Recent interferometric observations of HCN and CO 1-0 molecular emission from the Seyfert galaxy NGC 1068 have revealed an unusually large HCN/CO emission-line ratio at the galactic nucleus. We argue that the large HCN/CO intensity ratio is due, in part, to a selective depletion of gas-phase oxygen in the dense molecular clouds within the narrow-line region. The reduced oxygen abundance inferred from the HCN and CO millimeter wave observations is consistent with a similar oxygen depletion inferred from optical, ultraviolet, and X-ray spectral observations of the ionized gas component in the nucleus of NGC 1068. Our multiwavelength analysis provides the first quantitative link between the chemical properties of the molecular and ionized gas clouds in the immediate vicinity of an active galactic nucleus.
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Sternberg et al. (1994) studied this question.