GA-NIFS: NIRSpec reveals evidence for non-circular motions and AGN feedback in GN20
Hannah Übler, Francesco D’Eugenio, Michele Perna, Santiago Arribas, Gareth C Jones, Andrew J. Bunker, Stefano Carniani, S. Charlot, R. Maiolino, Bruno Rodríguez Del Pino, Chris J. Willott, Torsten Böker, G. Cresci, Nimisha Kumari, Isabella Lamperti, Eleonora Parlanti, Jan Scholtz, Giacomo Venturi
Abstract
ABSTRACT We present rest-frame optical data of the $z\sim 4$ submillimetre galaxy GN20 obtained with the JWST Near Infrared Spectrograph (NIRSpec) in integral field spectroscopy mode. The H$\alpha$ 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 ($\sigma \sim 90$ km s$^{-1}$), rotating disc ($v_{\rm rot}\sim 500$ 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 H$\alpha$ 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 $\sim 1000{-}2000$ km s$^{-1}$) in the H$\alpha$ + [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] $\lambda 6583$/H$\alpha \ \gt\ 0.4$ and of the Hα equivalent width EW(H$\alpha)\ \gt\ 6$ 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.