Browsing by Author "Zheng, Zhenya"

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    Galaxy Protoclusters as Drivers of Cosmic Reionization: I. Bubble Overlap at Redshift z ∼ 7 in LAGER-z7OD1
    (2026) Martin, Crystal L.; Hu, Weida; Wold, Isak G. B.; Faisst, Andreas; Moya Sierralta, Cristóbal Andrés; Malhotra, Sangeeta; Rhoads, James E.; Barrientos Parra, Luis Felipe; Harikane, Yuichi; Infante Lira, Leopoldo; Koekemoer, Anton M.; González López, Jorge; Ouchi, Masami; Xu, Junyan; Yang, Jiayang; Yung, L. Y. Aaron; Weaver, John R.; McCracken, Henry; Zheng, Zhenya; Wang, Junxian
    Since the launch of JWST, the sample size of reionization-era Lyα emitters (LAEs) has been steadily growing; yet inferences about the neutral hydrogen fraction in the intergalactic medium exhibit increasing variance at redshift z ≈ 7, possibly indicating significant field-to-field fluctuations in the progression of cosmic reionization. In this paper, we present new JWST/NIRSpec and Keck/LRIS spectra of nine LAEs in the redshift z ∼ 7 protocluster LAGER-z7OD1. Measurements of Lyα transmission and Lyα velocity offset along multiple sight lines map the Lyα damping wing optical depth across the galaxy overdensity. In the standard context of inside-out ionization, we estimate the radii of ionized bubbles, 0.69 Mpc (physical), based on the distance from each LAE to the first neutral patch along the sight line. The resulting 3D topology reveals three distinct subclusters where the ionized bubbles are approaching overlap. Five of the nine LAEs plausibly ionized their bubbles, where a few bursts of star formation and a modest escape fraction are sufficient. We demonstrate, however, that the actual ionized volumes are likely larger, at least = 0.42–1.29 Mpc (physical), based on an empirical model for interstellar attenuation of Lyα. Modeling galactic attenuation of Lyα significantly increases the inferred intergalactic transmission (thus enlarging the ionized path length). The error bars on the reddening correction allow fully overlapping bubbles, and our results are consistent with accelerated reionization in the protocluster.
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    GREEN PEA GALAXIES REVEAL SECRETS OF Ly alpha ESCAPE
    (IOP PUBLISHING LTD, 2016) Yang, Huan; Malhotra, Sangeeta; Gronke, Max; Rhoads, James E.; Dijkstra, Mark; Jaskot, Anne; Zheng, Zhenya; Wang, Junxian
    We analyze archival Ly alpha spectra of 12 "Green Pea" galaxies observed with the Hubble Space Telescope, model their Ly alpha profiles with radiative transfer models, and explore the dependence of the Ly alpha escape fraction on various properties. Green Pea galaxies are nearby compact starburst galaxies with [O III] lambda 5007 equivalent widths (EWs) of hundreds of angstrom. All 12 Green Pea galaxies in our sample show Ly alpha lines in emission, with an Ly alpha EW distribution similar to high-redshift Ly alpha emitters. Combining the optical and UV spectra of Green Pea galaxies, we estimate their Ly alpha escape fractions and find correlations between Ly alpha escape fraction and kinematic features of Ly alpha profiles. The escape fraction of Ly alpha in these galaxies ranges from 1.4% to 67%. We also find that the Ly alpha escape fraction depends strongly on metallicity and moderately on dust extinction. We compare their high-quality Ly alpha profiles with single H I shell radiative transfer models and find that the Ly alpha escape fraction anticorrelates with the derived H I column densities. Single-shell models fit most Ly alpha profiles well, but not the ones with the. highest escape fractions of Ly alpha. Our results suggest that low H I column density and low metallicity are essential for Ly alpha escape. and make a galaxy an Ly alpha emitter.