DECam Community Science Workshop 2018: Science Highlights, Coming Opportunities, LSST Synergies
May 21-22, 2018 • Tucson, Arizona
The LAGER Project: Probing Reionization at z~7 with the First Narrowband Filter on DECam [20.45 MB PDF]
The resonant properties of Lya photons provide powerful tests of reionization via the statistical analysis of Lya galaxies (LAEs). While hundreds of LAEs have been efficiently detected with deep narrowband surveys up to z = 6.6, they are largely missing at z >~ 7. Is the decline of LAEs at z >~ 7 due to neutral intergalactic medium (IGM), or a decline in CCD sensitivities at 1 micron, or a change in intrinsic properties of LAEs? To answer these questions, we are taking the definitive narrowband LAE survey project at z ~ 7 -- “Lyman Alpha Galaxies in the Epoch of Reionization (LAGER)”. This survey exploits DECam's uniquely large FOV and QE in the near-infrared, as well as a custom narrowband filter at 9640AA built for DECam. This survey is the largest narrowband survey project for z ~ 7 galaxies, and it is also the first narrowband imaging survey with DECam. By testing the apparent decline in the characteristic luminosity of 23 Lya galaxies found in the central 1.4deg x 1.4deg LAGER-COSMOS field, which is the largest Lya galaxy sample at z ~ 7 to date, we have constrained a neutral hydrogen fraction of the intergalactic medium (IGM) of ~40-60% at z ~ 7 (Zheng et al. 2017). More interestingly, we have found an excess of ultra luminous Lya galaxies indicating an ionized bubble in that epoch.
In this talk, I’ll also report the unique power of narrowband imaging with DECam.
Authors: Zhenya Zheng and the LAGER team