Cosmology and Nongalactic Astrophysics
Anisotropic redshift distributions in photometric galaxy clustering and their cosmological impact
Zekang Zhang, Yunhe Wang, Daniel Gruen et al. (+4 more)
Photometric
galaxy clustering is a major probe of large-scale structure whose interpretation relies on accurate characterization of the
galaxy redshift distribution, $n(z)$. Standard analyses assume the $n(z)$ of a selected lens sample to be isotropic, whereas observational systematics can imprint spatial variations. We quantify how this anisotropy biases angular
galaxy clustering, internal consistency, and cosmological inference. We develop an analytical formalism for clustering under spatially varying $n(z)$ and forward-model realistic observational systematics,
galaxy selection, and tomographic binning. For a fiducial magnitude-limited sample, modeling $w(\theta)$ with a single global $\bar n(z)$ underestimates the clustering signal by up to $\sim10\%$ at small scales in the highest-
redshift bin, decreasing towards lower
redshift. In a $2\times2$pt analysis, cosmological parameter shifts remain below $1\sigma$ for KiDS-like and DES-like setups. For an LSST-like setup retaining KiDS-like selection and observing-condition variation, $\sigma_8$ is biased low by $1.7\sigma$ and $\Omega_m$ high by $1.4\sigma$, while the high-
redshift galaxy bias shifts by up to $\sim4\sigma$. The anisotropy also affects whether the probes are consistent enough to combine: a calibrated posterior-predictive internal-consistency test finds the contaminated angular clustering improbable given the joint
cosmic-shear and
galaxy–
galaxy-
lensing constraints (median calibrated $\tilde p\approx8\times10^{-4}$ under LSST-like noise). Anisotropic
redshift distributions are therefore a potentially significant systematic for future photometric clustering analyses. Our forward model can be used to mitigate it given a realistic selection function and
galaxy population model.
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All authors Zekang Zhang, Yunhe Wang, Daniel Gruen, Hui Kong, Luca Tortorelli, Silvan Fischbacher, Ziang Yan
Astrophysics of Galaxies
ALMA-JELLY II. Constraining the radial profiles of the quenching timescales in ram-pressure-stripped galaxies
Roberto P. Infurna, Matteo Fossati, Alessandro Boselli et al. (+21 more)
We investigate the environmental quenching histories and spatial progression of ram-pressure stripping in 11
galaxies in the nearby Coma, Norma, and A1367 clusters. As part of the ALMA-JELLY large program, we combine high-sensitivity VLT/MUSE integral-field spectroscopy with ultraviolet-to-far-infrared photometry in 37 spatially resolved disc apertures. The sample spans $\log(M_*/\mathrm{M}\odot)\sim7.5-10.5$ and includes
galaxies undergoing active or recent ram-pressure stripping, identified through prominent H$\alpha$ or UV tails. We use
Bayesian spectrophotometric modelling with exponentially declining
star-formation histories and show with mock data that combining spectra and photometry breaks parameter degeneracies and improves quenching-age constraints. All
galaxies show quenched outer discs and relatively old ($\lesssim1$ Gyr) stellar populations. Massive
galaxies ($\log(M_*/\mathrm{M}_\odot)>9.5$) exhibit clear outside-in quenching: inner regions quench about 500 Myr later than their outskirts. The small scatter in quenching age with distance from the truncation radius, despite differences in environment and stripping geometry, points to a common evolutionary sequence. Low-mass and dwarf
galaxies instead show weak radial gradients, with quenching occurring more rapidly, typically within 300 Myr.
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All authors Roberto P. Infurna, Matteo Fossati, Alessandro Boselli, Michele Fumagalli, Jeffrey D.P. Kenney, Pavel Jáchym, Ming Sun, Elias Brinks, Françoise Combes, Patricia da Silva, Romana Grossová, Stephen Gwyn, Kokoro Hosogi, Alessandro Ignesti, Jin Koda, Jan Palouš, Nathanael Pichette, Sujith Ranasinghe, Tom C. Scott, Harrison J. Souchereau, Juhi Tiwari, Bernd Vollmer, Norbert Werner, Masafumi Yagi
Instrumentation and Methods for Astrophysics
Gnuastro: removing extended/diffuse outliers while coadding
Mohammad Akhlaghi, Héctor Vives Arias, Pablo Renard et al. (+2 more)
Deep astronomical images are produced by the coadding (also called "stacking") of several individual exposures. However, individual exposures are often plagued with many artifacts which will reduce the quality of the deep image if not properly removed. Most are removed during reduction/calibration, but the more diffuse may stay. To address this problem, the following new operators were introduced to the Arithmetic program in Gnuastro 0.23: 'madclip-maskfilled', 'sigclip-maskfilled' and 'collapse-*clip-fill-*'. They are able to mask many such outliers successfully by using all the exposures to find outlying pixels in each exposure and exploiting their contiguity. This research note is reproducible with Maneage, on the Git commit bf3815a.
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All authors Mohammad Akhlaghi, Héctor Vives Arias, Pablo Renard, Héctor Vázquez Ramió, Raúl Infante-Sainz
Earth and Planetary Astrophysics
Detecting transiting exoplanets in simulated PLATO data: A comparison of light curve filter and transit search algorithms
Geert Jan Talens, Leigh C. Smith, Luca Malavolta et al. (+3 more)
Aims: Our goal is to test and compare transit search methodologies, and provide recommendations as to the best practices to be implemented by the upcoming ESA PLATO mission, in order to achieve its goal of detecting Earth-like
planets in the habitable zones of Sun-like
stars. Methods: We generate simulated two-year PLATO light curves with injected
planets with sizes 0.5–2.0 $R_\oplus$, and compare the performance of the CETRA, umbra, and nuance transit search methods. CETRA and umbra require pre-filtered light curves and we test the biweight, Huber spline, Lowess, and YSD-Lowess filters. nuance uses a Gaussian process to model the stellar variability at all proposed transit parameters. Results: nuance achieves the best performance, recovering 61.2% signals using a simple harmonic oscillator Gaussian process kernel, and it performs especially well for both hot and fast-rotating
stars. However, when multiple Huber spline filter windows are considered, both CETRA and umbra can match nuance's performance. CETRA matches nuance with four windows, recovering 61.3% of signals. umbra matches nuance with two windows, recovering 61.7% of signals. Recovery rates exceeding nuance are possible by using more windows. The computational cost of running nuance is so high that running CETRA or umbra on multiple windows is preferred. Conclusions: The PLATO pipeline should use the Huber spline with a range of window sizes as its primary light curve filter. CETRA should be updated to use the warped least-squares templates implemented in umbra. The use of nuance should be considered for hot, rapidly rotating
stars.
