Modelling the evolution of PAH abundance in galaxies

TL;DR

This paper models the evolution of PAH abundance in galaxies by simulating dust grain processes, explaining metallicity dependence, and predicting PAH-to-dust ratios consistent with observations.

Contribution

It introduces a detailed dust evolution model that accounts for aromatization, shattering, and accretion, linking PAH abundance to galaxy metallicity.

Findings

PAH abundance correlates with metallicity in galaxies.

Shattering and accretion drive PAH abundance increase.

Model matches observed PAH-metallicity trends.

Abstract

We investigate the evolution of polycyclic aromatic hydrocarbon (PAH) abundance in a galaxy, which is a crucial step to understand the evolution of bright emission features in the mid-infrared range. We calculate the evolution of dust grain size distribution in a manner consistent with the physical conditions of the interstellar medium by post-processing our previous hydrodynamical simulation of an isolated disc galaxy. We also differentiate between aromatic and non-aromatic grains for carbonaceous dust species and explicitly considered the aromatization process. As a consequence, our model explains the metallicity dependence of PAH abundances in nearby galaxies well. The PAH abundance increase is driven particularly by the interplay between shattering and accretion (dust growth). The fast aromatization guarantees that the small carbonaceous grains trace PAHs very well. Since shattering and accretion are sensitive to the dust abundance, we predict that the PAH-to-dust abundance ratio increases as the metallicity increases. This is consistent with the observation data of nearby galaxies.