How LyC photons escape from compact star-forming regions in the Sunburst galaxy

The escape mechanism of ionizing (LyC) photons from a galaxy’s star-forming regions to intergalactic space is crucial to understanding the reionization process of the early universe. We investigate the characteristics of a compact star-forming complex with leaking LyC photons in the gravitationally lensed Sunburst galaxy at z=2.4. This galaxy provides unique opportunities to probe the physics of LyC escape down to tens of parsecs by utilizing HST’s high angular resolution and the lensing magnification. We measure the key physical quantities of the leaking complex including UV slope, Lyα, Hβ, and oxygen ([O II] and [O III]) emission lines based on HST images. We find remarkably blue UV slopes (< -2.5) in the multiply magnified regions of the leaking complex, which is bluer than those of star-forming galaxies and non-leaking regions in the galaxy. Moreover, there are significant correlations between the measured physical quantities of the leaking complex, such that bluer UV slopes are related to higher Lyα escape fraction and oxygen line ratio. Our findings would suggest that highly ionized, compact star-forming regions with little dust promote LyC photon escape in a galaxy.