Cosmology and Nongalactic Astrophysics
GW Microlensing: Degeneracy with Unlensed Precessing and Non-Spinning Gravitational-Wave Signals
Disha Hegde and Anupreeta More
With nearly 400 Gravitational Wave (GW) events detected by the LIGO-Virgo-KAGRA network and many more expected, similarities between signals produced by different astrophysical effects can complicate template-based searches and parameter estimation. In particular, GW modulations from
spin precession can resemble the beating pattern induced by microlensing from compact objects with masses of $10$-$10^5,M_\odot$. We investigate this degeneracy and assess whether machine learning can distinguish between these effects. We generate 20,000 simulated GW signals for each class with a network optimal signal-to-noise ratio above 20 and train a convolutional neural network on time-frequency (Q-transform) spectrograms. The classifier achieves up to 95% accuracy in Gaussian noise and 82% in real detector noise. We also study classification between microlensed (ML) and unlensed non-spinning (UN) signals, as well as between unlensed non-spinning (UN) and unlensed precessing (UP) signals. While distinguishing UN from UP remains difficult even in Gaussian noise, ML vs. UN classification reaches up to 80% accuracy in real noise. We identify the regions of parameter space where the classifier performs best and evaluate the ML-UN network on real GW events, finding that the model trained on Gaussian noise generalizes better than the one trained on real noise. This work presents the first low-latency machine-learning pipeline for distinguishing microlensed from unlensed non-spinning GW signals.
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Astrophysics of Galaxies
The S-PLUS Fifth Data-Release: Over 4500 square degrees of the Southern Sky and a multicolor view of the Hydra and Antlia galaxy clusters
Erik Vinicius Rodrigues de Lima, Gustavo Bernhard Oliveira Schwarz, Fábio Rafael Herpich et al. (+55 more)
We present the 5th data release (DR5) of the Southern Photometric Local Universe Survey (S-PLUS), covering 4592 square degrees across 2491 fields. Observations were conducted with the T80-South, a Brazilian robotic
telescope equipped with the Javalambre 12-filter system, containing five broad- and seven narrowband filters. Data products feature FITS images and extensive catalogs containing fluxes, magnitudes, and shape parameters for over 113 million detections. In addition, several value-added catalogs are provided, offering photometric
redshifts (photo-zs), object classifications, masks, and extinction coefficients. For the first time, this release includes coverage of 110 square degrees along the
Galactic disk, facilitating new research into
Galactic structure and
stellar populations. The release also provides full coverage of the Hydra Supercluster and numerous other nearby clusters with improved data reduction and calibration, enhancing photo-z accuracy, which is vital for large-scale structure studies. A preliminary analysis of the Hydra and Antlia
galaxy clusters up to $5 \times R_{200}$ yields an updated catalog of 1706 cluster members based on both spectroscopic and high-quality photo-zs. Our photometric data shows that both clusters have a similar proportion of
galaxies with an H$\alpha$ excess relative to their clustercentric distance, though Hydra has a higher fraction near its center. Additionally, the spatial distribution of all objects in our sample highlights a bridge connecting both clusters. We verify that S-PLUS DR5 provides a solid foundation for future scientific investigations, ranging from
Solar System studies to Cosmology.
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All authors Erik Vinicius Rodrigues de Lima, Gustavo Bernhard Oliveira Schwarz, Fábio Rafael Herpich, Felipe Almeida-Fernandes, Lilianne Nakazono, Eduardo Alberto Duarte Lacerda, André Santos, André Luiz Figueiredo, Luis Angel Gutiérrez-Soto, Marília Jobim Sartori, Marcos Antonio Fonseca-Faria, Maiara Sampaio Carvalho, Bárbara Cubillos Palma, Elismar Lösch, Gissel Pardo Montaguth, José Yuri Santos Silva, Liana Li, Marina Izabela, Natanael Magalhães Cardoso, Thais Santos-Silva, Paulo Afrânio Augusto Lopes, Pedro K. Humire, Roberta Vassallo Bordoni, Amanda Reis Lopes, Analía Viviana Smith Castelli, Ângela Cristina Krabbe, Augusto Damineli, Carlos Eduardo Ferreira Lopes, Ciria Lima-Dias, Clécio Roque de Bom, Daniela E. Olave-Rojas, Debasish Hazarika, Eduardo Telles, Erick Ghuron, Guilherme Limberg, Hélio Dotto Perottoni, Júlia Thainá-Batista, Laerte Sodré Jr., Lia Doubrawa, Marcelo Borges Fernandes, Murillo Marinello, Swayamtrupta Panda, Pierre Augusto Ré, Raimundo Lopes de Oliveira, Raquel Ruiz Valença, Ricardo Demarco, Roberto Cid-Fernandes, Rodrigo Facundo Haack, Sergio Torres-Flores, Stavros Akras, Timothy C. Beers, Vinicius M. Placco, Vitor Cernic, Victor Hugo Sasse, Antonio Kanaan, Tiago Ribeiro, William Schoennell, Cláudia Lúcia Mendes de Oliveira
Instrumentation and Methods for Astrophysics
Compressing radio interferometric visibility data into a probabilistic model using sparse Gaussian processes
Takafumi Tsukui
Next-generation
radio interferometers will produce massive data volumes, making it impractical to store original visibility measurements and later combine observations in $uv$ spatial frequency space. Visibility measurements at similar $uv$ locations measure the same signal but different noise realizations. In principle, these measurements can therefore be compressed by storing only the inferred mean visibility and its uncertainty. We propose modeling the visibility with a sparse Gaussian process (GP) and storing the resulting compact probabilistic model rather than raw visibilities. Using simulated Atacama Large Millimeter/submillimeter Array (ALMA) observations, we demonstrate that the sparse GP is flexible enough to represent the visibilities and recover images with high fidelity. We estimate compression factors of $10^3-10^5$ for an 8-hour Square Kilometre Array (SKA)-Mid observation, with further gains expected by extending the GP input space to include the spectral axis. Beyond data compression, the model exploits correlations in $uv$ space, boosting the signal-to-noise ratio compared with independent grid averaging. Once trained, the model can predict visibility and its uncertainty at any desired $uv$ coordinates, allowing imaging with arbitrary fields of view and image resolutions. The model may also be incrementally updated with new observations while filtering outliers based on the prediction.
