= Characteristic density of a Navarro--Frenk--White profile
{title2=$\rho_s$}
The \b[<characteristic density of a Navarro--Frenk--White profile>] is its <normalization> $\rho_s$ at fixed <scale radius of a Navarro--Frenk--White profile> $r_s$. It is not the density at that <radius>: substituting $r=r_s$ in the <NFW profile> gives $\rho(r_s)=\rho_s/4$. Once $r_s$ is fixed, doubling $\rho_s$ doubles the enclosed <mass> at every <radius>. This separates a profile's density <normalization> from its radial scale.
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