Jet formation studies in AGN: a search for new targets

Abstract

In recent years, the jet formation region in active galaxies has been imaged through mm-VLBI in few ideal targets, first and foremost M87. An important leap forward for understanding jet launching could be made by identifying a larger number of suitable objects, characterized by different accretion modes and jet powers. In this article, we present 1 cm and 7 mm VLBI data of a sample of 16 poorly explored radio galaxies, comprising both High-Excitation (HEG) and Low-Excitation Galaxies (LEG) and spanning a large range in radio power. The combination of the sources vicinity (z<0.1) with a large black hole mass ($\log M_{\mathrm{BH}}$>8.5) results in a high spatial resolution in units of Schwarzschild radii ($<10^3-10^4$ $R_{\mathrm{S}}$), necessary for probing the region where the jet is initially accelerated and collimated. We aim at identifying the best candidates for follow-up observations with current and future VLBI facilities. The observations were performed with the High Sensitivity Array, including Effelsberg and the phased-VLA, which 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 $\lesssim 10^3$ $R_{\mathrm{S}}$ is more than doubled by our study. All targets were detected at both frequencies, and several present two-sided jet structures. Several LEG jets show hints of limb-brightening. The core brightness temperatures are generally below the equipartition value, indicating that equipartition has not yet been reached and/or that the emission is de-boosted. Among LEG, we identify 3C31, 3C66B, and 3C465 as the most promising, combining a relatively high flux density (>50 mJy) with superb spatial resolution (<500 $R_{\mathrm{S}}$) at 7 mm. The powerful HEG 3C452 is interesting as well due to its highly symmetric, two-sided jet base.

Main: 7 pages, 2 figures. Appendix: 15 pages, 15 figures. Accepted in A&A

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Cited by in corpus (2)

• Dim cores of radio-bright AGN jets: VLBI and Gaia astrometry pinpoint different parsec-scale features
• The twin-jet system in the FRII radio galaxy 3C 452: A sub-parsec scale VLBI study