2011ApJ...728L..38N

We used the Nobeyama 45 m telescope to conduct a spectral line survey in the 3 mm band (85.1-98.4 GHz) toward one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068, and the prototypical starburst galaxy NGC 253. The beam size of this telescope is ∼ 18'', which was sufficient to spatially separate the nuclear molecular emission from the emission of the circumnuclear starburst region in NGC 1068. We detected rotational transitions of C₂H, cyclic-C₃H₂, and H¹³CN in NGC 1068. These are detections of carbon-chain and carbon-ring molecules in NGC 1068. In addition, the C₂H N = 1-0 lines were detected in NGC 253. The column densities of C₂ H were determined to be 3.4x10¹⁵/cm2 in NGC 1068 and 1.8x10¹⁵/cm2 in NGC 253. The column densities of cyclic-C₃H₂ were determined to be 1.7x10¹³/cm2 in NGC 1068 and 4.4x10¹³/cm2 in NGC 253. We calculated the abundances of these molecules relative to CS for both NGC 1068 and NGC 253, and found that there were no significant differences in the abundances between the two galaxies. This result suggests that the basic carbon-containing molecules are either insusceptible to AGN or are tracing cold (T_rot∼ 10 K) molecular gas rather than X-ray irradiated hot gas.