Event DetailsEvent Dates: Friday, July 11, 2014 - 12:00pmSeminar Location: CASA Conference Room C324Speaker Name(s): Matt MalloySpeaker Affiliation(s): University of Pennsylvania Seminar Type/SubjectScientific Seminar Type: Astrophysics Lunch SeminarEvent Details & Abstract: It has been more than 50 years since Gunn & Peterson noted that the lack of prominent absorption troughs in quasar spectra, blueward of the Lyman-alpha line, implied that hydrogen in the intergalactic medium is highly ionized. In 2001, the first observations of "Gunn-Peterson Troughs" were made using z ~ 6 quasar spectra. Despite this occurring more than a decade ago, the precise interpretation of these measurements, and their implications for hydrogen reionization, remain unclear. In this talk, I will briefly describe the possibility that neutral hydrogen islands exist among regions of highly-ionized gas in the IGM as late as z ~ 5 - 6, even though the common wisdom is that hydrogen reionization has completed by z ~ 6. I will then propose three tests by which existing quasar spectra can be used to search for remaining neutral hydrogen islands in the z ~ 5 - 6 IGM.