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Title: EXCITATION TEMPERATURE OF THE WARM NEUTRAL MEDIUM AS A NEW PROBE OF THE Lyα RADIATION FIELD

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{sub s}〉=7200{sub −1200}{sup +1800} 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.
Authors:
; ; ; ; ;  [1] ; ;  [2] ;  [3] ;  [4] ;  [5]
  1. Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)
  2. National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville, Socorro, NM 87801 (United States)
  3. Radio Astronomy Laboratory, UC Berkeley, 601 Campbell Hall, Berkeley, CA 94720 (United States)
  4. University of Tasmania, School of Maths and Physics, Private Bag 37, Hobart, TAS 7001 (Australia)
  5. Laboratoire AIM, Paris-Saclay, CEA/IRFU/SAp—CNRS—Université Paris Diderot, F-91191 Gif-sur-Yvette Cedex (France)
Publication Date:
OSTI Identifier:
22364005
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 781; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; EMISSION SPECTRA; ENERGY BALANCE; EXCITATION; HYDROGEN; INTERGALACTIC SPACE; INTERSTELLAR SPACE; LYMAN LINES; MILKY WAY; PROBES; RADIANT HEAT TRANSFER; RED SHIFT; SCATTERING; SENSITIVITY