SAMPLE VARIANCE OF THE COSMIC VELOCITY-FIELD

Since the cosmic peculiar velocity field depends strongly on small wav enumber modes, we cannot probe its universal properties unless we obse rve a sufficiently large region. We calculate the expected deviation ( sample variance) of the peculiar velocity dispersion from its universa l value in the case where the observed volume is finite. Using linear theory, we show that the sample variance remains as large as similar t o 10%, even if the observed region is as deep as 100 h(-1) Mpc, and th at it seriously affects the estimation of cosmological parameters from the peculiar velocity field.