Compact Radio Cores and Nuclear Activity in Seyfert Galaxies

Using recent high–resolution (<0.1”) radio observations of a large sample of Seyfert galaxies (Roy et al., 1994), we analyze the relations between their compact radio core emission and several nuclear and host galaxy properties (galaxy morphology, optical, infrared, X-ray, extended radio emissions, interaction parameters, and some emission line properties). We apply survival analysis techniques in order to exploit the information contained in the numerous ”censored” data (upper limits on fluxes). We find that Seyfert nuclei hosted in early–type galaxies are, on average, characterized by stronger radio core emission than the norm for Seyfert galaxies. Galaxies with a nearby companion display enhanced radio core emission with respect to objects without companions. Furthermore, we confirm that Seyfert types 2 host more powerful compact radio cores than types 1. Remarkably, radio core emission appears to be unrelated to optical, near–infrared, and far–infrared radiations, but shows some correlation with total radio emission and with tracers of nuclear activity such as the IRAS 12 and 25 μm band, hard X-ray and narrow–line emissions. This favours the view that Seyfert radio cores are typically powered by AGN rather than by radio supernovae. A link between radio core strength and bolometric luminosity is suggested, in analogy to what is observed in the cores of radio–quiet QSOs. Subject headings: galaxies: active – galaxies: Seyfert – galaxies: nuclei – radio continuum: galaxies