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

Abstract

We present observations with the Cosmic Origins Spectrograph onboard the\nHubble Space Telescope of five star-forming galaxies at redshifts z in the\nrange 0.2993-0.4317 and with high emission-line flux ratios\nO32=[OIII]5007/[OII]3727 ~ 8-27 aiming to detect the Lyman continuum (LyC)\nemission. We detect LyC emission in all galaxies with the escape fractions\nfesc(LyC) in a range of 2-72 per cent. A narrow Ly-alpha emission line with two\npeaks in four galaxies and with three peaks in one object is seen in\nmedium-resolution COS spectra with a velocity separation between the peaks Vsep\nvarying from ~153 km/s to ~345 km/s. We find a general increase of the LyC\nescape fraction with increasing O32 and decreasing stellar mass M*, but with a\nlarge scatter of fesc(LyC). A tight anti-correlation is found between fesc(LyC)\nand Vsep making Vsep a good parameter for the indirect determination of the LyC\nescape fraction. We argue that one possible source driving the escape of\nionizing radiation is stellar winds and radiation from hot massive stars.\n