Evolution of the Ultraviolet Upturn at $0.3<z<1$: exploring helium rich
  stellar populations
  We measure the near-UV (rest-frame $\sim 2400$\AA) to optical color for
early-type galaxies in 12 clusters at $0.3 < z < 1.0$. We show that this is a
suitable proxy for the more common far-ultraviolet bandpass used to measure the
ultraviolet upturn and find that the upturn is detected to $z=0.6$ in these
data, in agreement with previous work. We find evidence that the strength of
the upturn starts to wane beyond this redshift and largely disappears at $z=1$.
Our data is most consistent with models where early-type galaxies contain
minority stellar populations with non-cosmological helium abundances, up to
around 46\%, formed at $z \geq 3$, resembling multiple stellar population
globular clusters in our Galaxy. This suggests that elliptical galaxies and
globular clusters share similar chemical evolution and star formation
histories. The vast majority of the stellar mass in these galaxies also must
have been in place at $z > 3$.