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All authors Geert Jan Talens, Leigh C. Smith, Luca Malavolta, Lionel Garcia, Simon Hodgkin, Suzanne Aigrain
Cosmology and Nongalactic Astrophysics
Gravitational-Wave Image Multiplicity as a Topological Probe of Dark-Matter Core Collapse
Tonghua Liu, Kai Liao, Marek Biesiada et al. (+1 more)
Dark-matter self-interactions can drive subhalos through gravothermal core collapse, but conventional
lensing observables vary continuously with uncertain inner profiles. We show that gravitational-wave image multiplicity provides a discrete alternative. Near a macro-critical minimum, increasing subhalo central convergence opens two caustics in sequence, converting one detectable waveform into three and then five stationary images. Using weighted SASHIMI subhalos and an ET+CE selection model, we forecast almost 2 systems with at least three copies detectable in five years if dense remnants survive, compared with the prediction of 0.36 in 5yrs for standard CDM. The much more diagnostic second case is rare: the corresponding 5yrs yield with at least four detectable copies is 0.149, versus $1.55\times10^{-6}$ for CDM. According to the Poisson statistics, this gives only a 13.8% probability of at least one event detected in 5 years. Thus this is a rare-event, exposure-limited test rather than a guaranteed detection: a resolved second pair would be difficult to reconcile with the fiducial single-
halo CDM population, whereas a five-year null result would not by itself constrain remnant survival strongly.
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All authors Tonghua Liu, Kai Liao, Marek Biesiada, Bing Sun
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Magnetic Reconnection Heating of Thin Accretion Disks around Kerr Black Holes
Zhen Li
The
magnetic reconnection process near a black hole can efficiently convert
magnetic energy into the kinetic and thermal energy of
plasma outflows, enabling the extraction of rotational energy from a spinning black hole. However, its impact on the surrounding
accretion disk remains insufficiently explored. In this work, we develop a framework to investigate the 'heating' effect of
magnetic reconnection outflow
plasma on thin
accretion disks around Kerr black holes. We incorporate the energy and angular momentum fluxes of reconnection outflow into the disk conservation laws as additional source terms, yielding a modified radiative flux. We investigate the dependence of the modified radiative flux on the black hole
spin, reconnection radius,
plasma magnetization, and outflow orientation. For a fixed
magnetic field prescription, the contribution of the reconnection outflow
plasma to the modified radiative flux decreases as the black hole
spin increases. Its dependence on the reconnection radius differs inside and outside the ergosphere: inside, a smaller radius enhances disk heating through more efficient extraction of black hole rotational energy, whereas outside, a larger radius produces stronger heating due to reduced radial dilution of the outflow. The reconnection outflow
plasma contribution also increases with
plasma magnetization and the radial component of the outflow velocity. Our results demonstrate that
magnetic reconnection can provide an additional source of energy and angular momentum for relativistic
accretion disks, establishing a connection between
plasma processes near rotating black holes and the observable
accretion disk properties, providing a new perspective on the strong gravitational field regime.
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Cosmology and Nongalactic Astrophysics
Influence of the large-scale structure velocity field on halo mass assembly within cosmic filaments
Dannaé Díaz-Axtle, Petra Awad, Divya Rana et al. (+1 more)
The
cosmic web governs the growth of dark matter
halos through anisotropic matter flows, yet the role of local velocity-field dynamics in
halo mass assembly remains poorly understood. The velocity field carries non-linear information about matter transport that is not fully captured by density alone, particularly within filaments. We investigate this connection through velocity divergence and vorticity using dark matter
halos in the IllustrisTNG TNG50-1-Dark simulation at $z=0$.
Cosmic filaments are extracted with the 1-DREAM framework, and we statistically study how
halo mass relates to divergence, vorticity, and radial distance from filament spines across three overdensity regimes. The velocity field correlates strongly with the
cosmic web, with converging flows tracing filaments and vorticity arising primarily in overdense, non-linear regions. Within filaments, both divergence and vorticity show enhanced kinematic activity at intermediate distances from the spine, with amplitudes increasing with overdensity. We confirm a clear mass segregation, with more massive
halos preferentially located near filament centers. Most notably,
halos with masses $M \geq 10^{12} M_\odot$ are found almost exclusively in regions of low absolute divergence and low vorticity, while highly dynamical environments are dominated by low-mass
halos. We further find that
halos residing in kinematically calm regions assembled later and maintain higher recent
accretion rates than those in dynamically active environments, linking present-day velocity-field properties to
halo growth histories. These results demonstrate that the local kinematic state of the
cosmic flow encodes information about
halo mass and assembly beyond that contained in density alone, providing a complementary dynamical description of
halo growth within the
cosmic web.
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All authors Dannaé Díaz-Axtle, Petra Awad, Divya Rana, Henk Hoekstra
High Energy Astrophysical Phenomena
The effect of pressure confinement on the maximum mass of rapidly accreting supermassive stars
Lorenz Zwick, Christopher Tiede and Zoltán Haiman
We derive an extension of Chandrasekhar's pulsational stability criterion for relativistic
stars with a pressure boundary condition at the surface. We then apply the new criterion to hylotropes, a model describing rapidly accreting supermassive
stars with a core-envelope structure. We find that confinement typically stabilises
stars, delaying the onset of the general relativistic instability when the external pressure at the surface is roughly $\sim10^{-3}$ of the
stars' hydrostatic pressure scale. Beyond this value, the critical mass at marginal stability increases rapidly, exceeding the value of $\sim 10^5$ M$_{\odot}$ for helium burning, isolated $n=3$ polytropes by orders of magnitude. We discuss how the required pressure boundary conditions may be produced by the combined ram and
magnetic pressure supplied by the
accretion flow as it assembles the supermassive
star, and provide a fitting formula for the final mass before collapse. As a rough estimate assuming equipartition between
magnetic and thermal pressures in a standard $\alpha$-disk, we find that the critical mass doubles at
accretion rates of order $\dot M\sim100\,{\rm M_\odot}\,{\rm yr}^{-1}$, again increasing rapidly after this value. Our results show under what conditions, potentially realized in a subset of high
redshift halos, non-rotating SMS may collapse into black holes beyond the typical scale of heavy seeds.
