Cosmology and Nongalactic Astrophysics
Cosmology from HI galaxy surveys with the SKA
Ainulnabilah Nasirudin, Philip Bull, Ziad Sakr et al. (+8 more)
The 21cm line from neutral hydrogen is expected to be a ubiquitous (albeit faint) tracer of
galaxies in the late Universe. With SKAO-MID, large wide-field surveys of several million HI-containing
galaxies will become feasible, resulting in catalogues of sufficient size to measure large-scale structure observables such as
baryon acoustic oscillations and
redshift-space distortions. While optical
galaxy surveys over comparable areas are generally deeper,
radio surveys of this kind have a number of other advantages, such as broader sampling of the
halo mass function and the possibility of measuring luminosity distances via the Tully-Fisher relation. In this chapter, we provide predictions for the
galaxy number counts versus
redshift that will be achievable with a wide-field HI
galaxy survey on SKAO-MID, along with corresponding forecasts for cosmological observables. Given the substantial uncertainty in the HI mass function with
redshift, we bracket our predictions using a handful of different modelling methods.
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All authors Ainulnabilah Nasirudin, Philip Bull, Ziad Sakr, Joël Mayor, Benedict Bahr-Kalus, Hengxing Pan, Stefano Camera, José Fonseca, Liantsoa F. Randrianjanahary, Gabriella De Lucia, Marta Spinelli
Earth and Planetary Astrophysics
Colour changes of Jupiter's Oval BA through microphysical modelling
Asier Anguiano-Arteaga, Santiago Pérez-Hoyos, Agustín Sánchez-Lavega et al. (+1 more)
Jupiter's Oval BA undergoes recurrent colour changes whose physical origin remains uncertain. Radiative transfer
retrievals indicate that these changes occur in the upper chromophore haze of the
vortex annulus, around and above the 0.2-bar level, and are primarily associated with a decrease in optical depth, with no significant change in particle size or haze altitude. We apply a one-dimensional microphysical model to this haze layer, constrained by the retrieved aerosol properties of the red annulus in 2016 and the whiter annulus in 2020, and use it to reproduce the observed colour-change timescale of approximately 0.5 years. Our results indicate that this transition is best reproduced by changes in tropospheric vertical transport within a subsiding annulus, corresponding to preferred downwelling velocities of order $10^{-4}-10^{-3}$ m s$^{-1}$ at chromophore-bearing pressures. These small vertical velocities may help explain why no clear dynamical signature has yet been identified.
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All authors Asier Anguiano-Arteaga, Santiago Pérez-Hoyos, Agustín Sánchez-Lavega, Patrick G. J. Irwin
Cosmology and Nongalactic Astrophysics
A. Herle, N. E. Chisari, H. Hoekstra et al. (+1 more)
The intrinsic
alignment (IA) of
galaxies is one of the main contaminants to the weak
lensing shear signal. Efforts to model it often assume that the
alignment strength depends only on
halo mass. In this work, we use the 2.8 Gpc box-size run of the $\mathtt{FLAMINGO}$ suite to show that
alignment amplitude, in addition to
halo mass, depends on the formation
redshift of the host
haloes for an LRG-like sample. We show that the assembly histories of
galaxies and
haloes influence the
alignment signal. After correcting for their mass
evolution, we find that
haloes that formed earlier have a higher
alignment amplitude, as do their central
galaxies. We also explore the
redshift evolution of the
alignment signal by fitting the amplitude with a power-law in mass at different snapshots of the simulation. We find that the amplitude of this power-law increases steadily with
redshift, while the slope decreases with
redshift until $z\sim1$ and then flattens. We provide an empirical mass-
redshift intrinsic
alignment model fit on the $\mathtt{FLAMINGO}$ simulation. Furthermore, by tracking central
galaxies across snapshots, we show that the
alignment signal changes with
redshift beyond that associated with the change in mass, and that
galaxies tracked from higher
redshifts have a larger amplitude. Our results indicate that IA modeling in weak
lensing surveys cannot have arbitrarily small prior ranges, and complicate the implementation of HOD-based
alignment models for
gravity-only simulations. They also provide simulation-based guidelines for a
redshift evolution model of IA for use in observational studies.
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All authors A. Herle, N. E. Chisari, H. Hoekstra, D. Neumann
Cosmology and Nongalactic Astrophysics
The age of the Universe from a large sample of the oldest Galactic stars
Indranil Banik, Thenujaya Kudakolawa Kaluarachchige, Stephen Cookson et al. (+1 more)
We estimate the age of the Universe using the Xiang & Rix sample of 247,103 Milky Way
stars with low-resolution spectroscopy from LAMOST DR7 and $Gaia$ eDR3 parallaxes.
Stellar ages were estimated using YY isochrones up to 20 Gyr. We require consistency between YY ages and photometric FLAME ages based only on $Gaia$ data. To remove a population of
stars with unusually low vertical action for their age,
metallicity, and distance, we require old
stars to be metal-poor and $\alpha$-enriched. Our final sample of 146,810
stars within 5 kpc provides consistent
cosmic age estimates using several techniques of increasing rigour. Our main results use an MCMC reconstruction of the latent age distribution, though our iterative reconstruction is very similar. Applying an innovative approach to our MCMC reconstruction and its uncertainties, we find that the oldest
star has an age of $A_\star = 13.80^{+0.20}_{-0.16}$ Gyr. We conservatively estimate a systematic uncertainty of $\pm 0.4$ Gyr due to the choice of quality cuts, isochrone model, and initial helium abundance. Allowing 0.2 Gyr for the first long-lived
stars to form, our inferred $A_\star$ is consistent with the 13.6 Gyr expected in CMB-calibrated $\Lambda$CDM. This agreement casts doubt on solutions to the Hubble tension solely through new physics prior to recombination, which generally imply a
cosmic age of $12.9 \pm 0.2$ Gyr to match low
redshift probes. It is difficult for
stellar modelling uncertainties to reconcile such a low age with our result given the low
metallicities of the oldest
stars in our sample and independent asteroseismic constraints.
