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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 7 March

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

Quantum (quadratic) gravity: replacing the massive tensor ghost with an inverted harmonic oscillator-like instability

K. Sravan Kumar and João Marto

The quadratic theory of gravity is the unique renormalizable theory of quantum gravity in 4 dimensions, as proved by K. S. Stelle in 1977. Over the decades, the theory has been understood to contain a massive tensor ghost, and several attempts have been made to evade its adverse effects by proposing new quantization prescriptions and interpretations. In this paper, we show that the additional spin–2 of quadratic gravity can be turned into a healthy inverted harmonic oscillator (IHO)-like instability, which can be quantized consistently with direct-sum quantum field theory (DQFT), which incorporates geometric superselection sectors. Such modes possess a well-defined quantum description yet do not admit a particle interpretation and are not part of the asymptotic spectrum, being characterized by hyperbolic evolution and spacelike momentum support. We argue that, as a consequence, the extra spin–2 degree of freedom remains off-shell and effectively decoupled from ordinary matter fields, avoiding unitarity violations in observable processes. We argue that this IHO instability is a prevalent feature of fundamental physics, whether it concerns quantum fields on curved spacetimes or the Higgs $\mathbb{Z}_2$ symmetry breaking in the Standard Model of particle physics. Thus, we demonstrate that our new understanding of quadratic gravity offers a fundamental pathway to quantum gravity and a safe beginning for the Universe. Furthermore, we derive key observational predictions of this construction in the view of primordial gravitational waves with new bounds on the tensor-to-scalar ratio and the parity asymmetric features on the large angular scales.
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High Energy Astrophysical Phenomena

Flux Variations of Fast Radio Bursts and Their Persistent Radio Sources: Evidence for a Shared Progenitor

Xinming Li, Chenhui Niu, Jiaheng Zhang et al. (+24 more)

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients, some of which are associated with compact persistent radio sources (PRSs), hinting at a physical connection. While several models have been proposed to explain PRSs and their connection to FRBs, direct observational tests remain limited. Here, we report for the first time a correlated trend between the long-term variation of the PRS flux density and the burst energetics of FRB 20190520B and FRB 20240114A, suggesting a physical coupling between the PRS and FRB activity. We further examine additional repeaters with compact PRSs and find no clear correlation between PRS luminosity and burst activity, likely due to the limited observations. These results are consistent with scenarios in which both the PRS and FRB activity may be powered by a common energy reservoir, such as the magnetic or rotational energy of a magnetar.
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All authors Xinming Li, Chenhui Niu, Jiaheng Zhang, Di Li, Bing Zhang, Yuanpei Yang, Pei Wang, Junshuo Zhang, Yongkun Zhang, Ye Li, Jiarui Niu, Xiaoping Zheng, Yunwei Yu, Yi Feng, Bo Zhang, Fayin Wang, Yuhao Zhu, Aming Chen, Zexin Du, Jian Li, Weihong Li, Chenchen Miao, Weiyang Wang, Guanglei Wu, Aiyuan Yang, Jumei Yao, Rushuang Zhao

Earth and Planetary Astrophysics · Cross-listed from math.DS

Low-Energy and Low-Thrust Exploration Tour of Saturnian Moons with Full Lunar Surface Coverage

Chiara Pozzi, Mauro Pontani, Alessandro Beolchi et al. (+2 more)

This study presents the trajectory design for a mission touring Saturn's Inner Large Moons (Rhea, Dione, Tethys, Enceladus, and Mimas) engineered to meet observational requirements, including full surface coverage, while ensuring low fuel consumption and compatibility with current power and propulsion technologies (radioisotope thermoelectric generators and Hall effect thrusters). The tour begins at Rhea and ends at Mimas, using a trajectory concept that alternates between extended observation phases around each moon and Saturn centered low-thrust spiral arcs to transition efficiently to the next target. The J2-perturbed Circular Restricted Three-Body Problem is adopted to design exploration paths, with halo orbits serving as staging points for heteroclinic and homoclinic loops that enable prolonged, repeated, and comprehensive surface reconnaissance (including critical regions such as Enceladus poles, where geological activity produces intense plumes). Stable and unstable hyperbolic invariant manifolds of the halo orbits act as departure and arrival gateways for propelled inter-moon transfers, modeled in an ephemeris-based framework including gravitational perturbations from the moons, the Sun, and Saturn's oblateness. The dynamical model setup is guided by a rigorous perturbation analysis to maximize computational efficiency while maintaining high fidelity trajectory design. A locally optimal guidance law minimizes propellant consumption. The proposed tour offers an alternative to traditional flyby missions, providing comparable total duration but greater observing time and reduced fuel requirements, and advances previous work by achieving both complete lunar surface coverage and high-fidelity modeling.
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All authors Chiara Pozzi, Mauro Pontani, Alessandro Beolchi, Hadi Susanto, Elena Fantino

High Energy Astrophysical Phenomena

Supernovae interacting with Si and S-rich circumstellar matter from double white dwarf mergers

Takashi J. Moriya, Chengyuan Wu, Dongdong Liu et al. (+2 more)

We present that supernovae interacting with a dense Si and S-rich circumstellar matter like SN 2021yfj can originate from mergers of two white dwarfs. A C+O white dwarf accreting He from its non-degenerate He companion star can initiate a C burning frame at its surface propagating inward under certain conditions. Such a burning frame synthesizes intermediate mass elements such as Si and S, forming a hybrid WD with an outer Si+S-rich layer. After the He star companion becomes a white dwarf, the two white dwarfs can eventually merge. During the merger, the outer layers of the hybrid white dwarf can be tidally stripped, forming a dense Si and S-rich circumstellar matter. If a thermonuclear explosion is triggered in the merging white dwarfs, an explosion within a dense Si and S-rich circumstellar matter can be realized, resulting in SN 2021yfj-like events. We argue that the properties of SN 2021yfj can be reproduced by a dense Si and S-rich circumstellar matter having ~ 0.3 Msun within which an explosion having kinetic energy of ~ 4e50 erg and ejecta mass of ~ 0.3 Msun occurred. These properties are consistent with the double white dwarf merger scenario. This scenario can naturally explain the existence of He observed in SN 2021yfj. Because white dwarf mergers can also lead to the formation of He and C+O dense circumstellar matter, some Type Ibn and Icn supernovae may also originate from a similar evolutionary path.
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All authors Takashi J. Moriya, Chengyuan Wu, Dongdong Liu, Zheng-Wei Liu, Bo Wang

