NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-24 T20:41:45 PDT
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For refcode 2014A&A...567A.101P:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2014A&A...567A.101P Estimates of relativistic electron and proton energy densities in starburst galactic nuclei from radio measurements Persic, Massimo; Rephaeli, Yoel Abstract. The energy density of energetic protons, U_p_, in several nearby starburst nuclei (SBNs) has been directly deduced from gamma-ray measurements of the radiative decay of pi^0^ produced in interactions with ambient protons. Lack of sufficient sensitivity and spatial resolution makes this direct deduction unrealistic in the foreseeable future for even a moderately distant SBN. A more viable indirect method for determining U_p_ in star-forming galaxies is to use its theoretically based scaling to the energy density of energetic electrons, U_e_, which can be directly deduced from radio synchrotron and possibly also nonthermal hard X-ray emission. In order to improve the quantitative basis and diagnostic power of this leptonic method we reformulate and clarify its main aspects. Doing so we obtain a basic expression for the ratio U_p_/U_e_ in terms of the proton and electron masses and the power-law indices that characterize the particle spectral distributions in regions where the total particle energy density is at equipartition with that of the mean magnetic field. We also express the field strength and the particle energy density in the equipartition region in terms of the region's size, mean gas density, IR and radio fluxes, and distance from the observer, and determine values of U_p_ in a sample of nine nearby and local SBNs. Key words: astroparticle physics, ISM: magnetic fields, cosmic rays, galaxies: magnetic fields, galaxies: starburst
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