Astrophysics Papers

ALT We present an analytic forward model for the Lyman-alpha (Ly-alpha) forest flux field based on cubic-order large-scale structure perturbation theory (effective field theory) calculations. We validate our cubic model on two sets of hydrodynamic simulations spanning 2 ≤ z ≤ 4: the small-volume CAMELS suite, which spans a wide range of cosmological and astrophysical parameters, and the large-volume, high-resolution Sherwood simulations. We find qualitatively similar results for both at the power-spectrum level. The perturbative model reproduces the three-dimensional flux power spectrum of the simulations to ∼ 5% down to k ≃ 1-1.5 h Mpc⁻¹, depending on the redshift. This improves compared to previous quadratic perturbative forward models by up to 40%. Exploiting cosmic-variance cancellation in the field-level approach, we carry out precision measurements of the Lyman-alpha forest bias parameters from the CAMELS simulation suite. We use these measurements to analytically predict the shifts

ALT Galaxy cluster cores, characterised by old stellar population and suppressed star-formation are ideal for studying the environmental dependence of Type Ia supernovae (SNe Ia). It is unclear whether the diversity of SNe Ia, parametrised by light curve stretch, stems from distinct explosion mechanisms or varying initial conditions, both closely tied to progenitor age. We analyse the light curve stretch and colour distribution of photometrically identified SNe Ia within the galaxy clusters cores, utilising the Zwicky Transient Facility (ZTF) archival data. Using the AMPEL platform, we filter 89,025 ZTF transients spatially coincident with our galaxy cluster catalogues to identify 4,969 likely SN Ia candidates. We split this sample into three populations: core cluster SNe Ia r ≤ 0.5R₅₀₀, outer-core cluster SNe Ia 0.5R₅₀₀< r≤ 2R₅₀₀, and a reference population of non-cluster SN Ia. We present the largest sample of photometrically identified cluster SNe Ia to date, notably isolating a populat

ALT Rayleigh scattering (RS) of cosmic microwave background (CMB) photons by neutral hydrogen and helium, during and shortly after the last scattering surface, adds a frequency-dependent contribution to the CMB anisotropies that scales approximately as ν⁴ at leading order. The RS signal is most relevant at 200 GHz≲ν≲800 GHz and could be detected using future CMB experiments. Because RS acts in a frequency-dependent manner which is sensitive to the ionisation history of the cosmological recombination process, it provides an additional probe of the recombination history. This makes it a natural test of modified recombination scenarios, such as variable electron mass mₑ or fine-structure constant α, which have been proposed to ease the Hubble tension. The correlation between the RS and primary CMB signal, both in temperature and polarisation, further enhances its usefulness for constraining cosmological parameters. Using a multi-frequency Fisher analysis with realistic noise and foregrounds,

ALT Aims. We investigated the potential large-scale alignment of radio active galactic nuclei (AGN) jets in the proximity of the Shapley Supercluster (SSC) area and its correlation with the identified cosmic web structures. Methods. We analyzed 28 radio AGNs divided into two populations with comparable sky coverage north and south of a diffuse X-ray filamentary structure connecting clusters in the SSC core. We measured the average jet position angles (PAs) and combined them with spectroscopic redshifts to assess the persistence of the alignment along the line of sight. Results. We detected a significant large-scale alignment of the radio AGN jets with the foreground X-ray filament (oriented at PA ∼ 115° ± 10°). Both the northern (PA ∼ 117°) and southern (PA ∼ 129°) groups align with this axis, yielding an overall statistical significance of 4.5 σ (upper and lower bounds: 6.1σ, 3.8 σ). Although the projected alignment is highly significant, sparse spectroscopic coverage (seven sources spann

ALT Intensity maps of the 21 cm line and the Lyman-α (Lyα) forest trace the same cosmic volume at 2≲ z≲ 4. Their cross-power spectrum is insensitive to foregrounds that do not correlate between the two probes and, together with the Lyα auto-spectrum, separates the mean 21 cm brightness temperature from the neutral hydrogen (HI) bias. Effective field theory models of each tracer exist, but at one loop they carry tens of nuisance parameters. We test whether a minimal effective field theory (mEFT), consisting of the tree-level Kaiser model with leading-order counterterms and stochastic terms, previously validated for the Lyα auto-spectrum, describes the 21 cm auto-, Lyα auto- and cross-power spectra jointly. We use the Sherwood 80 h⁻¹Mpc hydrodynamical simulation with HI painted onto halos at z=2.4-4.2, and reduce sample variance with Zel'dovich control variates. Each spectrum is validated separately and then in a joint fit with shared parameters. With scale cuts kₘₐₓ=0.5, 1.2 and 2.0 h Mpc⁻¹

