Predicting interstellar radiation fields from chemical evolution models
  We present a new method to obtain the interstellar radiation field (ISRF) of
regions that contain stars, dust and gas. Starting from stellar spectra, we
first run the radiative transfer code Skirt to compute the mean intensity field
due to the stellar component alone. Then, we import that result to the
photoionisation code Cloudy to compute the emissivity and opacity of the given
mixture of gas and dust as a function of wavelength. Finally, we ask Skirt
again to compute the mean intensity field, adding the total contribution of
stars, gas and dust. This process is repeated iteratively, calling both codes
sequentially in order to obtain increasingly accurate estimates. We have
designed a first test, reminiscent of an HII region, that consists of a B star,
approximated as a black-body, surrounded by a spherical shell of gas and dust
with uniform density. We find that the results of our three-dimensional
radiative transfer method are in excellent agreement with a spherically
symmetric Cloudy simulation. As a realistic scientific application, we
calculate the interstellar radiation field of a Milky Way-like galaxy based on
two different chemical evolution models. Both of them give results broadly
consistent with previous ones reported in the literature for the interstellar
radiation field of our Galaxy, albeit they systematically underestimate the
mid-infrared emission, with significant differences in this range, as well as
in the ultraviolet, stemming from the input stellar and ISM properties. These
results show the feasibility of our method to incorporate radiative transfer to
chemical evolution models, increasing their predictive power and using this
interstellar radiation field to further constrain their parameters. Python
source code to implement our method is publicly available at
https://github.com/MarioRomeroC/Mixclask.
