Near - Infrared Spectroscopy of Sdss J 0303 - 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 −0.5 × 10 8 M⊙, the lowest mass observed for z ∼ 6 QSOs to date, and derive an Eddington ratio of 1.6 −0.6, amongst the highest value derived for QSOs at any redshift. The Spitzer 24μm 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. Subject headings: Galaxies: high-redshift — early Universe — quasars: emission lines — quasars: individual: SDSS J030331.40-001912.9