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 ≃ 3.1 in the GOODS-South field. With the average magnitude of R = 26.7 AB (M_UV = -18.8 and L ≃ 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 Å. We do not detect the LyC emission of these LAEs in the stacked F336W images either. The 3σ upper limit of LyC escape fractions is f_esc< 14-32 per cent. However, the high Ly α 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 α EW derived from typical galaxies at similar redshifts. Therefore, the UV luminosity and Ly α EW are not the best indicators for the LyC escape fraction.