GREEN PEA GALAXIES REVEAL SECRETS OF Ly? ESCAPE

In star-forming galaxies, a lot of Ly$\alpha$ photons were generated in HII regions surrounding massive stars. The escape of Ly$\alpha$ photons from galaxies is a key issue in studying high redshift galaxies and probing cosmic reionization with Ly$\alpha$. To understand Ly$\alpha$ escape, it is valuable to study high quality Ly$\alpha$ profiles in Ly$\alpha$ emitters. However, such studies are rare due to the faintness of high-z Ly$\alpha$ emitters and the lack of local analogs with high Ly$\alpha$ equivalent width. Here we show that "Green Pea" galaxies are the best local analogs of high-z Ly$\alpha$ emitters and their high quality Ly$\alpha$ profiles demonstrate low HI column density is the key to Ly$\alpha$ escape. The Ly$\alpha$ escape fraction shows correlations with a few features of Ly$\alpha$ profiles. We compared the Ly$\alpha$ profiles with outflowing HI shell radiative transfer model and found that the best-fit HI column density is anti-correlated with the Ly$\alpha$ escape fraction. We also found an anti-correlation between Ly$\alpha$ escape fraction and galactic metallicity. Our results support that LAEs with high Ly$\alpha$ escape fraction have low metallicity, low HI column density, and mild HI gas outflow.