Evolution of dust properties inside molecular clouds from coreshine modelling

Using observations to deduce dust properties, grain size distribution, and physical conditions in molecular clouds is a highly degenerate problem. The coreshine phenomenon, a scattering process at 3.6 and 4.5 mm that dominates absorption, has revealed its ability to explore the densest parts of clouds. We want to use this effect to constrain the dust parameters and investigate to what extent grain growth (at constant dust mass) inside molecular clouds is able to explain the coreshine observations ( 100 sources detected). We aim to find dust models that can explain a sample of Spitzer coreshine data but we also look at the consistency with near‐infrared data we obtained for a few clouds. We built a grid of dust models and investigated the key parameters to reproduce the general trend of surface brightnesses and intensity ratios of both coreshine and near‐infrared observations with the help of a 3D Monte‐Carlo radiative transfer code. The grid parameters allow to investigate the effect of coagulation upon spherical grains up to 5 mm in size derived from the DustEm diffuse interstellar medium grains. Fractal dimension, porosity, ices, and a handful of classical grain distributions were also tested. We used the near‐ and mostly mid‐ infrared intensity ratios as strong discriminants between dust models. We discuss the modeling parameters as well as the influence of the dust properties and the influence of embedded sources.