CONSTRAINTS ON THE FORMATION HISTORY OF THE ELLIPTIC 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 final sample consists of Washingto n system C and T-1 photometry for 143 globular cluster candidates with an expected contamination of no more than 10%. We find that the color distribution of the NGC 3923 globular cluster system (GCS) is broad a nd 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 confidence (>99%). Thi s evidence for more than one population in the GCS of NGC 3923 is simi lar to that previously noted for the four other elliptical galaxies fo r which similar data have been published. Furthermore, we find that th e NGC 3923 GCS is redder than the GCSs of previously studied elliptica l galaxies of similar luminosity. The median metallicity inferred from our (C-T-1)(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. Th is 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 luminous than NGC 3923, this result points to significant scatter about any tre nd of higher GCS metallicity with increasing galaxy luminosity. We als o show that there is a color gradient in the NGC 3923 GCS correspondin g to about -0.5 dex in Delta[Fe/H]/Delta log r. We conclude that the s hape of the color distribution of individual GCSs and the variation in mean color among the GCSs of ellipticals are difficult 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.