The low density ionized component of the interstellar medium and free-free absorption at high galactic latitudes

  • R. J. Reynolds
IV. SNe, SNRs, and Ionized Gas in the Interstellar Medium
Part of the Lecture Notes in Physics book series (LNP, volume 362)


At frequencies below 2 MHz the sky is opaque because of free-free absorption by warm, ionized interstellar gas. Diffuse H+ is now known to be a major component of the interstellar medium, having a surface density approximately one third that of the H I, a scale height ten times that of the cloud layer, and a power requirement comparable to that available from supernovae. While the origin of this gas is not yet understood, its existence clearly has an important bearing on the nature of the interstellar medium and lower Galactic halo. Faint line emission from the gas at optical wavelengths and its free-free absorption pattern against the Galactic synchrotron background at very low radio frequencies provide opportunities to explore in detail the distributions of both this ionized component of the interstellar medium and the synchrotron emissivity within the Galactic disk and halo.


Angular Resolution Interstellar Medium Emission Measure Column Density Galactic Disk 
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Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • R. J. Reynolds
    • 1
  1. 1.Department of PhysicsUniversity of Wisconsin-MadisonMadison

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