Circumnuclear Multi-phase Gas in Circinus Galaxy IV: absorption owing to high-$J$ CO rotational transitions

Abstract

We studied the absorption features of CO lines against the continuum originating from the heated dust in the obscuring tori around active galactic nuclei (AGNs). We investigated the formation of absorption lines corresponding to the CO rotational transitions using three-dimensional non-LTE line transfer simulations considering the dust thermal emission. As in Papers I--III of this series, we performed post-processed radiative transfer calculations using the "radiation-driven fountain model" (wada2016}, which yields a geometrically thick obscuring structure around the nucleus. This model is consistent with the spectral energy distribution of the nearest type-2 Seyfert galaxy, the Circinus galaxy. We found that the continuum-subtracted channel maps of $J=4-3$ and higher transitions show absorption regions along the disk mid-plane for an edge-on viewing angle. The spectra consist of multiple absorption and emission features, reflecting the internal inhomogeneous and turbulent structure of the torus. The deepest absorption feature is caused by the gas on the near-side of the torus between $r=10$ and 15 pc, which is located in front of the AGN-heated dust inside $r\simeq 5$ pc. We also found that a spatial resolution of 0.5--1.0 pc is necessary to resolve the absorption features. Moreover, the inclination angle must be close to the edge-on angle (i.e., $\sim 85^{\circ }$) to observe the absorption features. The findings of the present study imply that combining our radiation-hydrodynamic model with high-resolution observations of CO (7-6) by ALMA can provide new information about the internal structure of the molecular tori in nearby AGNs.

21 pages, 12 figures, accepted by Astrophysical Journal

References in corpus (12)

• Molecular line emission in NGC1068 imaged with ALMA. I An AGN-driven outflow in the dense molecular gas
• An Observed Fundamental Plane Relation for Supermassive Black Holes
• Molecular line emission in NGC1068 imaged with ALMA: II. The chemistry of the dense molecular gas
• Multi-phase Nature of a Radiation-Driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus
• Time-resolved infrared emission from radiation-driven central obscuring structures in Active Galactic Nuclei
• HCN to HCO^+ Millimeter Line Diagnostics of AGN Molecular Torus I : Radiative Transfer Modeling
• Geometrically thick obscuration by radiation-driven outflow from magnetized tori of active galactic nuclei
• Circumnuclear Multi-phase Gas in Circinus Galaxy I: Non-LTE calculations of CO lines
• Physically motivated X-ray obscurer models
• Radiation hydrodynamics models of Active Galactic Nuclei: Beyond the central parsec
• The Near-Infrared CO Absorption Band as a Probe to the Innermost Part of an AGN Obscuring Material
• Parsec-scale obscuring accretion disk with large scale magnetic field in AGN

Cited by in corpus (7)

• Supermassive black hole feeding and feedback observed on sub-parsec scales
• Self-consistent dust and non-LTE line radiative transfer with SKIRT
• Multiphase Gas Nature in the Sub-parsec Region of the Active Galactic Nuclei I: Dynamical Structures of Dusty and Dust-free Outflow
• Warm Absorbers in the Radiation-driven Fountain Model of Low-mass Active Galactic Nuclei
• Probing dynamics and thermal properties inside molecular tori with CO rovibrational absorption lines
• High resolution mapping of molecular tori with ALMA
• Broad line regions behind haze: Intrinsic shape of Br$\gamma$ line and its origin in a type-1 Seyfert galaxy