MILLIMETER-WAVE THERMAL DUST EMISSION FROM LUMINOUS MERGERS

We have observed several infrared-luminous galaxies which are in the p rocess of merging (Mkn 231, Arp 299, NGC 6240, NGC 520, and IRAS 17208 -0014) at 1.2 mm with the multi-channel bolometer at the IRAM 30-meter telescope. Such observations of the long-wavelength thermal dust emis sion provide an alternative to CO as a measure of the gas mass. Compar ing the masses of gas determined from the dust emission and from CO ob servations of these galaxies, we find that the conversion factor N(H-2 )/ICO(1-0) less than or similar to 0.5 10(20) cm(-2)(K kms(-1))(-1). O ur calculations are conservative. We have chosen a nu(2) emissivity; o ther emission laws result in higher dust temperatures. We have made ou r calculations assuming a metallicity of 2Z., which is low for a galac tic nucleus. We have not assumed any enhancement of the dust emission through agglomeration of dust particles nor destruction of grains. Fin ally, we have assumed that all of the gas associated with 1.2mm therma l dust emission is molecular. Expected deviations from these assumptio ns would all decrease the gas masses estimated from the thermal dust e mission, resulting in even lower values for the N(H-2)/I-CO conversion factor.