The Most Compact Bright Radio-loud AGNs. II. VLBA Observations of 10 Sources at 43 and 86 GHz

Abstract

Radio-loud active galactic nuclei (AGNs), hosting powerful relativistic jet outflows, provide an excellent laboratory for studying jet physics. Very long baseline interferometry (VLBI) enables high-resolution imaging on milli-arcsecond (mas) and sub-mas scales, making it a powerful tool to explore the inner jet structure, shedding light on the formation, acceleration and collimation of AGN jets. In this paper, we present Very Long Baseline Array (VLBA) observations of ten radio-loud AGNs at 43 and 86 GHz, which were selected from the Planck catalogue of compact sources and are among the brightest in published VLBI images at and below 15 GHz. The image noise levels in our observations are typically 0.3 mJy beam at 43 and 86 GHz, respectively. Compared with the VLBI data observed at lower frequencies from the literature, our observations with higher resolution (the highest resolution up to 0.07 mas at 86 GHz and 0.18 mas at 43 GHz) and at higher frequencies detected new jet components at sub-parsec scales, offering valuable data for studies of the physical properties of innermost jets. These include compactness factor of the radio structure (the ratio of core flux density to total flux density), and core brightness temperature (T b ). In all these sources, the compact core accounts for a significant -2 -fraction (> 60%) of the total flux density. Their correlated flux density at the longest baselines is higher than 0.16 Jy. The compactness of these sources make them good phase calibrators of mm-wavelength ground-based and space VLBI.

Characterizing the γ-Ray Emission from FR0 Radio Galaxies

“…Progress in this regard might be possible with state-of-the-art high-resolution and sensitive instruments such as the upcoming Square Kilometer Array (SKA). Very long baseline interferometry images with greater details and observations at higher frequencies would be beneficial for disentangling the core and jet components in these galaxies (Cheng et al 2018(Cheng et al , 2021Baldi et al 2021;Giovannini et al 2023). Constraints on the core magnetic field strength in FR0 jets could be obtained through polarization and Faraday rotation measurements with the Polarisation Sky Survey of the Universe's Magnetism, the Australian SKA Pathfinder telescope.…”