After the interaction: an efficiently star-forming molecular disk in NGC5195

TL;DR

This study presents detailed molecular gas observations of NGC5195, revealing its star formation efficiency and stellar populations, showing it has resettled and is forming stars efficiently after interaction with M51a.

Contribution

The paper provides new molecular gas maps and stellar population analysis of NGC5195, demonstrating its star formation properties and gas depletion timescale post-interaction.

Findings

Molecular gas depletion timescale is ~3.08 Gyr, similar to early-type galaxies.

High CN(1-0) intensity suggests enhanced diffuse PDRs.

Star formation efficiency is consistent with settled early-type galaxies.

Abstract

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.