Cosmic Ray Heating of the Warm Ionized Medium

Type Journal Article
Names Joshua Wiener, Ellen G. Zweibel, S. Peng Oh
Publication The Astrophysical Journal
Volume 767
Pages 87
Journal Abbreviation The Astrophysical Journal
Date April 1, 2013
DOI 10.1088/0004-637X/767/1/87;
ISSN 0004-637X
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Abstract Observations of line ratios in the Milky Way's warm ionized medium suggest that photoionization is not the only heating mechanism present. For the additional heating to explain the discrepancy, it would have to have a weaker dependence on the gas density than the cooling rate, \Lambda n_e^2. Reynolds et al. suggested turbulent dissipation or magnetic field reconnection as possible heating sources. We investigate here the viability of MHD-wave mediated cosmic ray heating as a supplemental heating source. This heating rate depends on the gas density only through its linear dependence on the Alfvén speed, which goes as n_e^{-1/2}. We show that, scaled to appropriate values of cosmic ray energy density, cosmic ray heating can be significant. Furthermore, this heating is stable to perturbations. These results should also apply to warm ionized gas in other galaxies.
Tags COSMIC RAYS, Galaxies: Halos, Galaxies: ISM, H II REGIONS, ISM: General, Magnetohydrodynamics: MHD
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