Radio Structures of Seyfert Galaxies. VIII. A Distance‐ and Magnitude‐Limited Sample of Early‐Type Galaxies

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Abstract
The VLA has been used at 3.6 and 20 cm to image a sample of about 50 early-type Seyfert galaxies with recessional velocities less than 7000 km s-1 and total visual magnitude less than 14.5. Emission-line ([O III] and Hα+[N II]) and continuum (green and red) imaging of this sample has been presented in a previous paper. In this paper, we present the radio results, discuss statistical relationships between the radio and other properties, and investigate these relationships within the context of unified models of Seyferts. The mean radio luminosities of early-type Seyfert 1's (i.e., Seyfert 1.0's, 1.2's, and 1.5's) and 2.0's are found to be similar (consistent with the unified scheme), and the radio luminosity is independent of morphological type within this sample. The fraction of resolved radio sources is larger in the Seyfert 2.0's (93%) than in the Seyfert 1's (64%). However, the mean radio extents of Seyfert 2.0's and 1's are not significantly different, although this result is limited by the small number of resolved Seyfert 1's. The nuclear radio structures of Seyfert 2.0's in the early-type sample tend to be aligned with the [O III] and Hα+[N II] structures, even though the radio extents are smaller than the [O III] and Hα+[N II] extents by a factor of ~2 to more than 5. This alignment, previously known for individual Seyferts with "linear" radio sources, is here shown to be characteristic of early-type Seyfert galaxies as a class. Seyfert 2.0's in the early-type sample also show a significant alignment between the emission-line ([O III] and Hα+[N II]) axes and the major axis of the host galaxy. These alignments are consistent with a picture in which the ionized gas represents ambient gas predominantly coplanar with the galaxy stellar disk. This ambient gas is ionized by nuclear radiation that may escape preferentially along and around the radio axis, and is compressed in shocks driven by the radio ejecta. We use this alignment to constrain the product of the velocity of the radio ejecta and the period of any large-angle precession of the inner accretion disk and jet: Vejecta × P ≥ 2 kpc. An investigation of a larger sample of Seyferts reveals the unexpected result that the Seyfert 1's with the largest radio extent (≥1.5 kpc) are all of type Seyfert 1.2. It appears that classification as this type of intermediate Seyfert depends on some factor other than the relative orientation of the nuclear-obscuring torus to the line of sight. Among all the other Seyferts, the distribution of radio extent with Seyfert intermediate type is consistent with the expectations of the unified scheme.
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