SDSS-IV MaNGA: Observational Evidence of a Density-bounded Region in a Lyα Emitter

Abstract

Using integral field unit spectroscopy, we present here the spatially resolved morphologies of [S ii ] λ 6717,6731/H α and [S ii ] λ 6717,6731/[O iii ] λ 5007 emission line ratios for the first time in a blueberry Ly α emitter (BBLAE) at z ∼ 0.047. Our derived morphologies show that the extreme starburst region of the BBLAE, populated by young (≤10 Myr), massive Wolf–Rayet stars, is [S ii ] deficient, while the rest of the galaxy is [S ii ] enhanced. We infer that the extreme starburst region is density-bounded (i.e., optically thin to ionizing photons), and the rest of the galaxy is ionization-bounded, indicating a Blister-type morphology. We find that the previously reported small escape fraction (10%) of Ly α photons is from our identified density-bounded H ii region of the BBLAE. This escape fraction is likely constrained by a porous dust distribution. We further report a moderate correlation between [S ii ] deficiency and inferred Lyman continuum (LyC) escape fraction using a sample of confirmed LyC leakers studied in the literature, including the BBLAE studied here. The observed correlation also reveals its dependency on the stellar mass and gas-phase metallicity of the leaky galaxies. Finally, the future scope and implications of our work are discussed in detail.