What distinguishes the host galaxies of radio-loud and radio-quiet AGNs?
  We compare the optical properties of the host galaxies of radio-quiet (RQ)
and radio-loud (RL) Type 2 active galactic nuclei (AGNs) to infer whether the
jet production efficiency depends on the host properties or is determined just
by intrinsic properties of the accretion flows. We carefully select galaxies
from SDSS, FIRST, and NVSS catalogs. We confirm previous findings that the
fraction of RL AGNs depends on the black-hole (BH) masses, and on the Eddington
ratio. The comparison of the nature of the hosts of RL and RQ AGNs, therefore,
requires pair-matching techniques. Matching in BH mass and Eddington ratio
allows us to study the differences between galaxies hosting RL and RQ AGNs that
have the same basic accretion parameters. We show that these two samples differ
predominantly in the host-galaxy concentration index, morphological type (in
the RL sample the frequency of elliptical galaxies becoming larger with
increasing radio loudness), and nebular extinction (galaxies with highest radio
loudness showing only low nebular extinction). Contrary to some previous
studies, we find no significant difference between our radio-loud and
radio-quiet samples regarding merger/interaction features.