ALT The joint analysis of weak gravitational lensing, photometric galaxy clustering, and their cross-correlation, the so-called 3×2pt analysis, is one of the primary probes Stage-IV surveys will use to constrain the dark-energy equation of state. Its accuracy depends critically on the calibration of the underlying photometric redshift distributions, n(z), whose residual uncertainties can bias cosmological inference. However, conventional parametric nuisance models may not adequately capture the full range of plausible n(z) uncertainties. We therefore present a cosmological inference framework that instead reconstructs n(z) on the fly using Gaussian Processes (GPs), replacing per-bin shift-and-width parameterisations by a non-parametric, data-driven model. We validate the method on synthetic Euclid-like 3×2pt data vectors representative of Euclid Data Release 1, sampling GP hyperparameters jointly with cosmological and nuisance parameters to reliably propagate n(z) uncertainties into the po

ALT Euclid is a surveying mission that is progressively imaging and spectroscopically mapping a wide area of extragalactic sky in visible and near infrared bands. The Euclid mission is, however, not restricted to the Euclid Wide Survey, but it includes data from various other survey components. This paper presents the Data Release 1 (DR1) status of the multiple Euclid surveys and fields, including the Euclid Deep Survey, Euclid Auxiliary Fields, calibration fields, the Euclid Medium-Deep Survey, the Euclid Ecliptic Survey, and the Independent Legacy Scientists' field, in addition to the Euclid Wide Survey. Some of these fields were observed during the initial Performance-Verification phase, others during the Phase-Diversity calibration campaign, and the majority during the subsequent science operations phase. This paper describes the different procedures of survey implementation applied in the various phases of the mission, from the set of requirements, constraints, and limitations, to the

ALT Analysing galaxy clustering in split environmental densities has been demonstrated to offer an advantage over standard two-point clustering for extracting cosmological information. A major challenge to realising this potential with the density-split (DS) technique is that the observations are in redshift space. This complicates its modelling, primarily because the density-split centres may not be conserved between real and redshift space. We develop a modelling framework that splits on the tracer-centred density PDF, rather than the volume-weighted density PDF commonly used in previous studies. We derive the linear bias associated with the threshold density in redshift space, enabling us to connect large-scale DS clustering to the density PDF. We find that the threshold density field consists of doughnut-like structures, which we term `Island(s)'. We propose an empirical model, analogous to the halo model framework, that comprises linear, non-linear, and stochastic terms and accurately

ALT Gravitational-wave observations have opened new opportunities to study massive object events like merging binary black holes. When combined with electromagnetic counterparts, accurate localization of gravitational-wave sources could allow us to identify their host galaxies and carry out follow-up studies, such as study the environment of merging black holes and determine the Hubble constant. One of the possible methods for precise localization is strong gravitational-wave lensing. Previous studies have considered strong gravitational-wave lensing with galaxy lenses. However, galaxy clusters have yet to be investigated due to the complexity of their mass structures. Here we take the list of known cluster lenses from the Hubble Frontier Fields, simulate lensing properties of gravitational waves from their reconstructions as they would be observed by the ground-based gravitational-wave detectors. When same model family is used in simulation and localization, we find that the correct lens

ALT The Euclid Data Release 1 (DR1) contains catalogues of sources covering 1900 deg2, including deep coverage of legacy fields that enable an extensive comparison between Euclid imaging and multiwavelength observations from other instruments. The Cosmic Evolution Survey (COSMOS) field, observed by Euclid and included in DR1, has been observed with the James Webb Space Telescope, resulting in the COSMOS2025 catalogue. We compare the Euclid DR1 photometry with the multiwavelength COSMOS2025 data to assess the accuracy of the photometric measurements produced by the different methods implemented in the OU-MER pipeline. We use both the Euclid Wide and Deep Surveys, focussing exclusively on extragalactic sources. We use the fluxes of COSMOS2025 to predict the expected fluxes in the Euclid bands via spectral energy distribution fitting, while the redshifts are either spectroscopic, for a sample of brighter sources, or photometric, to include fainter sources. Both the fluxes in the common Hyper

