Hubble Space Telescope Emission Line Galaxies at z ~ 2: The Lyα Escape Fraction
Schneider, Donald P.; Blanc, Guillermo A.; Gronwall, Caryl; Gawiser, Eric; Ciardullo, Robin; Drory, Niv; Zeimann, Gregory R.; Hagen, Alex; Hill, Gary J.; Gebhardt, Henry; Malz, A. I.
United States
Abstract
We compare the Hβ line strengths of 1.90 < z < 2.35 star-forming galaxies observed with the near-IR grism of the Hubble Space Telescope with ground-based measurements of Lyα from the HETDEX Pilot Survey and narrow-band imaging. By examining the line ratios of 73 galaxies, we show that most star-forming systems at this epoch have a Lyα escape fraction below ~6%. We confirm this result by using stellar reddening to estimate the effective logarithmic extinction of the Hβ emission line (c Hβ = 0.5) and measuring both the Hβ and Lyα luminosity functions in a ~100, 000 Mpc3 volume of space. We show that in our redshift window, the volumetric Lyα escape fraction is at most 4.4+2.1-1.2%, with an additional systematic ~25% uncertainty associated with our estimate of extinction. Finally, we demonstrate that the bulk of the epoch's star-forming galaxies have Lyα emission line optical depths that are significantly greater than that for the underlying UV continuum. In our predominantly [O III] λ5007-selected sample of galaxies, resonant scattering must be important for the escape of Lyα photons.