Detection of high Lyman continuum leakage from four low-redshift compact
  star-forming galaxies
  Following our first detection reported in Izotov et al. (2016), we present
the detection of Lyman continuum (LyC) radiation of four other compact
star-forming galaxies observed with the Cosmic Origins Spectrograph (COS)
onboard the Hubble Space Telescope (HST). These galaxies, at redshifts of
z~0.3, are characterized by high emission-line flux ratios [OIII]5007/[OII]3727
> 5. The escape fractions of the LyC radiation fesc(LyC) in these galaxies are
in the range of ~6%-13%, the highest values found so far in low-redshift
star-forming galaxies. Narrow double-peaked Lyalpha emission lines are detected
in the spectra of all four galaxies, compatible with predictions for Lyman
continuum leakers. We find escape fractions of Lyalpha, fesc(Lyalpha) ~20%-40%,
among the highest known for Lyalpha emitters (LAEs). Surface brightness
profiles produced from the COS acquisition images reveal bright star-forming
regions in the center and exponential discs in the outskirts with disc scale
lengths alpha in the range ~0.6-1.4 kpc. Our galaxies are characterized by low
metallicity, ~1/8-1/5 solar, low stellar mass ~(0.2 - 4)e9 Msun, high star
formation rates SFR~14-36 Msun/yr, and high SFR densities Sigma~2-35
Msun/yr/kpc^2. These properties are comparable to those of high-redshift
star-forming galaxies. Finally, our observations, combined with our first
detection reported in Izotov et al. (2016), reveal that a selection for compact
star-forming galaxies showing high [OIII]5007/[OII]3727 ratios appears to pick
up very efficiently sources with escaping Lyman continuum radiation: all five
of our selected galaxies are LyC leakers.
