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I BOSS and similarity with CMB

  1. Jul 16, 2016 #1
    In
    http://physicsworld.com/cws/article...ps-1-2-million-galaxies-in-the-early-universe
    we can see picture which was also measured.

    One paper about this is also:
    http://arxiv.org/pdf/1607.03155v1.pdf

    This picture is very similar as CMB picture measured by Planck spacecraft.
    https://en.wikipedia.org/wiki/Planck_(spacecraft)
    https://en.wikipedia.org/wiki/Planc...IA16874-CobeWmapPlanckComparison-20130321.jpg

    Are those two pictures really similar if we put one on another?
     
  2. jcsd
  3. Jul 18, 2016 #2

    mfb

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    Staff: Mentor

    Well, directly putting them on top of each other doesn't help - they are showing different regions in space. They are also showing different regions in time, so you don't get directly the same patterns - so you need cosmological models to figure out how the CMB fluctuations develop to galaxy patterns. As far as I understand the new galaxy map fits well to the models.
     
  4. Jul 20, 2016 #3
    Not really. You can test this out if you install Aladin which can show an SDSS catalogue on top of a CMB map. The clustering signal in the CMB and the galaxies are related but direct correlations between the CMB and galaxies are slim. I would be careful of correlation by eye however, you usually see what you want to and the BOSS galaxies aren't that homogeneous.

    There are correlations between galaxies in the modern universe and the observed CMB but these are secondary anisotropies, they were imprinted by the galaxies as the CMB light passed by. The primary anisotropy generated at the surface of last scattering wont be correlated significantly. Secondary correlations are usually quite weak. The main one is the Sunyaev–Zel'dovich effect where the CMB photons scatter off the hot electrons in the intra-cluster medium in galaxy clusters. This one can be seen by eye with either big clusters or good data as cold spots at low frequencies and hot spots at higher ones (this is a spectral distortion, the spectrum is no longer black body). However this is a very small scale effect, not visible in these images. There is a larger scale effect called in the Integrated Sachs-Wolfe effect where the accelerating universe causes small residual gravitational redshifts when CMB photons enter and leave a potential. The end result is that clusters leave hot spots and voids leave cold spots on the CMB. This occurs at much larger scales than the SZ effect but it is very small and can't be seen by eye, it can barely be detected statistically. There is also gravitational lensing where galaxies trace the mass in the universe which lenses the CMB. This is again small but it can dominate the very small scale CMB structures with the SZ effect but that’s not really resolved by Planck, it's best studied in polarisation.

    There may however be observational effects, namely dust. Galactic dust causes reddening but it can also contaminate CMB maps, however combined CMB maps are pretty good at removing foreground away from the galactic plane and BOSS does account for reddening.
     
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