Gravity's smoking gun?

We present a new constraint on the biased galaxy formation picture. Gravitational instability theory predicts that the two-point mass density correlation function, xi (r), has an inflection point at the separation r = r(0), corresponding to the boundary between the linear and nonlinear regime of clustering,xi similar or equal to 1. We show how this feature can be used to constrain the biasing parameter b(2) = xi (g)(r)/xi (r) on scales r similar or equal to r(0), where xi (g) is the galaxy-galaxy correlation function, which is allowed to differ from. We apply our method to real data: the,(r), estimated from the Automatic Plate Measuring (APM) galaxy survey. Our results suggest that the APM galaxies trace the mass at separations r greater than or similar to 5 5 h(-1) Mpc, where h is the Hubble constant in units of 100 km s(-1) Mpc(-1). The present results agree with earlier studies, based on comparing higher order correlations in the APM with weakly nonlinear perturbation theory. Both approaches constrain the b factor to be within 20% of unity. If the existence of the feature that we identified in the APM xi (g)(r)-the inflection point near xi (g) = 1-is confirmed by more accurate surveys, we may have discovered gravity's smoking gun: the long-awaited shoulder in, predicted by Gott and Rees 25 years ago.