The first high-redshift changing-look quasars
  We report on three redshift $z>2$ quasars with dramatic changes in their C IV
emission lines, the first sample of changing-look quasars (CLQs) at high
redshift. This is also the first time the changing-look behaviour has been seen
in a high-ionisation emission line. SDSS J1205+3422, J1638+2827, and J2228+2201
show interesting behaviour in their observed optical light curves, and
subsequent spectroscopy shows significant changes in the C IV broad emission
line, with both line collapse and emergence being displayed on rest-frame
timescales of $\sim$240-1640 days. These are rapid changes, especially when
considering virial black hole mass estimates of $M_{\rm BH} > 10^{9} M_{\odot}$
for all three quasars. Continuum and emission line measurements from the three
quasars show changes in the continuum-equivalent width plane with the CLQs seen
to be on the edge of the full population distribution, and showing indications
of an intrinsic Baldwin effect. We put these observations in context with
recent state-change models, and note that even in their observed low-state, the
C IV CLQs are generally above $\sim$5\% in Eddington luminosity.
