Radiation hydrodynamic simulation of the Haro 11 galaxy: the escape of LyC and Ly$α$ in a dwarf galaxy merger
Timmy Ejdetjärn, Göran Östlin, Joakim Rosdahl, Jérémy Blaizot, Oscar Agertz
TL;DR
This study uses high-resolution radiation-hydrodynamics (RAMSES-RT) with on-the-fly radiative transfer and post-processing (RASCAS) to simulate a Haro 11–like dwarf galaxy merger and to generate mock LyC, Lyα, and Hα observations across many sightlines. It finds that LyC escape fractions can increase by about an order of magnitude at pericentre passages and vary by ~2 orders of magnitude with viewing angle, while Lyα shows a milder response; knot C emerges as the dominant LyC source. The work qualitatively reproduces Haro 11’s morphology and emission patterns, and demonstrates how dynamical interactions and stellar feedback during mergers create escape channels for ionising radiation, with strong dependence on geometry. It provides a framework for interpreting LyC and Lyα leakage in local analogues to high-redshift reionisation galaxies and motivates further exploration of merger-driven leakage mechanisms. The results highlight the importance of viewing angle and gas dynamics in assessing the contribution of Lyman-continuum leaking systems to cosmic reionisation.
Abstract
The Haro 11 galaxy merger is the closest known Lyman Continuum (LyC) leaker and a strong Lyman-$α$ (Ly$α$) emitter, making it an important analogue of the high-$z$ galaxies that reionised the early Universe. To investigate how Haro 11's properties arise, we perform a radiation hydrodynamics simulation of the merger, and create mock observations of LyC, Ly$α$, and H$α$, from which we compute their luminosities ($L$) and escape fractions ($f_{\rm esc}$). We track these quantities along multiple sightlines as the two progenitor galaxies merge, from the first interaction until the system resembles present-day Haro 11. We find that $L$ and $f_{\rm esc}$ vary by 1-2 orders of magnitude for LyC due to sightline variations. At the two pericentre passages, the total $f_{\rm esc}^{\rm LyC}$ increases by roughly an order of magnitude. Conversely, $f_{\rm esc}^{\rm Lyα}$ shows a moderate increase at the pericentre passages, which affects the inference of LyC properties from Ly$α$. We attribute this to a displacement of the LyC-emitting stars relative to the \Lya-emitting gas, combined with an increased density from gas compression. Furthermore, $f_{\rm esc}^{\rm LyC}$ is boosted during star formation bursts, likely due to stellar feedback. As direct comparison with Haro 11, the simulation qualitatively matches its morphology and luminosities. We find that among the dense stellar knots, knot C is the main contributor to both intrinsic and escaping LyC emission. Additionally, the Ly$α$ spectra displays distinct features found in observations, implying similar gas conditions are present.