Michele Perna, Santiago Arribas, Luca Costantin, Pablo G. Pérez-González, C. Prieto-Jiménez, Bruno Rodríguez Del Pino, Francesco D'Eugenio, Isabella Lamperti, Filippo Mannucci, Hannah Übler, Giovanni Cresci, Torsten Böker, Andrew J. Bunker, Stefano Carniani, Stéphane Charlot, Roberto Maiolino, Elena Bertola, Daniel Ceverino, Chiara Circosta, Jan Scholtz, L. Ulivi, Giacomo Venturi
Collisional ring galaxies are a rare class of interacting systems, comprising only ∼ 0.01% of galaxies in the local Universe. Their formation is typically attributed to a head-on collision of a massive galaxy with a compact satellite (intruder), triggering density waves propagating outwards that produce the characteristic ring morphology. Here, we report the discovery and detailed analysis of the most distant ring galaxy known to date, at z=3.076, based on JWST data obtained within of the GA-NIFS programme. This work aims to characterise the physical and dynamical properties of and shed light on the formation of its ring. Specifically, we analysed the ionised gas properties, stellar populations, and gas kinematics of the system, and used the observed geometry to constrain the timescale of the collision. Our analysis is based on NIRSpec integral field spectrograph (IFS) data, including low-resolution (R spectroscopy covering 0.6--5.3 μm (∼0.2--1.3 μm rest-frame), and high-resolution (R spectroscopy covering 1.66--3.17 μm (0.4--0.8 μm rest-frame). Multi-wavelength techniques (e.g. emission line diagnostics, full spectral fitting, and gas dynamics) were applied to derive nebular gas conditions and stellar population properties. Gas kinematic analysis reveals that exhibits a rotating disc component with an additional radial expansion velocity of ∼ 200 ̨ms, consistent with a propagating collisional wave. Nebular line diagnostics indicate an intense star formation (star formation rate SFR ∼ 100 along the ring and in the nucleus. Stellar population analysis shows that the most recent star formation episode, occurring within the last ≈ 50 Myr, predominantly took place in the ring. We also identify a close companion, the intruder galaxy responsible for the collision, moving away with a relative velocity of ∼ 425 ̨ms. The evidence favours a collisional origin for the ring in though the presence of a recently formed bar (and hence a resonance ring) cannot be completely excluded. This discovery provides a unique window to the physics of galaxy interactions and the rapid assembly of stellar structures in the early Universe.