A Spectroscopic Study of Lyman Alpha Emission at z ~ 6 – 8 as a Probe of Cosmic Reionization

Intae Jung (UT Austin)
Friday, November 2, 2018 - 12:15pm

Cosmic reionization is the last major phase transition of the intergalactic medium, and scrutinizing the detailed evolution of the IGM is a key frontier in observational cosmology. Due to the resonant nature of Lyα scattering by neutral hydrogen, the presence of neutral hydrogen in the intergalactic medium (IGM) attenuates a Lyα emission strength. Thus, the distribution of Lyα emission provides a presently accessible method for studying the state of the IGM into the reionization era. We carried out 14 nights of deep spectroscopic observations using the Keck DEIMOS (optical) and MOSFIRE (near-infrared) spectrographs to search for Lyα emission from 178 photometric-redshift selected galaxies at z = 5.5 – 8.3 from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) survey. We study the Lyα emission strength through constraining the Lyα equivalent width (EW) distribution with our spectroscopic dataset by constructing detailed simulations of mock emission lines, accounting for the observational conditions (e.g., exposure time, wavelength coverage, and sky emission) and galaxy photometric redshift probability distribution functions. Our measure of the EW distribution at 6 < z < 7 with the Lyα emission lines detected from the DEIMOS observations provides additional evidence that the Lyα EW distribution declines at z > 6, suggesting an increasing fraction of neutral hydrogen in the IGM.  I will also present new results from our MOSFIRE observations, which include a new Lyα detection at z = 7.6 as well as an updated measure of the previously confirmed z=7.51 Lyα emission with longer exposure.

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