High Energy Astrophysical Phenomena

Anisotropic Diffusion in Pulsar Halos: Interpreting the asymmetric morphology of Geminga and Monogem halos measured by HAWC

Si-Zhe Wu, Chao-Ming Li and Ruo-Yu Liu

Pulsar halos are produced by electrons and positrons diffusing in the interstellar medium around their parent pulsar wind nebulae. Recent observations by HAWC and LHAASO have revealed asymmetric morphologies in the halos surrounding Geminga and Monogem. The anisotropic diffusion model provides a natural explanation for such asymmetries, where the morphology is determined by the viewing angle of the mean magnetic field, the Alfvénic Mach number ($M_{\rm A}$), and the pulsar distance. In this work, we model the measured morphologies based on this framework and constrain the properties of interstellar magnetic turbulence. We find that the mean magnetic field orientations within the two halos are different, implying that they reside in different magnetic coherence regions, whereas the Alfvénic Mach numbers are relatively close ($M_{\rm A}\sim 0.2$). The results suggest a local magnetic field coherence length of approximately 100pc. Our study demonstrates that the morphology of pulsar halos serves as a powerful diagnostic tool for the properties of interstellar magnetic fields, highlighting the need for more accurate morphological measurements and sophisticated diffusion modeling in future studies.
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Astrophysics of Galaxies

New black hole mass calibrations and the fundamental plane of the broad-line region size, luminosity, and velocity

Jong-Hak Woo, Jimin Kim, Hojin Cho et al. (+1 more)

We present a new calibration of the broad-line region (BLR) size-luminosity-velocity relation using a sample of 157 AGNs with reliable Hbeta time-delay (\lag) measurements from Wang & Woo 2024. By incorporating the Eddington ratio as a third parameter, we effectively correct the systematic offset of high-Eddington AGNs in the traditional BLR size-luminosity relation. The resulting three-parameter fit defines a fundamental plane in the 3-D space of the \lag, optical luminosity, and Hbeta velocity, with an intrinsic scatter of 0.21 dex. This tight correlation reflects the coupled effects of gas kinematics, photoionization, and BLR geometry. In turn, we develop a new method to infer \lag\ from the combination of optical luminosity and Hbeta velocity, and derive single-epoch black hole mass estimators by adopting either the full-width-at-half-maximum (FWHM) or line dispersion ($\sigma$) of the Hbeta line profile as the velocity indicator. The derived \lag shows a ~0.1 dex scatter, depending on the choice of calibrations. We show that the previous mass estimates based on the two-parameter size-luminosity relation with a 0.5 slope can be overestimated by up to 0.5 dex, demonstrating that the new mass estimator substantially changes the cosmic black hole mass density and the growth of black hole seeds in the early universe.
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All authors Jong-Hak Woo, Jimin Kim, Hojin Cho, Shu Wang

High Energy Astrophysical Phenomena

Interpreting Swift and NuSTAR Observations of the Low-Luminosity Active Galactic Nucleus NGC 4278 with Radiatively Inefficient Accretion Flows and Implications for Neutrino Emission

Abhishek Das, Qi Feng, Eleanor Young et al. (+3 more)

We report the first NuSTAR hard X-ray observations of the low-luminosity active galactic nucleus NGC 4278. The source is clearly detected beyond 10 keV with a hard X-ray spectrum consistent with a power law of photon index between 2.2 and 2.5 without evidence for a high-energy cutoff. The X-ray flux is low compared to the active state in 2021, but exhibits variability by a factor of ~2 on a timescale of a month. We discuss the origin of the hard X-ray emission and explore its connection to gamma rays and high-energy neutrinos. We explain the X-ray data, including both quiescent and active states, using a radiatively inefficient accretion flow (RIAF) model with a variable accretion rate. We also show that TeV gamma rays cannot escape from the RIAF disk, and very high-energy gamma rays observed in LHAASO are likely to originate from outer regions such as jets and winds, which is consistent with our results favoring a magnetically arrested disk. We also discuss hidden neutrino emission from RIAFs together with possible connections to coronae of active galactic nuclei with standard, radiatively efficient disks.
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All authors Abhishek Das, Qi Feng, Eleanor Young, Ashwani Pandey, Shigeo S. Kimura, Kohta Murase

Earth and Planetary Astrophysics

Water D/H in 3I/ATLAS as a Probe of Formation Conditions in Another Planetary System

Luis E. Salazar Manzano, Teresa Paneque-Carreño, Martin A. Cordiner et al. (+17 more)

Water reservoirs in the Solar System exhibit a deuterium enrichment that links back to the physical environment at the time of stellar birth. Gas-phase and ice-grain deuterium enrichments occur through chemical processes that operate at low temperatures ($<$~30~K) pointing towards an origin in the prestellar molecular cloud or in the outer parts of the protoplanetary disk. However, not all stars are born in environments similar to our Sun, nor do their subsequent evolutionary histories follow the same path. These environmental differences can be traced by the water deuterium-to-hydrogen (D/H) ratio. Here we use ALMA observations of the interstellar comet 3I/ATLAS to constrain the water D/H ratio in extrasolar cometary material. With a water D/H value of [D/H]$_{\mathrm{H_2O}} > 6.6\times10^{-3}$, 3I/ATLAS shows a deuterium enrichment exceeding Earth's ocean value by more than a factor of $\gtrsim40$ and typical Solar System cometary values by more than a factor of $\gtrsim30$. The elevated deuterium enrichment points to water that formed under colder, less irradiated conditions and from less thermally processed material, consistent with an origin in a planetary system that formed under different physical and chemical conditions than our own.
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All authors Luis E. Salazar Manzano, Teresa Paneque-Carreño, Martin A. Cordiner, Edwin A. Bergin, Hsing Wen Lin, Dariusz C. Lis, David W. Gerdes, Jennifer B. Bergner, Nicolas Biver, Dominique Bockelée-Morvan, Dennis Bodewits, Steven B. Charnley, Jacques Crovisier, Davide Farnocchia, Viviana V. Guzmán, Stefanie N. Milam, John W. Noonan, Anthony J. Remijan, Nathan X. Roth, John J. Tobin

