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

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 (>3 sigma) LyC flux in the range 880 < lambda(rest) < 910 angstrom. 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 less than or similar to z < 6 galaxies from the literature reported in last similar to 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 alpha emitters. We also discuss the possible existence of a correlation among the observed flux density ratio (F-v(LyC)/F-v(UV))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.