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1. SILVERRUSH. XIV. Ly α Luminosity Functions and Angular Correlation Functions from 20,000 Ly α Emitters at z  ∼ 2.2–7.3 from up to 24 deg ² HSC-SSP and CHORUS Surveys: Linking the Postreionization Epoch to the Heart of Reionization

   https://doi.org/10.3847/1538-4365/adb1c0  

   Umeda, Hiroya; Ouchi, Masami; Kikuta, Satoshi; Harikane, Yuichi; Ono, Yoshiaki; Shibuya, Takatoshi; Inoue, Akio K; Shimasaku, Kazuhiro; Liang, Yongming; Matsumoto, Akinori; et al (March 2025, The Astrophysical Journal Supplement Series)

   Abstract We present luminosity functions (LFs) and angular correlation functions (ACFs) derived from 18,960 Lyαemitters (LAEs) atz = 2.2−7.3 over a wide survey area of ≲24 deg²that are identified in the narrowband data of the HSC-SSP and CHORUS surveys. Confirming the large sample with 241 spectroscopically identified LAEs, we determine LyαLFs and ACFs in the brighter luminosity range down to 0.5L_⋆, and confirm that our measurements are consistent with previous studies but offer significantly reduced statistical uncertainties. The improved precision of our ACFs allows us to clearly detect one-halo terms at some redshifts, and provides large-scale bias measurements that indicate host halo masses of ∼10¹¹M_⊙overz ≃ 2−7. By comparing our LyαLF (ACF) measurements with reionization models, we estimate the neutral hydrogen fractions in the intergalactic medium to bex_Hi < 0.05 (= ${0.06}_{-0.03}^{+0.12}$) atz= 5.7 andx_Hi= $0.15_{-0.08}^{+0.10}$( ${0.21}_{-0.14}^{+0.19}$), $0.18_{-0.12}^{+0.14}$, and $0.75_{-0.13}^{+0.09}$atz= 6.6, 7.0, and 7.3, respectively. Our findings suggest that the neutral hydrogen fraction remains relatively low,x_Hi ≲ 0.2, atz = 5−7, but increases sharply atz > 7, reachingx_Hi ∼ 0.9 byz ≃ 8−9, as indicated by recent JWST studies. The combination of our results from LAE observations with recent JWST observations suggests that the major epoch of reionization occurred atz ∼ 7−8, likely driven by the emergence of massive sources emitting significant ionizing photons. 

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2. Measurement of off-shell Higgs boson production in the $H^{\ast }\to ZZ\to 4\ell$ decay channel using a neural simulation-based inference technique in 13 TeV pp collisions with the ATLAS detector

   https://doi.org/10.1088/1361-6633/adcd9a  

   The_ATLAS_Collaboration (May 2025, Reports on Progress in Physics)

   Abstract A measurement of off-shell Higgs boson production in the $H^{\ast }\to ZZ\to 4\ell$decay channel is presented. The measurement uses 140 fb⁻¹of proton–proton collisions at $\sqrt{s}=13$TeV collected by the ATLAS detector at the Large Hadron Collider and supersedes the previous result in this decay channel using the same dataset. The data analysis is performed using a neural simulation-based inference method, which builds per-event likelihood ratios using neural networks. The observed (expected) off-shell Higgs boson production signal strength in the $ZZ\to 4\ell$decay channel at 68% CL is ${0.87}_{-0.54}^{+0.75}$( ${1.00}_{-0.95}^{+1.04}$). The evidence for off-shell Higgs boson production using the $ZZ\to 4\ell$decay channel has an observed (expected) significance of 2.5σ(1.3σ). The expected result represents a significant improvement relative to that of the previous analysis of the same dataset, which obtained an expected significance of 0.5σ. When combined with the most recent ATLAS measurement in the $ZZ\to 2\ell 2\nu$decay channel, the evidence for off-shell Higgs boson production has an observed (expected) significance of 3.7σ(2.4σ). The off-shell measurements are combined with the measurement of on-shell Higgs boson production to obtain constraints on the Higgs boson total width. The observed (expected) value of the Higgs boson width at 68% CL is ${4.3}_{-1.9}^{+2.7}$( ${4.1}_{-3.4}^{+3.5}$) MeV. 

