Quasar Clustering and Spacetime Geometry

Abstract

The non-Euclidean geometry of spacetime induces an anisotropy in the apparent correlation function of high-redshift quasars. This effect can constrain the cosmological constant Λindependent of any assumptions about evolution of luminosities, sizes, or clustering. We examine the prospects for distinguishing between low-density (Ω_0=0.1-0.4) cosmological models with flat and open space geometry using the quasar samples anticipated from the 2dF and Sloan redshift surveys. We show that even these large quasar surveys are likely to reside in the "sparse sampling" regime, so that measurement errors in the correlation function obey Poisson statistics. As a result: (a) one can devise a simple maximum-likelihood scheme for estimating clustering parameters, (b) one can generate Monte Carlo realizations of correlation function measurements without creating artificial quasar distributions, and (c) for fixed quasar number, a deeper survey over a smaller area has greater statistical power than a shallow, large-area survey. Adopting recent (quite uncertain) estimates of the quasar correlation length, we find that the 2dF and Sloan samples can provide clear discrimination between flat and open geometries for Ω<= 0.2 but only marginal discrimination for Ω= 0.4. Clear discrimination is possible for Ω= 0.4 if the true quasar correlation length is a factor of two larger, and a high-density survey of 30,000 quasars in 200 square degrees would provide clear discrimination even for the lower correlation length.