A Measurement of Large-Scale Peculiar Velocities of Clusters of Galaxies: Results and Cosmological Implications

The Astrophysical Journal (Impact Factor: 5.99). 09/2008; 686(2). DOI: 10.1086/592947
Source: arXiv


Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3-year WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least > 300 h^{-1} Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities. Comment: Ap.J. (Letters), in press. 20 Oct issue (Vol. 686)

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    • "It can also be utilized to constrain dark matter-dark energy interaction [63] and modified gravity [64] [65]. Recently, a new regime of the kSZ effect generated by larger scale ( Gpc) inhomogeneities has been realized and applied to probe dark flows [66] [67] [68] [69] [70] [71] [72], test the Copernican principle [73] [74], and constrain the Figure 2. A schematic diagram of the kSZ effect in the collision spacetime. The solid circle (sphere) is the last scattering surface (LSS) seen by us, and the dashed circles (spheres) are the LSS of several representative free electrons, labelled by " e1 " , " e2 " and " e3 " respectively. "
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    ABSTRACT: Perhaps the most controversial idea in modern cosmology is that our observable universe is contained within one bubble among many, all inhabiting the eternally inflating multiverse. One of the few way to test this idea is to look for evidence of the relic inhomogeneities left by the collisions between other bubbles and our own. Such relic inhomogeneities induces a coherent bulk flow over gigaparsec scales. Therefore, bubble collisions leave unique imprints in the cosmic microwave background (CMB) through the kinetic Sunyaev Zel'dovich (kSZ) effect, temperature anisotropies induced by the scattering of photons from coherently moving free electrons in the diffuse intergalactic medium. The kSZ signature produced by bubble collisions has a unique directional dependence and is tightly correlated with the galaxy distribution; it can therefore be distinguished from other contributions to the CMB anisotropies. An important advantage of the kSZ signature is that it peaks on arcminute angular scales, where the limiting factors in making a detection are instrumental noise and foreground subtraction. This is in contrast to the collision signature in the primary CMB, which peaks on angular scales much larger than one degree, and whose detection is therefore limited by cosmic variance. In this paper, we examine the prospects for probing the inhomogeneities left by bubble collisions using the kSZ effect. We provide a forecast for detection using cross-correlations between CMB and galaxy surveys, finding that the detectability using the kSZ effect can be competitive with constraints from CMB temperature and polarization data.
    Journal of Cosmology and Astroparticle Physics 01/2015; 2015(06). DOI:10.1088/1475-7516/2015/06/046 · 5.81 Impact Factor
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    • "There are three famous CMB anomalies reported in the WMAP, namely the surprisingly low quadrupole [29] (first seen in COBE), alignment between low multipoles ( " axis of evil " ) [30] [31], and an hemispherical power asymmetry [32] [33] [34]. Based on WMAP data a uniform bulk flow of galaxy clusters is reported ( " dark flow " ) [35] [36]. Other data analyses that indicate a preferred axis include analysis of polarization of electromagnetic radiation propagating over cosmological scales [37] [38], and a " handedness " in the orientation of galaxies [39]. "
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    ABSTRACT: Motivated by the couplings of the dilaton in four-dimensional effective actions, we investigate the cosmological consequences of a scalar field coupled both to matter and a Maxwell-type vector field. The vector field has a background isotropy-violating component. New anisotropic scaling solutions which can be responsible for the matter and dark energy dominated epochs are identified and explored. For a large parameter region the universe expands almost isotropically. Using that the CMB quadrupole is extremely sensitive to shear, we constrain the ratio of the matter coupling to the vector coupling to be less than 10^(-5). Moreover, we identify a large parameter region, corresponding to a strong vector coupling regime, yielding exciting and viable cosmologies close to the LCDM limit.
    Journal of High Energy Physics 05/2012; 2012(10). DOI:10.1007/JHEP10(2012)066 · 6.11 Impact Factor
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    • "z ≤ 0.03) with amplitude larger than 400km/sec (Watkins, Feldman & Hudson 2009). The direction of the flow has been found consistently to be approximately in the direction l ≃ 282 • , b ≃ 6 • . Other independent studies have also found large bulk velocity flows on similar directions on scales of about 100h −1 M pc (Lavaux et. al., 2010) or larger (Kashlinsky et. al., 2009). The expected rms bulk flow in the context of ΛCDM normalized with WMAP5 (Ω 0m , σ 8 ) = (0.258, 0.796) on scales larger than 50h −1 M pc is approximately 110km/sec. The probability that a flow of magnitude larger than 400km/sec is realized in the context of the above ΛCDM normalization (on scales larger than 50h −1 M pc) is less than "
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    ABSTRACT: The consistency level of LCDM with geometrical data probes has been increasing with time during the last decade. Despite of these successes, there are some puzzling conflicts between LCDM predictions and dynamical data probes (bulk flows, alignment and magnitude of low CMB multipoles, alignment of quasar optical polarization vectors, cluster halo profiles). Most of these puzzles are related to the existence of preferred anisotropy axes which appear to be unlikely close to each other. A few models that predict the existence of preferred cosmological axes are briefly discussed.
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