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3. Constraining the Properties of Black Hole Seeds from the Farthest Quasars

   https://doi.org/10.3847/2041-8213/ad09e5  

   Fragione, Giacomo; Pacucci, Fabio (November 2023, The Astrophysical Journal Letters)

   Abstract Over 60 yr after the discovery of the first quasar, more than 275 such sources are identified in the epoch of reionization atz> 6. JWST is now exploring higher redshifts (z≳ 8) and lower-mass (≲10⁷M_⊙) ranges. The discovery of progressively farther quasars is instrumental to constraining the properties of the first population of black holes (BHs), or BH seeds, formed atz∼ 20–30. For the first time, we use Bayesian analysis of the most comprehensive catalog of quasars atz> 6 to constrain the distribution of BH seeds. We show that the mass distribution of BH seeds can be effectively described by combining a power law and a lognormal function tailored to the mass ranges associated with light and heavy seeds, assuming Eddington-limited growth and early seeding time. Our analysis reveals a power-law slope of $-{0.70}_{-0.46}^{+0.46}$and a lognormal mean of ${4.44}_{-0.30}^{+0.30}$. The inferred values of the Eddington ratio, the duty cycle, and the mean radiative efficiency are ${0.82}_{-0.10}^{+0.10}$, ${0.66}_{-0.23}^{+0.23}$, and ${0.06}_{-0.02}^{+0.02}$, respectively. Models that solely incorporate a power law or a lognormal distribution within the specific mass range corresponding to light and heavy seeds are statistically strongly disfavored, unlike models not restricted to this specific range. Our results suggest that including both components is necessary to comprehensively account for the masses of high-redshift quasars, and that both light and heavy seeds formed in the early Universe and grew to form the population of quasars we observe. 

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4. Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 < z < 6

   https://doi.org/10.3847/1538-4357/aceef4  

   Zhu, Yongda; Becker, George D.; Christenson, Holly M.; D’Aloisio, Anson; Bosman, Sarah E.; Bakx, Tom; D’Odorico, Valentina; Bischetti, Manuela; Cain, Christopher; Davies, Frederick B.; et al (September 2023, The Astrophysical Journal)

   Abstract The mean free path of ionizing photons,λ_mfp, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements ofλ_mfpfrom QSO spectra over the redshift range 5 <z< 6, including the first measurements atz≃ 5.3 and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs nearz∼ 5.5, for which we also acquire new [Cii] 158μm redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find ${\lambda }_{\mathrm{mfp}}={9.33}_{-1.80}^{+2.06}$, ${5.40}_{-1.40}^{+1.47}$, ${3.31}_{-1.34}^{+2.74}$, and ${0.81}_{-0.48}^{+0.73}$pMpc atz= 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate thatλ_mfpincreases steadily and rapidly with time over 5 <z< 6. Notably, we find thatλ_mfpdeviates significantly from predictions based on a fully ionized and relaxed IGM as late asz= 5.3. By comparing our results to model predictions and indirectλ_mfpconstraints based on IGM Lyαopacity, we find that the evolution ofλ_mfpis consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6. 

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5. COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens

   https://doi.org/10.3847/1538-4357/ad22de  

   Klein, Maxwell; Sharon, Keren; Napier, Kate; Gladders, Michael D; Khullar, Gourav; Bayliss, Matthew; Dahle, Håkon; Owens, M Riley; Stark, Antony; Brownsberger, Sasha; et al (February 2024, The Astrophysical Journal)

   Abstract We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy atz≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift ofz= 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitudez_AB= 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of thez= 1.001 cluster lens is $M(<5.″77)={1.079}_{-0.007}^{+0.023}\times {10}^{13}{M}_{☉}$, significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈μ_arc〉 = ${76}_{-20}^{+40}$, a factor of ${2.4}_{-0.7}^{+1.4}$greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈μ_arc〉 = ${92}_{-31}^{+37}$. We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to $\log \left(M_{\star }/M_{\odot }\right)=$9.7 ± 0.3 and SFR = ${10.3}_{-4.4}^{+7.0}$M_⊙yr⁻¹, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy. 

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