Multiphase Gas Structure in the Circumnuclear Region of NGC 5506 Observed with ALMA

TL;DR

This study uses ALMA observations to analyze the multiphase gas structure and kinematics of NGC 5506's circumnuclear disk, revealing thick, turbulent gas influenced by AGN activity and supernova-driven turbulence.

Contribution

First detailed ALMA study of multiphase gas and kinematics in NGC 5506's CND, highlighting the impact of AGN outflows and turbulence on disk structure.

Findings

CND dominated by rotation on scales of hundreds of parsecs.

HCO$^{+}$ emission is more concentrated toward the disk plane.

High velocity dispersion indicates geometrically thick structures.

Abstract

We present a study of the multiphase gas structure and kinematics of the circumnuclear disk (CND) of NGC 5506, a nearby edge-on Seyfert galaxy, at a spatial resolution of $\sim20$ pc. Observations of [C I](1-0), CO(3-2), and HCO$^{+}$(4-3) obtained with the Atacama Large Millimeter/submillimeter Array reveal the CND dominated by rotational motion on scales of several hundred parsecs. No significant differences in geometrical thickness or velocity structure are found between [C I](1-0) and CO(3-2) across the CND, whereas HCO$^{+}$(4-3) emission is more concentrated toward the disk plane. The ratio of velocity dispersion to rotational velocity, a proxy for disk scale height-to-radius ratio, is high ($\gtrsim0.9$) in the central region ($\lesssim30$ pc) for both [C I](1-0) and CO(3-2), indicating geometrically thick structures in both tracers. Regions where the [C I](1-0)/CO(3-2) ratio exceeds the CND average are spatially correlated with the [O III]$\lambda$5007 bicone observed with the Hubble Space Telescope, suggesting that CO is preferentially dissociated by the AGN-driven biconical ionized outflow. The observed CND scale height and velocity dispersions traced by [C I](1-0) and CO(3-2) are consistent with a model in which supernova-driven turbulence provides the vertical support for the CND.