Deriving accurate peculiar velocities (even at high redshift)
  The way that peculiar velocities are often inferred from measurements of
distances and redshifts makes an approximation, v_p = cz-H_0 D, that gives
significant errors even at relatively low redshifts (overestimates peculiar
velocity by ~ 100 km/s at z~0.04). Here we demonstrate where the approximation
breaks down, the systematic offset it introduces, and how the exact calculation
should be implemented.