High Energy Astrophysical Phenomena

Probing the Dispersion and Rotation Measure Contributions from Supernova Remnants in Fast Radio Burst Source Environments with 1D SNR Simulation

Zhao Joseph Zhang, Gaku Kawashima, Shiu-Hang Lee et al. (+3 more)

Fast radio bursts (FRBs) provide a sensitive probe of ionized baryons through their dispersion measure (DM). In addition to slowly evolving cosmological terms, at least two repeaters now show clear secular DM-decrease episodes: FRB~20190520B and FRB~20121102 , supporting a dense, dynamically evolving local environment. We adopt a forward-modeling approach and use time-dependent 1D SNR simulations for a young magnetar embedded in SN ejecta, combining single-star and binary-stripped progenitors with HD+NEI calculations to follow shock structure, ionization, and electron density. The shocked region contributes only limited DM ($\lesssim10\,{\rm pc\,cm^{-3}}$), while the dominant time-varying component is the unshocked ejecta, whose early behavior follows ${\rm DM}\propto t^{-\alpha}$ with $\alpha\simeq1.8$–$1.9$. Although shocked-region DM is small, shock-amplified magnetic fields can still generate substantial RM; in our shock-only RM framework, only the $11\,M_\odot$ SS model reproduces the FRB~20121102 RM evolution. Binary-stripped progenitors generally yield smaller DM than single-star models at fixed $M_{\rm ZAMS}$, with composition-dependent mean molecular weights introducing non-monotonic mass trends. Matching the observed ${\rm dDM}/{\rm d}t$ of FRB~20190520B (and the late-stage slope of FRB~20121102), we infer local SNR DM contributions of tens to hundreds ${\rm pc\,cm^{-3}}$. We also find GHz escape is allowed in most models, with $\tau_{\rm ff}=1$ typically reached by $t_{\rm esc}\lesssim70$ yr; for weakly ionized ejecta, the source can be nearly transparent from very early times. These results support a young CCSN/SNR origin for a substantial fraction of ${\rm DM}_{\rm source}$ and highlight that physically consistent local-environment modeling is essential for robust FRB cosmological DM inferences.
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All authors Zhao Joseph Zhang, Gaku Kawashima, Shiu-Hang Lee, Kentaro Nagamine, Bing Zhang, Yusei Fujimaru

Earth and Planetary Astrophysics

Multi-wavelength ALMA Imaging of HD 34282: Dust-trapping Signatures of a Vortex Candidate

Xiaoyi Ma, Fangyuan Yu, Ruobing Dong et al. (+8 more)

Azimuthal arcs in millimeter continuum emission from protoplanetary disks are often attributed to dust-trapping vortices, but definitive observational confirmation of vortices remains lacking. We present sub-0.1" resolution ALMA continuum observations of the HD 34282 disk at 0.9, 1.3, 2.1, and 3.1 mm. These observations resolve a bright azimuthal arc superposed on a compact double-gap, triple-ring morphology, most clearly at shorter wavelengths, and enable us to probe the physical origin of the arc. It exhibits a lower spectral index than the surrounding rings, consistent with enhanced grain growth and/or higher dust surface density of a dust-trapping vortex. Its azimuthal width decreases with increasing wavelength, consistent with tighter confinement of larger grains, or lower optical depths at longer wavelengths. These observations probe dust with Stokes numbers St < 0.03. Vortex models predict negligible peak shifts in this regime, consistent with the 1.3 to 3.1 mm data. At 0.9 mm, however, the arc peak is offset by 15 +/- 4 degree in the direction of disk rotation relative to longer wavelengths, and the near-side ring emission is locally dimmer compared to the far-side, likely reflecting optical-depth or temperature effects. These observations are consistent with azimuthal dust trapping, potentially associated with a vortex-induced pressure maximum.
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All authors Xiaoyi Ma, Fangyuan Yu, Ruobing Dong, Kiyoaki Doi, Akimasa Kataoka, Hauyu Baobab Liu, Feng Long, Takahiro Ueda, Huojun Li, Nienke van der Marel, Agnes Kospal

Astrophysics of Galaxies

Effect of gravity-driven longitudinal flows in filaments on angular momentum transport to embedded cores

Griselda Arroyo-Chávez, Shuo Kong and Enrique Vázquez-Semadeni

Different models of filament formation predict distinct patterns of angular momentum redistribution toward embedded cores, set by the underlying velocity-field structure, which can set the initial conditions for a preferential orientation between protostellar outflows and filaments. However, the absence of a dominant alignment in observations keeps this connection open to debate. We investigate whether gravity-driven longitudinal flows along filaments can redistribute angular momentum (AM) toward collapse centers. To this end, we analyze the distributions of 3D and 2D-projected angles between sink angular momentum vectors and host filament orientations in an SPH simulation of giant molecular cloud and filament formation. We also characterize the filament velocity field by measuring the angles between SPH particle velocity vectors and filament axes, and the degree of convergent flow toward filament density peaks. No preferred alignment between the sinks' AM and the filament direction is found at early evolutionary stages, neither in 3D nor in 2D. Later, however, a predominantly perpendicular configuration emerges in 3D. Tracking individual sinks indicates that this alignment is not primordial but develops as gravity strengthens. In individual filaments, the onset of perpendicular alignment coincides with the development of convergent longitudinal flows. Finally, we estimate the minimum excess fraction of intrinsically perpendicular 3D orientations needed for a projected sample to retain a detectable perpendicular alignment in 2D as a function of sample size, and the minimum sample size for the trend to be detectable in projection, which is at least $\sim 35$ measurements, making conclusions from limited 2D samples potentially misleading.
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High Energy Astrophysical Phenomena

Different polarized components of the quasar 3C 286 revealed by FAST

Pengfu Tian, Xiao Chen, Wen Yang et al. (+1 more)

