Dark dust II: Properties in the general field of the diffuse ISM by Ralf Siebenmorgen. on Monday 21 November

Distance estimates derived from spectroscopy or parallax have been unified by

considering extinction by large grains. The addition of such a population of

what is called Dark Dust to models of the diffuse interstellar medium is tested

against a contemporary set of observational constraints. The dark dust model

explains, by respecting representative solid-phase element abundances,

simultaneously the typical wavelength-dependent reddening, extinction, and

emission of polarized and unpolarized light by interstellar dust particles

between far UV and millimetre wavelengths. The physical properties of dark dust

are derived. Dark dust consists of micrometre-sized particles, which have been

recently detected in-situ. It provides significant wavelength-independent

reddening from the far UV to the near-infrared. Light absorbed by dark dust is

re-emitted in the submillimeter region by grains at dust temperatures of 8-12K.

Such very cold dust has been frequently observed in external galaxies. Dark

dust contributes to the polarisation at greater than about 1 mm to ~35% and at

shorter wavelengths marginally. Optical constants for silicate dust analogous

are investigated. By mixing 3% in mass of Mg$_{0.8}$Fe$^{2+}_{0.2}$ SiO$_3$ to

MgO$-$0.5 SiO$_2$ a good fit to the data is derived that still can accommodate

up to 5 - 10% of mass in dark dust. The extra diming of light by dark dust is

unexplored when discussing SN~Ia light curves and in other research. Previous

models that ignore dark dust do not account for the unification of the distance

scales.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.10146v1