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Physics Astrophysics

astro-ph Watch Astrophysics

Sunday 5 July

Cosmology and Nongalactic Astrophysics

KiDS-Legacy: The consistency test of the large-scale structure with Bernardeau-Nishimichi-Taruya transform

Shiming Gu, Ziang Yan, Ludovic van Waerbeke et al. (+10 more)

We perform the first $k$-cut cosmic shear analysis of the KiDS-Legacy survey. This method uses the Bernardeau-Nishimichi-Taruya (BNT) transform to construct weak-lensing kernels that are more localised than conventional ones, and remove information from selected physical scales while retaining the constraining power of the targeted range. Removing the scale of $k \geq 0.33~\mathrm{Mpc}^{-1}$ from the KiDS-Legacy pseudo-$C_\ell$ data vector, and using a covariance matrix whose Gaussian component is computed from the theoretical data vector, we find $S_8 = 0.798 \pm 0.045$. This agrees with both the fiducial KiDS-Legacy bandpower result and our no-$k$-cut pseudo-$C_\ell$ posterior to within $0.1\sigma$, indicating no significant bias from nonlinear astrophysical feedback at the precision of KiDS-Legacy. We also study the case in which the Gaussian covariance is computed from the observed data vector. In this setup, the same scale cut of $k < 0.33~\mathrm{Mpc}^{-1}$ gives a much lower $S_8=0.717_{-0.046}^{+0.047}$. Further $k$-cut tests reveal a mild scale-dependent trend, with larger physical scales preferring lower $S_8$ values and a maximum low- versus high-$k$ deviation of $1.80\sigma$. Mock tests show that this behaviour is not produced by the covariance prescription or data vector alone, but may arise from their interplay. These results show that BNT $k$-cuts provide both a mitigation strategy for nonlinear systematics and a diagnostic of weak-lensing inference pipelines.
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All authors Shiming Gu, Ziang Yan, Ludovic van Waerbeke, Francis Bernardeau, Hendrik Hildebrandt, Angus H. Wright, Maciej Bilicki, Christos Georgiou, Shun-Sheng Li, Laila Linke, Lauro Moscardini, Robert Reischke, Benjamin Stölzner

High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

Particle dynamics in nonlinear electromagnetic waves: chaos onset, diffusive heating, and wave surfing

Maxim Lyutikov

We investigate the dynamics of charged particles interacting with ultra-intense electromagnetic X-modes in strongly magnetized plasmas. We demonstrate that particle motion becomes chaotic for relative wave intensities $\delta = B_w/B_0 \gtrsim 0.25$ (not above the field reversal threshold $\delta \geq 1$). The transition to chaos occurs via the Chirikov resonance overlap mechanism and the related destruction of Kolmogorov-Arnold-Moser (KAM) tori. The maximum Lyapunov exponent increases logarithmically with $\delta$, even though the unmagnetized $\delta \to \infty$ limit is strictly integrable. In the $\delta \gg 1$ regime, incomplete re-laminarization of the phase space flow leads to two distinct populations: (i) the majority of particles undergoing stochastic diffusion, and (ii) a fraction of particles that become phase-locked with the wave, experiencing macroscopic intermittent surfing (Lévy flights). The 1D Particle-In-Cell simulations using the EPOCH code in the highly magnetized ($\sigma \gg 1$) and under-dense regime are generally consistent with the Hamiltonian single-particle theory. The dissipation fraction of the initial EM energy remains mild.
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Astrophysics of Galaxies

Radio Activity Across Accretion State Changes in Changing-look AGNs: Insights from FIRST and VLASS over Two Decades

Zhi-Qiang Chen, Wei-Jian Guo, Victoria A. Fawcett et al. (+8 more)

