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

• Published in: Monthly notices of the Royal Astronomical Society 2015-06, Vol.450 (1), p.317-332
• Main Authors: Carrick, Jonathan, Turnbull, Stephen J., Lavaux, Guilhem, Hudson, Michael J.
• Format: Article
• Language: English
• Subjects: Astrophysics; Austenitic stainless steels; Comparative analysis; Cosmic microwave background; Cosmology; Dark matter; Density; Galaxies; Red shift; Sampling; Sciences of the Universe; Star & galaxy formation; Universe
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stv547

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 −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* $\equiv \Omega _{\rm {m}}^{0.55}/b^* =$ 0.431 ± 0.021, suggesting $\Omega _{\rm {m}}^{0.55}\sigma _{\rm {8,lin}}$  = 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−1, 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 ± 23  km s− 1 towards l = 304° ± 11°, b = 6° ± 13°. Finally, the predicted bulk flow of a 50 h −1 Mpc Gaussian-weighted volume centred on the Local Group is 230 ± 30 km s−1, in the direction l = 293° ± 8°, b = 14° ± 10°, in agreement with predictions from Λ cold dark matter.