Cosmological parameters from the comparison of peculiar velocities with predictions from the 2M++ density field

Peculiar velocity measurements are the only tool available in the low-redshift Universe for mapping the large-scale distribution of matter and can thus be used to constrain cosmology. Using redshifts from the 2M++ redshift compilation, we reconstruct the density of galaxies within 200 <it>h</it>−1 Mpc, allowing for the first time good sampling of important superclusters such as the Shapley Concentration. We compare the predicted peculiar velocities from 2M++ to Tully–Fisher and SNe peculiar velocities. We find a value of β* <f>$\\equiv \\Omega _{\\rm {m}}^{0.55}/b^* =$</f> 0.431 ± 0.021, suggesting <f>$\\Omega _{\\rm {m}}^{0.55}\\sigma _{\\rm {8,lin}}$</f> = 0.401 ± 0.024, in good agreement with other probes. The predicted peculiar velocity of the Local Group arising from the 2M++ volume alone is 540 ± 40 km s−1, towards <it>l</it> = 268° ± 4°, <it>b</it> = 38° ± 6°, only 10° out of alignment with the cosmic microwave background dipole. To account for velocity contributions arising from sources outside the 2M++ volume, we fit simultaneously for β* and an external bulk flow in our analysis. We find that an external bulk flow is preferred at the 5.1σ level, and the best fit has a velocity of 159 ± 23 km s− 1 towards <it>l</it> = 304° ± 11°, <it>b</it> = 6° ± 13°. Finally, the predicted bulk flow of a 50 <it>h</it>−1 Mpc Gaussian-weighted volume centred on the Local Group is 230 ± 30 km s−1, in the direction <it>l</it> = 293° ± 8°, <it>b</it> = 14° ± 10°, in agreement with predictions from Λ cold dark matter.