Diverse properties of Ly α emission in low-redshift compact star-forming galaxies with extremely high [O III]/[O II] ratios

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of eight compact star-forming galaxies at redshifts z = 0.02811-0.06540, with low oxygen abundances 12 + log(O/H) = 7.43-7.82 and extremely high emission-line flux ratios O-32 = [O III] lambda 5007/[O II] lambda 3727 similar to 22-39, aiming to study the properties of Ly alpha emission in such conditions. We find a diversity in Ly alpha properties. In five galaxies Ly alpha emission line is strong, with equivalent width (EW) in the range 45-190 angstrom. In the remaining galaxies, weak Ly alpha emission with EW(Ly alpha) similar to 2-7 angstrom is superposed on a broad Ly alpha absorption line, indicating a high neutral hydrogen column density N(H I) similar to (1 - 3)x 10(21) cm(-2). We examine the relation between the Ly alpha escape fraction f(esc)(Ly alpha) and the Lyman continuum escape fraction f(esc)(LyC), using direct measures of the latter in eleven low-redshift LyC leakers, to verify whether f(esc)(Ly alpha) can be an indirect measure of escaping LyC radiation. The usefulness of O-32, of the Ly alpha equivalent width EW(Ly alpha), and of the Ly alpha peak separation V-sep as indirect indicators of Ly alpha leakage is also discussed. It is shown that there is no correlation between O-32 and f(esc)(Ly alpha). We find an increase of f(esc)(Ly alpha) with increasing EW(Ly alpha) for EW(Ly alpha) <100 angstrom, but for higher EW(Ly alpha) greater than or similar to 150 angstrom the f(esc)(Ly alpha) is nearly constant attaining the value of similar to 0.25. We find an anticorrelation between f(esc)(Ly alpha) and V-sep, though not as tight as the one found earlier between f(esc)(LyC) and V-sep. This finding makes V-sep a promising indirect indicator of both the Ly alpha and ionizing radiation leakage.