A Cautionary Tale of LyC Escape Fraction Estimates from High Redshift Galaxies

Measuring the escape fraction, $f_{\mathrm{e}\mathrm{s}\mathrm{c}}$, of ionizing, Lyman Continuum (LyC) 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 LyC 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 $f_{\mathrm{e}\mathrm{s}\mathrm{c}}^{\mathrm{P}\mathrm{D}\mathrm{F}}$ = 0.51${}_{-0.34}^{+0.33}$ 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${}_{-0.16}^{+0.33}$. Our results highlight the limitations of methods assuming average, smooth transmission functions. We also present MOSFIRE data for a sample of seven LyC candidates selected based on photometric redshifts at $z>3.4$, but find that all seven have overestimated photometric redshifts by $\mathrm{\Delta }z\sim 0.2$ making them unsuitable for LyC measurements. This results likely due to a bias induced by our selection criteria.