The Physics department colloquia are usually on Friday afternoons at 3:30 pm in Lapham Hall Room 160. Coffee and cookies are served at 3:15 pm in the same room. Anyone is welcome.

Early Star Forming Galaxies and Cosmic Reionization
Dr. Daniel P. Stark Asst. Professor, Dept. of Astronomy, The Univ. of Arizona

Deep infrared images from the Hubble and Spitzer Space Telescopes have recently pushed the cosmic frontier back to just 500 million years after the Big Bang, delivering the first large sample of galaxies at redshifts 7<z<10. Sometimes in this redshift window the hydrogen in the intergalactic medium transitioned from mostly neutral to ionized. Over the past five years, our understanding of this process of reionization has improved greatly. The census of early galaxies derived from deep Hubble imaging has provided new insight into the role of star forming galaxies in driving reionization, while follow-up spectroscopy has constrained the timescale over which the transition happened. Most recently, deep MOSFIRE spectra have begun to provide the first glimpse of the physical nature of early galaxies, hinting at a very different population from what has been observed at lower redshifts.

I will review the latest progress in our understanding of the first billion years of cosmic history and discuss the remaining challenges that must be addressed in advance of JWST.