Dwarf spheroidal satellites of the Milky Way from dark matter free tidal dwarf galaxy progenitors: maps of orbits

TL;DR

This study uses N-body simulations to show that some Milky Way satellite galaxies with high apparent mass-to-light ratios could be dark matter free tidal dwarf galaxies in a transient quasi-equilibrium phase, depending on their orbit and timing.

Contribution

It demonstrates that high apparent mass-to-light ratios in satellite galaxies can result from their orbital phase, challenging the dark matter hypothesis for these objects.

Findings

Certain orbits allow satellites to appear out-of-equilibrium for over 1 Gyr.

Progenitors with different densities reproduce observed properties at different orbital fractions.

A specific simulation matches properties of ultra-faint dwarf galaxies in the Milky Way.

Abstract

The long term time evolution of tidal dwarf satellite galaxies with two different initial densities orbiting a host galaxy that resembles the Milky Way has been studied using a large set of Newtonian N-Body simulations. From the simulations two maps of the orbital conditions that lead to quasi-equilibrium objects were constructed. It has been found that several orbits of the satellites allow for the existence, for about 1 Gyr or more, of out-of-equilibrium bodies with high apparent mass-to-light ratios. Within this framework the satellites in the quasi-stable phase reproduce the observed satellite properties for about 16% of the orbit for high density progenitors, and for about 66% for progenitors with lower densities An additional simulation for a single satellite with initial mass of 10^7 Msun and Plummer radius of 0.15 kpc leads to remnants in the quasi- equilibrium phase that simultaneously reproduce remarkably well the observational quantities of the UFDGs of the Milky Way. This satellite in the quasi-stable phase reproduces the observed satellite properties for about 42% of the orbit. The results suggest that a fraction of the observed satellites could plausibly be galaxies without dark matter that have true M/L ratios much lower than those measured. The inflated M/L ratios arise because they are observed at the right time, along the right orbit and during the quasi-equilibrium phase of their evolution. This is a viable explanation for the high M/L ratios observed in all satellites as long as the satellites are preferentially on certain orbits and are observed at certain times. This could arise within the TDG scenario if all satellites are created at the same time along a few specific orbits that are particularly susceptible to the quasi-equilibrium phase.