Radio signals from early direct collapse black holes

Abstract

We explore the possibility to detect the continuum radio signal from direct collapse black holes (DCBHs) by upcoming radio telescopes such as the SKA and ngVLA, assuming that after formation they can launch and sustain powerful jets at the accretion stage. We assume that the high-𝑧 DCBHs have similar jet properties as the observed radio-loud AGNs, then use a jet model to predict their radio flux detectability. If the jet power 𝑃 jet 10 42−43 erg s −1 , it can be detectable by SKA/ngVLA, depending on the jet inclination angle. Considering the relation between jet power and black hole mass and spin, generally, jetted DCBHs with mass 10 5 𝑀 can be detected. For a total jetted DCBH number density of ∼ 2.5 × 10 −3 Mpc −3 at 𝑧 = 10, about 100 deg −2 𝑧 −1 DCBHs are expected to be above the detection threshold of SKA1-mid (100 hours integration). If the jet "blob" emitting most of the radio signal is dense and highly relativistic, then the DCBH would only feebly emit in the SKA-low band, because of self-synchrotron absorption (SSA) and blueshift. Moreover, the free-free absorption in the DCBH envelope may further reduce the signal in the SKA-low band. Thus, combining SKAlow and SKA-mid observations might provide a potential tool to distinguish a DCBH from a normal star-forming galaxy.

Radio Power from Direct-Collapse Black Holes

“…Nascent DCBHs would be free of competing sources of radio emission in their host halos that are present in CR7, such as young supernova remnants (SNRs; Meiksin & Whalen 2013) and H II regions due to star formation (Condon 1992), because they form in halos before other stars. Yue & Ferrara (2021) recently estimated DCBH radio fluxes under the assumption that they drive strong jets and found that they should be detectable by the SKA and ngVLA at z ∼ 10, depending on the inclination angle of the jet. However, steady jets have only been observed in active galactic nuclei with luminosities L 0.01 L Edd , where L Edd is the Eddington limit, and intermittent jets have been seen in quasars at L ∼ L Edd (Merloni & Heinz 2008).…”