The Ly <i>α</i> and Continuum Origins Survey. II. The Connection between the Escape of Ionizing Radiation and Ly <i>α</i> Halos in Star-forming Galaxies

Abstract One of the current challenges in galaxy evolution studies is to establish the mechanisms that govern the escape of ionizing radiation from galaxies. Here, we investigate the connection between Lyman continuum (LyC) escape and the conditions of the circumgalactic medium (CGM), as probed by Ly α halos (LAHs) in emission. We use Ly α and UV continuum imaging data from the Ly α and Continuum Origins Survey (LaCOS), targeting 42 nearby ( z ≃0.3), star-forming galaxies with LyC observations (escape fractions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>≃</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0.49</mml:mn> </mml:math> ). LaCOS galaxies show extended Ly α emission ubiquitously, with LyC emitters (LCEs) having more compact Ly α morphologies than non-LCEs, and Ly α spatial offsets that do not exceed the extent of the UV continuum. We model the diffuse LAHs using a combined Sérsic plus exponential 2D profile, and find that the characteristic scale length of the Ly α halo is 10 times larger than the UV, on average. We unveil a significant anticorrelation between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> and the Ly α halo fraction (HF; or contribution of the halo to the total Ly α luminosity), which we propose as a new LyC indicator. Our observations show that halo scale lengths and HFs both scale positively with the optical depth of the neutral gas in the interstellar medium, revealing a picture in which Ly α and LyC photons in LCEs either emerge directly from the central starbursts or escape isotropically, and in the case of Ly α , minimize the number of scattering interactions in a less-extended CGM.

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Publication Details

Journal
The Astrophysical Journal
Published
2026-02-24
DOI
https://doi.org/10.3847/1538-4357/ae36a8
Citations
2
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
47.65
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article

The Ly α and Continuum Origins Survey. II. The Connection between the Escape of Ionizing Radiation and Ly α Halos in Star-forming Galaxies

Matthew Hayes, G. Ostlin, T. X. Thuan, Axel Runnholm et al.
2 citations
The Astrophysical Journal
Galaxies: Formation, Evolution, Phenomena
47.65
article

The Ly α and Continuum Origins Survey. II. The Connection between the Escape of Ionizing Radiation and Ly α Halos in Star-forming Galaxies

Matthew Hayes, G. Ostlin, T. X. Thuan, Axel Runnholm, L. Pentericci, Zhiyuan Ji, Sophia R. Flury, J. Chisholm, Omkar Bait, Intae Jung, Craig Carr, Alexandra Le Reste, Timothy M. Heckman, M. S. Oey, Alberto Saldana-Lopez, D. Schaerer, Hakim Atek, Xinfeng Xu, Anne E. Jaskot, R. Amorín, Jens Melinder, Claudia Scarlata, Alaina Henry, Floriane Leclercq, Yan Lin, Thibault Garel, Л. Г. Комарова
article en
2 citations

Abstract

Abstract One of the current challenges in galaxy evolution studies is to establish the mechanisms that govern the escape of ionizing radiation from galaxies. Here, we investigate the connection between Lyman continuum (LyC) escape and the conditions of the circumgalactic medium (CGM), as probed by Ly α halos (LAHs) in emission. We use Ly α and UV continuum imaging data from the Ly α and Continuum Origins Survey (LaCOS), targeting 42 nearby ( z ≃0.3), star-forming galaxies with LyC observations (escape fractions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>≃</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0.49</mml:mn> </mml:math> ). LaCOS galaxies show extended Ly α emission ubiquitously, with LyC emitters (LCEs) having more compact Ly α morphologies than non-LCEs, and Ly α spatial offsets that do not exceed the extent of the UV continuum. We model the diffuse LAHs using a combined Sérsic plus exponential 2D profile, and find that the characteristic scale length of the Ly α halo is 10 times larger than the UV, on average. We unveil a significant anticorrelation between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> and the Ly α halo fraction (HF; or contribution of the halo to the total Ly α luminosity), which we propose as a new LyC indicator. Our observations show that halo scale lengths and HFs both scale positively with the optical depth of the neutral gas in the interstellar medium, revealing a picture in which Ly α and LyC photons in LCEs either emerge directly from the central starbursts or escape isotropically, and in the case of Ly α , minimize the number of scattering interactions in a less-extended CGM.

The Astrophysical JournalVol. 999(1)
Université Claude Bernard Lyon 1 (FR), Northwestern University (US), University of Geneva (CH), California Institute of Technology (US), Centre National de la Recherche Scientifique (FR), Space Telescope Science Institute (US), University of Minnesota (US), University of Arizona (US), Johns Hopkins University (US), Universitat de València (ES), Stockholm University (SE), Williams College (US), University of Michigan (US), Astronomical Observatory of Rome (IT), Institut d'Astrophysique de Paris (FR), Sorbonne Université (FR), Centre de Recherche Astrophysique de Lyon (FR), Royal Observatory (GB), SKA Observatory (GB), Université Bourgogne Franche-Comté (FR), Instituto de Astrofísica de Andalucía (ES), Institut de Recherche en Astrophysique et Planétologie (FR), Infrared Processing and Analysis Center (US), University of Virginia (US), Zhejiang University (CN), The University of Texas at Austin (US), University of Edinburgh (GB)
Openalex Percentile: Top 1%
Galaxies: Formation, Evolution, Phenomena
47.65
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