Hubble Space Telescope Emission Line Galaxies at z ~ 2: The Lyα Escape Fraction
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2014
- DOI:
- 10.1088/0004-637X/796/1/64
- arXiv:
- arXiv:1409.8304
- Bibcode:
- 2014ApJ...796...64C
- Keywords:
-
- cosmology: observations;
- galaxies: evolution;
- galaxies: formation;
- galaxies: luminosity function;
- mass function;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 14 pages, 3 figures, Accepted to ApJ