---
DOAJ_listed: '1'
OA_place: publisher
OA_type: gold
PlanS_conform: '1'
_id: '20545'
abstract:
- lang: eng
  text: The H i gas distribution in damped Lyman $\alpha$ absorbers (DLAs) has remained
    elusive due to the point-source nature of background quasar emission. Observing
    DLAs against spatially extended background galaxies provides a new method for
    constraining their size and structure. Using the Keck Cosmic Web Imager, we present
    the first ‘silhouette’ image of a DLA at $z=3.34$, identified in the spectrum
    of a background galaxy at $z=3.61$. Although the silhouette remains unresolved
    due to limited spatial resolution, this represents a successful proof-of-concept
    for studying DLA morphology using extended background sources. Possible residual
    emission in the DLA trough suggests an optical depth contrast exceeding $10^7$
    in the internal structure, implying a sharp edge or patchy structure. A Lyman $\alpha$
    emitter (LAE) at $z_{\rm LAE}=3.3433\pm 0.0005$, consistent with the DLA redshift,
    is detected at an angular separation of $1{{_{.}^{\prime\prime}} }73\pm 0{{_{.}^{\prime\prime}}
    }28$ ($12.9\pm 2.1$ kpc). The DLA is surrounded by three galaxies within 140 kpc
    in projected distance and 500 km s$^{-1}$ in line-of-sight velocity, indicating
    that it resides in the circumgalactic medium of the LAE or within a galaxy group/protocluster
    environment. An O i  $\lambda 1302$ absorption at $z_{\rm OI}=3.3288\pm 0.0004$
    is also detected along the line of sight. This absorber may trace metal-enriched
    outflow from the LAE or a gas-rich galaxy exhibiting the highest star formation
    activity among the surrounding galaxies. Future large spectroscopic surveys of
    galaxies will expand such a DLA sample, and three-dimensional spectroscopy for
    it will shed new light on the role of intergalactic dense gas in galaxy formation
    and evolution.
acknowledgement: "We thank Seiji Fujimoto for discussions in the early stage of this
  work. We were supported by JSPS (Japan Society for the Promotion of Science) KAKENHI
  Grant Numbers 21H04489, 22H04939, 23H00131, 24H00002, 24K17095, 25K01038, and 25K01039.
  Some of the data presented herein were obtained at Keck Observatory, which is a
  private 501(c)3 non-profit organization operated as a scientific partnership among
  the California Institute of Technology,\r\nthe University of California, and the
  National Aeronautics and Space Administration. The Observatory was made possible
  by the generous financial support of the W. M. Keck Foundation. The authors wish
  to recognize and acknowledge the very significant cultural role and reverence that
  the summit of Maunakea has always had within the Native Hawaiian community. We are
  most fortunate to have the opportunity to conduct observations from this\r\nmountain.
  This research made use of MONTAGE. It is funded by the National Science Foundation
  under Grant Number ACI-1440620, and was previously funded by the National Aeronautics
  and Space Administration’s Earth Science Technology Office, Computation\r\nTechnologies
  Project, underCooperative Agreement Number NCC5-626 between NASA and the California
  Institute of Technology."
