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

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Abstract
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 structures are present in three out of four sources on scales of ~100 pc to ~1 kpc, and the 20 mas beam of the EVN enables us to resolve details within the radio structures on scales of less than 10 pc. Mrk 3 was also imaged using MERLIN, and the data were combined with the EVN data to 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 in a bright hot spot and resembles an FR II radio structure, while the eastern 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 nucleus lies approximately 1'' south of the position of the radio and optical brightness peaks, which probably represent a hot spot at the working surface of a radio jet. The EVN data also provide new evidence for a 100 pc radio 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 limits of resolution (~10 pc). We discuss the range of radio source size and morphology that can occur in the nuclei of Seyfert galaxies and the implications for Seyfert unification schemes and for radio surveys of large samples of objects.
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