On the agreement between COBE anisotropy results and specific predictions from clusters of galaxies
Abstract
The recent results from the COBE DMR experiment detect a large-angle anisotropy in the cosmic microwave background. These data indicate that the scale-invariant (n = 1) spectrum is preferred, with a amplitude at the horizon crossing of ɛ_H_=(5.4+/-1.6) x 10^-6^. This level is in remarkable agreement with the value of ɛ_H_~(1.5/b)(6+/-2.5)X 10^-6^, which was predicted to be the relevant one from a study of the distribution of Abell clusters at large scales which correspond to angles up to twice the COBE FWHM, where the value b ~ 1.5 was suggested by agreement with the observed large-scale peculiar velocities. This observational agreement indicates that on the very large scales the peculiar gravitational potential has been nearly constant from the epoch of last scattering to the present. This fact, together with the presence of large-scale flows, suggests that we live in a spatially flat Universe of critical density, where optical galaxies mildly biased with respect to the matter distribution, and with a power spectrum which, depending on the spectral index on small scales, has a tunrover to n = 1 in the 100-200 h^-1^ Mpc scale range. We also consider a `tilted' (n<1) cold dark matter model, and find that this model would need a small spectral index (n~ 0.3) to match the cluster normalization. However, such an index would yield too large a CMB anisotropy, even without the possible additional anisotropy due to the presence of a significant background of primordial gravitational waves.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 1993
- DOI:
- 10.1093/mnras/262.1.L43
- Bibcode:
- 1993MNRAS.262L..43S
- Keywords:
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- Anisotropic Media;
- Cosmic Background Explorer Satellite;
- Galactic Clusters;
- Relic Radiation;
- Astronomical Models;
- Gravitational Waves;
- Microwaves;
- Astrophysics