NIR spectroscopy of SDSS J0303-0019: a low luminosity, high Eddington
  ratio quasar at z~6
  We present sensitive near--infrared VLT ISAAC spectroscopic observations of
the z=6.08 quasar SDSS J030331.40-001912.9. This QSO is more than a magnitude
fainter than other QSOs at z~6 for which NIR spectroscopy has been obtained to
date and is therefore presumably more representative of the QSO population at
the end of Cosmic Reionization. Combining rest--frame UV continuum luminosity
with the width measurements of the Mg II and C IV lines, we derive a black hole
mass of 2(+1.0/-0.5) x 10^8 solar masses, the lowest mass observed for z~6 QSOs
to date, and derive an Eddington ratio of 1.6(+0.4/-0.6), amongst the highest
value derived for QSOs at any redshift. The Spitzer 24 micron non--detection of
this QSO does not leave space for a significant hot dust component in its
optical/near--infrared SED, in common with one other faint QSO at z=6, but in
contrast to more than twenty more z=6 QSOs and all known lower redshift QSOs
with sufficiently deep multi-wavelength photometry. We conclude that we have
found evidence for differences in the intrinsic properties of at least one z~6
QSO as compared to the lower--redshift population.
