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 \sim 1 Mpc .
Its apparent one-sidedness implies a moderate advancing speed ( \beta > 0.27 ) .
The kinematic age of 1 \times 10 ^ { 7 } year of the jet activity is consistent with the expected NLS1 phase of \sim 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 .