3C 286, a well-known radio calibrator, exhibits the stability in both of total flux density (FD) and polarization parameters. However, its stable and luminous interstellar radio signal may encounter interplanetary scintillation (IPS) due to density irregularities in the solar wind within the heliosphere. In this work, we analyze high-time-resolution observations of 3C 286 obtained with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) from 2019 to 2023. Our analysis reveals that IPS affects the polarized flux densities of the Stokes I, Q, and U parameters, whereas Stokes V shows no detectable IPS-induced variations. The IPS variations detected in Stokes I are synchronous with those in Stokes U, while those in Stokes Q exhibit greater randomness. The crosscorrelation function (CCF) results indicate no time delay between Stokes I and U, but a delay of approximately 2.8 seconds between Stokes I and Q. This suggests that the different polarized radio emissions of 3C 286 originate from distinct emission regions, specifically the core and the southwestern jet. Furthermore, the projections of the radio core and jet component onto the scintillation screen at 1 AU yield a solar wind plasma speed of $\sim 637$ km/s.
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All authors Pengfu Tian, Xiao Chen, Wen Yang, Wei Wang

Friday 6 March

Solar and Stellar Astrophysics

The diagnostic temperature discrepancy as evidence for non-Maxwellian coronal electrons

Victor Edmonds

Two independent electron temperature diagnostics applied to the quiet solar corona yield systematically different results. Radio brightness temperatures from the Nancay Radioheliograph indicate T_e ~ 0.6 MK, while hydrostatic scale-height modeling requires T_e ~ 1.5 MK. Both probe electrons; they disagree by a factor of R = 2.4 +/- 0.3. This discrepancy persists across eight years spanning solar minimum and is confirmed by LOFAR at lower frequencies. We consider turbulent scattering, which suppresses brightness temperature, but comparison with the FORWARD/PSIMAS Maxwellian model shows the standard thermal structure predicts ~1.6 MK; scattering accounts for the reduction toward observed MWA values but not the gap to 620 kK. The ratio R is also cycle-invariant despite measured variations in turbulence. We propose the residual discrepancy reflects non-Maxwellian electron velocity distributions. Radio bremsstrahlung samples the distribution core; ionization and scale heights are dominated by the suprathermal tail. For kappa distributions, the predicted ratio kappa/(kappa - 3/2) matches R = 2.4 at kappa ~ 2-3, consistent with spectroscopic measurements in active regions but in tension with perturbative predictions of kappa ~ 10-25. We predict Active Region cores should show a collapsed ratio (R <= 1.5) as collisionality restores thermal equilibrium.
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Astrophysics of Galaxies

Imaging the disk-halo interface of NGC 891: a 2.7 kpc-thick molecular gas disk

D. Jiménez-López, S. García-Burillo, M. Querejeta et al. (+2 more)

Halos surrounding spiral galaxies act as the bridges connecting the galactic disk and the intergalactic medium (IGM). They host a significant fraction of the baryonic mass in the Universe, and feedback from star formation (SF) or active galactic nuclei (AGN) likely plays an important role in regulating this vertical baryonic component. Despite its importance, the contribution of extraplanar molecular gas remains poorly understood. We aim to characterize the vertical extent and the kinematics of molecular gas traced by CO(2-1) emission in the nearby (D = 9.5 Mpc) spiral galaxy NGC 891, one of the best studied edge-on galaxies. We also compare our results with HI, H$\alpha$-traced DIG and dust maps from the literature. Our analysis is based on new CO(2-1) observations of NGC 891 obtained with the IRAM 30m telescope. We mapped two 6 kpc $\times$ 6 kpc regions on the northeastern side and the area surrounding the galactic center. We apply a careful method to estimate and remove the residual contribution of the error beam to the CO cube. The vertical extent of the molecular gas is best described by a two-component Gaussian fit, consisting of a bright thin disk component (deconvolved FWHM $\simeq$ 360 pc) and a fainter thick disk component (deconvolved FWHM $\simeq$ 1.1 kpc). Statistically significant CO(2-1) emission is detected up to 1.3-1.4 kpc above the disk midplane. We estimate that the thick molecular disk component contains up to 27% of the total molecular gas mass of the galaxy. Our results demonstrate that SF-driven feedback in a non-starburst galaxy can lift significant amounts of molecular gas to large vertical distances. We interpret the presence of extraplanar molecular gas in NGC 891 in the framework of a galactic fountain scenario, in which material is expelled from star-forming regions and transported toward the outer halo.
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All authors D. Jiménez-López, S. García-Burillo, M. Querejeta, A. Usero, P. Tarrío

Earth and Planetary Astrophysics

Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS

Martin Cordiner, Nathan X. Roth, Marco Micheli et al. (+16 more)

Interstellar objects provide the only directly observable samples of icy planetesimals formed around other stars, and can therefore provide insight into the diversity of physical and chemical conditions occurring during exoplanet formation. Here we report isotopic measurements of the interstellar comet 3I/ATLAS, which reveal an elemental composition unlike any Solar System body. The water in 3I/ATLAS is enriched in deuterium, at a level of D/H = (0.95 +- 0.06)%, which is more than an order of magnitude higher than in known comets, while its range of 12C/13C ratios (141-191 for CO2 and 123-172 for CO) exceeds typical values found in the Solar System, as well as nearby interstellar clouds and protoplanetary disks. Such extreme isotopic signatures indicate formation at temperatures $\lesssim30$ K in a relatively metal-poor environment, early in the history of the Galaxy. When interpreted with respect to models for Galactic chemical evolution, the carbon isotopic composition implies that 3I/ATLAS accreted roughly 10-12 billion years ago, following an early period of intense star formation. 3I/ATLAS thus represents a preserved fragment of an ancient planetary system, and provides direct evidence for active ice chemistry and volatile-rich planetesimal formation in the young Milky Way.
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All authors Martin Cordiner, Nathan X. Roth, Marco Micheli, Geronimo Villanueva, Davide Farnocchia, Steven Charnley, Nicolas Biver, Dominique Bockelee-Morvan, Dennis Bodewits, Colin Orion Chandler, Jacques Crovisier, Maria N. Drozdovskaya, Kenji Furuya, Michael S. P. Kelley, Stefanie Milam, John W. Noonan, Cyrielle Opitom, Megan E. Schwamb, Cristina A. Thomas

Cosmology and Nongalactic Astrophysics

Estimating the completeness of the QUBRICS Survey with 3501 QSO redshifts from Gaia DR3 spectra

Matteo Porru, Stefano Cristiani, Francesco Guarneri et al. (+9 more)

