDQ and CDQ limit the parameter range for the bulk Lorentz factor of the jet to a narrow region (3< gamma_j<10). The radio emission of radio weak quasars can be explained with exactly the same parameters for a powerful relativistic jet if secondary pair production, as suggested for radio loud jets, is inhibited. There is evidence that RIQ are the relativistically boosted population of radio weak quasar jets. Our diagram provides also a test for the unification of FR II radio galaxies with quasars as we can estimate the hidden disk luminosity of FR II galaxies and find that this is consistent with FRII being misdirected quasars.

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