Testing an indirect method for identifying galaxies with high levels of Lyman continuum leakage

Abstract

Using a sample of galaxies at $z\approx 3$ with detected Lyman Continuum (LyC) leakage in the SSA22 field, we attempt to verify a proposed indirect method for identifying cases with high LyC escape fraction $f_{\mathrm{esc}}$ based on measurements of the H${\hat{I}}^2$ equivalent width (EW) and the ${\hat{I}}^2$ slope of the UV continuum. To this end, we present Keck/MOSFIRE H${\hat{I}}^2$ emission line flux measurements of LyC galaxies (LCGs) at spectroscopic redshifts $z_{\mathrm{spec}}\sim 3.3$, Lyman break galaxies (LBGs) at photometric redshifts $z_{\mathrm{phot}}=2.7$--$3.7$, and Ly$\hat{I}\pm$ emitters at $z_{\mathrm{phot}}=3.1$. We also reconfirm the spectroscopic redshifts and measure the H${\hat{I}}^2$ emission line fluxes from 2 LCGs and 6 LBGs. For the LCG in our sample with the most extreme $f_{\mathrm{esc}}$, as revealed by the direct detection of LyC photons, we find that the EW(H${\hat{I}}^2$)--${\hat{I}}^2$ method gives a broadly consistent estimate for $f_{\mathrm{esc}}$, although the error bars remain very large. We also discuss how a combination of $f_{\mathrm{esc}}$ measurements based on direct and indirect methods can shed light on the LyC escape mechanism and the anisotropy of the leakage.

21 pages, 5figures, published in MNRAS