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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Sunday 6 September

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Distinguishing lensing and precessional modulation in binary black-hole inspiral waveforms

Tien N. Nguyen-Vo, Tamanjyot Singh, Benjamin McKallip et al. (+2 more)

Binary black holes (BBHs) emit gravitational waves (GWs) as they inspiral towards merger. These GWs can be gravitationally lensed by large-scale structure along the line of sight, potentially creating multiple images of the same source with fixed time delays determined by the lensing geometry. As the BBHs inspiral, the GW frequency increases, leading to successive constructive and destructive interference between the multiple images. BBHs also have spins $\mathbf{S}_i$ that may be misaligned with their orbital angular momentum $\mathbf{L}$. As the BBHs inspiral, these misaligned spins cause $\mathbf{L}$ to precess about the total angular momentum $\mathbf{J}$, modulating the GW emission similar to pulsar emission resulting from a misaligned jet rotating in and out of the line of sight. We investigate the ability of a single L-shaped GW detector to distinguish between these two sources of modulation. We find that precessional modulation can mimic the lensing modulation between two images with comparable magnifications when the time delay between the images is short enough that fewer than three interference fringes occur during the time the GW signal spends in the sensitivity band of the detector. As strong lensing is rare for GW sources at moderate redshift while misaligned spins are common for BBHs produced in certain formation channels, ruling out precessional modulation is essential to identifying genuinely lensed systems.
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All authors Tien N. Nguyen-Vo, Tamanjyot Singh, Benjamin McKallip, Michael Kesden, Lindsay King

Saturday 5 September

Cosmology and Nongalactic Astrophysics

Probing Dark matter-Baryon Interaction with S301–the Fastest Known Star in the Milky Way

Yugen Lin

The recent discovery of S301 provides an unique opportunity to investigate dark matter-baryon interaction in the innermost region of the Milky Way. S301 follows a highly eccentric orbit around Sgr~A*, and its pericenter distance is only around 12 AU with velocity about $25000\,{\rm km/s}$. These extreme properties make S301 highly sensitive to dark matter-baryon scattering in the center of galaxy, where the dark matter density may be strongly enhanced. We have calculated the orbit-averaged energy deposited rate in S301 via dark matter-proton scattering, and show that over a broad dark matter parameter space, cross sections satisfying the existing bounds from terrestrial experiments and astronomical observations can inject sufficient energy to modify the luminosity and evolution of S301. Our results establish S301 as an exceptionally sensitive probe of dark matter-baryon interactions and open a new avenue for probing dark matter interactions in high-density and high-velocity astrophysical environments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Inelastic dark matter and baryon flavor symmetry in light of LUX-ZEPLIN (LZ) experiment

Hyun Min Lee

We present a novel model for inelastic dark matter in a simple extension of the Standard Model (SM) with a local $U(1)'$ baryon flavor symmetry, such as $U(1)_{B_i-B_j}$ with $i\neq j$. In this framework, we realize a realistic flavor structure for the mixing Yukawa couplings due to higher dimensional operators or renormalizable couplings between the SM quarks and extra vector-like quarks that are anomaly-free by themselves. We regard a Dirac singlet fermion as being dark matter and obtaining a small mass splitting for inelastic dark matter, only after the $U(1)'$ symmetry is broken spontaneously. We show that there is a consistent parameter space for explaining both the LZ nuclear recoil event and the correct relic density for dark matter and the existing collider and indirect detection bounds are satisfied at the same time. In this case, we predict a relatively light $Z'$ boson with $10-20\,{\rm GeV}$ mass and a weak gauge coupling, suggesting a dedicated search at colliders. The future data with higher recoil energies at direct detection experiments will play a decisive role of discriminating between the scenarios of light and heavy dark matter.
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Cosmology and Nongalactic Astrophysics

Stacking HI in the dark: Towards detecting the reionization-epoch 21 cm signal in Lyman-$\alpha$ dark gaps

Barun Maity and Frederick B. Davies

The detection of the redshifted 21 cm signal from neutral hydrogen during the epoch of reionization remains one of the central challenges in contemporary cosmology. Although upcoming radio interferometers are expected to measure 21 cm fluctuations at a few percent precision, an independent confirmation is essential to ensure robustness against instrumental systematics and foreground contamination. In this work, we propose a novel real-space stacking technique to detect the 21 cm signal, guided by the presence of dark gaps in quasar absorption spectra during the late stages of reionization ($z \sim 5.0$-$6.1$). Using a semi-numerical reionization model, we show that stacking 21 cm images on long dark gaps (length, $L > 32~h^{-1}\mathrm{cMpc}$ and threshold flux, $F_{\mathrm{th}} < 0.005$) should reveal a strong emission signal with a peak mean-subtracted 21 cm brightness temperature of $\delta \tilde{T}_b \sim 2-3~ mK$ for a volume-weighted average neutral fraction of $x_{\mathrm{HI}} \sim 0.1$ at $z = 5.9$. We further extend our analysis to realistic reionization lightcones, incorporating thermal noise and foreground avoidance effects, generated for two different reionization histories. In an optimistic foreground avoidance scenario (wedge field of view $\theta < 20^\circ$), a sample of roughly 100 dark gaps is sufficient to achieve a combined root-sum-square signal-to-noise ratio exceeding 10 for both reionization models, while a more conservative wedge avoidance may require more dark gaps for a solid detection. Given the large number of quasars known at $z > 6$, a detection of this stacked signal may thus already be within reach of existing optical (i.e., VLT, Keck) and 21 cm observatories (i.e., HERA, SKA). This synergistic approach offers a promising pathway towards a direct and statistically robust detection of the cosmological 21 cm signal.
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Friday 4 September

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Initial conditions for inflation

Gerasimos Kouniatalis

We propose a single-field mechanism that dynamically prepares the initial conditions required for exponential plateau inflation. The inflaton is decomposed into a coarse-grained mode and a high-occupancy, approximately Gaussian band of relativistic nonzero modes. Gaussian–Hartree averaging of the potential produces an exact variance-dependent minimum, which places the coarse-grained field high on the plateau when the excitation variance is large. Under a translation-invariant microcanonical measure, the available phase-space volume is exponentially concentrated near this minimum, while an order-one homogeneous kinetic-energy fraction is exponentially atypical. During expansion, the preparation modes redshift as radiation, $\sigma^2\propto a^{-2}$ and $\rho_\chi\propto a^{-4}$. Although the induced minimum rapidly moves toward the vacuum, the force acting on the coarse-grained mode is bounded by an exponentially small factor, yielding analytic upper limits on its velocity, displacement, and kinetic fraction. We derive a sufficient condition for the subsequent number of slow-roll e-folds and exhibit a benchmark with more than 60 e-folds. The mechanism also motivates correlated finite-onset signatures: large-scale power suppression with decaying oscillations and a variance-convolution bispectrum.
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Cosmology and Nongalactic Astrophysics

Do DESI-DR2 BAO data imply a coupling of dark matter and dark energy?

