# Radio jet structures at ~100 parsec and larger scales of the $\gamma$-ray-emitting narrow-line Seyfert 1 galaxy PMN J0948+0022

## TL;DR

This study investigates the radio jet structures of the gamma-ray-emitting NLS1 galaxy PMN J0948+0022 at ~100 parsecs and larger scales, revealing stable, moderate-speed jets with energy conversion processes and a large-scale radio lobe.

## Contribution

First detailed analysis of multi-scale radio jet structures in PMN J0948+0022, linking pc-scale jet features with large-scale radio lobes and jet dynamics.

## Key findings

- Large-scale radio lobe indicates terminal shock and stable jet direction.
- Jet shows superluminal motions and energy conversion from kinetic to internal energy.
- Jet activity age aligns with typical NLS1 phase of ~10^7 years.

## Abstract

The narrow-line Seyfert 1 (NLS1) galaxy PMN J0948+0022 is an archetype of gamma-ray-emitting NLS1s in active galactic nuclei (AGNs). In this study, we investigate its radio structures using archival data obtained using the Karl G.~Jansky very large array (VLA) and the very long baseline array (VLBA). The new VLA images reveal an outermost radio emission separated by 9.1 arcsec. Its resolved structure and steep spectrum suggest a terminal shock in a radio lobe energized by the jet from the PMN J0948+0022 nucleus. This large-scale radio component is found at almost the same position angle as that of the pc-scale jet, indicating a stable jet direction up to ~1 Mpc. Its apparent one-sidedness implies a moderate advancing speed ($\beta>0.27$). The kinematic age of 1 x 10^7 year of the jet activity is consistent with the expected NLS1 phase of ~10^7 year in the AGN lifetime. The VLBA image reveals the jet structure at distances ranging from r=0.82 milliarcsec to 3.5 milliarcsec, corresponding to approximately 100 pc, where superluminal motions were found. The jet width profile ($\propto r^{1.12}$) and flux-density profile ($\propto r^{-1.44}$) depending on the distance $r$ along the jet suggest that the jet kinetic energy is converted into internal energy in this region. The jet is causally connected in a nearly conical streamline, which is supported by ambient pressure at 100 pc scales in the host galaxy of PMN J0948+0022.