Aromatic Species in the Molecular Universe

TL;DR

This paper reviews the significance, formation, and analysis of interstellar polycyclic aromatic hydrocarbons (PAHs), highlighting recent insights from the James Webb Space Telescope and laboratory studies.

Contribution

It provides a comprehensive overview of recent advances in understanding interstellar PAHs, integrating observational, laboratory, and theoretical perspectives.

Findings

JWST spectra reveal new PAH features

Laboratory studies improve chemical evolution models

PAHs influence interstellar medium processes

Abstract

Interstellar polycyclic aromatic hydrocarbon (PAHs) are an important component of the interstellar medium of galaxies, containing some 10 percent of the elemental carbon. Their vibrational emission dominates the mid-infrared spectra of galactic and extragalactic objects. PAHs control the heating of interstellar neutral gas and the charge balance of molecular clouds. PAHs are formed in the outflows from late type stars through chemical processes akin to those in sooting flames and then further processed in the interstellar medium by UV photolysis and strong shock waves. PAHs are also formed through ion molecule reactions and neutral radical reactions in dense cloud cores. The James Webb Space Telescope has provided a wealth of high-quality spectra that have provided new insights in the characteristics of the interstellar PAH family. Their analysis is supported by dedicated laboratory and quantum chemistry studies, feeding into detailed molecular physics models relevant to astronomical environments. Laboratory studies have also provided deeper insight in the chemical evolution of PAHs in the interstellar medium. This paper will review progress in the field and chart its future.