Radio Cores in Low-Luminosity AGN: ADAFs or Jets?

Radio Cores in Low-Luminosity AGN: ADAFs or Jets?

Falcke H.1, Nagar N.M2., Wilson A.S.2, Ho L.C.3, Ulvestad J.S.4

1Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany (
2Dept. of Astronomy, University of Maryland, College Park, MD 20742-2421, USA (wilson,
3Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA (
4NRAO, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (

in "Black Holes in Binaries and Galactic Nuclei", ESO Workshop 1999, eds. L. Kaper, E.P.J. van den Heuvel, and P.A. Woudt, Springer Verlag, p. 218


We have surveyed two large samples of nearby low-luminosity AGN with the VLA to search for flat-spectrum radio cores, similar to Sgr A* in the Galactic Center. Roughly one third of all galaxies are detected (roughly one half if H II transition objects are excluded from the sample), many of which have compact radio cores. Follow-up observations with the VLBA have confirmed that these cores are non-thermal in origin, with brightness temperatures of >=108 K. The brightest of these are resolved into linear structures. The radio spectral indices of the cores are quite flat (alpha~0), with no evidence for the highly inverted radio cores predicted in the ADAF model. Spectrum and morphology of the compact radio emission is typical for radio jets seen also in more luminous AGN. The emission-line luminosity seems to be correlated with the radio core flux. Together with the VLBI observations this suggests that optical and radio emission in at least half the low-luminosity Seyferts and LINERs are black hole powered. We find only a weak correlation between bulge luminosity and radio flux and an apparently different efficiency between elliptical and spiral galaxies for producing radio emission at a given optical luminosity.

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Questions: Heino Falcke,