The masses of spiral galaxies

It has been pointed out by Pismis and Maupome(1978) that the total mass of galaxies, and especially of spiral galaxies, decreases as the Hubble type varied from Sa through Sc and irregular galaxy types, and that masses determined on the basis of the hydrogen 21-cm line are higher than optically determined ones. These trends are presently investigated by means of a Brandt (1962) analytic rotation curve that has been adjusted to optical observations in order to include galaxy masses up to the last point observed. While the computed masses are, predictably, higher, the previously noted mass decrease with Hubble type is confirmed. It is noted, however, that there is an unexplained discrepancy in the earlier, Sa and Sab types, characterized by radio masses which are smaller than the optically determined ones.