The cosmic Mach number - Direct comparisons of observations and models

A robust method is used to derive the cosmic Mach number, M, from existing peculiar velocity data sets. For the IR Tully-Fisher distances of spirals in the Local Supercluster of Aaronson et al. (1979, 1982), M of 1.03 and a characteristic distance from the Local Group of 1464 km/s are found. For the elliptical galaxy sample of Faber et al. (1987, 1988), M of 0.57, with a characteristic distance of 2572 km/s is found. These results are compared with Monte Carlo simulations of the observational realizations drawn from numerical simulations of the universe based on various scenarios, including the standard cold dark matter (CDM) scenario. The effect of velocity bias on the derived Mach number is found to be small. Only 5 percent of the CDM simulations have M as large as or larger than that derived for the Aaronson et al. sample.