Jet-accretion system in the nearby mJy Radio Galaxies
  It is generally thought that FRII Radio Galaxies host thin optically thick
disks, while FRIs are powered by Advected Dominated Accretion Flows. The
sources with an efficient engine are optically classified as High Excitation
Radio Galaxies (HERGs) and those with an inefficient motor as Low Excitation
Radio Galaxies (LERGs). Recently, the study of Radio Galaxies down to mJy
fluxes has cast serious doubts on the LERG-FRI and HERG-FRII correspondence,
revealing that many LERGs show FRII radio morphologies. The FR catalogs
recently compiled by Capetti et al. (2017a,b) and Baldi et al. (2018) have
allowed us to explore this issue in the local ($z\le 0.15$) mJy Universe. Our
statistical study shows that the majority of nearby mJy objects are in a late
stage of their life. FRII-LERGs appear more similar to the old FRI-LERGs than
to the young FRII-HERGs. FRII-LERGs may be aged HERGs that, exhausted the cold
fuel, have changed their accretion regime or a separate LERG class particularly
efficient in launching jets. Exploiting the empirical relations which convert
L$_{\rm [OIII]}$ and L$_{\rm 1.4~GHz}$ into accretion power and jet kinetic
power, respectively, we observed that LERGs with similar masses and accretion
rates seem to expel jets of different power. We speculate that intrinsic
differences related to the black hole properties (spin and magnetic field at
its horizon) can determine the observed spread in jet luminosity. In this view,
FRII-LERGs should have the fastest spinning black holes and/or the most intense
magnetic fluxes. On the contrary, compact LERGs (i.e. FR0s) should host
extremely slow black holes and/or weak magnetic fields.