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Solar and Stellar Astrophysics
Solar Cycle Variation of the Distribution of Photospheric Magnetic Flux Features
Callan N. Noble, Clare E. Parnell and Thomas Neukirch
We use statistical tools to analyse data from the
Solar Dynamics Observatory Helioseismic and
Magnetic Imager to determine the distribution of the
magnetic flux of photospheric
magnetic features and its variation over a full
solar cycle. In particular, we use statistical figures of merit to test how well different types of probability density function represent the
magnetic flux distribution inferred from the data and how their shape changes over the
solar cycle. Our analysis shows that a double power law provides the best representation of the data over the full
solar cycle and we present the dependence of the power law exponents on the phase of the
solar cycle. The nature of the observed flux distributions at different times during the
solar cycle is significant because it could be used to try and infer information about
solar magnetic field generation mechanisms. We discuss potential implications of a double power law distribution for
solar magnetic field generation.
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Cosmology and Nongalactic Astrophysics
Standard Reconstruction Shifts the Optimal Input Scale for CNN-Based Density-Field Reconstruction
Koichiro Nakashima, Kiyotomo Ichiki and Atsushi J. Nishizawa
We investigate convolutional neural network (CNN) methods for reconstructing the high-
redshift density field from late-time large-scale structure, focusing on how the physical scale of the CNN input changes when standard first-order reconstruction is applied beforehand. Using dark-matter-only $N$-body simulations, we compare three approaches: a single-input CNN, a dual-input CNN combining two physical scales, and a single-input CNN applied to the density field after standard reconstruction. We vary the physical side length of the input sub-box over $L_\mathrm{sub}\sim38$-$380~h^{-1}\mathrm{Mpc}$ while keeping its numerical size fixed at $39^3$ voxels, allowing us to examine the trade-off between spatial context and resolution. For the CNN applied directly to the evolved density field, the reconstruction performs best at $L_\mathrm{sub}\sim150$-$200~h^{-1}\mathrm{Mpc}$. After standard reconstruction, however, the preferred scale shifts to $L_\mathrm{sub}\sim38$-$114~h^{-1}\mathrm{Mpc}$. The single-input CNN after standard reconstruction consistently outperforms both the single- and dual-input CNNs without standard reconstruction according to the normalized loss, density probability distribution, Kullback-Leibler divergence, residual field, and
Fourier-space correlation. These results indicate that coherent large-scale displacements are more efficiently recovered by perturbative reconstruction, while the CNN is better suited to modelling the remaining quasi-linear and non-linear
evolution on smaller scales. The preferred post-reconstruction input range includes the effective receptive scale of approximately $60~h^{-1}\mathrm{Mpc}$ adopted in previous hybrid reconstruction studies. Our findings therefore support a physically motivated separation of scales between analytic and data-driven reconstruction and demonstrate the advantage of combining the two approaches.
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Astrophysics of Galaxies
Chemical Evolution of Galaxies: Past, Present and Future
Francesca Matteucci
In this paper I will describe the basic principles of chemical
evolution of
galaxies, its main ingredients and uncertainties. By means of chemical
evolution we can perform the so-called
galactic archaeology, which consists in reconstructing the history of
star formation of
galaxies and in particular of the Milky Way, starting from the observed
stellar and gas abundances.
Galactic archaeology is a powerful tool to predict also the behaviour of
galaxies at high
redshift. In particular, we adopt the "time-delay model" which is a way of interpreting the [X/Fe] vs. [Fe/H] relations (X is the abundance of a specific chemical element) in terms of different timescales of the
stellar progenitors of the chemical elements relative to Fe, which is the indicator of "
metallicity". I will then describe how we can reconstruct the
star formation histories of
galaxies of different morphological type (spirals, ellipticals) starting from the available observations. Particular
attention will be paid to the study of the Milky Way which is the best studied
galaxy at the moment. I will start describing the first chemical
evolution models and then the most recent ones, the main difference between the old and new models being the observational data to compare with. Finally, I will foresee which could be the future improvements to chemical models and what constraints can we derive to better understand
galaxy evolution.
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High Energy Astrophysical Phenomena
A cosmic-ray loaded nascent outflow driven by a massive star cluster
Marianne Lemoine-Goumard, Lucia Härer, Lars Mohrmann et al. (+6 more)
Cosmic rays are widely held to drive
outflows from
star-forming
galaxies and profoundly influence
galaxy evolution. Direct evidence for
cosmic-ray carrying
outflows is however lacking. At the same time there is increasing awareness of the importance of massive
star clusters in the acceleration of
cosmic rays in
galaxies. Here we report on the discovery of a nascent
outflow driven by the massive
star cluster Westerlund 1. Giga-electronvolt gamma-ray emission coincident with a cavity visible in atomic hydrogen traces the emergence of a population of relativistic electrons out of the
Galactic Disc. The emission is offset from tera-electronvolt gamma-ray radiation surrounding the cluster, but connects to it smoothly spectrally and spatially. The implied energy density of co-accelerated
protons and
nuclei, assuming standard non-thermal electron/
proton injection efficiencies, is at least an order of magnitude higher than that in the general interstellar medium. These particles therefore have the potential to dynamically influence the
outflow. This discovery suggests that
cosmic-ray loaded
outflows may be a common feature of young massive
star clusters, with implications for the transport of
cosmic rays into the
halo of the
Galaxy.
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All authors Marianne Lemoine-Goumard, Lucia Härer, Lars Mohrmann, Romain Bernet, Jim Hinton, Giada Peron, Brian Reville, Luigi Tibaldo, Thibault Vieu
Instrumentation and Methods for Astrophysics
Radial velocity and atmospheric parameter calculations for the GaiaNIR spectrograph
Szabolcs Mészáros, David Hobbs, Anna Liptrott et al. (+8 more)
Context. The upcoming GaiaNIR mission is currently planning to add a near-infrared spectrograph to its payload in order to enhance its scientific return, particularly for mapping the
dust-obscured regions of the Milky Way. Aims. This study aims to identify the optimal wavelength region between 800 and 2300 nm for the proposed GaiaNIR spectrograph to maximize the precision of radial velocities and atmospheric parameters. Methods. To find its spectral range, we generated 10000 synthetic spectra from the BOSZ library across a wide range of
stellar parameters, with resolutions varying from 5000 to 20000. By cross-correlating these mock observations with ideal templates, we assessed the statistical scatter of velocity residuals to isolate six candidate windows for further atmospheric parameter testing. Results. Our analysis finds that the 1926 - 1968 nm window at R = 16100 - 20100 in the K-band is the preferred strategic choice, because it has the potential to reach radial velocity precision for the brightest FGKM
stars of about 160 - 260 m/s depending on resolution, while providing precision of the atmospheric parameters close to
Gaia's Radial Velocity Spectrometer. We also identified a second region between 1158 and 1202 nm (R = 9300 - 11600), that has slightly lower radial velocity precision, but at a wider temperature range than the K-band. Both regions make it possible to derive abundances of ten species at these resolutions: O, Na, Mg, Si, Ca, Ti, V, Cr, Mn, Ni in the K-band, and Mg, Si, K, Ca, Ti, V, Cr, Mn, Co, Ni between 1158 - 1202 nm. Conclusions. The K-band delivers sufficiently precise measurements for the mission's primary cool
star targets while taking advantage of significantly lower interstellar extinction, enabling the mapping of the
dust-obscured regions of the Milky Way.
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All authors Szabolcs Mészáros, David Hobbs, Anna Liptrott, David Katz, Ricardo Schiavon, Viktória Pap, Anthony G. A. Brown, George Seabroke, Joss Bland-Hawthorn, Ronny Blomme, Nicholas A. Walton
Earth and Planetary Astrophysics
Accuracy Analysis of VLBI Universal Time Measurement Based on a GNSS Single-Station Regional Ionospheric Model
Xu-chong Duan, Dang Yao, Yuan-wei Wu et al. (+3 more)
Universal Time (UT1) is a key parameter characterizing Earth's rotation, and very long baseline interferometry (VLBI) is the mainstream technique for measuring UT1. To address the limitations in the timeliness and accuracy of existing global ionospheric models for single-frequency VLBI UT1 measurements, we construct a single-station regional ionospheric model using GNSS data from the VLBI stations on the Jilin-Kashi baseline. We apply this model to VLBI observations and compare its correction performance with that of a global predictive model and a global post-processed model. The results show that the line-of-sight ionospheric delays and baseline corrections calculated with the single-station regional model have precision close to that of the global post-processed model and are substantially better than those of the global predictive model. After correction with the single-station regional model, the derived UT1 values differ from the US Naval Observatory (USNO) reference values by a mean bias of -15.6 us and an RMS deviation of 82.3 us, both better than the results obtained with the other two model classes. A single-station regional ionospheric model constructed independently from GNSS data available at VLBI stations can effectively correct single-frequency VLBI observations and support quasi-real-time high-precision UT1 measurements. It therefore has important value for improving the timeliness of independent UT1 products.
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All authors Xu-chong Duan, Dang Yao, Yuan-wei Wu, Zhe Zhang, Jia Liu, Xu-hai Yang
Solar and Stellar Astrophysics
Three-dimensional evolution of a solar filament with multipoint observations
Qingmin Zhang, Jun Dai, Beili Ying et al. (+6 more)
In this paper, we first devise a geometrical model, featuring a
torus-like flux rope based on the shape of 3DCORE model. The global shape of the
torus is an ellipse, while the cross sections are circular along the
torus. The thinnest point is located between the Sun center and photosphere. Deflections and inclination are considered as well. Using multiwavelength observations from perspectives of Earth, Ahead-STEREO (STA), and
Solar Orbiter, we apply the model to three-dimensional (3D) reconstructions and tracking of the filament eruption, which was associated with a
flare and a coronal mass ejection (CME) on 2024 October 8. The morphology, direction, and true velocity ($\sim$433 km/s) of the eruptive filament are obtained. It is found that the filament propagates nonradially, deflecting slightly eastward by $\sim$10 degrees and significantly southward by $\sim$40 degrees. Trajectory of the filament in the ecliptic plane reveals that the filament moves toward STA. The true direction of the eruptive filament using imaging and spectral observations is mutually verified by 3D reconstructions. The heliocentric distance of the filament increases from $\sim$1.68 to $\sim$2.94
solar radii within 35 minutes. Based on the results of 3D reconstructions, the true speed of the CME leading edge is evaluated to be 1046$-$1145 km/s.
