• Dwek, Eli
• Arendt, Richard G.
• Zubko, Viktor

Abstract

We present new interstellar dust models which have been derived by simultaneously fitting the far ultraviolet to near infrared extinction, the diffuse infrared emission and, unlike previous models, the elemental abundances constraints on the dust for different interstellar medium abundances. The fitting problem is a typical ill-posed inversion problem, in which the grain size distribution is the unknown, which we solve by using the method of regularization. We reproduce the Li & Draine (2001, ApJ, 554, 778) results, however their model requires an excessive amount of silicon to be locked up in dust: 48 ppm (atoms per million of H atoms), significantly more than the upper limit imposed by solar (34 ppm) or B star (19 ppm) abundance constraints.A major conclusion of this paper is that there exist several distinct interstellar dust models that simultaneously fits the observed extinction, infrared emission, and abundances constraints. We find four classes of acceptable interstellar dust models. The first class is identical in composition to the Li & Draine model, consisting of PAHs, bare graphite and silicate grains, but with different size distributions that are optimized to comply with the above constraints. The second class of models contains in addition to PAHs, bare graphite and silicate grains, composite particles consisting of different mixtures of silicate, amorphous carbon, organic refractory material, water ice, and voids. The dust models with the composites are also more consistent with the available infrared extinction data. The third and fourth classes of models comprise of the first and second classes, respectively, with the graphite grains completely replaced by amorphous carbon grains. We have found simple analytical approximations to all the size distributions of the dust components in the models. We used Monte Carlo simulations in conjunction with the regularization method to estimate the uncertainties in the size distributions.

Topics

• impedance spectroscopy
• amorphous
• Carbon
• grain
• grain size
• simulation
• composite
• Silicon
• void
• refractory