Changing-look active galactic nuclei (CL-AGNs) provide a unique opportunity to probe the coupling between accretion flows and relativistic jets in supermassive black holes. We investigate the long-term radio behavior of CL-AGNs over approximately 20 years by combining FIRST and VLASS observations with quasi-simultaneous optical spectroscopy and photometry. From a parent sample of 1092 CL-AGNs, we identify 58 sources with radio detections. Radio-detected CL-AGNs exhibit systematically higher radio kinetic efficiency, quantified by \(P_{\rm j}/L_{\rm bol}\), than both typical radio-detected AGNs and radio transients, consistent with their preference for low Eddington ratios. At the population level, the expected anti-correlation between radio emission and accretion rate is weak. However, a clear source-by-source anti-correlation emerges in a small subset of CL-AGNs with continuous multi-epoch coverage. We further identify four radio transients, including both radio turn-on and turn-off events, and one source exhibiting a multiwavelength flare that may be indicative of tidal disruption event-like activity. These results suggest that radio activity in CL-AGNs is not governed by instantaneous accretion state changes but is instead regulated by long-term accretion history and jet evolution, with additional stochastic or transient channels contributing in rare cases.
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All authors Zhi-Qiang Chen, Wei-Jian Guo, Victoria A. Fawcett, Jun-Jie Jin, Wen-Ke Ren, Heng-Xiao Guo, Min-Feng Gu, Yan-Mei Chen, Lu Feng, Hu Zou, Qi-Rong Yuan

Astrophysics of Galaxies

Euclid Q1 reveals spatial variations of the extinction law in the dense cloud LDN 1641

Rui Chen, Shu Wang, Xiaodian Chen et al. (+1 more)

Dust extinction laws are essential for precision photometry and provide a direct probe of grain properties, but their behaviour in dense molecular clouds remains poorly constrained at high extinction. Using Euclid Quick Data Release 1 (Q1) imaging of the Orion A dark cloud Lynds Dark Nebula 1641 (LDN 1641), we measured the extinction law from the broad Visible Instrument (VIS) band and the Near-Infrared Spectrometer and Photometer (NISP) $Y$, $J$, and $H$ bands along sightlines reaching $A_V\sim 30$ mag towards the cloud core. We derived colour-excess ratios $E(\lambda-H)/E(Y-H)$ from linear fits to colour–colour diagrams of $(\lambda-H)$ versus $(Y-H)$ and converted them into relative extinctions, $A_\lambda/A_H$. The near-infrared extinction in LDN 1641 is well described by a power law, $A_\lambda\propto \lambda^{-\alpha}$, with $\alpha=1.57 \pm 0.06$, corresponding to $A_{\rm VIS}/A_H=4.23 \pm 0.24$, $A_Y/A_H=2.13 \pm 0.18$, and $A_J/A_H=1.47 \pm 0.11$. We further find significant spatial variations: $\alpha$ changes by up to $27\%$, with systematically smaller values and therefore flatter extinction curves in higher-extinction regions. This flattening is consistent with an enhanced large-grain population and supports substantial grain growth from the diffuse outskirts to the dense core of a single molecular cloud.
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All authors Rui Chen, Shu Wang, Xiaodian Chen, Kun Wang

Earth and Planetary Astrophysics

Assessing the Impact of Varying HSO Cross Sections on Photochemical Models: Implications for the Spectral Characterization of Terrestrial Exoplanets

Alexandre Branco, Clara Sousa-Silva, Wynter Broussard et al. (+5 more)

