The effect of tides on the Fornax dwarf spheroidal galaxy

TL;DR

This study uses N-body simulations to evaluate how tidal interactions with the Milky Way affect the structure and dark matter content estimates of the Fornax dwarf galaxy, finding minimal impact on observable properties.

Contribution

It provides a detailed simulation-based analysis showing tidal effects have limited influence on Fornax's observable structure and kinematics, challenging common assumptions.

Findings

Tidal effects cause up to 20% dark matter loss within 1.6 kpc.

Stellar structure and kinematics are only mildly affected by tidal interactions.

Dark-to-luminous mass ratio within 1.6 kpc is 5-6, increasing to 16-18 within 3 kpc.

Abstract

Estimates of the mass distribution and dark-matter (DM) content of dwarf spheroidal galaxies (dSphs) are usually derived under the assumption that the effect of the tidal field of the host galaxy is negligible over the radial extent probed by kinematic data-sets. We assess the implications of this assumption in the specific case of the Fornax dSph by means of N-body simulations of a satellite orbiting around the Milky Way. We consider observationally-motivated orbits and we tailor the initial distributions of the satellite's stars and DM to match, at the end of the simulations, the observed structure and kinematics of Fornax. In all our simulations the present-day observable properties of Fornax are not significantly influenced by tidal effects. The DM component is altered by the interaction with the Galactic field (up to 20% of the DM mass within 1.6 kpc is lost), but the structure and kinematics of the stellar component are only mildly affected even in the more eccentric orbit (more than 99% of the stellar particles remain bound to the dwarf). In the simulations that successfully reproduce Fornax's observables, the dark-to-luminous mass ratio within 1.6 kpc is in the range 5-6, and up to 16-18 if measured within 3 kpc.