2007 Fiscal Year Final Research Report Summary
Numerical Astronomy using molecular and atomic line transfer calculations in the ALMA-era.
| Project/Area Number |
16204012
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Astronomy
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| Research Institution | National Astronomical Observatory of Japan |
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Principal Investigator |
MIYAMA Shoken National Astronomical Observatory of Japan, Director (00166191)
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| Co-Investigator(Kenkyū-buntansha) |
TOMISAKA Kohji National Astronomical Observatory of Japan, Theoretical Astrophysics Division, Professor (70183879)
WADA Keiichi National Astronomical Observatory of Japan, Theoretical Astrophysics Division, Associate Professor (30261358)
OMUKAI Kazuyuki National Astronomical Observatory of Japan, Theoretical Astrophysics Division, Associate Professor (70390622)
KOHNO Kotaro The University of Tokyo, Graduate School of Department of Science, Associate Professor (80321587)
TOMOHARU Oka The University of Tokyo, Graduate School of Department of Science, Assistant Professor (10291056)
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| Project Period (FY) |
2004 – 2007
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| Keywords | Numerical Simulation / Radiative Transfer / Interstellar matter |
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| Research Abstract |
We explore millimeter line diagnostics of an obscuring molecular torus modeled by a hydrodynamic simulation with three-dimensional non-local thermodynamic equilibrium radiative transfer calculations. Based on the results of a high-resolution hydrodynamic simulation of the molecular torus around an active galactic nucleus, we calculate the intensities of the HCN and HCO+ rotational lines as two representative high-density tracers. Three-dimensional radiative transfer calculations shed light on a complicated excitation state in the inhomogeneous torus, even though a spatially uniform chemical structure is assumed. We find that similar transition coefficients for the HCN and HCO+ rotational lines lead to a natural concordance of the level population distributions of these molecules and a line ratio RHCN/HC0+<〜1 for the same molecular abundance value over 2 orders of magnitude. Our results suggest that HCN must be much more abundant than HCO+ (yHCN>〜10yHCO+) in order to obtain the high ratio (RHCN/HCO+-2) observed in some nearby galaxies. There is a remarkable dispersion in the relation between integrated intensity and column density, indicative of possible shortcomings of the HCN (1-0) and HCO+ (1-0) lines as high-density tracers. The internal structures of inhomogeneous molecular tori down to subparsec scales in external galaxies will be revealed by the forthcoming Atacama Large Millimeter/submillimeter Array. Three-dimensional radiative transfer calculations of molecular lines with a high-resolution hydrodynamic simulation prove to be a powerful tool to provide a physical basis for molecular-line diagnostics of the central regions of external galaxies.
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