We present a study of the molecular gas properties in a sample of 98 H I – flux selected spiral galaxies within ∼25 Mpc, using the CO J = 3 − 2 line observed with the James Clerk Maxwell Telescope. We use the technique of survival analysis to incorporate galaxies with CO upper limits into our results. Comparing the group and Virgo samples, we find a larger mean H2 mass in the Virgo galaxies, despite their lower mean H I mass. This leads to a significantly higher H2 to H I ratio for Virgo galaxies. Combining our data with complementary Hα star formation rate measurements, Virgo galaxies have longer molecular gas depletion times compared to group galaxies, due to their higher H2 masses and lower star formation rates. We suggest that the longer depletion times may be a result of heating processes in the cluster environment or differences in the turbulent pressure. From the full sample, we find that the molecular gas depletion time has a positive correlation with the stellar mass, indicative of differences in the star formation process between low- and high-mass galaxies, and a negative correlation between the molecular gas depletion time and the specific star formation rate.

Document Type


Publication Date


Notes/Citation Information

Published in Monthly Notices of the Royal Astronomical Society, v. 456, issue 4, p. 4384-4406.

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

The copyright holders have granted the permission for posting the article here.

Digital Object Identifier (DOI)


Funding Information

The research of C.D.W. is supported by grants from NSERC (Canada). We acknowledge financial support to the DAGAL network from the People Programme (Marie Curie Actions) of the European Unions Seventh Framework Programme FP7/2007-2013/ under REA grant agreement number PITN-GA-2011-289313 and from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2013-41243-P.

Due to the large number of funding sources, only the first few are listed in this section. For the complete list of funding sources, please download this article.