  Gas giants orbiting interior to the ice line are thought to have been
displaced from their formation locations by processes that remain debated. Here
we uncover several new metallicity trends, which together may indicate that two
competing mechanisms deliver close-in giant planets: gentle disk migration,
operating in environments with a range of metallicities, and violent
planet-planet gravitational interactions, primarily triggered in metal-rich
systems in which multiple giant planets can form. First, we show with 99.1%
confidence that giant planets with semi-major axes between 0.1 and 1 AU
orbiting metal-poor stars ([Fe/H]<0) are confined to lower eccentricities than
those orbiting metal-rich stars. Second, we show with 93.3% confidence that
eccentric proto-hot Jupiters undergoing tidal circularization primarily orbit
metal-rich stars. Finally, we show that only metal-rich stars host a pile-up of
hot Jupiters, helping account for the lack of such a pile-up in the overall
Kepler sample. Migration caused by stellar perturbers (e.g. stellar Kozai) is
unlikely to account for the trends. These trends further motivate follow-up
theoretical work addressing which hot Jupiter migration theories can also
produce the observed population of eccentric giant planets between 0.1 and 1
AU.
