The Lyman-alpha and Continuum Origins Survey II: the connection between the escape of ionizing radiation and Lyman-alpha 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$\alpha$ halos (LAHs) in emission. We use Ly$\alpha$ and UV continuum imaging data from the Lyman alpha and Continuum Origins Survey (LaCOS), targeting 42 nearby ($z\simeq 0.3$), star-forming galaxies with LyC observations (escape fractions of $f_{\mathrm{esc}}^{\mathrm{LyC}}\simeq 0.01-0.49$). LaCOS galaxies show extended Ly$\alpha$ emission ubiquitously, with LyC emitters (LCEs) having more compact Ly$\alpha$ morphologies than non-LCEs, and Ly$\alpha$ 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$\alpha$ halo is ten times larger than the UV, on average. We unveil a significant anti-correlation between $f_{\mathrm{esc}}^{\mathrm{LyC}}$ and the Ly$\alpha$ Halo Fraction (HF, or contribution of the halo to the total Ly$\alpha$ luminosity), that 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 ISM, revealing a picture in which Ly$\alpha$ and LyC photons in LCEs either emerge directly from the central starbursts or escape isotropically and, in the case of Ly$\alpha$, minimize the number of scattering interactions in a less-extended CGM.

arXiv comment18 pages, 12 figures, 2 tables; accepted for publication in ApJ on January 10, 2026

References in corpus (145)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Correcting for the Effects of Interstellar Extinction
• Cosmic-Ray Rejection by Laplacian Edge Detection
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• In the Beginning: The First Sources of Light and the Reionization of the Universe
• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• Radiative transfer in a clumpy universe: IV. New synthesis models of the cosmic UV/X-ray background
• The Circumgalactic Medium
• The Relationship Between Stellar Light Distributions of Galaxies and their Formation Histories
• Effect of Reionization on the Structure Formation in the Universe
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• The transition from Population III to normal galaxies: Ly-a and HeII 1640 emission and the ionising properties of high redshift starburst galaxies
• New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
• Massloss of galaxies due to a UV-background
• Galactic Reddening in 3D from Stellar Photometry - An Improved Map
• An updated analytic model for the attenuation by the intergalactic medium
• JADES NIRSpec Spectroscopy of GN-z11: Lyman-$\alpha$ emission and possible enhanced nitrogen abundance in a $z=10.60$ luminous galaxy
• Diffuse Lyman Alpha Emitting Halos: A Generic Property of High Redshift Star Forming Galaxies
• Cosmic Reionization after Planck: Could Quasars Do It All?
• Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies
• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction
• Low-redshift Lyman continuum leaking galaxies with high [OIII]/[OII] ratios
• The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at $z\sim 3$
• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-Bright, Star-Forming Galaxies with High Escape Fractions
• Extended Lyman alpha haloes around individual high-redshift galaxies revealed by MUSE
• Lyman continuum leaking from the compact star-forming dwarf galaxy J0925+1403
• The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization
• The Origin and Optical Depth of Ionizing Radiation in the "Green Pea" Galaxies
• Ly$\alpha$ emission from Green Peas: the role of circumgalactic gas density, covering, and kinematics
• J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons
• A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems
• Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies
• Galaxy Formation and Reionization: Key Unknowns and Expected Breakthroughs by the James Webb Space Telescope
• Lyman-alpha spectral properties of five newly discovered Lyman continuum emitters
• Lyman-alpha Cooling Emission from Galaxy Formation
• Fluorescent Ly-alpha emission from the high-redshift intergalactic medium
• A test for partial correlation with censored astronomical data
• Lyman Alpha Blobs as an Observational Signature of Cold Accretion Streams into Galaxies
• The Lyman Continuum Escape Survey: Ionizing Radiation from [O III]-Strong Sources at a Redshift of 3.1
• Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionisation
• The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters
• The MUSE Hubble Ultra Deep Field Survey: II. Spectroscopic redshifts and comparisons to color selections of high-redshift galaxies
• The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics
• Diffuse Lyman-alpha Halos around Galaxies at z=2.2-6.6: Implications for Galaxy Formation and Cosmic Reionization
• Nearly all the sky is covered by Lyman-alpha emission around high redshift galaxies
• The Far-Ultraviolet Continuum Slope as a Lyman Continuum Escape Estimator at High-redshift
• Radiative Transfer Modeling of Lyman Alpha Emitters. I. Statistics of Spectra and Luminosity
• Lyman continuum leakage from low-mass galaxies with Mstar < 1.E8 Msun
• The Lyman alpha Reference Sample: II. HST imaging results, integrated properties and trends
• Diffuse Lyman Alpha Haloes around Lyman Alpha Emitters at z=3: Do Dark Matter Distributions Determine the Lyman Alpha Spatial Extents?
• Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy
• The Lyman alpha Reference Sample: Extended Lyman alpha Halos Produced at Low Dust Content
• Lyman-alpha Emission from Structure Formation
• The Lyman-alpha Reference Sample: I. Survey outline and first results for Markarian 259
• Line Transfer through Clumpy, Large-Scale Outflows: Lyman Alpha Absorption and Halos around Starforming Galaxies
• New Insights on Ly-alpha and Lyman Continuum Radiative Transfer in the Greenest Peas
• The origin of the escape of Lyman alpha and ionizing photons in Lyman Continuum Emitters
• An uncontaminated measurement of the escaping Lyman continuum at $z\sim 3$
• Lyman Radiation Hydrodynamics of Turbulent H II Regions in Molecular Clouds: A Physical Origin of LyC Leakage and the Associated Ly$\alpha$ Spectra
• A young star-forming galaxy at z = 3.5 with an extended Ly\,$\alpha$ halo seen with MUSE
• Lyman alpha Radiative Transfer in Cosmological Simulations using Adaptive Mesh Refinement
• LyC escape from SPHINX galaxies in the Epoch of Reionization
• Neutral gas properties of Lyman continuum emitting galaxies: column densities and covering fractions from UV absorption lines
• Optically-Thin Spatially-Resolved Mg II Emission Maps the Escape of Ionizing Photons
• The Low-Redshift Lyman Continuum Survey. Unveiling the ISM properties of low-$z$ Lyman continuum emitters
• Probing the faint end of the Galaxy luminosity function at z=3 with Ly-alpha emission
• On the Form of the HII Region Luminosity Function
• Diverse properties of Ly-alpha emission in low-redshift compact star-forming galaxies with extremely high [OIII]/[OII] ratios
• Resolved Spectroscopy of a Gravitationally Lensed L* Lyman-break Galaxy at z~5
• The MUSE Hubble Ultra Deep Field Survey XIII. Spatially resolved spectral properties of Lyman alpha haloes around star-forming galaxies at z > 3
• A Close Relationship between Lyman Alpha and Mg II in Green Pea Galaxies
• Statistical Properties of Diffuse Lyman-alpha Halos around Star-forming Galaxies at z~2
• A new technique for finding galaxies leaking Lyman-continuum radiation: [SII]-deficiency
• The LyAlpha Line Profiles of Ultraluminous Infrared Galaxies: Fast Winds and Lyman Continuum Leakage
• Resonant line transfer in a fog: Using Lyman-alpha to probe tiny structures in atomic gas
• JADES: Discovery of extremely high equivalent width Lyman-alpha emission from a faint galaxy within an ionized bubble at z=7.3
• Kinematics and Optical Depth in the Green Peas: Suppressed Superwinds in Candidate LyC Emitters
• The physical origins and dominant emission mechanisms of Lyman-alpha halos: results from the TNG50 simulation in comparison to MUSE observations
• HDUV: The Hubble Deep UV Legacy Survey
• HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794
• Witnessing the onset of reionisation via Lyman-$\alpha$ emission at redshift 13
• On the contribution of fluorescence to Ly$\alpha$ halos (LAHs) around star forming galaxies
• No strong dependence of Lyman continuum leakage on physical properties of star-forming galaxies at $3.1\lesssim \mathbf{z}\lesssim 3.5$
• Lyman-$\alpha$ as a tracer of cosmic reionisation in the SPHINX radiation-hydrodynamics cosmological simulation
• An Introductory Review on Cosmic Reionization
• What is the Physical Origin of Strong Lya Emission? I. Demographics of Lya Emitter Structures
• On the Diffuse Lyman-alpha Halo Around Lyman-alpha Emitting Galaxies
• UV absorption lines and their potential for tracing the Lyman continuum escape fraction
• The Kinematics of Extended Lyman-alpha Emission in a Low Mass, Low Metallicity Galaxy at z = 2.3
• Deciphering Lyman-$\alpha$ Emission Deep into the Epoch of Reionisation
• The Diversity of Diffuse Ly$\alpha$ Nebulae around Star-Forming Galaxies at High Redshift
• Simulating the diversity of shapes of the Lyman-$\alpha$ line
• The VANDELS survey: a measurement of the average Lyman-continuum escape fraction of star-forming galaxies at z=3.5
• New Constraints on the Escape of Ionizing Photons From Starburst Galaxies Using Ionization-Parameter Mapping
• Peering into cosmic reionization: the Ly$\alpha$ visibility evolution from galaxies at $z$ = 4.5-8.5 with JWST
• The Low-redshift Lyman-continuum Survey: [S II]-deficiency and the leakage of ionizing radiation
• The UV and Ly$\alpha$ Luminosity Functions of galaxies and the Star Formation Rate Density at the end of HI reionization from the VIMOS Ultra-Deep Survey (VUDS)
• Neutral Gas Properties and Ly$\alpha$ Escape in Extreme Green Pea Galaxies
• Small-scale Intensity Mapping: Extended Ly$\alpha$, H$\alpha$ and Continuum emission as a Probe of Halo Star Formation in High-redshift Galaxies
