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Measuring the escape fraction, f esc, of ionizing, Lyman continuum (Ly C) radiation is key to our understanding of the process of cosmic reionization. In this paper, we provide a methodology for recovering the posterior probability distribution of the Ly C escape fraction, |$f_{\rm esc}^{\rm PDF}$|⁠ , considering both the observational uncertainties and ensembles of simulated transmission functions through the intergalactic medium (IGM). We present an example of this method applied to a VUDS galaxy at z = 3.64 and find |$f_{\rm esc}^{\rm PDF}$| = 0.51 |$^{+0.33}_{-0.34}$| and compare this to the values computed assuming averaged IGM transmission with and without consideration of detection bias along average sightlines yielding |$f_{\rm esc}^{\langle T \rangle }$| = 1.40 |$^{+0.80}_{-0.42}$| and |$f_{\rm esc}^{\rm bias}$| = 0.82 |$^{+0.33}_{-0.16}$|⁠. Our results highlight the limitations of methods assuming average, smooth transmission functions. We also present MOSFIRE data for a sample of seven Ly C candidates selected based on photometric redshifts at z > 3.4, but find that all seven have overestimated photometric redshifts by Δ z ∼ 0.2 making them unsuitable for Ly C measurements. This results likely due to a bias induced by our selection criteria. [ABSTRACT FROM AUTHOR]

In this work, we investigate upper limits on the global escape fraction of ionizing photons (⁠|$f_{\rm esc/global}^{\rm abs}$|⁠) 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 < λrest < 910 Å. The nine-galaxy stacked spectrum reveals no significant LyC flux with an upper limit of |$f_{\rm esc}^{\rm abs} \le 0.06$|⁠. In the next step of our analysis, we join all estimates of |$f_{\rm esc}^{\rm abs}$| 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 |$f_{\rm esc}^{\rm abs}$| upper limit ≤0.084 for the galaxies recognized as non-LyC leakers. After including all known detections from literature |$f_{\rm esc/global}^{\rm abs}$| upper limit ≤0.088 for all galaxies examined for LyC flux. Furthermore, |$f_{\rm esc}^{\rm abs}$| 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 |$(F_{\nu }^{\mathrm{ LyC}}/F_{\nu }^{\mathrm{ UV}})_{\rm obs}$| and Lyman α equivalent width EW(Lyα), where we confirm the existence of moderately significant correlation among galaxies classified as non-LyC leakers. [ABSTRACT FROM AUTHOR]

Understanding the relationship between the underlying escape fraction of Lyman continuum (LyC) photons (f esc) emitted by galaxies and measuring the distribution of observed f esc values at high redshift is fundamental to the interpretation of the reionization process. In this paper, we perform a statistical exploration of the attenuation of LyC photons by neutral hydrogen in the intergalactic medium using ensembles of simulated transmission functions. We show that LyC-detected galaxies are more likely to be found in sightlines with higher than average transmission of LyC photons. This means that adopting a mean transmission at a given redshift leads to an overestimate of the true f esc for LyC-detected galaxies. We note, however, that mean values are appropriate for f esc estimates of larger parent samples that include LyC non-detected galaxies. We quantify this IGM transmission bias for LyC detections in photometric and spectroscopic surveys in the literature and show that the bias is stronger for both shallower observations and for fainter parent samples (i.e. Ly α emitters versus Lyman break galaxies). We also explore the effects of varying the underlying probability distribution function (PDF) of f esc on recovered values, showing that the underlying f esc PDF may depend on sample selection by comparing with observational surveys. This work represents a first step in improved interpretation of LyC detections in the context of understanding f esc from high-redshift galaxies. [ABSTRACT FROM AUTHOR]

Identifying non-contaminated sample of high-redshift galaxies with escaping Lyman continuum (LyC) flux is important for understanding the sources and evolution of cosmic reionization. We present CLAUDS (CFHT Large Area u -band deep survey) u -band photometry of the COSMOS field to probe LyC radiation from spectroscopically confirmed galaxies at |$z$| ≥ 3.5 and outside the standard Lyman-break galaxy colour-selection expectations. Complementary to the CLAUDS data, we use Subaru multifilter photometry, Hubble Space Telescope (HST) multifilter imaging, and the spectroscopic surveys D10K, VUDS, and 3D-HST. We present a sample of Lyman continuum galaxy (LCG) candidates in the redshift range 3.5 ≲ |$z$| ≲ 5.1. Here, we introduce 5 LCG candidates, where two are flagged quality 1 and three quality 2. The estimated |$f_{\rm esc}^{\rm abs}$| for quality 1 candidates are in the range |$\sim 5 - 73{{\ \rm per\ cent}}$| and |$\sim 30 - 93{{\ \rm per\ cent}}$|⁠. These estimates are based on our derived parameters from individual galaxies as inputs to a range of BPASS models as well as mean intergalactic medium (IGM) and maximal intergalactic and circumgalactic media (IGM+CGM) transmission. We conclude that our search for LCGs is most likely biased to lines of sight with low H  i densities or free from Lyman limit systems. Our two best LCG candidates have EW (Lyα) ≤ 50 Å and we find no correlation or anticorrelation between EW (Lyα), |$f_{\rm esc}^{\rm abs}$|⁠ , and R obs, the ratio of ionizing to non-ionizing observed flux in the measured passbands. Stacking candidates without solid LyC detections (S/N < 3) results in an estimated |$f_{\rm esc}^{\rm abs}$| from galaxies not greater than |$1{{\ \rm per\ cent}}$|⁠. [ABSTRACT FROM AUTHOR]