Interstellar radiation as a Maxwell field: Improved numerical scheme and application to the spectral energy density

Abstract

The existing models of the interstellar radiation field (ISRF) do not produce a Maxwell field. Here, the recent model of the ISRF as a Maxwell field is improved by considering separately the different frequencies at the stage of the fitting. Using this improved procedure: (i) It is checked in detail that the model does predict extremely high values of the spectral energy density (SED) on the axis of a galaxy, which however decreases very rapidly when ρ\rho , the distance to the axis, is increased from zero. (ii) The difference between the SED values (with ρ=1\rho =1 or 8kpc8\hspace{0.33em}{\rm{kpc}}), as predicted either by this model or by a recent radiation transfer model, is reduced significantly. (iii) The slower decrease of the SED with increasing altitude zz, as compared with the radiation transfer model, is confirmed. We also calculate the evolutions of the SED at large ρ\rho . We interpret these evolutions by determining asymptotic expansions of the SED at large zz, and also ones at large ρ\rho .

Keywords

• maxwell equations
• axial symmetry
• interstellar radiation field