Deriving accurate peculiar velocities (even at high redshift)

Theway that peculiar velocities are often inferred frommeasurements of distances and redshifts makes an approximation, νp = cz - H0D, that gives significant errors even at relatively low redshifts (overestimates by Δvp 100 km s-1 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.