Globular Clusters as Tracers of Stellar Bimodality in Elliptical Galaxies: The Case of NGC 1399

Abstract

Globular cluster systems (GCS) frequently show a bi-modal distribution of the cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. In the particular case of NGC 1399 the results show that the galaxy brightness profile and colour gradient as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so called "blue" and "red" globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn=3.3 +/- 0.3 in the case of the red globulars and Sn=14.3 +/- 2.5 for the blue ones. We stress that this result is not necessarily conflicting with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about 6 times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X ray emiting hot gas associated with NGC 1399, is emphasized. The impact of a relatively unconspicuous low metallicity population, that shares the properties of the blue globulars, as a possible source of chemical enrichment early in the formation history of the galaxy is also briefly discussed.