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All authors Indranil Banik, Thenujaya Kudakolawa Kaluarachchige, Stephen Cookson, Harry Desmond
Instrumentation and Methods for Astrophysics
A First-Order Assessment of Permanent Magnet Deflection for Space Radiation Protection
Valerio Parisi, Roberto Capuzzo Dolcetta, Fabrizio Frezza et al. (+1 more)
We present a preliminary feasibility assessment of a
magnetic shield designed to protect a space probe from
cosmic radiation via
magnetic deflection using neodymium permanent magnets. This work is grounded in theoretical considerations whose preliminary indications are intended to serve as the basis for future Monte Carlo simulations and laboratory validation. The novelty of our approach lies in the use of a
magnetic shield; its competitiveness with conventional passive absorbing shielding is not investigated here but warrants dedicated future work. The primary objective is to protect a spacecraft from the flux of charged particles emitted by the Sun. To this end, we combine theoretical modeling and numerical simulations, followed by the construction of a prototype for laboratory testing and, potentially, for future experimental validation at the CubeSat scale.
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All authors Valerio Parisi, Roberto Capuzzo Dolcetta, Fabrizio Frezza, Luca Lunati
Astrophysics of Galaxies
Evolution of Chemistry in the envelope of HOt corinoS (ECHOS). III. Sulphur chemistry in the Class 0 objects HH 212 and NGC 1333 IRAS 4A
P. Fernández-Ruiz, A. Fuente, G. Esplugues et al. (+7 more)
Our goal is to find chemical diagnostics to determine the physical conditions in protostellar envelopes and help establish the development of matter during the formation of a low-mass
star, as well as investigating a possible variation of sulphur depletion during the
star formation process at the scale of the cold envelope. With observations with the Yebes-40m and IRAM-30m
telescopes, we estimate column densities of sulphur-bearing species in the Class 0 objects HH212 and NGC1333 IRAS4A. A neural emulator of the chemical code Nautilus is used to constrain the chemical time, density, gas temperature,
cosmic ray ionization rate, and sulphur elemental abundance in the cold envelope of these objects. We compare the resulting abundances of these species with those towards the Class 0 object B335. While sulphur-bearing species containing carbon chains are between 3 and 7 times more abundant in B335 than in the other two objects, sulphur
oxides and nitrogen-bearing species are 3 times more abundant in NGC1333 IRAS4A. Our chemical modelling shows that, while the chemistry of HH212 and NGC1333 IRAS4A is well reproduced considering a gas temperature of 25 K and a sulphur depletion of a factor of 100 in their envelopes, significant differences are found in their average density and
cosmic ray ionization rate. Comparing with similar studies in pre-
stellar and protostellar cores, we derive an increase in the SO/CS and SO$_2$/C$_2$S ratios of about two orders of magnitude and a potential decrease in the HCS$^+$/CS ratio of a factor of 10 in the transition from the pre-
stellar to the Class 0 phase. Sulphur compounds are good evolutionary tracers of the pre- to protostellar phase transition, with oxygen-bearing species being more abundant than those containing carbon in the evolved sources. Nonetheless, sulphur depletion in the cold envelope of Class 0 objects remains similar to that in starless cores.
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All authors P. Fernández-Ruiz, A. Fuente, G. Esplugues, D. Navarro-Almaida, P. Riviére-Marichalar, T. Alonso-Albi, M. Rodríguez-Baras, A. Asensio Ramos, C. Westendorp Plaza, L. Moral-Almansa
Solar and Stellar Astrophysics
Unravelling the nonthermal emissions from the quiet solar corona with the SKA
Surajit Mondal, Divya Oberoi, Rohit Sharma et al. (+4 more)
Investigation of the nonthermal emissions from the quiet
solar corona has been rather limited. This primarily stems from the fact that the emission is expected to be quite weak and very high dynamic range images are required to detect such emissions. Although, the few detections of the nonthermal emissions have all come from the
radio band, the past observations had several issues, the most important being the low image fidelity and lack of simultaneous broadband observation capability. Recent observations have been able to tackle many of these prior difficulties using modern instrumentation, and have produced multiple interesting results. In spite of these improvements, multiple challenges remain. For example, most of the recent investigations were only able to focus on the brightest of these events, due to rather poor spectroscopic snapshot PSF of the instruments. The SKA, with its excellent sensitivity as well as its exquisite spectroscopic snapshot PSF would be a game-changer in this field. It would not only allow us to detect and characterise these emissions in Stokes I, but would also allow us to investigate their polarisation properties as well. The high angular resolution offered by the SKA will allow a unique association of the detected
radio transients with their thermal counterparts. This would enable us to investigate the thermal-nonthermal energy partition even for these rather weak transient emissions, which in turn would allow validation of particle acceleration and
magnetic reconnection theories in a regime vastly different from that done previously. In addition, characterization of the nonthermal emissions of these weak coronal transients may also provide a new probe to understand how energy is transferred from the photosphere and dumped into the corona, and thus serve as a new tool to tackle the coronal heating problem.
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All authors Surajit Mondal, Divya Oberoi, Rohit Sharma, Peijin Zhang, Devojyoti Kansabanik, Xingyao Chen, Eduard Kontar
Solar and Stellar Astrophysics
Constraining the model-based uncertainties of asteroseismic magnetic field measurements in red giants
L. Buchele, L. Bugnet, N. Muntean et al. (+1 more)
Magnetic fields inside red
giants are measured using shifts to the oscillation frequencies. However, in the asymptotic framework, converting a frequency shift into a radial
magnetic field strength requires knowing the global
magnetic sensitivity. This parameter (also called the core structure parameter) must be inferred from
stellar models, introducing a source of uncertainty. We seek to understand how the global
magnetic sensitivity depends on
stellar properties such as mass and
metallicity, and to quantify the model-based uncertainty on
magnetic field measurements. We also explore which
stellar properties are key to finding a precise and accurate estimate of the global
magnetic sensitivity. Using MESA models, we examine how the global
magnetic sensitivity changes with mass,
metallicity, and age. We then create a set of synthetic
stars and test how well we recover the sensitivity parameter. We consider different grid construction approaches and the choice of which observables are used in the fitting process. We find that the global
magnetic sensitivity shows a stronger dependence on mass for higher mass models and a stronger
metallicity dependence for lower
metallicity models. Our approach recovers the sensitivity parameter well, with an uncertainty of 10% when precise
metallicity measurements are used. We apply our method to
stars with existing
magnetic field measurements. In most cases, the dominant source of uncertainty remains observational, although precise modeling can significantly reduce the
magnetic field uncertainty for
stars with exceptional data. With careful fitting, models yield accurate values for the global
magnetic sensitivity. We recommend that future work obtain the global
magnetic sensitivity using both asteroseismic and high-quality spectroscopic data. Under these conditions, we recommend adopting a model-based uncertainty of 10% on the sensitivity parameter.
