THE BULGE HALO LUMINOSITY OF M33 AND ITS GLOBULAR-CLUSTER POPULATION

We use the method of surface photometry to constrain the bulge luminosity of M33. Analysis of blue and 12-mu-m images places a conservative upper limit of M(upsilon) = - 15 on the bulge luminosity of M33. Although there is a clear power-law component in the surface brightness profile of M33 interior to R = 0.5 kpc, it represents less than 2% of the total luminosity. More stringent limits come by considering the relatively blue colors observed in the inner regions of M33. It is unclear if this power law component represents a bulge or a more extended halo component. By itself, the presence of a puny bulge/halo in a disk galaxy is not very interesting. However, Schommer et al. [AJ, 101, 873 (1991a)] have recently shown that M33 has a significant population of old globular clusters that are distributed in a kinematic halo. Relative to its low bulge/halo luminosity, M33 therefore appears to have a very large number of globular clusters. Hence, M33 provides us with a clear example of galaxy formation which allowed for the formation of globulars but not another conspicuous manifestation of Population II.