Determining Bias with Cumulant Correlators

Abstract

The first non-trivial cumulant correlator of the galaxy density field $Q_{21}$ is examined from the point of view of biasing. It is shown that to leading order it depends on two biasing parameters $b$, and $b_2$, and on $q_{21}$, the underlying cumulant correlator of the mass. As the skewness $Q_3$ has analogous properties, the slope of the correlation function $-\gamma$, $Q_3$, and $Q_{21}$ uniquely determine the bias parameter on a particular scale to be $b = \gamma/6(Q_{21}-Q_3)$, when working in the context of gravitational instability with Gaussian initial conditions. Thus on large scales, easily accessible with the future Sloan Digital Sky Survey and the 2 Degree Field Survey, it will be possible to extract $b$, and $b_2$ from simple counts in cells measurements. Moreover, the higher order cumulants, $Q_N$, successively determine the higher order biasing parameters. From these it is possible to predict higher order cumulant correlators as well. Comparing the predictions with the measurements will provide internal consistency checks on the validity of the assumptions in the theory, most notably perturbation theory of the growth of fluctuations by gravity and Gaussian initial conditions. Since the method is insensitive to $\Omega$, it can be successfully combined with results from velocity fields, which determine $\Omega^{0.6}/b$, to measure the total density parameter in the universe.