Lyman Continuum Escape Fraction in Ly$α$ Emitters at $z\simeq3.1$

Abstract: We measure the LyC escape fraction in 54 faint Lyman Alpha Emitters (LAEs) at $z\simeq3.1$ in the GOODS-South field. With the average magnitude of $R=26.7$ AB ($M_{UV}=-18.8$, $L\simeq0.1L^*$), these galaxies represent a population of compact young dwarf galaxies. Their properties are likely to resemble those in the galaxies responsible for reionising the Universe at $z>6$. We do not detect LyC emission in any individual LAEs in the deep {\em HST} F336W images, which covers the rest-frame 820\r{A}. 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 $f_{\rm esc}<14-32\%$. However, the high Ly$\alpha$ rest-frame equivalent width, low stellar mass and UV luminosity of these LAEs suggest that they should have $f_{\rm esc}>50\%$. The low LyC escape fraction from this work and other stacking analysis suggest that the LyC leaking galaxies with $f_{\rm esc} > 50\%$ at $z=2-3$ do not follow the relation between the $f_{\rm esc}$ and UV luminosity and Ly$\alpha$ equivalent width (EW) derived from typical galaxies at similar redshift. Therefore, the UV luminosity and Ly$\alpha$ equivalent width (EW) are not the best indicators for the LyC escape fraction.