Find in Library

We present the results from high-resolution observations carried out with the <i>e</i>MERLIN UK-array and the European VLBI network (EVN) for a sample of 15 FR 0s, i.e., compact core-dominated radio sources associated with nearby early-type galaxies (ETGs), which represent the bulk of the local radio galaxy population. The 5 GHz <i>e</i>MERLIN observations available for five objects exhibit sub-mJy core components and reveal pc-scale twin jets for four out of five FR 0s once the <i>e</i>MERLIN and JVLA archival visibilities data are combined. The 1.66 GHz EVN observations available for 10 FR 0s display one- and two-sided jetted morphologies and compact cores. The pc-scale core emission contributes, on average, to about one tenth of the total extended radio emission, although we noted an increasing core contribution for flat-/inverted-spectrum sources. We found an unprecedented linear correlation between the pc-scale core luminosity (∼10<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mn>21.3</mn></mrow></msup></semantics></math></inline-formula>–10<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mn>23.6</mn></mrow></msup></semantics></math></inline-formula> W Hz<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></semantics></math></inline-formula>) and [O III] line luminosity, generally considered as proxy of the accretion power, for a large sample of LINER-type radio-loud low-luminosity active nuclei, all hosted in massive ETGs, which include FR 0s and FR Is. This result represents further evidence of a common jet–disc coupling in FR 0s and FR Is, despite then differing in kpc-scale radio structure. For our objects and for other FR 0 samples reported in the literature, we estimated the jet brightness sidedness ratios, which typically range between one and three. This parameter roughly gauges the jet bulk Lorentz factor <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Γ</mi></semantics></math></inline-formula>, which turns out to range from 1 to 2.5 for most of the sample. This corroborates the scenario that FR 0s are characterized by mildly relativistic jets, possibly as a result of lower-spinning black holes (BHs) than the highly spinning BHs of relativistic-jetted radio galaxies, FR Is.