Gemini GNIRS near-infrared spectroscopy of 50 quasars at z>~5.7

TL;DR

This study uses near-infrared spectroscopy to analyze 50 quasars at redshifts above 5.7, revealing that their spectral properties and black hole characteristics are similar to lower-redshift quasars, indicating mature, actively accreting supermassive black holes.

Contribution

First comprehensive near-IR spectral analysis of 50 high-redshift quasars showing their properties match those of lower-redshift counterparts, suggesting early black hole maturity.

Findings

High-z quasars have similar spectra to low-z quasars when matched in luminosity.

No evidence of super-Eddington accretion or hypermassive black holes in the sample.

Mild excess of weak CIV lines in high-z quasars.

Abstract

We report initial results from a large Gemini program to observe z>~5.7 quasars with GNIRS near-IR spectroscopy. Our sample includes 50 quasars with simultaneous ~0.85-2.5 micron spectra covering the rest-frame ultraviolet and major broad emission lines from Ly-alpha to MgII. We present spectral measurements for these quasars and compare to their lower-redshift counterparts at z=1.5-2.3. We find that when quasar luminosity is matched, there are no significant differences between the rest-UV spectra of z>~5.7 quasars and the low-z comparison sample. High-z quasars have similar continuum and emission line properties and occupy the same region in the black hole mass and luminosity space as the comparison sample, accreting at an average Eddington ratio of ~0.3. There is no evidence for super-Eddington accretion or hypermassive (>10^10 Msun) black holes within our sample. We find a mild excess of quasars with weak CIV lines relative to the control sample. Our results, corroborating earlier studies but with better statistics, demonstrate that these high-z quasars are already mature systems of accreting supermassive black holes operating with the same physical mechanisms as those at lower redshifts.