Nuclear 11.3$\mu$m PAH emission in local active galactic nuclei

TL;DR

This study uses mid-infrared imaging and spectroscopy to examine the survival of PAH molecules near AGNs, finding they persist close to the nucleus due to protective material, challenging the idea of their destruction by AGN radiation.

Contribution

It provides observational evidence that PAH molecules can survive in nuclear regions of AGNs, highlighting the role of surrounding material in shielding them from radiation.

Findings

PAH emission detected near AGN nuclei and extended regions

Equivalent width increases with distance from the nucleus

PAH molecules likely survive due to shielding by surrounding material

Abstract

We present Gran Telescopio CANARIAS CanariCam 8.7$\mu$m imaging and 7.5-13$\mu$m spectroscopy of six local systems known to host an active galactic nucleus (AGN) and have nuclear star formation. Our main goal is to investigate whether the molecules responsible for the 11.3$\mu$m polyclyclic aromatic hydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We detect 11.3$\mu$m PAH feature emission in the nuclear regions of the galaxies as well as extended PAH emission over a few hundred parsecs. The equivalent width (EW) of the feature shows a minimum at the nucleus but increases with increasing radial distances, reaching typical star-forming values a few hundred parsecs away from the nucleus. The reduced nuclear EW are interpreted as due to increased dilution from the AGN continuum rather than destruction of the PAH molecules. We conclude that at least those molecules responsible for the 11.3$\mu$m PAH feature survive in the nuclear environments as close as 10pc from the AGN and for Seyfert-like AGN luminosities. We propose that material in the dusty tori, nuclear gas disks, and/or host galaxies of AGN is likely to provide the column densities necessary to protect the PAH molecules from the AGN radiation field.