Excitation Temperature of the Warm Neutral Medium as a New Probe of the Lyα Radiation Field

Type Journal Article
Names Claire E. Murray, Robert R. Lindner, Snežana Stanimirović, W. M. Goss, Carl Heiles, John Dickey, Nickolas M. Pingel, Allen Lawrence, Jacob Jencson, Brian L. Babler, Patrick Hennebelle
Publication The Astrophysical Journal Letters
Volume 781
Pages L41
Journal Abbreviation The Astrophysical Journal Letters
Date February 1, 2014
DOI 10.1088/2041-8205/781/2/L41
ISSN 0004-637X
URL http://adsabs.org/2014ApJ.781L.41M
Library Catalog labs.adsabs.harvard.edu
Abstract We use the Karl G. Jansky Very Large Array to conduct a high-sensitivity survey of neutral hydrogen (H I) absorption in the Milky Way. In combination with corresponding H I emission spectra obtained mostly with the Arecibo Observatory, we detect a widespread warm neutral medium component with excitation temperature \langle T_s\rangle = 7200^{+1800}_{-1200}\,K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Lyα scattering, the most probable additional source of excitation, is more important in the interstellar medium (ISM) than previously assumed. Our results demonstrate that H I absorption can be used to constrain the Lyα radiation field, a critical quantity for studying the energy balance in the ISM and intergalactic medium yet notoriously difficult to model because of its complicated radiative transfer, in and around galaxies nearby and at high redshift.
Tags ISM: clouds, ISM: structure
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