Molecular gas around low-luminosity AGN in late-type spirals
  We have studied the molecular gas in the vicinity of low-luminosity active
galactic nuclei (AGNs) in three bulge-less spiral galaxies: NGC 1042, NGC 4178,
and NGC 4395. The (1-0) and (2-1) transitions of gaseous carbon monoxide (CO)
are clearly detected within the central kpc of all three galaxies. In the case
of NGC 4395, this constitutes the first reported detection of CO. In general,
the CO emission is faint, as may be expected from their less-than-spectacular
star formation activity. Interestingly, however, both face-on galaxies in our
sample (which allow an unimpeded view of their nucleus) show an elevated
intensity ratio CO(2-1)/CO(1-0) when compared to similar late-type spirals
without an AGN. We discuss that this is unlikely due to a very compact CO
source. Instead, we speculate that even energetically weak AGN can impact the
physical state of the surrounding gas. We do not detect any tracers of dense
molecular gas such as HCN or HCO+, but the sensitivity of our observations
allows us to establish upper limits that lie at the low end of the range
observed in more energetic AGN. The derived gas density is less than
n(H2)\approx 2e03 cm^-3 which is significantly lower than in most other nearby
galaxies. The scarcity of dense gas suggests that the conditions for star
formation are poor in these nuclei.
