Lyman continuum escape fraction in Ly α emitters at z ≃ 3.1

Abstract

We measure the Lyman continuum (LyC) escape fraction in 54 faint Lyman-alpha emitters (LAEs) at z similar or equal to 3.1 in the GOODS-South field. With the average magnitude of R = 26.7 AB (M-UV = -18.8 and L similar or equal to 0.1L*), these galaxies represent a population of compact young dwarf galaxies. Their properties are likely to resemble those in the galaxies responsible for reionizing the Universe at z > 6. We do not detect LyC emission in any individual LAEs in the deep HST F336W images, which covers the rest-frame 820 angstrom. We do not detect the LyC emission of these LAEs in the stacked F336W images either. The 3 sigma upper limit of LyC escape fractions is f(esc) < 14-32 per cent. However, the high Ly alpha rest-frame equivalent width (EW), low stellar mass, and UV luminosity of these LAEs suggest that they should have f(esc) > 50 per cent. The low LyC escape fraction from this work and other stacking analyses suggests that the LyC-leaking galaxies with f(esc) > 50 per cent at z = 2-3 do not follow the relation between f(esc) and UV luminosity and Ly alpha EW derived from typical galaxies at similar redshifts. Therefore, the UV luminosity and Ly alpha EW are not the best indicators for the LyC escape fraction.