The validity of 21 cm spin temperature as a kinetic temperature indicator in atomic and molecular gas

Abstract

The 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 with 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 Lyman alpha ($Ly\alpha$), 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 $T_K$, cases where they fail, as well as the effects of $Ly\alpha$ pumping on the 21 cm spin temperature. We also show that the $Ly\alpha$ excitation temperature rarely traces the gas kinetic temperature.

arXiv commentAccepted for publication in ApJ

References in corpus (19)

• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• Enhanced cosmic-ray flux toward zeta Persei inferred from laboratory study of H3+ - e- recombination rate
• Wouthuysen-Field coupling strength and application to high-redshift 21 cm radiation
• The Spin-Kinetic Temperature Coupling and the Heating Rate due to Lyman Alpha Scattering before Reionization: Predictions for 21cm Emission and Absorption
• The Millennium Arecibo 21-cm Absorption Line Survey. I. Techniques and Gaussian Fits
• The Spin Temperature of Warm Interstellar H I
• The H II Region/PDR Connection: Self-Consistent Calculations of Physical Conditions in Star-Forming Regions
• Molecular Hydrogen in Star-forming regions: implementation of its micro-physics in Cloudy
• A Magnetically-Supported Photodissociation Region in M17
• The spin temperature of high-redshift damped Lyman-$\alpha$ systems
• Grain size distributions and photo-electric heating in ionized media
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• Molecular Hydrogen in the Damped Ly alpha Absorber of Q1331+170
• Implications of 21cm observations for damped Ly-$\alpha$ systems
• The Detection of Magnetic Fields Toward M17 through the HI Zeeman Effect
• Physical Conditoins in Orion's Veil II: A Multi-Component Study of the Line of Sight Toward the Trapezium
• Spin Exchange Rates in Proton-Hydrogen Collisions
• Fluorescent excitation of Balmer lines in gaseous nebulae: case D
• Accurate Hydrogen Spectral Simulations with a Compact Model Atom

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• Ly-alpha Radiative Transfer: Monte-Carlo Simulation of the Wouthuysen-Field Effect
• Spin Temperature and Density of Cold and Warm HI in the Galactic Disk - Hidden HI -
• Physical conditions in two high-redshift H${}_2$-bearing GRB-DLAs, 120815A and 121024A
• Physical Properties and HI-to-H2 Transition Across Taurus Linear Edge