A cautionary tale of Ly C escape fraction estimates from high-redshift galaxies. Issue 4 (7th March 2022)

• Record Type: Journal Article
• Authors: Bassett, R; Ryan-Weber, E V; Cooke, J; Meštrić, U; Prichard, L J; Rafelski, M; Iwata, I; Sawicki, M; Gwyn, S; Arnouts, S
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 511:Issue 4(2022)
• Page Start: 5730
• Page End: 5741
• Publication Date: 2022-03-07
• Subjects: intergalactic medium -- galaxies: ISM -- dark ages, reionization, first stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac270
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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.