Effects of stochastic heating on the SED of the 13 Gyr-old Milky Way model (see Sect. 7.1). All the SEDs shown hereafter were averaged over all viewing angles. For emission lines, only the peak was plotted; its height was computed assuming a Gaussian profile with a full width at half maximum of 160 km s⁻¹ (Mocz et al. 2012). Black line: stochastically heated grains. Red line: all grains were assumed to have reached their equilibrium temperature.