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All authors Qingmin Zhang, Jun Dai, Beili Ying, Ye Qiu, Li Feng, Chuan Li, Hongqiang Song, Yue Zhou, Zongyi Li
Astrophysics of Galaxies
Testing various assumptions for radiolysis, non-diffusive chemistry, and chemical desorption in cold cores
V. Wakelam and T. Tu
To study interstellar gas and grain chemistry, gas-phase astrochemical models have been developed since the early 1980s and gas-grain models since the 1990s. Each published model includes various assumptions mainly for surface processes. In this paper, we compare recently added mechanisms for grain surface chemistry, namely, non-diffusive chemistry, radiolysis, and chemical desorption. Several formalisms for these processes have been added to our astrochemical model Nautilus, and we tested them, comparing the predicted gas-phase and ice abundances. Our predictions are also compared to gas and ice observed compositions. Our main findings are that radiolysis itself does not influence the results. Non-diffusive chemistry can have an impact on the gas-phase and ice species, but it depends on the adopted formalism. In particular, the one of Shingledecker & Herbst (2018) changes the main reservoirs of the species in the ices, impacting the species in the gas-phase as well. The adopted formalism for chemical desorption can produce differences in the gas-phase by up to a factor of ten. Last, our standard model, without non-diffusive chemistry and with the chemical desorption from Fredon et al. (2021), produces the best results in relation to observed gas-phase abundances, while the ice observed agreement is unchanged. The formalism for some grain surface processes are important even for gas-phase abundances. More experiments are needed to constrain their efficiency, however. For the chemical desorption, each formalism relies on an uncertain parameter, which is the fraction of the energy actually delivered to the products, that can be adjusted to reproduce the experiments.
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High Energy Astrophysical Phenomena
Stable X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613
Wei Yu, Sinan Allak, Zi-Xu Yang et al. (+3 more)
Aims. We investigate the
evolution of X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613 during its 2023 outburst, with the aim of probing the inner
accretion flow geometry across spectral states. Methods. We analyzed NICER observations covering the low-hard state (LHS) and hard-intermediate state (HIMS). The time lags were computed using
Fourier-based techniques, and we constructed lag-frequency and lag-energy spectra. To obtain a robust estimate of the soft lag amplitude, we focused on a frequency range in which the reverberation signal dominates and remains stable, thereby minimizing contamination from hard lags and phase-wrapping effects. Results. The soft lag amplitude increases rapidly from the LHS to the early HIMS and then stays near 10 ms throughout the HIMS. In the frequency range in which reverberation lags prevail, the lag shows little dependence on
Fourier frequency. On the other hand, the observed low-frequency lags change from hard-lag dominated to soft-lag dominated, with amplitudes comparable to those measured at higher frequencies. Conclusions. These results suggest that the reverberation lag varies little during the HIMS, consistent with a relatively stable inner
accretion geometry during this state. The apparent
evolution of the lag amplitude from the LHS to the HIMS can be largely explained by the diminishing effect of hard lags and does not necessarily require significant changes in the intrinsic light-travel timescale. Swift J1727.8-1613 therefore provides a case in which the reverberation signal can be studied with reduced contamination over a broad frequency range, offering new insight into the
evolution of the
accretion geometry in black hole X-ray binaries.
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All authors Wei Yu, Sinan Allak, Zi-Xu Yang, Xiao Fan, Andrea Santangelo, Tian-hao Xie
Solar and Stellar Astrophysics
Explainable AI for Solar Flare Prediction: Quantitative Magnetic Field Analysis of Model-Focused Regions
Z. Zheng, Q. Hao, C. Li et al. (+4 more)
Solar flares are intense energy release events in the
solar atmosphere that may pose significant space weather hazards, which makes developing reliable prediction models essential. Although deep learning methods, particularly convolutional neural networks (CNNs), demonstrate strong predictive performance when using
solar magnetograms, their scientific credibility is undermined by a lack of physical interpretability. Explainable artificial intelligence (XAI) offers a potential solution. However, current XAI studies in
solar flare prediction are largely qualitative and lack systematic, theory-based, quantitative validation. We present a quantitative XAI framework that can decipher the physical basis of CNN-based
solar flare prediction models. Using gradient-weighted class activation mapping (Grad-CAM), we identify model-focused regions (MFRs) in
solar magnetograms. Then, we perform two key analyses to evaluate the predictive capability of
magnetic parameters derived from MFRs and to quantitatively characterize their
magnetic complexity. Our results reveal a strong physical correlation between MFRs and
flare occurrence. Specifically,
magnetic features extracted from MFRs demonstrate high predictive power for
flares.
Flare-producing active regions are characterized by magnetically complex configurations that are dominated by a single polarity rather than by balanced or purely unipolar structures. This finding is consistent with established physical theories of
magnetic systems prone to
flares. Our results suggest that CNNs can learn physically meaningful representations when trained on large-scale observations. Integrating XAI with quantitative
magnetic field analysis improves the physical interpretability of deep learning-based
flare prediction models, making them useful tools for prediction and modeling investigation in
solar physics.