Characterization of exoplanet atmospheres requires a close interplay between observations, modelling and experimental data. The accuracy of input data used in atmospheric models is essential, as it impacts our interpretation of planetary spectra with retrieval codes. Molecular absorption cross sections in the Ultraviolet-Visible range are fundamental input parameters, determining chemical kinetics, particularly on temperate terrestrial planets. However, several atmospheric species remain poorly, or even entirely uncharacterised. This is the case for HSO, a radical with unconstrained photolysis cross sections, often approximated by hydroperoxyl (HO2). Sulphur chemistry can strongly influence the composition of rocky exoplanets, particularly in anoxic environments where volcanic SO2 – the main source of HSO – is more efficiently photolysed, and sulphur aerosols like S8 can form. HSO photolysis contributes to the formation of such sulphur chains, which have been proposed as indirect signatures of volcanic outgassing. Assessing the sensitivity of photochemical models to different UV-Visible cross-section prescriptions for HSO is therefore important for guiding its prioritization among poorly characterised atmospheric species. Here, we derive an updated HSO cross-section prescription from simulated HSO2 data, providing a more reliable representation of HSO photolysis than HO2. We compare results from these new cross sections to the default prescription for temperate terrestrial planets with Archean-like atmospheres. We find that our updated HSO cross-section prescription enhances aerosol scattering and absorption signatures in transmission, emission and reflection spectra for planets orbiting G- and K-type stars.
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All authors Alexandre Branco, Clara Sousa-Silva, Wynter Broussard, Edward W. Schwieterman, Sukrit Ranjan, Vera Topcik, Olivier D. S. Demangeon, Pedro Machado

Instrumentation and Methods for Astrophysics

A 3D-Printed Millimeter-Wave Inline Waveguide-to-Coplanar-Waveguide Transition to Enable Dense Spectrometer Arrays for Intensity Mapping Surveys

Austin Stover, Juliang Li, Peter Sharpe et al. (+4 more)

We present a 3D-printed millimeter-wave, octave-bandwidth, in-line waveguide-to-coplanar-waveguide transition designed to enable focal planes with dense arrays of on-chip spectrometers. These arrays will enable compelling surveys of the large-scale structure of the universe through millimeter-wave intensity mapping. The transition consists of a four-step ridge-waveguide transformer that couples light from a rectangular waveguide onto a coplanar waveguide via an electrical connection made with indium bump bonds. We develop a tolerance-aware optimization approach to identify high-performance transition geometries that are robust to manufacturing variations; the same formulation can be applied to other tolerance-sensitive design problems. We also describe the implementation of a custom apparatus and procedure for bump-bonding a silicon chip to a metallized 3D-printed component. We detail the fabrication of the coplanar waveguide chip and three-dimensional waveguide structure, simulations and metrology of a test device, and room temperature reflectance measurements of this device. The room temperature metrology and reflection measurements are consistent with a model that predicts a coupling efficiency of $\mathord{\sim} 95\%$ at cryogenic temperatures in the 85-170 GHz frequency range.
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All authors Austin Stover, Juliang Li, Peter Sharpe, Morgana Iacocca, Audrey Scott, Jessica Zebrowski, Jeff McMahon

Astrophysics of Galaxies

Measurements of magnetic fields in circumnuclear matter with the SKA telescopes

Satoko Sawada-Satoh and Yuki Kudoh

Magnetic fields are thought to regulate the angular momentum transfer in active galactic nuclei (AGNs), yet their strength and structure in circumnuclear regions remain poorly constrained across spatial scales and gas phases. We present a unified observational framework for probing circumnuclear magnetic fields using complementary diagnostics: direct measurements via the Zeeman effect in HI absorption and megamaser emission, and indirect constraints from broadband Faraday rotation of polarized continuum radiation. These approaches provide access to magnetized gas spanning spatial scales from ~100 parsec (pc) circumnuclear disks down to sub-pc regions near supermassive black holes (SMBHs). The Square Kilometre Array (SKA) telescopes are expected to revolutionize such investigations through their outstanding sensitivities, wide frequency ranges and high spatial resolutions achievable via very long baseline interferometry (VLBI). These capabilities will enable the detection and detailed characterization of weakly polarized emission from magnetized circumnuclear matter, which has remained largely inaccessible with current instruments. In this chapter, we review previous measurements of magnetic fields in galactic nuclei and discuss the breakthroughs that SKA observations are expected to provide in elucidating the physical conditions and processes shaping AGN environments.
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Astrophysics of Galaxies

There and back again: the quasi-interstellar objects

John C. Forbes, Michele T. Bannister, Chris Lintott et al. (+1 more)