QSOs are essential for investigating the structure and evolution of the Universe. Historically, their identification has been concentrated in the northern hemisphere, primarily due to the sky coverage of major astronomical surveys. The QUBRICS survey, started in 2019 to address this asymmetry, has identified more than 1300 new bright (i<19.5) high-redshift (2.5<z<6) QSOs in the southern sky. We aim to quantify, using an independent QSO sample, the completeness and recall of the QUBRICS QSO selection methods, based on XGB (eXtreme Gradient Boosting) and PRF (Probabilistic Random Forest), since completeness is a fundamental metric for ensuring the statistical robustness of QSO-based cosmological investigations. A subset of Gaia DR3 sources with low-resolution spectra was analyzed, obtaining a sample of 3501 QSOs. To determine how many QSOs were correctly identified as candidates, we crossmatched this independent sample with the datasets used for selection: 894 QSOs with z>2.5 fell within the XGB dataset footprint, of which 152 were unclassified and thus eligible for completeness testing. Similarly, 675 QSOs with z>2.5 were within the PRF dataset footprint, including 69 unclassified objects. The XGB correctly identified as candidates 136 (89%) of the 152 QSOs with z>2.5 present in its dataset as unclassified objects. The PRF correctly identified as candidates 46 (66%) of the 69 QSOs with z>2.5 present in its dataset as unclassified objects. These findings confirm the high efficiency of the QUBRICS selection methods (recall=89%) and provide the completeness estimate for spectroscopically confirmed QSOs (82%), necessary for cosmological studies using QUBRICS data. This work also provides reliable redshifts for 1223 new QSOs (median redshift z=2.1 and magnitude G=17.8), that will help improve the performance of future selections.
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All authors Matteo Porru, Stefano Cristiani, Francesco Guarneri, Giorgio Calderone, Andrea Grazian, Konstantina Boutsia, Andrea Trost, Valentina D'Odorico, Guido Cupani, Catarina M.J. Marques, Francesco Chiti Tegli, Fabio Fontanot

High Energy Astrophysical Phenomena

A clean broad iron line in GS 1354–64 as seen by XRISM

Honghui Liu, Lingda Kong, Oluwashina K. Adegoke et al. (+13 more)

We present a spectroscopic analysis of XRISM and NuSTAR observations of the black hole X-ray binary GS~1354–64 during its 2026 outburst. A total number of 3.5 million photons are collected by the microcalorimeter Resolve on board XRISM, providing an unprecedented high-resolution view of the iron line profile. A clean broad iron line is found in the data, without significant narrow features. Modeling the broad iron line with relativistic reflection from the inner accretion disk suggests a rapidly spinning black hole (a>0.98) in the system. Measurements of the disk inclination angle from the reflection method are model-dependent. This work demonstrates the power of X-ray microcalorimeters in studying the inner accretion flow and constraining black hole parameters.
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All authors Honghui Liu, Lingda Kong, Oluwashina K. Adegoke, Jiachen Jiang, Cosimo Bambi, Andrew C. Fabian, Adam Ingram, Swati Ravi, James F. Steiner, Qingcang Shui, Dominic J. Walton, Yerong Xu, Andrew J. Young, Yuexin Zhang, Zuobin Zhang, Andrea Santangelo

Cosmology and Nongalactic Astrophysics

Empirical signatures of velocity and density cascades in the Local Universe probed by the CosmicFlows4 dataset

Yves Grosdidier and Hélène M. Courtois

Aims: Our aim is to characterise the multiscale statistical properties of the reconstructed velocity and density fields of the nearby Universe, identify possible scaling regimes, quantify intermittency, and assess indications for the transition towards large-scale homogeneity within the range probed by current data. Methods: We analysed the Cosmicflows-4 three-dimensional velocity and density-contrast cubes using absolute structure functions of arbitrary order, $q$. The analysis was performed within a volume extending to $z \lesssim 0.08$ ($\simeq 350~\mathrm{Mpc}$ $h^{-1}$). Structure function scaling exponents $\zeta(q)$ were estimated from configuration-space statistics. Intermittency was characterised using the universal multifractal formalism, and the probability density functions of increments were examined. Results: Two regimes were detected. Small separations are dominated by reconstruction smoothing and show a nearly linear $\zeta(q)$ behaviour. At larger separations, a scaling regime appears with $\zeta_\rho(1)\simeq0.3$ ($D_\rho\approx3.7$) and $\zeta_v(1)\simeq0.4$. The correlation function follows $\xi(r)\sim r^{-1.4}$ over $[45,250]~\mathrm{Mpc}\,h^{-1}$, implying $D_2\simeq1.6$. Non-linear $\zeta(q)$ and Lévy-stable increment probability density functions (PDFs) indicate intermittency and strong non-Gaussianity. The velocity increments show a systematic negative skewness suggestive of a cascade-like asymmetry associated with amplification of negative compressive gradients.
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High Energy Astrophysical Phenomena

Study of UV line and continuum variabilities in the Broadline Seyfert 1 Galaxy ESO 141-G55

Mayukh Pahari, Veda Samhita, Harikumar N. et al. (+2 more)

We present the results from a 3-year-long Ultraviolet monitoring campaign of the broad line Seyfert 1 galaxy ESO 141-G55 using International Ultraviolet Explorer (IUE). By modelling all individual, extinction-corrected UV spectra in 1150-1978 A and 1850-3348 A wavelength range, we have observed a significant variability in both UV continuum and line fluxes. Variabilities due to ionised UV lines like SiIV, CIV and HeII are delayed with respect to the UV continuum by 2.92$^{+0.54}_{-0.61}$, 4.41$^{+0.44}_{-0.54}$, 4.11$^{+0.35}_{-0.81}$ days, respectively. At a distance of $\sim$0.004c, an outer accretion disc can be a possible site for the origin of UV lines.
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All authors Mayukh Pahari, Veda Samhita, Harikumar N., Anurag Baruah, Vivek Shinde

Astrophysics of Galaxies

On the relation between magnetic field strength and gas density in the interstellar medium. II. Density uncertainties and diffuse gas constraints

David Whitworth, Amit Seta, Ralph E. Pudritz et al. (+4 more)

