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ABSTRACT Hydrogen emission lines can provide extensive information about star-forming galaxies in both the local and high-redshift Universe. We present a detailed Lyman continuum (LyC), Lyman-α (Lyα), and Balmer line (Hα and Hβ) radiative transfer study of a high-resolution isolated Milky Way simulation using the state-of-the-art Arepo-RT radiation hydrodynamics code with the SMUGGLE galaxy formation model. The realistic framework includes stellar feedback, non-equilibrium thermochemistry accounting for molecular hydrogen, and dust grain evolution in the interstellar medium (ISM). We extend our publicly available Cosmic Lyα Transfer (COLT) code with photoionization equilibrium Monte Carlo radiative transfer and various methodology improvements for self-consistent end-to-end (non-)resonant line predictions. Accurate LyC reprocessing to recombination emission requires modelling pre-absorption by dust ($$f_\text{abs} \approx 27.5\,\rm{per\,\,cent}$$), helium ionization ($$f_\text{He} \approx 8.7\,\rm{per\,\,cent}$$), and anisotropic escape fractions ($$f_\text{esc} \approx 7.9\,\rm{per\,\,cent}$$), as these reduce the available budget for hydrogen line emission ($$f_\text{H} \approx 55.9\,\rm{per\,\,cent}$$). We investigate the role of the multiphase dusty ISM, disc geometry, gas kinematics, and star formation activity in governing the physics of emission and escape, focusing on the time variability, gas-phase structure, and spatial spectral, and viewing angle dependence of the emergent photons. Isolated disc simulations are well-suited for comprehensive observational comparisons with local Hα surveys, but would require a proper cosmological circumgalactic medium (CGM) environment as well as less dust absorption and rotational broadening to serve as analogs for high-redshift Lyα emitting galaxies. Future applications of our framework to next-generation cosmological simulations of galaxy formation including radiation-hydrodynamics that resolve ≲10 pc multiphase ISM and ≲1 kpc CGM structures will provide crucial insights and predictions for current and upcoming Lyα observations.
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Tidally offset neutral gas in Lyman continuum emitting galaxy Haro 11
ABSTRACT Around 400 Myr after the big bang, the ultraviolet emission from star-forming galaxies reionized the Universe. Ionizing radiation (Lyman continuum, LyC) is absorbed by cold neutral hydrogen gas (H i) within galaxies, hindering the escape of LyC photons. Since the H i reservoir of LyC emitters has never been mapped, major uncertainties remain on how LyC photons escape galaxies and ionize the intergalactic medium. We have directly imaged the neutral gas in the nearby reionization-era analogue galaxy Haro 11 with the 21 cm line to identify the mechanism enabling ionizing radiation escape. We find that merger-driven interactions have caused a bulk offset of the neutral gas by about $$6\,$$ kpc from the centre of the galaxy, where LyC emission production sites are located. This could facilitate the escape of ionizing radiation into our line of sight. Galaxy interactions can cause both elevated LyC production and large-scale displacement of H i from the regions where these photons are produced. They could contribute to the anisotropic escape of LyC radiation from galaxies and the reionization of the Universe. We argue for a systematic assessment of the effect of environment on LyC production and escape.
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- Award ID(s):
- 2009894
- PAR ID:
- 10486788
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 528
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 757-770
- Size(s):
- p. 757-770
- Sponsoring Org:
- National Science Foundation
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