Weiqiang Yang, Sibo Zhang, Dinorah Barbosa et al. (+3 more)

We revisit an interacting dark matter (DM) – dark energy (DE) model characterized by the interaction function $Q = \Gamma \rho_x$, where $\Gamma$ is a constant coupling parameter and $\rho_x$ is the energy density of DE. This type of interaction is independent of the Hubble rate or other external parameters, but depends only on the fundamental properties of DE, such as its equation of state (EoS), $w_x$. We pay special attention to $w_x$ and study three distinct interacting scenarios distinguished by the nature of $w_x$, i.e. $w_x =-1$ (when DE corresponds to the vacuum energy), $w_{x} < -1$ (when DE has a phantom behavior), and $w_x > -1$ (quintessential DE). We constrain all of them using the most recent cosmological datasets, including CMB from Planck 2018, BAO from DESI DR2, and three compilations of SNIa (PantheonPlus, Union3, and DES-Dovekie). Our analyses reveal that evidence of interaction is supported in scenarios with $w_x =-1$ and $w_x < -1$ when all three datasets are combined, but from the Bayesian evidence analysis, $\Lambda$CDM remains favored over these interacting scenarios. Regarding the $S_8$ parameter, when $w_x > -1$, this interacting scenario leads to mildly lower estimates across all datasets.
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All authors Weiqiang Yang, Sibo Zhang, Dinorah Barbosa, Marco Antonio Alvarez, Supriya Pan, Leila Graef

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Macroscopic dark matter constraints for extended mass functions

Zachary S. C. Picker, Andrew Buchanan, Melissa Diamond et al. (+1 more)

We compile and recompute a subset of the landscape of constraints for macroscopic dark matter (macros), explicitly including the dependence on the fraction of dark matter in macros $f_{\rm dm}$. This allows us to map these constraints to scenarios with extended mass functions for the macros, which is a generic outcome for many of the assembly processes relevant to macro formation. We compute a number of examples of constraints for extended mass functions, finding that in many cases, wider mass functions can be severely constrained by just the interactions of the tails of the distributions. Finally, we present the code and data required for computing these limits and generating these plots in a publicly accessible repository.
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All authors Zachary S. C. Picker, Andrew Buchanan, Melissa Diamond, Joseph Bramante

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

High-sensitivity Ultralight Dark Matter detector: Parametrically Amplified Casimir Devices

Muping Chen, Hideo Iizuka, Kyohei Mukaida et al. (+2 more)

We propose the use of sphere-and-plate Casimir force measurement setups to detect ultralight vector dark matter. We demonstrate that sub-picometer signals can be parametrically amplified to be detectable. We present a novel improvement that allows the continuous tuning of the natural frequency of the system, opening new research opportunities at the submicron scale. We show that the improved setup can determine the dark matter mass with high accuracy, significantly expand the detectable mass range, and achieve the best sensitivity to date in the $8\times10^{-14}\sim1\times10^{-12}{\rm~ eV}$ mass range.
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All authors Muping Chen, Hideo Iizuka, Kyohei Mukaida, Kazunori Nakayama, Burkhant Suerfu

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Halo mass, star formation, and morphology in galaxies: A morphology-dependent connection between halo environment and star formation activity

G. Mountrichas, F. Shankar, F. J. Carrera et al. (+1 more)

Understanding the mechanisms responsible for quenching star formation in galaxies requires disentangling the roles of internal structure and large-scale environment. We investigate how galaxy morphology and specific star formation rate (sSFR) relate to the typical masses of host dark-matter halos (DMHs), and whether the halo–star formation connection depends on morphology. We analyse non-active galaxies in the VIPERS and Stripe 82 fields at $0.5 \leq z \leq 1.2$, combining DESI-based Sérsic classifications with stellar masses and SFRs from spectral energy distribution fitting. Galaxies are separated into disc- and bulge-dominated systems and divided into quantile-based sSFR bins designed to minimise stellar-mass differences between morphologies. Each bin is characterised by its median $\Delta{\rm MS}=\log {\rm SFR}-\log {\rm SFR}_{\rm MS}$, and characteristic DMH masses are inferred from projected galaxy cross-correlations. The halo-mass relation with star formation activity depends strongly on morphology: disc-dominated galaxies show little variation in halo mass across the probed $\Delta{\rm MS}$ range, whereas bulge-dominated galaxies occupy lower-mass halos at high $\Delta{\rm MS}$ and higher, mutually consistent halo masses toward lower $\Delta{\rm MS}$. These trends are unlikely to be driven mainly by stellar-mass differences. Typical halo mass alone therefore does not map cleanly onto quiescence; instead, the connection between halo environment and star formation activity is stronger in bulge-dominated than in disc-dominated galaxies.
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All authors G. Mountrichas, F. Shankar, F. J. Carrera, A. Georgakakis

Cosmology and Nongalactic Astrophysics

How Cluster Pressure Profiles Scale: Mass, Redshift, and Intrinsic Scatter

S. Andreon and F. Castagna

[shortened] The thermal pressure profile of the intracluster medium is critical for cluster cosmology and understanding galaxy-cluster astrophysics. We determine the population-averaged pressure profile of Sunyaev-Zel'dovich (SZ) selected clusters, characterize its intrinsic scatter, and measure its scaling with mass and redshift. We select 60 clusters from the South Pole Telescope (SPT) SZ catalog with $0.08<z<0.6$, requiring high signal-to-noise and 5 element resolution on Planck-SPT Compton-$y$ maps. We model spherical three-dimensional pressure profiles from the Compton-$y$ maps using a hierarchical Bayesian framework with restricted cubic splines. We adopt an updated weak-lensing-calibrated Compton-$Y$–mass scaling relation, effectively removing hydrostatic mass bias from the inferred masses. Our model accounts for cluster-to-cluster profile variations, line-of-sight foreground and background contributions, and outliers from intrinsically distinct clusters or projection effects. The code is publicly available. We derive the population-averaged pressure profile and find minimal intrinsic scatter at intermediate radii ($0.4 \le r/r_{500} \le 0.7$). Our pressure profile is approximately 40% lower than previous estimates at all radii, due to the unbiased mass scaling. We find suggestive, though not conclusive, evidence that the adopted mass dependence may require revision by removing the additional $M^{0.12}$ scaling introduced by Arnaud et al. 2010. We constrain departures from self-similar evolution in the mean profile to less than 0.1–0.2 dex and evolution of the intrinsic scatter to less than 8% per $\Delta z=0.1$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.IM

Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31

David Rubin and Istvan Szapudi

Minute- and sub-minute microlensing provides a direct probe of compact dark matter at asteroid-mass scales, where primordial black holes with MPBH <~ 10^-10 Msol would produce short-duration, finite-source-suppressed amplifications of stars in extragalactic fields. To enable these measurements, we present FLASH: Fast Lensing And Sub-minute High-accuracy photometry with JWST, a pipeline designed to recover such events from JWST/NIRCam imaging by preserving detector-ramp time information and performing high-precision crowded-field photometry. FLASH begins from Level 1 NIRCam data products, applies microlensing-oriented detector calibration (including improved treatment of non-linearity and position-dependent detector calibration), and extracts forced multi-band light curves in crowded fields. We apply the pipeline to two public JWST/NIRCam datasets targeting the disk of M31 with 21.5 s cadence: GO-4735 and GO-2609. Although these observations are suboptimal as a microlensing survey, they provide a stringent test of JWST time-domain performance in a high-surface-brightness, crowded stellar field. Using these data with our own microlensing simulations, we derive the first JWST-based microlensing constraints toward M31, finding fPBH <~ 100 for MPBH~ 10^-9 Msol. Our results demonstrate that JWST is a competitive platform for high-cadence microlensing and that a dedicated, continuous NIRCam monitoring program could substantially improve constraints on compact dark matter below the current ground-based frontier.
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Cosmology and Nongalactic Astrophysics

Analytic bispectrum covariance for galaxy survey cosmology

Utkarsh Giri, Henry S. Grasshorn Gebhardt and Olivier Dore

The bispectrum of galaxy distribution remains an underutilized statistic in cosmological data analysis. This can be attributed to mathematical and computational challenges associated with a proper modeling of the signal and its covariance. While recent theoretical advances have made it possible to analytically model the bispectrum signal and covariance using perturbation theory, a fully non-Gaussian analytical treatment of the covariance for a realistic survey with window remains elusive. The full bispectrum covariance of observed galaxies is a non-Gaussian six-point function with each of its legs convolved with a complex window function. Although it has so far proven intractable, the problem is well-posed. In this article, we present the derivation, implementation, and validation of a numerical routine for the analytic calculation of the bispectrum covariance for a spherical window, carried out by a large language model (LLM). The derivation uncovered terms that vanish in the windowless case but that dominate the covariance for triangles with survey scale modes. As a development benchmark for the implementation, we used the sample covariance of the halo bispectrum measured from 6000 fiducial Quijote halo catalogs in real space. Over several iterations of refinement, the LLM converged on a regime-specific numerical scheme for the covariance matrix calculation, mixing exact and approximate approaches, resulting in a highly optimized, tractable and accurate covariance across scales and shapes, using only tree-level models for the input polyspectra. Closing the loop still required human expertise, which illustrates what human-AI collaboration in research may look like in the near term.
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Cosmology and Nongalactic Astrophysics

Exploring the dark sector through galaxy dynamics in clusters

Andrea Biviano, Lorenzo Pizzuti and Antonaldo Diaferio

Galaxy clusters are among the most powerful laboratories to probe fundamental physics, from the formation of cosmic structures to the nature of dark matter, dark energy, and gravity. Realizing their full potential requires accurate and unbiased determinations of their mass profiles, a longstanding challenge in cluster cosmology. In this context, the kinematics of member galaxies in clusters has become a key tool to reconstruct the mass distribution and to investigate the dynamical properties of clusters. The advent of large spectroscopic datasets has enabled the application of increasingly sophisticated models and robust techniques, which make kinematic analyses competitive with other probes of cluster dynamics. In this review, we provide a comprehensive overview of cluster kinematics, covering the main methods to infer dynamical masses and mass profiles, their physical assumptions, and the impact of systematics such as deviation from dynamical equilibrium, triaxiality, and substructures. We discuss the complementarity with other techniques to investigate the structure of clusters and highlight recent applications to tests cosmological models. We focus in particular on the role of kinematical studies in constraining the dark sector (dark matter and dark energy) and in providing novel insights into the behavior of gravity at Mpc scales. Finally, we outline current limitations and future prospects, emphasizing that the combination of improved modeling and forthcoming spectroscopic surveys will establish cluster kinematics as a fundamental probe in the era of precision cosmology.
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Cosmology and Nongalactic Astrophysics

Tracing the Cosmic Origins: Machine Learning Reconstruction of the Primordial Density Field from EoR Observations

Anchal Saxena, P. Daniel Meerburg, Guochao Sun et al. (+2 more)

Reconstructing the initial conditions of the Universe from late-time tracers would unlock cosmological information buried by non-linear structure formation and astrophysics. We reconstruct the initial density field at $z\sim300$ from simulated 21-cm and CO(1-0) line-intensity maps at $z\sim8$ generated with LIMFAST. Using a three-dimensional U-Net, we reconstruct the initial conditions and evaluate its impact on cosmological parameter constraints. The two tracers probe complementary environments: 21-cm emission traces neutral, low-density regions of the intergalactic medium, while CO traces overdense, star-forming regions. To emulate realistic observations, we model instrumental effects for SKA1-Low- and COMAP-ERA-like surveys, including finite angular resolution and thermal noise. We assess reconstruction performance through the cross-correlation coefficient between reconstructed and true initial density fields, $|C(k)|$. In the noiseless case, combining both tracers delivers the most accurate recovery across ionisation states, with $|C(k)| \gtrsim$ 0.90 for $k \lesssim$ 0.75 Mpc$^{-1}$. With observational effects, small-scale information is degraded, but combining tracers still achieves $|C(k)| \gtrsim$ 0.70 for $k \lesssim$ 0.3 Mpc$^{-1}$. To quantify information gain, we perform simulation-based inference of cosmological parameters from power-spectrum summaries before and after reconstruction. In both noiseless and noisy settings, reconstruction tightens parameter constraints: uncertainties on $\sigma_8$ and $n_{\rm s}$ improve by $\sim2\times$, with smaller but consistent gains for other parameters. This is further confirmed using Kullback-Leibler divergence diagnostics for an ensemble of observations. These results indicate that joint analysis of future 21-cm and CO surveys, combined with such reconstruction, can partially recover otherwise inaccessible cosmological information.
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All authors Anchal Saxena, P. Daniel Meerburg, Guochao Sun, Tzu-Ching Chang, Lluís Mas-Ribas

