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Galaxy Protoclusters as Drivers of Cosmic Reionization: I. Bubble Overlap at Redshift z ~ 7 in LAGER-z7OD1

Crystal L. Martin, Weida Hu, Isak G. B. Wold, Andreas Faisst, Cristobal Moya-Sierralta, Sangeeta Malhotra, James E. Rhoads, Luis Felipe Barrientos, Yuichi Harikane, Leopoldo Infante, Anton Koekemoer, Jorge Gonzalez Lopez, Masami Ouchi, Junyan Xu, Jiayang Yang, L. Y. Aaron Yung, John R. Weaver, Henry McCracken, Zhenya Zheng, Junxian Wang

TL;DR

This study leverages JWST/NIRSpec and Keck/LRIS spectroscopy of nine Ly$\\alpha$ emitters in the $z \sim 6.93$ protocluster LAGER-z7OD1 to map Ly$\\alpha$ transmission and velocity offsets, enabling estimates of ionized-bubble radii around galaxies. By analyzing damping-wing attenuation and correcting for interstellar transmission, it finds $R_{\min} = 0.07$–$0.69$ Mpc for individual bubbles and converges on larger effective extents, $R_{ism} = 0.42$–$1.29$ Mpc, when considering galactic attenuation. The data reveal three sub-clusters with bubbles approaching overlap, supporting a picture of accelerated reionization within a overdense protocluster. These results highlight how early, clustered galaxy assembly can drive topology changes in cosmic reionization through bubble growth and overlap.

Abstract

Since the launch of JWST, the sample size of reionization-era Lyman-alpha-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 Lyman-alpha-transmission and Lyman-alpha velocity offset along multiple sightlines map the Lyman-alpha damping wing optical depth across the galaxy overdensity. In the standard context of inside-out ionization, we estimate radii of ionized bubbles (R(min) = 0.07 - 0.69 Mpc) based on the distance from each LAE to the first neutral patch along the sightline. The resulting 3D topology reveals three distinct sub-clusters where the ionized bubbles are approaching overlap. Five of the nine LAEs plausibly ionized their bubbles, 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 R(ism) = 0.42 - 1.29 Mpc, based on an empirical model for interstellar attenuation of Lyman-alpha. Modeling galactic attenuation of Lyman-alpha significantly increases the inferred intergalactic transmission (thus enlarging the ionized pathlength). The errorbars on the reddening correction allow fully overlapping bubbles, and our results are consistent with accelerated reionization in the protocluster.

Galaxy Protoclusters as Drivers of Cosmic Reionization: I. Bubble Overlap at Redshift z ~ 7 in LAGER-z7OD1

TL;DR

This study leverages JWST/NIRSpec and Keck/LRIS spectroscopy of nine Ly emitters in the protocluster LAGER-z7OD1 to map Ly transmission and velocity offsets, enabling estimates of ionized-bubble radii around galaxies. By analyzing damping-wing attenuation and correcting for interstellar transmission, it finds – Mpc for individual bubbles and converges on larger effective extents, – Mpc, when considering galactic attenuation. The data reveal three sub-clusters with bubbles approaching overlap, supporting a picture of accelerated reionization within a overdense protocluster. These results highlight how early, clustered galaxy assembly can drive topology changes in cosmic reionization through bubble growth and overlap.

Abstract

Since the launch of JWST, the sample size of reionization-era Lyman-alpha-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 Lyman-alpha-transmission and Lyman-alpha velocity offset along multiple sightlines map the Lyman-alpha damping wing optical depth across the galaxy overdensity. In the standard context of inside-out ionization, we estimate radii of ionized bubbles (R(min) = 0.07 - 0.69 Mpc) based on the distance from each LAE to the first neutral patch along the sightline. The resulting 3D topology reveals three distinct sub-clusters where the ionized bubbles are approaching overlap. Five of the nine LAEs plausibly ionized their bubbles, 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 R(ism) = 0.42 - 1.29 Mpc, based on an empirical model for interstellar attenuation of Lyman-alpha. Modeling galactic attenuation of Lyman-alpha significantly increases the inferred intergalactic transmission (thus enlarging the ionized pathlength). The errorbars on the reddening correction allow fully overlapping bubbles, and our results are consistent with accelerated reionization in the protocluster.
Paper Structure (9 sections, 1 figure, 1 table)

This paper contains 9 sections, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. Observations
  3. Broadband Imaging of LAEs
  4. NIRSpec Multi-object Spectroscopy
  5. Keck/LRIS Multislit Spectroscopy
  6. Results
  7. NIRCam Imaging of LAEs
  8. Registration of Ly$\alpha$ and NIRCam Images
  9. The UV Continuum Level & W(Ly$\alpha$)

Figures (1)

  • Figure 1: NIRCam images of LAGER-z7OD LAEs. The centroid of the Ly$\alpha$ nebulae (tiny white circles) lie between the clumps discovered in the rest-UV and rest-optical images. Each cutout is 2$.\!\!^{\prime\prime}$25 by 2$.\!\!^{\prime\prime}$25; north is up and east is the left. The 1$.\!\!^{\prime\prime}$0 diameter black circles illustrate the PSF of the LAGER narrowband images. The smaller white circle is the SDOM.