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Solar and Stellar Astrophysics
MINCE IV. A detailed analysis of 37 metal-poor and subsolar metallicity stars
L. Sgatti, G. Cescutti, L. Lombardo et al. (+13 more)
The project called Measuring at Intermediate
metallicity Neutron-Capture Elements (MINCE) primarily focuses on the photospheric abundances of several
neutron-capture (NC) elements from high-quality spectra of metal-poor
stars within the
metallicity range of ${\rm -2.5 \leq\![Fe/H]\!\leq -1.5}$, aiming to provide homogeneous information on their chemical compositions. Furthermore, based on the Gaia mission, chemical abundances can now be coupled with kinematic properties, enabling investigations of the constituent substructures of the Milky Way. We analyse the fourth sample of MINCE
stars in terms of atmospheric parameters and chemical composition. The results are then compared with the previously analysed MINCE samples. The observations were conducted with HARPS-N (${\rm R \approx 120\,000}$) at the Telescopio Nazionale Galileo (TNG) and FIES (${\rm R \approx 67\,000}$ ) at the Nordic Optical
Telescope (NOT), providing optical spectra with a high signal-to-noise ratio (S/N) and high resolution. We then used the methods developed in previous MINCE works and Gaia photometric data to obtain the stellar atmospheric parameters. The chemical abundances were analysed using 1D-LTE model atmospheres. We present the photospheric abundances in 37
stars of up to 26 elements, including $\alpha$, iron-peak, light-odd, and 10 NC$-$elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu). Kinematic properties and membership assessments are provided for all
stars. The MINCE catalogue is thus expanded by 13 thin-disc
stars, 9 thick-disc
stars, 1
star in a transition zone between the thin and thick disc, 9
stars of the
halo, and 5 Gaia-Sausage-Enceladus
stars. The results agree excellently with previous MINCE works. The comparison with a Gaia Sausage Enceladus GCE model is consistent with the scenario of a major
accretion event on the Milky Way from a dwarf
galaxy.
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All authors L. Sgatti, G. Cescutti, L. Lombardo, C. T. Nguyen, P. Bonifacio, E. Caffau, L. Monaco, R. Lallement, L. Magrini, M. Franchini, C. J. Hansen, A. Mucciarelli, A. Korn, A. Kucinskas, E. Spitoni, S. Lucatello
Cosmology and Nongalactic Astrophysics
2+1 is not 3: Angular bispectrum and Super-Sample Covariance on the light cone
Fabien Lacasa and Julien Grain
Observations of the Large Scale Structure sit on the light cone. Cosmological statistics must then be projected from 3D to angular space. For the bispectrum and higher orders, the polyspectra crucially depend on the angles between
Fourier modes in addition to their moduli. This leads to delicate cancellations in the squeezed limit and make Limber's approximation fail. This is problematic for predicting the Super-Sample Covariance (SSC), with no known full-sky computation of the angle-dependent terms. Here we develop a new analytical approach to the angular bispectrum, writing
Fourier vectors as derivatives that we project on the sphere and tackle with
spin-weighted spherical harmonics. We find bispectrum equations free of cancellations and amenable to beyond-Limber numerical methods. Limber's approximation becomes well-behaved and works in the squeezed limit and any other configuration. We then derive the consequence for the covariance between 1-point (e.g. cluster or peak counts) and 2-point statistics (e.g.
galaxy clustering, weak
lensing or 21cm), which relates to the squeezed bispectrum. The results split into intra-survey covariance and SSC, where we find significant differences with past literature. Our results are in line with the 2+1 geometry of the light cone, having e.g. temporal derivatives in addition to spatial ones. We also find that the tidal term is degenerate with the simpler growth-only term. The total SSC contains a wealth of new terms including wide-angle effects and responses to the background velocity. However we show numerically that it is well approximated by a single term with a density-only response. This ultimately makes our results simpler than past literature. This full-sky result should be more representative than the past flat-sky limit for large survey areas, thus being the one relevant for coming observations with e.g. Euclid, LSST and Roman.