Cosmology and Nongalactic Astrophysics

Early against Late: A contrast on dark energy in the light of DESI DR2

Miguel A. Zapata, Karim Carrion and Gabriela Garcia-Arroyo

Recent findings from Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation (BAO) measurements, combined with Type Ia supernovae and Cosmic Microwave Background (CMB) data, suggest potential parameter-level deviations from $\Lambda\text{CDM}$. However, parameter exclusions omit prior-volume penalties, whereas Bayesian evidence uncovers a stark dichotomy between early- and late-time dynamics. To quantify this effect, we perform a Bayesian model comparison that explicitly accounts for the cosmological epoch of dark energy dynamics, contrasting two schemes acting in opposite epochs of cosmic history: pre-recombination Early Dark Energy (EDE) and late-time Chevallier–Polarski–Linder (CPL), both measured against a baseline $\Lambda$CDM. We validate the learned harmonic-mean estimator against UltraNest (at background level) before applying it to the CMB analysis. Background-only data already disfavor both extensions, yielding {$\ln B_{\Lambda\text{CDM},\text{EDE}} = 1.48 \pm 0.18$ and $\ln B_{\Lambda\text{CDM},\text{CPL}} = 2.36 \pm 0.24$}. Including CMB sharpens this result: {EDE is very strongly rejected ($\ln B_{\Lambda\text{CDM},\text{EDE}} \approx 12.61 \pm 0.17$)} with its early-time fraction constrained to $10^3\,\Omega_e^{\rm EDE} = 2.0^{+0.6}_{-1.0}$, whereas CPL remains only mildly disfavored ($\ln B_{\Lambda\text{CDM},\text{CPL}} \approx 2.34 \pm 0.18$), even though 2D parameter posteriors for both models display a multi-$\sigma$ deviation from $\Lambda\text{CDM}$. Thus, Bayesian evidence weakens reported preferences for dark energy dynamics, with the impact depending on the cosmic epoch involved, confirmed by our functional reconstructions of $w_{\rm de}(z)$ and $\Omega_{\rm de}(z)$ from posterior samples.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Fast Bayesian Inference for Long-Duration Gravitational-Wave Signals in 3G detectors

Anand S. Sengupta

Third-generation (3G) gravitational-wave detectors will observe binary-neutron-star inspirals for nearly a day, so Earth's rotation becomes part of the signal rather than a negligible correction. This destroys the usual separation between intrinsic and extrinsic parameters and creates a major computational bottleneck for Bayesian inference. We show that the exact five-harmonic Jaranowski-Krolak-Schutz (JKS) decomposition restores the separation of the rotating antenna amplitude response from the computationally expensive intrinsic waveform calculations. By sampling the intrinsic waveform on a frequency grid set by its phase curvature and then applying error-controlled relative binning, likelihood evaluations for a 21.3-h signal are accelerated by O(10^4), making day-long 3G signal inference practical.
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Cosmology and Nongalactic Astrophysics

Supernovae Unite: Host-Galaxy Mass Measurements of Type Ia Supernovae and Their Impact on Cosmology

J. Lee, R. Camilleri, T. M. Davis et al. (+22 more)

Current consensus suggests that Type Ia supernova (SN Ia) brightnesses post light-curve standardization correlate with their host-galaxy stellar masses, which must be accounted for to obtain accurate cosmological constraints. For example, Vincenzi et al. (2025) showed that different host-galaxy stellar mass measurements for the same dataset produce redshift-dependent differences of order $\sim 0.01$ mag, large enough to appreciably shift cosmological constraints. We present internally consistent host-galaxy stellar masses remeasured using aperture photometry and spectral energy distribution (SED) fitting for SN-Unite, which combines the spectroscopic Pantheon+ and the photometric Dark Energy Survey five-year (DES-SN5YR) samples into the largest SN Ia cosmology sample to date, with 2884 likely SNe Ia. We find that photometry and SED fitting choices shift SN-Unite Flat$w$CDM parameters well below statistical uncertainties. Our stellar masses differ from the Pantheon+ data release partly due to a redshift-dependent internal inconsistency within Pantheon+, while remaining largely consistent with the DES-SN5YR (DES-Dovekie) data release. When the Pantheon+ subsample of SN-Unite is combined with Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) measurements, the significance for time-evolving dark energy increases from 3.4$\sigma$ to 4.0$\sigma$ based on the maximum a posteriori when our newly derived host-galaxy stellar masses replace the Pantheon+ data-release host-galaxy stellar masses, while DES-Dovekie remains virtually unchanged, consistent with the findings of Hoyt et al. (2026). By remeasuring the host-galaxy stellar masses using a consistent framework throughout the whole sample, we improve the robustness of the SN-Unite cosmological constraints against systematic differences in host-galaxy stellar mass measurements.
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All authors J. Lee, R. Camilleri, T. M. Davis, D. Rubin, K. Bechtol, L. Galbany, M. Sako, M. Sullivan, T. E. Müller-Bravo, D. Scolnic, M. Vincenzi, D. Brout, C. Lidman, A. Möller, P. Shah, M. Acevedo, P. Armstrong, B. A. Bassett, R. C. Chen, H. T. Diehl, J. Frieman, K. Grech, B. Popovic, B. O. Sánchez, B. E. Tucker

2609.05321 · 4 Sep · 25 pages, 10 figures. Companion paper to Supernovae Unite: Combining Pantheon+ and DES-SN5YR. The host-galaxy stellar mass measurements and photometry will be publicly available upon acceptance of the paper. V2: For our Youtube Cosmology Talks, see https://www.youtube.com/watch?v=KT-j65gRnOQ. Removed inactive datalinks and fixed MAP significance. Submitted to the Astrophysical Journal

Abstract PDF $GLXY ×8$SNOV ×3$RDSH ×2$CSMC ×1 +1

Cosmology and Nongalactic Astrophysics

Euclid. A two-point correlation approach to diagnosing star-related systematics in the Euclid spectroscopic survey

Euclid Collaboration: I. Risso, B. R. Granett, E. Branchini et al. (+297 more)