ALT Standard siren cosmology depends on several modelling assumptions, including the underlying source population, galaxy catalogue, and detection selection function. Quantifying the effect of each choice typically requires a full, independent analysis. As gravitational-wave catalogs grow incrementally, much computational effort is spent re-analysing largely overlapping datasets. We apply the recently developed ASPIRE (Accelerated Sequential Posterior Inference via Reuse) sampler to the joint estimation of cosmological and population parameters with dark sirens. ASPIRE updates existing posterior samples into the posterior under a new hypothesis without restarting from the prior. It combines normalising flows with a sequential Monte Carlo (SMC) scheme to produce accurate posteriors and unbiased evidence estimates. Applying ASPIRE to a number of dark siren analysis cases with GWTC-5.0, we recover posteriors consistent with nested sampling, while recording a performance improvement of between

ALT We introduce Kinessence models where combining K-mouflage and quintessence leads to phantom-crossing of the dark energy equation of state and sign-switching of the dark energy density. This is realised by joining a dark scalar sector comprising K-essence kinetic terms and a quintessence potential together with a Yukawa coupling to matter. We investigate the dynamics of these models in the Jordan frame at the background and perturbative levels. We concentrate on the effective equation of state and the matter fraction for the background. The CMB spectra, the linear power spectrum and the growth of structure via fσ₈ are also analysed at the perturbative level. The quintessence potential drives the acceleration of the Universe at low redshift with an equation of state greater than -1. The Yukawa coupling to matter leads to a phantom crossing behaviour depending on its strength. The potential fifth force mediated by the scalar field is screened by the K-mouflage mechanism triggered by the K

ALT This paper describes the Euclid DR1 photometric masks, which trace spatial variations in the survey properties (e.g. satellite position angles, integration time, sky tiling, and survey footprint); in the instrumental performance of Euclid and the external data (EXT) it uses (e.g. survey coverage, depth, PSF width, quality flags, systematic effects and astrometric uncertainties); and in possible contamination from sky emission (e.g. galactic extinction and zodiacal light emission). Among this, the effective coverage mask is particularly important as it defines the effective survey area and can be used to exclude spurious objects when selecting Euclid photometric samples for scientific analyses. The Euclid photometric masks are built for each observed sky region (tile) and are provided as full-sky HEALPix maps (nested ordering and explicit indexing) at Nside = 16 384, equating to a resolution of 12"88, for both the Euclid Wide Survey (EWS) and Euclid Deep Survey (EDS). We estimate the to

ALT Accurate photometric-redshift estimation and calibration of the weak-lensing point-spread function (PSF) for Euclid require complementary ground-based optical imaging with high photometric precision and spatial homogeneity. The Organisation Unit for External Data (OU-EXT) integrates heterogeneous ground-based surveys into the Euclid Science Ground Segment (SGS), delivering uniformly calibrated, co-added images, and associated PSF models. To minimise systematics in spectral energy distribution (SED) reconstruction and photometric-redshift estimation, these data must achieve relative photometric stability at the ∼10 mmag level on Euclid-tile scales. We present the ground-based imaging component of Euclid Data Release 1 (DR1), comprising ∼2500 deg² across the wide, deep, and auxiliary fields. We summarise the OU-EXT production workflow and validation framework, and quantify the achieved data quality of the co-added products in terms of depth, photometric zero-point stability, and spatial

ALT This paper describes the contents of the Euclid First Data Release (DR1), together with the set of papers that document the data-processing and the data products. DR1 consists of two parts: first `DR1-Foundation', releasing images, spectra, and catalogues in November 2026. Second, the shear measurements and the `Level 3' products required for cosmological analyses will be added in June 2027 to complete the full DR1. This data set contains around a billion catalogued objects, mainly from the Euclid Wide Survey (1975 deg²) and the Euclid Deep Fields (77 deg²)

