Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios.

We present observations with the Cosmic Origins Spectrograph (COS) 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 O32 = [O  iii ] λ5007/[O  ii ] λ3727 ∼ 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 Lyα 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 ∼153 to ∼345 km s−1. We find a general increase of the LyC escape fraction with increasing O32 and decreasing stellar mass M ⋆, but with a large scatter of f esc(LyC). A tight anticorrelation 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. [ABSTRACT FROM AUTHOR]