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Title: COLLISIONAL EXCITATION OF THE [C II] FINE STRUCTURE TRANSITION IN INTERSTELLAR CLOUDS

Abstract

We analyze the collisional excitation of the 158 {mu}m (1900.5 GHz) fine structure transition of ionized carbon in terms of line intensities produced by simple cloud models. The single C{sup +} fine structure transition is a very important coolant of the atomic interstellar medium (ISM) and of photon-dominated regions in which carbon is partially or completely in ionized form. The [C II] line is widely used as a tracer of star formation in the Milky Way and other galaxies. Excitation of the [C II] fine structure transition can be via collisions with hydrogen molecules, atoms, and electrons. Analysis of [C II] observations is complicated by the fact that it is difficult to determine the optical depth of the line. We discuss the excitation of the [C II] line, deriving analytic results for several limiting cases and carry out numerical solutions using a large velocity gradient model for a more inclusive analysis. For antenna temperatures up to 1/3 of the brightness temperature of the gas kinetic temperature, the antenna temperature is linearly proportional to the column density of C{sup +} irrespective of the optical depth of the transition. This is appropriately referred to as the effectively optically thin approximation. We reviewmore » the critical densities for excitation of the [C II] line by various collision partners, briefly analyze C{sup +} absorption, and conclude with a discussion of C{sup +} cooling and how the considerations for line intensities affect the behavior of this important coolant of the ISM.« less

Authors:
; ; ;  [1]
  1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
Publication Date:
OSTI Identifier:
22089797
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal, Supplement Series
Additional Journal Information:
Journal Volume: 203; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0067-0049
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANTENNAS; APPROXIMATIONS; ASTROPHYSICS; CARBON; CARBON IONS; CARBON MONOXIDE; ELECTRONS; EXCITATION; FINE STRUCTURE; GHZ RANGE; HYDROGEN; INTERSTELLAR SPACE; ION COLLISIONS; MILKY WAY; MOLECULES; PHOTONS; STARS

Citation Formats

Goldsmith, Paul F., Langer, William D., Pineda, Jorge L., and Velusamy, T., E-mail: Paul.F.Goldsmith@jpl.nasa.gov. COLLISIONAL EXCITATION OF THE [C II] FINE STRUCTURE TRANSITION IN INTERSTELLAR CLOUDS. United States: N. p., 2012. Web. doi:10.1088/0067-0049/203/1/13.
Goldsmith, Paul F., Langer, William D., Pineda, Jorge L., & Velusamy, T., E-mail: Paul.F.Goldsmith@jpl.nasa.gov. COLLISIONAL EXCITATION OF THE [C II] FINE STRUCTURE TRANSITION IN INTERSTELLAR CLOUDS. United States. doi:10.1088/0067-0049/203/1/13.
Goldsmith, Paul F., Langer, William D., Pineda, Jorge L., and Velusamy, T., E-mail: Paul.F.Goldsmith@jpl.nasa.gov. Thu . "COLLISIONAL EXCITATION OF THE [C II] FINE STRUCTURE TRANSITION IN INTERSTELLAR CLOUDS". United States. doi:10.1088/0067-0049/203/1/13.
@article{osti_22089797,
title = {COLLISIONAL EXCITATION OF THE [C II] FINE STRUCTURE TRANSITION IN INTERSTELLAR CLOUDS},
author = {Goldsmith, Paul F. and Langer, William D. and Pineda, Jorge L. and Velusamy, T., E-mail: Paul.F.Goldsmith@jpl.nasa.gov},
abstractNote = {We analyze the collisional excitation of the 158 {mu}m (1900.5 GHz) fine structure transition of ionized carbon in terms of line intensities produced by simple cloud models. The single C{sup +} fine structure transition is a very important coolant of the atomic interstellar medium (ISM) and of photon-dominated regions in which carbon is partially or completely in ionized form. The [C II] line is widely used as a tracer of star formation in the Milky Way and other galaxies. Excitation of the [C II] fine structure transition can be via collisions with hydrogen molecules, atoms, and electrons. Analysis of [C II] observations is complicated by the fact that it is difficult to determine the optical depth of the line. We discuss the excitation of the [C II] line, deriving analytic results for several limiting cases and carry out numerical solutions using a large velocity gradient model for a more inclusive analysis. For antenna temperatures up to 1/3 of the brightness temperature of the gas kinetic temperature, the antenna temperature is linearly proportional to the column density of C{sup +} irrespective of the optical depth of the transition. This is appropriately referred to as the effectively optically thin approximation. We review the critical densities for excitation of the [C II] line by various collision partners, briefly analyze C{sup +} absorption, and conclude with a discussion of C{sup +} cooling and how the considerations for line intensities affect the behavior of this important coolant of the ISM.},
doi = {10.1088/0067-0049/203/1/13},
journal = {Astrophysical Journal, Supplement Series},
issn = {0067-0049},
number = 1,
volume = 203,
place = {United States},
year = {2012},
month = {11}
}