Oscar Agertz

The Haro 11 galaxy merger is the closest known Lyman continuum (LyC) leaker and a strong Lyman-α (Lyα) 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, Lyα, and Hα, from which we compute their luminosities (L) and escape fractions (f_esc). We track these quantities along multiple sightlines as the two progenitor galaxies merge, from the first interaction until the system resembles the presentday Haro 11. We find that L and f_esc vary by 1–2 orders of magnitude for LyC due to sightline variations. At the two pericentre passages, the total f^LyC_esc increases by roughly an order of magnitude. Conversely, f^Lyα_esc shows a moderate increase at the pericentre passages, which affects the inference of LyC properties from Lyα. We attribute this to a displacement of the LyC-emitting stars relative to the Lyα-emitting gas, combined with an increased density from gas compression. Furthermore, f^LyC_esc 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 Lyα spectra displays distinct features found in observations, implying similar gas conditions are present.