Lyman continuum leakage from low-mass galaxies with Mstar < 1.E8 Msun

TL;DR

This study investigates Lyman continuum leakage in low-mass galaxies, revealing that velocity separation of Ly-alpha peaks is a strong indicator of LyC escape, but lower stellar mass does not necessarily mean higher escape fractions.

Contribution

It provides new observational evidence linking LyC escape fractions to Ly-alpha peak separation in low-mass galaxies, expanding understanding beyond higher-mass samples.

Findings

LyC escape fractions range from 11-35% in detected galaxies.

Vsep correlates strongly with LyC escape fraction.

No observed increase in LyC leakage with decreasing stellar mass.

Abstract

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine low-mass star-forming galaxies at redshifts, z, in the range 0.3179-0.4524, with stellar masses Mstar < 10^8 M and veruny high specific star-formation rates sSFR~150-630 Gyr^{-1}, aiming to study the dependence of leaking Lyman continuum (LyC) emission on stellar mass and some other characteristics of the galaxy. We detect LyC emission in four out of nine galaxies with escape fractions, fesc(LyC), in the range of 11-35 per cent, and establish upper limits for fesc(LyC) in the remaining five galaxies. We observe a narrow Ly-alpha emission line with two peaks in seven galaxies and likely more complex Ly-alpha profiles in the two remaining galaxies. The velocity separation between the peaks Vsep varies in the range from ~229 km/s to ~512 km/s. Our additional data on low-mass galaxies confirm and strengthen the tight anti-correlation between fesc(LyC) and Vsep found for previous low-redshift galaxy samples with higher stellar masses. Vsep remains the best indirect indicator of LyC leakage. It is better than O32 on which fesc(LyC) depends weakly, with a large scatter. Finally, contrary to expectations, we find no increase of fesc(LyC) with decreasing galaxy stellar mass Mstar.