Structural Transition in the NGC 6251 Jet: An Interplay with the Supermassive Black Hole and Its Host Galaxy

TL;DR

This study reveals a structural transition in the NGC 6251 jet from parabolic to conical shape near the SMBH, highlighting the interplay between the jet, black hole, and host galaxy, based on high-resolution VLBI observations.

Contribution

It provides the first detailed analysis of the jet's structural transition at milliarcsecond scales and links this to the SMBH's sphere of influence, advancing understanding of AGN jet physics.

Findings

Jet transitions from parabolic to conical shape at 1-2 x 10^5 Schwarzschild radii

Jet pressure profiles support physical origin of the structural transition

Comparison with M87 jet suggests a common AGN jet process

Abstract

The structure of the NGC 6251 jet on the milliarcsecond scale is investigated using images taken with the European VLBI Network and the Very Long Baseline Array. We detect a structural transition of the jet from a parabolic to a conical shape at a distance of (1-2) x 10^5 times the Schwarzschild radius from the central engine, which is close to the sphere of gravitational influence of the supermassive black hole (SMBH). We also examine the jet pressure profiles with the synchrotron minimum energy assumption to discuss the physical origin of the structural transition. The NGC 6251 jet, together with the M87 jet, suggests a fundamental process of structural transition in the jets of active galactic nuclei (AGNs). Collimated AGN jets are characterized by their external galactic medium, showing that AGN jets interplay with the SMBH and its host galaxy.