Abstract
Recent observations of the dwarf elliptical galaxy Scl-dE1 (Sc22) in the Sculptor group of galaxies revealed an extended globular cluster (Scl-dE1 GC1), which exhibits an extremely large core radius of about 21.2 pc. The authors of the discovery paper speculate on whether this object could reside in its own dark matter halo and/or if it might have formed through the merging of two or more star clusters. In this paper, we present N-body simulations to explore thoroughly this particular formation scenario. We follow the merger of two star clusters within dark matter haloes of a range of masses (as well as in the absence of a dark matter halo). In order to obtain a remnant which resembles the observed extended star cluster, we find that the star formation efficiency has to be quite high (around 33 per cent) and the dark matter halo, if present at all, has to be of very low mass, i.e. raising the mass-to-light ratio of the object within the body of the stellar distribution by at most a factor of a few. We also find that expansion of a single star cluster following mass loss provides another viable formation path. Finally, we show that future measurements of the velocity dispersion of this system may be able to distinguish between the various scenarios we have explored.
Highlights
The general understanding of low luminosity stellar systems is that they come in two distinct flavours
The first simulations we perform are of two star clusters which merge under their own gravity without a dark matter (DM) halo present
Our simulations suggest that mass-to-light ratios of only a few would be expected if the object is formed by the merger of two star clusters, and they are consistent with there being no dynamically significant amount of DM within the stellar distribution of the extended globular clusters (EGC)
Summary
The general understanding of low luminosity stellar systems is that they come in two distinct flavours. Assuming that the simulation results in a merged object which resides in the centre of the DM halo, thereby having a large relaxation-time (of order a Hubble time or longer), this is an appropriate approximation since we would expect that binary formation and two-body encounter would have only a minor effect on our results. Another advantage is that Superbox allows us to set different levels of resolution for the different levels of high-resolution grids used in the code. Two-body effects, like binary formation and twobody relaxation are neglected, since they do not play an important role if the final object resides in a DM potential
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