A relation between circumnuclear HI, dust, and optical cores in low-power radio galaxies

TL;DR

This study explores the relationships between neutral hydrogen, dust, and optical cores in low-power radio galaxies, revealing correlations that inform understanding of galactic feeding mechanisms without evidence of a compact torus.

Contribution

It identifies physical relations between HI, dust, and optical cores in low-power radio galaxies, aiding future studies of kinematics and feeding mechanisms.

Findings

HI absorption always associated with dust presence

Optical core absence correlates with high HI column density

No evidence of a parsec-scale obscuring torus in these galaxies

Abstract

From new observations and literature data we investigate the presence of HI, dust, and optical cores in the central kiloparsec of low-power radio galaxies. The goal of this pilot study is to identify physical relations between these components, which can help us to study kinematics and feeding mechanisms in future samples of active galaxies. Our results are consistent with neutral gas being associated with dust on sub-kiloparsec scales. Objects that have HI absorption always have significant amounts of dust in their host galaxy. If there is no visible dust in the host galaxy, there is also no HI absorption. The presence of an unresolved optical core correlates with the HI column density, with the core being absent in high column density sources. This work opens a path for studying the kinematics of cold material in the central regions of active galaxies by combining information of HI absorption and molecular lines. Consistent with previous work, we find no evidence for a compact, parsec-scale obscuring torus in low-power radio galaxies.