The Universe is Brighter in the Direction of Our Motion: Galaxy Counts and Fluxes are Consistent with the CMB Dipole

Abstract

An observer moving with respect to the cosmic rest frame should observe a concentration and brightening of galaxies in the direction of motion and a spreading and dimming in the opposite direction. The velocity inferred from this dipole should match that of the cosmic microwave background (CMB) temperature dipole if galaxies are on average at rest with respect to the CMB rest frame. However, recent studies have claimed a many-fold enhancement of galaxy counts and flux in the direction of the solar motion compared to the CMB expectation, calling into question the standard cosmology. Here we show that the sky distribution and brightness of extragalactic radio sources are consistent with the CMB dipole in direction and velocity. We use the first epoch of the Very Large Array Sky Survey combined with the Rapid Australian Square Kilometer Array Pathfinder Continuum Survey to estimate the dipole via several different methods, and all show similar results. Typical fits find a $331_{-107}^{+161}$ km s${}^{-1}$ velocity dipole with apex $(\ell ,b)=(271_{-58}^{+55},56_{-35}^{+13})$ in Galactic coordinates from source counts and $399_{-199}^{+264}$ km s${}^{-1}$ toward $(\ell ,b)=(301_{-30}^{+30},43_{-17}^{+19})$ from radio fluxes. These are consistent with the CMB-solar velocity, 370 km s${}^{-1}$ toward $(\ell ,b)=(264,48)$, and show that galaxies are on average at rest with respect to the rest frame of the early universe, as predicted by the canonical cosmology.

arXiv comment11 pages, 5 figures, 1 table. Accepted by ApJL

References in corpus (25)

• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Planck 2018 results. I. Overview and the cosmological legacy of Planck
• The GMRT 150 MHz All-sky Radio Survey: First Alternative Data Release TGSS ADR1
• Planck 2018 results. III. High Frequency Instrument data processing and frequency maps
• The Rapid ASKAP Continuum Survey I: Design and First Results
• A Test of the Cosmological Principle with Quasars
• The Molonglo Galactic Plane Survey (MGPS-2): Compact Source Catalogue
• A Quick Look at the $3$GHz Radio Sky I. Source Statistics from the Very Large Array Sky Survey
• The Rapid ASKAP Continuum Survey Paper II: First Stokes I Source Catalogue Data Release
• Cosmic radio dipole from NVSS and WENSS
• Detection of the velocity dipole in the radio galaxies of the NRAO VLA Sky Survey
• Cosmic flow from 2MASS redshift survey: The origin of CMB dipole and implications for LCDM cosmology
• Large peculiar motion of the solar system from the dipole anisotropy in sky brightness due to distant radio sources
• Dipoles in the Sky
• The Cosmic Radio Dipole: Estimators and Frequency Dependence
• Astrometric Limits on the Stochastic Gravitational Wave Background
• Large angular scale multipoles at redshift ~0.8
• Planck intermediate results. LVI. Detection of the CMB dipole through modulation of the thermal Sunyaev-Zeldovich effect: Eppur si muove II
• Future dark energy constraints from measurements of quasar parallax: Gaia, SIM and beyond
• Secular Extragalactic Parallax: Measurement Methods and Predictions for Gaia
• Direct geometrical measurement of the Hubble constant from galaxy parallax: predictions for the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope