Very ampleness of the canonical bundle of surfaces of type (1, 2, 2) on abelian threefolds

Abstract

The present work deals with the canonical map of smooth, compact complex surfaces of general type in a polarization of type $(1,2,2)$ on an abelian threefold. A natural and classical question is whether the canonical system of such surfaces is very ample in the general case. In this work, we provide a positive answer to this question. First, we describe the structure of the canonical map of those smooth ample surfaces of type $(1,2,2)$ in an abelian threefold which are bidouble cover of principal polarizations. Then, we study the general behavior of the canonical map of general ample surfaces $\mathcal{S}$, yielding a $(1,2,2)$-polarization on an abelian threefold $A$ which is isogenous to a product. By combining these descriptions, we show that the canonical map yields a holomorphic embedding when $A$ and $\mathcal{S}$ are both sufficiently general. It follows, in particular, a proof of the existence of canonical irregular surfaces in $\mathbb{P}^5$ with numerical invariants $p_g = 6$, $q = 3$ and $K^2 = 24$.