Study of the Inner Structure of the Molecular Torus in IRAS 08572+3915 NW with Velocity Decomposition of CO Rovibrational Absorption Lines

Abstract

Understanding the inner structure of the clumpy molecular torus surrounding the active galactic nucleus is essential in revealing the forming mechanism. However, spatially resolving the torus is difficult because of its size of a few parsecs. Thus, to probe the clump conditions in the torus, we performed the velocity decomposition of the CO rovibrational absorption lines ($\Delta v=0\to 1,\Delta J=\pm 1$) at $\lambda \sim 4.67\mu \mathrm{m}$ observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the high-resolution spectroscopy ($R\sim 10,000$) of Subaru Telescope. Consequently, we found that each transition had two outflowing components, i.e., (a) and (b), both at approximately $\sim -160\mathrm{km}{\mathrm{s}}^{-1}$, but with broad and narrow widths, and an inflowing component, i.e., (c), at approximately $\sim +100\mathrm{km}{\mathrm{s}}^{-1}$, which were attributed to the torus. The ratios of the velocity dispersions of each component lead to those of the rotating radii around the black hole of $R_{\mathrm{rot},\mathrm{a}}:R_{\mathrm{rot},\mathrm{b}}:R_{\mathrm{rot},\mathrm{c}}\approx 1:5:17$, indicating the torus where clumps are outflowing in the inner regions and inflowing in the outer regions if a hydrostatic disk with ${\sigma }_V\propto R_{\mathrm{rot}}^{-0.5}$ is assumed. Based on the kinetic temperature of components (a) and (b) of $\sim 720\mathrm{K}$ and $\sim 25\mathrm{K}$ estimated from the level population, the temperature gradient is $T_{\mathrm{kin}}\propto R_{\mathrm{rot}}^{-2.1}$. Magnetohydrodynamic models with large density fluctuations of two orders of magnitude or more are necessary to reproduce this gradient.

Accepted for publication in ApJ, 27 pages, 13 figures, 6 tables, Minor changes after proof (v3)

References in corpus (16)

• Array Programming with NumPy
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• AGN Dusty Tori: I. Handling of Clumpy Media
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• AGN dust tori at low and high luminosities
• An image of the dust sublimation region in the nucleus of NGC 1068
• Multi-phase Nature of a Radiation-Driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus
• Modelling the spectral energy distribution of ULIRGs II: The energetic environment and the dense interstellar medium
• ALMA 0.02"-resolution observations reveal HCN-abundance-enhanced counter-rotating and outflowing dense molecular gas at the NGC 1068 nucleus
• 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
• On the evolution of gas clouds exposed to AGN radiation. I. Three-dimensional radiation hydrodynamic simulations
• The Near-Infrared CO Absorption Band as a Probe to the Innermost Part of an AGN Obscuring Material
• Multiphase Circumnuclear Gas in a Low-$\beta$ Disk: Turbulence and Magnetic Field Reversals
• A systematic study of ULIRGs using near-infrared absorption bands reveals a strong UV environment in their star-forming regions