Interstellar Absorption of the Galactic Polar Low‐Frequency Radio Background Synchrotron Spectrum as an Indicator of Clumpiness in the Warm Ionized Medium
| Autor: | J. D. Peterson, W. R. Webber |
|---|---|
| Rok vydání: | 2002 |
| Předmět: |
Local Interstellar Cloud
Physics Electron density Astrophysics::High Energy Astrophysical Phenomena Synchrotron radiation Astronomy and Astrophysics Cosmic ray Astrophysics::Cosmology and Extragalactic Astrophysics Astrophysics Galactic plane Galaxy Radio spectrum Space and Planetary Science Emissivity Astrophysics::Galaxy Astrophysics |
| Zdroj: | The Astrophysical Journal. 575:217-224 |
| ISSN: | 1538-4357 0004-637X |
| DOI: | 10.1086/341258 |
| Popis: | In the standard model of low-frequency synchrotron radiation propagation through the Galaxy, the absorbing warm ionized medium (WIM) is considered to be a thick slab of thermal electrons of uniform density. When the calculated polar radio spectrum is compared with the observed Galactic background radio spectrum, it is found that this model requires a much higher electron density ne or much lower temperature Te than permitted by current observations. A more realistic plane-parallel model, in which electron density, temperature, and cosmic-ray electron emissivity have smooth distributions with height z above the Galactic plane, is also found to suffer from the same setbacks as the standard model. However, a plane-parallel model in which the absorbing WIM has a clumpy distribution with clump densities of ~0.2 cm-3 and filling factor of 0.08-0.15 agrees with both the low-frequency radio synchrotron spectrum and the observational parameters ne(z = 0) ≈ 0.025 cm-3, Te ≈ 7000 K, and DM ≈ 23 pc cm-3. The clumpy WIM model also supports the idea of a local interstellar cloud (LIC), which is required to provide adequate absorption below ~0.5 MHz. This LIC appears to become optically thick only below ~0.1 MHz where future radio measurements may be used to determine the emissivity spectrum and, therefore, the local interstellar cosmic-ray electron spectrum at energies of ~40 MeV. |
| Databáze: | OpenAIRE |
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