The relationship between magnetic field strength and gas density is essential to understand the interstellar medium and star formation. Zeeman measurements in dense atomic and molecular gas phases have traditionally been used to directly probe magnetic field strengths in the Milky Way. This allowed derivation of a relationship between magnetic field strength $B$ and gas number density $n$. We recently generalized this relation as a two-part power-law with non-zero slopes and a transition density given as $B/B_0 \propto (n/n_0)^{\alpha_1}$ for $n \le n_0$ and $(n/n_0)^{\alpha_2}$ for $n > n_0$. Here, we extend our previous hierarchical Bayesian framework by incorporating a large body of pulsar observations that probe the diffuse interstellar medium and explicitly modelling density uncertainties through a log-density intrinsic scatter $R_n$ applied to all densities. We also account for magnetic field geometry and measurement uncertainties through a magnetic hyperparameter to estimate $B$. This results in a stronger constraint on the diffuse gas part of the $B$–$n$ relation. Our results confirm a non-zero exponent in the diffuse gas and a broad transition density with our best model and data set yielding maximum a posteriori results of $\alpha_1 = 0.20^{+0.01}_{-0.03}$, $\alpha_2 = 0.65^{+0.06}_{-0.07}$, $n_0 = 3330^{+270}_{-3220}\,\text{cm}^{-3}$, and $B_0 = 10.11^{+0.71}_{-5.97}\,\mu\text{G}$.
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All authors David Whitworth, Amit Seta, Ralph E. Pudritz, Mordecai-Mark Mac Low, Juan D. Soler, Aina Palau, Ralf S. Klessen

Astrophysics of Galaxies

Caught in the web: galaxy mergers along cosmic filaments

Carolina Dulcien, Yara L. Jaffe, Jacob P. Crossett et al. (+31 more)

Galaxy clusters grow through the accretion of galaxies from groups, filaments, and other clusters. During this process, galaxies may undergo pre-processing in lower-density environments, where galaxy-galaxy mergers and other interactions can significantly alter their properties prior to cluster infall. We investigate the role of galaxy mergers in the pre-processing of galaxies prior to cluster infall by studying the spatial distribution of mergers across the cosmic web. We use a sample of 43,922 galaxies targeted by the 4MOST CHANCES survey in and around 33 low-redshift clusters (z < 0.07). Using Zoobot, a deep-learning framework trained on Galaxy Zoo data, we identify 698 galaxy mergers. We measure their distances to cosmic web filaments and compare them with those of non-merging galaxies. We find that galaxy mergers are significantly closer to filaments than the non-merging galaxy population, with this trend being strongest beyond the cluster virial radius. This suggests that filaments provide conditions conducive to mergers, possibly moderating relative velocities and enhancing gas availability. Our findings support a scenario in which filaments play a key role in transforming galaxies through pre-processing by promoting mergers before they enter cluster cores where star formation quenches.
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All authors Carolina Dulcien, Yara L. Jaffe, Jacob P. Crossett, Raul Baier-Soto, Hugo Mendez-Hernandez, Christopher P. Haines, Guillermo Cabrera-Vives, Patricio Olivares, P. Vasquez-Bustos, Maria Argudo-Fernandez, Javiera Vivanco, Lawrence Bilton, Clecio R. Bom, Giuseppe D'Ago, Alexis Finoguenov, Ulrike Kuchner, Ciria Lima-Dias, Paola Merluzzi, Antonela Monachesi, Diego Pallero, Nicolas Tejos, Gabriel S. M. Teixeira, Cristobal Sifon, Maiara S. Carvalho, Ricardo Demarco, Eduardo Ibar, Gissel P. Montaguth, Franco Piraino-Cerda, Umberto Rescigno, Vitor Sampaio, Gustavo B. Oliveira Schwarz, Rory Smith, Benedetta Vulcani, Nicola Malavasi

Cosmology and Nongalactic Astrophysics

BICEP/Keck XXI: Constraints on Early-Universe Parity Violation from Multipole-Dependent Birefringence

BICEP/Keck Collaboration: P. A. R. Ade, Zeeshan Ahmed, Mandana Amiri et al. (+93 more)

We present the first constraints on multipole-dependent cosmic birefringence using CMB polarization data from the BK18 dataset, which combines observations from BICEP2, Keck Array, and BICEP3 at frequencies of 95, 150, and 220 GHz. Photon coupling to an axion-like field leads to the rotation of CMB polarization, inducing non-zero EB cross-correlations. We show that a multipole-dependent rotation beta(l) imprints a distinct signature in the polarization spectra that can be constrained. Specifically, we consider an Early Dark Energy (EDE) scenario in which a pseudoscalar field couples to photons through a Chern-Simons interaction, generating a polarization rotation with multipole dependence. We introduce a phenomenological beta(l) as a step function, obtaining constraints on the step function size consistent with zero, with uncertainties less than 0.15 degrees (68% CL). In addition, using multi-frequency EE, BB, and EB cross-spectra, along with robust BICEP/Keck foreground treatment and likelihood framework, we derive constraints on the axion-photon coupling amplitude g for several choices of EDE parameters. For the baseline best-fit value f_{EDE} = 0.087 from the Planck 2018 analysis, we obtain g = 0.11 +/- 0.37 (68% CL), consistent with previous limits.
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All authors BICEP/Keck Collaboration: P. A. R. Ade, Zeeshan Ahmed, Mandana Amiri, Denis Barkats, Ritoban Basu Thakur, Colin A. Bischoff, Dominic Beck, James J. Bock, Hans Boenish, Victor Buza, Brianna Cantrall, James R. Cheshire IV, Jake Connors, James Cornelison, Michael Crumrine, Ari Jozef Cukierman, Edward Denison, Lionel Duband, Michael Echter, Miranda Eiben, Brodi D. Elwood, Sofia Fatigoni, Jeffrey P. Filippini, Antonio Fortes, Min Gao, Christos Giannakopoulos, Neil Goeckner-Wald, David C. Goldfinger, Stephen Gratton, James A. Grayson, Annsley Greathouse, Paul K. Grimes, Grantland Hall, George Halal, Mark Halpern, Emma Hand, Sam A. Harrison, Shawn Henderson, Thuong Hoang, Johannes Hubmayr, Howard Hui, Kent D. Irwin, Jae Hwan Kang, Kirit S. Karkare, Sinan Kefeli, J. M. Kovac, Chao-Lin Kuo, Kekoa Lasko, King Lau, Margaret Lautzenhiser, Amber Lennox, Tongtian Liu, Scott Mackey, Nolan Maher, Koko G. Megerian, Lorenzo Minutolo, Lorenzo Moncelsi, Yuka Nakato, H. T. Nguyen, Roger O'Brient, Scott Paine, Anika Patel, Matthew A. Petroff, Anna R. Polish, Thomas Prouve, Clement Pryke, Carl D. Reintsema, Steffen Richter, Thibault Romand, Maria Salatino, Alessandro Schillaci, Benjamin Schmitt, Robert Schwarz, Chris D. Sheehy, Baibhav Singari, Ahmed Soliman, Tyler St Germaine, Aaron Steiger, Bryan Steinbach, Rashmi Sudiwala, Grant Teply, Keith L. Thompson, Carole Tucker, Anthony D. Turner, Clara Vergès, Abigail G. Vieregg, Albert Wandui, Alexis C. Weber, Justin Willmert, Chin Lin Wong, Wai Ling K. Wu, Hung-I Yang, Cyndia Yu, Lingzhen Zeng, Cheng Zhang, Silvia Zhang

