The nature of compact radio-loud AGN selected by LOFAR
We investigate the nature of low-luminosity radio-loud AGN selected from LoTSS DR1. We have selected 55 radiative AGN candidates from LoTSS DR1 at redshift z<0.1. We show using high-frequency VLA observations that only 10 objects show extended radio emission (<3 kpc), 42 are compact at the angular limiting resolution of 0.35 arcsec (<1 kpc in projected physical size), while 3 are undetected. The extended objects display a wide range of radio morphologies: doubles, two-jet, core-jet, elongated, and complex. We discuss their radio spectra which range from steep to flat/inverted spectra and span the range seen in other compact AGN such as CSOs, CSSs, and GPSs. Assuming SSA for flat/inverted radio spectrum compact objects, we predict small physical sizes on parsec scales. The compact objects do not occupy a special position on the P-D diagram but share a region with low-radio power CSOs. Finally, we compare their radio properties with those of so-called “FR0s”. These differ from our targets mainly in their classification: FR0s are typically associated with low-excitation radio galaxies, whereas our objects are high-excitation radio galaxies. Studying these objects in the larger LoTSS DR2 will further our understanding of AGN feedback.