The Euclid spectroscopic survey will measure galaxy clustering with unprecedented precision, requiring stringent control of observational and instrumental systematics. Star-related effects may contaminate spectroscopic images through photometric persistence and imperfect masking of stars. We characterized their impact on galaxy clustering analyses, focusing on angular features identifiable in the data. We used angular and spatial auto- and cross-correlation statistics. For galaxies, we used mock spectroscopic catalogues from the EuclidLargeMocks in a 330 deg2 region of the Euclid Wide Survey (EWS). For stars, we used Gaia and 2MASS catalogues in the same area. To simulate photometric persistence, we implemented a simplified detector-level model calibrated on spectroscopic measurements and varied its strength to introduce different interloper fractions. For stellar masking, we modelled inconsistencies between the mask applied to the data and to the random catalogue. We measured star-star, galaxy-galaxy, and star-galaxy angular correlation functions using the Landy–Szalay estimator, and quantified deviations from the expected null star-galaxy correlation. We also evaluated the large-scale impact of such systematics through the three-dimensional two-point correlation function (2PCF). Photometric persistence produces a characteristic feature in the star-galaxy angular cross-correlation at scales of order 100", corresponding to the Euclid dithering pattern and grism dispersion geometry, and a spurious positive signal approximately constant up to 1{\deg}. Star-galaxy cross-correlation can detect residual persistence at contamination levels as low as 10% in a Data Release 1 spectroscopic catalogue. In contrast, stellar-mask mismatches produce strong small-scale angular signatures but have negligible impact on the large-scale 2PCF under realistic EWS conditions.
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All authors Euclid Collaboration: I. Risso, B. R. Granett, E. Branchini, A. Veropalumbo, B. Kubik, P. Monaco, J. Comparat, A. Hall, N. Aghanim, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, F. J. Castander, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, H. Degaudenzi, S. de la Torre, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, W. Gillard, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, S. Hemmati, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, N. Mauri, E. Medinaceli, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, C. Moretti, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, W. J. Percival, V. Pettorino, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, F. Rizzo, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, M. Scodeggio, A. Secroun, E. Sihvola, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, F. Caro, T. Castro, J. A. Escartin Vigo, J. García-Bellido, T. Gasparetto, J. Macias-Perez, R. Maoli, R. B. Metcalf, A. A. Nucita, M. Pöntinen, E. Sarpa, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, J. A. Acevedo Barroso, Y. Akrami, I. T. Andika, S. Anselmi, M. Archidiacono, G. Aricò, F. Atrio-Barandela, M. Baes, L. Bazzanini, J. Bel, D. Bertacca, M. Bethermin, F. Beutler, L. Blot, M. Bonici, M. L. Brown, S. Bruton, B. Camacho Quevedo, P. Carrilho, C. S. Carvalho, F. Cogato, T. E. Collett, S. Conseil, S. Contarini, A. R. Cooray, P. Corcho-Caballero, B. Csizi, O. Cucciati, S. Davini, T. de Boer, F. De Paolis, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, A. Enia, Y. Fang, A. Farina, A. Finoguenov, A. Franco, Y. Fu, K. Ganga, E. Gaztanaga, Z. Ghaffari, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, M. Guidi, C. M. Gutierrez, H. Hildebrandt, J. Hjorth, M. Jauzac, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, J. Kim, C. C. Kirkpatrick, A. Kovács, I. Kovačić, K. Koyama, S. Kruk, M. C. Lam, F. Leclercq, L. Legrand, M. Lembo, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, L. Linke, S. J. Liu, F. Mannucci, F. R. Marleau, C. J. A. P. Martins, M. Miluzio, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, S. Nesseris, L. Nicastro, F. Oppizzi, F. Pace, D. Paoletti, G. Parimbelli, F. Passalacqua, K. Paterson, L. Patrizii, C. Pattison, R. Paviot, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, G. Rodighiero, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, A. Schneider, D. Sciotti, E. Sellentin, S. Serjeant, L. C. Smith, J. G. Sorce, I. Szapudi, M. Talia, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, C. Uhlemann, C. Valieri, A. Venhola, D. Vergani, G. Verza, S. Vinciguerra, M. von Wietersheim-Kramsta, N. A. Walton, L. Wang, A. H. Wright

Cosmology and Nongalactic Astrophysics

Supernovae Unite: Combining Pantheon+ and DES-SN5YR

Ryan Camilleri, Jaemyoung Lee, Tamara Davis et al. (+21 more)

We present the Hubble diagram and cosmological constraints resulting from the combination of the Pantheon+ and DES-SN5YR supernova (SN) samples, which we refer to as Unite. Unite updates Pantheon+, including methodology improvements that the DES sample enabled, and adds the new SN from the DES survey. This represents the most comprehensive and internally consistent SN Ia dataset available, consisting of 2884 likely type Ia supernovae. This work features consistent SN Ia modelling, sample selection, and bias corrections. We also redetermine host-galaxy stellar masses for over 98% of the sample using a consistent framework. Using Unite alone, for a flat universe with a cosmological constant (Flat-$\Lambda$CDM), we find $\Omega_{\rm m} = 0.310^{+0.012}_{-0.011}$. We further present constraints using the Unite sample combined with Cosmic Microwave Background and both DES and DESI Baryon Acoustic Oscillation data. We find strong evidence of tension between CMB measurements and the combined BAO and supernova datasets when fitting a model with constant dark energy equation of state ($w$), which is alleviated when allowing $w$ to vary with time. For a flat universe with dark energy that has a time-evolving equation of state parametrized by $w_0$ and $w_a$ we find $(\Omega_{\rm m},w_0,w_a) = (0.305\pm0.004,-0.861^{+0.044}_{-0.042},-0.60^{+0.17}_{-0.19})$ with a dark energy Figure of Merit of 315. This corresponds to a $\sim30\%$ reduction in the area of the $w_0-w_a$ confidence region relative to previous constraints from the combination of DES Y6, DESI-DR2, and CMB data (arXiv:2605.27221). The Bayesian evidence indicates only weak preference for time evolving dark energy, whereas frequentist analyses yield a preference over Flat-$\Lambda$CDM at a significance of $3.3\sigma$ ($3.1\sigma$) when using the maximum $\textit{a posteriori}$ probability (maximum likelihood).
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All authors Ryan Camilleri, Jaemyoung Lee, Tamara Davis, David Rubin, Paul Shah, Dan Scolnic, Chris Lidman, Brodie Popovic, Koby Grech, Maria Vincenzi, Dillon Brout, Maria Acevedo, Patrick Armstrong, Bruce Bassett, Keith Bechtol, Rebecca Chen, Herman Diehl, Josh Frieman, Lluís Galbany, Anais Möller, Masao Sako, Bruno Sánchez, Mark Sullivan, Brad Tucker

2609.05053 · 4 Sep · 26 pages, 22 figures. The Unite Hubble diagram and likelihood will be made publicly available upon acceptance of the paper; v2 Including a link to our Youtube Cosmology Talks video, see https://www.youtube.com/watch?v=KT-j65gRnOQ. Removed inactive datalinks, fixed MAP significance, and adjusted the manuscript format for submission to PASA. Submitted to PASA