A population of interstellar objects (ISOs) exist that originate from the Solar System, rather than from other stars. Such a foreground could challenge straightforward analysis of the ISO sample expected to be gathered by upcoming sky surveys. We assess whether small bodies unbound from the Solar System can experience dynamical evolution in the Galactic potential that places them on re-encounter trajectories. We find that these 'quasi-interstellar objects' (quasi-ISOs) primarily depart the Solar System through erosion of the outer Oort cloud in the past few hundred Myr, excluding the most recent ~10 Myr. After orbiting in the Milky Way potential nearby the Sun but beyond the tidal radius, those ejected on certain orbits can re-encounter the Solar System. Meanwhile, the larger population of ISOs produced by the Solar System early in its life will be too spread-out in the Galaxy to contribute significantly to the observed sample. We predict that quasi-ISOs will be intrinsically rare and have $v_\infty$ values of order 0.1 km s$^{-1}$, easily distinguishable from ISOs from other stars, meaning that the observed ISO sample will be truly Galactic. The detection of a quasi-ISO would imply larger-than-expected losses from the Oort cloud, or a particularly catastrophic erosion event 10-300 Myr ago that would not be detectable any other way.
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All authors John C. Forbes, Michele T. Bannister, Chris Lintott, Matthew J. Hopkins

Instrumentation and Methods for Astrophysics

The Amerigo Vespucci as a traveling laboratory for studying the cosmic-ray fluxes at sea level

Davide Cerasole, Federica Cuna, Gaia De Palma et al. (+13 more)

We have installed and operated a plastic scintillator detector counter to measure the flux of cosmic radiation during the 2023-2025 tour of the historical vessel Amerigo Vespucci. The Vespucci is the oldest ship of the Italian Navy and serves as a training vessel for Navy cadets. During its tour, some experiments were hosted onboard the vessel, providing unique opportunities for scientists working in different fields. We installed our detector upon the Vespucci's departure from Darwin in early October 2024. The detector collected cosmic-ray data during the journey from Darwin to Trieste, where the worldwide tour ended in March 2025. After about one month of stop in Trieste, the ship continued its tour in the Mediterranean sea, and arrived in Genova on June 10, 2025. We performed measurements of the cosmic radiation reaching the sea level across a wide latitude range, from 15{\deg} S to about 45{\deg} N. The lowest rate (averaged over all azimuth angles) was measured at a geographic latitude of about 7{\deg} N, and was about 16% less than the highest value, which was measured at Trieste, the northernmost location of the journey. Latitude effects on the cosmic radiation flux at sea level are due to the quasi-dipole geomagnetic field configuration, tilted by an angle of about 11{\deg} with respect to Earth's rotational axis.
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All authors Davide Cerasole, Federica Cuna, Gaia De Palma, Riccardo Di Tria, Leonardo Di Venere, Fabio Gargano, Mario Giliberti, Francesco Licciulli, Antonio Liguori, Pierpaolo Loizzo, Francesco Loparco, Leonarda Lorusso, Mario Nicola Mazziotta, Giuliana Panzarini, Roberta Pillera, Davide Serini

Solar and Stellar Astrophysics

Probing Flare-Associated Eruptions on AB Doradus via X-ray Absorption Variations

Shweta Didel, Jeewan C Pandey and Abhishekh K Srivastava

In this work, we investigate eruptive phenomena associated with X-ray flares on AB Doradus using observations from XMM-Newton. Our aim is to detect such events with the help of continuous X-ray absorption. The variation in the hydrogen column density (NH) is used as a primary diagnostic to detect such absorption or spectral hardening in the soft X-ray band below 1 - 2 keV. These variations may represent the signatures of the eruptive processes associated with flares, such as stellar prominences, failed eruptions, or coronal mass ejections. We applied time-resolved spectroscopy technique to track changes in the absorption parameter during flaring episodes. Our analysis shows statistically significant enhancements in the NH, spanning from 0.3 - 3.4 x 10^20 cm^-2 during the flare and post-flare intervals. Out of six data sets, two sets containing multiple-overlapped flares show significant fluctuations and remaining showed no such variations in NH. These variations indicate the presence of dynamic absorbing material along the line of sight and point to ongoing physical processes within the stellar corona.
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Instrumentation and Methods for Astrophysics

