Published online by Cambridge University Press: 28 March 2018
We consider homeomorphisms $f,h$ generating a faithful
$\mathit{BS}(1,n)$-action on a closed surface
$S$, that is,
$hfh^{-1}=f^{n}$ for some
$n\geq 2$. According to Guelman and Liousse [Actions of Baumslag–Solitar groups on surfaces. Discrete Contin. Dyn. Syst. A 5 (2013), 1945–1964], after replacing
$f$ by a suitable iterate if necessary, we can assume that there exists a minimal set
$\unicode[STIX]{x1D6EC}$ of the action, included in
$\text{Fix}(f)$. Here, we suppose that
$f$ and
$h$ are
$C^{1}$ in a neighborhood of
$\unicode[STIX]{x1D6EC}$ and any point
$x\in \unicode[STIX]{x1D6EC}$ admits an
$h$-unstable manifold
$W^{u}(x)$. Using Bonatti’s techniques, we prove that either there exists an integer
$N$ such that
$W^{u}(x)$ is included in
$\text{Fix}(f^{N})$ or there is a lower bound for the norm of the differential of
$h$ depending only on
$n$ and the Riemannian metric on
$S$. Combining the last statement with a result of Alonso, Guelman and Xavier [Actions of solvable Baumslag–Solitar groups on surfaces with (pseudo)-Anosov elements. Discrete Contin. Dyn. Syst. to appear], we show that any faithful action of
$\mathit{BS}(1,n)$ on
$S$ with
$h$ a pseudo-Anosov homeomorphism has a finite orbit containing singularities of
$h$; moreover, if
$f$ is isotopic to the identity, it is entirely contained in the singular set of
$h$. As a consequence, there is no faithful
$C^{1}$-action of
$\mathit{BS}(1,n)$ on the torus with
$h$ Anosov.