Seyfert galaxies: Nuclear Radio Structure and Unification
  A radio study of a carefully selected sample of 20 Seyfert galaxies that are
matched in orientation-independent parameters, which are measures of intrinsic
active galactic nuclei (AGN) power and host galaxy properties is presented to
test the predictions of the unified scheme hypothesis. Our sample sources have
core flux densities greater than 8 mJy at 5 GHz on arcsec-scales due to the
feasibility requirements. These simultaneous pc-scale and kpc-scale radio
observations reveal (i) that Seyfert 1 and Seyfert 2 galaxies have equal
tendency to show compact radio structures on mas-scales, (ii) the distributions
of pc-scale and kpc-scale radio luminosities are similar for both Seyfert 1 and
Seyfert 2 galaxies, (iii) no evidence for relativistic beaming in Seyfert
galaxies, (iv) similar distributions of source spectral indices in spite of the
fact that Seyferts show nuclear radio flux density variations, and (v) the
distributions of projected linear size for Seyfert 1 and Seyfert 2 galaxies are
not significantly different as would be expected in the unified scheme. The
latter could be mainly due to a relatively large spread in the intrinsic sizes.
We also find that a starburst alone cannot power these radio sources. Finally,
an analysis of the kpc-scale radio properties of the CfA Seyfert galaxy sample
shows results consistent with the predictions of the unified scheme.
