Collimated radio and optical emission associated with the Seyfert galaxy Markarian 78

Publisher Website
Google Scholar
Abstract
It is well established that the radio structures of Seyfert nuclei show strong evidence for the collimated ejection of relativistic plasma from a compact nucleus. There is now increasing evidence that the ionizing continuum in these objects is anisotropic and that both the relativistic plasma and optical continuum may have a related collimation mechanism. In order to investigate this relationship we have made a detailed study of the radio structure and distribution of ionized gas in the Seyfert galaxy Mkn 78. The structure and velocity field of the ionized gas associated with this galaxy have been investigated using long-slit spectroscopy and narrow-band imaging primarily at [O III] λ5007 Å. High-sensitivity images of the radio continuum have been made using the VLA at 2, 6 and 20 cm. The radio continuum shows a highly elongated structure consistent with the collimated ejection of relativistic plasma at |$\text {PA}\approx90^\circ$| and |$\approx 270^\circ$|⁠. The [O III] emission from the narrow-line region (NLR) appears elongated along similar PAs, and individual [O III] components appear to be associated with structures in the radio. This association is accounted for by a simple model in which radio-emitting components are moving with velocities of order 500 km s−1, compressing and shock-heating the ambient medium. Weak [O III] emission (ENLR) extends out to ≈ 10 kpc to the west, with a fan-shaped structure, which is consistent with it being ionized by collimated UV from the nucleus. The opening angle of this ionizing continuum would need to be |$\sim 50 ^\circ$|⁠. There is a marked decrease in intensity through the centre of this feature which aligns approximately with the PA of elongation of the radio and NLR emission. The lines from the ENLR gas are relatively narrow and appear to be consistent with simple rotation, although non-circular motions also appear to be present, as the ENLR gas shows evidence of |$\approx 100\enspace \text {km}\enspace \text s^{-1}$| line-splitting, as well as significant asymmetries between velocity fields in the eastern and western regions.

This publication has 0 references indexed in Scilit: