Spectral radii and star-factors with large components

Abstract

Let $G$ be a connected graph with $n$ vertices. The isolated toughness of $G$, denoted by $I(G)$, is defined by $I(G)=\min\left\{\frac{|S|}{i(G-S)}:S\subseteq V(G) \ \mbox{and} \ i(G-S)\geq2\right\}$ if $G$ is not complete, or $I(G)=+\infty$ if $G$ is complete. A graph $G$ is called isolated $r$-tough if $I(G)\ge r$. A spanning subgraph $H$ of $G$ is called a $\{K_{1,j}:m\le j\le 2m\}$-factor of $G$ if every component of $H$ is isomorphic to an element of $\{K_{1,j}:m\le j\le 2m\}$. Let $\ddot{I}(G)$, $q(G)$ and $\hat{I}¼(G)$ denote the adjacency spectral radius, the signless Laplacian spectral radius and the distance spectral radius of $G$, respectively. Let $m$ and $b$ be two positive integers with $m\ge 2$. In this paper, we first establish a lower bounds on the adjacency spectral radius of a connected isolated $\frac{mb-1}{b}$-tough graph $G$ to guarantees that $G$ contains a $\{K_{1,j}:m\le j\le 2m\}$-factor. Second, we establish a lower bounds on the signless Laplacian spectral radius of a connected isolated $\frac{mb-1}{b}$-tough graph $G$ to ensures that $G$ contains a $\{K_{1,j}:m\le j\le 2m\}$-factor. Finally, we create an upper bounds on the distance spectral radius of a connected isolated $\frac{mb-1}{b}$-tough graph $G$ with a $\{K_{1,j}:m\le j\le 2m\}$-factor. Furthermore, we construct some extremal graphs to claim that all the bounds obtained in this paper are sharp.

15 pages