The effect of tides on the Fornax dwarf spheroidal galaxy

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 datasets. 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.

Tidal features of classical Milky Way satellites in a Λ cold dark matter universe

“…The initial DM mass adopted in Battaglia et al (2015) was 3 × 10 9 M⊙, which is similar to the infall mass of F2, 4 × 10 9 M⊙. The infall stellar mass in our simulation is lower than their initial stellar mass (5 × 10 7 M⊙ versus our value of 3×10 6 M⊙).…”

“…The solid lines denote the profiles at infall (z ∼ 2.2 for F2 and z ∼ 0.86 for SL2), and the dashed lines denote the profiles at later times. For F2 we also show the initial stellar density profile from Battaglia et al (2015) as a purple dash-dotted line. The dark matter profiles for both F2 and SL1 continuously become shallower and lose mass in the outer region due to tidal disruption.…”

“…This result can be explained by the large radial motions of stripped stars along the stellar stream. Battaglia et al (2015) construct a set of N-body simulations to study the effect of tides on Fornax. However, contrary to our results, they do not find any evidence for stellar tidal features.…”

“…The infall stellar mass in our simulation is lower than their initial stellar mass (5 × 10 7 M⊙ versus our value of 3×10 6 M⊙). In addition, in order to increase the possibility of generating stellar tidal disruption, Battaglia et al (2015) assumed a cored DM density profile.…”

“…Peñarrubia et al (2008) find that once stars start to be stripped from a dSph, the dark-to-luminous mass ratio increases, and consider the implications of this for the known dSphs. Battaglia et al (2015) simulate subhaloes with orbits and structural properties that match the Fornax dSph, and find that the structure and kinematics of the stars are only mildly affected by tidal interactions. Klimentowski et al (2007) study how unbound particles affect the interpretation of stellar kinematics, with a specific application to Fornax.…”