THE DETERMINATION OF DUST MASS IN GALAXIES

Using the observed data of galaxies at 60, 100, 345, and 761 mum, we present a simple and systematic way to examine the uncertainties in the determination of dust mass owing to uncertainties in the dust emissivity law, imprecision in the observed data, inexact modeling of the temperature distribution, and the presence of a correlation between grain size and temperature. Our results for 12 galaxies generally confirm conclusions reached in previous works. They show that while emission by warm dust at a single temperature can account for the spectra at lambda greater than or similar to 60 mum of a large number of galaxies in our sample when observational uncertainties are taken into account and with the freedom of choice of emissivity law, temperature distributions with large amounts of cold dust can fit the data better. To reduce the large uncertainties in the dust mass determination, observations at long submillimeter wavelengths (lambda greater-than-or-equal-to 761 mum) are crucial in order to narrow down the possible range of emissivity law, and highly accurate S100 mum/S345 mum and S100 mum/S761 mum flux density ratios are needed. With the presently available data for the 12 galaxies, our best estimates for the ratios of infrared luminosity to gas mass range from 2 to 23 and average 9.