Polycyclic Aromatic Hydrocarbon Emission in the Central Regions of Three Seyferts the Implication for Underlying Feedback Mechanisms

TL;DR

This study uses JWST observations to analyze PAH emission in three Seyfert galaxies, revealing how different feedback mechanisms influence PAH properties and offering insights into AGN feedback modes.

Contribution

It provides new insights into how AGN feedback affects PAH characteristics, combining model predictions with JWST data to distinguish environments with different PAH ionization and size distributions.

Findings

High fraction of neutral small PAHs linked to shock-heated environments.

Severe photo-ionization affects large ionized PAHs near AGN.

PAH properties vary significantly across different Seyferts and regions.

Abstract

We analyze JWST MIRI/MRS IFU observations of three Seyferts and showcase the intriguing polycyclic aromatic hydrocarbon (PAH) emission characteristics in regions of $\sim 500\,\rm pc$ scales over or around their active galactic nuclei (AGN). Combining the model predictions and the measurements of PAH features and other infrared emission lines, we find that the central regions containing a high fraction of neutral PAHs with small sizes, e.g., those in ESO137-G034, are in highly heated environments, due to collisional shock heating, with hard and moderately intense radiation fields. Such environments are proposed to be associated with inhibited growth or preferential erosion of PAHs, decreasing the average PAH size and the overall abundance of PAHs. We additionally find that the central regions containing a high fraction of ionized PAHs with large sizes, e.g., those in MCG-05-23-016, are likely experiencing severe photo-ionization because of the radiative effects from the radiative shock precursor besides the AGN. The severe photo-ionization can contribute to the ionization of all PAHs and further destruction of small PAHs. Overall, different Seyferts, even different regions in the same galaxy, e.g., those in NGC\,3081, can contain PAH populations of different properties. Specifically, Seyferts that exhibit similar PAH characteristics to ESO137-G034 and MCG-05-23-016 also tend to have similar emission line properties to them, suggesting that the explanations for PAH characteristics of ESO137-G034 and MCG-05-23-016 may also apply generally. These results have promising application in the era of JWST, especially in diagnosing different (i.e., radiative, and kinetic) AGN feedback modes.