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All authors L. Buchele, L. Bugnet, N. Muntean, E. Hatt
Earth and Planetary Astrophysics
Unveiling the Mysteries of Lightning: Exploring its fundamental Physical Processes with SKA-LOW
Brian M Hare, Sjoerd Bouma, Stijn Buitink et al. (+15 more)
Lightning is a surprisingly poorly understood phenomena. It consists of a wide variety of complex processes such as initiation, propagation, connection to ground, even emission of high-energy radiation. However, due to the extreme challenges in observing lightning at fast time scales, small spatial scales, and behind obscuring clouds, these processes are not well understood. In the past, interferometers such as the LOFAR
radio telescope have provided unique insight and discoveries into the physics of lightning. The new SKA-LOW being built in western Australia will provide unrivaled spectral bandwidth and sensitivity, which will be combined with high resolution resulting from large
antenna baselines. We will use SKA-LOW to observe lightning in order to explore its fundamental
plasma physics, such as how it initiates and propagates. SKA's high bandwidth will allow us to test how lightning emits VHF radiation, giving tremendous insight into precisely how the
plasma behaves. SKA's sensitivity will allow us to explore extremely faint lightning processes, such as the very first
radio emission from a lightning flash. Here, we detail the lightning physics that can be explored with SKA, as well as the observation strategy needed explore such physics.
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All authors Brian M Hare, Sjoerd Bouma, Stijn Buitink, Arthur Corstanje, Steve Cummer, Joseph Dwyer, Vital De Henau, Tim Huege, Philipp Laub, Ningyu Liu, Marten A.A. Lourens, Katie Mulrey, Anna Nelles, Olaf Scholten, Chris Sterpka, Karen Terveer, Paulina Ťureková, Keito Watanabe
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Hidden quantum-informatic symmetries of quasi-de Sitter backgrounds
Suddhasattwa Brahma, Jaime Calderon-Figueroa, Xiancong Luo et al. (+1 more)
We investigate how degeneracies in quasi-de Sitter backgrounds, in the sense of Wands' duality, are reflected in real-space
quantum correlations of
primordial perturbations. Using the continuous-variable Gaussian formalism for coarse-grained scalar fluctuations, we construct the covariance
matrix of a pair of spatially localized modes in inflationary spacetime, and extract the
symplectic invariants of the system. For a generic Wands-dual pair of backgrounds, we find that while the individual entries of the covariance
matrix are highly background-dependent, the
symplectic eigenvalues – and hence the
entanglement entropy, mutual information,
quantum discord and log-negativity – all coincide for the two dual realizations. Our results unveil a new ”
quantum-informatic
symmetry” of the de Sitter
vacuum, according to which local linear
entanglement witnesses constructed from coarse-grained fields cannot distinguish between Wands-dual inflationary histories, even though their background trajectories differ. We show that the special nature of the Wands-duality
symmetry (of being local, scale-independent canonical transformations) is at the heart of this duality.
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All authors Suddhasattwa Brahma, Jaime Calderon-Figueroa, Xiancong Luo, Vincent Vennin
Cosmology and Nongalactic Astrophysics
Correcting the hydrostatic mass for non-thermal gas motions: a comparison of two approaches
Théo Lebeau, Nabila Aghanim, Jenny Sorce et al. (+1 more)
An accurate estimation of the mass of
galaxy clusters is key to precisely and unbiasedly constraining cosmological parameters through their number count. The hydrostatic mass, estimated from the properties of the intracluster medium (ICM) assuming hydrostatic
equilibrium, sphericity, and thermal-only pressure, is known to be biased by 10 to 20%, most likely due to non-thermal pressure support from gas motions. Two corrections have been proposed: i) replacing the thermal pressure by the total pressure $P_\mathrm{tot}=P_\mathrm{th}+P_\mathrm{nth}$, or ii) adding effective mass terms derived from the gas momentum equation. We compare these approaches using a numerical replica of the Virgo cluster as a case study, estimating corrected masses from 3D radial profiles in different cluster regions and from projected sightline velocities mimicking XRISM observations. We find that the two methods do not yield the same results in 3D: the non-thermal pressure correction increases the mass by a growing amount with radius (from a few per cent in the core to $\sim$40% at the virial radius), whereas the effective mass terms provide a correction that varies less with radius. When estimated from projections, the two methods agree to within a few per cent for a given sightline, but the non-thermal pressure fraction is underestimated by about a factor of 2 compared to the 3D case. Furthermore, projection effects can change the inferred non-thermal pressure fraction by up to a factor of 2, particularly when the sightline is aligned with
cosmic filaments.
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All authors Théo Lebeau, Nabila Aghanim, Jenny Sorce, Stefano Ettori
High Energy Astrophysical Phenomena
Distinct spin properties and astrophysical origin of low mass binary black holes in gravitational wave data
Elizabeth Flanagan, Jakob Stegmann, Isobel Romero-Shaw et al. (+3 more)
We analyze the effective-
spin distribution of binary black hole mergers in GWTC-5.0 as a function of primary black hole mass using hierarchical
Bayesian inference. We model the population as a mixture of two
spin components separated by a transition mass scale inferred directly from the data. We find strong evidence for a transition at $\tilde{m} = 15.2^{+4.3}_{-3.6}\, M_\odot$. Mock-catalog analyses show that such a transition is unlikely to arise from finite-sample fluctuations of a mass-independent $\chi_{\rm eff}$ population and the posterior predictive distributions of $\chi_{\rm eff}$ inferred below and above the transition are clearly distinct. Below the transition mass, the effective-
spin distribution is narrow, peaks at a small positive value $\chi_{\rm eff}>0$, but also shows significant support for negative $\chi_{\rm eff}$. Above the transition, the distribution is broader and its peak shifts to values consistent with $\chi_{\rm eff}\simeq0$, making its support at both positive and negative $\chi_{\rm eff}$ roughly similar. These findings suggest that the dominant merger population concentrated around $10\,M_{\odot}$ is statistically distinct from the rest and that it arises from a different formation channel. We show that this low-mass population is broadly consistent with formation from massive
stellar multiples in the field: it may either arise from isolated binary
star evolution but only if black hole natal kicks below $\tilde{m}$ are generally very large ($\gtrsim100\,\rm km/s$) or be caused by the dynamical
evolution of hierarchical triples. In contrast, isolated binary
evolution with standard fallback kick models cannot reproduce the support for negative $\chi_{\rm eff}$.
