Emergence of large densities in a chemotaxis system with signal-dependent motility

In this paper, we focus on the emergence of large densities of a cell population in finite time in the following parabolic-elliptic Keller-Segel system with signal-dependent motility and a source term of logistic type \begin{equation} \begin{cases} u_{\varepsilon t} = Δ(e^{-v_\varepsilon}u_\varepsilon) + \varepsilon(κu_\varepsilon - μu_\varepsilon^2) ,\\ 0 =Δv_{\varepsilon}-v_\varepsilon+ u_{\varepsilon}. \end{cases} \end{equation} in a smooth bounded domain $Ω\subseteq\mathbb{R}^2$ with homogenuous Neumann boundary conditions and parameters $κ,μ>0$ and $\varepsilon\in(0,1)$. We will show that the solution $u_\varepsilon$ can exceed any certain value $M>0$ before a time $T(M)>0$ under the condition that $\varepsilon>0$ is sufficiently small. To prove the result, we show convergence of classical solutions of the first system to classical solutions of the corresponding limit system as $\varepsilon\searrow 0$ \begin{equation} \begin{cases} u_t=Δ(e^{-v}u),\\ -Δv+v=u. \end{cases} \end{equation} The main challenge is to find suitable bounds for $u_\varepsilon$ and $v_\varepsilon$, that are $\varepsilon$-independent, in Lebesgue and Hölder spaces, whereas for fixed $\varepsilon>0$ global existence and boundedness is known.