GA-NIFS: NIRSpec reveals evidence for non-circular motions and AGN feedback in GN20

Abstract

We present rest-frame optical data of the z ∼ 4 submillimetre galaxy GN20 obtained with the JWST Near Infrared Spectrograph (NIRSpec) in integral field spectroscopy mode. The Hα emission is asymmetric and clumpy and extends over a projected distance of >15 kpc. To first order, the large-scale ionized gas kinematics are consistent with a turbulent (σ ∼ 90 km s−1), rotating disc (vrot ∼ 500 km s−1), congruent with previous studies of its molecular and ionized gas kinematics. However, we also find clear evidence for non-circular motions in the Hα kinematics. We discuss their possible connection with various scenarios, such as external perturbations, accretion, or radial flows. In the centre of GN20, we find broad-line emission (full width at half-maximum ∼ 1000−2000 km s−1) in the Hα + [N II] complex, suggestive of fast, active galactic nucleus-driven winds or, alternatively, of the broad-line region of an active black hole. Elevated values of [N II] λ6583/Hα > 0.4 and of the Hα equivalent width EW(Hα) > 6 Å throughout large parts of GN20 suggest that feedback from the active black hole is able to photoionize the interstellar medium. Our data corroborate that GN20 offers a unique opportunity to observe key processes in the evolution of the most massive present-day galaxies acting in concert, over 12 billion years ago.