2024MNRAS.527..281I

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine most metal-deficient compact star-forming galaxies with oxygen abundances 12 + log(O/H) = 6.97-7.23, redshifts z = 0.02811-0.13320, and stellar masses M_⋆ ≤ 10⁷ M_⊙. We aim to study the properties of Ly α emission in these extremely metal-deficient objects. We find that all nine galaxies are Ly α emitters (LAEs). We examine various relations between the Ly α escape fraction f_esc(Ly α) and other characteristics - such as absolute UV magnitude, oxygen abundance, O₃₂ ratio, stellar mass, Lyman-alpha luminosity, and equivalent width EW(Ly α), ionizing photon production efficiency ξ_ion and velocity separation V_sep between the two peaks of the Ly α profile - of a large sample of LAEs, including our lowest metallicity galaxies and other objects from the literature. We find a relatively tight correlation between f_esc(Ly α) and two characteristics, EW(Ly α) and V_sep, whereas no correlation is found between f_esc(Ly α) and the oxygen abundance. We also find a relatively tight relation between the Ly α and LyC escape fractions. We propose to use the latter relation to estimate indirectly the escaping ionizing radiation in LAEs, when direct measurements of LyC emission are not possible. We show that the global properties of low-z LAEs are very similar to those of z > 6 galaxies. They are thus ideal local proxies for studying physical processes during the epoch of reionization of the Universe.