2017/10/03 by C. Mazzucchelli, E. Bañados, B. P. Venemans +21
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aa9185
29 pages, 18 figures; accepted by ApJ
arxiv created 2017/10/03 · arxiv updated 2017/11/15
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\gtrsim6.5 quasars show large blueshifts of the broad CIV 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 (M\rmBH∼0.3-5 × 109 M\odot) via modeling of the MgII 2798Å emission line and rest-frame UV continuum; we find that quasars at high redshift accrete their material (with ⟨ (Lbol/LEdd) ⟩ = 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 FeII/MgII 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.