GA-NIFS: Co-evolution within a highly star-forming galaxy group at <i>z</i> ∼ 3.7 witnessed by JWST/NIRSpec IFS
Bruno Rodríguez Del Pino, Michele Perna, Santiago Arribas, Francesco D’Eugenio, Isabella Lamperti, P. G. Pérez-González, Hannah Übler, Andrew J. Bunker, Stefano Carniani, S. Charlot, R. Maiolino, Chris J. Willott, Torsten Boeker, Jacopo Chevallard, G. Cresci, Mirko Curti, Gareth C. Jones, Eleonora Parlanti, Jan Scholtz, Giacomo Venturi
Abstract
We present NIRSpec IFS observations of a galaxy group around the massive GS_4891 galaxy at z ∼ 3.7 in GOODS-South that includes two other two systems, GS_4891_n to the north and GS_28356 to the east. These observations, obtained as part of the GTO Galaxy Assembly – NIRSpec IFS (GA-NIFS) program, allow us to study for the first time the spatially resolved properties of the interstellar medium (ISM) and the ionised gas kinematics of a galaxy at this redshift. Leveraging the wide wavelength range spanned with the high-dispersion grating (with resolving power R = 2700) observations, covering from [O II ] λλ 3726, 29 to [S II ] λλ 6716, 31, we explore the spatial distribution of the star formation rate, nebular attenuation, and gas metallicity, together with the mechanisms responsible for the excitation of the ionised gas. GS_4891 presents a clear gradient of gas metallicity (as traced by 12 + log(O/H)) by more than 0.2 dex from the southeast (where a star-forming clump is identified) to the northwest. The gas metallicity in the less massive northern system, GS_4891_n, is also higher by 0.2 dex than at the centre of GS_4891, suggesting that inflows of lower-metallicity gas might be favoured in higher-mass systems. The kinematic analysis shows that GS_4891 presents velocity gradients in the ionised gas consistent with rotation. The region between GS_4891 and GS_4891_n does not present high gas turbulence, which, together with the difference in gas metallicities, suggests that these two systems might be in a pre-merger stage. Finally, GS_4891 hosts an ionised outflow that extends out to r out = 1.5 kpc from the nucleus and reaches maximum velocities, v out , of approximately 400 km s −1 . Despite entraining an outflowing mass rate of Ṁ out ∼ 4 M ⊙ yr −1 , the low associated mass-loading factor, η ∼ 0.04, implies that the outflow does not have a significant impact on the star formation activity of the galaxy.