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We present the results of Karl G. Jansky Very Large Array (VLA) observationsto study the properties of FR0 radio galaxies, the compact radio sourcesassociated with early-type galaxies which represent the bulk of the localradio-loud AGN population. We obtained A-array observations at 1.5, 4.5, and7.5 GHz for 18 FR0s from the FR0CAT sample: these are sources at $z<0.05$,unresolved in the FIRST images and spectroscopically classified as lowexcitation galaxies (LEG). Although we reach an angular resolution of $\sim$0.3arcsec, the majority of the 18 FR0s is still unresolved. Only four objects showextended emission. Six have steep radio spectra, 11 are flat cores, while oneshows an inverted spectrum. We find that 1) the ratio between core and totalemission in FR0s is $\sim$30 times higher than in FRI and 2) FR0s share thesame properties with FRIs from the nuclear and host point of view. FR0s differfrom FRIs only for the paucity of extended radio emission. Different scenarioswere investigated: 1) the possibility that all FR0s are young sourceseventually evolving into extended sources is ruled out by the distribution ofradio sizes; 2) similarly, a time-dependent scenario, where a variation ofaccretion or jet launching prevents the formation of large-scales radiostructures, appears to be rather implausible due to the large abundance ofsub-kpc objects 3) a scenario in which FR0s are produced by mildly relativisticjets is consistent with the data but requires observations of a larger sampleto be properly tested.

High-resolution VLA observations of FR0 radio galaxies: properties and nature of compact radio sources