Analytic formulas for frequency and size dependence of absorption and scattering efficiencies of astronomical polycyclic aromatic hydrocarbons

TL;DR

This paper derives analytic formulas for the frequency and size dependence of absorption and scattering efficiencies of polycyclic aromatic hydrocarbons (PAHs) in interstellar dust, complementing previous work on silicate and graphite grains.

Contribution

It provides the first analytic formulas for PAHs' scattering and absorption spectra across a broad wavelength range, enhancing dust extinction models.

Findings

PAHs significantly contribute to interstellar extinction.

Analytic formulas enable efficient modeling of PAH optical properties.

Comparison shows PAHs' role varies with wavelength and size.

Abstract

In a series of two recent papers, the frequency and size distribution dependence of extinction spectra for astronomical silicate and graphite grains was analyzed by us in the context of MRN type interstellar dust models. These grains were taken to be homogeneous spheres following the power law $(a^{-3.5})$ size distribution which is very much in use. The analytic formulas were obtained for the graphite and silicate grains in wavelength range 1000\AA - 22,500\AA and their utility was demonstrated. In this paper of the series, we present analytic formulas for the scattering and absorption spectrum of another important constituent of interstellar dust models, namely, the polycyclic aromatic hydrocarbons (PAHs). Relative contribution of the PAHs to extinction {\it vis a vis} carbonaceous classical grains has been examined.