Possible evidence of destroying small PAH particles by radiation from AGNs

Abstract

The issue of destroying small polycyclic aromatic hydrocarbon (PAH) particles by radiation from AGNs is examined through optical narrow-emission line ratios of a sample of type II AGNs. We find that narrow-line ratios [OI]λ6300/Hα and [SII]λ6716, λ6731/Hα have prominent correlations with the PAH 11.3/7.7 ratio in our selected sample of AGNs. Because of the marginal (and in some cases no) dependence of the PAH ratio on the gas metallicity, a possible explanation for the correlations is the destruction of small PAH particles by the hard ionizing field associated with the AGNs.