The role of the charge state of PAHs in ultraviolet extinction

TL;DR

This study investigates how the charge state of polycyclic aromatic hydrocarbons (PAHs) influences ultraviolet extinction curves in space, using detailed dust models and spectral calculations to match observations.

Contribution

It introduces a comprehensive model combining classical dust particles and PAHs in various charge states to explain extinction curve variations.

Findings

PAH charge states affect UV extinction features

Mixtures of PAHs and dust reproduce observed curves

Charge-related spectral changes match observed variations

Abstract

Aims: We explore the relation between charge state of polycyclic aromatic hydrocarbons (PAHs) and extinction curve morphology. Methods: We fit extinction curves with a dust model including core-mantle spherical particles of mixed chemical composition (silicate core, $sp^2$ and $sp^3$ carbonaceous layers), and an additional molecular component. We use exact methods to calculate the extinction due to classical particles and accurate computed absorption spectra of PAHs in different charge states, for the contribution due to the molecular component, along a sample of five rather different lines of sight. Results: A combination of classical dust particles and mixtures of real PAHs satisfactorily matches the observed interstellar extinction curves. Variations of the spectral properties of PAHs in different charge states produce changes consistent with the varying relative strengths of the bump and non-linear far-UV rise.