From Cosmicflows distance moduli to unbiased distances and peculiar velocities

Abstract

Surveys of galaxy distances and radial peculiar velocities can be used to reconstruct the large scale structure. Other than systematic errors in the zero-point calibration of the galaxy distances the main source of uncertainties of such data are errors on the distance moduli, assumed here to be Gaussian and thus turn into lognormal errors on distances and velocities. Naively treated, it leads to spurious nearby outflow and strong infall at larger distances. The lognormal bias is corrected here and tested against mock data extracted from a $\Lambda$CDM simulation, designed to statistically follow the grouped Cosmicflows-3 (CF3) data. Considering a subsample of data points, all of which have the same true distances or same redshifts, the lognormal bias arises because the means of the distributions of observed distances and velocities are skewed off the means of the true distances and velocities. Yet, the medians are invariant under the lognormal transformation. That invariance allows the Gaussianization of the distances and velocities and the removal of the lognormal bias. This Bias Gaussianization correction (BGc) algorithm is tested against mock CF3 catalogs. The test consists of a comparison of the BGC estimated with the simulated distances and velocities and of an examination of the Wiener filter reconstruction from the BGc data. Indeed, the BGc eliminates the lognormal bias. The estimation of Hubble's ($H_0$) constant is also tested. The residual of the BGc estimated $H_0$ from the simulated values is $0.6\pm 0.7{\mathrm{kms}}^{-1}{\mathrm{Mpc}}^{-1}$ and is dominated by the cosmic variance. The BGc correction of the actual CF3 data yields $H_0=75.8\pm 1.1{\mathrm{kms}}^{-1}{\mathrm{Mpc}}^{-1}$ .

14 pages, 16 figures, accepted for publication in MNRAS

References in corpus (12)

• The Laniakea supercluster of galaxies
• The 6dF Galaxy Survey: Peculiar Velocity Field and Cosmography
• SFI++ I: A New I-band Tully-Fisher Template, the Cluster Peculiar Velocity Dispersion and H0
• The Hestia project: simulations of the Local Group
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• The Dipole Repeller
• Deriving accurate peculiar velocities (even at high redshift)
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• The Cosmic V-Web
• Cosmicflows-3: The South Pole Wall
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Cited by in corpus (14)

• Cosmicflows-4
• The Sloan Digital Sky Survey Peculiar Velocity Catalogue
• Evaluating bulk flow estimators for CosmicFlows-4 measurements
• Cosmicflows-4: The Baryonic Tully-Fisher Relation Providing ~10,000 Distances
• Large-scale motions and growth rate from forward-modelling Tully-Fisher peculiar velocities
• Identification of Basins of Attraction in the Local Universe
• Hamiltonian Monte Carlo reconstruction from peculiar velocities
• Field-Based Physical Inference From Peculiar Velocity Tracers
• Galaxy flows within 8,000 km/s from Numerical Action methods
• A Local Universe model for constrained simulations
• Testing Bayesian reconstruction methods from peculiar velocities
• Modeling the Cosmic Dispersion Measure in the D < 120 Mpc Local Universe
• Statistically bias-minimized peculiar velocity catalogs from Gibbs point processes and Bayesian inference
• An effective $\mathbf{\Lambda }$-Szekeres modelling of the local Universe with Cosmicflows-4