2021MNRAS.508.4443M

In this work, we investigate upper limits on the global escape fraction of ionizing photons (f_esc/global^abs) from a sample of galaxies probed for Lyman-continuum (LyC) emission characterized as non-LyC and LyC leakers. We present a sample of nine clean non-contaminated (by low-redshift interlopers, CCD problems, and internal reflections of the instrument) galaxies that do not show significant (>3σ) LyC flux in the range 880 < λ_rest < 910 Å. The nine-galaxy stacked spectrum reveals no significant LyC flux with an upper limit of f_ esc_^abs ≤0.06. In the next step of our analysis, we join all estimates of f_esc^abs upper limits derived from different samples of 2 <= z < 6 galaxies from the literature reported in last ∼20 yr and include the sample presented in this work. We find the f_esc^abs upper limit <=0.084 for the galaxies recognized as non-LyC leakers. After including all known detections from literature f_esc/global^abs upper limit <=0.088 for all galaxies examined for LyC flux. Furthermore, f_esc^abs upper limits for different groups of galaxies indicate that the strongest LyC emitters could be galaxies classified as Lyman α emitters. We also discuss the possible existence of a correlation among the observed flux density ratio (F_ν^LyC/F_ν^UV)_obs and Lyman α equivalent width EW(Lyα), where we confirm the existence of moderately significant correlation among galaxies classified as non-LyC leakers.