The JCMT Nearby Galaxies Legacy Survey I. Star Forming Molecular Gas in Virgo Cluster Spiral Galaxies

TL;DR

This study maps star-forming molecular gas in Virgo Cluster spiral galaxies using CO J=3-2 emission, revealing insights into gas properties, star formation efficiency, and environmental effects within the cluster.

Contribution

First large-area CO J=3-2 maps of Virgo Cluster spirals combined with multi-wavelength data, highlighting the line's effectiveness as a dense gas tracer and environmental impacts on molecular gas.

Findings

CO J=3-2 correlates better with star formation rate surface density than CO J=1-0.

NGC 4254 has higher star formation efficiency, possibly due to its first cluster passage.

NGC 4569 shows a gradient in gas properties indicating interaction with the intracluster medium.

Abstract

We present large-area maps of the CO J=3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J=1-0, 24 micron, and Halpha images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our sample (NGC 4254, NGC4321, and NGC 4569), we obtain molecular gas masses of 7E8-3E9 Msun and disk-averaged instantaneous gas depletion times of 1.1-1.7 Gyr. We argue that the CO J=3-2 line is a better tracer of the dense star forming molecular gas than the CO J=1-0 line, as it shows a better correlation with the star formation rate surface density both within and between galaxies. NGC 4254 appears to have a larger star formation efficiency(smaller gas depletion time), perhaps because it is on its first passage through the Virgo Cluster. NGC 4569 shows a large-scale gradient in the gas properties traced by the CO J=3-2/J=1-0 line ratio, which suggests that its interaction with the intracluster medium is affecting the dense star-forming portion of the interstellar medium directly. The fourth galaxy in our sample, NGC 4579, has weak CO J=3-2 emission despite having bright 24 micron emission; however, much of the central luminosity in this galaxy may be due to the presence of a central AGN.