Browsing by Author "Zhen-Ya Zheng"

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    A Lyman-α protocluster at redshift 6.9
    (2021) Weida Hu; Junxian Wang; Leopoldo Infante; James E. Rhoads; Zhen-Ya Zheng; Huan Yang; Sangeeta Malhotra; L. Felipe Barrientos; Chunyan Jiang; Jorge González-López; Gonzalo Prieto; Lucia A. Perez; Pascale Hibon; Gaspar Galaz; Alicia Coughlin; Santosh Harish; Xu Kong; Wenyong Kang; Ali Ahmad Khostovan; John Pharo; Francisco Valdes; Isak Wold; Alistair R. Walker; XianZhong Zheng
    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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    LAGER Lyα Luminosity Function at z ∼ 7: Implications for Reionization
    (2022) Isak G. B. Wold; Sangeeta Malhotra; James Rhoads; Junxian Wang; Weida Hu; Lucia A. Perez; Zhen-Ya Zheng; Ali Ahmad Khostovan; Alistair R. Walker; L. Felipe Barrientos; Jorge González-López; Santosh Harish; Leopoldo Infante; Chunyan Jiang; John Pharo; Cristóbal Moya-Sierralta; Franz E. Bauer; Gaspar Galaz; Francisco Valdes; Huan Yang
    We present a new measurement of the Ly alpha luminosity function (LF) at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z similar to 7 intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of 6.1 x 10(6) Mpc(3) is double that of the next largest z similar to 7 survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify N = 95 new z = 6.9 Ly alpha emitter (LAEs) candidates, characterize our survey's completeness and reliability, and compute Ly alpha LFs. The best-fit Schechter LF parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Ly alpha luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to 6.9. This is consistent with an intergalactic medium that was fully ionized as early as redshift z similar to 7 or with a volume-averaged neutral hydrogen fraction of x (H I) < 0.33 at 1 sigma.