Embedding globular clusters in dark matter minihaloes solves the cusp–core and timing problems in the Fornax dwarf galaxy

Abstract

We use a fully GPU N-body code to demonstrate that dark matter minihalos, as a new component of globular clusters, resolves both the timing and cusp-core problems in Fornax if the five globular clusters were recently accreted (2-4 Gyr ago) by Fornax. Under these assumptions, the infall of these globular clusters does not occur and no star clusters form in the centre of Fornax in accordance with observations. Crossings of globular clusters with a DM minihalo near the Fornax centre induce a cusp-to-core transition of the dark matter halo and hence resolve the cusp-core problem in this dwarf galaxy. The dark matter core size depends on the frequency of globular cluster crossings. Our simulations clearly demonstrate also that between the passages, dark matter halo can regenerate its cusp. Moreover, our models are in good agreement with constraints on the dark matter masses of globular clusters as our clusters have lost a large fraction of their initial dark matter minihalos. These results provide circumstantial evidence for the universal existence of dark matter halos in globular clusters.

Assessing the Fornax globular cluster timing problem in different models of dark matter

“…For the galactic center of Fornax we use an updated measurement [20], based on surface brightness modelling. This estimate is ≈ 160 pc off relative to the center defined by previous works [2,16,18,29,31,44], leading to different projected radii of GCs. We set the distance to Fornax as 147 ± 4 kpc [17].…”

“…Many explanations were suggested for the GC timing puzzle [22][23][24][25][26][27][28][29][30][31][32][33][34][35], of which an exciting class of ideas entails a modification to the nature of dark matter, going beyond CDM [29,[32][33][34][35]. In particular, Refs.…”

The survival of globular clusters in a cuspy Fornax

“…This simple model suggests that only one GC, Frn 4, was born at a small radial distance, r init = 700 pc, which is approximately the half-light radius of the present-day Fornax (as given by McConnachie 2012). For the remaining four GCs, the initial distances are larger than 1.5 kpc, which suggests that at least some of them were accreted (see also Boldrini et al 2020). This result is in good agreement with our model prediction that around half of the present-day surviving GCs are of accreted origin.…”

“…Another possibility has been proposed by Boldrini, Mohayaee & Silk (2020) who have shown that if the GCs are surrounded by their own DM minihaloes, then there is no 'GC timing problem' even in cuspy haloes. Finally, it is worth mentioning that tidal streams produced by the disruption of GCs stripped from dwarf galaxies can perhaps be used to distinguish between a central cusp or a core in the halo of the dwarf from which the GC was stripped (Malhan, Valluri & Freese 2020).…”

Testing for Dark Matter in the Outskirts of Globular Clusters

“…One possibility is that some halo clusters formed at or near the center of small dark matter halos. Tidal fields in an assembling galaxy later remove the outer dark matter, but clusters can retain dark matter within their tidal radii to the present day (Ibata et al 2013;Boldrini et al 2020;Carlberg & Keating 2021). An example is the cluster NGC 6715 (M54), located at the center of the Sagittarius dwarf galaxy, an accreted dwarf galaxy being dispersed into the Milky Way (Ibata et al 1997;Vasiliev & Belokurov 2020).…”