Cosmology with Peculiar Velocities: Observational Effects

Abstract

In this paper we investigate how observational effects could possibly bias cosmological inferences from peculiar velocity measurements. Specifically, we look at how bulk flow measurements are compared with theoretical predictions. Usually bulk flow calculations try to approximate the flow that would occur in a sphere around the observer. Using the Horizon Run 2 simulation we show that the traditional methods for bulk flow estimation can overestimate the magnitude of the bulk flow for two reasons: when the survey geometry is not spherical (the data do not cover the whole sky), and when the observations undersample the velocity distributions. Our results may explain why several bulk flow measurements found bulk flow velocities that seem larger than those expected in standard ΛCDM cosmologies. We recommend a different approach when comparing bulk flows to cosmological models, in which the theoretical prediction for each bulk flow measurement is calculated specifically for the geometry and sampling rate of that survey. This means that bulk flow values will not be comparable between surveys, but instead they are comparable with cosmological models, which is the more important measure.

11 pages, 5 figures. Accepted for publication in MNRAS

References in corpus (10)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Improved Distances to Type Ia Supernovae with Multicolor Light Curve Shapes: MLCS2k2
• Cosmological parameters from the comparison of peculiar velocities with predictions from the 2M++ density field
• A critical look at cosmological perturbation theory techniques
• Cosmic Bulk Flow and the Local Motion from Cosmicflows-2
• The peculiar velocity field: constraining the tilt of the Universe
• The Velocity Field of the Local Universe from Measurements of Type Ia Supernovae
• 2MTF IV. A bulk flow measurement of the local Universe
• Large-scale Cosmic Flows from Cosmicflows-2 Catalog
• Tracing the cosmic velocity field at z ~ 0.1 from galaxy luminosities in the SDSS DR7

Cited by in corpus (3)

• The Local Perspective on the Hubble Tension: Local Structure Does Not Impact Measurement of the Hubble Constant
• The Redshift-Space Momentum Power Spectrum I: Optimal Estimation From Peculiar Velocity Surveys
• 2MTF - VII. 2MASS Tully-Fisher survey final data release: distances for 2,062 nearby spiral galaxies