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All authors Z. Zheng, Q. Hao, C. Li, P.F. Chen, J.R. Hu, M.D. Ding, C. Fang
Earth and Planetary Astrophysics
Debris Evolution from Spacecraft Fragmentation in Earth-Moon Distant Retrograde Orbits
Yuyan Wu, Peng Shu and Yuqiang Li
With the rapid surge in lunar exploration and the planned expansion of cislunar infrastructure, cislunar space has become a strategic focal point for global aerospace activities. This proliferation of spacecraft heightens the risk of fragmentation events, such as unintended explosions or orbital collisions which serve as the primary source of hazardous orbital debris. Given the potential threat these fragments pose to mission safety and long-term orbital sustainability, it is imperative to investigate their dynamical behavior within the Earth-Moon system. This study evaluates the dispersion of debris clouds following potential breakup events on Distant Retrograde Orbits (DROs) over a 30-day propagation period. The Circular Restricted Three-Body Problem (CR3BP) model is used to construct the reference orbits, while the NASA Standard Breakup Model is applied to simulate fragment generation at multiple locations along three DROs of varying sizes. These fragments are then propagated using the Bicircular Restricted Four-Body Problem (BCR4BP) for 30 days. To account for the variability of these events, multiple initial positions along each orbit are analyzed to capture a comprehensive range of post-explosion scenarios. Our analysis quantifies the fate of fragments within this window, specifically focusing on the escape mechanisms and the percentages of debris that either depart from the Earth-Moon gravitational sphere of influence or impact the lunar surface. Furthermore, we introduce an analytical approach to assess the potential collision risk to resident space objects operating within the vicinity of the parent orbit. The results provide insights into debris
evolution and offer a foundation for developing safety guidelines for future cislunar activities.
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Instrumentation and Methods for Astrophysics
Torsional-X Seismometer for Lunar Decihertz Gravitational-Wave Detection
Yulin Xia, Denis Martynov, Huan Yang et al. (+1 more)
The lunar gravitational-wave
antenna concept uses the Moon as a resonant detector instrumented with precision seismometers, targeting the decihertz band between ground- and space-based observatories. We propose a compact monolithic fused-silica torsional-X seismometer that re-engineers garden-gate acceleration-to-rotation transduction for this regime through a high-tension dual-fiber suspension. Its designed millihertz-scale resonance and ultra-low mechanical dissipation enable a nearly order-of-magnitude improvement around $0.1\,\mathrm{Hz}$ compared with existing lunar seismometer concepts. Achieving this performance requires room-temperature operation, where fused-silica exhibits low mechanical loss, together with subdominant actuation noise. We demonstrate a room-temperature
vacuum prototype validating the operating principle and core mechanical design, and derive requirements for a future lunar implementation capable of approaching the target sensitivity.
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All authors Yulin Xia, Denis Martynov, Huan Yang, Haixing Miao
Cosmology and Nongalactic Astrophysics
Update on the Physics of the Cosmic Microwave Background (2015-2025)
Martin Bucher
We review the present status of observations of the
Cosmic Microwave Background. This book chapter is an update to an earlier review "Physics of the
Cosmic Microwave Background Anisotropy" that appeared a decade ago in the compilation "One Hundred Years of General Relativity: From Genesis and Empirical Foundations to Gravitational Waves, Cosmology and
Quantum Gravity." The earlier contribution summarized the state of the field then as well as the underlying cosmology and gravitational physics. This contribution reports on what new has occurred in the field during the intervening time 2015-2025. We also review future prospects.
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Earth and Planetary Astrophysics
Distant TNO Inclinations as a Constraint on Primordial Cluster Perturbations in the Presence of Planet Nine
Avni Bansal, Ian Brunton, Konstantin Batygin et al. (+2 more)
The Sun was almost certainly born in a
stellar cluster, implying some degree of external forcing from neighboring
stars during the
Solar System's infancy. Published estimates of the strongest relevant
stellar encounter, however, span a broad range, from relatively gentle perturbations to violently disruptive flybys. The modest inclination dispersion of the distant trans-Neptunian population has previously been used to argue that strong
primordial encounters were unlikely and that the outer
Solar System was not violently stirred at birth. In this work, we independently examine this constraint and ask whether this conclusion holds in the presence of
Planet Nine. Because
Planet Nine can reshape the distant trans-Neptunian population over gigayear timescales, the extent to which the present-day inclination distribution preserves a direct record of
primordial cluster excitation is a priori unclear. To address this question, we compare long-term N-body integrations in which distant test particles begin either in strongly cluster-perturbed configurations or in comparatively quiescent ones, and are then evolved under the influence of the known
giant planets, the
Galactic tide, the effects of passing
stars, and
Planet Nine. We find that
Planet Nine does not transform a highly excited
primordial population into one resembling the observed low-inclination distant sample. Instead, comparisons between the simulated and the observed distant TNO populations indicate that the observed distant TNOs are most consistent with a relatively mildly perturbed birth environment, even in the presence of
Planet Nine. If this comparatively low inclination dispersion is confirmed to be an intrinsic feature of the distant TNO population, rather than an artifact of observational bias, it constitutes a robust constraint on the severity of
primordial cluster perturbations.