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Cosmology and Nongalactic Astrophysics
Assembly Bias in eRASS1 X-ray Galaxy Clusters: Accounting for Non-uniform Survey Exposure
Jitendra Joshi, Divya Rana and Surhud More
Halo assembly bias describes the dependence of
halo clustering on properties beyond
halo mass and provides a means of connecting
halo assembly history to the large-scale matter distribution. We develop and test a relative clustering methodology for measuring differences in the large-scale bias of two
halo populations using the ratio of their cluster–
galaxy pair counts. In the linear regime, this ratio can be related to the difference in cluster bias, while the
galaxy autocorrelation independently constrains the
galaxy bias. We apply the method to a volume-limited X-ray selected
galaxy clusters from the eROSITA eRASS1 catalogue, dividing them into high- and low-temperature subsamples with matched distributions in X-ray luminosity,
redshift, and exposure. We first verify the validity of the linear approximation, finding $\xi(r)\ll1.0$ over $4$–$10\,h^{-1}\mathrm{Mpc}$. The joint clustering analysis yields $b_{\rm g}=1.610^{+0.018}_{-0.019}$ and a bias difference $\Delta b=0.8\pm1.1$. DES Y3 weak gravitational
lensing measurements provide an independent test of the
halo masses, yielding $\log(M_{200\mathrm{m}}/h^{-1}M_\odot)=14.33^{+0.07}_{-0.07}$ and $14.33^{+0.10}_{-0.09}$ for the high- and low-temperature samples, respectively, with a mass difference of $\Delta\log M_{200\mathrm{m}}=-0.01\pm0.12$. We therefore find no statistically significant evidence for assembly bias at the $1\sigma$ level, but our measurement is consistent with the bias difference measured for analogous
halo populations in the FLAMINGO simulation. The result therefore does not rule out assembly bias at the level expected from the simulation, while demonstrating that the relative clustering methodology provides a framework for future assembly-bias measurements with larger X-ray cluster and
galaxy surveys.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Self-field of a moving string
Richard A. Battye, Lukasz P. Bunio and Steven J. Cotterill
We discuss the effectiveness of the recently proposed quantity $J_{s}$ in suppressing the contribution of a string's self-field to its spectrum, which is used in field theory simulations to track the emission of
axions by decaying
cosmic strings. We compute the contribution of the self-field to the spectrum of this quantity and to the usually computed spectrum of $\phi\partial_{t}\alpha$ for an infinitely long straight string. Although we demonstrate that the $J_s$ approach is a substantial improvement, we also point out that this highly symmetric model doesn't capture the full contribution of the self-field to the spectrum emitted by strings of a more complex shape, which are typical in network simulations. We then illustrate this point numerically using a simulation of a sinusoidally perturbed straight string. For this simple configuration, we managed to separate the contribution from the self-field and the radiation to the spectrum of $J_{s}$, using the self-field subtraction method. This allows us to show that the spectrum of $J_{s}$ is still dominated by the $n=1$ mode of the string's oscillation, which can be attributed to the self-field and is largely suppressed when the self-field is removed. We also demonstrate that this mode is predominantly sourced by variations along the direction parallel to the string, which is missing in the unconnected segment model, used by arXiv:2512.13653 to claim the effectiveness of $J_{s}$ in suppressing the self-field's contribution to the spectrum.
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Instrumentation and Methods for Astrophysics
PYRA and MYTHRA: new statistical analysis for image reconstruction
Julien Drevon, Margaux Abello, Florentin Millour et al. (+2 more)
Image reconstruction in optical interferometry remains a challenging inverse problem due to sparse
Fourier sampling and the strong dependence of the reconstructed images on user-defined parameters. We present PYRA (Python for MiRA) and MYTHRA (Mean Astrophysical Images with PYRA), two tools designed to improve the robustness and reproducibility of interferometric imaging. PYRA automatically generates large ensembles of MiRA reconstructions by exploring a wide range of reconstruction parameters, while MYTHRA statistically analyzes the resulting images to identify the most consistent solutions and derive a final averaged image with associated uncertainty estimates. The methodology is validated using the blind
datasets of the 2024 Interferometric Imaging Contest, where our reconstruction strategy achieved the best overall score. We further apply the method to VLTI/MATISSE observations of the triple AGB system {\pi}1 Gru and the A[e] supergiant 3 Pup. These results demonstrate that statistical analysis of large reconstruction ensembles provides a powerful framework for assessing image reliability and reducing reconstruction artifacts in optical interferometry.
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All authors Julien Drevon, Margaux Abello, Florentin Millour, Anthony Meilland, Armando Domiciano de Souza
Solar and Stellar Astrophysics
SPAMMS: 3D spectroscopic modeling of stellar surfaces. II. Implementation of Kurucz and TLUSTY model atmospheres
D. Galán-Diéguez, M. Abdul-Masih, C. Allende Prieto et al. (+3 more)
Context. Accurate stellar spectra are essential to derive stellar properties. Traditional model atmospheres often oversimplify phenomena that break spherical
symmetry, such as rotational deformation or multiplicity. The Spectroscopic PAtch Model for Massive
Stars (SPAMMS) accounts for these effects, but its applicability has been limited by the spectral types covered by its model atmosphere grids. Aims. We aim to extend the parameter space of the model atmosphere grids available to SPAMMS, enabling spectral synthesis across a broader range of stellar types. Methods. We computed specific intensities, $I\left(\lambda,\mu\right)$, for $101$ emergent angles using PRISMAS (Pipeline of Radiative Intensity Synthesis for Meshed Atmospheric Surfaces), and pre-computed LTE and non-LTE atmospheres from two ATLAS9-Kurucz grids and the TLUSTY-based OSTAR2002 and BSTAR2006 models. Results. The intensity grids cover effective temperatures from $3500$ to $55000\,\mathrm{K}$ and surface gravities from $0.0$ to $5.0\,\mathrm{dex}$, spanning O- to K-type
stars. They include
metallicities from $0$ to $30\,\mathrm{Z_\odot}$ and microturbulent velocities of $1$, $3$, $5$, and $10\,\mathrm{km\,s^{-1}}$. The spectral range extends from $3000$ to $9000\,\mathring{\mathrm{A}}$ with $\Delta\lambda=0.01\,\mathring{\mathrm{A}}$. As a proof of concept, we modelled with SPAMMS a rapidly rotating B-type
star and an eclipsing Algol-type binary. Conclusions. The new LTE-Kurucz and NLTE-TLUSTY grids substantially expand the parameter space accessible to SPAMMS. The code can now generate synthetic spectra for a broader range of stellar types and geometries, including rapidly rotating and multiple systems – providing a more comprehensive framework for modelling non-spherical stellar surfaces.
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All authors D. Galán-Diéguez, M. Abdul-Masih, C. Allende Prieto, S.R. Berlanas, A. Herrero, H. Sana
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Deterministic denoising of long-duration gravitational-wave signal candidates with $\alpha$-(de)blending
Przemysław Figura and Michał Bejger
We present a deterministic machine-learning method for denoising candidate signals from all-sky searches for continuous gravitational waves from rotating
neutron stars. Using the time-domain $F$-statistic search pipeline, we post-process the resulting $F(f,\dot{f})$ candidate patterns with iterative $\alpha$-(de)blending, a deterministic
diffusion-type generative model implemented as a U-Net, well suited to the non-Gaussian, correlated noise of the $F$-statistic output. Two models, trained on data based on simulated 6- and 12-day time-domain segments with software-injected signals similar to the LVK hardware injections, are tested by comparing deblended images to the library of expected signal patterns via the Structural Similarity Index Measure. In general the method recovers the correct sky-position-dependent pattern for signal-to-noise ratios $\rho \gtrsim 4$, moderately below typical all-sky detection thresholds, with recovery depending strongly on pattern morphology, demonstrating that deterministic
diffusion-based denoising may serve as a consistency/veto tool ahead of the semi-coherent coincidence stage. We also discuss limitations and possible improvements of the method.
