Resonant scattering of X-ray emission lines in the hot intergalactic medium

TL;DR

Resonant scattering of X-ray lines in the hot intergalactic medium can significantly affect observational data, offering a new method to probe the physical properties and velocity fields of the IGM.

Contribution

This paper explores how resonant scattering impacts X-ray observations of the IGM and proposes its use as a diagnostic tool for IGM properties.

Findings

Resonant scattering causes distortions in X-ray surface brightness.

It affects element abundance measurements and spectral line shapes.

Velocity fields influence the magnitude of scattering effects.

Abstract

While very often a hot intergalactic medium (IGM) is optically thin to continuum radiation, the optical depth in resonant lines can be of order unity or larger. Resonant scattering in the brightest X-ray emission lines can cause distortions in the surface brightness distribution, spurious variations in the abundance of heavy elements, changes in line spectral shapes and even polarization of line emission. The magnitude of these effects not only depends on the density, temperature and ionization state of the gas, but is also sensitive to the characteristics of the gas velocity field. This opens a possibility to use resonant scattering as a convenient and powerful tool to study IGM properties. We discuss the application of these effects to galaxy clusters.