Abstract PDF $SNOV ×4$DATA ×2$BAYS ×1$CSMC ×1 +1

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Probing Dark Matter with Strongly Lensed Binary Black Hole Mergers: Prospects in the Near Future

Koustav N. Maity, Souvik Jana, Ankur Barsode et al. (+2 more)

Gravitational-wave~(GW) transients, strongly lensed by intervening galaxies and clusters, are expected to constitute a small fraction ($\sim 0.1$-$0.5\%$) of the events detectable by ground-based detectors. A strongly lensed binary black hole (BBH) merger will produce multiple copies of the GW signal arriving at different times at the detector. The abundance and time-delay distribution of these lensed events are sensitive to the mass, density profile, and redshift distribution of the lens population, and in turn, to the underlying nature of dark matter. Jana et al. (Phys.Rev.Lett. 135 (2025) 11, 111402) recently proposed a method to constrain the masses of warm dark matter (WDM) particles making use of the strongly lensed events detectable by next-generation GW detectors. In this work, we investigate the prospects of constraining the mass of the WDM particle using upcoming observations of the upgraded LIGO-Virgo-KAGRA network. This requires a careful modeling of the detector selection effects. The upcoming fifth observing run (O5) is expected to yield only a modest bound, since only a few lensed pairs are expected at that early stage. By the sixth observing run (O6), we forecast a bound on the WDM particle mass, $m_{\rm wdm}^{-1} \lesssim 0.1$-$0.2\text{keV}^{-1}$ ($m_{\rm wdm} \gtrsim 5$-$10\text{keV}$), which is comparable to the tightest existing astrophysical constraints. Runs beyond O6 will tighten the constraint by roughly an order of magnitude. Strongly lensed GWs therefore offer a complementary, competitive, and independent probe of dark matter.
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All authors Koustav N. Maity, Souvik Jana, Ankur Barsode, Tejaswi Venumadhav, Parameswaran Ajith

Cosmology and Nongalactic Astrophysics

Expanding the scope of dark siren cosmology: Inferring the population properties of gravitational wave-hosting galaxies

Rachel Gray, Daniel Williams and Alexander Papadopoulos

The field of gravitational wave "dark siren" cosmology is facing a number of challenges surrounding the way in which galaxy catalogue data is incorporated into the analysis. The three biggest challenges are adequately compensating for galaxy catalogue incompleteness, robust treatment of galaxy redshift and source properties, and the as-yet unknown host galaxy weighting model. We present an updated methodology for inferring cosmological parameters using dark sirens and incomplete galaxy catalogues. By switching to a sampled redshift prior, rather than one which is pre-computed on a grid, we can jointly infer parameters which describe the population of gravitational-wave hosting galaxies, alongside the gravitational wave population and cosmological model. Using the cosmological inference software gwcosmo, we reproduce a subset of GWTC-5.0 cosmology results, then extend the analysis to jointly infer the host galaxy weighting model - the first measurement of its kind to do so - leading to an updated measurement of the Hubble constant with $H_0 = {71.9}_{-7.5}^{+9.1}$ km s$^{-1}$ Mpc$^{-1}$ (median and 68% symmetric credible interval). This innovative new method opens the door to solving several of the biggest challenges currently facing the field of dark siren cosmology.
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Cosmology and Nongalactic Astrophysics

Late-Time Emergence of Dark Energy and Its Interaction with Dark Matter

Sibo Zhang, Weiqiang Yang, Supriya Pan et al. (+3 more)

We present an interacting scenario between dark energy (DE) and dark matter (DM), where DE has an emergent nature, that means, DE was absent in the early universe but it becomes effective only at late times. We consider two specific emergent DE models, one with no free parameters and the other featuring two parameters describing the speed and epoch of the transition. We constrain both scenarios using the cosmic microwave background (CMB) measurements from the Planck 2018 release, baryon acoustic oscillations from DESI DR2, and three different compilations of Type Ia supernovae (PantheonPlus, DES-Dovekie, and Union3). Our analysis indicates that current cosmological probes are not able to tightly constrain the speed of the transition. For both scenarios, the posterior distribution of the interaction parameter is shifted away from zero at more than 95% CL whenever the CMB data are combined with any of these additional probes, with the preferred direction corresponding to a transfer of energy from DE to DM. While CMB alone yields a high value of $H_0$, in agreement with local determinations, this effect is reduced when DESI is added and disappears once supernova data are included. In contrast, the clustering parameter $S_8$ is consistently shifted toward lower values in the combined datasets, and it is correlated with the preference for a negative interaction. However, according to the $\Delta \chi^2_{\rm min}$ and Bayesian evidence, none of the interacting models is favored over $\Lambda$CDM or $w_0w_a$CDM, indicating that the interaction does not rescue these emergent DE models. Our results therefore highlight the limitations of these scenarios in addressing current cosmological tensions, while pointing to the crucial role of future data in further assessing their viability.
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All authors Sibo Zhang, Weiqiang Yang, Supriya Pan, Olga Mena, Eleonora Di Valentino, Subenoy Chakraborty

Cosmology and Nongalactic Astrophysics

A guide to choosing data compression methods for cosmological inference

Susan Pyne, Benjamin Joachimi, Calum Gordon et al. (+1 more)

We provide a pedagogical guide to help researchers choose an appropriate compression method for cosmological inference and numerical covariance estimation, trading off the balance between information loss and complexity. We describe methods used in the literature, categorising them by the form of the loss function – Fisher information, mutual information, or mean squared error – and by whether they are linear or non-linear. We consider in detail the linear compression methods: massively optimised parameter estimation and data compression (MOPED), canonical correlation analysis (CCA), principal component analysis, and linear neural networks. We also investigate simple non-linear methods based on neural networks with similar architectures but different loss functions. We use tomographic weak lensing power spectra as example data vectors, deriving constraints on the cosmological parameters $\Omega_\mathrm{m}$, $\sigma_8$, $w_0$ and $w_a$ from compressed data. For our figure of merit (FoM) we use the log determinant of the Fisher matrix, which approximates the covariance of the full posterior well. MOPED and a Fisher information-based linear neural network both achieve lossless compression. Neural networks with loss functions which optimise mutual information achieve at most 84 per cent of the uncompressed FoM and those which minimise mean squared errors achieve at most 72 per cent. We show how to determine whether MOPED will retain information even if the fiducial cosmology is not known with certainty, and demonstrate a strategy for CCA which results in an FoM close to that of MOPED while requiring only an approximate idea of where the bulk of the posterior mass is located.
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All authors Susan Pyne, Benjamin Joachimi, Calum Gordon, Kiyam Lin

Cosmology and Nongalactic Astrophysics

Studies on the dark sector interaction from joint analysis of cosmological probes

