SYNCHROTRON AND COMPTON SPECTRA FROM A STEADY-STATE ELECTRON DISTRIBUTION

• Published in: The Astrophysical journal Vol. 805; no. 2; pp. 1 - 7
• Main Authors: Rephaeli, Y., Persic, M.
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 01.06.2015
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BREMSSTRAHLUNG; COMPARATIVE EVALUATIONS; COSMIC ELECTRONS; COSMIC PROTONS; Density distribution; EMISSION SPECTRA; ENERGY DENSITY; ENERGY LOSSES; Estimates; GALAXIES; galaxies: spiral; galaxies: starburst; GALAXY CLUSTERS; MAGNETIC FIELDS; Mathematical analysis; radiation mechanisms: non-thermal; RELATIVISTIC RANGE; Spectra; SPECTRAL DENSITY; STAR EVOLUTION; STARS; STEADY-STATE CONDITIONS; Synchrotrons
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/805/2/111

ABSTRACT Energy densities of relativistic electrons and protons in extended galactic and intracluster regions are commonly determined from spectral radio and (rarely) γ-ray measurements. The time-independent particle spectral density distributions are commonly assumed to have a power-law (PL) form over the relevant energy range. A theoretical relation between energy densities of electrons and protons is usually adopted, and energy equipartition is invoked to determine the mean magnetic field strength in the emitting region. We show that for typical conditions, in both star-forming and starburst (SB) galaxies, these estimates need to be scaled down substantially due to significant energy losses that (effectively) flatten the electron spectral density distribution, resulting in a much lower energy density than deduced when the distribution is assumed to have a PL form. The steady-state electron distribution in the nuclear regions of SB galaxies is calculated by accounting for Coulomb, bremsstrahlung, Compton, and synchrotron losses; the corresponding emission spectra of the latter two processes are calculated and compared to the respective PL spectra. We also determine the proton steady-state distribution by taking into account Coulomb and production losses, and briefly discuss implications of our steady-state particle spectra for estimates of proton energy densities and magnetic fields.