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All authors Elizabeth Flanagan, Jakob Stegmann, Isobel Romero-Shaw, Thomas Callister, Aleksandra Olejak, Fabio Antonini
Earth and Planetary Astrophysics
Relativistic Time Scales and Transformations in the Solar System
Hong-Bo Jin, Jinsong Ping, Min Liu et al. (+1 more)
Each
solar-system observable is characterised by celestial reference system (CRS) coordinate time, proper time on its world line, and the transformation between them. Ephemerides and Deep Space Network (DSN) tracking use the International Astronomical Union (IAU) barycentric and body-centric hierarchy, now extended to cislunar and Mars work. The IERS Conventions, Moyer radiometric models, and recent lunar-time papers distribute metric, scale, and tracking formulae across separate manuals. Merged Chang'e- or Tianwen-class data can acquire microsecond-level range and Doppler biases unless proper time $\tau$ is mapped consistently to barycentric and body-centric coordinate times. We present a unified 1PN documentation chain: tabulated harmonic Christoffel symbols through $\mathcal{O}(c^{-4})$, the barycentric-geocentric-terrestrial coordinate-time sequence,
Fermi normal coordinates, null-geodesic observables, and a 1PN two-way range-rate expansion, applied in parallel to Mars (MCRS/MCG) and lunar (LCRS/TCL) body-centric systems. The chain yields a Mars areoid-geoid metric clock-rate difference of $\sim$48~$\mu$s\,day$^{-1}$ and lunar selenoid-geoid rates of $\sim$57.4-58.7~$\mu$s\,day$^{-1}$ consistent with published nested coefficients. Mars-range Shapiro-rate terms reach $10^{-12}$-$10^{-13}$. Multi-CRS consistency relies on documented transformation chains rather than a single master clock.
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All authors Hong-Bo Jin, Jinsong Ping, Min Liu, Mingyuan Wang
Instrumentation and Methods for Astrophysics
Open Science in Astrophysics: Citation Benefits of Open Code, Open Data, and Open Access
Parth Joshi and Rupert Croft
We analyze the relationship between open-accessibility in data, code, and paper text in astrophysics using a sample of 53,194 peer reviewed papers published between January 2021 and April 2025, drawn from NASA's Astrophysics Data System (ADS). We measure eleven quantities: open accessibility of text, open-code status, open-data status, number of grants received, code size, programming
language, data repository size, citation count, number of authors, paper length, and publication date. We break down citation advantages based on six astrophysical sub-fields:
Solar System,
Planet,
Stellar, ISM, High Energy, and
Galaxies+Cosmology, determined by keywords. This is accomplished by tuning a multivariate least-squares regression model with alongside partial correlations and non-parametric tests to isolate the contribution of each facet of openness. After controlling for the aforementioned quantities, we find significant citation advantages associated with all three forms of openness: open data (+32%, p < 10^-24), open access (+26%, p < 10^-67), and open code (+16%, p = 0.003). The open-data citation advantage is present in all six sub-fields, and especially in
Galaxies+Cosmology and ISM, which have the strongest cultures of sharing simulation outputs and observational data products. Open-code and open-data sharing rates are highest in
Galaxies+Cosmology and HEA (~0.9% and ~2.9%), reflecting their more developed community data infrastructure, and lowest in
Solar System and ISM, where data is distributed on platforms not taken into account by this study. Our findings support the long held notion that public access comes with concrete personal incentives for authors in terms of citations.
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Solar and Stellar Astrophysics
SPHEREx 0.75 to 5 $\mu$m Spectra for a Sequence of Nearby Brown Dwarfs
Zafar Rustamkulov, J. Kirkpatrick, Rachel Akeson et al. (+21 more)
The SPHEREx all-sky survey has now measured the R$\sim$40-100 infrared spectra of thousands of nearby brown
dwarfs in the chemically rich 0.75-5 $\mu$m range. The survey's wide spectral coverage and high S/N permits flux measurements that capture several broadband molecular absorption features, and upwards of 80$\%$ of the total bolometric luminosity of most brown
dwarfs. Atmospheric models are known to yield systematic disagreements in the inferred temperatures and radii of brown
dwarfs, necessitating benchmarking against observations. In this work, we present SPHEREx spectra across a broad sequence of 37 nearby field brown
dwarfs, ranging from L0 to Y4 ($\sim$2500-250 K) and compare them to theoretical expectations. We additionally compile spectra for separate low-
gravity and low-
metallicity objects, and show how they trend with constant spectral type. We fit the measured spectra to the well-known forward model grids Sonora Diamondback, Elf Owl, BT-Settl, ATMO2020 and ATMO2020++ and compare their goodness-of-fit as a function of wavelength, spectral type, and treatment of clouds and chemistry. We find that the models continue to struggle to simultaneously fit the J/H/K peaks and the 4 $\mu$m opacity window, especially in L/T transition objects. The largest deviations appear around the chemistry-sensitive CO$_2$ and CO features. Despite these offsets, the models broadly capture their trends across the L/T transition, with the observed sample of field
dwarfs strongly preferring the weak vertical mixing ($k_\mathrm{zz}$ = 10$^4$ cm$^2$s$^{-1}$) Elf Owl models over strong mixing. The spectra shown here along with future SPHEREx data will help guide improvements to models.
