Nuclear 11.3 μm PAH emission in local active galactic nuclei

Abstract

We present Gran Telescopio CANARIAS CanariCam 8.7$\\mu$m imaging and\n7.5-13$\\mu$m spectroscopy of six local systems known to host an active galactic\nnucleus (AGN) and have nuclear star formation. Our main goal is to investigate\nwhether the molecules responsible for the 11.3$\\mu$m polyclyclic aromatic\nhydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We\ndetect 11.3$\\mu$m PAH feature emission in the nuclear regions of the galaxies\nas well as extended PAH emission over a few hundred parsecs. The equivalent\nwidth (EW) of the feature shows a minimum at the nucleus but increases with\nincreasing radial distances, reaching typical star-forming values a few hundred\nparsecs away from the nucleus. The reduced nuclear EW are interpreted as due to\nincreased dilution from the AGN continuum rather than destruction of the PAH\nmolecules. We conclude that at least those molecules responsible for the\n11.3$\\mu$m PAH feature survive in the nuclear environments as close as 10pc\nfrom the AGN and for Seyfert-like AGN luminosities. We propose that material in\nthe dusty tori, nuclear gas disks, and/or host galaxies of AGN is likely to\nprovide the column densities necessary to protect the PAH molecules from the\nAGN radiation field.\n