• Tracing Lyman-alpha and Lyman Continuum Escape in Galaxies with Mg II Emission
• Ubiquitous broad-line emission and the relation between ionized gas outflows and Lyman continuum escape in Green Pea galaxies
• Continuum subtracting Lyman-alpha images: Low redshift studies using the Solar Blind Channel of HST/ACS
• On the sizes of ionized bubbles around the highest redshift galaxies. Spectral shapes of the Lyman-alpha emission from galaxies
• JADES: Primaeval Lyman-$\alpha$ emitting galaxies reveal early sites of reionisation out to redshift $z\sim 9$
• Tracing the simulated high-redshift circum-galactic medium with Lyman alpha emission
• The MUSE eXtremely Deep Field: Individual detections of Lyα haloes around rest-frame UV-selected galaxies at z~2.9-4.4
• The Lensed Lyman-Alpha MUSE Arcs Sample (LLAMAS) : I. Characterisation of extended Lyman-alpha haloes and spatial offsets
• Surface Brightness Profile of Lyman-$\alpha$ Halos out to 320 kpc in HETDEX
• Predicting LyC emission of galaxies using their physical and Ly$\alpha$ emission properties
• The Circumgalactic Medium of Extreme Emission Line Galaxies at z ~ 2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyman-alpha Emission in the KBSS-KCWI Survey
• Early Results from GLASS-JWST XXII: Rest frame UV-optical spectral properties of Lyman-alpha emitting galaxies at 3 $<$ z $<$ 6
• The Low-Redshift Lyman Continuum Survey: Optically Thin and Thick Mg II Lines as Probes of Lyman Continuum Escape
• The Effect of Bi-conical Outflows on Ly$\alpha$ Escape From Green Peas
• Ly-alpha emission in low-redshift most metal-deficient compact star-forming galaxies
• SILVERRUSH. IX. Lya Intensity Mapping with Star-Forming Galaxies at z=5.7 and 6.6: A Possible Detection of Extended Lya Emission at $\gtrsim$100 comoving kpc around and beyond the Virial-Radius Scale of Galaxy Dark Matter Halos
• The Size and Pervasiveness of Ly$\alpha$-UV Spatial Offsets in Star-Forming Galaxies at $z\sim 6$
• The dominant origin of diffuse Ly$\alpha$ halos around LAEs explored by SED fitting and clustering analysis
• The Atomic Gas Mass of Green Pea Galaxies
• A bottom-up search for Lyman-continuum leakage in the Hubble Ultra Deep Field
• Lyα Halos around [O III]-Selected Galaxies in HETDEX
• Unveiling Luminous Ly$\alpha$ Emitters at $z\approx 6$ through JWST/NIRCam Imaging in the COSMOS Field
• Median Surface Brightness Profiles of Lyman-$\alpha$ Haloes in the MUSE Extremely Deep Field
• Linking Mg II and [O II] spatial distribution to ionizing photon escape in confirmed LyC leakers and non-leakers
• SILVERRUSH. XI. Intensity Mapping for Lya Emission Extending over $100-1000$ comoving kpc around $z\sim 2-7$ LAEs with Subaru HSC-SSP and CHORUS Data
• Two types of Lyman-alpha emitters envisaged from hierarchical galaxy formation
• Witnessing an extreme, highly efficient galaxy formation mode with resolved Ly$\alpha$ and LyC emission
• The Lyman Alpha Reference Sample. VIII. Characterizing Lyman-Alpha Scattering in Nearby Galaxies
• On the evolution of the size of Lyman alpha halos across cosmic time: no change in the circumgalactic gas distribution when probed by line emission
• Low-redshift Lyman Continuum Survey: Radio continuum properties of low-$z$ Lyman continuum emitters
• The Lyman Alpha Reference Sample XII: Morphology of extended Lyman alpha emission in star-forming galaxies
• UV & Ly$\alpha$ halos of Ly$\alpha$ emitters across environments at z=2.84
• HI Imaging of a Blueberry Galaxy Suggests a Merger Origin
• The Lyman $\alpha$ Reference Sample XIV: Lyman $\alpha$ imaging of 45 low redshift star-forming galaxies and inferences on global emission
• The Lyman-alpha and Continuum Origins Survey. I. Survey description and Ly$\alpha$ imaging
• Redshift evolution of Lyman continuum escape fraction after JWST
• A public grid of radiative transfer simulations for Lyman-alpha and metal lines in idealised galactic outflows
• The Importance of Dust Distribution in Ionizing-photon Escape: NIRCam and MIRI Imaging of a Lyman Continuum-emitting Galaxy at z ~ 3.8
• The Lyman Alpha Reference Sample XV. Relating Ionised Gas Kinematics with Lyman-$\alpha$ observables
• The Ly$\alpha$ and Continuum Origins Survey. III. Investigating the Link between Galaxy Morphology, Merger Properties and LyC Escape
• Modelling LAEs in the Epoch of Reionization with OBELISK
• FAST H I 21 cm study of blueberry galaxies

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• Deep JWST spectroscopy of galaxies in a candidate ionized bubble at $z=8.7$: probing reionization at pMpc scales with Ly$\alpha$ emission