We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of five star-forming galaxies at redshifts z in the range 0.2993 – 0.4317 and with high emission-line flux ratios O _ { 32 } = [ O iii ] \lambda 5007/ [ O ii ] \lambda 3727 \sim 8 – 27 aiming to detect the Lyman continuum ( LyC ) emission .
We detect LyC emission in all galaxies with the escape fractions f _ { esc } ( LyC ) in a range of 2 – 72 per cent .
A narrow Ly \alpha emission line with two peaks in four galaxies and with three peaks in one object is seen in medium-resolution COS spectra with a velocity separation between the peaks V _ { sep } varying from \sim 153 km s ^ { -1 } to \sim 345 km s ^ { -1 } .
We find a general increase of the LyC escape fraction with increasing O _ { 32 } and decreasing stellar mass M _ { \star } , but with a large scatter of f _ { esc } ( LyC ) .
A tight anti-correlation is found between f _ { esc } ( LyC ) and V _ { sep } making V _ { sep } a good parameter for the indirect determination of the LyC escape fraction .
We argue that one possible source driving the escape of ionizing radiation is stellar winds and radiation from hot massive stars .