PAGaN II: The Evolution of AGN Jets on Sub-Parsec Scales

TL;DR

This study presents high-resolution VLBI observations of eight AGNs, revealing jet component kinematics, spectral index distributions, and jet expansion behaviors, advancing understanding of AGN jet evolution on sub-parsec scales.

Contribution

First VLBI imaging results from the PAGaN project showing detailed jet component kinematics and spectral properties of AGNs at multiple frequencies.

Findings

Detected superluminal jet motions up to 5c.

Spectral index maps show flat cores and steep jets, with variations by AGN type.

Jet diameters increase with distance, following a global relation d≈0.2r.

Abstract

We report first results from KVN and VERA Array (KaVA) VLBI observations obtained in the frame of our Plasma-physics of Active Galactic Nuclei (PAGaN) project. We observed eight selected AGN at 22 and 43 GHz in single polarization (LCP) between March 2014 and April 2015. Each source was observed for 6 to 8 hours per observing run to maximize the $uv$ coverage. We obtained a total of 15 deep high-resolution images permitting the identification of individual circular Gaussian jet components and three spectral index maps of BL Lac, 3C 111 and 3C 345 from simultaneous dual-frequency observations. The spectral index maps show trends in agreement with general expectations -- flat core and steep jets -- while the actual value of the spectral index for jets shows indications for a dependence on AGN type. We analyzed the kinematics of jet components of BL Lac and 3C 111, detecting superluminal proper motions with maximum apparent speeds of about $5c$. This constrains the lower limits of the intrinsic component velocities to $\sim0.98c$ and the upper limits of the angle between jet and line of sight to $\sim$20$\deg$. In agreement with global jet expansion, jet components show systematically larger diameters $d$ at larger core distances $r$, following the global relation $d\approx0.2r$, albeit within substantial scatter.