article_processing_charge: Yes
article_type: original
author:
- first_name: Fuga
  full_name: Komori, Fuga
  last_name: Komori
- first_name: Akio K
  full_name: Inoue, Akio K
  last_name: Inoue
- first_name: Ken
  full_name: Mawatari, Ken
  last_name: Mawatari
- first_name: Yuma
  full_name: Sugahara, Yuma
  last_name: Sugahara
- first_name: Hideki
  full_name: Umehata, Hideki
  last_name: Umehata
- first_name: Rhythm
  full_name: Shimakawa, Rhythm
  last_name: Shimakawa
- first_name: Satoshi
  full_name: Yamanaka, Satoshi
  last_name: Yamanaka
- first_name: Takuya
  full_name: Hashimoto, Takuya
  last_name: Hashimoto
- first_name: Jorryt J
  full_name: Matthee, Jorryt J
  id: 7439a258-f3c0-11ec-9501-9df22fe06720
  last_name: Matthee
  orcid: 0000-0003-2871-127X
- first_name: Toru
  full_name: Misawa, Toru
  last_name: Misawa
citation:
  ama: Komori F, Inoue AK, Mawatari K, et al. The first direct imaging of the silhouette
    of a damped Lyman α system along the line-of-sight to a background galaxy. <i>Monthly
    Notices of the Royal Astronomical Society</i>. 2025;543(3):2943-2957. doi:<a href="https://doi.org/10.1093/mnras/staf1622">10.1093/mnras/staf1622</a>
  apa: Komori, F., Inoue, A. K., Mawatari, K., Sugahara, Y., Umehata, H., Shimakawa,
    R., … Misawa, T. (2025). The first direct imaging of the silhouette of a damped
    Lyman α system along the line-of-sight to a background galaxy. <i>Monthly Notices
    of the Royal Astronomical Society</i>. Oxford University Press. <a href="https://doi.org/10.1093/mnras/staf1622">https://doi.org/10.1093/mnras/staf1622</a>
  chicago: Komori, Fuga, Akio K Inoue, Ken Mawatari, Yuma Sugahara, Hideki Umehata,
    Rhythm Shimakawa, Satoshi Yamanaka, Takuya Hashimoto, Jorryt J Matthee, and Toru
    Misawa. “The First Direct Imaging of the Silhouette of a Damped Lyman α System
    along the Line-of-Sight to a Background Galaxy.” <i>Monthly Notices of the Royal
    Astronomical Society</i>. Oxford University Press, 2025. <a href="https://doi.org/10.1093/mnras/staf1622">https://doi.org/10.1093/mnras/staf1622</a>.
  ieee: F. Komori <i>et al.</i>, “The first direct imaging of the silhouette of a
    damped Lyman α system along the line-of-sight to a background galaxy,” <i>Monthly
    Notices of the Royal Astronomical Society</i>, vol. 543, no. 3. Oxford University
    Press, pp. 2943–2957, 2025.
  ista: Komori F, Inoue AK, Mawatari K, Sugahara Y, Umehata H, Shimakawa R, Yamanaka
    S, Hashimoto T, Matthee JJ, Misawa T. 2025. The first direct imaging of the silhouette
    of a damped Lyman α system along the line-of-sight to a background galaxy. Monthly
    Notices of the Royal Astronomical Society. 543(3), 2943–2957.
  mla: Komori, Fuga, et al. “The First Direct Imaging of the Silhouette of a Damped
    Lyman α System along the Line-of-Sight to a Background Galaxy.” <i>Monthly Notices
    of the Royal Astronomical Society</i>, vol. 543, no. 3, Oxford University Press,
    2025, pp. 2943–57, doi:<a href="https://doi.org/10.1093/mnras/staf1622">10.1093/mnras/staf1622</a>.
  short: F. Komori, A.K. Inoue, K. Mawatari, Y. Sugahara, H. Umehata, R. Shimakawa,
    S. Yamanaka, T. Hashimoto, J.J. Matthee, T. Misawa, Monthly Notices of the Royal
    Astronomical Society 543 (2025) 2943–2957.
date_created: 2025-10-27T08:18:07Z
date_published: 2025-09-25T00:00:00Z
date_updated: 2025-12-01T15:07:43Z
day: '25'
ddc:
- '520'
department:
- _id: JoMa
doi: 10.1093/mnras/staf1622
external_id:
  isi:
  - '001592326700001'
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has_accepted_license: '1'
intvolume: '       543'
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issue: '3'
language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
month: '09'
oa: 1
oa_version: Published Version
page: 2943-2957
publication: Monthly Notices of the Royal Astronomical Society
publication_identifier:
  eissn:
  - 1365-2966
  issn:
  - 0035-8711
publication_status: published
publisher: Oxford University Press
quality_controlled: '1'
scopus_import: '1'
status: public
title: The first direct imaging of the silhouette of a damped Lyman α system along
  the line-of-sight to a background galaxy
tmp:
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  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
  short: CC BY (4.0)
type: journal_article
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volume: 543
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...