Isophotal Structure and Dust Distribution in Radio-Loud Elliptical Galaxies

TL;DR

This study examines the relationship between isophotal shapes and dust structures in radio-loud elliptical galaxies, revealing how viewing angle influences observed galaxy morphology and linking dust features to galaxy merger history.

Contribution

It provides new insights into how dust morphology correlates with isophotal shape and viewing angle, supporting merger-based galaxy evolution models.

Findings

Edge-on disks are associated with boxy isophotes.

Round, face-on disks are linked to round or elliptical isophotes.

Dusty filamentary lanes are found in disky, younger merger remnants.

Abstract

We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxies, imaged in the optical and near-infrared as part of Hubble Space Telescope snapshot surveys. We present a sample-wide trend between host galaxy isophotal structure and the inclination of dusty circumnuclear disks at the centers of 13 of these objects. We find that galaxies containing edge-on disks are invariably seen to possess boxy isophotes, while round, face-on disks are seen exclusively in objects with round or elliptical isophotes. Dust-rich sources with disky isophotes are observed only to possess dust in the form of extended filamentary lanes, and not in settled distributions like disks. As we do not expect that edge-on and face-on disks reside in different populations of galaxies, we conclude that perceived isophotal boxiness is dependent upon the angle at which the observer views the host galaxy's axis of symmetry. We discuss our results in the context of dissipative merger scenarios, and infer that dusty disks primarily reside in old, boxy remnants of gas-poor galaxy mergers, whereas filamentary dust lanes reside in younger disky remnants of gas-rich mergers.