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

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 $\sim 20$ pc. Observations of C I, 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 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 ($\gtrsim 0.9$) in the central region ($\lesssim 30$ pc) for both C I and CO(3-2), indicating geometrically thick structures in both tracers. Regions where the C I/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 and CO(3-2) are consistent with a model in which supernova-driven turbulence provides the vertical support for the CND.