Parsec-scale jets of FR0 radio galaxies

Radio galaxies (RGs) are active galactic nuclei (AGN) able to launch relativistic jets, the most energetic phenomena in the Universe, which can have a large impact on galaxy evolution. Current high-sensitivity and high-resolution surveys have shed new light on properties of RGs, particularly in the local Universe (z10 kpc) jet emission, is emerging from recent studies and is revolutionising our idea of an ordinary RG. These compact sources show host and nuclear characteristics similar to those of FRI RGs. However, in the radio band, while FR0s and FRIs share the same core properties, the kpc-scale diffuse component dominant in FRI is missing in FR0s. VLBI observations of FR0s can probe the parsec-scale region to study their actual capability of launching jets with respect to FRIs. I will present VLBA, EVN and eMERLIN observations of a sample of FR0s, which provide evidence that parsec-scale jets in FR0s are mildly relativistic with a bulk velocity on the order of 0.5c or less. A jet structure with a thin inner relativistic spine surrounded by a low-velocity sheath could be in agreement with the observed FR0 properties