Globular clusters in galaxies beyond the Local Group. III. NGC 4594 (The SOMBRERO).

The Sombrero galaxy is found to contain a large and structurally well-defined system of globular clusters. The present star counts on two deep U and V prime focus plates reveal a total of (1200 + or - 100) clusters to V(lim) of about 23.1 and (515 + or - 100) to U(lim) of about 23. Their spatial distribution matches the halo light curve adequately for r less than 2 arcmin (following roughly an r to the -2nd power radial dependence), but in the central approximately 2 arcmin of the system there appear to be far fewer bright clusters than expected relative to the halo light. Although the inner (r not greater than 5 arcmin) isophotes of the halo are unquestionably elliptical in projection, no measurable ellipticity is found in the cluster distribution. The specific frequency of the globular cluster population with respect to the halo luminosity is S = 3 + or - 1, about a factor of 2 lower than in most ellipticals and similar to other known large spirals. It is suggested that this galaxy (an Sa type) provides one of the strongest individual pieces of evidence that the halos of disk systems are fundamentally less efficient than ellipticals at producing globular clusters.