Max Tegmark's library: gaussianity
Figure 1: If you remove these five COBE DMR pixels,
the non-Gaussianity detection is no longer statistically significant
Please click here to get the postscript
file with the paper. Here's a viewgraph with fig
1 (color) - you can also click on the image above. Click
if you are interested in other research of mine.
Is the cosmic microwave background really non-Gaussian?
& Max Tegmark
Two recent papers have claimed detection of non-Gaussian features in the
COBE DMR sky maps of the cosmic microwave background. We confirm these
results, but argue that Gaussianity is still not convincingly ruled out.
Since a score of non-Gaussianity tests have now been published, one might
expect some mildly significant results even by chance. Moreover, in the
case of one measure which yields a detection, a bispectrum statistic, we
find that if the non-Gaussian feature is real, it may well be due to detector
noise rather than a non-Gaussian sky signal, since a signal-to-noise analysis
localizes it to angular scales smaller than the beam. We study its spatial
origin in case it is nonetheless due to a sky signal (eg, a cosmic string
wake or flat-spectrum foreground contaminant). It appears highly localized
in the direction b=39.5, l=257, since removing a mere 5 pixels inside a
single COBE beam area centered there makes the effect statistically insignificant.
We also test Guassianity with an eigenmode analysis which allows a sky
map to be treated as a random number generator. A battery of tests of this
generator all yield results consistent with Gaussianity.
astro-ph/9904254, published in ApJL
We got inpired to write this paper by two reported detections
Ferreira, Magueijo & Gorski (1998)
Pando, Valls-Gabaud & Fang (1998)
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This page was last modified July 17, 2000.