MERLIN radio observations of CfA Seyferts

We present new 1.6-GHz (18-cm) MERLIN maps of 15 Seyfert galaxies, with ang ular resolutions typically 0.1 to 0.3 arcsec. These and previous observatio ns are used to investigate the properties of 19 of the 24 CfA Seyfert galax ies brighter than 2 mJy at 8.4 GHz. This is the first time a significant fr action of the CfA sample has been mapped at this frequency with subarcsecon d resolution, and our observations provide the highest resolution radio map s 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 2 0 pc are found in three previously unresolved radio sources, and only four sources show single, unresolved radio components. The mean 1.6 to 8.4 GHz s pectral index of 31 radio components is alpha = - 0.6 +/- 0.1 (S proportion al to nu (alpha)), and approximately 25 per cent of the components have a s pectral 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 secon dary components. The low-resolution infrared (IRAS) emission from Seyfert g alaxies is usually dominated by kiloparsec-scale, extranuclear emission reg ions.