Superdisks and the structural asymmetry of radio galaxies

TL;DR

This paper studies a unique class of radio galaxies with superdisks, exploring their asymmetric morphology, proposing a merger-based formation model, and investigating how jet-medium interactions influence hotspot brightness.

Contribution

It introduces a new model for superdisk formation via galaxy mergers and examines the impact of asymmetry on jet interactions and hotspot brightness in radio galaxies.

Findings

Asymmetric jet interactions affect hotspot brightness.

Superdisks likely formed through galaxy mergers.

Possible link between superdisks and X-shaped radio sources.

Abstract

We present a sample of 16 radio galaxies, each of which is characterized by a wide, elongated emission gap with fairly sharp and straight edges between the two radio lobes. This particular subset of the 'superdisk' radio galaxies is chosen because of a highly asymmetric location of the host elliptical galaxy relative to the gap's central axis. In addition to posing a considerable challenge to the existing models, such a morphology also means that the two jets traverse highly unequal distances through the superdisk material. One thus has a possibility to directly investigate if the marked asymmetry between the two jets' interaction with the (much denser) ambient medium, during their propagation, has a significant import for the brightness of the hotspot forming near each jet's extremity. We also propose a new explanation for the formation of superdisks through the merger of a smaller elliptical galaxy with the massive host, in which the gas attached to the infalling galaxy deposits its angular momentum into the host's circumgalactic gas, thereby causing it to flatten into a fat pancake, or superdisk. The asymmetric location of the host galaxy can be assisted by the kick imparted to it during the merger. We also suggest a physical link between these radio galaxies and those with X-shaped and Z-symmetric radio lobes, commonly believed to arise from mergers of two galactic nuclei, each harboring a supermassive black hole.