Work

The challenge in illuminating the invisible: constraining LyC escape with Bayesian modelling and symbolic regression

Year: 2026

Type: article

Abstract: ABSTRACT Direct observations of Lyman continuum (LyC) radiation from galaxies during the epoch of reionization (EoR) are impeded by absorption in the intergalactic medium, requiring indirect methods to infer the escape fraction of ionizing photons ($f_\mathrm{esc}^{\mathrm{LyC}}$). One approach is to develop and validate such methods on local analogues of the high-redshift galaxies with directly detected LyC leakage. In this study, we constrain $f_\mathrm{esc}^\mathrm{LyC}$ using a Bayesian spectral energy distribution (SED) fitting framework built in prospector, which incorporates a non-parametric star formation history, a flexible dust attenuation curve, self-consistent nebular emission, and fibre aperture-loss corrections. Our methodology jointly fits broad-band photometry and emission-line fluxes. We apply six models to the Low-redshift LyC Survey (LzLCS), a sample of local galaxies with physical properties comparable to EoR galaxies, and evaluate them based on their ability to recover the observed flux and their relative Bayesian evidence. The best-performing model is further assessed through a parameter recovery test, demonstrating that $f_\mathrm{esc}^\mathrm{LyC}$ can be recovered within uncertainties. Building on these results, we present updated $f_\mathrm{esc}^\mathrm{LyC}$ estimates for the LzLCS sample, with a median of 4 per cent, and values reaching as high as 51 per cent, with 26 of 64 galaxies having a cosmologically relevant $f_\mathrm{esc}^\mathrm{LyC}$ ($\gtrsim 5~{{\ \rm per\ cent}}$). Additionally, we present a revised ultraviolet $\beta$-slope versus $\log _{10}(f_\mathrm{esc}^\mathrm{LyC})$ relation, derived using symbolic regression with pysr trained on a synthetic data set generated with prospector: $\log _{10}(f_\mathrm{esc}^\mathrm{LyC}) = (-2.30 \pm 1.28)\beta - (6.26 \pm 2.91)$, ($\sigma = 0.43$ dex). The relation successfully reproduces the $f_\mathrm{esc}^\mathrm{LyC}$ obtained from full SED fitting of the LzLCS sample within $1\sigma$.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag984

Authors: Amanda Stoffers, Sandro Tacchella, Charlotte Simmonds, Benjamin D Johnson, Roberto Maiolino

Institutions: University of Cambridge, University of Chile, Center for Astrophysics Harvard & Smithsonian, University College London

Language: English

Topic: Galaxies: Formation, Evolution, Phenomena

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,046

Funders: UK Research and Innovation, University of Cambridge, UK Wind Energy Research - Centre for Doctoral Training, Science and Technology Facilities Council