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Earth and Planetary Astrophysics · Cross-listed from gr-qc
Testing the equivalence principle with lunar laser ranging residuals from different planetary and lunar ephemerides
Jun Ke, Jie Luo, Qin Li et al. (+2 more)
Lunar
laser ranging (LLR) provides a sensitive test of the equivalence principle (EP) through a possible synodic perturbation in the Earth–Moon distance. In this work, we develop an independent LLR data-reduction framework and investigate this signature in the post-fit O–C residuals obtained with the EPM21, INPOP21, and DE430 planetary and lunar ephemerides. The same observation model and parameter-adjustment procedure are applied to the three ephemerides, allowing their residual-based results to be compared within a consistent framework. To account for the nonuniform distribution of LLR observations over the synodic angle $D$, the residuals are fitted with cosine and sine harmonics up to the third order. Signal-injection tests are also performed to quantify the attenuation of a possible $\cos D$ signal during the parameter adjustment. After correcting for signal attenuation, solar radiation pressure, and the thermal response of the lunar retroreflectors, the preferred EPM21, INPOP21, and DE430 solutions yield $\Delta(m_g/m_i)_{\rm EM}=(0.900\pm3.183)\times10^{-14}$, $(0.496\pm3.624)\times10^{-14}$, and $(2.669\pm7.048)\times10^{-14}$, respectively. The EPM21 and INPOP21 results are based on observations from 1970 to 2024, whereas the DE430 solution was obtained using observations up to 2016. All three estimates are consistent with zero within their uncertainties. This work demonstrates that residual-based analysis can provide an independent and transparent EP test, while also offering guidance for assessing sampling and ephemeris-dependent effects in future high-precision LLR studies.
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All authors Jun Ke, Jie Luo, Qin Li, Yu-Jie Tan, Cheng-Gang Shao
High Energy Astrophysical Phenomena
Spectro-polarimetric study of the black hole X-ray binary Swift J1727.8-1613 in the JED-SAD framework
R. Muhammad, P.-O. Petrucci, W. Zhang et al. (+10 more)
Context. Swift J1727.8-1613 is an X-ray binary observed during its 2023-2024 outburst, including bright and dim hard states with similar X-ray polarimetric signatures but fluxes differing by two orders of magnitude. Aims. We aim to reproduce the spectro-polarimetric properties of these two hard states. Methods. We modelled their spectra in the JED-SAD framework and computed the X-ray polarisation properties of the best-fit configurations with the MONK general relativistic radiative transfer code. Results. Both spectra are well reproduced within the JED-SAD framework, although the dominant radiative process differs: self-Comptonised bremsstrahlung in the bright state and self-Comptonised synchrotron in the dim state. In the bright state, the simulated polarisation fraction remains below the observed value of about 4%, while the polarisation angle differs from the observations by 90 degrees because of the JED's large vertical optical depth. In contrast, the dim state's simulated polarisation fraction is about 3% and its polarisation angle is perpendicular to the disk, both broadly consistent with IXPE measurements. The dim-state results are largely insensitive to the
magnetic field configuration because of Faraday depolarisation. Conclusions. The dim hard state's spectro-polarimetric properties are well reproduced, whereas those of the bright state are not. We discuss a non-thermal particle distribution and electron scattering in an
accretion-disk wind as possible explanations for the observed bright-state polarisation.
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All authors R. Muhammad, P.-O. Petrucci, W. Zhang, J. Ferreira, R. Belmont, J. Malzac, G. Marcel, G. Matt, M. Parra, T. Bouchet, N. Barnier, M. Clavel, G. Henri
Astrophysics of Galaxies
Highly Ionized Oxygen in the Circumgalactic Medium of TNG100 Galaxies: Distributions, Thermal States, and Ionization Mechanisms
Yossi Oren, Amiel Sternberg, Christopher F. McKee et al. (+1 more)
We investigate the origin of the highly ionized oxygen species, O VI, O VII, and O VIII, in the circumgalactic medium (CGM) of
galaxies at
redshifts $z \approx 0$, by post-processing the outputs of the Illustris TNG100 simulation alongside analytic modeling. Our computations are broadly consistent with observations, and we provide convenient functional fits for the predicted mean oxygen ion column densities as functions of
halo virial mass. We determine the relative roles of electron impact collisional ionization versus photoionization by the metagalactic radiation field in producing the ions for
halo masses ranging from $10^{10.5}$ to $10^{14.5}$~M$_\odot$. We also determine the thermal gas phases, virialized hot, intermediate temperature, or cool, within which the ions reside. If the
halo virial temperature is below the gas temperature at which the ion fractions are maximal for collisional ionization
equilibrium (CIE), then photoionization dominates the overall CGM ion mass and column density. When photoionization dominates, the ions are produced primarily in the shock heated virialized phase. If the virial temperature is above the gas temperatures at which the ion fractions are maximal for CIE, then collisions dominate the ionization. However, if the virial temperature is much larger than the ion CIE peak temperature a substantial portion of the ion mass may reside within the intermediate temperature phase as opposed to the hot virialized gas. For MW-mass
halos, the O VI and O VII are produced collisionally, and the O VIII by photoionization, all three in the hot, virialized phase.
