Quasars are galaxies hosting accreting supermassive black holes ; due to their brightness , they are unique probes of the early universe .
To date , only few quasars have been reported at z > 6.5 ( < 800 Myr after the Big Bang ) .
In this work , we present six additional z \gtrsim 6.5 quasars discovered using the Pan-STARRS1 survey .
We use a sample of 15 z \gtrsim 6.5 quasars to perform a homogeneous and comprehensive analysis of this highest-redshift quasar population .
We report four main results : ( 1 ) the majority of z \gtrsim 6.5 quasars show large blueshifts of the broad C IV 1549Å emission line compared to the systemic redshift of the quasars , with a median value \sim 3 \times higher than a quasar sample at z \sim 1 ; ( 2 ) we estimate the quasars ’ black hole masses ( M _ { BH } \sim 0.3 - 5 \times 10 ^ { 9 } M _ { \odot } ) via modeling of the Mg II 2798Å emission line and rest-frame UV continuum ; we find that quasars at high redshift accrete their material ( with \langle ( L _ { \mathrm { bol } } / L _ { \mathrm { Edd } } ) \rangle = 0.39 ) at a rate comparable to a luminosity-matched sample at lower - redshift , albeit with significant scatter ( 0.4 dex ) ; ( 3 ) we recover no evolution of the Fe II /Mg II abundance ratio with cosmic time ; ( 4 ) we derive near zone sizes ; together with measurements for z \sim 6 quasars from recent work , we confirm a shallow evolution of the decreasing quasar near zone sizes with redshift .
Finally , we present new millimeter observations of the [ CII ] 158 \mu m emission line and underlying dust continuum from NOEMA for four quasars , and provide new accurate redshifts and [ CII ] /infrared luminosities estimates .
The analysis presented here shows the large range of properties of the most distant quasars .