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

Abstract

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 Mpc/h, 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 $β^* \equiv Ω_{\rm{m}}^{0.55}/b^* = 0.431 \pm 0.021$, suggesting $\hat{I}{\text{c◯}}_{\mathrm{m}}^{0.55}\ddot{I}{ƒ}_{8,\mathrm{lin}}=0.401\pm 0.024$, in good agreement with other probes. The predicted peculiar velocity of the Local Group arising from the 2M++ volume alone is $540\pm 40$ km/s, towards $l=268\pm 4,b=38\pm 6$, only $10^{\circ }$ 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 5.1$\ddot{I}ƒ$ level, and the best fit has a velocity of $159\pm 23$ km/s towards $l=304\pm 11,b=6\pm 13$. Finally, the predicted bulk flow of a 50 Mpc/h Gaussian-weighted volume centred on the Local Group is $230\pm 30$ km/s, in the direction $l=293\pm 8,b=14\pm 10$, in agreement with predictions from $\hat{I}›$CDM.

17 pages. MNRAS, in press. Density and peculiar velocity grids available at http://cosmicflows.uwaterloo.ca or http://cosmicflows.iap.fr