Star-forming clump detection in nearby galaxies using Faster R-CNN and $ugrizy$ imaging data from CLAUDS and HSC-SSP

Jürgen J. Popp, Hugh Dickinson, Stephen Serjeant et al. (+4 more)

Giant Star-forming Clumps (GSFCs) are kpc-scale regions of enhanced star-formation with stellar masses of $10^7$ to $10^9\,M_\odot$ that are commonly observed in high-redshift galaxies but are rarely detected in low-redshift ($z\lesssim0.5$) galaxy analogues. However, the availability of wide-field galaxy survey data makes it possible to identify potential star-forming clumps in large samples of low-redshift galaxies using object detection models that are based on Deep Learning (DL) techniques. We apply a novel DL-based object detection model to galaxies observed by the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) and CFHT Large Area U-band Deep Survey (CLAUDS). Our model is based on the the Faster Region-Based Convolutional Neural Network (Faster R-CNN or FRCNN) object detection framework but expanded to process the six $ugrizy$ filter band images simultaneously and identify not only clumps and their locations in the host galaxy but also additional contaminants. By adopting the Zoobot foundation DL-model as a feature extraction backbone, we also demonstrate one of the first applications of Zoobot in a downstream task for object detection. Our model achieves a detection completeness of $\gtrsim 0.9$ and purity of $\gtrsim 0.8$ which were validated on a large set of real galaxies into which simulated clumps were injected.
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All authors Jürgen J. Popp, Hugh Dickinson, Stephen Serjeant, Lucy F. Fortson, Tobias Géron, Brooke D. Simmons, Vihang Mehta

Solar and Stellar Astrophysics

Testing an Ap-like Magnetic Braking Origin for the Extended Main Sequence in Young Open Clusters

Chengyuan Li

Young open clusters commonly exhibit extended or split upper main sequences, which are widely interpreted as signatures of broad, and in some cases bimodal, stellar rotation distributions. The physical origin of the component commonly associated with slow rotation in this framework remains debated. One proposed channel invokes merger-induced magnetic braking analogous to that seen in Ap stars, which predicts that a large fraction of the relevant stars should host strong, stable surface magnetic fields and exhibit the Ap-like chemical peculiarity responsible for the characteristic $5200\,\mathrm{\AA}$ flux depression. We test this prediction using Gaia XP spectra of A-type stars in a sample of eight young open clusters and a diagnostic of the $5200\,\mathrm{\AA}$ flux depression. If Ap-like magnetic braking made a dominant contribution to the extended main-sequence phenomenon, a substantially enhanced incidence of $5200\,\mathrm{\AA}$ depression would be expected. Instead, we find no evidence for such a large excess. These results disfavour Ap-like magnetic braking as the dominant explanation for the extended main sequence in young open clusters, while leaving open magnetic or non-magnetic channels that would not produce a clear Ap-like $5200\,\mathrm{\AA}$ signature.
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Astrophysics of Galaxies

Set them free: extending RAMCOAL to model massive black hole triplets in hydrodynamical simulations of galaxies

Kunyang Li, Ricarda S. Beckmann, Yohan Dubois et al. (+1 more)

