The Effects Of Biconical Outflows On Ly Alpha Escape From Green Peas

We analyze the spectra of 10 Green Pea galaxies, previously studied by Henry et al., using a semi-analytical line transfer model to interpret emission and absorption features observed in UV galactic spectra. We focus our analysis on various ionization states of silicon, associated with the cool (similar to 10(4) K) and warm (similar to 10(5) K) gas. By analyzing low-ionization lines, we study the relationships between the distribution and kinematics of the outflowing H I gas and the observed Ly alpha escape fraction, f(esc)(Ly alpha), as well as the Ly alpha emission peak separation, Delta(peak). We find that outflow geometries that leave a portion of the source uncovered along the line of sight create the best conditions for Ly alpha escape and have narrow peak separations, while geometries that block the observer's view of the source create the worst conditions for Ly alpha escape and have large peak separations. To isolate the effects of outflow kinematics, we restrict our testing set to galaxies with spherical outflows and find that f(esc)(Ly alpha) and the Ly alpha luminosity both increase with the extent of the galactic winds. A simple estimate suggests that the collisional excitation of neutral hydrogen by free electrons in the cool gas of the winds can account for the Ly alpha luminosity observed in these objects. Finally, we speculate on the relationship between outflows and the escape of ionizing radiation from the circumgalactic medium.