The bright end of the galaxy luminosity function at z ~ 7: before the
  onset of mass quenching?
  We present the results of a new search for bright star-forming galaxies at z
~ 7 within the UltraVISTA DR2 and UKIDSS UDS DR10 data, which together provide
1.65 sq deg of near-infrared imaging with overlapping optical and Spitzer data.
Using a full photo-z analysis to identify high-z galaxies and reject
contaminants, we have selected a sample of 34 luminous (-22.7 < M_UV < -21.2)
galaxies with 6.5 < z < 7.5. Crucially, the deeper imaging provided by
UltraVISTA DR2 confirms all of the robust objects previously uncovered by
Bowler et al. (2012), validating our selection technique. Our sample includes
the most massive galaxies known at z ~ 7, with M_* ~ 10^{10} M_sun, and the
majority are resolved, consistent with larger sizes (r_{1/2} ~ 1 - 1.5 kpc)
than displayed by less massive galaxies. From our final sample, we determine
the form of the bright end of the rest-frame UV galaxy luminosity function (LF)
at z ~ 7, providing strong evidence that the bright end of the z = 7 LF does
not decline as steeply as predicted by the Schechter function fitted to fainter
data. We consider carefully, and exclude the possibility that this is due to
either gravitational lensing, or significant contamination of our galaxy sample
by AGN. Rather, our results favour a double power-law form for the galaxy LF at
high z, or, more interestingly, a LF which simply follows the form of the
dark-matter halo mass function at bright magnitudes. This suggests that the
physical mechanism which inhibits star-formation activity in massive galaxies
(i.e. AGN feedback or some other form of `mass quenching') has yet to impact on
the observable galaxy LF at z ~ 7, a conclusion supported by the estimated
masses of our brightest galaxies which have only just reached a mass comparable
to the critical `quenching mass' of M_* = 10 ^{10.2} M_sun derived from studies
of the mass function of star-forming galaxies at lower z.
