Quasiconvexity in $3$-manifold groups

Abstract

In this paper, we study strongly quasiconvex subgroups in a finitely generated $3$--manifold group ${\pi }_1(M)$. We prove that if $M$ is a compact, orientable $3$--manifold that does not have a summand supporting the Sol geometry in its sphere-disc decomposition then a finitely generated subgroup $H\le {\pi }_1(M)$ has finite height if and only if $H$ is strongly quasiconvex. On the other hand, if $M$ has a summand supporting the Sol geometry in its sphere-disc decomposition then ${\pi }_1(M)$ contains finitely generated, finite height subgroups which are not strongly quasiconvex. We also characterize strongly quasiconvex subgroups of graph manifold groups by using their finite height, their Morse elements, and their actions on the Bass-Serre tree of ${\pi }_1(M)$. This result strengthens analogous results in right-angled Artin groups and mapping class groups. Finally, we characterize hyperbolic strongly quasiconvex subgroups of a finitely generated $3$--manifold group ${\pi }_1(M)$ by using their undistortedness property and their Morse elements.

36 pages. Version 2 incorporates the referee's comments. To appear in Mathematische Annalen