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All authors Avni Bansal, Ian Brunton, Konstantin Batygin, Gabriele Pichierri, David Nesvorný
Astrophysics of Galaxies
Identifying and Distinguishing Quenching Galaxies with Spatially Resolved Star Formation in Mock CASTOR and NGRST Observations
Cameron Lawlor-Forsyth, Michael L. Balogh, Sean L. McGee et al. (+1 more)
We present synthetic images of
galaxies that are in the stages of
star formation quenching for the Cosmological Advanced Survey
Telescope for Optical and UV Research (CASTOR) and Nancy Grace Roman Space
Telescope (NGRST), based on simulations coming from the IllustrisTNG suite, as processed using the
stellar population synthesis library galaxev. We account for the effects of
dust and various sources of noise to produce mock observations that should mirror real observations. Using these synthetic images, we fit photometric observations in binned circular annuli using FAST++ and a flexible
star formation history, and recover well the spatially resolved
stellar mass and
star formation rate. We thereby measure various indicators (morphological metrics) of spatially resolved
star formation activity in the context of
galaxy quenching. We find that we are able to distinguish quenching
galaxies from a mass-matched control sample of normal
star forming
galaxies. We additionally find that we can distinguish various quenching mechanisms, where
galaxies consistent with an inside-out quenching signature can be separated from
galaxies that display an outside-in signature. Using machine learning techniques the accuracy of this classification is reliable, and the progress through the quenching episode can be estimated for the different populations of quenching
galaxies. We make predictions for the abundance of the various quenching populations in proposed surveys for CASTOR and NGRST, and find that these surveys will enable the classifications of thousands of quenching
galaxies out to intermediate
redshifts, and more when considering higher
redshifts.
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All authors Cameron Lawlor-Forsyth, Michael L. Balogh, Sean L. McGee, Gregory H. Rudnick
Solar and Stellar Astrophysics
Oscillation Period Properties of Sunspots in the 8-10 $\mu$m Infrared Band: A Multi-Dataset Analysis
Suo Liu
Sunspot oscillations probe
magnetic-
plasma interactions in the
solar atmosphere. We investigate oscillation periods in six sunspot active regions observed in the 8-10 um band with the Accurate Infra-red
Magnetic-field
Solar Telescope (AIMS) at Lenghu Observatory. Light curves were extracted from umbra, penumbra, and quiet Sun regions. Wavelet analysis was applied using four methods: pixel-wise with mean/median aggregation, and spatial mean/median prior to analysis. The weighted mean period is more physically meaningful than the dominant period, better representing multi-mode oscillations. A consistent period sequence holds across all
datasets: umbra (U) < penumbra (P) < quiet Sun (Q), with typical values of 260-313 s, 286-374 s, and 294-382 s. This pattern is recovered with 100% consistency by pixel-wise mean/median and spatial median methods. Spatial mean shows 1/6 full, 3/6 partial, and 2/6 inconsistency. Spatial smoothing increases periods by up to 21%, most strongly in the umbra. All peak ratios are below 0.3 (mean 0.14 +/- 0.03), confirming multi-mode oscillations. These results establish the 8-10 um band as a valuable diagnostic window for sunspot magneto-convection and wave propagation.
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Astrophysics of Galaxies
The FAST HI 21-cm Absorption Blind Survey. III. OH Absorption Search in the 21-cm Absorber Sample and Continued HI Absorption Search
Wenkai Hu, Yougang Wang, Jeremy Darling et al. (+11 more)
We present the first blind search for OH 18-cm absorption with the Five-hundred-meter Aperture Spherical
Telescope (FAST), conducted alongside the HI 21-cm absorption search. Our previous FAST blind HI absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FASHI data (394.4 hr and 1622.1 deg$^{2}$) together with FATHOMER observations, yielding four known and three new HI absorbers, for a total of 41 HI absorption systems. We search for OH absorption in 19 HI absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber towards PKS 1413+135 was re-detected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between $N_{\rm{OH}}$ and $N_{\rm{HI}}$, applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an $N_{\rm{OH}}$-$N_{\rm{HI}}$ correlation or
redshift evolution of $N_{\rm{OH}}$/$N_{\rm{HI}}$. Finally, spectral stacking sets 3$\sigma$ OH column density upper limits of 4.93, 1.64, and 1.72 $T_{\rm{ex}}$/$c_{\rm{f,OH}}\times$10$^{12}$cm$^{-2}$K$^{-1}$ for associated, intervening, and combined samples, corresponding to [\rm{OH}]/[\rm{HI}] ratios of $<$1.66$\times$10$^{-8}$, $<$1.42$\times$10$^{-8}$, and $<$0.90$\times$10$^{-8}$, assuming $T_{\rm{ex}}$=10K for OH and $T_{\rm{s}}$=100K for HI. These results place the strongest constraints to date on the OH content in
radio-selected HI absorbers and establish a blind-survey
benchmark for future studies of molecular gas in HI-selected systems. They also demonstrate that known HI 21-cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.
