Physical Properties of Massive Compact Starburst Galaxies with Extreme
  Outflows
  We present results on the nature of extreme ejective feedback episodes and
the physical conditions of a population of massive ($\rm M_* \sim 10^{11}
M_{\odot}$), compact starburst galaxies at z = 0.4-0.7. We use data from
Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame
optical and near-IR spectra of 14 starburst galaxies with extremely high star
formation rate surface densities (mean $\rm \Sigma_{SFR} \sim 3000 \,M_{\odot}
yr^{-1} kpc^{-2}$) and powerful galactic outflows (maximum speeds v$_{98} \sim$
1000-3000 km s$^{-1}$). Our unique data set includes an ensemble of both
emission [OII]$\lambda\lambda$3726,3729, H$\beta$,
[OIII]$\lambda\lambda$4959,5007, H$\alpha$, [NII]$\lambda\lambda$6548,6583, and
[SII]$\lambda\lambda$6716,6731) and absorption MgII$\lambda\lambda$2796,2803,
and FeII$\lambda$2586) lines that allow us to investigate the kinematics of the
cool gas phase (T$\sim$10$^4$ K) in the outflows. Employing a suite of line
ratio diagnostic diagrams, we find that the central starbursts are
characterized by high electron densities (median n$_e \sim$ 530 cm$^{-3}$), and
high metallicity (solar or super-solar). We show that the outflows are most
likely driven by stellar feedback emerging from the extreme central starburst,
rather than by an AGN. We also present multiple intriguing observational
signatures suggesting that these galaxies may have substantial Lyman continuum
(LyC) photon leakage, including weak [SII] nebular emission lines. Our results
imply that these galaxies may be captured in a short-lived phase of extreme
star formation and feedback where much of their gas is violently blown out by
powerful outflows that open up channels for LyC photons to escape.
