In recent years, the jet formation region in active galaxies has been imaged through millimeter very long baseline interferometry (mm-VLBI) for a few ideal targets, in particular, M87. An important leap forward for understanding jet launching could be taken by identifying a larger number of suitable objects, characterized by different accretion modes and jet powers. In this article, we present 1cm and 7mm VLBI data of a sample of 16 poorly explored radio galaxies, comprising both highexcitation (HEGs) and low-excitation galaxies (LEGs), spanning a broad range in terms of radio power. There are several -ray emitters among this sample. The sources proximity (z~8.5) implies a high spatial resolution in units of Schwarzschild radii (<10^3^-10^4^RS), necessary for probing the region where the jet is initially accelerated and collimated. We aim to identify the best candidates for follow-up observations with current and future VLBI facilities. The observations were performed with the High Sensitivity Array (HSA), including the Eelsberg telescope and the phased Very Large Array (VLA). The addition of elements with a large collecting area has allowed us to characterize the sub-parsec properties of these faint jets and to estimate their core brightness temperature and orientation. The number of sources imaged on scales 50mJy) with a superb spatial resolution (<500RS) at 7mm. The powerful HEG 3C 452 is interesting as well, due to its highly symmetric, two-sided jet base. Most sources are expected to become prime targets for future experiments with the next generation Event Horizon Telescope (ngEHT) and next generation Very Large Array (ngVLA).

Cone search capability for table J/A+A/695/A118/list (List of fits files)