The Globular Cluster System in the Outer Regions of NGC 4472

Abstract

We have undertaken a study of the globular cluster (GC) systems of a large sample of elliptical and spiral galaxies in order to test speciÐc predictions of galaxy formation models. Here we present results for the Ðrst elliptical in the study, the giant Virgo cluster galaxy NGC 4472 (M49). The galaxy was observed in three Ðlters (BV R) using the wide-Ðeld Mosaic Imager on the Kitt Peak 4 m telescope. The Mosaic images roughly double the radial coverage of previous CCD observations of NGC 4472. We have combined the Mosaic data with published spectroscopic data and archival HST observations in order to study NGC 4472Ïs GC system in detail, and to fully characterize the amount of contamination in our sample of GC candidates. We Ðnd that the radial proÐle of the GC system is Ðt fairly well by a de Vaucouleurs law of the form r1@4 out to 17@ (D80 kpc), but that log p GC \ (3.38 ^ 0.08) [ (1.56 ^ 0.05) the observed proÐle falls slightly below the de Vaucouleurs law between 17@ and 23@, the limit of the data. The bimodal color distribution observed in previous studies is apparent in our data. We Ðnd a small metallicity gradient in the inner 8@ of the total GC system due to the increasing ratio of blue to red clusters, consistent with results from past studies. The gradient vanishes, however, when the entire radial extent of the data is taken into account. We estimate a total of D5900 GCs in NGC 4472 out to 23@, yielding a speciÐc frequency of 3.6 ^ 0.6 within this radius. This speciÐc frequency value is smaller than that found by previous studies of NGC 4472. We examine the implications of these results with regard to predictions made by four di †erent galaxy formation models, and we Ðnd that all four models have at least one inconsistency with the data.