Cosmology and Nongalactic Astrophysics

Signatures of Extended Dark Energy Parametrisations in Structure Formation under Background Constraints

Greco A. Peña, Mario H. Amante, Javier Chagoya et al. (+3 more)

We study structure formation in alternative cosmological models constrained by background observations, including $\Lambda$CDM, wCDM, the Chevallier-Polarski-Linder parametrisation and a flexible Chebyshev expansion of the dark energy equation of state. The models are constrained using baryon acoustic oscillations, cosmic microwave background, cosmic chronometers and strong lensing measurements. Using the best-fitting parameters, we generate cosmology-dependent initial conditions and perform N-body simulations to analyse the matter power spectrum, halo mass function and halo density profiles. Although all models remain broadly consistent with $\Lambda$CDM at the background level, differences in the physical matter density $\Omega_{0m}h^2$ and in the expansion history $H(z)$ lead to distinct growth histories that are amplified by non-linear evolution. We find a clear hierarchy in the power spectrum amplitude and in $\sigma_8$, with the Chebyshev and CPL models exhibiting enhanced small-scale power, earlier halo formation at $z\gtrsim2$ and a migration of excess toward higher masses at late times. The wCDM model displays milder and partially compensating effects driven by its different expansion history. When expressed in terms of the scaled radius $r/R_{200c}$, halo density profiles show a high degree of universality across cosmologies, indicating that internal halo structure is largely governed by the same gravitational dynamics. These results demonstrate that even modest background-level variations in $w(z)$ can translate into coherent non-linear signatures, highlighting the constraining power of large-scale structure observables in extended dark energy models.
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All authors Greco A. Peña, Mario H. Amante, Javier Chagoya, Cristian Barrera-Hinojosa, C. Ortiz, Graeme Candlish

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

Spectral sirens cosmology from binary black holes populations with sharper mass features

Tom Bertheas, Vasco Gennari, Danièle Steer et al. (+1 more)

Spectral-sirens inference enables the extraction of cosmological parameters from gravitational-wave data alone, without electromagnetic counterparts or galaxy catalogs. We introduce new parametric mass functions for the binary black hole population built as linear combination of truncated power-laws that capture significant structure across the mass spectrum. On analysing the latest gravitational-wave transient catalog, GWTC-4.0, we show that power-laws-only population models constrain the Hubble constant to $H_0 = 53.3^{+14.0}_{-10.8} ~\rm km \,s^{-1} \,Mpc^{-1}$ at $68\%$ confidence level. After probing the robustness of the results with respect to several modelling assumptions, we further test alternative cosmological models, establishing competitive constraints on modified gravitational-wave propagation, while bounds on the dark energy equation-of-state parameters remain uninformative. Projecting to the future O5 observing run with larger datasets at higher redshifts, we forecast substantial improvements in $H_0$ and modified propagation parameters. Our results highlight the strong interplay between the black hole mass distribution and inferred cosmology.
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All authors Tom Bertheas, Vasco Gennari, Danièle Steer, Nicola Tamanini

Astrophysics of Galaxies

A differentiable and optimizable 3D model for interpretation of observed spectral data cubes

T. Grassi, J. E. Pineda, S. Spezzano et al. (+6 more)

Molecular spectral cubes of prestellar cores encode the information on the physical and chemical properties of these objects along the line of sight. To retrieve this information, we need an interpretable model that reproduces the observed spectra. We designed a differentiable 3D geometrical model that produces synthetic observations from the parameterized density and velocity fields, and that can be efficiently optimized to reproduce the real data cubes. The model has been applied to p-NH2D and N2D+ spectral cubes in the prestellar core L1544. The optimized model suggests that to reproduce the observed velocity difference between p-NH2D and N2D+ in L1544, an asymmetric structure in density and velocity is necessary.
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All authors T. Grassi, J. E. Pineda, S. Spezzano, D. Arzoumanian, F. Lique, Y. Misugi, E. Redaelli, S. S. Jensen, P. Caselli

Astrophysics of Galaxies

The Binary Populations of Stellar Streams are Set by Cluster Dynamics

Anya Phillips, Charlie Conroy, Jacob Nibauer et al. (+5 more)

We present a suite of direct N-body simulations of low mass ($<10^4~M_{\odot}$) globular cluster streams initialized with observationally-motivated binary demographics in order to understand the effect of in-cluster dynamical processing on the stream binary population. The models are initialized with a range of stellar densities and cluster orbits, and Poisson variation in the number of massive and short-lived stars. Wide binaries are disrupted on short timescales by internal tides and on long timescales by two-body encounters. Tides are most important prior to impulsive mass loss-driven cluster expansion. Close binaries ($P_{\rm orb}<10^2~\rm yr$) are most abundant at the stream center due to cluster mass segregation. The wide binary fraction and the degree of binary segregation in the resulting stream are sensitive to the initial cluster density and massive star fraction. In mock radial velocity surveys of the simulated streams, undetectable binaries have velocity amplitudes of $\sim$$0.5$-$1~\rm km~s^{-1}$, adding $\sim0.1~\rm km\ s^{-1}$ of velocity dispersion to the streams, and are dynamically depleted by $\sim10$-$60\%$ compared to the initial binary population. Custom N-body models of Milky Way streams with binaries will allow a holistic understanding of their dynamical structures in advance of upcoming multi-epoch spectroscopic surveys.
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All authors Anya Phillips, Charlie Conroy, Jacob Nibauer, Long Wang, Vedant Chandra, Ana Bonaca, Jay Strader, Morgan MacLeod

