XDR Chemistry in the Circumnuclear Disk of NGC 1068
We have studied the feedback in°uence that the central engine of the Seyfert 2 galaxy NGC 1068 may have on the chemistry of the 200 pc circumnuclear gas disk (CND). With this purpose, we have conducted a multispecies/ multi-transition survey of molecular gas in the CND of NGC 1068 using the IRAM 30m telescope. Abundances of several molecular species have been estimated, including HCN, CN, CS, HCO+, SiO and HOC+. We report on the detection of signi¯cant SiO emission in this galaxy, as well as on the ¯rst extragalactic detection of the active radical HOC+. We conclude that the chemistry of the molecular gas reservoir in the CND can be best explained in the framework of X-ray Dominated Region (XDR) models.