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

February 2014 • 2014ApJ...781L..41M

Authors • Murray, Claire E. • Lindner, Robert R. • Stanimirović, Snežana • 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 \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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2014ApJ...781L..41M
• PDF https://stacks.iop.org/2041-8205/781/L41/pdf
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2014ApJ...781L..41M
• PREPRINT http://arxiv.org/abs/1401.1215
• ELECTR https://doi.org/10.1088%2F2041-8205%2F781%2F2%2FL41