The possible accretion discs of GN-z11 at redshift <i>z</i> = 10.6, MoM-z14 at <i>z</i> = 14.44, and other high-redshift objects

ABSTRACT The James Webb Space Telescope has enabled the discovery of active galactic nuclei at high redshifts. The intrinsic ultraviolet (UV) spectrum of GN-z11 at redshift $z=10.6$ has a spectral slope compatible with a standard accretion disc. By fitting a disc model to its spectrum, we find that the mass of the black hole must be above $1.12\times 10^7 \, {{\rm M}_{\odot }}$ so that it lies below the Eddington limit. We define this mass as the Eddington mass of the black hole. We note that the spectral shape is consistent with that of accreting stellar mass black hole sources in their soft state, for which no variability is expected. MoM-z14 is a more distant object at $z=14.44$ and has a similar UV slope. Disc model-fitting gives a similar result but a lower mass accretion rate. We also examine three further high-redshift objects: GS-z14-1, GHZ2, and PAN-z14-1 at $z=13.86$, 12.34, and 13.53, again obtaining similar results. If sub-Eddington accretion discs are indeed the origin of much of the UV emission from these objects, then the existence of massive black holes less than 304 and 290 Myr after the big bang points either to exceptional black hole seeds or to primordial black holes. The observed spread of UV spectral slopes in high-redshift objects suggests that our approach may be relevant to about half of that population.