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Green Pea Galaxies Reveal Secrets of Ly$��$ Escape

Authors :: Yang, Huan
Malhotra, Sangeeta
Gronke, Max
Rhoads, James E.
Dijkstra, Mark
Jaskot, Anne
Zheng, Zhenya
Wang, Junxian
Publication Year :: 2015
Publisher :: arXiv, 2015.
Abstract: We analyze archival Ly$��$ spectra of 12 "Green Pea" galaxies observed with the Hubble Space Telescope, model their Ly$��$ profiles with radiative transfer models, and explore the dependence of Ly$��$ escape fraction on various properties. Green Pea galaxies are nearby compact starburst galaxies with [OIII]$��$5007 equivalent widths of hundreds of ��. All 12 Green Pea galaxies in our sample show Ly$��$ lines in emission, with a Ly$��$ equivalent width distribution similar to high redshift Ly$��$ emitters. Combining the optical and UV spectra of Green Pea galaxies, we estimate their Ly$��$ escape fractions and find correlations between Ly$��$ escape fraction and kinematic features of Ly$��$ profiles. The escape fraction of Ly$��$ in these galaxies ranges from 1.4% to 67%. We also find that the Ly$��$ escape fraction depends strongly on metallicity and moderately on dust extinction. We compare their high-quality Ly$��$ profiles with single HI shell radiative transfer models and find that the Ly$��$ escape fraction anti-correlates with the derived HI column densities. Single shell models fit most Ly$��$ profiles well, but not the ones with highest escape fractions of Ly$��$. Our results suggest that low HI column density and low metallicity are essential for Ly$��$ escape, and make a galaxy a Ly$��$ emitter.<br />9 figures, ApJ accepted