Revised masses of dust and gas of SCUBA Local Universe Survey far-infrared bright galaxies based on a recent CO survey

Abstract

Recent CO measurements of an essentially complete subsample of galaxies from the SCUBA Local Universe Survey (SLUGS) are used to examine their implications for dust and gas masses in this sample. Estimates of dust masses are affected by a contribution to the SCUBA brightness measurements by CO(3–2) emission, and molecular gas masses by the use of a modified value of the CO-to-H 2 conversion factor X. The average dust mass is reduced by 25–38 per cent, which has no bearing on earlier conclusions concerning the shape of the dust mass luminosity function derived from the SLUGS. The value of X found from the CO survey, when applied together with the reduction in dust masses, leads to lower estimates for the mean gas-to-dust mass ratios, where the gas includes both H 2 and H i . For the CO sample, the mean global ratio is reduced from approximately 430 to about 320–360, but is further reduced to values near 50 when applied to the nuclear regions relevant to the CO observations. We discuss these results and suggest that the differences between the nuclear and outer regions may simply reflect differences in metallicity or the existence of considerable amounts of unobserved cold dust in the outer regions of these galaxies.