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.

The contribution of discrete sources to the sky temperature at 144 MHz

“…The other two deep fields do not constrain this because their completeness corrections are not reliable below this flux density level. We note that the implied downturn at the lowest flux densities is already in tension with some of the models proposed by Ewall-Wice et al (2020), which would imply flat or rising S 2 n below 1 mJy when we combine their sources with the star-forming galaxy population. However, we are at the limits of what can be done with the small numbers of sources in our EN1 sample and deeper LOFAR observations are needed to constrain the population at the lowest flux densities.…”

“…The existence of this background has motivated more exotic physical and astrophysical explanations, such as a role for radio-loud primordial black holes (e.g. Ewall-Wice, Chang, & Lazio 2020).…”

Can the Local Bubble explain the radio background?

“…An absorption feature of less than 1 per cent of the radio background emission has indeed been found by the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) at these frequencies (Bowman et al 2018). For the interpretation of the absorption feature as of cosmological origin, it is important to understand whether the radio E-mail: M.G.H.Krause@herts.ac.uk synchrotron background is produced locally or at high redshift (e.g., Monsalve et al 2019;Ewall-Wice et al 2020).…”

Tight constraints on the excess radio background at z = 9.1 from LOFAR

“…Bowman et al 2018;Feng & Holder 2018). Astrophysical sources such as supernovae or accreting supermassive black holes (Biermann et al 2014;Ewall-Wice et al 2018;Ewall-Wice, Chang & Lazio 2019;Jana, Nath & Biermann 2019;Mirocha & Furlanetto 2019) could produce such an extra radio background. However, these sources would need to be several orders of magnitude more efficient in producing synchrotron radiation than corresponding sources at low redshifts (see Sharma 2018;Ewall-Wice et al 2019), which is not very likely.…”

“…Astrophysical sources such as supernovae or accreting supermassive black holes (Biermann et al 2014;Ewall-Wice et al 2018;Ewall-Wice, Chang & Lazio 2019;Jana, Nath & Biermann 2019;Mirocha & Furlanetto 2019) could produce such an extra radio background. However, these sources would need to be several orders of magnitude more efficient in producing synchrotron radiation than corresponding sources at low redshifts (see Sharma 2018;Ewall-Wice et al 2019), which is not very likely. An extra radio background can also be created by more exotic agents such as active neutrinos (Chianese et al 2018), dark matter (Fraser et al 2018;Pospelov et al 2018), or superconducting cosmic strings (Brandenberger, Cyr & Schaeffer 2019).…”