Published online by Cambridge University Press: 11 August 2014
Let $(X,{\it\sigma}_{X}),(Y,{\it\sigma}_{Y})$ be one-sided subshifts and ${\it\pi}:X\rightarrow Y$ a factor map. Suppose that $X$ has the specification property. Let ${\it\mu}$ be a unique invariant Gibbs measure for a sequence of continuous functions ${\mathcal{F}}=\{\log f_{n}\}_{n=1}^{\infty }$ on $X$, which is an almost additive potential with bounded variation. We show that ${\it\pi}{\it\mu}$ is a unique invariant Gibbs measure for a sequence of continuous functions ${\mathcal{G}}=\{\log g_{n}\}_{n=1}^{\infty }$ on $Y$. When $(X,{\it\sigma}_{X})$ is a full shift, we characterize ${\mathcal{G}}$ and ${\it\mu}$ by using relative pressure. This ${\mathcal{G}}$ is a generalization of a continuous function found by Pollicott and Kempton in their work on factors of Gibbs measures for continuous functions. We also consider the following question: given a unique invariant Gibbs measure ${\it\nu}$ for a sequence of continuous functions ${\mathcal{F}}_{2}$ on $Y$, can we find an invariant Gibbs measure ${\it\mu}$ for a sequence of continuous functions ${\mathcal{F}}_{1}$ on $X$ such that ${\it\pi}{\it\mu}={\it\nu}$? We show that such a measure exists under a certain condition. In particular, if $(X,{\it\sigma}_{X})$ is a full shift and ${\it\nu}$ is a unique invariant Gibbs measure for a function in the Bowen class, then there exists a preimage ${\it\mu}$ of ${\it\nu}$ which is a unique invariant Gibbs measure for a function in the Bowen class.