Jianfeng Meng, Xiaofeng Yang, Yunliang Ren et al. (+4 more)

We test whether constraints on the nonlinear interaction $\xi$IDE are stable under different treatments of the Type Ia supernovae absolute calibration. Fermi GRBs measurements and the Amati-relation parameters are fitted jointly with PantheonPlus SNe Ia, DESI DR2 BAO, and an updated cosmic-chronometer compilation. We compare the PantheonPlus-SH0ES route, which retains the SN absolute calibration, with the PantheonPlus-only route, in which the SN absolute magnitude is analytically marginalized. The GOLD GRB sample is adopted for the main analysis, while the FULL GRB sample is used to assess sample dependence. For the interaction parameter $\gamma\equiv\xi+3w$, where $\gamma=0$ denotes the non-interacting limit, the GOLD sample gives $\gamma=1.453^{+1.297}_{-1.597}$ for the PantheonPlus-SH0ES and $\gamma=-0.634^{+1.668}_{-2.486}$ for the PantheonPlus-only. Although the posterior medians correspond to opposite directions of energy transfer, neither route excludes $\gamma=0$ at 68% credibility, and the reconstructed interaction rate remains consistent with zero over the redshift range considered. Replacing the GOLD sample with the FULL sample produces negligible changes in the interaction constraints. Moreover, $w$CDM and CPL achieve likelihood improvements comparable to that of $\xi$IDE, while the information criteria do not consistently favor the interacting model. A redshift-bin diagnostic finds no significant redshift evolution of the Amati relation. We find no compelling evidence for a dark sector interaction that is robust to the choice of SN calibration or specifically favored over noninteracting dark energy extensions.
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All authors Jianfeng Meng, Xiaofeng Yang, Yunliang Ren, Bohao Wang, Jingze Li, Kang Jiao, Xiongwei Liu

Thursday 3 September

Cosmology and Nongalactic Astrophysics

Implementation of frequency-correlated noise in CMB component separation: Method, Validation, and Early Applications

L. Zapelli, M. Bersanelli, L. P. L. Colombo et al. (+24 more)

Parametric component separation methods used in cosmic microwave background (CMB) analyses commonly assume instrumental noise to be uncorrelated between frequency channels. This approximation may become insufficient for experiments whose design naturally introduces cross-channel correlations, such as interferometric or multi-band bolometric systems. This work aims to provide a consistent framework to include frequency-correlated noise in Commander2 and to quantify its impact on component separation in controlled and instrument-motivated simulations. We generalized the amplitude sampling of the Commander2 framework to consistently handle dense frequency-frequency noise covariance matrices, modifying the likelihood evaluation and parallel architecture. The implementation is validated on low-resolution simulations of a simplified CMB-S4-like configuration. We applied the generalized framework to instrument-motivated simulations of the QUBIC bolometric interferometer, using representative noise models derived from end-to-end simulations. Validation tests show excellent convergence and agreement between sampled parameters and analytical maximum-likelihood estimates. Accounting for frequency correlations reduces the width of the maximum-likelihood residual distributions by up to 8% on average, and up to 11% for individual parameters, relative to the diagonal-noise approximation. In QUBIC-based simulations, accounting for an anti-correlated noise produces posterior widths reduced by about 60%, while a positive-correlation test increases them by about 40%. This shows that neglecting cross-channel correlations can lead to incorrect posterior estimates in either direction. The generalized implementation presented here enables the Commander2 software to consistently propagate such correlations into parameter estimation, providing a framework for assessing their impact in future CMB analyses.
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All authors L. Zapelli, M. Bersanelli, L. P. L. Colombo, A. Mennella, L. G. Bachar, E. Battistelli, I. Bekkaoui, L. A. Bianchi, A. Coppolecchia, B. Costanza, P. De Bernardis, G. De Gasperis, S. Ferazzoli, M. Galloway, B. García, M. Gervasi, N. Mirón-Granese, J-Ch. Hamilton, T. Laclavère, J. G. S. Lunde, S. Masi, Y. Moulane, S. Paradiso, I. D. Queirolo, M. Regnier, G. E. Romero, C. G. Scóccola

Cosmology and Nongalactic Astrophysics

The Super-Sample Covariance of Line-Intensity Mapping Power Spectrum

Sefa Pamuk, José Luis Bernal and Azadeh Moradinezhad Dizgah

In this work, we provide the first derivation of the line-intensity mapping (LIM) power spectrum super-sample covariance (SSC) from first principles, and also derive as a by-product the non-Gaussian in-box contributions to the covariance for the first time. Previous studies have typically modelled the LIM power spectrum covariance using either the Gaussian approximation or estimates obtained from mocks or the data itself, neglecting uncertainties related to whether the limited volume surveyed sits in a cosmological overdensity. This contribution, known as the SSC or, depending on the context, the field-to-field variance, cannot be estimated from the data, but it is crucial for a correct inference of global quantities, i.e., for ensemble-averaged parameters rather than the actual values just within the patch of the Universe observed. For our derivation, we employ a combination of the halo model and standard perturbation theory that allows us to capture the nonlinearity and non-Gaussianity of the covariance. After a successful validation of our predictions against painted N-body simulations, we explore different scenarios related to current and future LIM experiments, quantifying the relative importance of the non-Gaussian in-box and SSC. We find that the newly derived contributions to the LIM power spectrum covariance are crucial at intermediate and small scales, especially for cases in which the covariance is not dominated by instrumental noise. We find that the relative relevance of the SSC with respect to the other covariance contributions is roughly independent of the survey volume, but does depend on the specific response of the power spectrum to large-scale modes for each line and redshift. Therefore, the impact of the SSC will be increasingly significant for parameter inference from the current and the next generation high signal-to-noise LIM surveys.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

H I Absorbers as Beacons of Hidden Structure at $z \sim 3$: Multi-Component, Metal-Rich Absorption System near a Protocluster

Kentaro Koretomo, Nobunari Kashikawa, Toru Misawa et al. (+12 more)

