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An uncontaminated measurement of the escaping Lyman continuum at z ∼ 3

Pahl, Anthony J. and Shapley, Alice and Steidel, Charles C. and Chen, Yuguang and Reddy, Naveen A. (2021) An uncontaminated measurement of the escaping Lyman continuum at z ∼ 3. Monthly Notices of the Royal Astronomical Society, 505 (2). pp. 2447-2467. ISSN 0035-8711. doi:10.1093/mnras/stab1374.

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Observations of reionization-era analogues at z ∼ 3 are a powerful tool for constraining reionization. Rest-ultraviolet observations are particularly useful, in which both direct and indirect tracers of ionizing-photon production and escape can be observed. We analyse a sample of 124 z ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey, with sensitive spectroscopic measurements of the Lyman continuum region. We present a method of removing foreground contamination from our sample using high-resolution, multiband Hubble Space Telescope imaging. We re-measure the global properties of the cleaned sample of 13 individually detected Lyman continuum sources and 107 individually undetected sources, including a sample-averaged absolute escape fraction of f_(esc, abs) = 0.06 ± 0.01 and a sample-averaged ratio of ionizing to non-ionizing ultraviolet flux density of 〈f₉₀₀/f₁₅₀₀〉_(out) = 0.040 ± 0.006, corrected for attenuation from the intergalactic and circumgalactic media. Based on composite spectra, we also recover a strong positive correlation between 〈f₉₀₀/f₁₅₀₀〉_(out) and Lyα equivalent width (W_λ(Lyα⁠)) and a negative correlation between 〈f₉₀₀/f₁₅₀₀〉_(out) and UV luminosity. As in previous work, we interpret the relationship between 〈f₉₀₀/f₁₅₀₀〉_(out) and W_λ(Lyα⁠) in terms of the modulation of the escape of ionizing radiation from star-forming galaxies based on the covering fraction of neutral gas. We also use a W_λ(Lyα⁠)-weighted 〈f₉₀₀/f₁₅₀₀〉_(out) to estimate an ionizing emissivity from star-forming galaxies at z ∼ 3 as ϵ_(LyC) ≃ 5.5 × 10²⁴ erg s⁻¹ Hz⁻¹ Mpc⁻³. This estimate, evaluated using the uncontaminated sample of this work, affirms that the contribution of galaxies to the ionizing background at z ∼ 3 is comparable to that of active galactic nuclei.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Pahl, Anthony J.0000-0003-4464-4505
Shapley, Alice0000-0003-3509-4855
Steidel, Charles C.0000-0002-4834-7260
Chen, Yuguang0000-0003-4520-5395
Reddy, Naveen A.0000-0001-9687-4973
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 May 6. Received 2021 May 5; in original form 2021 April 5. Published: 22 May 2021. Support for program HST-GO-15287.001 was provided by the National Aeronautics and Space Administration (NASA) through a grant from the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. CS and YC were supported in part by the Caltech/Jet Propulsion Laboratory President’s and Director’s program. We wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, most of the observations presented herein would not have been possible. Data Availability Statement: The HST data presented in this article are publicly available from the Mikulski Archive for Space Telescopes. The ground-based data presented here will be shared on reasonable request to the corresponding author.
Group:Astronomy Department
Funding AgencyGrant Number
JPL President and Director's FundUNSPECIFIED
Subject Keywords:galaxies: high-redshift – dark ages, reionization, first stars – cosmology: observations
Issue or Number:2
Record Number:CaltechAUTHORS:20210821-170423382
Persistent URL:
Official Citation:Anthony J Pahl, Alice Shapley, Charles C Steidel, Yuguang Chen, Naveen A Reddy, An uncontaminated measurement of the escaping Lyman continuum at z ∼ 3, Monthly Notices of the Royal Astronomical Society, Volume 505, Issue 2, August 2021, Pages 2447–2467,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110372
Deposited By: Tony Diaz
Deposited On:21 Aug 2021 17:27
Last Modified:21 Aug 2021 17:27

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