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All authors Yossi Oren, Amiel Sternberg, Christopher F. McKee, Yakov Faerman
Solar and Stellar Astrophysics
A Self-consistent Model for the Generation of Coronal Condensations: The Effects of Turbulent Wave Dissipation
M. McMurdo, V. Jercic, T. Van Doorsselaere et al. (+1 more)
Prominences and coronal rain are two manifestations of coronal condensations whose formation mechanisms remain only partially understood. While previous studies have explored how localised steady or
stochastic heating can trigger thermal instability and condensations, the role of wave driven energy transport and dissipation has not been extensively investigated. In the solar atmosphere, Alfven and kink waves are an abundant source of energy capable of contributing both to coronal heating and
plasma structuring, making them compelling candidates in the formation processes of the structures we observe in the corona. We aim to explore how Alfven and kink wave energy and their dissipation influence the formation and
evolution of condensations in coronal
magnetic structures. In particular, we investigate each waves role independently of parameterised external heating mechanisms to isolate whether either wave can trigger condensations. We perform 2.5D simulations using the open source MPI AMRVAC code extended with the newly developed UAWSoM module. This module self consistently evolves Alfven and kink wave energy and their feedback on the
plasma through wave pressure and heating terms. We examine the conditions under which condensations form, their morphology, and their dynamical
evolution. Our results show that for our range of parameters, in 2.5D MHD, Alfven waves did not trigger the formation of prominences or condensations. We find that if the radius of the fine scale structures supporting the kink waves is of the order of 100 km, then kink waves can trigger coronal rain that differs considerably in its morphology from coronal rain triggered by parameterised heating functions. Through the use of UAWSoM, we have established that Alfven and kink waves leave distinct thermodynamic signatures on coronal loops, given the same wave energy injection.
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All authors M. McMurdo, V. Jercic, T. Van Doorsselaere, C. Froment
Astrophysics of Galaxies
The WISSH quasars project XIII. A multi-epoch study of ultra-fast broad absorption line outflows at cosmic noon
A. Deconto-Machado, G. Vietri, E. Piconcelli et al. (+22 more)
Ultra-fast broad absorption line outflows (uBAL, ~0.1-0.2c) represent some of the most extreme manifestations of
quasar-driven winds. We aim to investigate the variability of uBALs through their characterisation across different epochs and multiple ionic species. The main goal is to constrain their physical properties, locations, and kinetic powers to evaluate their potential impact on the respective
quasar host
galaxies. We performed a multi-epoch analysis of three hyper-luminous
quasars from the WISSH sample, namely WISSH53, WISSH56, and WISSH71, at
redshifts z=3.628, 4.101, and 3.567, respectively. New and archival spectra, spanning up to ~23 years of monitoring in the observed frame, were used in the analysis. We modeled absorption associated with the CIV transition with Gaussian components, accounting for covering factor variations. A conservative analysis of multi-ion profiles (PV, Lyalpha, NV, SiIV) was also performed, considering the same uBAL velocity as CIV. We derived ionic column density, as well as ionisation parameters, which allowed us to estimate lower and upper limits on distances and kinetic powers of the outflows. The CIV uBALs in the three sources exhibit velocities up to ~0.2c and show significant variability across epochs, likely driven by changes in ionisation state and/or transverse gas motion. The analysis of the multiple troughs highlights the dominant mechanisms causing variability and enables the derivation of robust lower and upper limits of the physical and energetic properties of the outflows. Outflow distances are constrained from the broad line region (BLR) radius (~1 pc) up to a few hundred parsecs, and kinetic powers of individual troughs reach up to ~25% of the
quasar bolometric luminosity, in the most extreme cases. Our results demonstrate that extreme outflows such as the uBALs are able to inject sufficient kinetic energy to affect the host medium.
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All authors A. Deconto-Machado, G. Vietri, E. Piconcelli, S. Bisogni, T. Misawa, A. Gargiulo, G. Lanzuisi, A. Travascio, M. Bischetti, L. Zappacosta, E. Bertola, G. Cresci, F. la Franca, M. Gaspari, F. Salvestrini, C. Vignali, A. Luminari, E. Marini, F. Tombesi, A. Bongiorno, S. Carniani, C. Feruglio, F. Fiore, E. Glikman, V. Testa
Solar and Stellar Astrophysics
A new method to cleanly separate hot and cool populations using just Gaia and 2MASS photometry
J. Maíz Apellániz and M. Pantaleoni González
We have developed a photometric method that produces clean hot (intrinsically blue) populations using Gaia and 2MASS photometry alone with [a] a very small (false positives < 1%) contamination from cool (intrinsically red) luminous sources, [b] independent of extinction (limited only by S/N), and [c] with only small losses (false negatives < 10%) of real OB
stars. Applying the method to Gaia DR3 data we are able to recover extinguished OB
stars down to E(G_BP-G_RP) = 5, producing a catalog of ~2x10^5 candidate OB
stars that reaches beyond the Scutum-Centaurus arm. This method can potentially extend the sample of known OB
stars by an order of magnitude, which would yield a large leap in our knowledge of the populations of compact-object progenitors, including gravitational-wave sources.
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High Energy Astrophysical Phenomena
Discovery of Two Consecutive Profile Change Events in the Millisecond Pulsar PSR J0437-4715
Rami F. Mandow, Andrew Zic, J. R. Dawson et al. (+19 more)
The closest and brightest millisecond
pulsar (MSP), PSR J0437-4715, is a high-priority
pulsar for precision timing experiments, including the Parkes
Pulsar Timing Array (PPTA) project, where it is used for both
pulsar timing and for polarization calibration. Using approximately seven years of observations obtained with the Ultra-Wideband Low-Frequency receiver on Murriyang, CSIRO's Parkes
radio telescope, we investigate the long-term spectro-polarimetric variability of PSR J0437-4715. We report the discovery of two consecutive discrete profile change events exhibiting the same phase-localised morphological variations, the first such behaviour reported in any MSP. Both events affect three phase-localised regions of the pulse profile that exhibit coupled and anti-correlated temporal
evolution. We also identified, and corrected for, systematic profile variability induced by polarization calibration errors arising from long-term drift of the polarimetric properties of the receiver. The profile change exhibits frequency-dependent
evolution in total intensity, together with variations in linear polarization, position angle and fractional linear polarization. These results confirm a magnetospheric origin for the events rather than propagation effects caused by the interstellar medium, and provide potential new constraints on MSP emission models.
