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Program Information for 2017B-0330


PI: Sangeeta Malhotra, Arizona State U., sangeeta.malhotra@asu.edu
Address: School of Earth and Space Exploration, PO Box 871404, Tempe, AZ 85287-1404 USA

CoI: Zhenya Zheng, SHAO
CoI: James Rhoads, Arizona State U.
CoI: Junxian Wang, University of Science & Technology of China
CoI: Alistair Walker, CTIO
CoI: Leopoldo Infante, Pontificia Universidad Catolica de Chile
CoI: Linhua Jiang, Peking University
CoI: Chunyan Jiang, SHAO
CoI: Weida Hu, University of Science & Technology of China
CoI: Pascale Hibon, ESO
CoI: Alicia Gonzalez, Arizona State U.

Title: LAGER: Lyman Alpha Galaxies in the Epoch of Reionization (LAEs at z ~ 7 with DECam)

Abstract: High redshift Ly$alpha$ emitting galaxies (LAEs) provide a powerful probe of the cosmic reionization. LAEs can be efficiently detected with deep narrowband imaging surveys. However, prior to our LAGER program, only a handful of $zsim 7$ narrowband-selected LAEs had been spectroscopically confirmed; while hundreds have been confirmed at $z = 6.5$. Does $z = 7$ represent the epoch of reionization, when Ly$alpha$ photons from galaxies are severely scattered by the neutral IGM, or is the lack of z $gtrsim$ 7 objects due to technical difficulties in finding them with declining survey efficiencies beyond 1 micron? Our survey of Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) is the largest narrowband LAE survey at $zsim$ 7, and will answer these questions. Using an optimally designed narrowband filter NB964 on Dark Energy Camera (DECam), LAGER will select over a hundred $zsim$ 7.0 LAE candidates in a total survey area of 12 deg$^2$ (4 fields). In our first fully observed field (COSMOS), we have published 27 photometric candidates (Zheng et al. 2017, arXiv:1703.02985), and have spectroscopically confirmed 3 of the most luminous LAEs (Hu et al. in prep). The luminosity function of LAEs deviates from Schechter function, showing an excess of bright objects. This resembles recent results for LAEs at z=6.5 (Matthee et al 2015), and continuum selected objects at $z>7$ (Bowler et al 2014). It may indicate patchiness in reionization, or different conditions in galaxy formation [e.g. weak or absent feedback] during the first 800 Myr. In either case, it would be good to verify this in more than one field. In this proposal, we request 3 DECam nights to finish the second LAGER field in CDFS, bring it to our full target depth in NB964 and in Y- band. This would help to constrain the Ly$alpha$ equivalent width distribution and anchor the faint end slope of Ly$alpha$ at $zsim$ 7 for a robust measurement of the bright end excess. Thus we will have two distinct fields with deep imaging to quantify cosmic variance and inhomogeneties. Observations of our third field are scheduled for May 2017. CDF-S is a very important field due to broadband photometry of unmatched depth and reliability. %Each field contains several

Program Type: Standard/Extragalactic

Scheduled Nights:
Run 1 (2017B):  CT-4m/DECam -- 3n on Dec 24 - Dec 27 2017


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