Evidence for the Late Arrival of Hot Jupiters in Systems with High
  Host-star Obliquities
  It has been shown that hot Jupiters systems with massive, hot stellar
primaries exhibit a wide range of stellar obliquities. On the other hand, hot
Jupiter systems with low-mass, cool primaries often have stellar obliquities
close to zero. Efficient tidal interactions between hot Jupiters and the
convective envelopes present in lower-mass main sequence stars have been a
popular explanation for these observations. If this explanation is accurate,
then aligned systems should be older than misaligned systems. Likewise, the
convective envelope mass of a hot Jupiter's host star should be an effective
predictor of its obliquity. We derive homogeneous stellar parameters --
including convective envelope masses -- for hot Jupiter host stars with
high-quality sky-projected obliquity inferences. Using a thin disk stellar
population's Galactic velocity dispersion as a relative age proxy, we find that
hot Jupiter host stars with larger-than-median obliquities are older than hot
Jupiter host stars with smaller-than-median obliquities. The relative age
difference between the two populations is larger for hot Jupiter host stars
with smaller-than-median fractional convective envelope masses and is
significant at the 3.6-$\sigma$ level. We identify stellar mass, not convective
envelope mass, as the best predictor of stellar obliquity in hot Jupiter
systems. The best explanation for these observations is that many hot Jupiters
in misaligned systems arrived in the close proximity of their host stars long
after their parent protoplanetary disks dissipated. The dependence of observed
age offset on convective envelope mass suggests that tidal realignment
contributes to the population of aligned hot Jupiters orbiting stars with
convective envelopes.
