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

TL;DR

This study uses JWST/NIRSpec integral field spectroscopy to reveal complex gas kinematics, non-circular motions, and evidence of AGN feedback in the high-redshift galaxy GN20, shedding light on early galaxy evolution.

Contribution

First detailed integral field spectroscopic analysis of GN20 at z~4, uncovering non-circular motions and AGN feedback effects in a massive early galaxy.

Findings

Detection of asymmetric, clumpy Hα emission extending over 15 kpc.

Evidence of non-circular motions possibly due to external perturbations or accretion.

Broad emission lines indicating AGN-driven winds or active black hole activity.

Abstract

We present rest-frame optical data of the z~4 sub-millimeter galaxy GN20 obtained with JWST/NIRSpec in integral field spectroscopy (IFS) mode. The H$\alpha$ emission is asymmetric and clumpy and extends over a projected distance of more than 15 kpc. To first order, the large-scale ionised gas kinematics are consistent with a turbulent ($\sigma\sim90$ km/s), rotating disc ($v_{\rm rot}\sim500$ km/s), congruent with previous studies of its molecular and ionised 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 (FWHM $\sim1000-2000$ km/s) in the H$\alpha$+[N II] complex, suggestive of fast, AGN-driven winds or, alternatively, of the broad-line region of an active black hole. Elevated values of [N II]$\lambda6583$/H$\alpha>0.4$ and EW(H$\alpha)>6$ \r{A}, throughout large parts of GN20 suggest that feedback from the active black hole is able to photo-ionise the interstellar medium. Our data corroborates 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.