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摘要
We present new molecular gas maps of NGC5195 (alternatively known as M51b) from the Combined Array for Research in Millimeter Astronomy, including (CO)-C-12(1- 0), (CO)-C-13(1- 0), CN(1(0,2)-0(0,1)), CS(2- 1), and 3 mm continuum. We also detected HCN(1- 0) and HCO+(1- 0) using the Onsala Space Observatory. NGC 5195 has a (CO)-C-12/(C13) CO ratio (R-=12/13 - 11.4 +/- 0.5) 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 gas in photo-dissociation regions. Stellar template fitting of the nuclear spectrum of NGC 5195 shows two stellar populations: an 80% mass fraction of old (greater than or similar to 10 Gyr) and a 20% mass fraction of intermediate-aged (approximate to 1 Gyr) stellar populations. This provides a constraint on the timescale over which NGC 5195 experienced enhanced star formation during its interaction with M51a. The average molecular gas depletion timescale in NGC 5195 is tau(dep) = 3.08 Gyr, a factor of similar to 2 larger than the depletion timescales in nearby star- forming galaxies, but consistent with the depletion seen in CO-detected early-type galaxies. While radio continuum emission at centimeter and millimeter wavelengths is present in the vicinity of the nucleus of NGC 5195, we find it is most likely associated with nuclear star formation rather than radio-loud AGN activity. Thus, despite having a substantial interaction with M51a similar to 1/2 Gyr ago, the molecular gas in NGC 5195 has resettled and is currently forming stars at an efficiency consistent with settled early-type galaxies.
- 出版日期2016-10-20
