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Published May 2023 | Published
Journal Article Open

The connection between the escape of ionizing radiation and galaxy properties at z ∼ 3 in the Keck Lyman continuum spectroscopic survey


The connection between the escape fraction of ionizing radiation (f_(esc)) and the properties of galaxies, such as stellar mass (⁠M_∗⁠), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 z ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multiband photometry that places constraints on stellar population parameters. We construct composite spectra from subsamples binned as a function of galaxy property and quantify the ionizing-photon escape for each composite. We find a significant anti-correlation between f_(esc) and M_∗⁠, consistent with predictions from cosmological zoom-in simulations. We also find significant anti-correlation between f_(esc) and E(B−V), encoding the underlying physics of LyC escape in our sample. We also find no significant correlation between fesc and either stellar age or specific SFR (= SFR/M_∗⁠), challenging interpretations that synchronize recent star formation and favorable conditions for ionizing escape. The galaxy properties now shown to correlate with fesc in the KLCS are Lyα equivalent width, UV Luminosity, M_∗⁠, SFR, and E(B−V), but not age or sSFR. This comprehensive analysis of galaxy properties and LyC escape at high redshift will be used to guide future models and observations of the reionization epoch.

Additional Information

© 2023 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 (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). We acknowledge support from NSF AAG grants 0606912, 0908805, 1313472, 2009313, 2009085, and 2009278. Support for program HST-GO-15287.001 was provided by 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 was supported in part by the Caltech/JPL President's and Director's program. Based in part on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/IRFU, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at Terapix available at the Canadian Astronomy Data Centre as part of the Canada–France–Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. We thank D. Kelson for the use of his FourCLift FourStar Reduction code and for his assistance with it. 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. The HST data referenced 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.

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August 22, 2023
August 22, 2023