The Evolution of NGC 7465 as Revealed by its Molecular Gas Properties
  We present ALMA observations of CO isotopologues and high-density molecular
tracers (HCN, HCO+, CN, etc.) in NGC 7465, an unusually gas-rich early-type
galaxy that acquired its cold gas recently. In the inner 300 pc, the molecular
gas kinematics are misaligned with respect to all other galaxy components; as
the gas works its way inward it is torqued into polar orbits about the stellar
kinematically-decoupled core (KDC), indicating that the stellar KDC is not
related to the current gas accretion event. The galaxy also exhibits unusually
high 12CO/13CO line ratios in its nucleus but typical 13CO/C18O ratios. Our
calculations show that this result does not necessarily indicate an unusual
[12CO/13CO] abundance ratio but rather that 12CO (1-0) is optically thin due to
high temperatures and/or large linewidths associated with the inner decoupled,
misaligned molecular structure. Line ratios of the higher-density tracers
suggest that the densest phase of molecular gas in NGC 7465 has a lower density
than is typical for nearby galaxies, possibly as a result of the recent gas
accretion. All of the observed molecular properties of NGC 7465 are consistent
with it having acquired its molecular (and atomic) gas from a spiral galaxy.
Further detailed studies of the CO isotopologues in other early-type galaxies
would be valuable for investigating the histories of those that may have
acquired their gas from dwarfs. Finally, these ALMA data also show an
unidentified line source that is probably a background galaxy similar to those
found at z=1-3 in blind CO surveys.
