Extending the Dynamic Range of Galaxy Outflow Scaling Relations: Massive Compact Galaxies with Extreme Outflows

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 log(M-*/M-circle dot) = 10.4-11.5, star formation rates (SFRs) of 20-500 M-circle dot yr(-1), and ultra-compact (a few 100 pc) central star-forming regions. We measure their gas kinematics using the Mg II lambda lambda 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 (Sigma(SFR)), M-*, and SFR/M-*. The HizEA galaxies extend the dynamic range of the scaling relations by a factor of similar to 2-4 in outflow velocity and an order of magnitude in SFR and Sigma(SFR). The ensemble scaling relations exhibit strong correlations between outflow velocity, SFR, SFR/R, and Sigma(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 Sigma(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 Sigma(SFR) is one of the most important properties governing the velocities of galactic winds.