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All authors Zafar Rustamkulov, J. Kirkpatrick, Rachel Akeson, Michael W Werner, Matthew Ashby, Tzu-Ching Chang, Shuang-Shuang Chen, Asantha Cooray, Brendan Crill, Olivier Dore, C. Dowell, Andreas Faisst, Howard Hui, Woong-Seob Jeong, Miju Kang, Phil Korngut, Carey Lisse, Daniel Masters, Gary Melnick, Chi Nguyen, Roberta Paladini, Volker Tolls, Yujin Yang, Michael Zemcov
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Finite modular Coleman-Weinberg inflation
Yoshihiko Abe, Komei Goto, Tetsutaro Higaki et al. (+2 more)
We propose a modular symmetric inflationary model based on a Coleman–Weinberg potential generated by integrating out heavy vector-like
quarks that couple to the complex modulus field $\tau$ through modular forms. In this framework, the imaginary part of modulus $\tau$ plays the role of the inflaton, while the real part is identified with a heavy
axion. We show that the model successfully explains the current cosmological observations. We further discuss reheating through modulus-dependent gauge kinetic functions and the cosmology of the
axion. The
axion oscillation dominates over the Universe after the reheating via inflaton decay, and then it decays before Big Bang Nucleosynthesis in the viable parameter region. The
quantum fluctuation of the
axion can be of order $\mathcal{O}(1)\% $ of that of the inflaton, which would induce isocurvature perturbations that may be detectable in future observations.
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All authors Yoshihiko Abe, Komei Goto, Tetsutaro Higaki, Junichiro Kawamura, Tatsuo Kobayashi
High Energy Astrophysical Phenomena
FRB20250613A: a remarkable repeating FRB with apparent millisecond-timescale scattering variations
T. Dial, A. T. Deller, Alexa C. Gordon et al. (+8 more)
FRB20250613A is a repeating FRB discovered by the Australian SKA Pathfinder and localised to a low-
metallicity dwarf galaxy at a
redshift of $z = 0.0987 \pm 0.0001$. FRB 20250613A exhibits a plethora of exotic features that likely overlay the imprint of the circum-burst environment on some intrinsic features of the source. Here we perform a comprehensive analysis of bursts detected by ASKAP, MeerKAT, and the Murriyang Parkes
radio telescopes. Bursts during the MeerKAT epoch show a large apparent variance in scattering on timescales of minutes to hours. Polarimetric analysis of the full sample shows spectral depolarisation with variability on timescales of days and changes in rotation measure of $\sim$ 300 rad m$^{-2}$ over days to months. This suggests a highly turbulent magneto-ionised environment. We find significant preference for separations of $\sim$6.8$\pm$0.8 ms in multi-component bursts that we suggest is likely intrinsic to the burst emission mechanism. Finally, we find that a subset of bursts exhibit variations in these propagation effects on burst components separated by just milliseconds, that are difficult to explain by changing sightlines, but plausibly due to non-linear
plasma effects in the circum-burst environment caused by the high field strength of the FRB emission. These properties, which demand a nearby turbulent screen of material, are all consistent with the FRB progenitor being embedded in the dense
stellar wind of a Be
star binary companion, objects which are relatively plentiful in low-mass and low-
metallicity galaxies like the FRB20250613A host.
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All authors T. Dial, A. T. Deller, Alexa C. Gordon, P. A. Uttarkar, R. M. Shannon, Ziteng Wang, M. Caleb, Wen-fai Fong, Marcin Glowacki, Kelly Gourdji, Joscha N. Jahns-Schindler
Astrophysics of Galaxies
Dissecting the 3D chemo-dynamical structures of NGC~1381: A galaxy hosting an ancient slow bar with an accretion-related bulge and thick disc
Yunpeng Jin, Ling Zhu, Shude Mao et al. (+4 more)
We applied the barred population-orbit superposition method developed in our 2025 papers to construct 3D chemo-dynamical models for the barred S0
galaxy NGC~1381 in the Fornax cluster. Based on the
stellar orbits in the models, we decomposed NGC~1381 into six components: (1) a dynamically warm
nuclear disc with $f_{\rm nucl}\sim5\%$; (2) a rigidly rotating, BP/X-shaped bar with $f_{\rm bar}\sim30\%$; (3) a dynamically hot, spheroidal bulge with $f_{\rm bulge}\sim17\%$; (4) a dynamically cold thin disc with $f_{\rm thin}\sim28\%$; (5) a vertically extended thick disc with $f_{\rm thick}\sim16\%$; and (6) a dynamically hot, spatially diffuse
stellar halo with $f_{\rm halo}\sim5\%$. The
nuclear disc, bar, and thin disc are metal-rich ($[Z/\rm H]\gtrsim0$), $\alpha$-poor ($\rm[Mg/Fe]\lesssim0.2$), and old ($\sim13\rm\,Gyr$), corresponding to in situ formation in the early Universe. The bulge, thick disc, and
stellar halo are metal-poor ($[Z/\rm H]\lesssim0$), $\alpha$-rich ($\rm[Mg/Fe]\gtrsim0.2$), and younger than or comparable in age to the in situ components, suggesting ex situ formation via minor mergers. Further analysis of
stellar population gradients reveals that the thick disc and
stellar halo, with their flat
metallicity and [Mg/Fe] gradients, are likely dominated by a similar ex situ population. In contrast, the bulge exhibits a negative
metallicity gradient ($\nabla[Z/\rm H]_{bulge}<0$), which might originate from either predominantly ex situ
stars or a mixture of in situ and ex situ
stars; its ex situ fraction cannot be quantified with the current data. Our modelling also reveals a slow bar ($\mathcal{R}=2.40_{-0.27}^{+0.54}$), with a bar pattern speed of $\rm\Omega_p=34_{-7}^{+4}\,km\,s^{-1}\,kpc^{-1}$, a bar length of $R_{\rm bar}=2.24_{-0.22}^{+0.43}\rm\,kpc$, and a corotation radius of $R_{\rm CR}=5.38_{-0.28}^{+1.59}\rm\,kpc$, consistent with its ancient formation time.
