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Date and Time of the Query: 2019-08-26 T00:09:09 PDT
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For refcode 2014ApJ...781L..41M:
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2014ApJ...781L..41M Excitation Temperature of the Warm Neutral Medium as a New Probe of the Ly-{alpha} Radiation Field Murray, Claire E.; Lindner, Robert R.; Stanimirovic, Snezana; Goss, W. M.; Heiles, Carl; Dickey, John; Pingel, Nickolas M.; Lawrence, Allen; Jencson, Jacob; Babler, Brian L.; Hennebelle, Patrick 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 <T_s> = 7200^{+1800}_{-1200}_\,K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Ly-{alpha} 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 Ly-{alpha} 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. Key words: ISM: clouds, ISM: structure
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