The California Legacy Survey IV. Lonely, Poor, and Eccentric: A Comparison Between Solitary and Neighborly Gas Giants

We compare systems with single giant planets to systems with multiple giant planets using a catalog of planets from a high-precision radial velocity survey of FGKM stars. Our comparison focuses on orbital properties, planet masses, and host star properties. We use hierarchical methods to model the orbital eccentricity distributions of giant singles and giant multis, and find that the distributions are distinct. The multiple giant planets typically have moderate eccentricities and their eccentricity distribution extends to $e=0.47$ (90th percentile), while the single giant planets have a pile-up of nearly circular orbits and a long tail that extends to $e=0.77$. We determine that stellar hosts of multiple giants are distinctly more metal-rich than hosts of solitary giants, with respective mean metallicities $0.228\pm0.027$ vs. $0.129\pm0.019$ dex. We measure the distinct occurrence distributions of single and multiple giants with respect to orbital separation, and find that single gas giants have a $\sim$2.3$\sigma$ significant hot ($a<0.06$) Jupiter pile-up not seen among multi giant systems. We find that the median mass ($\msini$ ) of giants in multiples is nearly double that of single giants (1.71 $\mjup$ vs. 0.92 $\mjup$ ). We find that giant planets in the same system have correlated masses, analogous to the `peas in a pod' effect seen among less massive planets.