H I gas traces the large-scale structure and provides the primary fuel for star formation. High-$z$ protoclusters are ideal laboratories to study how H I gas is accreted and consumed during the formation of the most massive structures in the Universe. However, much remains unknown about the distribution and physical state of their H I gas. We examine a rare configuration in which a protocluster candidate is located in front of a quasar at $z=3.09$. Our spectroscopic campaign confirms a protocluster at $z=3.079$: however, no corresponding strong H I absorption is found in the background quasar spectrum. Instead, we serendipitously discover a prominent H I absorption feature at $z\sim 3.01$, offset by $\sim 60$ cMpc from the centre of the protocluster. Spanning an exceptionally broad velocity range of $\sim 2000$ km s$^{-1}$ ($\sim 40$ cMpc), this absorption is decoupled from the confirmed member galaxies. Detailed kinematic modelling reveals this absorption comprises five distinct components rather than a single cloud. Moreover, one of these components exhibits a super-solar metallicity ($[\mathrm{O/H}] = +1.19^{+0.91}_{-0.78}$). We propose two physical scenarios for this unique system: (1) an additional, hidden massive protocluster along the line of sight, and/or (2) metal-rich outflows and metal-poor inflows driven by a single massive galaxy. The discovery highlights that while protoclusters are not universally associated with strong H I absorption, targeting the strong H I absorbers may serve as a beacon for uncovering massive, metal-rich protoclusters or complex gas kinematics in the early Universe.
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All authors Kentaro Koretomo, Nobunari Kashikawa, Toru Misawa, Jun Toshikawa, Yoshihiro Takeda, Hisakazu Uchiyama, Junya Arita, Shunta Shimizu, Ryo Emori, Kei Ito, Satoshi Kikuta, Mariko Kubo, Yoshiaki Ono, Marcin Sawicki, Rhythm Shimakawa

Cosmology and Nongalactic Astrophysics

Model Predictive Scoring Shows Specific BAO Observations (not SNIa) Drives $w_0w_a$ Tension

Tanveer Karim, Joshua S. Speagle and Renée Hložek

The recent analyses of DESI DR2 BAO, Planck CMB and various Supernovae datasets have shown preferences for evolving dark energy at various levels of significance, under frequentist model comparison tests. However, the same analysis done with a pure Bayesian model comparison test can lead to the opposite conclusion due to the impact of $w_0w_a$ priors. In contrast to these in-sample model comparison route, we approach the problem along a third axis – which model better predicts unseen data. We use the Expected Log Predictive Density (ELPD) metric to score the predictiveness of $\Lambda$CDM and $w_0w_a$CDM models, using the leave-one-redshift-block-out cross-validation estimator. The comparison metric $\Delta$ELPD is out-of-sample, unlike $\Delta \chi^2_{\rm MAP}$ and Bayes Factor, and insensitive to prior width, unlike the Bayes factor. Aggregated, we find modest preferences for $w_0 w_a$CDM, primarily driven by the BAO. Decomposing the $\Delta$ELPD score by redshift we find that a single BAO block, LRG2 ($z = 0.706$), supplies the entire BAO preference. Interestingly, the biggest outlier point, LRG1, contributes little to the model predictive scoring because both $\Lambda$CDM and $w_0w_a$CDM fail to predict the observation by equal amount. On the other hand, all SNIa datasets' $\Delta$ELPD scores are consistent with $0$, indicating that at an out-of-distribution predictive level, the $w_0w_a$CDM tension is entirely driven by one BAO point, not SNIa.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Widespread Inflows Reveal Baryonic Cycling in Star-forming and Quiescent Galaxies

Hassen M. Yesuf, Ravi Joshi, Yuxuan Zou et al. (+8 more)

Cool-gas inflows, required to sustain star formation, have been fundamental in simulations yet remained observationally elusive. Using DESI spectroscopy of ~30,000 galaxies, we identify coherent inflowing gas (~100 km/s) in 20-50% of the sample, yielding a population-level census of gas flows. We uncover a striking inversion: inflows are detected in quiescent galaxies, whereas star-forming systems are dominated by gravitationally bound outflows. At fixed age, galaxies with inflows, outflows, or no/weak flows share similar masses, environments, and structures, indicating that these properties do not differentiate flow states. Instead, gas-flow state is linked to stellar population age and recent evolutionary history, consistent with age-dependent gas flows in two regimes. In some star-forming galaxies, elevated star formation surface densities drive outflows that recycle on ~0.5 Gyr timescales, consistent with a galactic fountain. In quiescent systems, low-level “drizzling” inflows persist, consistent with slowly cooling enriched halo gas and weak radio-mode nuclear activity. Broad gas-phase metallicity distributions—and absence of a pristine dilution signature—indicate that detected inflows are predominantly recycled or enriched. Detectability is modulated by dust, ionization, and geometry: in star-forming disks, inflowing gas lies near the disk plane and is obscured or ionized, while outflow hosts exhibit higher dust and metal content. As star formation declines, cold-outflow signatures weaken, and recycled or slowly cooling gas is more readily detected as inflow. Post-starburst galaxies provide snapshots of this transition. Our results resolve the scarcity of observed inflows, provide evidence for widespread gas accretion and recycling in present day galaxies, and establish an observational framework linking gas flows to star formation, chemical evolution, and galaxy structure.
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All authors Hassen M. Yesuf, Ravi Joshi, Yuxuan Zou, Feng Yuan, Luis C. Ho, Lin Lin, Lei Hao, Shiyin Shen, Connor Bottrell, Fulai Guo, John D. Silverman

Cosmology and Nongalactic Astrophysics

It's All About the Environment: Local $f_{\rm NL}$ from a Dark Matter Conditioned Multitracer Analysis

Julius Adolff and Uroš Seljak

Primordial non-Gaussianity (PNG) offers a powerful test of inflationary physics beyond the simplest single-field scenarios. In large-scale structure, biased tracers respond to local-type PNG with a distinctive scale-dependent signature that is strongest on large scales, but single-tracer measurements are fundamentally limited by cosmic variance. Multitracer methods can mitigate this limitation; however, many existing proposals require splitting tracers using a wide range of halo masses which are often not available, or using secondary halo properties that are not directly observable. Here we develop and validate an alternative strategy based on splitting a tracer sample by its large-scale dark matter environment. We derive a theoretical framework for the $f_{\rm NL}$ response of environmentally selected tracers and test it in $N$-body simulations, confirming consistency between separate-universe predictions and direct power-spectrum inference. To enable observational implementation, we show that a simple linear-theory reconstruction of the dark matter environment from halos yields unbiased $f_{\rm NL}$ constraints in $\mathtt{Quijote}$ simulations. Forecasts for the DESI LRG sample indicate that environmental multitracing can improve constraints on local PNG by a factor of 2-3 relative to conventional single-tracer analyses for high density tracers, comparable to gains achieved when halo formation time is assumed to be perfectly known. We develop an analytic model explaining why the gains are smaller for a halo environment split and why separate-universe predictions fail in this case. Unlike approaches that require modeling assembly bias or inferring secondary halo properties, our method relies only on linear theory. These results establish environmental multitracer techniques as a promising route toward $\sigma(f_{\rm NL})\sim 1$ with upcoming galaxy surveys.
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