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

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 ∼20 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 (≳0.9) in the central region (≲30 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 ] λ 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.