After the interaction: an efficiently star-forming molecular disk in
  NGC5195
  We present new molecular gas maps of NGC5195 (alternatively known as M51b)
from the Combined Array for Research in Millimeter Astronomy (CARMA), including
12CO(1-0), 13CO(1-0), CN(1-0), and CS(2-1). NGC5195 has also been detected in
3mm continuum. NGC5195 has a 12CO/13CO ratio consistent with normal
star-forming galaxies. The CN(1-0) intensity is higher than is seen in an
average star-forming galaxy, possibly enhanced in the diffuse
photo-dissociation regions. Stellar template fitting of the nuclear spectrum of
NGC5195 shows two stellar populations: an 80% mass fraction of old (>10Gyr) and
a 20% mass fraction of intermediate-aged (~1Gyr) stellar populations, providing
a constraint on the timescale over which NGC5195 experienced enhanced star
formation during its interaction with M51a. The average molecular gas depletion
timescale in NGC5195 is: tdep=3.08Gyr, a factor of ~2 larger than the depletion
timescales in nearby star-forming galaxies, but consistent with the depletion
seen in CO-detected early-type galaxies. While the radio continuum emission at
centimeter and millimeter wavelengths is present in the vicinity of the nucleus
of NGC5195, we find it is most likely associated with nuclear star formation
rather than a radio-loud AGN. Thus, despite having a substantial interaction
with M51a ~1/2Gyr ago, the molecular gas in NGC5195 has resettled and is
forming stars at an efficiency consistent with settled early-type galaxies at
the present time.
