[KSCI] Korea Science Citation Index Service

http://dx.doi.org/10.5303/JKAS.2021.54.6.183

ONE-DIMENSIONAL TREATMENT OF MOLECULAR LINE RADIATIVE TRANSFER IN CLUMPY CLOUDS

Park, Yong-Sun (Department of Physics and Astronomy, Seoul National University)

Publication Information

Journal of The Korean Astronomical Society / v.54, no.6, 2021 , pp. 183-190 More about this Journal

Abstract

We have revisited Monte Carlo radiative transfer calculations for clumpy molecular clouds. Instead of introducing a three-dimensional geometry to implement clumpy structure, we have made use of its stochastic properties in a one-dimensional geometry. Taking into account the reduction of spontaneous emission and optical depth due to clumpiness, we have derived the excitation conditions of clumpy clouds and compared them with those of three-dimensional calculations. We found that the proposed approach reproduces the excitation conditions in a way compatible to those from three-dimensional models, and reveals the dependencies of the excitation conditions on the size of clumps. When bulk motions are involved, the applicability of the approach is rather vague, but the one-dimensional approach can be an excellent proxy for more rigorous three-dimensional calculations.

Keywords

line: formation; radiative transfer; methods: numerical; ISM: molecules; ISM: clouds;

Citations & Related Records

Reference

1	Bernes, C. 1978, A Program for Solving Non-LTE, Radiative Transfer Problems with the Monte Carlo Method, Stockholms Obs. Rep. 15
2	Brinch, C., & Hogerheijde, M. R. 2010, LIME - A Flexible, Non-LTE Line Excitation and Radiation Transfer Method for Millimeter and Far-infrared Wavelengths, A&A, 523, 25
3	Hogerheijde, M. R., & van der Tak, F. F. S. 2000, An Accelerated Monte Carlo Method to Solve Two-dimensional Radiative Transfer and Molecular Excitation. With Applications to Axisymmetric Models of Star Formation, A&A, 362, 697
4	Leung, C. M., & Liszt, H. S. 1976, Radiation Transport and Non-LTE Analysis of Interstellar Molecular Lines. I. Carbon Monoxide., ApJ, 208, 732 DOI
5	Park, Y.-S., & Hong, S. S. 1995, Excitation and Line Profiles of CO Molecules in Clumpy Interstellar Clouds, A&A, 300, 890
6	van der Tak, F. F. S., Black, J. H., Schoier, F. L., et al. 2007, A Computer Program for Fast Non-LTE Analysis of Interstellar Line Spectra. With Diagnostic Plots to Interpret Observed Line Intensity Ratios, A&A, 468, 627 DOI
7	Asensio Ramos, A., & Elitzur, M. 2018, MOLPOP-CEP: An Exact, Fast Code for Multi-level Systems, A&A, 616, A131 DOI
8	Bernes, C. 1979, A Monte Carlo Approach to Non-LTE Radiative Transfer Problems, A&A, 73, 67
9	Blitz, L., & Stark, A. A. 1986, Detection of Clump and Interclump Gas in the Rosette Molecule Cloud Complex, ApJL, 300, L89 DOI
10	Hennebelle, P., & Falgarone, E. 2012, Turbulent Molecular Clouds, A&ARv, 20, 55 DOI
11	Juvela, M., 1998 Clumpy Cloud Models for CS and C³⁴S Spectra Observed Towards Southern Massive Star Forming Cores, A&A, 329, 659
12	Juvela, M., & Padoan, P. 2005, Multiresolution Radiative Transfer for Line Emission, ApJ, 618, 744 DOI
13	Molaro, M., Khatri, R., & Sunyaev, R. A. 2016, Probing the Clumping Structure of Giant Molecular Clouds through the Spectrum, Polarisation and Morphology of X-ray Reflection Nebulae, A&A, 589, 88
14	Moore, E. M., & Marscher, A. P. 1995, Observational Probes of the Small-scale Structure of Molecular Clouds, ApJ, 452, 671 DOI
15	Quenard, D. Bottinelli, S., & Caux, E. 2017, Modelling the 3D Physical Structure of Astrophysical Sources with GASS, MNRAS, 468, 685 DOI
16	Rybarczyk, D. R., Stanimirovic, S., Zweibel, E. G., et al. 2020, Small-scale Structure Traced by Neutral Hydrogen Absorption in the Direction of Multiple-component Radio Continuum Sources, ApJ, 893, 152 DOI
17	Yang, B., Stancil, P. C., Balakrishnan, N., & Forrey, R. C. 2010, Rotational Quenching of CO Due to H₂ Collisions, ApJ, 718, 1062 DOI
18	Goldreich, P., & Kwan, J. 1974, Molecular Clouds, ApJ, 189, 441 DOI