Radio Emission from the First Quasars at $z \sim$ 6-15

Abstract

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 10$^4$ - 10$^5$ M$_{\odot}$ black holes at $z \sim$ 20 - 25, which then rapidly grow in the low-shear environments of rare, massive halos fed by strong accretion flows. Sensitive new radio telescopes such as the Next-Generation Very Large Array (ngVLA) and the Square Kilometer Array (SKA) could probe the evolution of these objects at much earlier times. Here, we estimate radio flux from the first quasars at $z \sim$ 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 $\times$ 10$^9$ M$_{\odot}$ black hole at $z =$ 7.1, at much earlier stages of evolution, $z \sim$ 14 - 15, with 100 hr integration times in targeted searches. The advent of these new observatories, together with the James Webb Space Telescope (JWST), Euclid, and the Roman Space Telescope (RST), will inaugurate the era of $z \lesssim$ 15 quasar astronomy in the coming decade.