Radio Signatures of a Massive Black Hole in GHZ9 at z $\sim$ 10

TL;DR

This paper assesses the detectability of a massive black hole in galaxy GHZ9 at z~10 via radio observations, showing that next-generation radio telescopes could confirm its presence within reasonable observation times.

Contribution

It provides the first estimates of radio fluxes from a high-redshift black hole candidate and evaluates the capabilities of SKA and ngVLA for their detection.

Findings

ngVLA can detect GHZ9's radio emission in 1 hour

SKA requires up to 100 hours for detection

Radio signals can be distinguished from other sources

Abstract

Synergies between the {\em James Webb Space Telescope} ({\em JWST}) and the {\em Chandra} X-ray observatory have advanced the observational frontier by detecting a handful of active galactic nuclei (AGNs) beyond $z \sim$ 10. In particular, the recent discovery of a candidate $\rm 8 \times 10^7~M_{\odot}$ black hole (BH) in the galaxy GHZ9 at $z =$ 10.4 favors massive seed formation channels for these objects. Motivated by prospects for their detection in radio by recent studies, we estimate radio fluxes for GHZ9 and explore the possibility of their detection with the Square Kilometer Array (SKA) and next-generation Very Large Array (ngVLA). We find that ngVLA should be able to detect radio emission from GHZ9 for integration times as short as 1 hr while SKA will require integration times of up to 100 hr. We also find that radio emission from the BH can be distinguished from that due to H II regions and supernovae in its host galaxy. The detection of a few hundred nJy radio signal at frequencies $> 2$ GHz will be a smoking gun for the presence of a BH in GHZ9.