Dust emission and scattering in dense interstellar clouds

Abstract

Dust has a crucial role in the physics of interstellar medium (ISM) and it is one of the main tracers used in studies of dense clouds. Its importance has been accentuated by the large amounts of data available from the recent fleet of infrared and submillimetre satellites. These observations are providing further insights into the properties of interstellar dust grains and the changes they undergo during the star formation process.We examine some of the evidence for dust evolution coming from submillimetre dust emission and from light scattering at near-infrared and mid-infrared wavelengths. Planck and Herschel satellite observations have covered the peak of large grain emission, enabling studies of large cloud areas with unprecedented sensitivity and detail. The data are confirming results from earlier studies where changes of submillimetre dust opacity and spectral index were first reported. The changes are connected to dust evolution and growth as dust moves from diffuse ISM to molecular clouds and into pre-stellar clumps. Corroborating evidence on dust growth has been obtained recently from mid-infrared where enhanced scattering, the ‘coreshine’ phenomenon, is attributed to the growth of up to micron-sized dust particles.We will summarise results of previous infrared and submillimetre studies. We will describe ongoing work on Herschel data, done partly in the context of the programme Galactic Cold Cores (GCC). We will also discuss recent results from the Spitzer project Hunting coreshine, where the mid-infrared scattering is investigated in a partly related sample. We will also touch on some of the problems and modelling challenges encountered in these studies.