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1. The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data Set

   https://doi.org/10.3847/2041-8213/ad6f9f  

   Abbott, DES_Collaboration_T_M_C; Acevedo, M.; Aguena, M.; Alarcon, A.; Allam, S.; Alves, O.; Amon, A.; Andrade-Oliveira, F.; Annis, J.; Armstrong, P.; et al (October 2024, The Astrophysical Journal Letters)

   Abstract We present cosmological constraints from the sample of Type Ia supernovae (SNe Ia) discovered and measured during the full 5 yr of the Dark Energy Survey (DES) SN program. In contrast to most previous cosmological samples, in which SNe are classified based on their spectra, we classify the DES SNe using a machine learning algorithm applied to their light curves in four photometric bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey of the host galaxies. After accounting for the likelihood of each SN being an SN Ia, we find 1635 DES SNe in the redshift range 0.10 <z< 1.13 that pass quality selection criteria sufficient to constrain cosmological parameters. This quintuples the number of high-qualityz> 0.5 SNe compared to the previous leading compilation of Pantheon+ and results in the tightest cosmological constraints achieved by any SN data set to date. To derive cosmological constraints, we combine the DES SN data with a high-quality external low-redshift sample consisting of 194 SNe Ia spanning 0.025 <z< 0.10. Using SN data alone and including systematic uncertainties, we find Ω_M= 0.352 ± 0.017 in flat ΛCDM. SN data alone now require acceleration (q₀< 0 in ΛCDM) with over 5σconfidence. We find $({\mathrm{\Omega }}_{\mathrm{M}},w)=({0.264}_{-0.096}^{+0.074},-{0.80}_{-0.16}^{+0.14})$in flatwCDM. For flatw₀w_aCDM, we find $({\mathrm{\Omega }}_{\mathrm{M}},w_0,w_a)=({0.495}_{-0.043}^{+0.033},-{0.36}_{-0.30}^{+0.36},-{8.8}_{-4.5}^{+3.7})$, consistent with a constant equation of state to within ∼2σ. Including Planck cosmic microwave background, Sloan Digital Sky Survey baryon acoustic oscillation, and DES 3 × 2pt data gives (Ω_M,w) = (0.321 ± 0.007, −0.941 ± 0.026). In all cases, dark energy is consistent with a cosmological constant to within ∼2σ. Systematic errors on cosmological parameters are subdominant compared to statistical errors; these results thus pave the way for future photometrically classified SN analyses. 

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2. Constraining Cosmology with Double-source-plane Strong Gravitational Lenses from the AGEL Survey

   https://doi.org/10.3847/1538-4357/ae092e  

   Bowden, Duncan J; Sahu, Nandini; Shajib, Anowar J; Tran, Kim-Vy; Barone, Tania M; G_C, Keerthi Vasan; Ballard, Daniel J; Collett, Thomas E; Dalessandro, Faith; Ferrami, Giovanni; et al (October 2025, The Astrophysical Journal)

   Double-source-plane strong gravitational lenses (DSPLs), with two sources at different redshifts, are independent cosmological probes of the dark energy equation of state parameterwand the matter density parameter Ω_m. We present the lens model for the DSPL AGEL035346−170639 and infer cosmological constraints from this system for flat Λ cold dark matter and flatwCDM cosmologies. From the joint posterior ofwand Ω_min the flatwCDM cosmology, we extract the following median values and 1σuncertainties: $w=-1.52_{-0.33}^{+0.49}$and ${\mathrm{\Omega }}_{\mathrm{m}}=0.192_{-0.131}^{+0.305}$from AGEL0353 alone. Combining our measurements with two previously analyzed DSPLs, we present the joint constraint on these parameters from a sample of three, the largest galaxy-scale DSPL sample used for cosmological measurement to date. The combined precision ofwfrom three DSPLs is higher by 15% over AGEL0353 alone. Combining DSPL and cosmic microwave background (CMB) measurements improves the precision ofwfrom CMB-only constraints by 39%, demonstrating the complementarity of DSPLs with the CMB. Despite their promising constraining power, DSPLs are limited by sample size, with only a handful discovered so far. Although ongoing and near-future wide-area sky surveys will increase the number of known DSPLs by up to two orders of magnitude, these systems will still require dedicated high-resolution imaging and spectroscopic follow-ups like those presented in this paper. Our ASTRO 3D Galaxy Evolution with Lenses collaboration is undertaking such follow-up campaigns for several newly discovered DSPLs and will provide cosmological measurements from larger samples of DSPLs in the future. 