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All authors Wenkai Hu, Yougang Wang, Jeremy Darling, Zheng Zheng, James R. Allison, Elaine M. Sadler, Wenxiu Yang, Yichao Li, Yidong Xu, Jie Wang, Fengquan Wu, Di Li, Ming Zhu, Xuelei Chen
High Energy Astrophysical Phenomena
High-Density Sound Speed and Post-Merger Dynamics
John Stroud, David Radice and Sanjay Reddy
The density dependence of the speed of sound in cold
neutron star matter remains poorly constrained and is central to determining the high-density equation of state (EOS). While binary
neutron star (BNS) merger simulations increasingly incorporate detailed microphysics, the direct impact of the sound-speed in the
neutron star core on observable signatures has not been systematically explored. We address this by introducing a simplified parametrization that suppresses microphysics while allowing controlled variation of the sound speed at supranuclear densities through its derivative with respect to the
baryon chemical potential. Using the WhiskyTHC code, we perform a suite of fully relativistic BNS merger simulations and identify correlations between the sound-speed slope parameter and key merger outcomes, including remnant properties and post-merger GW frequencies. These results demonstrate that multimessenger observables are sensitive to the behavior of matter at the highest densities reached in
neutron star cores. We further analyze gravitational-wave signals from the CoRe database of binary
neutron star merger simulations employing more realistic equations of state. Our analysis reveals approximately EOS-independent relations between the derivative of the sound speed and the peak post-merger gravitational-wave frequency. Although these relations cannot be considered truly quasi-universal, they nonetheless indicate that post-merger gravitational waves retain measurable information about the EOS at he highest densities. At the same time, the remaining EOS dependence highlights the difficulty of isolating the underlying high-density physics and motivates the development of targeted parameterized frameworks for interpreting future multimessenger observations.
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Cosmology and Nongalactic Astrophysics
Morphological Bias: How Ellipticals and Spirals Trace the Cosmic Web Differently
Paula S. Ferreira, Carlos A.P. Bengaly and Renyue Cen
We present a data-driven measurement of
galaxy bias and scale-dependent relative bias for elliptical and spiral
galaxies using angular auto- and cross-power spectra from DES and DESI Legacy Imaging Surveys DR8. We introduce the cross-tracer clustering ratio (CTCR), the ratio of auto- to cross-power spectra, which isolates the relative clustering of morphological tracers as a function of angular multipole $\ell$. Across both surveys, ellipticals are more strongly clustered than spirals; the cleanest constraints come from DESI, where the two
redshift distributions are well matched. The difference is scale dependent: the relative bias is near unity on large scales ($\ell \lesssim 50$) and rises toward smaller scales, reaching $2.9$–$4.0\sigma$ per bin at $\ell = 200$ with an inverse-variance-weighted amplitude $\Delta b = +0.56 \pm 0.06$. A complementary linear-bias analysis confirms that ellipticals are positively biased relative to the matter field, while spirals are consistent with weak bias or anti-bias. The results are robust to two covariance
estimators, contamination tests, luminosity splits, and comparisons with two N-body mock catalogs. Throughout, we present the CTCR as an effective clustering ratio that is an upper bound on the physical bias ratio, adopting an assumption-light strategy appropriate for a first measurement; the joint multi-spectrum decomposition required to extract the physical bias ratio is identified as future work. These findings provide empirical evidence that
galaxy morphology imprints both the amplitude and scale dependence of
galaxy bias, and establish the CTCR as a useful observable for testing
halo occupation and assembly-bias models with future imaging surveys.
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Astrophysics of Galaxies
22 Newly Identified Repeating Changing-look AGNs and Evidence for Extreme Broad-line Region Breathing
Litao Zhu, Zhongxiang Wang, Alok C. Gupta et al. (+5 more)
Changing-look active
galactic nuclei (CL AGNs) show the appearance or disappearance of broad emission lines on timescales of years. Among them, the repeating CL (RCL) AGNs may provide a clear clue for our understanding of the CL transitions because the same
nucleus crosses some physical boundaries more than once. We search for RCL AGNs in known CL-AGN samples using long-term multi-band light curves, and selected 34 candidates for spectroscopic follow-up. We confirm 25 RCL AGNs, including 22 newly identified cases. Properties of these RCL AGNs are analyzed. The observed rest-frame intervals of the second transitions are mostly 3–4 yr, while the variations of the optical light curves suggest that some transitions might occur on timescales of several months. The latest spectra show that the on/off states correspond to higher/lower Eddington-ratio, in the expected direction relative to the parent CL-AGN samples. As seven RCL AGNs are well covered by nearly continuous single-band light curves, their on/off states can be found to follow multi-year optical excursions, and their Eddington ratios vary consistently with the photometric changes. We also find that the H$\beta$-only transitions occur at higher Eddington ratios than the transitions involving both H$\alpha$ and H$\beta$, suggesting a line-dependent Broad-Line-Region (BLR) visibility threshold. These results support a picture in which different
accretion-flow processes drive reversible changes in the central ionizing emissions, while the observed RCL transitions are produced by the BLR breathing across line-dependent visibility thresholds.
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All authors Litao Zhu, Zhongxiang Wang, Alok C. Gupta, Yiyang Zeng, P. U. Devanand, Karan Dogra, Riya Bhowmick, Ju-Jia Zhang
Solar and Stellar Astrophysics
Investigation of projected rotational velocities of Be-type stars in LAMOST DR7
Zhicun Liu, Jiao Li, Jiaming Liu et al. (+3 more)
Stellar rotation plays a key role in the transfer of angular momentum, and a large sample of Be-type
stars with reliable projected rotational velocities is crucial for understanding their formation and
evolution. In this work, we derive the projected rotational velocities ($v$\,sin\,$i$) of 479 Be-type
stars using the
Fourier transform method, based on their LAMOST Medium-resolution Survey (MRS) spectra. Our results suggest that the
Fourier transform method can provide reliable $v$\,sin\,$i$ values for Be-type
stars by analyzing the \ion{He}{1}\,lines at 4922, 5015, 5047, and 6678 \,Åin their LAMOST MRS spectra. A K-S test indicates that Be-type
stars with different H$\alpha$ emission line morphologies exhibit different $v$\,sin\,$i$ distributions, and Be-type
stars with double-peaked emission have a higher fraction of rapid rotators than those with single-peak emission. The $v$\,sin\,$i$ distributions of our Be-type
stars in the field, OB associations, and clusters show no significant differences. The deconvolved $v$\,sin\,$i$ distribution of our entire Be-type
star sample does not exhibit a bimodal distribution but rather a single peak at $v\approx260$\,km$\cdot$s$^{-1}$. Based on the analysis of 105
stars in our sample, we find that the mean equatorial rotational velocity is 0.74 times the critical velocity. Furthermore, we investigate the relationship between $v$\,sin\,$i$ and the H$\alpha$ peak separation velocity for Be-type
stars exhibiting double-peak H$\alpha$ emission lines, using Pearson and Spearman rank correlation coefficients.
