Ternary and Quaternary Curves of Small Fixed Genus and Gonality with Many Rational Points

Abstract

We extend the computations from our previous paper arXiv:2005.07054 to determine the maximum number of rational points on a curve over $\mathbb{F}_3$ and $\mathbb{F}_4$ with fixed gonality and small genus. We find, for example, that there is no curve of genus 5 and gonality 6 over a finite field. We propose two conjectures based on our data. First, an optimal curve of genus $g$ has gonality at most $\lfloor \frac{g+3}{2} \rfloor$. Second, a curve of gonality $\gamma$ and large genus over $\mathbb{F}_q$ has $\gamma(q+1)$ rational points.