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

TL;DR

This paper improves a Maxwell field model of the interstellar radiation field by refining frequency considerations, leading to more accurate spectral energy density predictions and better understanding of its spatial variations.

Contribution

The paper introduces an improved numerical scheme for modeling the interstellar radiation field as a Maxwell field, accounting for frequency separation during fitting.

Findings

High spectral energy density values on galaxy axes decrease rapidly with distance.

Reduced differences between models at different galactic radii.

Confirmed slower decrease of spectral energy density with altitude compared to previous models.

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, that however decrease very rapidly when $\rho $, the distance to the axis, is increased from zero. (ii) The difference between the SED values (with $\rho =1\,$kpc or $8\,$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 $z$, as compared with the radiation transfer model, is confirmed. We also calculate the evolutions of the SED at large $\rho $. We interpret these evolutions by determining asymptotic expansions of the SED at large $z$, and also ones at large $\rho $.