Numerical Models for the Diffuse Ionized Gas in Galaxies. I. Synthetic
  spectra of thermally excited gas with turbulent magnetic reconnection as
  energy source
  Aims: The aim of this work is to verify whether turbulent magnetic
reconnection can provide the additional energy input required to explain the up
to now only poorly understood ionization mechanism of the diffuse ionized gas
(DIG) in galaxies and its observed emission line spectra.
  Methods: We use a detailed non-LTE radiative transfer code that does not make
use of the usual restrictive gaseous nebula approximations to compute synthetic
spectra for gas at low densities. Excitation of the gas is via an additional
heating term in the energy balance as well as by photoionization. Numerical
values for this heating term are derived from three-dimensional resistive
magnetohydrodynamic two-fluid plasma--neutral-gas simulations to compute energy
dissipation rates for the DIG under typical conditions.
  Results: Our simulations show that magnetic reconnection can liberate enough
energy to by itself fully or partially ionize the gas. However, synthetic
spectra from purely thermally excited gas are incompatible with the observed
spectra; a photoionization source must additionally be present to establish the
correct (observed) ionization balance in the gas.
