Quantifying the Bull's Eye Effect

Abstract

We have used N-body simulations to develop two independent methods to quantify redshift distortions known as the Bull's Eye effect (large scale infall plus small scale virial motion). This effect depends upon the mass density, $Ω_0$, so measuring it can in principle give an estimate of this important cosmological parameter. We are able to measure the effect and distinguish between its strength for high and low values of $Ω_0$. Unlike other techniques which utilize redshift distortions, one of our methods is relatively insensitive to bias. In one approach, we use path lengths between contour crossings of the density field. The other is based upon percolation. We have found both methods to be successful in quantifying the effect and distinguishing between values of $Ω_0$. However, only the path lengths method exhibits low sensitivity to bias.