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, and Mrk 463E, made with the European VLBI Network (EVN). Linear radio struc tures are present in three out of four sources on scales of similar to 100 pc to similar to 1 kpc, and the 20 mas beam of the EVN enables us to resolv e details within the radio structures on scales of less than 10 pc. Mrk 3 w as also imaged using MERLIN, and the data were combined with the EVN data t o improve the sensitivity to extended emission. We find an unresolved flat- spectrum core in Mrk 3, which we identify with the hidden Seyfert 1 nucleus in this object, and we also see marked differences between the two highly collimated radio jets emanating from the core. The western jet terminates i n a bright hot spot and resembles an FR II radio structure, while the easte rn jet has more in common with an FR I source. In the case of Mrk 463E, we use the radio and optical structure of the source to argue that the true nu cleus lies approximately 1 " south of the position of the radio and optical brightness peaks, which probably represent a hot spot at the working surfa ce of a radio jet. The EVN data also provide new evidence for a 100 pc radi o 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 lim its of resolution (similar to 10 pc). We discuss the range of radio source size and morphology that can occur in the nuclei of Seyfert galaxies and th e implications for Seyfert unification schemes and for radio surveys of lar ge samples of objects.