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Published April 20, 2011 | Published
Journal Article Open

The Dense Molecular Gas in the Circumnuclear Disk of NGC 1068

Abstract

We present a 190-307 GHz broadband spectrum obtained with Z-Spec of NGC 1068 with new measurements of molecular rotational transitions. After combining our measurements with those previously published and considering the specific geometry of this Seyfert 2 galaxy, we conduct a multi-species Bayesian likelihood analysis of the density, temperature, and relative molecular abundances of HCN, HNC, CS, and HCO+. We find that these molecules trace warm (T>100 K) gas of H_2 number densities 10^(4.2)-10^(4.9) cm^(–3). Our models also place strong constraints on the column densities and relative abundances of these molecules, as well as on the total mass in the circumnuclear disk. Using the uniform calibration afforded by the broad Z-Spec bandpass, we compare our line ratios to X-ray-dominated region (XDR) and photon-dominated region models. The majority of our line ratios are consistent with the XDR models at the densities indicated by the likelihood analysis, lending substantial support to the emerging interpretation that the energetics in the circumnuclear disk of NGC 1068 are dominated by accretion onto an active galactic nucleus.

Additional Information

© 2011 American Astronomical Society. Received 2010 October 12; accepted 2011 February 17; published 2011 March 25. We thank the anonymous referee for a thorough and constructive report, and we also express our gratitude to the staff at the Caltech Submillimeter Observatory. We acknowledge the following grants and fellowships in support of this work: NASA SARA grants NAGS-11911 and NAGS-12788, an NSF Career grant AST-0239270, and a Research Corporation Award RI0928 to J.G.; a Caltech Millikan fellowship and JPL Director's fellowship to C.M.B.; an NRAO Jansky fellowship and NSF grant AST-087990 to J.E.A.; a NASA GSRP fellowship to L.E.; and an NSF GRFP fellowship to J.K.

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