STScI Preprint #1326
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 <10 pc. Mrk 3 was also imaged using MERLIN and the data 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 hotspot and resembles an FRII radio structure, whilst the eastern jet has more in common with an FRI source. In Mrk 463E, we use the radio and optical structure of the source to argue that the true nucleus lies approximately 1 arcsec south of the position of the radio and optical brightness peaks, which probably represent a hotspot 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 which can occur in the nuclei of Seyfert galaxies and the implications for Seyfert unification schemes and for radio surveys of large samples of objects.
1 Space Telescope Science Institute, 3700 San Martin Drive,Baltimore, MD 21218, U.S.A.
2 Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, U.K.
3 Arecibo Observatory, P.O. Box 995, Arecibo, Puerto Rico, PR00613, U.S.A.
4 NRAL, University of Manchester, Jodrell Bank, Macclesfield SK119DL, U.K.
5 Joint Institute for VLBI in Europe, P.O. Box 2, 7990 AA,Dwingeloo, the Netherlands
6 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, the Netherlands