Masses and Mass-To-Light Ratios of Galaxies

Abstract

Is there more to a galaxy than meets the eye (or can be seen on a photo graph)?Many decades ago, Zwicky (1933) and Smith (1936) showed that if the Virgo cluster of galaxies is bound, the total mass must considerably exceed the sum of the masses of the individual member galaxies; i.e. there appeared to be "missing mass" in the cluster.As more data became avail able, the discrepancy persisted between masses of individual galaxies determined fr om optical rotation curves and the larger average galaxy mass needed to bind groups and clusters (e.g.Neyman, Page & Scott 1961).Recently, however, new information has pointed toward larger total masses fo r individual galaxies, thus decreasing the traditional discrepancy between various methods of mass measurement.Arguing that thin self gravitating stellar disks are unstable against bar-like modes, Ostriker & Peebles (1973) suggested that the disks of normal spiral galaxies must be imbedded in optically undetected, stabilizing massive halos.Ostriker,1974) and Einasto, Kaasik & Saar (1974) collected observational evidence in support of the existence of such halos (although Burbidge 1975 used similar data to reach the opposite conclusion).At nearly the same time, high-resolution 21-cm observations of nearby galaxies were showing that H I often extends well beyond the optical 1 Supported in part by the Alfred P.