Stochastic heating of small grains is often mentioned as a primary cause of large infrared (IR) fluxes from star-forming galaxies, e.g. at 24mu m. If the mechanism does work at a galaxy-wide scale, it should show up at smaller scales as well. We calc
ulate temperature probability density distributions within a model protostellar core for four dust components: large silicate and graphite grains, small graphite grains, and polycyclic aromatic hydrocarbon particles. The corresponding spectral energy distributions are calculated and compared with observations of a representative infrared dark cloud core. We show that stochastic heating, induced by the standard interstellar radiation field, cannot explain high mid-IR emission toward the centre of the core. In order to reproduce the observed emission from the core projected centre, in particular, at 24mu m, we need to increase the ambient radiation field by a factor of about 70. However, the model with enhanced radiation field predicts even higher intensities at the core periphery, giving it a ring-like appearance, that is not observed. We discuss possible implications of this finding and also discuss a role of other non-radiative dust heating processes.
A one-dimensional method for reconstructing the structure of prestellar and protostellar clouds is presented. The method is based on radiative transfer computations and a comparison of theoretical and observed intensity distributions at both millimet
er and infrared wavelengths. The radiative transfer of dust emission is modeled for specified parameters of the density distribution, central star, and external background, and the theoretical distribution of the dust temperature inside the cloud is determined. The intensity distributions at millimeter and IR wavelengths are computed and quantitatively compared with observational data. The best-fit model parameters are determined using a genetic minimization algorithm, which makes it possible to reveal the ranges of parameter degeneracy as well. The method is illustrated by modeling the structure of the two infrared dark clouds IRDC-320.27+029 (P2) and IRDC-321.73+005 (P2). The derived density and temperature distributions can be used to model the chemical structure and spectral maps in molecular lines.
