Globular Clusters as Probes of Galaxy Evolution: NGC 5128

Abstract

We present the results of our analysis of the photometric data of globular clusters in the elliptical galaxy NGC 5128 (Cen A). We show that the integrated colour U-B can be an effective metallicity indicator for simple stellar populations. This is because it is sensitive to metallicity via the opacity effect but relatively insensitive to the effective main sequence turn-off temperature of the population (and thus to age) when Teff ~ 7000-12000K, that is, when the Balmer Jump is strong. This flat U-B vs Teff relation is a result of the fact that the blueing effect of the optical continuum with increasing temperature is temporarily stopped by the Balmer Jump which becomes greater with temperature in this range. In this study we use U-B and B-V as metallicity and age indicators, respectively. We first show that the use of the U-B vs B-V two-colour diagram roughly yields the metallicities and ages of the Milky Way globular clusters independently determined, and then apply the technique to the clusters in NGC 5128. There is a large range in U-B, which corresponds to [Fe/H] of -2.0 through over +0.3. The large uncertainties from the data and the models currently prevent us from pinning down their ages and metallicities. Although a constant age for all these clusters cannot be ruled out, there is a hint of the metal-rich clusters being younger. Significance of these results and caveats of the analysis are discussed.

14 pages, 8 figures, Accepted MNRAS, Table 1 available on email request

References in corpus (17)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• A standard stellar library for evolutionary synthesis: I. Calibration of theoretical spectra
• The Formation of Giant Elliptical Galaxies and Their Globular Cluster Systems
• The Ages of Elliptical Galaxies in a Merger Model
• Globular Cluster Systems I: V-I Color Distributions
• The Ages and Abundances of the M87 Globular Clusters
• Uncertainties of Synthetic Integrated Colors as Age Indicators
• A Young Blue Tidal Stream in NGC 5128
• The Globular Cluster System of NGC 5128 I. Survey and Catalogs
• VLT spectroscopy of NGC3115 globular clusters
• Evidence for An Intermediate-Age, Metal-rich Population of Globular Clusters in NGC 4365
• The Relative Ages of the Globular Cluster Subpopulations in M87
• The radio/optical alignment and the recent star formation associated with ionized filaments in the halo of NGC 5128 (Centaurus A)
• Constraints on the Formation History of the Elliptical Galaxy NGC 3923 from the Colors of Its Globular Clusters
• Deep VLT search for globular clusters in NGC 5128: color-magnitude diagrams and globular cluster luminosity function
• On the Formation of Galaxy Halos: Comparing NGC 5128 and the Local Group Members
• Globular Clusters in the Inner Regions of NGC5128 (Cen A)

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