Heating of the interstellar gas by cosmic rays and warm transparent ionized plasma observed by pulsar dispersions

Abstract

Electron densities in different locations of our galaxy are obtained in pulsar astronomy by dividing the dispersion measure (DM) by the distance of the pulsar to Earth. The properties of the interstellar plasma are related to its heating by cosmic rays. Following the present analysis, DM’s measurements are obtained with different properties of the corresponding plasmas at different temperatures. (1) For relatively low temperatures (around and below 10,000 (K)), the state of molecular, atomic and ionized hydrogen is analyzed by the interstellar medium model with partially ionized plasma. In this region, various spectroscopic effects are obtained. (2) For temperatures above this limit, the interstellar gas is found to be a completely ionized medium, and this plasma is defined as warm ionized medium (WIM) plasma. We show in the first part of the paper that this plasma is transparent, as obtained from the solution of Saha’s equation. The index of refraction of the WIM plasma is real, but the plasma can be observed by dispersion measurements. (3) For very high temperatures (around 1 million (K)), the plasma is defined as hot ionized medium, where X-rays are obtained. We concentrate in the present work on the analysis of WIM plasma. We calculate the mass densities of this plasma and compare it with dark matter mass densities, which are found to be larger. But some factors which may reduce this difference are discussed.