We investigate the physical origins of the Balmer decrement anomalies in GS-NDG-9422 (Cameron et al. 2023) and RXCJ2248-ID (Topping et al. 2024) galaxies at $z\sim 6$ whose $\mathrm{H}α/\mathrm{H}β$ values are significantly smaller than $2.7$, the latter of which also shows anomalous $\mathrm{H}γ/\mathrm{H}β$ and $\mathrm{H}δ/\mathrm{H}β$ values beyond the errors. Because the anomalous Balmer decrements are not reproduced under the Case B recombination, we explore the nebulae with the optical depths smaller and larger than the Case B recombination by physical modeling. We find two cases quantitatively explaining the anomalies; 1) density-bounded nebulae that are opaque only up to around Ly$γ$-Ly8 transitions and 2) ionization-bounded nebulae partly/fully surrounded by optically-thick excited H{\sc i} clouds. The case of 1) produces more H$β$ photons via Ly$γ$ absorption in the nebulae, requiring fine tuning in optical depth values, while this case helps ionizing photon escape for cosmic reionization. The case of 2) needs the optically-thick excited H{\sc i} clouds with $N_2\simeq 10^{12}-10^{13}$ $\mathrm{cm^{-2}}$, where $N_2$ is the column density of the hydrogen atom with the principal quantum number of $n=2$. Interestingly, the high $N_2$ values qualitatively agree with the recent claims for GS-NDG-9422 with the strong nebular continuum requiring a number of $2s$-state electrons and for RXCJ2248-ID with the dense ionized regions likely coexisting with the optically-thick clouds. While the physical origin of the optically-thick excited H{\sc i} clouds is unclear, these results may suggest gas clouds with excessive collisional excitation caused by an amount of accretion and supernovae in the high-$z$ galaxies.
Probing the Physical Origin of the Balmer Decrement in the Broad-line Region of Nearby Active Galactic Nuclei via Spectral Variability
Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Department of Astronomy and Atmospheric Sciences, Kyungpook National University（庆北大学天文与大气科学系）；Department of Astronomy, Yonsei University（延世大学天文系）；Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文系）
A Mysteriously Tight H$α$-[O III] Correlation and Non-Case B Balmer Decrements Revealed by the Spectra from the James Webb Space Telescope NIRSpec Instrument
Identifying signatures of inflow onto face-on galaxies using the Balmer decrement
Columbia University（哥伦比亚大学）；Tsinghua University（清华大学）；Rensselaer Polytechnic Institute（伦斯勒理工学院）；The University of Texas at Dallas（德克萨斯大学达拉斯分校）；York University（约克大学）
Balmer Decrements and Nebular-Stellar Reddening in JADES Galaxies at $2.7<z<7$
University of California, Los Angeles（加州大学洛杉矶分校）；University of Kentucky（肯塔基大学）；University of California, Riverside（加州大学河滨分校）；University of Arizona（亚利桑那大学）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）
Environmental Regulation of Dust and Star Formation Unveiled by Subaru Dual Narrow-band Imaging: Degree-scale Balmer Decrement Mapping across a z = 0.9 Supercluster
ABCD: The Nuclear Structure of the Little Red Dots Revealted through Absorption, Break, Continuum, and Decrement
Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究院）；Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文学系）；Max-Planck-Institut für Extraterrestrische Physik (MPE)（马克斯·普朗克地外物理研究所）
FRESCO: Constraining Dust Attenuation and Star-Formation Rates of $z\sim 2$ Star-Forming Galaxies with JWST Paschen and Ground-Based Balmer Emission Line Observations
University of California, Riverside（加州大学河滨分校）；University of Geneva（日内瓦大学）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究院）；Yale University（耶鲁大学）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心（CSIC-INTA））；University of California, Los Angeles（加州大学洛杉矶分校）
Balmer Transition Signatures from Gas-Enshrouded, Dust-Poor Active Galactic Nuclei
Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文学系）
Early Results from GLASS-JWST. XXVI. Spatially Resolved Star Formation and Balmer Decrements at $1.1<z<2.3$ from NIRISS Slitless Spectroscopy
School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS)（中国科学院大学天文与空间科学学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Department of Physics and Astronomy, University of California Davis（加州大学戴维斯分校物理与天文学系）；Centre for Astrophysics and Supercomputing, Swinburne University of Technology（斯威本科技大学天体物理学与超级计算中心）；Department of Physics and Astronomy, University of California, Los Angeles（加州大学洛杉矶分校物理与天文学系）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）
The MAGPI Survey: Emission Line Products Data Release and the Role of Spectroscopic Aperture Covering Fraction on the Balmer Decrement-Stellar Mass Relation
The AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. II. Implications for Nebular Dust Corrections, Nebular SFRs, and Differential Reddening
University of California, Riverside（加州大学河滨分校）；University of California, Los Angeles（加州大学洛杉矶分校）；University of California, Davis（加州大学戴维斯分校）；University of Arizona（亚利桑那大学）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理学研究所）；California Institute of Technology（加州理工学院）；University College London（伦敦大学学院）
Evidence of violation of Case B recombination in Little Red Dots
Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Jodrell Bank Centre for Astrophysics, University of Manchester（曼彻斯特大学乔德雷尔银行天体物理学中心）；Department of Astronomy, University of Geneva（日内瓦大学天文学系）
研究通过分析Little Red Dots的氢巴尔末线比值，发现其中一些天体偏离Case B重组预期，可能与尘埃消光或高密度气体有关。
Spatially Resolved Nebular-Stellar Reddening with JWST/NIRISS
INAF – Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；University of California, Los Angeles（加州大学洛杉矶分校）；Space Telescope Science Institute（太空望远镜科学研究所）；Johns Hopkins University（约翰斯·霍普金斯大学）；California Institute of Technology（加州理工学院）；Stockholm University（斯德哥尔摩大学）；Minnesota Institute for Astrophysics（明尼苏达天体物理研究所）
Do little red dots really form a distinct class of astronomical objects?
Université Paris-Saclay（巴黎萨克雷大学）；Université Paris Cité（巴黎西岱大学）；CEA（法国原子能和替代能源委员会）；CNRS（法国国家科学研究中心）；INAF – Osservatorio di Astrofisica e Scienza dello Spazio（意大利国家天体物理研究所空间天文学和天体物理学观测站）；University of Massachusetts Amherst（马萨诸塞大学阿默斯特分校）；Colby College（科尔比学院）；Nanjing University（南京大学）
LEGGOS III: Mapping Star Formation and Dust in Gravitationally Lensed Galaxies with $\textit{SUMAC}$, a UMAP and Clustering Framework
University of Washington（华盛顿大学）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；University of Maryland, Baltimore County（马里兰大学巴尔的摩分校）；Stockholm University（斯德哥尔摩大学）