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3. Multiprobe cosmology from the abundance of SPT clusters and DES galaxy clustering and weak lensing

   https://doi.org/10.1103/PhysRevD.111.063533  

   Bocquet, S; Grandis, S; Krause, E; To, C; Bleem, L E; Klein, M; Mohr, J J; Schrabback, T; Alarcon, A; Alves, O; et al (March 2025, Physical Review D)

   Cosmic shear, galaxy clustering, and the abundance of massive halos each probe the large-scale structure of the Universe in complementary ways. We present cosmological constraints from the joint analysis of the three probes, building on the latest analyses of the lensing-informed abundance of clusters identified by the South Pole Telescope (SPT) and of the auto- and cross-correlation of galaxy position and weak lensing measurements ( $3\times 2\mathrm{pt}$) in the Dark Energy Survey (DES). We consider the cosmological correlation between the different tracers and we account for the systematic uncertainties that are shared between the large-scale lensing correlation functions and the small-scale lensing-based cluster mass calibration. Marginalized over the remaining $\mathrm{\Lambda }$cold dark matter ( $\mathrm{\Lambda }\mathrm{CDM}$) parameters (including the sum of neutrino masses) and 52 astrophysical modeling parameters, we measure ${\mathrm{\Omega }}_{\mathrm{m}}=0.300\pm 0.017$and ${\sigma }_8=0.797\pm 0.026$. Compared to constraints from primary cosmic microwave background (CMB) anisotropies, our constraints are only 15% wider with a probability to exceed of 0.22 ( $1.2\sigma$) for the two-parameter difference. We further obtain $S_8\equiv {\sigma }_8({\mathrm{\Omega }}_{\mathrm{m}}/0.3{)}^{0.5}=0.796\pm 0.013$which is lower than the measurement at the $1.6\sigma$level. The combined SPT cluster, DES $3\times 2\mathrm{pt}$, and datasets mildly prefer a nonzero positive neutrino mass, with a 95% upper limit $\sum m_{\nu }<0.25\mathrm{eV}$on the sum of neutrino masses. Assuming a $w\mathrm{CDM}$model, we constrain the dark energy equation of state parameter $w=-1.15_{-0.17}^{+0.23}$and when combining with primary CMB anisotropies, we recover $w=-1.20_{-0.09}^{+0.15}$, a $1.7\sigma$difference with a cosmological constant. The precision of our results highlights the benefits of multiwavelength multiprobe cosmology and our analysis paves the way for upcoming joint analyses of next-generation datasets. Published by the American Physical Society2025 

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4. Detailed Chemical Abundances of Stars in the Outskirts of the Tucana II Ultrafaint Dwarf Galaxy*

   https://doi.org/10.3847/1538-3881/aca416  

   Chiti, Anirudh; Frebel, Anna; Ji, Alexander P; Mardini, Mohammad K; Ou, Xiaowei; Simon, Joshua D; Jerjen, Helmut; Kim, Dongwon; Norris, John E (January 2023, The Astronomical Journal)

   Abstract We present chemical abundances and velocities of five stars between 0.3 and 1.1 kpc from the center of the Tucana II ultrafaint dwarf galaxy (UFD) from high-resolution Magellan/MIKE spectroscopy. We find that every star is deficient in metals (−3.6 < [Fe/H] < −1.9) and in neutron-capture elements as is characteristic of UFD stars, unambiguously confirming their association with Tucana II. Other chemical abundances (e.g., C, iron peak) largely follow UFD trends and suggest that faint core-collapse supernovae (SNe) dominated the early evolution of Tucana II. We see a downturn in [α/Fe] at [Fe/H] ≈ −2.8, indicating the onset of Type Ia SN enrichment and somewhat extended chemical evolution. The most metal-rich star has strikingly low [Sc/Fe] = −1.29 ± 0.48 and [Mn/Fe] = −1.33 ± 0.33, implying significant enrichment by a sub-Chandrasekhar mass Type Ia SN. We do not detect a radial velocity gradient in Tucana II ( ${\mathit{dv}}_{\mathrm{helio}}/d{\theta }_1=-{2.6}_{-2.9}^{+3.0}$km s⁻¹kpc⁻¹), reflecting a lack of evidence for tidal disruption, and derive a dynamical mass of $M_{1/2}\left(r_h\right)={1.6}_{-0.7}^{+1.1}\times {10}^6$M_⊙. We revisit formation scenarios of the extended component of Tucana II in light of its stellar chemical abundances. We find no evidence that Tucana II had abnormally energetic SNe, suggesting that if SNe drove in situ stellar halo formation, then other UFDs should show similar such features. Although not a unique explanation, the decline in [α/Fe] is consistent with an early galactic merger triggering later star formation. Future observations may disentangle such formation channels of UFD outskirts. 

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5. Observation of the Galactic Center PeVatron beyond 100 TeV with HAWC

   https://doi.org/10.3847/2041-8213/ad772e  

   Albert, A; Alfaro, R; Alvarez, C; Andrés, A; Arteaga-Velázquez, J C; Avila_Rojas, D; Ayala_Solares, H A; Babu, R; Belmont-Moreno, E; Bernal, A; et al (September 2024, The Astrophysical Journal Letters)

   Abstract We report an observation of ultrahigh-energy (UHE) gamma rays from the Galactic center (GC) region, using 7 yr of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum ( $\mathit{d}N/\mathit{d}E=\varphi {\left(E/26\mathrm{TeV}\right)}^{\gamma }$), whereγ= −2.88 ± 0.15_stat− 0.1_sysandϕ= 1.5 × 10⁻¹⁵(TeV cm²s)⁻¹ $\pm {0.3}_{\mathrm{stat}}{}_{-{0.13}_{\mathrm{sys}}}^{+{0.08}_{\mathrm{sys}}}$extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to 100 TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A* (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant (>5σ), with the spectrum extending to >100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the GC. 

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