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Session 23 - High Luminosity AGN and QSOs.
Oral session, Monday, June 10
Union Theater,
Radio continuum spectra for 32 radio quiet quasars (RQQs) and 7 luminous Seyfert 1 galaxies, obtained at the VLA and typically covering four frequencies in the observed range 1.5 to 14.9 GHz, will be presented. Two samples are considered, one selected for IRAS detections and on average at low redshift (16 objects), and the other selected by radio and optical properties and covering a range of redshifts up to z = 2.6 (23 objects). We find the radio spectral shapes in both samples to be quite heterogeneous, and catagorize the spectra into four general classes similar to those defined by Kuhr et al (1979) for radio loud objects: straight, concave, convex, and complex. The relative frequencies of these classifications in our radio quiet samples are similar to the frequencies seen in radio loud quasars and radio galaxies. Radio quiet and radio loud quasars have similar spectral shapes.
About 40% of the RQQs studied here appear to have flat or inverted spectral components, and evidence is found for variability in 7 sources, based on comparison with a single previous observation from the literature. At least 5 of these variable sources show flat or inverted radio spectra, and none have straight, steep spectra. We have detected one of our sources with VLBI, and essentially all the flux appears to reside in a compact, subparsec core. This source has an inverted spectrum, and is variable, strongly indicating partially-opaque synchrotron emission. Thus the cores of radio quiet quasars appear to be scaled-down versions of those found in radio loud objects. Radio quiet quasar spectra probably include contributions from three components, in varying degrees: optically thin synchrotron from star-forming regions in the disk of the host galaxy and in a circumnuclear starburst; optically thin synchrotron from an extended (perhaps jet-like) component powered by the active nucleus; and partially opaque synchrotron from a compact, VLBI-scale core. All three of these components may play a role in the radio spectra of low-redshift quasars, but only the latter two are significant contributors in luminous, high-redshift objects.
