GA-NIFS: High prevalence of dusty and metal-enriched outflows in massive and luminous star-forming galaxies at <i>z</i>   ∼  3–9

We present the search and characterisation of ionised outflows in a sample of 15 star-forming systems at z ∼ 3 − 9 with no evidence of active galactic nuclei (AGNs) observed with the JWST/NIRSpec instrument in Integral Field Spectroscopic mode (IFS) as part of the ‘Galaxy Assembly with NIRSpec IFS’ (GA-NIFS) program. Some of the target systems are comprised of various individual galaxies, adding up to a total of 40 individual objects. Our sample encompasses the high mass end of the galaxy populations, with most of the sample having stellar masses within log 10 ( M ★ /M ⊙ ) = 9.5 − 11, while previous studies on high-z star formation driven outflows generally contain galaxies of log 10 ( M ★ /M ⊙ ) < 9.5. Leveraging the spatially resolved information and rest-frame optical coverage provided by NIRSpec IFS data, we analysed the [O III ] λ 5007 and H α emission lines to search for broad kinematic components associated with galactic outflows. Crucially, the IFS observations allowed us to directly isolate the regions hosting the outflows, rather than relying on integrated spectra. We identified signatures of ionised outflows in 16 individual galaxies/regions (in 13 out of 15 systems), although we consider two of them only as ‘candidates’, as they could be related to mergers or tidal interactions. After constraining their spatial location and extent, we characterised the integrated properties of the outflowing gas and evaluated the impact on the host galaxies. We find that the outflowing gas is more dust attenuated (by A V ∼ 0.59 mag on average) and metal enriched (∼0.13 dex) than the interstellar medium of the host galaxies, suggesting that outflows contribute to distributing dust and metals around them. The outflows identified in this study present velocity dispersions within σ out ∼ 130 − 340 km s −1 and outflow velocities V out ∼ 170 − 600 km s −1 . Considering also less luminous and less massive star-forming galaxies from previous works, there is a statistically significant correlation between outflow velocity ( v out ) and star formation rate (SFR). The generally low mass-loading factors ( η = Ṁ out /SFR < 1, in nine out of 14 outflows) obtained for the ionised outflows suggest that they do not suppress star formation in the host galaxies. Moreover, their velocities are not high enough to escape their hosts and reach the circumgalactic medium. Our results indicate that ejective feedback through ionised outflows is inefficient in high-mass and luminous star-forming galaxies within the first 2 Gyr of cosmic time.