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

The long-term time evolution of tidal dwarf satellite galaxieswith 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 (M/L) ratios. Within this framework, the satellites in the quasi-stable phase reproduce the observed satellite properties for about 16 per cent of the orbit for high-density progenitors and for about 66 per cent for progenitors with lower densities. An additional simulation for a single satellite with initial mass of 10⁷ M_⊙ 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 ultrafaint dwarf galaxies of the Milky Way. This satellite in the quasi-stable phase reproduces the observed satellite properties for about 42 per cent 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 tidal dwarf galaxies scenario if all satellites are created at the same time along a few specific orbits that are particularly susceptible to the quasi-equilibrium phase.