Imaging Atomic and Highly Excited Molecular Gas in a z=6.42 Quasar Host
  Galaxy: Copious Fuel for an Eddington-Limited Starburst at the End of Cosmic
  Reionization
  We have imaged CO(J=7-6) and CI(3P2-3P1) emission in the host galaxy of the
z=6.42 quasar SDSS J114816.64+525150.3 (hereafter: J1148+5251) through
observations with the Plateau de Bure Interferometer. The region showing
CO(J=7-6) emission is spatially resolved, and its size of 5 kpc is in good
agreement with earlier CO(J=3-2) observations. In combination with a revised
model of the collisional line excitation in this source, this indicates that
the highly excited molecular gas traced by the CO J=7-6 line is subthermally
excited (showing only 58+/-8% of the CO J=3-2 luminosity), but not more
centrally concentrated. We also detect CI(3P2-3P1) emission in the host galaxy
of J1148+5251, but the line is too faint to enable a reliable size measurement.
  From the CI(3P2-3P1) line flux, we derive a total atomic carbon mass of
M_CI=1.1x10^7 M_sun, which corresponds to ~5x10^-4 times the total molecular
gas mass. We also searched for H2O(J_KaKc=2_12-1_01) emission, and obtained a
sensitive line luminosity limit of L'_H2O<4.4x10^9 K kms pc^2, i.e., <15% of
the CO(J=3-2) luminosity. The warm, highly excited molecular gas, atomic gas
and dust in this quasar host at the end of cosmic reionization maintain an
intense starburst that reaches surface densities as high as predicted by (dust
opacity) Eddington limited star formation over kiloparsec scales.
