NIR spectroscopy of SDSS J0303-0019: a low luminosity, high Eddington ratio quasar at z~6

TL;DR

This study presents near-infrared spectroscopy of a faint z~6 quasar, revealing a low black hole mass and high Eddington ratio, suggesting intrinsic differences from more luminous, higher-redshift quasars.

Contribution

First spectroscopic analysis of a faint z~6 quasar, showing its low black hole mass and high accretion rate, indicating diversity in early universe quasar properties.

Findings

Black hole mass of approximately 2 x 10^8 solar masses.

Eddington ratio of about 1.6, among the highest at any redshift.

Lack of significant hot dust component in the SED.

Abstract

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.