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All authors Rami F. Mandow, Andrew Zic, J. R. Dawson, Shuangqiang Wang, Małgorzata Curyło, Bhavnesh Bhat, Michael J. Keith, N. D. Ramesh Bhat, Emma Carli, Shi Dai, Valentina Di Marco, Simon C.-C. Ho, Agastya Kapur, Wenhua Ling, Marcus E. Lower, Bradley W. Meyers, Saurav Mishra, D. J. Reardon, Sparrow Roch, Karolina Rozko, Christopher J. Russell, R. M. Shannon
High Energy Astrophysical Phenomena
Physics-Informed Neural Networks and Data-Driven Models for GRB X-ray Light-Curve Gap Reconstruction
Ayush Garg, Ritik Kumar, Maria G. Dainotti et al. (+3 more)
Temporal gaps in Swift-XRT X-ray afterglows of gamma-ray bursts (GRBs) limit how precisely the standard empirical plateau function constrains three parameters: the plateau end time $T_a$, the plateau flux $F_a$, and the post-plateau decay index $\alpha$. These parameters underpin the luminosity-time and fundamental-plane correlations of GRB plateaus so that smaller measurement uncertainties can improve the statistical power of GRBs as cosmological probes. As the fifth study in a series on light-curve reconstruction, this work
benchmarks four models on a parent sample of 545 Swift-XRT GRBs: a Physics-Informed Neural Network (PINN) with seven afterglow-motivated priors, ReFANN, a Siamese dual-branch network with Monte Carlo dropout, and
Polynomial Quantile Regression (PQR). All four reduce the fractional uncertainties in $\log T_a$, $\log F_a$, and $\alpha$ relative to the original observations. The PINN with a broken power-law prior gives the largest reductions ($\sim$41-49%), at a higher outlier rate ($\sim$15-20%), while ReFANN, Siamese network and PQR give more modest reductions ($\sim$19-27%) with outlier fractions $\lesssim$4%, across a wider range of light-curve morphologies. A reduced-$\chi^2$ prior-selection scheme recovers a morphological classification consistent with independent labelling, though it does not match the best single-prior reduction. Together, these results provide a systematic
benchmark of physics-informed and data-driven reconstruction strategies for irregularly sampled GRB afterglows.
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All authors Ayush Garg, Ritik Kumar, Maria G. Dainotti, Vipul Sharma, Amit Shukla, Dieter H. Hartmann
Solar and Stellar Astrophysics
Results on young stellar clusters with the WEAVE LIFU
J. Maíz Apellániz, G. Holgado, C. Fariña et al. (+1 more)
We present the first results of two Spanish TAC programs using the WEAVE LIFU that have been obtaining data since October 2023. The first one is obtaining high-resolution multi-epoch spectroscopy of the nine stellar clusters that contain a minimum number of 3 O-type
stars (and many more B
stars) within the field of view of the WEAVE LIFU and that are accessible from La Palma with the purpose of studying the spectroscopic multiplicity of the OB
stars. The second program is obtaining single-shot low-resolution spectroscopy of as many stellar clusters with OB
stars as possible with the purpose of characterizing the OB-
star population in those regions that are too crowded to be properly studied with the guaranteed time SCIP program. That program has already observed 54 clusters in a wide range of environments, from H II regions to gas-free clusters, and distances, from clusters in the solar neighbourhood to (nearby) extragalactic systems. We also present the tools developed for this program, which include a data cube processing and visualisation utility and UNWIND, a code that fits and subtracts the ISM signature in the observed spectra.
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All authors J. Maíz Apellániz, G. Holgado, C. Fariña, S. R. Berlanas
Solar and Stellar Astrophysics
Riemann Map Operator for Solar Front Diagnostics
Olena Podladchikova
Identifying a shock from a moving solar brightness front requires relating the observed emission to changes in the
plasma state. The Riemann framework describes shocks, rarefactions and other waves as parts of a pattern connecting different states. We present the Riemann Map Operator (RMO), an inverse diagnostic framework implemented as a web application to help observers identify magnetohydrodynamic (MHD) shock families from incomplete measurements. RMO tests candidate local connections against conservation laws,
entropy requirements and characteristic conditions, while retaining observational uncertainties and model assumptions. We demonstrate the approach with five solar examples and a complementary in-situ comparison. An event combining extreme-ultraviolet (EUV) imaging and spectroscopy admits both fast and slow shock connections within the tested conditions. For an EUV-
radio event, we derive an upstream-flow constraint that would exclude ordinary slow shocks within the adopted model, provided both diagnostics sample the same front. A
flare-loop
benchmark reproduces the published spectral profiles and recovers slow-shock ordering in the isothermal limit. The Solar Orbiter comparison recovers an Alfvenic relation between measured velocity and
magnetic-field changes. Together, the examples show how RMO connects observations to admissible MHD interpretations and identifies the additional measurements needed to distinguish them.
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Instrumentation and Methods for Astrophysics
FOSSIL: Thermo-mechanical architecture
Valentin Sauvage, Clémence de Jabrun, Sylvain Martin et al. (+13 more)
FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) is a proposed ESA M8 mission tailored to measure the spectral distortions of the
Cosmic Microwave Background (CMB) with a sensitivity three orders of magnitude beyond the COBE/FIRAS legacy measurement. Achieving this sensitivity demands an extraordinarily challenging cryogenic architecture: the scientific instrument must be maintained at the lowest achievable temperature (4.5 K), while the detector focal plane assembly operates at 50 mK. This paper presents the thermal architecture of the FOSSIL payload and instrument, from the spacecraft service module at 293 K down to the sub-kelvin detector stage. The thermal design draws on heritage from the Planck and ARIEL missions and relies on a staged passive cooling chain comprising a multi-layer insulation blanket, three V-groove radiators (operating at approximately 130 K, 90 K, and 50 K), and a 25 K actively cooled shield fed by an ESA-provided 4 K cryocooler chain. Sub-kelvin temperatures are achieved via a multi-stage adiabatic demagnetisation refrigerator (ADR) system developed for NewAthena/X-IFU, providing continuous cooling at 1.8 K and 350 mK, and 50 mK with an 80% duty cycle. The Focal Plane Assembly (FPA), which houses four Kinetic Inductance Detector (KID) arrays at 50 mK, is thermally isolated from the 4.5~K bench via a carbon-fibre reinforced
polymer (CFRP) hexapod structure with staged heat interception. We present the steady-state thermal budget across all stages, demonstrating comfortable margins at every temperature level, and discuss key thermal design drivers on the Blackbody Internal Reference (BBIR).
