A low pre-infall mass for the Carina dwarf galaxy from disequilibrium modelling.

Uğur Ural,Justin I Read,Matthew G Walker,Mark I Wilkinson

doi:10.1038/ncomms8599

Uğur Ural, Justin I Read + Show 2 more

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https://doi.org/10.1038/ncomms8599

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Abstract

Dark matter-only simulations of galaxy formation predict many more subhalos around a Milky Way-like galaxy than the number of observed satellites. Proposed solutions require the satellites to inhabit dark matter halos with masses 109–1010 Msun at the time they fell into the Milky Way. Here we use a modelling approach, independent of cosmological simulations, to obtain a pre-infall mass of Msun for one of the Milky Way's satellites: Carina. This determination of a low halo mass for Carina can be accommodated within the standard model only if galaxy formation becomes stochastic in halos below ∼1010 Msun. Otherwise Carina, the eighth most luminous Milky Way dwarf, would be expected to inhabit a significantly more massive halo. The implication of this is that a population of ‘dark dwarfs' should orbit the Milky Way: halos devoid of stars and yet more massive than many of their visible counterparts.

Highlights

Way-like galaxy than the number of observed satellites
This determination of a low halo mass for Carina can be accommodated within the standard model only if galaxy formation becomes stochastic in halos below B1010 Msun
Numerical models predict that thousands of dark matter subhalos should be found orbiting the Milky Way and Andromeda, yet only a few tens have been found to date[4,5]

Summary

Introduction

Proposed solutions require the satellites to inhabit dark matter halos with masses 109–1010 Msun at the time they fell into the Milky Way. Here we use a modelling approach, independent of cosmological simulations, to obtain a pre-infall mass of. A popular resolution of this issue is to place stars only in the most massive satellite halos, implying a total or ‘virial’ mass for the Milky Way dSphs of B1010 Msun (see Fig. 1). Several solutions have been proposed, including lowering the mass of the Milky Way halo[10], or the central stellar velocity dispersion of the dSphs through the action of stellar feedback[11] These still require the Milky Way dSphs to inhabit dark matter halos with pre-infall masses greater than B109 Msun[4]

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