= Galaxy density contrast
{title2=$\delta_g=(n_g-\bar n_g)/\bar n_g$}
The <galaxy density contrast> measures a fractional departure of galaxy number density from its ensemble or survey mean. Linear <galaxy bias> relates its large-scale three-dimensional component to the matter <density contrast> by $\delta_g=b_g\delta_m$. An angular sample averages this field with its normalized redshift selection; a <probability density> $p(z)$ per unit <cosmological redshift> corresponds to a distance kernel $H(z)p(z)/c$ in a spatially flat background.
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