Low-redshift Lyman continuum leaking galaxies with high [OIII]/[OII] ratios

TL;DR

This study observes five low-redshift star-forming galaxies with high [OIII]/[OII] ratios, detecting Lyman continuum emission and establishing correlations between escape fractions, emission line ratios, and velocity separations, highlighting potential indicators of ionizing radiation escape.

Contribution

First detection of LyC emission in galaxies with high O32 ratios at low redshift, establishing Vsep as an indirect indicator of LyC escape fraction.

Findings

LyC escape fractions range from 2% to 72%.

A tight anti-correlation exists between fesc(LyC) and Vsep.

LyC escape fraction increases with O32 and decreases with stellar mass.

Abstract

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 O32=[OIII]5007/[OII]3727 ~ 8-27 aiming to detect the Lyman continuum (LyC) emission. We detect LyC emission in all galaxies with the escape fractions fesc(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 Vsep varying from ~153 km/s to ~345 km/s. We find a general increase of the LyC escape fraction with increasing O32 and decreasing stellar mass M*, but with a large scatter of fesc(LyC). A tight anti-correlation is found between fesc(LyC) and Vsep making Vsep 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.