Images from the Hubble Space Telescope Advanced Camera for Surveys are used to carry out a new photometric study of the globular clusters ( GCs ) in M104 , the Sombrero galaxy .
The primary focus of our study is the characteristic distribution function of linear sizes ( SDF ) of the GCs .
We measure the effective radii for 652 clusters with PSF-convolved King and Wilson dynamical model fits .
The SDF is remarkably similar to those measured for other large galaxies of all types , adding strong support to the view that it is a “ universal ” feature of globular cluster systems .

We use the Sombrero and Milky Way data and the formation models of Baumgardt & Kroupa ( 2007 ) to develop a more general interpretation of the size distribution function for globular clusters .
We propose that the shape of the SDF that we see today for GCs is strongly influenced by the early rapid mass loss during their star forming stage , coupled with stochastic differences from cluster to cluster in the star formation efficiency ( SFE ) and their initial sizes .
We find that the observed SDF shape can be accurately predicted by a simple model in which the protocluster clouds had characteristic sizes of 0.9 \pm 0.1 pc and SFEs of 0.3 \pm 0.07 .

The colors and luminosities of the M104 clusters show the clearly defined classic bimodal form .
The blue sequence exhibits a mass/metallicity relation ( MMR ) , following a scaling of heavy-element abundance with luminosity of Z \sim L ^ { 0.3 } very similar to what has been found in most giant elliptical galaxies .
A quantitative self-enrichment model provides a good first-order match to the data for the same initial SFE and protocluster size that were required to explain the SDF .

We also discuss various forms of the globular cluster Fundamental Plane ( FP ) of structural parameters , and show that useful tests of it can be extended to galaxies beyond the Local Group .
The M104 clusters strongly resemble those of the Milky Way and other nearby systems in terms of such test quantities as integrated surface density and binding energy .