A Lyman alpha halo around a quasar at redshift z=6.4
  We present long-slit spectroscopic data which reveals extended Lyman alpha
emission around the z=6.417 radio-quiet quasar CFHQS J2329-0301. The Lyman
alpha emission is extended over 15 kpc and has a luminosity of > 8 x 10^36 W,
comparable to the most luminous Lyman alpha halos known. The emission has
complex kinematics, in part due to foreground absorption which only partly
covers the extended nebula. The velocity ranges from -500 km/s to +500 km/s,
with a peak remarkably close to the systemic velocity identified by broad MgII
emission of the quasar. There is no evidence for infall or outflow of the halo
gas. We speculate that the Lyman alpha emission mechanism is recombination
after quasar photo-ionization of gas sitting within a high-mass dark matter
halo. The immense Lyman alpha luminosity indicates a higher covering factor of
cold gas compared to typical radio-quiet quasars at lower redshift.
