What makes a galaxy radio-loud?
  We compare the Spectral Energy Distribution (SED) of radio-loud and
radio-quiet AGNs in three different samples observed with SDSS: radio-loud AGNs
(RLAGNs), Low Luminosity AGNs (LLAGNs) and AGNs in isolated galaxies (IG-AGNs).
All these galaxies have similar optical spectral characteristics. The median
SED of the RLAGNs is consistent with the characteristic SED of quasars, while
that of the LLAGNs and IG-AGNs are consistent with the SED of LINERs, with a
lower luminosity in the IG-AGNs than in the LLAGNs. We infer the masses of the
black holes (BHs) from the bulge masses. These increase from the IG-AGNs to the
LLAGNs and are highest for the RLAGNs. All these AGNs show accretion rates near
or slightly below 10% of the Eddington limit, the differences in luminosity
being solely due to different BH masses. Our results suggests there are two
types of AGNs, radio quiet and radio loud, differing only by the mass of their
bulges or BHs.
