Galactic tides and the Crater II dwarf spheroidal: a challenge to LCDM?

The unusually low velocity dispersion and large size of Crater II pose a challenge to our understanding dwarf galaxies in the Lambda Cold Dark Matter (LCDM) cosmogony. suggests either dark halo mass much lower than minimum expected from hydrogen cooling limit arguments, or one that is late stages extreme tidal stripping. interpretation has been favoured recent work supported by small pericentric distances consistent with available kinematic estimates. We use N-body simulations examine this detail, assuming Navarro-Frenk-White (NFW) profile for II's progenitor halo. Our main finding that, although can indeed result effect tides, inconsistent hypothesis. This because stripped match observed are also reduced sizes smaller half-light radius II. Unless its substantially overestimated, reconciling system LCDM requires (i) it not bound near equilibrium (unlikely, given crossing time shorter elapsed since pericentre), (ii) deviates assumed NFW profile. latter alternative may signal baryons affect inner cusp even extremely faint dwarfs or, more intriguingly, effects associated intimate nature matter, such as finite self-interactions, other deviations canonical paradigm.