Large disparity in cosmic reference frames determined from the sky distributions of radio sources and the microwave background radiation

Abstract

The angular distribution of the Cosmic Microwave Background Radiation (CMBR) in sky shows a dipole asymmetry, ascribed to the observer's motion (peculiar velocity of the solar system!), relative to the local comoving coordinates. The peculiar velocity thus determined turns out to be 370 km s −1 in the direction RA= 168 • , Dec= −7 • . On the other hand, a dipole asymmetry in the sky distribution of radio sources in the NRAO VLA Sky Survey (NVSS) catalog, comprising 1.8 million sources, yielded a value for the observer's velocity to be ∼ 4 times larger than the CMBR value, though the direction turned out to be in agreement with that of the CMBR dipole. This large difference in observer's speeds with respect to the reference frames of NVSS radio sources and of CMBR, confirmed since by many independent groups, is rather disconcerting as the observer's motion with respect to local comoving coordinates should be independent of the technique used to determine it. A genuine difference in relative speeds of two cosmic reference frames could jeopardize the cosmological principle, thence it is crucial to confirm such discrepancies using independent samples of radio sources. We here investigate the dipole in the sky distribution of radio sources in the recent TIFR GMRT Sky Survey (TGSS) dataset, comprising 0.62 million sources, to determine observer's motion. We find a significant disparity in observer's speeds relative to all three reference frames, determined from the radio source datasets and the CMBR, which does not fit with the cosmological principle, a starting point for the standard modern cosmology.

Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs and the Discordance Seen with the Cosmological Principle

“…Let N 1 (θ) be the cumulative number of sources in the sky zone between the great circle at θ = 90 • and a parallel circle at angle θ in S 1 , while N 2 (θ) is the cumulative number of sources in the symmetrically placed, corresponding zone in the opposite hemisphere S 2 , i.e., N 2 (θ) is the cumulative number of sources lying between θ = 90 • and π − θ. Then we obtain the dipole component D θ along θ, from [12]…”

“…The NRAO VLA Sky Survey (NVSS), comprising 1.8 million radio sources [4], showed a statistically significant dipole asymmetry corresponding to a velocity ∼4 times the CMBR value [5], something that was not only unexpected, but appeared initially almost preposterous, however, confirmed subsequently by many independent groups [6][7][8][9]. Further, in the TIFR GMRT Sky Survey (TGSS) [10], comprising 0.62 million sources [11], a very significant (>10σ) dipole anisotropy, amounting to a velocity ∼10 times the CMBR value, was detected [9,12]. However, equally surprising, the direction of motion in both cases has turned out to be along the CMBR dipole.…”

“…However, for a moving observer, Σr i will yield a net vector along the direction of motion [18]. Then the peculiar speed v of the observer could be obtained from [5,12]…”

“…The results for the three bins are also presented in Table 1. Here, N is the total number of sources in the corresponding W1 bin, RA and Dec give the dipole direction in the sky, D is the dipole value computed from D = 3Σ cos θ i /(2Σ| cos θ i )], with error ∆D = 3/(2Σ| cos θ i |) [5,12,18]. Then the peculiar speed of the observer, or rather of the solar system, is computed from D = [2 + x(1 + α)](v/c).…”

Testing the cosmological principle in the radio sky

“…More stringent tests require the far higher number densities delivered by large galaxy surveys. The simplest way to test consistency with the CMB is to measure the dipole of a (sufficiently wide) galaxy survey, which should be aligned with the direction of the CMB dipole [10,11,12,13,14,15,16,17,18,19,20,21,22]. For currently available data sets, the matter dipole direction is not inconsistent with the CMB, but the amplitude is too large, probably arising from the quality of current data sets.…”