Solid State Astrophysics: Probing Interstellar Dust and Gas Properties with X-rays

TL;DR

This paper discusses how X-ray observations can uniquely probe the composition, structure, and distribution of interstellar dust and gas across a wide range of environments, complementing other wavelengths.

Contribution

It highlights the potential of X-ray spectroscopy to measure interstellar medium properties that are difficult to access with UV, optical, IR, or radio methods.

Findings

X-ray absorption reveals detailed gas abundances and dust composition.

X-ray scattering halos map dust distribution across the galaxy.

X-ray techniques cover a broad range of column densities.

Abstract

The abundances of gas and dust (solids and complex molecules) in the interstellar medium (ISM) as well as their composition and structures impact practically all of astrophysics. Fundamental processes from star formation to stellar winds to galaxy formation all scale with the number of metals. However, significant uncertainties remain in both absolute and relative abundances, as well as how these vary with environment, e.g., stellar photospheres versus the interstellar medium (ISM). While UV, optical, IR, and radio studies have considerably advanced our understanding of ISM gas and dust, they cannot provide uniform results over the entire range of column densities needed. In contrast, X-rays will penetrate gas and dust in the cold (3K) to hot (100,000,000K) Universe over a wide range of column densities (log NH=20-24 cm^-2), imprinting spectral signatures that reflect the individual atoms which make up the gas, molecule or solid. *X-rays therefore are a powerful and viable resource for delving into a relatively unexplored regime for determining gas abundances and dust properties such as composition, charge state, structure, and quantity via absorption studies, and distribution via scattering halos.*