High-redshift galactic outflows: orientation effects, kinematics, and metallicity in TNG50 and SERRA

Galactic outflows driven by central black holes and supernovae play a crucial role in the formation and evolution of galaxies. Recently, JWST/NIRSpec observations have provided the first detections of warm ionised outflows in low-mass (M_⋆ ∼ 10^7 _⊙) galaxies at high redshifts (z>3), revealing an occurrence rate of 25-40% depending on the intensity of the emission lines. This fraction is lower than predicted by theoretical models and simulations, which suggest that fast outflowing gas should be a common feature of all star-forming galaxies in the early Universe. M In order to better understand the discrepancies between simulations and observations, we identified and characterised outflows in high-redshift galaxies using the TNG50 cosmological and SERRA zoom-in simulations. Our study examines how outflow detectability depends on the line of sight, explores the properties of the fast gas, and investigates its relationship with key galactic properties. We analysed approximately 6 , _⊙. Outflows in the immediate vicinity of each galaxy were identified using a Gaussian mixture model algorithm that uses the gas velocity, star formation rate, and location as input parameters. We subsequently compared the simulated outflows to those observed in the JWST/JADES NIRSpec survey. galaxies from TNG50 and 3 --10^ galaxies from SERRA over the redshift ranges z=3--5 and z=4--5, respectively, spanning stellar masses of M_⋆ = 10^ 7.5 11 M Outflow masses in both TNG50 and SERRA broadly reproduce the JWST/JADES measurements within roughly 0.5 dex, though simulations tend to predict slightly higher values, suggesting that optical emission lines capture only a fraction of the multiphase outflow. However, simulated outflow velocities are typically an order of magnitude lower than those inferred from observations. TNG50 indicates a clear orientation dependence since outflows in face-on galaxies are approximately 15 percent more likely to be detected than in edge-on systems, with this difference increasing to nearly 40 percent for more massive, disc-shaped galaxies.