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All authors Yunpeng Jin, Ling Zhu, Shude Mao, Marie Martig, Francesca Pinna, Glenn van de Ven, Yuchen Ding
Solar and Stellar Astrophysics
Optimization Algorithm for Determining the Source Surface Radius Based on Parker Solar Probe in situ Measurements from Encounters 1 to 19
Shiouhe Wang, Fang Shen, Yi Yang et al. (+2 more)
The Potential Field Source Surface (PFSS) extrapolation is a method for estimating the large scale coronal
magnetic field from photospheric magnetograms. The source surface serves as the outer boundary of its solution domain, and is typically a spherical surface. An appropriate source surface radius ($R_{ss}$) enables more accurate identification of the coronal
magnetic field
topology and estimation of the open flux, thereby potentially enhancing the accuracy of space weather modeling. We prove the well-posedness of the PFSS forward problem and establish the existence and uniqueness of the optimal source surface by combining compactness of the admissible set with continuity of the objective functional. The objective functional is the mean squared error (MSE) between PFSS extrapolation and Parker
Solar Probe (PSP) radial
magnetic field measurements after Parker spiral backmapping and radial scaling for Encounters 1-19. The optimization
algorithm is validated with an analytical solution, and Advanced Composition Explorer (ACE) in situ measurements are used as an independent cross-validation
dataset. Additional evaluation metrics and Pareto analysis are used to identify the dominant metrics between open flux and polarity prediction accuracy. Our results show that the optimal $R_{ss}$ derived from the
algorithm generally increase from
solar minimum into the ascending phase of
solar cycle 25. The optimized solution improves open flux agreement while preserving or improving polarity prediction accuracy relative to $2.5R_{s}$. The Pareto frontiers show a transition for dominant metrics from open flux during
solar minimum to polarity prediction accuracy during the ascending phase.
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All authors Shiouhe Wang, Fang Shen, Yi Yang, Xueshang Feng, Jiansen He
High Energy Astrophysical Phenomena
Mapping the Dense Circumstellar Environments of SNe Ibn, SNe Icn, and Fast Blue Optical Transients
Kang-Rui Ni, Yu-Hao Zhang, Liang-Duan Liu et al. (+2 more)
SNe Ibn and SNe Icn are stripped-envelope explosions whose optical emission is commonly linked to interaction with H-poor circumstellar material (CSM), whereas fast blue optical transients (FBOTs) form an observational class of rapidly evolving, blue, and luminous events with diverse proposed power sources. We present a uniform comparison of these transients to test whether they are separated in optical light-curve and fitted physical parameter space. We compile multiband optical light curves of 25 SNe Ibn, SNe Icn, and FBOTs, measure same-band observables with Gaussian-process reconstructions, and model the data with the unified TransFit-CSM framework. In the observed (g)-band peak-luminosity–rise-time and decline–rise-time planes, the three classes are not cleanly separated: FBOTs preferentially occupy the luminous and rapidly evolving end of the distribution, but show limited overlap with part of the Ibn/Icn population. Their extinction-corrected peak colors span a broadly overlapping blue region, with FBOTs extending to bluer colors. Unified CSM-interaction fits, including shock heating and an effective inner heating component, yield overlapping CSM and ejecta parameter distributions. These results indicate that the optical light curves of SNe Ibn, SNe Icn, and at least some FBOTs can be compared within a common dense-CSM interaction framework, while the most extreme FBOTs may still require additional power sources or non-thermal components.
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All authors Kang-Rui Ni, Yu-Hao Zhang, Liang-Duan Liu, Yun-Wei Yu, Ji-an Jiang
Astrophysics of Galaxies
Optically Selected Superthin Galaxies Remain Thin in the Near-infrared
Jianhong Hu, Cheng Li and Dandan Xu
We investigate whether
galaxies identified as superthin in optical images remain superthin in the near-infrared (NIR), and how their extreme disk morphology is related to environment. From a nearby volume-limited sample, we select 210 superthin
galaxies using two-dimensional bulge/disk decomposition of SDSS $r$-band images, requiring the disk component to have a minor-to-major axis ratio $b/a<1/9$. We measure disk shapes from SDSS $griz$ to UKIDSS $JHK$ bands. Both the major- and minor-axis scales decrease from the optical to the NIR, reaching $\sim0.6$ of their $r$-band values in the $K$ band, but the disk axis ratio remains nearly unchanged. Thus, optically selected superthin
galaxies remain superthin in the NIR, suggesting that any NIR-dominant thick component, if present, is not prominent enough to alter the fitted disk shape. Reanalysis of our sample and a previous superthin sample shows that earlier reported NIR thickening is mainly due to a magnitude- and band-dependent bias in one-dimensional fitting. We further compare their environments with matched control samples using projected cross-correlations, reconstructed local overdensities, and large-scale-structure classifications. Superthin
galaxies show lower clustering on $\sim0.1$–$1\,h^{-1}\,\mathrm{Mpc}$ scales and lower overdensities at $1\,h^{-1}\,\mathrm{Mpc}$, but similar large-scale clustering and no clear residual dependence on large-scale-structure type. These results are consistent with a higher central-
galaxy fraction and lower satellite fraction in the superthin sample, while the similar large-scale clustering points to comparable typical
halo masses relative to the controls. This
halo-occupation interpretation is qualitatively consistent with simulation-based scenarios in which high host-
halo spin helps build extended thin disks, although the present data do not directly measure
halo spin.
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High Energy Astrophysical Phenomena
Heavy element dust explains the late-time spectra of kilonovae
Nanae Domoto, Kenta Hotokezaka and Daniel Kasen
Neutron star mergers are a leading site of $r$-process, producing radioactively powered optical and infrared transients known as kilonovae. Observations of the kilonovae AT2017gfo, associated with the gravitational-wave event GW170817, and AT2023vfi, associated with GRB 230307A, have enabled measurements of the mass of ejected $r$-process material and the identification of heavy elements in the ejecta. However, late-time observations reveal strong infrared emission with temperature below 1000 K, which is difficult to explain by atomic absorption and emission processes alone. In this paper, we show that kilonova ejecta provide conditions favorable for the formation of
dust grains composed of refractory $r$-process elements including Zr, W, and Os. We calculate the kinetic formation of
dust grains using reaction rate coefficients of W as a proxy, finding that
dust forms efficiently, particularly in slow ejecta. This stands in contrast to a previous study that relied on a classical nucleation framework. By performing radiative transfer simulations that incorporate
dust formation, we demonstrate that $r$-process
dust naturally explains the observed late-time infrared emission. The formation and abundance of $r$-process
dust are highly sensitive to the ejecta mass, composition, and expansion velocity. Infrared emission from $r$-process
dust can therefore serve a new probe of heavy-element production in
neutron star mergers.
