Subarcsecond-Scale Optical and Radio Structure Correlations in Seyfert Galaxies

Extract

An unanswered question in the study of Seyferts is the nature of the relationship between the extended radio-continuum and optical emission-line gas. Detailed comparison is difficult as most Seyferts have radio structure on sub-arcsecond scales, while most optical imaging is on 1–2″ scales. Despite this, some basic features have emerged. Extended radio and optical emission regions are generally aligned in projection, but the overall optical emission extends to much greater galactocentric radii. Pedlar et al. (1989) and Whittle et al. (1986) have reported a tendency for optical emission knots to lie behind the radio lobes, interpreted in terms of the “cooling length” of gas heated by a radiative bowshock driven into the ISM by a jet. In NGC 1068 (Cecil et al. 1990) and M51 (Cecil 1988), however, ambient gas appears to be piling up ahead of a radio lobe at the terminus of the radio jet.