Too big to fail? The puzzling darkness of massive Milky Way subhaloes

Abstract We show that dissipationless Λ cold dark matter simulations predict that the majority of the most massive subhaloes of the Milky Way are too dense to host any of its bright satellites (LV > 105 L⊙). These dark subhaloes have peak circular velocities at infall of Vinfall= 30–70 km s-1 and infall masses of (0.2–4) × 1010 M⊙. Unless the Milky Way is a statistical anomaly, this implies that galaxy formation becomes effectively stochastic at these masses. This is in marked contrast to the well-established monotonic relation between galaxy luminosity and halo circular velocity (or halo mass) for more massive haloes. We show that at least two (and typically four) of these massive dark subhaloes are…

• NS
  National Science Foundation

  Awards: AST-1009973, 1009973
• NA
  National Aeronautics and Space Administration

  Award: NNX09AD09G
• VC
  Virgo Consortium