2023ApJ...951..105D

We investigate galactic winds in the HizEA galaxies, a collection of 46 late-stage galaxy mergers at z = 0.4-0.8, with stellar masses of $\mathrm{log}({M}_{* }/{M}_{\odot })=10.4\mbox{--}11.5$, star formation rates (SFRs) of 20-500 M_⊙ yr^–1, and ultra-compact (a few 100 pc) central star-forming regions. We measure their gas kinematics using the Mg IIλλ 2796,2803 absorption lines in optical spectra from MMT, Magellan, and Keck. We find evidence of outflows in 90% of targets, with maximum outflow velocities of 550-3200 km s^–1. We combine these data with ten samples from the literature to construct scaling relations for outflow velocity versus SFR, star formation surface density (Σ_SFR), M_*, and SFR/M_*. The HizEA galaxies extend the dynamic range of the scaling relations by a factor of ∼2-4 in outflow velocity and an order of magnitude in SFR and Σ_SFR. The ensemble scaling relations exhibit strong correlations between outflow velocity, SFR, SFR/R, and Σ_SFR, and weaker correlations with M_* and SFR/M_*. The HizEA galaxies are mild outliers on the SFR and M_* scaling relations, but they connect smoothly with more typical star-forming galaxies on plots of outflow velocity versus SFR/R and Σ_SFR. These results provide further evidence that the HizEA galaxies' exceptional outflow velocities are a consequence of their extreme star formation conditions rather than hidden black hole activity, and they strengthen previous claims that Σ_SFR is one of the most important properties governing the velocities of galactic winds.