Compact sources in the Bologna Complete Sample: high-resolution VLA observations and optical data

Context. Among radio galaxies, compact sources are a class of objects that are not yet well understood, and most of them cannot be included in classical populations of compact radio sources (flat-spectrum or compact steep-spectrum sources). Aims. Our main goal is to analyze the radio and optical properties of a sample of compact sources and compare them with Faranoff-Riley I and II extended radio galaxies. Methods. We selected in the Bologna Complete Sample a subsample of compact sources, naming it the C BCS sample. We collected new and literature subarcsecond resolution multi-frequency VLA images and optical data. We compared total and nuclear radio power with optical emission line measurements. Results. The [OIII] luminosity - 408 MHz total power relation found in high-and low-excitation galaxies as well as in young (CSS) sources holds also for the C BCSs. However, C BCSs present higher [OIII] luminosity than expected at a given total radio power, and they show the same correlation as core radio galaxies, but with a higher radio power. Conclusions. The C BCSs appear to be the high-power tail of core radio galaxies. For most of the C BCSs, the morphology seems to be strongly dependent on the presence of dense environments (e. g., cluster or HI-rich galaxies) and on a young age or restarted radio activity.