Dust evolution from pre-stellar cores
Dust is the only tracer that is present from the edge of the interstellar cloud to the densest part, inside which stars and planets will form, named pre-stellar cores. It allows to trace the density structure of the cloud, of the core(s), and of the subsequent protoplanetary disk where it becomes a major actor of the planet formation. Dust grains evolve from bare simple elongated shape in the diffuse medium to large icy aggregates with irregular shapes inside dense cores.
While dust properties in the diffuse medium are well-constrained, dust models able to explain multi-wavelength observations for dense environment including large grains are still lacking. Grain growth is expected from mid and far infrared (FIR) observations but to fulfil all observational constraints, a dust model must at least be consistent in terms of dust composition but also dust shape and size distribution. The way dust grains absorb and scatter light does not depend on temperature but relies mainly on dust geometry (size and shape). On the contrary, the emission process implies a degeneracy between dust properties and temperatures. Hence, the retrieval of dust properties (size, composition, shape) from observations is a degenerate problem that requests multi-wavelength observations and multiple tracers among which absorption, scattering, polarization of the incoming radiation field, and thermal emission at long wavelengths.
I will present how NIKA2 observations are crucial to better constrain dust properties. In this framework, I will introduce SIGMA: a new flexible dust model in open access (Lefèvre et al. 2019). We rely on effective medium theory to compute refractive indexes from laboratory measurements and Mie theory applied to a distribution of hollow spheres to mimic non–spherical dust shapes. In particular I will illustrate how I reproduce the expected impact when balancing the iron fraction between silicates and other iron components making iron rich silicates less emissive at NIKA2 wavelengths compared to iron–poor silicates (Demyk et al. 2017a, 2017b). I will also discuss the impact of ice mantle thickness.