title: A low pre-infall mass for the Carina dwarf galaxy from disequilibrium modelling.
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 10(9)-10(10 )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 3.6(-2.3)(+3.8) × 10(8) 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 ∼10(10 )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.
authors.affiliation: Leibniz Institute für Astrophysik Potsdam, An der Sternwarte 16, Potsdam 14482, Germany.
authors.forename: Uğur
authors.initials: U
authors.lastname: Ural
authors.affiliation: Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK.
authors.forename: Mark I
authors.initials: MI
authors.lastname: Wilkinson
authors.affiliation: Astrophysics Research Group, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK.
authors.forename: Justin I
authors.initials: JI
authors.lastname: Read
authors.affiliation: Department of Physics, McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennyslvania 15213, USA.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Walker