A class of chemotaxis systems with growth source and nonlinear secretion

In this paper, we are concerned with a class of parabolic-elliptic chemotaxis systems encompassing the prototype $$\left\{\begin{array}{lll} &u_t = \nabla\cdot(\nabla u-\chi u\nabla v)+f(u), & x\in \Omega, t>0, \\[0.2cm] &0= \Delta v -v+u^\kappa, & x\in \Omega, t>0 \end{array}\right.$$ with nonnegative initial condition for $u$ and homogeneous Neumann boundary conditions in a smooth bounded domain $\Omega\subset \mathbb{R}^n(n\geq 2)$, where $\chi>0$, $\kappa>0$ and $f$ is a smooth growth source satisfying $f(0)\geq 0$ and $$f(s)\leq a-bs^\theta, \quad s\geq 0, \text{with some} a\geq 0, b>0, \theta>1.$$ Firstly, it is shown, either $$\kappa<\frac{2}{n}\quad \& \quad f\equiv 0,$$ or $$\theta>\kappa+1,$$ or $$\theta-\kappa=1, \ \ b\geq \frac{(\kappa n-2)}{\kappa n}\chi, \eqno(*)$$ that the corresponding initial-value problem admits a unique classical solution that is uniformly bounded in space and time. Our proof is elementary and semigroup-free. Whilst, with the particular choices $\theta=2$ and $\kappa=1$, Tello and Winkler \cite{TW07} use sophisticated estimates via the Neumann heat semigroup to obtain the global boundedness under the strict inequality in ($\ast$). Thereby, we improve their results to the "borderline" case $b=(\kappa n-2)/(\kappa n)\chi$ in this regard. Next, for an unbounded range of $\chi$, the system is shown to exhibit pattern formations, and, the emerging patterns are shown to converge weakly in $L^\theta(\Omega)$ to some constants as $\chi\rightarrow \infty$. While, for small $\chi$ or large damping $b$, precisely $b>2\chi$ if $f(u)=u(a-bu^\kappa)$ for some $a, b>0$, we show that the system does not admit pattern formation and the large time behavior of solutions is comparable to its associated ODE+algebraic system.