Massive black hole binaries (MBHBs), and the higher-order multiples produced by repeated galaxy mergers, spend part of their lives in dynamical regimes that cosmological simulations cannot resolve, even though these regimes set their merger delays, spins, recoils, and host-galaxy context. We extend the RAMCOAL framework to follow such subgrid massive black hole triplets directly within hydrodynamical galaxy simulations. As in the original staged binary model, the black holes start as sink particles, pass through a dynamical-friction phase, and settle into bound binaries that harden through stellar scattering, gas torques, circumbinary-disc coupling, and gravitational-wave emission. When a hierarchical triplet becomes chaotic, RAMCOAL maps the encounter onto a library of three-body outcomes from direct N-body experiments and updates the surviving system, following the resulting mergers, exchanges, and ejections together with the accretion and spin evolution of each black hole. Using isolated-galaxy tests with contrasting geometries, we show that the encounter geometry alone can change which pair finally merges, and after how long. We demonstrate the first triplet MBH dynamical evolution all the way to coalescence inside a live hydrodynamical simulation. This establishes an end-to-end capability to predict triplet-driven MBH coalescences self-consistently coupled to the evolving host galaxy. Because each MBHB coalescence carries its environmental history through the subgrid phase, RAMCOAL offers a route toward merger catalogues that link the gravitational-wave signatures of coalescing black holes to the galaxies in which they form.
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All authors Kunyang Li, Ricarda S. Beckmann, Yohan Dubois, Marta Volonteri

High Energy Astrophysical Phenomena

Measuring the Angular Auto-power Spectrum of Fast Radio Burst Dispersion Measures as a Robust Cosmological Probe and Baryon Tracer

Bao Wang, Zhiyu Lu, Yang Liu et al. (+2 more)

Fluctuations in the cosmic electron density are imprinted on the dispersion measures (DMs) of fast radio bursts (FRBs), making DMs a promising probe of cosmology and the spatial distribution of ionized baryons. In this work, we present the first measurement of the angular auto-power spectrum of FRB DMs, using 3455 apparently non-repeating bursts from the CHIME/FRB Catalog 2. We detect an angular correlation signal at $>3\sigma$ significance, associated with large-scale electron-density fluctuations. By fitting the measured spectrum to theoretical models, we constrain two key parameter combinations: $\Omega_{\rm b}h^2$-$H_0$, which probes the cosmic baryon density and expansion rate, and $\Omega_{\rm b}h^2$-$f_{\rm d}$, which traces the baryon fraction in cosmic large-scale structure (LSS). We further assess the robustness of the power-spectrum method against systematic uncertainties arising from the assumed FRB redshift distribution and from the DM contributions of host galaxies (${\rm DM}_{\rm host}$), the Galactic halo (${\rm DM}^{\rm MW}_{\rm halo}$), and the Milky Way interstellar medium (${\rm DM}^{\rm MW}_{\rm ISM}$), using mock samples. Our results demonstrate that the angular power spectrum is largely insensitive to uncorrelated DM components such as ${\rm DM}_{\rm host}$, thereby effectively mitigating the impact of poorly constrained host-galaxy systematics. In contrast to the traditional ${\rm DM}_{\rm LSS}$-$z$ relation, this method does not require individual redshift measurements–it relies only on the overall redshift distribution–and it partially breaks the parameter degeneracies in the $\Omega_{\rm b}h^2$-$H_0$ and $\Omega_{\rm b}h^2$-$f_{\rm d}$ planes. These findings establish the DM angular power spectrum as a robust cosmological probe and a powerful baryon tracer.
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All authors Bao Wang, Zhiyu Lu, Yang Liu, Jun-Jie Wei, Xue-Feng Wu

Solar and Stellar Astrophysics

Aditya-L1/VELC observations of CME associated broadening of 5303Å coronal emission line

K. Sasikumar Raja, V. Muthu Priyal, R. Ramesh et al. (+2 more)

We present Aditya-L1/VELC spectroscopic observations of 5303Å coronal emission line widths before and after coronal mass ejections (CMEs) which showed coronal dimming. The sit & stare mode of observations enabled us to study the changes in the line widths for the `limb' CMEs noticed on 16 July 2024 and 05 August 2024. The emission line widths during the pre-CME phase are higher than the thermal values in both the cases. After the onset of the CMEs, the widths increased further by ${\approx}15\%$ on 16 July 2024 and ${\approx}7\%$ on 05 August 2024. We find that the power spectral density (PSD) distributions of the line widths for the two events exhibits a power-law behavior. The PSD slopes, measured before and after the CMEs are nearly the same, and close to the Kolmogorov slope of ${-5/3}$. The results suggest that the observed larger than thermal width of the 5303Å emission line, before and after CMEs, is mostly due to turbulence. The additional increase in the line widths after the onset of the CMEs in both the cases are likely because of enhanced turbulence caused by the CME associated coronal dimmings and subsequent coronal magnetic field reconfiguration.
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All authors K. Sasikumar Raja, V. Muthu Priyal, R. Ramesh, Jagdev Singh, Prasad Subramanian

