Parsec-scale radio cores in spiral galaxies

We have used the Parkes–Tidbinbilla Interferometer to search for compact ( < 0.03 arcsec) radio continuum cores in 54 nearby spiral galaxies, 22 of which have Seyfert nuclei. In contrast to the radio cores of elliptical galaxies, the few parsec-scale cores seen in spirals usually have steep radio spectra, with an apparent median spectral index of – 1.0. At present, it is not clear whether this is because the radio cores of spiral galaxies are larger than those in ellipticals (and so are partly resolved by the interferometer), or whether the core spectra of ellipticals and spirals are intrinsically different.