We analyze archival Lyα spectra of 12 "Green Pea" galaxies observed with the Hubble Space Telescope, model their Lyα profiles with radiative transfer models, and explore the dependence of Lyα escape fraction on various properties. Green Pea galaxies are nearby compact starburst galaxies with [OIII]λ5007 equivalent widths of hundreds of \AA. All 12 Green Pea galaxies in our sample show Lyα lines in emission, with a Lyα equivalent width distribution similar to high redshift Lyα emitters. Combining the optical and UV spectra of Green Pea galaxies, we estimate their Lyα escape fractions and find correlations between Lyα escape fraction and kinematic features of Lyα profiles. The escape fraction of Lyα in these galaxies ranges from 1.4% to 67%. We also find that the Lyα escape fraction depends strongly on metallicity and moderately on dust extinction. We compare their high-quality Lyα profiles with single HI shell radiative transfer models and find that the Lyα escape fraction anti-correlates with the derived HI column densities. Single shell models fit most Lyα profiles well, but not the ones with highest escape fractions of Lyα. Our results suggest that low HI column density and low metallicity are essential for Lyα escape, and make a galaxy a Lyα emitter.
@article{arxiv.1506.02885,
title = {Green Pea Galaxies Reveal Secrets of Ly$\alpha$ Escape},
author = {Huan Yang and Sangeeta Malhotra and Max Gronke and James E. Rhoads and Mark Dijkstra and Anne Jaskot and Zhenya Zheng and Junxian Wang},
journal= {arXiv preprint arXiv:1506.02885},
year = {2016}
}