The Complex North Transition Region of Centaurus A: Radio Structure

TL;DR

This study uses deep VLA radio imaging to explore the complex transition regions of Centaurus A, revealing new extended emissions, pressure differences, and evidence supporting a galactic wind as the energy flow mechanism.

Contribution

It provides the first detailed radio imaging of the North Transition Region, identifying new structures and challenging previous jet interpretations, suggesting a galactic wind as the energy transport.

Findings

Discovery of extended emission around the Inner Lobes.

The North Middle Lobe is overpressured relative to the ISM.

No evidence of a collimated jet from the AGN.

Abstract

We present deep radio images of the inner 50 kpc of Centaurus A, taken with the Karl G. Jansky Very Large Array (VLA) at 90cm. We focus on the Transition Regions between the inner galaxy - including the active nucleus, inner radio lobes, and star-forming disk - and the outer radio lobes. We detect previously unknown extended emission around the Inner Lobes, including radio emission from the star-forming disk. We find that the radio-loud part of the North Transition Region, known as the North Middle Lobe, is significantly overpressured relative to the surrounding ISM. We see no evidence for a collimated flow from the Active Galactic Nucleus (AGN) through this region. Our images show that the structure identified by Morganti et al. (1999) as a possible large-scale jet appears to be part of a narrow ridge of emission within the broader, diffuse, radio-loud region. This knotty radio ridge is coincident with other striking phenomena: compact X-ray knots, ionized gas filaments, and streams of young stars. Several short-lived phenomena in the North Transition Region, as well as the frequent re-energization required by the Outer Lobes, suggest that energy must be flowing through both Transition Regioins at the present epoch. We suggest that the energy flow is in the form of a galactic wind.