The Mass Distribution in the Nearby Universe

We present a new reconstruction of the mass density and the peculiar velocityfields in the nearby universe using recent measurements of Tully-Fisherdistances for a sample of late spirals. We find significant differences betweenour reconstructed fields and those obtained in earlier work: overdensities tendto be more compact while underdense regions, consisting of individual voids,are more abundant. Our results suggest that voids observed in redshift surveysof galaxies represent real voids in the underlying matter distribution. Whilewe detect a bulk velocity of $\sim$ 300 \kms, within a top-hat window 6000 \kmsin radius, the flow is less coherent than previously claimed, exhibiting abifurcation towards the Perseus-Pisces and the Great Attractor complexes. Thisis the first time that this feature is seen from peculiar velocitymeasurements. The observed velocity field resembles, more closely than anyprevious reconstruction, the velocity field predicted from self-consistentreconstructions based on all-sky redshift surveys. This better match is likelyto affect estimates of the parameter $\beta = \Omega^{0.6}/b$ and itsuncertainty based on velocity-velocity comparisons.Comment: accepted for publication in ApJ Letter