Probing dynamics and thermal properties inside molecular tori with CO rovibrational absorption lines

Abstract

A recent hydrodynamic model, "radiation-driven fountain model" (Wada et al. 2016), presented a dynamical picture that active galactic nuclei (AGNs) tori sustain their geometrical thickness by gas circulation around AGNs, and previous papers confirmed that this picture is consistent with multi-wavelength observations of nearby Seyfert galaxies. Recent near-infrared observations implied that CO rovibrational absorption lines ($\Delta J=\pm 1$, $v=0-1$, $\lambda \sim 4.7$ $\mu \mathrm{m}$) could probe physical properties of the inside tori. However, the origin of the CO absorption lines has been under debate. In this paper, we investigate the origin of the absorption lines and conditions for detecting them by performing line radiative transfer calculations based on the radiation-driven fountain model. We find that CO rovibrational absorption lines are detected at inclination angles ${\theta }_{\mathrm{obs}}=50-80$ ${}^{\circ }$. At the inclination angle ${\theta }_{\mathrm{obs}}=77$ ${}^{\circ }$, we observe multi-velocity components: inflow ($v_{\mathrm{LOS}}=30$ $\mathrm{km}{\mathrm{s}}^{-1}$), systemic ($v_{\mathrm{LOS}}=0\mathrm{km}{\mathrm{s}}^{-1}$), and outflows ($v_{\mathrm{LOS}}=-75,-95,$ and $-105$ $\mathrm{km}{\mathrm{s}}^{-1}$). The inflow and outflow components ($v_{\mathrm{LOS}}=30$ and $-95$ $\mathrm{km}{\mathrm{s}}^{-1}$) are collisionally excited at the excitation temperature of $186$ and $380$ K up to $J=12$ and $4$, respectively. The inflow and outflow components originate from the accreting gas on the equatorial plane at $1.5$ pc from the AGN center and the outflowing gas driven by AGN radiation pressure at $1.0$ pc, respectively. These results suggest that CO rovibrational absorption lines can provide us with the velocities and kinetic temperatures of the inflow and outflow in the inner a-few-pc regions of AGN tori, and the observations can probe the gas circulation inside the tori.

19 pages, 17 figures, 3 tables, accepted by The Astrophysical Journal

References in corpus (13)

• Multi-phase Nature of a Radiation-Driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus
• Thermal imaging of dust hiding the black hole in the Active Galaxy NGC 1068
• 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
• The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High Velocity CO
• 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
• Warm Absorbers in the Radiation-driven Fountain Model of Low-mass Active Galactic Nuclei
• Circumnuclear Multi-phase Gas in Circinus Galaxy IV: absorption owing to high-$J$ CO rotational transitions

Cited by in corpus (6)

• Hard X-Ray to Radio Multiwavelength SED Analysis of Local U/LIRGs in GOALS Sample with Self-consistent AGN Model Including Polar-dust Component
• 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 Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Ro-vibrational Absorptions
• Systematic Study of the Inner Structure of Molecular Tori in Nearby U/LIRGs using Velocity Decomposition of CO Rovibrational Absorption Lines
• Broad line regions behind haze: Intrinsic shape of Br$\gamma$ line and its origin in a type-1 Seyfert galaxy