Heating of the Warm Ionized Medium by Low-energy Cosmic Rays
Abstract
In light of evidence for a high ionization rate due to low-energy cosmic rays (LECR) in diffuse molecular gas in the solar neighborhood, we evaluate their heat input to the warm ionized medium (WIM). LECR are much more effective at heating plasma than they are at heating neutrals. We show that the upper end of the measured ionization rates corresponds to a local LECR heating rate sufficient to maintain the WIM against radiative cooling, independent of the nature of the ionizing particles or the detailed shape of their spectrum. Elsewhere in the Galaxy the LECR heating rates may be higher than those measured locally. In particular, higher fluxes of LECR have been suggested for the inner Galactic disk, based on the observed hard X-ray emission, with correspondingly larger heating rates implied for the WIM. We conclude that LECR play an important and perhaps dominant role in the thermal balance of the WIM.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2016
- DOI:
- 10.3847/0004-637X/818/1/23
- arXiv:
- arXiv:1512.07335
- Bibcode:
- 2016ApJ...818...23W
- Keywords:
-
- cosmic rays;
- Galaxy: disk;
- ISM: general;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- To appear in ApJ (6 pages, 3 figures)