This work stands apart: nearby studies focus on intermediate-mass black holes, shadows of giant black holes against ancient light, and neutrino signatures of dark matter. Neighboring works investigate black hole growth and their influence on galaxies, but dynamical mass measurements at high redshifts have so far failed. Previous attempts at z>6 found no clear black hole signal due to complex gas kinematics or carbon ionization. This work is the first to select an object where the sphere of influence is large enough and obscuration protects the [C ii] line from destruction.
Observations of the [C ii] 157.7 μm line in quasar W2246–0526 were made with ALMA using a synthesized beam of 0.089″×0.053″ (uniform weighting) and 0.13″×0.09″ (natural). The data were divided into elliptical rings, and in each spectrum a Gaussian component for the host galaxy turbulence and components for outflows were extracted. The velocity dispersion profile, excluding outflows, was modeled including the black hole gravity, the galaxy mass (Sersic profile), and beam smearing. The black hole mass was determined using Markov chain Monte Carlo.
The gas velocity dispersion increases toward the center from 186 km/s at 1.5 kpc to 300 km/s in the central beam. The best model gives a black hole mass of 6.3±0.14×10⁹ M☉ and a galaxy mass within a radius of 1.31+0.34−0.39×10¹⁰ M☉. The black hole's sphere of influence has a diameter of 2.30+0.78−0.40 kpc, four times larger than predicted from low resolution due to unaccounted outflows. The Eddington ratio of 1.58±0.04 indicates super-Eddington accretion. A model without a black hole yields an unrealistically compact galaxy and a worse χ² (10.13 vs. 4.38), confirming the need for a black hole.
Unlike neighbors that searched for dynamical masses in unobscured quasars at z>6 and found no signal, this work shows that heavily obscured quasars are ideal targets: dust shields X-ray radiation, preserving the [C ii] line near the nucleus. The agreement of the dynamical mass with the Mg II-based estimate confirms the reliability of the empirical method for hyperluminous quasars. This opens the way to statistically test mass–luminosity relations in the early universe.
The method can be applied to a sample of heavily obscured quasars to gather statistics on dynamical masses and calibrate single-epoch estimates. Observations with even higher resolution (e.g., with a next-generation interferometer) would resolve the spheres of influence of less massive black holes. Studying outflows and their connection to super-Eddington accretion will clarify the feedback mechanism.
The result will impact studies of galaxy–black hole coevolution, calibration of empirical mass estimation methods, and models of feedback during super-Eddington accretion.
Expand the sample of obscured quasars with high-resolution [C ii]; study in detail the kinematics of outflows and their connection to accretion.
This work directly addresses the unresolved problem of supermassive black hole–galaxy coevolution: why distant quasars host overmassive black holes relative to local relations. Dynamical masses are necessary to distinguish a real deviation from systematic errors in empirical methods.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This work provides the first dynamical measurement of the mass of a supermassive black hole at z = 4.6, based on the increase in gas velocity dispersion in the [C ii] line toward the center of the heavily obscured quasar W2246–0526. Modeling that accounts for outflows and beam smearing yields a mass of 6.3×10⁹ M☉ and a sphere of influence with a diameter of 2.3 kpc.
Where its strength is
By targeting an obscured quasar, where dust shields the X-ray emission and preserves the [C ii] line near the nucleus, this work opens a new class of objects for dynamical black hole mass measurements in the early Universe.
Where it could go next
Worth trying
Why this may matter
This work paves the way for systematic measurements of supermassive black hole masses in the early Universe, which is critical for understanding their rapid growth and coevolution with galaxies.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.56, against a usual 0.64. It looks like few have drilled nearby.
The black hole in W2246–0526 has a mass equivalent to about 6.3 billion Suns, and its sphere of influence extends 2300 light-years, which is like the distance from the Sun to the nearest star multiplied by 500.