Automorphisms of $\mathbb{C}^3$ Commuting with a $\mathbb{C}^+$-Action

Let $\rho$ be an algebraic action of the additive group $\mathbb{C}^+$ on the three-dimensional affine space $\mathbb{C}^3$. We describe the group $\textrm{Cent}(\rho)$ of polynomial automorphisms of $\mathbb{C}^3$ that commute with $\rho$. A particular emphasis lies in the description of the automorphisms in $\textrm{Cent}(\rho)$ coming from algebraic $\mathbb{C}^+$-actions. As an application we prove that the automorphisms in $\textrm{Cent}(\rho)$ that are the identity on the algebraic quotient of $\rho$ form a characteristic subgroup of $\textrm{Cent}(\rho)$.