2015MNRAS.450..317C

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 h-1Mpc, 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* ≡Ω_m^0.55/b^* = 0.431±0.021, suggesting Ω_m^0.55σ_8,lin = 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, towards l = 268°±4°, b = 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±23kms- 1 towards l = 304°±11°, b = 6°±13°. Finally, the predicted bulk flow of a 50 h-1Mpc Gaussian-weighted volume centred on the Local Group is 230±30 km/s, in the direction l = 293°±8°, b = 14°±10°, in agreement with predictions from Λ cold dark matter.