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 & 6.5 quasars discovered using the Pan-STARRS1 survey. We use a sample of 15 z & 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 &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 ∼3× higher than a quasar sample at z ∼1; (2) we estimate the quasars’ black hole masses (MBH ∼0.3−5 × 109 M☉) 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 h(Lbol/LEdd)i = 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 ∼ 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 µm 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.
|Original language||English (US)|
|State||Published - Oct 3 2017|
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