Washington Photometry of the Globular Cluster System of NGC 4472. II. The Luminosity Function and Spatial Structure

Abstract

We present a comprehensive study of the luminosity function and spatialstructure of the globular cluster system of NGC 4472, the brightestgalaxy in Virgo, based on deep wide-field Washington CT_1 CCD images.The globular cluster luminosity function shows a peak at T_1 = 23.3 +/-0.1 mag, about 1.5 mag brighter than our 50% completeness limit.Comparing this value with that of the Galactic globular clusters, weestimate the true distance modulus to NGC 4472 to be (m - M)_0 = 31.2+/- 0.2 (corresponding to a distance of 17.4 +/- 1.6 Mpc). With ourlarge sample (~2000) of bright globular clusters over a wide field, wemake a definitive investigation of the spatial structures of themetal-poor and metal-rich cluster populations and find that they aresystematically different: (1) the metal-rich clusters are more centrallyconcentrated than the metal-poor clusters; and (2) the metal-richclusters are elongated roughly along the major axis of the parentgalaxy, while the metal-poor clusters are essentially sphericallydistributed. In general, the metal-rich clusters closely follow theunderlying halo starlight of NGC 4472 in terms of spatial structure andmetallicity, while the metal-poor clusters do not. The global value ofthe specific frequency of the globular clusters in NGC 4472 is estimatedto be S_N = 4.7 +/- 0.6. The local specific frequency increases linearlyoutward from the center of NGC 4472 until ~5.5{\prime}, beyond which itlevels off at S_N ~ 8.5 until the limit of our data at 7'. The specificfrequency of both the metal-rich and metal-poor populations showssimilar behavior. However, S_N of the metal-poor clusters is about afactor of 2 greater than that of the metal-rich clusters in the outerregions. Implications of these results for the origin of the globularclusters in NGC 4472 are discussed. These results are consistent withmany of the predictions of both the model of episodic in situ formationplus tidal stripping of globular clusters given by Forbes et al. and theAshman {\amp} Zepf merger formation model, but each of the models alsohas some problems.