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All authors Valentin Sauvage, Clémence de Jabrun, Sylvain Martin, Bruno Maffei, Nabila Aghanim, Anaïs Besnard, Bruno Borgo, Ivan Charles, Xavier Coulon, Sandrine Couturier, Francesco Cuttaia, Jean-Marc Duval, Morgane Loquet Le Gall, Giorgio Savini, Luca Terenzi, Berend Winter
Earth and Planetary Astrophysics
Spectral Evolution of Ceres' Surface and Implications for Space Weathering
Qing Zhang, Jian-Yang Li, Yazhou Yang et al. (+2 more)
The surface of Ceres exposed to the space environment will be gradually altered, but the
evolution of its spectral properties remains poorly understood. Here we analyze visible and infrared spectra acquired by the Dawn mission to investigate spectral variations across different surface units. We identify local shifts of a few nm toward shorter wavelengths in the 2.7 $\mu$m band center, predominantly associated with freshly exposed slumping and impact materials. Our analysis suggests that compositional variations in Ceres' regolith are unlikely the explanation for the band center shift, and therefore it may represent a spectral
evolution within 10$^6$ years. Combining previous studies about the spectral reddening on Ceres, we propose a two-stage spectral
evolution on Ceres. The blue-shifted regions are interpreted as the youngest materials. Within 10$^6$ years after exposure, these materials become spectrally bluer, the 2.7 $\mu$m band weakens, and its center shifts toward longer wavelengths. Then the
evolution is characterized by spectral reddening and strengthening of the 2.7 $\mu$m band without the band center shift. Based on the previous laboratory work and observations on other C-complex asteroids, we suggest that the observed spectral variations may be attributed to the chemical and/or physical changes of the regolith, possibly associated with space weathering.
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All authors Qing Zhang, Jian-Yang Li, Yazhou Yang, Minge Liu, Yang Liu
Astrophysics of Galaxies
A comparative analysis of the long-term optical variability characteristics of narrow and broad-line Seyfert 1 galaxies at z > 0.8
Aratrika Dey, Stalin C.S., Akshith S. et al. (+1 more)
We present the results on a comparative analysis of the long-term optical variability characteristics of high-
redshift narrow-line Seyfert 1 (NLSy1)
galaxies and broad-line Seyfert 1 (BLSy1)
galaxies. Our sample spanning the
redshift range of $0.8 < z < 2.6$, comprises 2490 NLSy1 and 2490 BLSy1
galaxies matched in the optical brightness$-$
redshift plane. We used V-band data from the Catalina Real-Time Transient Survey covering a baseline of 5$-$9 years, and g, r, and i-band data from the Zwicky Transient Facility spanning 5 to 6 years. To characterise variability we estimated the amplitude of variability ($\sigma_m$). We found that NLSy1
galaxies generally exhibit lower $\sigma_m$ compared to BLSy1
galaxies. In both the NLSy1 and BLSy1
galaxy samples, we observed a wavelength dependent variability using data from Zwicky Transient Facility, with $\sigma_m$ gradually increasing towards shorter wavelengths. We found an anti-correlation between $\sigma_m$ and Eddington ratio in the g, r, and i bands for BLSy1
galaxies, whereas this anti-correlation is observed only in the r and i bands for NLSy1
galaxies. For both NLSy1 and BLSy1
galaxies, we found no correlation between $\sigma_m$ in g, r, and i bands and black hole mass. In both the samples, we found that $\sim$90% of the sources showed a bluer when brighter trend. We found no significant time lag between variations in g and r bands in both BLSy1 and NLSy1
galaxies. The observed long-term trends in the optical light curves of our high
redshift sample of BLSy1 and NLSy1
galaxies could be driven by variations in the
accretion disk.
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All authors Aratrika Dey, Stalin C.S., Akshith S., Suvendu Rakshit
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Did LZ see modified gravity?
Basabendu Barman
We investigate whether the recently reported high-energy nuclear recoil event by the LUX-ZEPLIN (LZ) collaboration can be interpreted as a signal of freeze-in dark matter (DM) in a non-standard cosmological history. We consider DM production from the Standard Model thermal bath during an era of modified expansion preceding Big Bang nucleosynthesis. Requiring consistency with the observed DM abundance, cosmological and
collider constraints, we identify viable parameter regions that can accommodate the LZ event. Our results demonstrate the potential of direct detection experiments to probe non-standard cosmological histories and, more broadly, alternative theories of
gravity.
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Instrumentation and Methods for Astrophysics
Nii-MALA: A Fast Metropolis-Adjusted Langevin Sampler with Radial Velocity Benchmarks
Jian Jiao, Sheng Jin, Wenxin Jiang et al. (+1 more)
Markov chain Monte Carlo is widely used for model assessment and parameter fitting in astronomy and astrophysics, leading to numerous ready-to-use packages implementing various sampling techniques. For large-scale analyses involving many individual targets, computational efficiency becomes paramount, as it dictates the overall runtime. We introduce Nii-MALA, a high-performance C implementation of the Metropolis-Adjusted Langevin
Algorithm, which leverages Message Passing Interface for parallelization and incorporates automatic differentiation backends for gradient evaluation. The code offers flexible control via a configuration file, allowing users to specify the proposal step sizes for all model parameters across parallel chains. We validate its effectiveness on 15- and 30-dimensional Gaussian distributions and a bimodal distribution, and further
benchmark it against several other codes using radial velocity data from 51 Pegasi b. Our
benchmarks confirm the efficiency of Langevin sampling over random-walk sampling in obtaining the effective sample size, particularly as the dimensionality of the target function increases. This algorithmic advantage can be effectively leveraged when paired with an efficient automatic differentiation library. However, for complex functions commonly encountered in astronomy—such as radial velocity orbital fitting—the derivative-dependent Langevin sampler shows lower efficiency than parallel tempering or alternative sampling approaches, as revealed by effective sample size analysis.
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All authors Jian Jiao, Sheng Jin, Wenxin Jiang, Dong-Hong Wu