ALT Recent cosmological observations motivate alternatives to ΛCDM with evolving dark energy. We compare three such models, each introducing one additional cosmological parameter: F42, with equation of state w(a)=w₀/√a, and two smooth sign-changing effective dark-energy profiles, Ag and Qui. All models are implemented within VCDM, which determines the background and linear perturbations without introducing an additional propagating gravitational degree of freedom. We use CMB observations from SPT, Planck, and ACT, combined with DESI DR2 distance measurements, with and without the DESY5 Dovekie supernova sample. All three alternatives improve the best-fit likelihood relative to ΛCDM. When supernovae are included, the Akaike information criterion favors F42, while Ag and Qui remain nearly indistinguishable from ΛCDM on this criterion. The Bayesian evidence, however, does not establish a robust preference among the three alternatives. Our results show that improved fits to current observation

ALT We present a genus topology analysis of the large-scale distribution of galaxies in the Sloan Digital Sky Survey Data (SDSS), comparing the observed topology with mock galaxy samples from the Horizon Run 4 (HR4) N-body simulation and four cosmological hydrodynamical simulations. We construct nine volume-limited samples and measure their genus curves at Gaussian smoothing scales of 4–12 h⁻¹Mpc. Overall, the modern galaxy models reproduce the observed genus statistics substantially better than the HGC, HOD, and SAM models examined by Choi et al. (2010). Among the models considered here, the HR4 Most-Bound-Halo Particle galaxy-assignment model shows somewhat better overall agreement with the SDSS topology than IllustrisTNG300 and FLAMINGO. The observed scale dependences of the genus shift parameter Δνf and void abundance parameter A_V are somewhat steeper than those predicted by the simulations, but their joint discrepancy from HR4 is not statistically significant. The smaller-volume TNG1

ALT Velocity gradients compatible with rotation have been reported across certain nearby cosmic filaments. We show that rotational momentum might be generated in filaments in the local Universe in the presence of a cosmological constant (local dark energy) based on the theorem stating the general function for the equivalence of the gravitational field of a sphere and that of a point mass. We investigated how the cosmological constant modifies the finite-time acquisition and retention of angular momentum in an open filamentary core. Although its isotropic force exerts no direct axial torque, rotational motion can be seeded by tidal interactions with surrounding matter and incoming streams. Early tidal torques establish an imbalance in axial angular momentum, while the subsequent orbit crossing amplifies the resulting rotation, and ultimately, the cosmological constant is able to modify tidal-mode growth and finite-time angular momentum delivery.

ALT We study how an extended spherical collapse model (ESCM), including shear, vorticity and chameleon screening, modifies the collapse threshold δc(z) and δc(M), the turnaround density δₜ, the turnaround radius Rₜ and the halo mass function in the Hu-Sawicki f(R) model, and whether these quantities can distinguish f(R) from General Relativity (GR). Unlike the standard spherical collapse model (SSCM), in the ESCM δc depends on mass, redshift and |fR0|; we use it to compute the halo mass function with the excursion set approach. Between GR and the large-field (LF) limit of f(R), δc differs by a few percent within the ESCM and by about 20% between GR in the ESCM and the LF limit in the SSCM; δₜ differs by about 27-29% and Rₜ by about 6.5%. With screening, the difference between GR and screened δc is 2.5% for |fR0|=10⁻⁴ (F4) and vanishes for |fR0|=10⁻⁶ (F6); for δₜ it is larger than 20% (F4), about 10% (F5) and 0 (F6); for Rₜ about 6.5% (F4), 3% (F5) and 0 (F6). Since observations exclude F4

ALT Recent data from cosmological galaxy surveys combined with cosmic microwave background (CMB) data give a preference for a departure from ΛCDM, favoring a model with an evolving dark energy equation of state or a small neutrino mass. However, recent works have shown that the electron scattering optical depth to the CMB (τ) can reduce this preference if τ∼0.09, larger than that preferred by CMB low-ℓ E-mode polarization data. With standard monotonic hydrogen reionization histories, such a high value of τ is in strong tension with spectroscopic galaxy data constraining the end of reionization. Thus, high-τ models are restricted to non-standard reionization scenarios, where astrophysical sources inject an appreciable amount of ionizing photons at early times. One recently studied model for this is a supermassive population III star scenario, where radiative feedback from a self-annihilating dark matter particle enables a pathway to form M∼10⁵ M⊙ stars that, upon collapse, photoionize a sur