The Validity of 21 cm Spin Temperature as a Kinetic Temperature Indicator in Atomic and Molecular Gas
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationThe Validity of 21 cm Spin Temperature as a Kinetic Temperature Indicator in Atomic and Molecular Gas 2017, 843 (2):149 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2017. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractThe gas kinetic temperature (T-K) of various interstellar environments is often inferred from observations that can deduce level populations of atoms, ions, or molecules using spectral line observations; H I 21 cm is perhaps the most widely used, and has a long history. Usually the H I 21 cm line is assumed to be in thermal equilibrium. and the populations are given by the Boltzmann distribution. A variety of processes, many involving Ly alpha, can affect the 21 cm line. Here we show how this is treated in the spectral simulation code Cloudy, and present numerical simulations of environments where this temperature indicator is used, with a detailed treatment of the physical processes that determine level populations within H-0. We discuss situations where this temperature indicator traces TK, cases where it fails, as well as the effects of Lya pumping on the 21 cm spin temperature. We also show that the Lya excitation temperature rarely traces the gas kinetic temperature.
VersionFinal published version
SponsorsNSF [1108928, 1109061, 1412155]; NASA [10-ATP10-0053, 10-ADAP10-0073, NNX12AH73G, ATP13-0153]; STScI [HST-AR-13245, GO-12560, HST-GO-12309, GO-13310.002-A, HST-AR-13914]