2024MNRAS.527L..37L

Nearly 300 quasars have now been found at z > 6, including nine at z > 7. They are thought to form from the collapse of supermassive primordial stars to 10⁴-10⁵ M_⊙ black holes at z ∼ 20-25, which then rapidly grow in the low-shear environments of rare, massive haloes fed by strong accretion flows. Sensitive new radio telescopes such as the Next-Generation Very Large Array (ngVLA) and the Square Kilometre Array (SKA) could probe the evolution of these objects at much earlier times. Here, we estimate radio flux from the first quasars at z ∼ 6-15 at 0.5-12.5 GHz. We find that SKA and ngVLA could detect a quasar like ULAS J1120+0641, a 1.35 × 10⁹ M_⊙ black hole at z = 7.1, at much earlier stages of evolution, z ∼ 14-16, with 100 h integration times in targeted searches. The advent of these new observatories, together with the JWST, Euclid, and the Roman Space Telescope, will inaugurate the era of z ≲ 15 quasar astronomy in the coming decade.