High Energy Astrophysical Phenomena

Enhanced Neutrino Cooling from Parity-Doubled Nucleons in Neutron Star Cooling Simulations

Rodrigo Negreiros, Liam Brodie, Jan Steinheimer et al. (+2 more)

Although restoration of chiral symmetry is predicted by quantum chromodynamics to take place at high baryon density, most modeling of neutron star interiors disregards a chiral phase transition. We model neutron star cores with a parity doublet model, which allows for dynamical chiral symmetry restoration and predicts the appearance of the parity partners of nucleons and hyperons at large densities, as well as deconfined quark matter. We study the thermal evolution of neutron stars, focusing for the first time on the impact of Urca processes involving the parity partners in neutron star cooling simulations. We find that Urca processes for the parity partners of the nucleons significantly affect the thermal evolution of massive stars and allow for improved agreement with observed surface temperature and ages.
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All authors Rodrigo Negreiros, Liam Brodie, Jan Steinheimer, Veronica Dexheimer, Robert D. Pisarski

High Energy Astrophysical Phenomena

Thermalization of Neutrinos in a Neutron Star Merger Simulation

Mark G. Alford, Liam Brodie, Francois Foucart et al. (+1 more)

We study the neutrino distributions that arise in a simulation of a neutron star merger that uses a Monte Carlo (MC) neutrino transport scheme. In a snapshot taken 1 ms after merger, we calculate relevant observables to test when neutrinos behave like a thermalized gas, and when a free-streaming picture is more appropriate. We find that in hot, dense regions where neutrino-matter interactions are frequent, MC neutrino and antineutrino distributions are consistent with thermalized neutrinos. In moderately warm regions, where neither approximation is expected to hold, we find significant departures from the predictions of the thermalized-neutrino approximation, particularly for the (anti)neutrino average opacity and net rate of absorption per baryon, even when average energies appear approximately thermal. At lower temperatures, MC results approach the free-streaming limit. Our results demonstrate that energy-averaged agreement with thermalized-neutrino assumptions does not guarantee accurate weak interaction rates. Non-equilibrium aspects of the neutrino distribution are therefore crucial for neutrino-mediated microphysics such as composition evolution in the early post-merger phase.
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All authors Mark G. Alford, Liam Brodie, Francois Foucart, Alexander Haber

Cosmology and Nongalactic Astrophysics

The Cluster Evolutionary Reference Ensemble at Low-$z$ (CEREAL) Sample of Galaxy Clusters I: X-ray Morphological Properties and Demographics

Laurel White, Michael McDonald, Steven W. Allen et al. (+8 more)

With rapid improvements in the assembly of large samples of galaxy clusters, we are approaching the ability to study clusters at $z\gtrsim2$. Evolutionary studies comparing these distant clusters to the clusters in our local universe depend heavily on the reliability of low-redshift cluster samples, most of which are subject to X-ray selection effects, biasing them to relaxed, cool core clusters. Here, we introduce the Cluster Evolutionary Reference Ensemble At Low-$z$ (CEREAL) sample, composed of Chandra X-ray observations of 169 galaxy clusters that have been selected from the Planck Sunyaev-Zel'dovich catalog. CEREAL has a simple and well-understood selection function, spans an order of magnitude in mass at $z\sim0.15$, and has uniform, high-resolution X-ray follow-up. We present the full sample and provide results based on X-ray surface brightness properties, finding significantly more non-cool core systems than in X-ray-selected samples. We use surface brightness concentration (c$_\mathrm{SB}$) as a proxy for cool core strength and centroid shift ($w$) to measure dynamical state. Over the full sample, we find a cool core (c$_\mathrm{SB} > 0.075$) fraction of $0.39_{-0.04}^{+0.04}$, a strong cool core (c$_\mathrm{SB} > 0.155$) fraction of $0.13_{-0.03}^{+0.03}$, and a dynamically relaxed ($w<0.01$) fraction of $0.42_{-0.04}^{+0.04}$. We find no mass dependence in the fraction of clusters that appear relaxed or have cool cores. We quantify the rarity of X-ray-bright central point sources (L$_\mathrm{nuc,~2-10~keV} > 10^{43}$ erg s$^{-1}$), finding them to be intrinsically rare ($0.7_{-0.5}^{+1.2}$% of massive, low-z clusters) with a notable increase in occurrence rate at the centers of cool cores.
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All authors Laurel White, Michael McDonald, Steven W. Allen, Marshall W. Bautz, Michael Calzadilla, Gordon P. Garmire, Julie Hlavacek-Larrondo, Ralph Kraft, Adam B. Mantz, Taweewat Somboonpanyakul, Alexey Vikhlinin

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Fundamental Limits of Quantum Sensors for Gravitational Wave Detection

Sergio Gaudio

Recent advances in quantum sensing—optical clocks, frequency-dependent squeezing below the standard quantum limit, and quantum magnetometers—raise a natural question: can these technologies detect gravitational waves directly, or enhance existing detectors? We show that the answer is set primarily by the coupling mechanism between wave and sensor. From the tidal Hamiltonian in Fermi normal coordinates we identify three physically distinct mechanisms by which a gravitational wave couples directly to a quantum system, and derive their transducer gains within linearized general relativity and non-relativistic quantum mechanics. Internal atomic coupling yields a transducer gain $G_A = 2.4\times 10^{-20}$, with vanishing first-order energy shifts for all $J=0$ clock states—a $\sim\!10^{35}$ deficit relative to laser interferometry. Center-of-mass (Doppler) coupling reaches strain sensitivities of $\sim\!10^{-18}$, still $10^4$ above LISA requirements. Only light-propagation coupling provides the enormous transducer gain that makes laser and atom interferometry viable. For detectors of this third kind we quantify the quantum enhancement accessible through the noise architecture: LISA's noise budget is predominantly classical, capping the combined enhancement at $\mathcal{E}\approx 1.04$, while ground-based detectors in the shot-noise-dominated regime achieve $\mathcal{E}=1.6$–$2.1$. Atom interferometers exploit the same mechanism to target the 0.01–10~Hz band.
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