How to Suppress the Shot Noise in Galaxy Surveys

Galaxy surveys are one of the most powerful means to extract cosmological information and for a given volume the attainable precision is determined by the galaxy shot noise ${\sigma }_n^2$ relative to the power spectrum $P$. It is generally assumed that shot noise is white and given by the inverse of the number density $\overline{n}$. In this Letter we argue one may considerably improve upon this due to mass and momentum conservation. We explore this idea with $N$-body simulations by weighting central halo galaxies by halo mass and find that the resulting shot noise can be reduced dramatically relative to expectations, with a 10–30 suppression at $\overline{n}=4\times {10}^{-3}(h/\mathrm{Mpc}{)}^3$. These results open up new opportunities to extract cosmological information in galaxy surveys and may have important consequences for the planning of future redshift surveys.