2001MNRAS.327..369T

We present new 1.6-GHz (18-cm) MERLIN maps of 15 Seyfert galaxies, with angular resolutions typically 0.1 to 0.3arcsec. These and previous observations are used to investigate the properties of 19 of the 24 CfA Seyfert galaxies brighter than 2mJy at 8.4GHz. This is the first time a significant fraction of the CfA sample has been mapped at this frequency with subarcsecond resolution, and our observations provide the highest resolution radio maps available for several sources. We use our observations to measure the two-point spectral indices of compact radio components, and we investigate the correlation between infrared and radio emission shown by Seyfert galaxies.

Our results can be summarized as follows. Resolved structures as small as 20pc are found in three previously unresolved radio sources, and only four sources show single, unresolved radio components. The mean 1.6 to 8.4GHz spectral index of 31 radio components is alpha=-0.6±0.1 (S∼nu^alpha), and approximately 25 per cent of the components have a spectral index flatter than alpha=-0.3. The spectral index distributions of type 1 and type 2 Seyferts are statistically indistinguishable. The cores of multiple-component sources tend to have flatter radio spectra than secondary components. The low-resolution infrared (IRAS) emission from Seyfert galaxies is usually dominated by kiloparsec-scale, extranuclear emission regions.