Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73K Cosmic Microwave Background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole $\ell_{peak}=(197 \pm 6)$, with an amplitude $DT_{200}=(69 \pm 8)\mu K$. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary scenarios.

Abstract:

We derive an expression for the angular power spectrum of cosmic microwave background anisotropies due to gravity waves generated by a stochastic magnetic field and compare the result with current observations; we take into account the non-linear nature of the stress energy tensor of the magnetic field. For almost scale invariant spectra, the amplitude of the magnetic field at galactic scales is constrained to be of order 10^{-9} Gauss. If we assume that the magnetic field is damped below the Alfven damping scale, we find that its amplitude at 0.1 h^{-1}Mpc, B_\lambda, is constrained to be B_\lambda<7.9 x10^{-6} e^{3n} Gauss, for n<-3/2, and B_\lambda<9.5x10^{-8} e^{0.37n} Gauss, for n>-3/2, where n is the spectral index of the magnetic field and H_0=100h km s^{-1}Mpc^{-1} is the Hubble constant today.

Abstract:

The motions of galaxies can be used to constrain the cosmological density parameter Omega and the clustering amplitude of matter on large scales. The mean relative velocity of galaxy pairs, estimated from the Mark III survey, indicates that Omega = 0.35 +0.35/-0.25. If the clustering of galaxies is unbiased on large scales, Omega = 0.35 +/- 0.15, so that an unbiased Einstein-de Sitter model (Omega = 1) is inconsistent with the data.