We recently published the discovery of the first black hole X-ray binary in a globular cluster. This object is located in a bright globular cluster around the Virgo elliptical NGC 4472. Here we propose to obtain HST PC images of this black-hole hosting globular cluster and a sample of other NGC 4472 globulars. We will use these data to determine the structural parameters of both the globular cluster known to have a black hole and a control sample of other NGC 4472 clusters. This will test recent theoretical predictions how black holes affect the structural parameters of globular clusters, and more generally will allow for the first time constraints on any relationship between the presence of a black hole and the surface brightness profiles of globular clusters. The deep WFPC2 images outside of the galaxy's central regions will also be invaluable for studying how the sizes and luminosity function of globular clusters depend on distance from the center of the galaxy, and thus address questions about the origin of the size differences between metal-rich and metal-poor clusters and the shape of the globular cluster luminosity function. In addition, parallel NIC3 images will allow the optical to near-infrared colors of NGC 4472 globular cluster to be determined over a wide range of galactocentric radii.

We propose to obtain HST PC images in F555W of the globular cluster in NGC 4472 that has been recently discovered to host a black hole X-ray binary, and also four other PC fields with similarly bright globular clusters for comparison to the black-hole hosting cluster. We will use two orbits for each pointing which will be observed with a four point dither to maximize spatial resolution and cosmic ray removal. Two orbits with the PC in F555W will allow a reliable determination of the surface brightness profile over a broad enough radial range to distinguish between clusters of different concentrations. In addition to our principal targets on the PC, we will also use the WF data from WFPC2 in a number of ways described in the justification. These include determining the sizes for globular clusters over a wide range of galactocentric radii, as well as constraining any dependence of the the globular cluster luminosity function on distance from the galactic center. We will also obtain parallel NIC3 exposures in order to constrain the optical to near-infrared colors of NGC 4472 globular clusters over a range of galactocentric distances. 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