The identification of z-dropouts in Pan-STARRS1: three quasars at
  6.5<z<6.7
  Luminous distant quasars are unique probes of the high redshift intergalactic
medium (IGM) and of the growth of massive galaxies and black holes in the early
universe. Absorption due to neutral Hydrogen in the IGM makes quasars beyond a
redshift of z~6.5 very faint in the optical $z$-band, thus locating quasars at
higher redshifts require large surveys that are sensitive above 1 micron. We
report the discovery of three new z>6.5 quasars, corresponding to an age of the
universe of <850 Myr, selected as z-band dropouts in the Pan-STARRS1 survey.
This increases the number of known z>6.5 quasars from 4 to 7. The quasars have
redshifts of z=6.50, 6.52, and 6.66, and include the brightest z-dropout quasar
reported to date, PSO J036.5078+03.0498 with M_1450=-27.4. We obtained
near-infrared spectroscopy for the quasars and from the MgII line we estimate
that the central black holes have masses between 5x10^8 and 4x10^9 M_sun, and
are accreting close to the Eddington limit (L_Bol/L_Edd=0.13-1.2). We
investigate the ionized regions around the quasars and find near zone radii of
R_NZ=1.5-5.2 proper Mpc, confirming the trend of decreasing near zone sizes
with increasing redshift found for quasars at 5.7<z<6.4. By combining R_NZ of
the PS1 quasars with those of 5.7<z<7.1 quasars in the literature, we derive a
luminosity corrected redshift evolution of
R_NZ,corrected=(7.2+/-0.2)-(6.1+/-0.7)x(z-6) Mpc. However, the large spread in
R_NZ in the new quasars implies a wide range in quasar ages and/or a large
variation in the neutral Hydrogen fraction along different lines of sight.
