Warm Sub-Saturns Orbiting Single Stars Are Spin-Orbit Aligned

In this work, we show that warm sub-Saturns orbiting single stars are predominantly aligned, in contrast to hot sub-Saturns, which are frequently misaligned, with the two populations differing at the 3.2 sigma level. Because both populations are observed around cool stars, they are free from the ambiguity introduced by the T eff - lambda dependence. Together with the established alignment of warm Jupiters, this demonstrates, among single-star systems, that spin-orbit misalignment arises specifically in the close-in ``hot-Jupiter-analog'' regime, where tidal circularization is efficient (tau e< tau age) and high-eccentricity migration is expected to operate. We further find that the transition between aligned and misaligned sub-Saturns occurs at wider orbital separations (a final/R p = 338 plus or minus27) than for Jupiters (a final/R p = 117 plus or minus9), consistent with the expectation that the lower masses (smaller M p/M*) and stronger tidal dissipation (lower Q p) of sub-Saturns allow them to be circularized into wider final orbits within their lifetimes. Taken together, these results provide the clearest direct evidence to date that, in single-star systems, spin-orbit misalignments are produced by high-eccentricity migration. If this framework is correct, spin-orbit misalignments may also emerge among hot-Jupiter analogs in other mass regimes, including hot brown dwarfs around hot stars at a final/R p 100 and isolated hot super-Earths at a final/R p 1000, with the corresponding transition locations shifted by the dependence of the orbital-circularization timescale on M p/M* and Q p.