The JCMT Nearby Galaxies Legacy Survey X. Environmental Effects on the Molecular Gas and Star Formation Properties of Spiral Galaxies

TL;DR

This study investigates how environment influences molecular gas and star formation in nearby spiral galaxies, revealing that cluster galaxies like those in Virgo have higher molecular gas content and longer depletion times than group galaxies.

Contribution

It provides new insights into environmental effects on molecular gas properties and star formation efficiencies in spiral galaxies within 25 Mpc.

Findings

Virgo galaxies have higher H2 masses despite lower HI masses.

Virgo galaxies exhibit longer molecular gas depletion times.

Depletion time correlates positively with stellar mass and negatively with specific star formation rate.

Abstract

We present a study of the molecular gas properties in a sample of 98 HI - flux selected spiral galaxies within $\sim25$ 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 H$_{2}$ mass in the Virgo galaxies, despite their lower mean HI mass. This leads to a significantly higher H$_{2}$ to HI ratio for Virgo galaxies. Combining our data with complementary H$\alpha$ star formation rate measurements, Virgo galaxies have longer molecular gas depletion times compared to group galaxies, due to their higher H$_{2}$ 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.