Upper limits on the escape fraction of ionizing radiation from galaxies at $2\lesssim z<6$

Abstract

In this work, we investigate upper limits on the global escape fraction of ionizing photons ($f_{esc/global}^{\mathrm{abs}}$) from a sample of galaxies probed for Lyman-continuum (LyC) emission characterized as non-LyC and LyC leakers. We present a sample of 9 clean non-contaminated (by low redshift interlopers, CCD problems and internal reflections of the instrument) galaxies which do not show significant ($>$ $3\sigma$) LyC flux between 880Å $<{\lambda }_{rest}<$ 910Å. The 9 galaxy stacked spectrum reveals no significant LyC flux with an upper limit of $f_{\mathrm{esc}}^{\mathrm{abs}}\le 0.06$. In the next step of our analysis, we join all estimates of $f_{\mathrm{esc}}^{\mathrm{abs}}$ upper limits derived from different samples of $2\lesssim z<6$ galaxies from the literature reported in last $\sim$20 years and include the sample presented in this work. We find the $f_{\mathrm{esc}}^{\mathrm{abs}}$ upper limit $\le$ 0.084 for the galaxies recognized as non-LyC leakers. After including all known detections from literature $f_{esc/global}^{\mathrm{abs}}$ upper limit $\le$ 0.088 for all galaxies examined for LyC flux. Furthermore, $f_{\mathrm{esc}}^{\mathrm{abs}}$ upper limits for different groups of galaxies indicate that the strongest LyC emitters could be galaxies classified as Lyman alpha emitters. We also discuss the possible existence of a correlation among the observed flux density ratio $(F_{\nu }^{LyC}/F_{\nu }^{UV}{)}_{\mathrm{obs}}$ and Lyman alpha equivalent width EW(Ly$\alpha )$, where we confirm the existence of moderately significant correlation among galaxies classified as non-LyC leakers.

17 pages, 5 Figures

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