The Astrodust+PAH Model: A Unified Description of the Extinction, Emission, and Polarization from Dust in the Diffuse Interstellar Medium

TL;DR

This paper introduces a unified dust model combining astrodust and PAHs that explains interstellar extinction, emission, and polarization in the diffuse medium, aligning with observational constraints.

Contribution

It proposes a single-composition model for large grains and distinct PAH varieties, providing a comprehensive explanation for observed dust properties in the interstellar medium.

Findings

Reproduces Galactic extinction and emission wavelength dependence.

Matches observed polarization fractions without frequency dependence.

Aligns with solid phase abundance constraints.

Abstract

We present a new model of interstellar dust in which large grains are a single composite material, ``astrodust,'' and nanoparticle-sized grains come in distinct varieties including polycyclic aromatic hydrocarbons (PAHs). We argue that a single-composition model for grains larger than $\sim$0.02 $\mu$m most naturally explains the lack of frequency dependence in the far-infrared (FIR) polarization fraction and the characteristic ratio of optical to FIR polarization. We derive a size distribution and alignment function for 1.4:1 oblate astrodust grains that, with PAHs, reproduce the mean wavelength dependence and polarization of Galactic extinction and emission from the diffuse interstellar medium while respecting constraints on solid phase abundances. All model data and Python-based interfaces are made publicly available.