Compact Starburst Galaxies With Fast Outflows: Central Escape Velocities And Stellar Mass Surface Densities From Multiband Hubble Space Telescope Imaging

We present multiband Hubble Space Telescope imaging that spans rest-frame near-ultraviolet through nearinfrared wavelengths (lambda(rest) = 0.3-1.1 mu m) for 12 compact starburst galaxies at z = 0.4-0.8. These massive galaxies (M-star similar to 10(11) M-circle dot) are driving very fast outflows (v(max) = 1000-3000 km s(-1)), and their light profiles are dominated by an extremely compact starburst component (half-light radius similar to 100 pc). Our goal is to constrain the physical mechanisms responsible for launching these fast outflows by measuring the physical conditions within the central kiloparsec. Based on our stellar population analysis, the central component typically contributes approximate to 25% of the total stellar mass, and the central escape velocities v(esc, central) approximate to 900 km s(-1) are a factor of two smaller than the observed outflow velocities. This Requires physical mechanisms that can accelerate gas to speeds significantly beyond the central escape velocities, and it makes clear that these fast outflows are capable of traveling into the circumgalactic medium, and potentially beyond. We find central stellar densities Sigma(e, central) approximate to 3 x 10(11) M-circle dot kpc(-2) comparable to theoretical estimates of the Eddington limit, and we estimate Sigma(1) surface densities within the central kiloparsec comparable to those of compact massive galaxies at 0.5 < z < 3.0. Relative to "red nuggets" and "blue nuggets" at z similar to 2, we find significantly smaller r(e) values at a given stellar mass, which we attribute to the dominance of a young stellar component in our sample and the better physical resolution for rest-frame optical observations at z similar to 0.6 versus z similar to 2. We compare to theoretical scenarios involving major mergers and violent disk instability, and we speculate that our galaxies are progenitors of power-law ellipticals in the local universe with prominent stellar cusps.