094339

Understanding the major sources of high-energy ionizing photons and where theyoperate is key to determining how reionization of the Universe proceeds at z >6. This program will target a carefully selected sample of 11 star-forminggalaxies with strong nebular He II emission where photoionization modelingsuggests ultra-luminous X-ray sources (ULXs) are the most plausible source ofhigh-energy ionizing photons. The results will provide a critical benchmark forULX ionizing impact including a first constraint on the EUV-to-soft X-rayionizing continuum from extreme emission line galaxies powered by ULXs. [truncated! Please see actual data for full text]