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. 
Katherine Alatalo (1), Rebeca Aladro (2,3), Kristina Nyland (4),   Susanne Aalto (3), Theodoros Bitsakis (5), John S. Gallag...
astro-ph.GA