The Leakage of Lyman-continuum Photons from a Major Merger at z ∼ 1

Abstract We report the detection of Lyman-continuum (LyC) photons from a massive interacting system at z = 1.097 in the Hubble Ultra Deep Field. The LyC detection is made in the far-ultraviolet F154W band of the UVIT telescope on board AstroSat. Both JWST and Hubble Space Telescope (HST) imaging of the system reveal signs that it is a likely merger. In particular, high-resolution imaging in the JWST bands reveals an infrared-luminous object within the system that is faint in the bluer HST bands. The ionized gas kinematics from the MUSE-UDF data supports the merger hypothesis. We estimate that the entire system is leaking more than 8% of its ionizing photons to the intergalactic medium. The spectral-energy-distribution-derived stellar masses of the two components indicate that this is a major merger with a mass ratio of 1.13 ± 0.37. This detection hints at the potential contribution of massive interacting systems at higher redshifts, when major mergers were more frequent, to the ionizing budget of the Universe.