Light Propagation in Inhomogeneous Universes I: Methodology and Preliminary Results

Abstract

We describe a numerical algorithm which simulates the propagation of light in inhomogeneous universes, using the multiple lens-plane method. The deformation and deflection of light beams as they interact with each lens plane are computed using the filled-beam approximation. We use a N-body code to simulate large-scale structure formation in the universe. We extend the length resolution of the simulations to sub-Megaparsec scales by using a Monte-Carlo method for locating galaxies according to the underlying distribution of background matter. The observed galaxy 2-point correlation function and morphology-density relation are reproduced. This algorithm constitutes a major improvement over previous methods. We test this algorithm for three different CDM models: an Einstein-de Sitter model, an open model, and a flat model with a nonzero cosmological constant. In each case, we compute the shear and magnification caused by the presence of inhomogeneities. Our results are the following: (1) The magnification is totally dominated by the convergence; the shear contributes less than one part in 10^4. (2) Most of the cumulative shear and magnification is contributed by matter located at intermediate redshifts z=1-2. (3) The redshift where the largest contribution to shear and magnification occurs is model-dependent. (4) The bulk of the shear and magnification does not originate from direct hits with galaxies, but rather from the tidal influence of nearby and more distant galaxies, and background matter. (5) The average contributions of background matter and nearby galaxies to the shear is comparable for models with small Omega0. For the Einstein-de Sitter model, the contribution of the background matter exceeds the one of nearby galaxies by nearly one order of magnitude.

One latex files and 13 figures. Submitted to The Astrophysical Journal (Mar 1997)

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