S316p.107 — Twins born in different environments? Nuclei of two dSphs: isolated galaxy KKS3 and ESO269-66, a close neighbor of NGC5128

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Aug 10th at 6:00 PM until 7:30 PM

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Author(s): Margarita Sharina2, Igor Karachentsev2, Alexei Kniazev1

Institution(s): 1. South African Astronomical Observatory, 2. Special Astrophysical Observatory RAS

The close vicinity of giant neighbors determines the environmental mechanisms that have been considered responsible for the evolution of dwarf spheroidal galaxies (dSphs). In the recent years, Karachentsev and collaborators have reported on the discovery of a few truly isolated dSphs in the Local volume. This study focuses on one of these unusual objects, KKs3 (MV=-12.3 mag). It contains a massive globular cluster (GC) (MV=-8.5 mag) near its optical center. We have performed the estimation of its radial velocity using a medium-resolution spectrum obtained with the RSS spectrograph at the Southern African Large Telescope (SALT). The signal-to-noise ratio in the spectrum was sufficient to estimate the age and metallicity for the GC using simple stellar population models, and the methods of full spectrum fitting and Lick index diagnostic diagrams. The results contribute to the knowledge about the origin of massive star clusters and their host dSphs.
In the same way we have analyzed another luminous GC (MV=-10) in the center of ESO269-66 (MB=-15.4), a close dSph neighbor of the giant S0 Cen A. The cluster was observed with SALT in the same instrumental configuration. The structure and star formation histories of the two galaxies look rather similar. Both of them have experienced several star-forming events. The most recent ones occurred 1÷2 Gyr ago, and most powerful bursts happened 12÷14 Gyrs ago. Our analysis has shown that both GCs appear to be 1÷2 Gyr younger and 0.2÷0.3 dex more metal-rich than the most ancient metal-poor stars in the host dSphs. We examine signatures of multiple stellar population in the GCs using out data. Since central star-forming bursts were extended in time, the massive clusters might be considered as nuclei of the galaxies.