  We report the phase diagram of two-dimensional hard ellipses as obtained from
replica exchange Monte Carlo simulations. The replica exchange is implemented
by expanding the isobaric ensemble in pressure. The phase diagram shows four
regions: isotropic, nematic, plastic, and solid (letting aside the hexatic
phase at the isotropic-plastic two-step transition [PRL 107, 155704 (2011)]).
At low anisotropies, the isotropic fluid turns into a plastic phase which in
turn yields a solid for increasing pressure (area fraction). Intermediate
anisotropies lead to a single first order transition (isotropic-solid).
Finally, large anisotropies yield an isotropic-nematic transition at low
pressures and a high-pressure nematic-solid transition. We obtain continuous
isotropic-nematic transitions. For the transitions involving quasi-long-range
positional ordering, i. e. isotropic-plastic, isotropic-solid, and
nematic-solid, we observe bimodal probability density functions. This supports
first order transition scenarios.
