The Radio Scream from black holes at Cosmic Dawn: a semi-analytic model for the impact of radio-loud black holes on the 21 cm global signal

ABSTRACT

We use a semi-analytic model to explore the potential impact of a brief and violent period of radio-loud accretion on to black holes (The Radio Scream) during the Cosmic Dawn on the H i hyperfine 21 cm signal. We find that radio emission from supermassive black hole seeds can impact the global 21 cm signal at the level of tens to hundreds of per cent provided that they were as radio loud as $z\(≈ 1 black holes and obscured by gas with column depths of NH ≳ 1023 cm−2. We determine plausible sets of parameters that reproduce some of the striking features of the EDGES absorption feature including its depth, timing, and side steepness while producing radio/X-ray backgrounds and source counts that are consistent with published limits. Scenarios yielding a dramatic 21 cm signature also predict large populations of ∼\)\mu$Jy point sources that will be detectable in future deep surveys from the Square Kilometer Array (SKA). Thus, 21 cm measurements, complemented by deep point-source surveys, have the potential to constrain optimistic scenarios where supermassive black hole progenitors were radio loud.