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Solar and Stellar Astrophysics
White Dwarf Classification of DESI DR1 Spectra1
Larissa L. Amorim, Weligton.N. Costa Junior, S. O. Kepler et al. (+3 more)
We present a new catalog of spectroscopically confirmed white
dwarfs from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. We visually classified 44,417 white
dwarf spectra and derived atmospheric parameters for 29,072 DA white
dwarfs through spectroscopic model fitting. The resulting mass distribution is non-Gaussian, with a mean mass of $0.677\,M_\odot$, consistent with previous studies. We identify 547
magnetic white
dwarfs by detecting Zeeman splitting, including 84 new discoveries, and estimate their
magnetic field strengths using off-centered, inclined dipole models when possible. We compare our
magnetic field determinations with previous measurements and find overall good agreement. Finally, we investigate the relation between
stellar properties and magnetism, finding that
magnetic white
dwarfs are systematically more massive than the general white
dwarf population and that intermediate-strength
magnetic fields are already present in
stars that have not yet entered the crystallization phase. This result suggests that crystallization is unlikely to be the sole mechanism responsible for the origin of
magnetic fields in white
dwarfs.
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All authors Larissa L. Amorim, Weligton.N. Costa Junior, S. O. Kepler, Joao Gabriel Leite Medeiros, Detlev Koester, Alejandra D. Romero
Earth and Planetary Astrophysics · Cross-listed from physics.space-ph
VLBI Tracking of the JUICE Mission: Two Years of Cruise Phase Operations and Performance Analysis
Oliver James White, Guifre Molera Calves, Jasper Edwards et al. (+2 more)
The JUpiter ICy moons Explorer (JUICE) mission, launched by the European Space Agency (ESA) in April 2023, represents one of the most ambitious deep space exploration endeavours targeting Jupiter's icy moons. This paper presents results from the Very Long Baseline Interferometry (VLBI)
radio telescope tracking conducted by the University of Tasmania during the first two years of JUICE's cruise phase operations. We have conducted over 100 tracking sessions capturing the spacecraft across different orbital regimes as JUICE progresses through its complex cruise trajectory towards Jupiter. Our analysis focuses on three key areas: Doppler residual characterisation, mission performance indicator extraction, and
solar wind scintillation pattern analysis (including space weather
forecasting). UTAS measurements demonstrate the enhanced capabilities that VLBI networks provide for deep space mission support, particularly for precision orbit determination and spacecraft health diagnosis. The results showcase the UTAS VLBI array as a valuable complement to traditional tracking infrastructure, offering Southern Hemisphere coverage and enhanced
geometric diversity for deep space missions.
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All authors Oliver James White, Guifre Molera Calves, Jasper Edwards, Giuseppe Cimo, Dominic Dirkx
Astrophysics of Galaxies
Exploring the synergies of $[\mathrm{O\,II}]\lambda 3727$ with MUSE spectroscopy in PHANGS H II regions
Eric Habjan, Kathryn Kreckel, Christopher Faesi et al. (+16 more)
Spatially resolved maps of gas-phase
metallicity provide key constraints on the chemical enrichment and mixing processes that drive
galaxy evolution, but measurements based only on strong lines remain highly uncertain and dependent on emission-line coverage. In this work, we present a joint analysis of SITELLE observations, covering the $[O II]\lambda\lambda3726,3729$ doublet, with PHANGS-MUSE spectroscopy covering 4800-9300 Angstroms, including $H\beta$, $[O III]\lambda4959,5007$, $[N II]\lambda6584$, $H\alpha$, $[S II]\lambda\lambda6716,6731$, and $[S III]\lambda9069$, within five nearby spiral
galaxies. By combining these data, we construct a homogeneous catalog of emission-line fluxes for 604 ionized nebulae, 556 of which are classified as H II regions. This enables a comparison of eight widely used strong-line
metallicity calibrations, five new strong-line calibrations, and an investigation of ionization-parameter diagnostics. We recover known systematic offsets among calibrations, but also find that many exhibit very low scatter, less than 0.03-0.04 dex, in radial
metallicity gradients. We find that $[S III]/[S II]$ exhibits minimal secondary dependence on
metallicity or extinction, suggesting that it may be a more robust tracer of ionization parameter than $[O III]/[O II]$. No significant outliers are identified in O/H or N/O within the sampled regions, indicating internally consistent abundance trends across the inner disks probed by our data. We provide a publicly available catalog of all measured emission-line fluxes, designed to support future investigations, including temperature modeling and strong-line abundance calibrations.
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All authors Eric Habjan, Kathryn Kreckel, Christopher Faesi, Francesco Belfiore, Brent Groves, J. Eduardo Méndez-Delgado, Ryan J. Vaught, Laurie Rousseau-Nepton, Fabian Scheuermann, F. Fabián Rosales-Ortega, Hsi-An Pan, Daniel A. Dale, Thomas G. Williams, Ralf S. Klessen, Oleg V. Egorov, Timo Kravtsov, Amirnezam Amiri, Kathryn Grasha, Eric Emsellem
High Energy Astrophysical Phenomena
An equal mass ratio supermassive binary black holes in Q J0158-4325 with periodic microlensing signature?
Changshuo Yan, Youjun Lu, Junqiang Ge et al. (+1 more)
This study aims to test whether a supermassive binary black hole (SMBBH) system with a triple-disk
accretion structure can explain the observed $\sim$173-day periodic microlensing variations and spectral energy distribution (SED) of the gravitationally lensed
quasar Q J0158-4325. We construct a triple-disk model for the SMBBH system, incorporating realistic
accretion disk structures, orbital motion, and microlensing effects. The model is used to simulate optical and X-ray microlensing light curves and SEDs, which are compared with long-term optical monitoring, X-ray observations, and UV-optical spectra from HST and XSHOOTER.
Bayesian analysis and MCMC fitting are applied to constrain model parameters. The model successfully reproduces the periodic microlensing variations. Combined light curve and SED fitting favor a high mass ratio ($q>0.5$) SMBBH system with total mass $\sim 10^{9.5}M_\odot$, and nearly equal-mass binaries ($q\sim1$) provides the best agreement with both the optical/UV spectrum and the microlensing signal. This model predicts larger X-ray microlensing amplitudes than in the optical, but, the available X-ray observations lack the precision needed to place strong constraints. We emphasize the need for future high-cadence monitoring to resolve remaining uncertainties. This study demonstrates the effectiveness of combining multi-wavelength microlensing signatures with spectral modeling to provide robust constraints on SMBBH systems, with the developed framework applicable to other lensed
quasars for identifying and characterizing candidate SMBBHs.
