Polycyclic aromatic hydrocarbons with SPICA

TL;DR

SPICA's advanced capabilities will significantly enhance the understanding of PAHs and VSGs in various astrophysical environments, enabling detailed chemical and physical characterization across different cosmic settings.

Contribution

This paper outlines how SPICA's high sensitivity and resolution will improve the study of PAHs and VSGs, advancing their use as probes of astrophysical conditions.

Findings

Potential to identify individual PAHs through far-IR bands

Probing chemical evolution from VSGs to PAHs in regions

Using PAH populations as tracers in diverse environments

Abstract

Thanks to high sensitivity and angular resolution and broad spectral coverage, SPICA will offer a unique opportunity to better characterize the nature of polycyclic aromatic hydrocarbons (PAHs) and very small grains (VSGs), to better use them as probes of astrophysical environments. The angular resolution will enable to probe the chemical frontiers in the evolution process from VSGs to neutral PAHs, to ionized PAHs and to "Grand-PAHs" in photodissotiation regions and HII regions, as a function of G$_0$/n (UV radiation field / density). High sensitivity will favor the detection of the far-IR skeletal emission bands of PAHs, which provide specific fingerprints and could lead to the identification of individual PAHs. This overall characterization will allow to use PAH and VSG populations as tracers of physical conditions in spatially resolved protoplanetary disks and nearby galaxies (using mid-IR instruments), and in high redshift galaxies (using the far-IR instrument), thanks to the broad spectral coverage SPICA provides. Based on our previous experience with ISO and Spitzer we discuss how these goals can be reached.