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Durham University

Department of Physics

Staff profile

Publication details for Dr Nigel Metcalfe

Mazzucchelli, C., Bañados, E., Venemans, B. P., Decarli, R., Farina, E. P., Walter, F., Eilers, A.-C., Rix, H.-W., Simcoe, R., Stern, D., Fan, X., Schlafly, E., Rosa, G. De, Hennawi, J., Chambers, K. C., Greiner, J., Burgett, W., Draper, P. W., Kaiser, N., Kudritzki, R.-P., Magnier, E., Metcalfe, N., Waters, C. & Wainscoat, R. J. (2017). Physical Properties of 15 Quasars at z ≳ 6.5. The Astrophysical Journal 849(2): 91.

Author(s) from Durham


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 CIV 1549\AAemission 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 MgII 2798\AAemission 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.