Measuring bulk motion of X-ray clusters via the kinematic Sunyaev-Zeldovich effect: summarizing the "dark flow" evidence and its implications

Abstract

In this review we present a comprehensive discussion of peculiar velocity field measured recently on very large scales with a novel method using X-ray galaxy clusters as tracers. The measurement is based on the kinematic component of the Sunyaev-Zeldovich (KSZ) effect produced by Compton scattering of cosmic microwave background (CMB) photons off the hot intracluster gas, and uses a large catalog of X-ray selected clusters and all-sky CMB maps obtained with the WMAP satellite. The method probes the dipole of the CMB temperature field evaluated at the cluster positions and within the apertures in which the CMB monopole contribution vanishes, thereby isolating the signal remaining from the KSZ effect produced by coherently moving clusters. The detection of a highly significant dipole out to the depth of at least ~ 800 Mpc casts doubt on the notion that gravitational instability from the observed mass distribution is the sole -- or even dominant -- cause of the detected motions. Rather it appears that the flow may extend across the entire observable Universe. Possible implications include the possibility to constrain the primeval preinflationary structure of space-time and its landscape, and/or the need for modifications of presently known physics (e.g. arising from a higher-dimensional structure of gravity). We review these possibilities in light of the measurements described here and specifically discuss the prospects of future measurements and the issues they should resolve. We address the consistency of these large-scale velocity measurements with those obtained on smaller scales by studies using galaxies as tracers, and resolve the discrepancies with two recent claims based on modified CMB analysis schemes.

arXiv commentPhysics Reports, draft version - comments welcome! Manuscript with all figures at full resolution is available from http://www.kashlinsky.info/bulkflows/physicsreport

References in corpus (10)

• Planck Early Results: The Planck mission
• Planck early results: first assessment of the High Frequency Instrument in-flight performance
• Planck early results. VI. The High Frequency Instrument data processing
• The effect of peculiar velocities on supernova cosmology
• Hubble flow variance and the cosmic rest frame
• Measuring the Galaxy Cluster Bulk Flow from WMAP data
• Measuring our Peculiar Velocity by "Pre-deboosting" the CMB
• Detected fluctuations in SDSS LRG magnitudes: Bulk flow signature or systematic?
• TeVeS/MOND is in harmony with gravitational redshifts in galaxy clusters
• Coherent Combination of Baryon Acoustic Oscillation Statistics and Peculiar Velocity Measurements from Redshift Survey

Cited by in corpus (9)

• Challenges for $\Lambda$CDM: An update
• Is the Observable Universe Consistent with the Cosmological Principle?
• Establishing homogeneity of the universe in the shadow of dark energy
• First measurement of the bulk flow of nearby galaxies using the cosmic microwave background
• Constraining spatial variations of the fine structure constant using clusters of galaxies and Planck data
• Cosmic Microwave Background filters and the Dark-Flow measurement
• Dynamical Shortcomings in the Generalized SU(2) Proca Theory: Challenges for Cosmic Acceleration
• Horndeski in motion
• Non-perfect-fluid space-times in thermodynamic equilibrium and generalized Friedmann equations