SDSS-IV MaNGA: an observational evidence of density bounded region in a Lyman-$α$ emitter

Abstract

Using Integral Field Unit (IFU) spectroscopy, we present here the spatially resolved morphologies of [SII]λ6717,6731/Hα and [SII]λ6717,6731/[OIII]λ5007 emission line ratios for the first time in a Blueberry Lyman-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 [SII]-deficient, while the rest of the galaxy is [SII]-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 Lyα photons is from our identified densitybounded HII region of the BBLAE. This escape fraction is likely constrained by a porous dust distribution.We further report a moderate correlation between [SII]-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.