Limits on Lyman Continuum escape from z=2.2 H-alpha emitting galaxies
  The leakage of Lyman continuum photons from star forming galaxies is an
elusive parameter. When observed, it provides a wealth of information on star
formation in galaxies and the geometry of the interstellar medium, and puts
constraints on the role of star forming galaxies in the reionization of the
universe. H-alpha-selected galaxies at z~2 trace the highest star formation
population at the peak of cosmic star formation history, providing a base for
directly measuring Lyman continuum escape. Here we present this method, and
highlight its benefits as well as caveats. We also use the method on 10 H-alpha
emitters in the Chandra Deep Field South at z=2.2, also imaged with the Hubble
Space Telescope in the ultraviolet. We find no individual Lyman continuum
detections, and our stack puts a 5 sigma upper limit on the average absolute
escape fraction of <24%, consistent with similar studies. With future planned
observations, the sample sizes would rapidly increase and the method presented
here would provide very robust constraints on the escape fraction.
