Identifying reionization-epoch galaxies with extreme levels of Lyman continuum leakage in James Webb Space Telescope surveys. Issue 4 (10th December 2019)

• Record Type: Journal Article
• Authors: Giri, Sambit K; Zackrisson, Erik; Binggeli, Christian; Pelckmans, Kristiaan; Cubo, Rubén
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 491:Issue 4(2020)
• Page Start: 5277
• Page End: 5286
• Publication Date: 2019-12-10
• Subjects: gravitational lensing: strong -- galaxies: high-redshift -- dark ages, reionization, first stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz3416
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The James Webb Space Telescope ( JWST ) NIRSpec instrument will allow rest-frame ultraviolet/optical spectroscopy of galaxies in the epoch of reionization (EoR). Some galaxies may exhibit significant leakage of hydrogen-ionizing photons into the intergalactic medium, resulting in faint nebular emission lines. We present a machine learning framework for identifying cases of very high hydrogen-ionizing photon escape from galaxies based on the data quality expected from potential NIRSpec observations of EoR galaxies in lensed fields. We train our algorithm on mock samples of JWST /NIRSpec data for galaxies at redshifts z = 6–10. To make the samples more realistic, we combine synthetic galaxy spectra based on cosmological galaxy simulations with observational noise relevant for z ≳ 6 objects of a brightness similar to EoR galaxy candidates uncovered in Frontier Fields observations of galaxy cluster Abell-2744 and MACS-J0416. We find that ionizing escape fractions ( f esc ) of galaxies brighter than m AB, 1500 ≈ 27 mag may be retrieved with mean absolute error Δ f esc ≈ 0.09(0.12) for 24 h (1.5 h) JWST /NIRSpec exposures at resolution R = 100. For 24 h exposure time, even fainter galaxies ( m AB, 1500 < 28.5 mag) can be processed with Δ f esc ≈ 0.14. This framework simultaneously estimates the redshift of these galaxies with a relative error less than 0.03 for both 24 ( m AB, 1500 < 28.5 mag) and 1.5 h ( m AB, 1500 < 27 mag) exposure times. We also consider scenarios where just a minor fraction of galaxies attain high f esc and present the conditions required for detecting a subpopulation of high- f esc galaxies within the data set.