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The physics of Lyman-α escape from disc-like galaxies

Accepted version
Peer-reviewed

Type

Article

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Abstract

jats:titleABSTRACT</jats:title> jats:pHydrogen 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 (fabs≈27.5percent), helium ionization (fHe≈8.7percent), and anisotropic escape fractions (fesc≈7.9percent), as these reduce the available budget for hydrogen line emission (fH≈55.9percent). 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.</jats:p>

Description

Keywords

line: profiles, radiative transfer, methods: numerical, ISM: dust, extinction, ISM: kinematics and dynamics

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

517

Publisher

Oxford University Press (OUP)