Heating and Ionization of H i Regions by Discrete Soft X-Ray and Subcosmic-Ray Sources

Abstract

view Abstract Citations (3) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heating and Ionization of H i Regions by Discrete Soft X-Ray and Subcosmic-Ray Sources Silk, Joseph ; Lea, Susan M. Abstract We calculate the nonuniform ionization of a homogeneous interstellar medium produced by discrete sources of soft X-rays and subcosmic rays. Our procedure is to first solve the ionization equation appropriate to the type of source considered, and then obtain the electron density n (r) as a function of radial distance r from the source. We next use this function to evaluate the expected electron density n which would be observed at a random point in the Galaxy, under the assumption that the ionization sources are uniformly distributed. The clumpiness of the ionization can be obtained by calculating ne2>. A similar procedure is applied to time-dependent models of the interstellar medium. We present a simplified model for the ionization of intercloud matter by bursts of both soft X-rays and sub- cosmic rays, and calculate the resulting mean and root mean square ionization. We also calculate the ionization and heating rates, and solve the energy equation for a mean temperature. Our results are displayed as contours of ionization fraction, ionization rate, and temperature plotted as a function of the source parameters, specifically source strength and mean separation. Our principal conclusions are that available soft X-ray sources (both observed and plausibly hypothesized) can produce significant ionization, especially of the intercloud medium, whereas the uncertainty in subcosmic-ray fluxes and propagation precludes any statement from being made about their importance in ionizing the interstellar medium. Moreover, ionization by soft X-ray (or subcosmic ray) bursts produces considerable clumpiness ( ), and measurement of this parameter offers a potential means of distinguishing between steady and time-dependent heating models of the interstellar medium. Subject headings: cosmic rays - excitation and ionization - interstellar matter - X-rays Publication: The Astrophysical Journal Pub Date: June 1973 DOI: 10.1086/152180 Bibcode: 1973ApJ...182..731S full text sources ADS |