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 _ { o } , corresponding to the boundary between the linear and nonlinear regime of clustering , \xi \simeq 1 .
We show how this feature can be used to constrain the biasing parameter , b ^ { 2 } \equiv \xi _ { g } ( r ) / \xi ( r ) on scales r \simeq r _ { o } , where \xi _ { g } is the galaxy-galaxy correlation function , allowed to differ from \xi .
We apply our method to real data : the \xi _ { g } ( r ) , estimated from the APM galaxy survey .
Our results suggest that the APM galaxies trace the mass at separations r \gtrsim 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 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 \xi , predicted by Gott and Rees 25 years ago .