“…The main objective of this work is to deduce the following equilibrium equation ∂ tρ = div x ρ∇ x δE(ρ) δρ (1.4) by taking the overdamped limit ε → 0 in system (1.1) under the framework of relative entropy method. This method is an efficient mathematical tool for establishing the limiting processes and stabilities among thermomechanical theories, see [6,7,16,17,19,24,31,32] for instance. With the various choices of the functional E(ρ), the corresponding models spanned from the system of isentropic gas dynamics and variants of the Euler-Poisson system [29,33,35] leading to the porous medium equation and nonlinear aggregation-diffusion equations in the overdamped limit, see [15,26,27,28,30,34] and references therein.…”