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Cosmic flows

  1. Nov 25, 2008 #1

    wolram

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    arXiv:0811.3606 (cross-list from astro-ph) [ps, pdf, other]
    Title: Large-scale cosmic flows and moving dark energy
    Authors: Jose Beltran Jimenez, Antonio L. Maroto
    Comments: 5 pages, 2 figures. Corrected references
    Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
    Large-scale matter bulk flows with respect to the cosmic microwave background have very recently been detected on scales of 100 Mpc/h and 300 Mpc/h using two different techniques showing an excellent agreement in the motion direction. The unexpectedly large measured amplitudes are however difficult to understand within the context of standard LCDM cosmology. In this work we show that the existence of such a flow could be signalling the presence of moving dark energy at the time when photons decouple from matter. We also study the relation between the direction of the CMB dipole and the preferred axis observed in the quadrupole in this scenario.
     
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  3. Nov 25, 2008 #2

    wolram

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    [7] arXiv:0811.3690 [pdf]
    Title: Distances and peculiar velocities of spiral galaxies in the 2MFGC and SFI++ samples
    Authors: Yu.N.Kudrya, V.E. Karachentseva, I.D. Karachentsev, S.N.Mitronova, W.K.Huchtmeier
    Comments: 19 pages, 6 figures. Accepted for publication in Astrophysics
    Subjects: Astrophysics (astro-ph)
    We compare infrared Tully-Fisher (TF) distances and peculiar velocities derived for spiral galaxies from the two largest datasets: the 2MASS selected Flat Galaxy Catalog, 2MFGC [19, 20] and the Arecibo General Catalog with I-band photometry, SFI++ [30,7]. These samples contain peculiar velocities for ~3000 and ~4000 objects, respectively. Based on a sub-sample of ~1000 common deeply inclined galaxies, we reach the following conclusions. Irrespective to high (SFI++) or low (2MFGC) quality of the used photometric data, about 10% of the galaxies in both samples deviate considerably from the main body of the TF relation. After their deletion, the standard TF scatters drops to 0.47^m (2MFGC) and 0.40^m (SFI++). The TF distances, derived from two the samples, demonstrate a high degree of mutual agreement with a correlation coefficient \ro=+0.95 and \sigma(H_0r)=837 km/s. Peculiar velocities of the galaxies are also correlated with \ro=0.56-0.59 and \sigma(V_pec)=610 km/s. We find that the bulk motion of the 2MFGC and SFI++ galaxies on a typical scale of H_0r~5700 km/s can be represented by a dipole solution with the amplitude V=297+/-23 km/s directed towards l=292+/-4 degr., b=-12+/-3 degr., being only slightly sensitive to different modifications of the TF relaton.
     
  4. Nov 25, 2008 #3

    wolram

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    http://www.nasa.gov/centers/goddard/news/topstory/2008/dark_flow.html

    WASHINGTON -- Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), scientists have identified an unexpected motion in distant galaxy clusters. The cause, they suggest, is the gravitational attraction of matter that lies beyond the observable universe.

    "The clusters show a small but measurable velocity that is independent of the universe's expansion and does not change as distances increase," says lead researcher Alexander Kashlinsky at NASA's Goddard Space Flight Center in Greenbelt, Md. "We never expected to find anything like this."
     
  5. Nov 25, 2008 #4

    wolram

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    http://eprintweb.org/S/authors/All/tu/Tully/2

    Cosmic flow from 2MASS redshift survey: The origin of CMB dipole and implications for LCDM cosmology
    G. Lavaux, R. Brent Tully, R. Mohayaee and S. Colombi
    Received. 20 October 2008 Last updated. 20 October 2008
    Abstract. We generate the peculiar velocity field for the 2MASS Redshift Survey (2MRS) catalog using an orbit-reconstruction algorithm. The reconstructed velocities of individual objects in 2MRS are well-correlated with the peculiar velocities obtained from high-precision observed distances within 3,000 km/s. We estimate the mean matter density to be 0.31 +/- 0.05 by comparing observed to reconstructed velocities in this volume. The reconstructed motion of the Local Group in the rest frame established by distances within 3,000 km/s agrees with the observed motion and is generated by fluctuations within this volume, in agreement with observations. Then, we reconstruct the velocity field of 2MRS in successively larger radii, to study the problem of convergence towards the CMB dipole. We find that less than half of the amplitude of the CMB dipole is generated within a volume enclosing the Hydra-Centaurus-Norma supercluster at around 40 Mpc/h. Although most of the amplitude of the CMB dipole seems to be recovered by 120 Mpc/h, we observe no convergence up to this scale. We develop a new statistical model which allows us to estimate cosmological para meters from the reconstructed growth of convergence of the velocity of the Local Group towards the CMB dipole motion. For scales up to 50 Mpc/h, assuming a Local Group velocity of 627 km/s, we estimate Omega_m h^2 = 0.08 +/- 0.03 and sigma_8=0.84 +/- 0.47, in agreement with WMAP5 measurements at the 1 to 2-sigma level. However, for scales up to 100 Mpc/h, we obtain Omega_m h^2 = 0.05 +/- 0.02 and sigma_8=1.31 +/- 0.80, which agrees only at the 2 to 3-sigma level with WMAP5 results. Weighing our likelihood analysis by the probability of occurrence of the velocity of the Local Group does not change the aforementioned disagreement.
     
  6. Nov 26, 2008 #5
    Very nice, thanks for the heads up on these. I saw the first one somewhere - do you know if it was referenced in a news article?
     
  7. Nov 26, 2008 #6

    wolram

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    Sorry, i hardly ever read news articles other than SciAm and science news.
     
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