Feedback and dynamical masses in high- z galaxies: the advent of high-resolution NIRSpec spectroscopy

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Stellar feedback is an essential step in the baryon cycle of galaxies, but it remains unconstrained beyond Cosmic Noon. We study the dynamical mass and gas-flow properties of a sample of 16 sub-L star-forming galaxies at 4≤ z≤ 7.6, using high-resolution James Webb Space Telescope Near InfraRed Spectrograph (NIRSpec) observations. From the velocity dispersion of the (resolved) emission lines (σ gas ~(km~s⁻¹) 38-96) and the galaxy size (rₑ=400-960~pc), we estimate dynamical masses of log Mdyn/ M=9.25-10.25. Stellar-to-dynamical mass ratios are low (log M/Mdyn∈ [-0.5,-2]) and decrease with increasing star formation rate surface density (Σ SFR). We estimate gas surface densities assuming a star formation law, but the gas masses do not balance the baryon-to-dynamical mass ratios, requiring a lower star formation efficiency. Evidence of ionized outflows is found in five galaxies, based on broad components reproducing the emission-line wings. We only observe outflows from galaxies undergoing recent bursts of star formation SFR₁₀/SFR₁₀₀≥ 1, with elevated Σ SFR and low M/Mdyn. This links high gas surface densities to increased outflow incidence and lower M/Mdyn. With moderate outflow velocities (vflow ~(km~s⁻¹)=150-250) and mass outflow rates (Ṁflow/ M yr⁻¹=0.2-5), these high-redshift galaxies appear more efficient at removing baryons than low-redshift galaxies with similar M, showing mass-loading factors of Ṁflow/ SFR=0.04-0.4. For their dynamical mass, outflow velocities exceed the escape velocities, meaning they may eventually enrich the circumgalactic medium.