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arXiv · 2111.13721

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

Aaron Smith·Rahul Kannan·Sandro Tacchella·Mark Vogelsberger·Lars Hernquist·Federico Marinacci·Laura V. Sales·Paul Torrey·Hui Li·Yuan-Chen Yeh·Jia Qi
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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-alpha (Lyα), and Balmer line (Hα and H\b{eta}) radiative transfer study of a high-resolution isolated Milky-Way simulation using the Arepo-RT radiation hydrodynamics code with the SMUGGLE galaxy formation model. The realistic framework includes stellar feedback, non-equilibrium thermochemistry, and dust grain evolution in the interstellar medium (ISM). We extend our Cosmic Lyα Transfer (COLT) code with photoionization equilibrium Monte Carlo radiative transfer for self-consistent end-to-end (non-)resonant line predictions. Accurate LyC reprocessing to recombination emission requires modelling pre-absorption by dust (27.5%), helium ionization (8.7%), and anisotropic escape fractions (7.9%), as these reduce the available budget for hydrogen line emission (55.9%). 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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Aaron Smith, Rahul Kannan, Sandro Tacchella, Mark Vogelsberger, Lars Hernquist, Federico Marinacci, Laura V. Sales, Paul Torrey, Hui Li, Yuan-Chen Yeh, Jia Qi. 2022-09-26. The physics of Lyman-alpha escape from disc-like galaxies. https://doi.org/10.1093/mnras%2Fstac2641

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