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All authors Zhicun Liu, Jiao Li, Jiaming Liu, Xiao-Long Wang, Guozhen Hu, Wenyuan Cui
Solar and Stellar Astrophysics
Silicate Clouds, SiO, and Molecular Trends across the L-T Sequence: A JWST/MIRI LRS Spectral Library of Brown Dwarfs
Sam Barber, Stanimir Metchev, Genaro Suárez et al. (+9 more)
We present the results of a survey program with JWST's MIRI LRS that obtained 5$-$14 $\mu$m R~100 spectra of twenty-three L0$-$T6
dwarfs. This spectral type range spans the formation, growth, and sedimentation of silicate condensate clouds, as well as the appearance of methane and ammonia in the atmospheres of brown
dwarfs. The initial onset of silicate absorption at spectral type L0 as well as the
evolution of this feature with spectral type are both examined in unprecedented detail. We detect 7.5$-$9.5 $\mu$m gas-phase SiO absorption for the first time in
dwarf stars, with detections in M5.5$-$L2.5
dwarfs from combined Spitzer IRS and JWST spectra. This feature has previously been detected in K and M
giants, with stronger absorption in these
giants than in higher-
gravity M
dwarfs. In contrast, low-
gravity L
dwarfs show weaker SiO absorption than field-
gravity L
dwarfs. We also confirm water, ammonia, and methane absorption trends with spectral type previously seen in Spitzer IRS observations. We report the possible detection of CS2 in a T3.5
dwarf, although confirmation would require higher-dispersion spectroscopy. We find two newly resolved binaries, confirm two near-equal flux unresolved candidate binaries, and identify two additional possible non-equal flux binaries. After accounting for contamination by resolved and candidate binaries, we find that single field
dwarfs are ~0.15$-$0.20 mag underluminous compared to existing empirical relations. The presented spectral library offers a spectrophotometrically calibrated basis for future interpretation of JWST MIRI spectra of brown
dwarfs or of directly imaged or transiting
exoplanets.
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All authors Sam Barber, Stanimir Metchev, Genaro Suárez, Samantha Lambier, Paulo A. Miles-Páez, Étienne Artigau, Beth Biller, Adam J. Burgasser, Jacqueline Faherty, Gregory Mace, Caroline V. Morley, Johanna M. Vos
Astrophysics of Galaxies
Gas-Phase Metallicity and Nitrogen Abundances in Low-Mass Galaxies Down to $M_\star\simeq10^{5.7}\,M_\odot$ at $z\simeq4.5$–$10.1$ from JWST Lensing Cluster Surveys
Hiroya Umeda, Masami Ouchi, Kimihiko Nakajima et al. (+7 more)
We analyze 405 deep JWST/NIRSpec spectra of
star-forming
galaxies at $z=4.5$–$10.1$ from DREAMS and other
lensing-cluster surveys to study chemical enrichment in intrinsically faint, low-mass
galaxies. The sample covers $M_{\rm UV}\simeq-12$ to $-22$ and reaches $M_\star\simeq10^{5.7}\,M_\odot$, with 50% of the sources at $M_{\rm UV}>-17.5$ magnified by $\mu>3$. From individual spectra and mass-binned stacks, we derive the gas-phase
metallicity together with nitrogen and carbon abundances using the rest-frame UV and optical lines. \Add{We derive new empirical strong-line
metallicity calibrations using direct-method measurements from
stellar-mass-binned stacks, reaching a representative
stellar mass of $M_\star\simeq10^{6.6}\,M_\odot$. Applying these calibrations, we trace the $z\sim6$ mass–
metallicity relation down to $M_\star\simeq10^{6.6}\,M_\odot$, where it reaches $12+\log({\rm O/H})\simeq7.2$, with a low-mass slope slightly steeper than the local relation and in broad agreement with hydrodynamical simulations.} In the $M_\star\simeq10^{7.7}\,M_\odot$ stack, N/O from N\,iv]\,$\lambda\lambda\,1483,1486$ exceeds that from [N\,ii]\,$\lambda6583$ by $\simeq1.4$ dex. The UV–optical difference could indicate a localized, highly ionized N-rich component whose high N/O and subsolar C/O resemble nitrogen-rich globular-cluster populations with $M_\star\lesssim10^6\,M_\odot$. \Add{The combination of these abundance patterns and a He\,ii\,\W4686/H$\beta$ ratio of $\simeq0.03$, well above BPASS predictions, suggests that WR
stars may contribute both
prompt CNO-cycle enrichment and hard ionizing radiation, with the inferred WR population potentially supplying enough nitrogen to account for the excess on globular-cluster scales.
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All authors Hiroya Umeda, Masami Ouchi, Kimihiko Nakajima, Kuria Watanabe, Yuichi Harikane, Yuki Isobe, Moka Nishigaki, Ono Yoshiaki, Hidenobu Yajima, Yi Xu