Radiation hydrodynamic simulation of the Haro 11 galaxy: the escape of LyC and Ly$\alpha$ in a dwarf galaxy merger

TL;DR

This study uses radiation hydrodynamics simulations to explore how galaxy mergers like Haro 11 facilitate the escape of LyC and Ly$ extalpha$ radiation, shedding light on processes relevant to cosmic reionization.

Contribution

It provides the first detailed simulation of Haro 11's merger, linking gas dynamics and star formation to LyC and Ly$ extalpha$ escape, with implications for high-redshift galaxy analogues.

Findings

LyC escape fraction varies by 1-2 orders of magnitude with sightline.

Pericentre passages increase LyC escape fraction by about an order of magnitude.

Star formation bursts boost LyC escape due to stellar feedback.

Abstract

The Haro 11 galaxy merger is the closest known Lyman Continuum (LyC) leaker and a strong Lyman-$\alpha$ (Ly$\alpha$) 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$\alpha$, and H$\alpha$, 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, $f_{\rm esc}^{\rm Ly\alpha}$ shows a moderate increase at the pericentre passages, which affects the inference of LyC properties from Ly$\alpha$. 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$\alpha$ spectra displays distinct features found in observations, implying similar gas conditions are present.