Studying Lyman-? Escape In Green Pea Galaxies

Hydrogen Ly? emission line is a powerful tool to study high redshift galaxies and probe reionization.As Lya is a resonance line,to use Ly? tool,we need to under-stand how Lya escape out of a galaxy.Green Pea galaxies are nearby compact starburst galaxies with strong[O?]A5007 emission line.In my PhD thesis,I used Green Peas as analogs of high-z Ly?-emitting galaxies to study Ly? escape in details.We also studied az?5.7 Ly? emission line with ultra-broad redwing.We used HST/COS to observe the UV spectra of 20 Green Peas.Combining it with five other small samples scattered in the archive,I assembled the first statistical sample of 43 Green Peas and studied their Ly? properties.The Lya equivalent width distribution of Green Pea is similar to that of high-z Ly? emitters(LAEs),showing Green Peas generally are the best nearby analogs of high-z LAEs.In Ly? escape process,the resonant scatterings by HI gas can significantly modify the Lya line profile.Many Green Peas in our sample show double-peaked Ly? profiles.We found that the Ly? escape fraction anti-correlates with a few Lya kinematic features-blue peak velocity,red peak velocity,and the Full Width at Half Maximum of the red portion of Lya profile.We explored the dependence of Lya escape on many galactic properties measured from SDSS optical spectra and HST UV spectra and images.We found many correla-tions-Ly? escape fraction generally increases at lower dust extinction,lower metallic-ity,lower stellar mass,higher[O?]/[O?]ratio,larger gas outflow velocity,and smaller HI gas column density.The Lya escape fraction doesn't have an obvious relation with UV morphology and the sizes of Green Peas.Many of these relations are unclear in previous studies.We fit an empirical linear relation between Ly? escape fraction,dust extinction,and Ly? red peak velocity.This relation can be used to predict the Ly? escape fraction of LAEs and isolate the effect of intergalactic medium scatterings from Lya escape.As JWST can measure the dust extinction and Lya,red peak velocity of some z>7-LAEs,this relation makes it possible to measure the intergalactic HI column density along the line of sight of each LAE and probe reionization with their Lya lines.We also studied the Ly? and UV sizes of Green Pea galaxies using their HST/COS 2D spectra.This is the first science result that uses the spatial information in COS 2D spectra.We found that most Green Peas(including 5 Lyman-continuum leakers)have Ly? sizes about 2 to 4 times larger than UV continuum sizes.We showed for the first time that Ly? sizes at different frequencies are different in some LAEs.These results indicate that Ly? size tends to be more compact at fewer HI scatterings and higher Ly?escape fraction.