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A cautionary tale of Ly C escape fraction estimates from high-redshift galaxies

Abstract : Measuring the escape fraction, fesc, 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 Δz ~ 0.2 making them unsuitable for Ly C measurements. This results likely due to a bias induced by our selection criteria.
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Submitted on : Friday, May 13, 2022 - 1:52:13 PM
Last modification on : Saturday, June 25, 2022 - 3:17:13 AM

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R. Bassett, E. V. Ryan-Weber, J. Cooke, U. Meštrić, L. J. Prichard, et al.. A cautionary tale of Ly C escape fraction estimates from high-redshift galaxies. Monthly Notices of the Royal Astronomical Society, 2022, 511, pp.5730-5741. ⟨10.1093/mnras/stac270⟩. ⟨insu-03667432⟩

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