Constraints on the Formation History of the Elliptical Galaxy Ngc 3923 from the Colors of Its Globular Clusters

We present a study of the colors of globular clusters associated with the elliptical galaxy NGC 3923. Our nal sample consists of Washington system C and T1 photometry for 143 globular cluster candidates with an expected contamination of no more than 10%. We nd that the color distribution of the NGC 3923 globular cluster system (GCS) is broad and appears to have at least two peaks. A mixture modeling analysis of the color distribution indicates that a two component model is favored over a single component one at a high level of con dence (> 99%). This evidence for more than one population in the GCS of NGC 3923 is similar to that previously noted for the four other elliptical galaxies for which similar data have been published. Furthermore, we nd that the NGC 3923 GCS is redder than the GCSs of previously studied elliptical galaxies of similar luminosity. The median metallicity inferred from our (C T1)0 colors is [Fe/H]med = 0:56, with an uncertainty of 0.14 dex arising from all sources of uncertainty in the mean color. This is more metal rich than the median metallicity found for the GCS of M87 using the same method, [Fe/H]med = 0:94. Since M87 is more luminous than NGC 3923, this result points to signi cant scatter about any trend of higher GCS metallicity with increasing galaxy luminosity. We also show that there is a color gradient in the NGC 3923 GCS corresponding to about -0.5 dex in [Fe=H]= logr. We conclude that the shape of the color distribution of individual GCSs and the variation in mean color among the GCSs of ellipticals are di cult to understand if elliptical galaxies are formed in a single protogalactic collapse. Models in which ellipticals and their globular clusters are formed in more than one event, such as a merger scenario, are more successful in accounting for these observations. 2