Globular clusters as tracers of the host galaxy mass distribution: the Fornax dSph test case

TL;DR

This study investigates the orbital history and survival of globular clusters in the Fornax dwarf galaxy to understand its dark matter profile, using semi-analytical models and N-body simulations, challenging previous assumptions about its dark matter content.

Contribution

The paper combines semi-analytical dynamical friction models and N-body simulations to assess globular cluster evolution in Fornax, providing new insights into its dark matter distribution.

Findings

Globular clusters may have an in-situ origin with circular orbits.

The Milky Way accelerates globular cluster decay by 15%.

Survival probability of clusters exceeds 50% even with cuspy profiles.

Abstract

The Fornax dwarf spheroidal galaxy is the most massive satellites of the Milky Way, claimed to be embedded in a huge dark matter halo, and the only among the Milky Way satellites hosting five globular clusters. Interestingly, their estimated masses, ages and positions seem hardly compatible with the presence of a significant dark matter component, as expected in the $\Lambda$ CDM scheme. Indeed, if Fornax would have a CDM halo with a standard density profile, all its globular clusters should have sunk to the galactic centre many Gyr ago due to dynamical friction. Due to this, some authors proposed that the most massive clusters may have formed out of Fornax and later tidally captured. In this paper we investigate the past evolution of the Fornax GC system by using both a recently developed, semi-analytical treatment of dynamical friction and direct $N$-body simulations of the orbital evolution of the globular clusters within Fornax and of Fornax galaxy around the Milky Way. Our results suggest that an "in-situ" origin for all the clusters is likely if their observed positions are close to their spatial ones and their orbits are almost circular. Moreover, the Milky Way seems to accelerate the GC decay reducing the decay time of $15\%$. Nevertheless, our results indicate that the GCs survival probability exceeds $50\%$, even in the case of cuspy density profiles. We conclude that more detailed data are required to shed light on the Fornax dark matter content, to distinguish between a cuspy or a cored profile.