Parsec‐Scale Radio Structures in the Nuclei of Four Seyfert Galaxies

We present 18-cm radio maps of four Seyfert nuclei, Mrk 1, Mrk 3, Mrk 231 andMrk 463E, made with the European VLBI Network (EVN). Linear radio structuresare present in three out of four sources on scales of ~100 pc to ~1 kpc, andthe 20-mas beam of the EVN enables us to resolve details within the radiostructures on scales of <10 pc. Mrk 3 was also imaged using MERLIN and the datacombined with the EVN data to improve the sensitivity to extended emission. Wefind an unresolved flat-spectrum core in Mrk 3, which we identify with thehidden Seyfert 1 nucleus in this object, and we also see marked differencesbetween the two highly-collimated radio jets emanating from the core. Thewestern jet terminates in a bright hotspot and resembles an FRII radiostructure, whilst the eastern jet has more in common with an FRI source. In Mrk463E, we use the radio and optical structure of the source to argue that thetrue nucleus lies approximately 1 arcsec south of the position of the radio andoptical brightness peaks, which probably represent a hotspot at the workingsurface of a radio jet. The EVN data also provide new evidence for a 100-pcradio jet powering the radio source in the Type 1 nucleus of Mrk 231. However,the Seyfert 2 galaxy Mrk 1 shows no evidence for radio jets down to the limitsof resolution (~10 pc). We discuss the range of radio source size andmorphology which can occur in the nuclei of Seyfert galaxies and theimplications for Seyfert unification schemes and for radio surveys of largesamples of objects.Comment: 23 pages, 7 postscript figures (supplied as separate files), uses AAS aaspp4 LaTeX style file, to appear in the 10 June 1999 issue of The Astrophysical Journa