Letter to the Editor

Constraints on supermassive black hole binaries from JWST and NANOGrav

¹ Département de Physique Théorique, Université de Genève, 24 quai Ernest-Ansermet, 1211 Genève 4, Switzerland
e-mail: hamsa.padmanabhan@unige.ch
² Astronomy department, Harvard University, 60 Garden Street, Cambridge, MA 02138, USA
e-mail: aloeb@cfa.harvard.edu

Received: 8 January 2024
Accepted: 25 March 2024

Abstract

We use the recent statistics of dual active galactic nuclei (AGN) in the James Webb Space Telescope (JWST) data at z ∼ 3.4 to address two aspects of the feedback and evolution scenarios of supermassive black hole binaries. We find that the JWST data provide evidence for the members of a binary BH being ‘lit’ at the same time, rather than independently – a scenario which is consistent with gas-rich mergers being responsible for concurrent AGN activity. This conclusion is supported by the recent NANOGrav Pulsar Timing Array (PTA) measurements, whose upper limits on the stochastic gravitational wave strain amplitude lie below those expected from extrapolating the dual AGN fraction. The results indicate either a ‘stalling’ of the binaries at the separations probed by NANOGrav, or rapid gas-driven inspirals.