Thick Disks, and an Outflow, of Dense Gas in the Nuclei of Nearby Seyfert Galaxies

TL;DR

This study reveals that dense molecular gas in the nuclei of nearby Seyfert galaxies often forms thick disks and outflows, with detailed kinematic analysis showing commonality and specific physical properties of the gas.

Contribution

It provides high-resolution observations and a combined analysis of multiple Seyfert galaxies, demonstrating the prevalence of thick disk structures and characterizing the physical state of circumnuclear gas.

Findings

Thick disk structures are common in Seyfert nuclei.

A relation between HCN luminosity and dynamical mass suggests a 10% gas fraction.

Molecular clouds near AGN are not self-gravitating.

Abstract

We discuss the dense molecular gas in central regions of nearby Seyfert galaxies, and report new arcsec resolution observations of HCN(1-0) and HCO$^+$(1-0) for 3 objects. In NGC 3079 the lines show complex profiles as a result of self-absorption and saturated continuum absorption. H$^{13}$CN reveals the continuum absorption profile, with a peak close to the galaxy's systemic velocity that traces disk rotation, and a second feature with a blue wing extending to $-350$km s$^{-1}$ that most likely traces a nuclear outflow. The morphological and spectral properties of the emission lines allow us to constrain the dense gas dynamics. We combine our kinematic analysis for these 3 objects, as well as another with archival data, with a previous comparable analysis of 4 other objects, to create a sample of 8 Seyferts. In 7 of these, the emission line kinematics imply thick disk structures on radial scales of $\sim$100pc, suggesting such structures are a common occurrence. We find a relation between the circumnuclear LHCN and Mdyn that can be explained by a gas fraction of 10% and a conversion factor {\alpha}HCN $\sim$ 10 between gas mass and HCN luminosity. Finally, adopting a different perspective to probe the physical properties of the gas around AGN, we report on an analysis of molecular line ratios which indicates that the clouds in this region are not self-gravitating.