Detections of C2H, cyclic-C3H2, and H13CN in NGC 1068
  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 active
galactic nucleus 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 C2H were determined to be 3.4 x 10^15 cm^-2 in NGC
1068 and 1.8 x 10^15 cm^-2 in NGC 253. The column densities of cyclic-C3H2 were
determined to be 1.7 x 10^13 cm^-2 in NGC 1068 and 4.4 x 10^13 cm^-2 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.
