A Molecular Line Survey toward the Nearby Galaxies NGC 1068, NGC 253,
  and IC 342 at 3 mm with the Nobeyama 45-m Radio Telescope: Impact of an AGN
  on 1 kpc Scale Molecular Abundances
  It is important to investigate the relationships between the power sources
and the chemical compositions of galaxies for understanding the scenario of
galaxy evolution. We carried out an unbiased molecular line survey towards AGN
host galaxy NGC1068, and prototypical starburst galaxies, NGC 253 and IC 342,
with the Nobeyama 45-m telescope in the 3-mm band. The advantage of this line
survey is that the obtained spectra have the highest angular resolution ever
obtained with single-dish telescopes. In particular, the beam size of this
telescope is ~15"--19", which is able to spatially separate the nuclear
molecular emission from that of the starburst ring (d~30") in NGC 1068. We
successfully detected approximately 23 molecular species in each galaxy, and
calculated rotation temperatures and column densities. We estimate the
molecular fractional abundances with respect to 13CO and CS molecules and
compare them among three galaxies in order to investigate the chemical
signatures of an AGN environment. As a result, we found clear trends on the
abundances of molecules surrounding the AGN on 1 kpc scale. HCN, H13CN, CN,
13CN, and HC3N are more abundant, and CH3CCH is deficient in NGC 1068 compared
with the starburst galaxies. High abundances of HCN, H13CN, and HC3N suggest
that the circumnuclear disk in NGC 1068 is in a high-temperature environment.
The reason for the non-detection of CH3CCH is likely to be dissociation by high
energy radiation or less sublimation of a precursor of CH3CCH from grains.
