VLBI Imaging of Parsec-scale Radio Structures in Nearby Low-luminosity AGN

TL;DR

This study uses high-resolution VLBI observations to image and analyze the parsec-scale radio structures of nearby low-luminosity AGN, revealing core dominance, jet morphologies, and correlations with black hole and emission line luminosities.

Contribution

It provides the first high-resolution VLBI imaging of a diverse sample of nearby LLAGN, uncovering core structures, jet morphologies, and correlations that enhance understanding of their radio emission mechanisms.

Findings

High detection rate of 23 out of 36 sources with VLBI imaging.

Most sources exhibit compact, core-dominated radio structures.

Detected correlations between radio luminosity, black hole mass, and emission line luminosities.

Abstract

We report the results of high-resolution 5 GHz Very Long Baseline Array and European VLBI Network observations of 36 nearby galaxies, an extension of the Legacy e-MERLIN Multi-band Imaging of Nearby Galaxies (LeMMINGs) survey. Our sample includes 21 low ionization nuclear emission regions (LINERs), 4 Seyferts, 3 absorption line galaxies (ALGs), and 8 HII galaxies. We achieved an unprecedented detection rate, successfully imaging 23 out of 36 sources with a detection threshold of $\sim$20 $\mu$Jy beam$^{-1}$. The radio sizes are typically of $\leq$ 5 pc. Core identification was achieved in 16 sources, while 7 others were identified as core candidates. Radio luminosities of the sample range from 10$\rm ^{34}$ to 10$\rm ^{38}$ erg s$^{-1}$. Our analysis reveals a predominance of compact core structures, with ten sources exhibiting a one-sided core jet morphology and NGC 2146 exhibiting a rare two-sided jet structure. The study advances our understanding of the compactness of radio sources at various scales, indicating a core-dominated nature in all but one galaxy NGC2655. We find moderate to strong correlations between radio luminosity, black hole mass, optical [O III] line luminosity, and hard X-ray luminosity, suggesting a common active galactic nucleus (AGN) core origin. These results provide new insights into the fundamental plane of black hole activity and support the role of the synchrotron process in Low-luminosity AGN (LLAGN) radio emission.