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

TL;DR

This study uses spatially resolved spectroscopy to identify a density-bounded star-forming region in a nearby Lyman-alpha emitter, providing insights into LyC photon escape mechanisms and galaxy morphology.

Contribution

It presents the first spatially resolved emission line ratio morphologies in a Blueberry Lyman-alpha emitter, revealing a density-bounded starburst region and its relation to LyC escape.

Findings

The extreme starburst region is density-bounded and [SII]-deficient.

The Lyα photon escape fraction is linked to the density-bounded region.

A correlation exists between [SII]-deficiency and LyC escape fraction.

Abstract

Using Integral Field Unit (IFU) spectroscopy, we present here the spatially resolved morphologies of [SII]$\lambda$6717,6731/H$\alpha$ and [SII]$\lambda$6717,6731/[OIII]$\lambda$5007 emission line ratios for the first time in a Blueberry Lyman-$\alpha$ emitter (BBLAE) at z $\sim$ 0.047. Our derived morphologies show that the extreme starburst region of the BBLAE, populated by young ($\leqslant$ 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 Ly$\alpha$ photons is from our identified density-bounded 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.