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[40.12] Globular Cluster Systems of Dwarf Ellipticals

B.W. Miller (Leiden)

The globular cluster (GC) systems of dwarf elliptical (dE) galaxies are very similar to the metal-poor globular cluster populations in giant ellipticals and spirals. The properties used for the comparison are the globular cluster specific frequency (S_N=N_c10^0.4(M_V+15)), the shape of the globular cluster luminosity function, and the cluster color distribution. S_N of dEs is in the range 2--6, similar to giant ellipticals (Durrell et al.\ 1996; Miller et al.\ 1998). Spiral galaxies typically have S_N<1. In addition, nucleated dEs have values of S_N about twice that of non-nucleated dEs (Miller et al.\ 1998). The luminosity function (LF) of the GC candidates is consistent with a Gaussian with a peak at M_V⁰\approx-7.0 and a width \sigma_V\approx1.4~mag. The LFs of globular cluster systems of giant ellipticals are also Gaussian shaped with a peak at M_V⁰\approx-7.4. Also, with a mean color of \langle V\!-\!I\rangle\approx0.95, the GCs in dEs are similar to the old and metal-poor ([{\rm Fe/H}]\approx-1.5) GC populations in nearby gaint ellipticals and spirals. Star clusters in dEs tend to be bluer than both the background light of the galaxies and the bright nuclei. If this color difference is due to metallicity, then the GCs are between 0.0 and 0.4 dex more metal-poor than the stars in bodies of the galaxies. The nuclei have a range of colors, or metallicities, between those of the GCs and the stellar background light. Alternatively, these color differences may imply age differences between the GCs, nuclei, and stars in the galaxies. However, it appears that GCs in dwarf ellipticals formed at about the same time and with similar efficiencies as the oldest GCs in giant ellipticals and spirals. This supports the idea that there was a common era of early cluster formation. This could be explained if these old GCs were formed preferentially in dwarf galaxy sized fragments that latter merged into larger galaxies.

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