Browsing by Author "Hibon, Pascale"

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    A Lyman-α protocluster at redshift 6.9
    (2021) Hu, Weida ; Wang, Junxian ; Infante, Leopoldo ; Rhoads, James E. ; Zheng, Zhen-Ya ; Yang, Huan ; Malhotra, Sangeeta ; Barrientos, L. Felipe ; Jiang, Chunyan ; González-López, Jorge ; Prieto, Gonzalo; Perez, Lucia A. ; Hibon, Pascale; Galaz, Gaspar ; Coughlin, Alicia ; Harish, Santosh ; Kong, Xu ; Kang, Wenyong ; Khostovan, Ali Ahmad; Pharo, John ; Valdes, Francisco ; Wold, Isak ; Walker, Alistair R. ; Zheng, XianZhong
    Protoclusters, the progenitors of the most massive structures in the Universe, have been identified at redshifts of up to 6.6 (refs. (1-6)). Besides exploring early structure formation, searching for protoclusters at even higher redshifts is particularly useful to probe the reionization. Here we report the discovery of the protocluster LAGER-z7OD1 at a redshift of 6.93, when the Universe was only 770 million years old and could be experiencing rapid evolution of the neutral hydrogen fraction in the intergalactic medium(7,8). The protocluster is identified by an overdensity of 6 times the average galaxy density, and with 21 narrowband selected Lyman-alpha galaxies, among which 16 have been spectroscopically confirmed. At redshifts similar to or above this record, smaller protogroups with fewer members have been reported(9,10). LAGER-z7OD1 shows an elongated shape and consists of two subprotoclusters, which would have merged into one massive cluster with a present-day mass of 3.7 x 10(15) solar masses. The total volume of the ionized bubbles generated by its member galaxies is found to be comparable to the volume of the protocluster itself, indicating that we are witnessing the merging of the individual bubbles and that the intergalactic medium within the protocluster is almost fully ionized. LAGER-z7OD1 thus provides a unique natural laboratory to investigate the reionization process.
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    Design for the First Narrowband Filter for the Dark Energy Camera: Optimizing the LAGER Survey for z ∼ 7 Galaxies
    (2019) Zheng, Zhen-Ya; Rhoads, James E.; Wang, Jun-Xian; Malhotra, Sangeeta; Walker, Alistair; Mooney, Thomas; Jiang, Chunyan; Hu, Weida; Hibon, Pascale; Jiang, Linhua; Infante, Leopoldo; Barrientos, L. Felipe; Galaz, Gaspar; Valdes, Francisco; Wester, William; Yang, Huan; Coughlin, Alicia; Harish, Santosh; Kang, Wenyong; Khostovan, Ali Ahmad; Kong, Xu; Perez, Lucia A.; Pharo, John; Wold, Isak; Zheng, XianZhong
    We present the design for the first narrowband filter, NB964, for the Dark Energy Camera (DECam), which is operated on the 4-m Blanco Telescope at the Cerro Tololo Inter-American Observatory. The NB964 filter profile is essentially defined by maximizing the power of searching for Lyman-alpha emitting galaxies (LAEs) in the epoch of reionization, with the consideration of the night sky background in the near-infrared and the DECam quantum efficiency. The NB964 filter was manufactured by Materion in 2015. It has a central wavelength of 964.2 nm and a full width at half maximum (FWHM) of 9.2 nm. An NB964 survey named Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) has been ongoing since December 2015. Here, we report results of lab tests, on-site tests, and observations with the NB964 filter. The excellent performances of this filter ensure that the LAGER project is able to detect LAEs at z similar to 7 with a high efficiency.