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All authors Changshuo Yan, Youjun Lu, Junqiang Ge, Erlin Qiao
High Energy Astrophysical Phenomena
Three-Dimensional Simulations of Type Ia Supernova Remnants I: Effects of a Main-Sequence Companion Star
Jingxiao Luo, Gilles Ferrand, Zhengwei Liu et al. (+2 more)
Type Ia
supernovae (SNe Ia) serve as one of
cosmic standard candles, but their exact progenitor channel is still an open question. SNe Ia commonly come from binary
star evolution. Therefore, one of the major differences among the proposed progenitor channels is whether there is a more-or-less intact companion
star remaining at the time of explosion, which causes the SN ejecta to be more asymmetrical. As the SN ejecta evolved into
supernovae remnants (SNR), the imprint formed by the companion interaction may affect the morphology of the SNR. In addition, the progenitor systems may have experienced different mass transfer histories and therefore led to formation of different circumstellar material (CSM) environments, which may also affect the early
evolution of SNR. In this study, we use GADGET and RAMSES codes to simulate these physical effects and follow the
evolution into early-phases of SNRs. In our simulations, we consider different ejecta models and track the element distribution. We compare our simulation with actual observations and conclude that despite some SNRs having morphology resemblance to our simulation results, their highly asymmetric expansion rates are hard to explain by interaction between SN ejecta and a companion
star alone.
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All authors Jingxiao Luo, Gilles Ferrand, Zhengwei Liu, Xuefei Chen, Zhanwen Han
High Energy Astrophysical Phenomena
Multiwavelength periodic microlensing signatures of macrolensed supermassive binary black holes
Changshuo Yan and Youjun Lu
The microlensing of lensed
quasars presents a promising avenue for understanding the structure of
accretion disks around supermassive binary black holes (SMBBHs). We investigated the microlensing signatures in multiband (optical, UV, and X-ray) light curves of active SMBBH systems, focusing on how these signatures depend on the mass ratio, separation, and
accretion rate. We analyzed the periodic fluctuations in microlensing light curves induced by the orbital motion of SMBBHs. We examined the relation between the mass ratio and the period of variations in light curves across optical, UV, and X-ray bands. We find that the periodic fluctuations in the light curves depend on the mass ratio of the black holes: for nearly equal masses, variations occur at half the orbital period, whereas for low mass ratios, the period corresponds to the orbital period influenced by the secondary mini-disk. Furthermore, all optical, UV, and X-ray light curves exhibit the same period and phase, but the amplitude of variation is greater in the UV and X-ray bands than in the optical bands. These light curves provide insights into the motion and radiation regions of the disks through wavelength-dependent periodic variations, although they yield limited constraints on the system's black hole mass or Eddington ratio, which can instead be derived from the spectral energy distribution (SED). Integrating microlensing data with SED observations is crucial for accurately constraining the parameters of SMBBH systems.
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Cosmology and Nongalactic Astrophysics
Variability in Supermassive Black-Hole Accretion Rates in Fuzzy Dark Matter Cores due to Black-Hole Wandering
Eric Ludwig, Philip Mocz and Victor Robles
Soliton cores in fuzzy dark matter (FDM) deepen
nuclear potentials and have been proposed to strongly boost Bondi
accretion, potentially aiding rapid black-hole growth at high
redshift. We test this in live Schrodinger-Poisson FDM cores coupled to isothermal gas, evolving a moving black hole that grows via a strictly mass-conserving sink. We measure boosts relative to the initial mean-density Bondi rate. Low-mass seeds, with initial black-hole masses less than about 10^6
solar masses, do not sustain large boosts: black-hole wandering and
soliton sloshing drive bursty
accretion, with dense gas only intermittently present near the black hole. Intermediate seeds, with initial black-hole masses around 10^7
solar masses, produce the most durable enhancement, reaching boosts of order 100 for sound speed cs = 60 km/s, while hotter gas approaches near-background Bondi rates. High-mass seeds, with initial black-hole masses around 10^8
solar masses, quickly exhaust the sink-scale reservoir and become supply-limited, suppressing long-lived growth despite the deepened potential. In general, central-potential deepening, for example by a
soliton halo, does not guarantee long-lived fueling: sustained boosts emerge only when the black hole remains dynamically confined within the dense
nuclear gas region. Our results suggest that SMBH formation channels relying on
soliton-enhanced
accretion alone are unlikely to provide sufficient early growth.
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Instrumentation and Methods for Astrophysics
GTLS: A GPU-accelerated method for periodic transit detection
Quanquan Hu, Jian Ge, Luoxi Jin et al. (+1 more)
Computational efficiency is a critical requirement for transit searches in modern large-scale photometric surveys. We present Graphics Processing Units Transit Least Squares (GTLS), a GPU-accelerated implementation of the Transit Least Squares
algorithm designed to reduce the computational cost of periodic transit detection while preserving TLS-like sensitivity to transit-shaped signals. GTLS parallelizes the dominant steps of the TLS search, including phase folding, transit-duration evaluation, moving-window depth estimation, and chi-squared calculation. Using Kepler-like long-cadence light curves and synthetic Kepler-like time series, we
benchmark GTLS against the reference CPU implementation of TLS and the GPU-based BLS implementation in cuvarbase. On an AMD Ryzen 9 7950X CPU and an NVIDIA RTX 4090 GPU, GTLS processes a 3000-day synthetic light curve in approximately 138 seconds, compared with 3289 seconds for TLS. With two RTX 4090 GPUs, the runtime is reduced to approximately 79 seconds. In recovery tests, GTLS achieves detection performance statistically consistent with TLS, with a precision of 9.3 percent and recall of 79.4 percent, compared with 9.4 percent and 81.1 percent for TLS. These results demonstrate that GTLS enables efficient TLS-style searches for large photometric data sets from Kepler, TESS, PLATO, ET, and future missions. The source code is publicly available.
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All authors Quanquan Hu, Jian Ge, Luoxi Jin, Kevin Willis