High Energy Astrophysical Phenomena

Constraining Pulsar Radiative Geometry via Multi-wavelength Modeling

Tong Zhao, Shunshun Cao and Renxin Xu

We propose that jointly modeling the thermal X-ray pulse profiles and the polarization position angles offers an effective means of locating the polarization orientation focus of the pulsar's coherent radiation. From the X-ray pulse-profile measurement we constrain the colatitude of the center of the thermal X-ray emission, which corresponds to the center of in-falling particles within the polar cap, while the RVM fitting yields the inclination angle of the focus point of polarization orientations. Thus, consistency between these two independent angle measurements would imply that the RVM fit faithfully recovers the inclination of the plasma flow center, and this center coincides with the polarization orientation focus. Conversely, the discrepancy would suggest that the polarization state of the radio emission changes as it propagates because the evolution of wave modes during wave propagation in the magnetosphere strongly depends on magnetic field orientations.
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Saturday 4 July

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

ACT-DR6 consistent inflation in generalised entropic cosmology and $f(Q)$ gravity

Shin'ichi Nojiri and Sergei D. Odintsov

Within the framework of generalised entropic cosmology and its equivalent $f(Q)$ gravity, we construct inflationary scenarios consistent with recent Atacama Cosmology Telescope (ACT) observations combined with Planck-BAO data. We work with $f(Q)$ gravity and use the reconstruction scheme from which one can obtain an arbitrary cosmological evolution consistent with desirable theoretical or observational considerations. Explicit inflationary cosmologies of the above theory, which pass ACT-Data Release 6 (DR6) data combined with Planck and BAO, are obtained. For $f(Q)$ gravity coupled with scalar, we obtain ACT inflation for large classes of $f(Q)$ via the choice of the scalar potentials. The entropic cosmology based on generalised entropy, which includes most of the known entropies like Tsallis, Rényi, Barrow, etc as a particular case, is investigated. The corresponding FRW equations, depending on the parameters of generalised entropy, are presented. Using the correspondence between the generalised entropy and $f(Q)$ gravity, we obtain generalised entropic inflation, which is consistent with the ACT-DR6. At the next step, the entropic gravity coupled with scalar is considered. It is demonstrated how one can obtain ACT-DR6-consistent inflation for such a theory based on any generalised entropy considered in this paper via the choice of scalar potentials. These findings may point towards the correct unifying entropy of the early universe.
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Astrophysics of Galaxies

Assembly bias from nuisance to probe I: the relation between galactic conformity and the linear matter clustering

Nelson Padilla, Ivan Lacerna and Dante Paz

Two-halo galactic conformity is commonly interpreted as a manifestation of galaxy assembly bias, but its statistical structure and physical origin remain unclear. We aim to write the quenched-neighbour statistic in correlation-function form, test whether its scale dependence follows the linear matter correlation function $\xi_{\rm mm}^{\rm lin}(r)$, and separate the contributions of halo-mass bias and assembly bias to its amplitude. Using galaxies in IllustrisTNG300-1 at $z=0$, we measure the two-halo galactic conformity statistic of quenched neighbours at distance $r$, $\Delta f_{Q}(r)$, and related quantities in real space, compute the required correlations, perform shuffling tests at fixed halo mass, compare several $\Delta f$ observables, and explore the transformed family $G_n$. We show explicitly that $\Delta f_{Q}(r)$ can be written directly in terms of correlation functions and that, over $\sim 2$–$40\,h^{-1}\,\mathrm{Mpc}$, it is well described by $A_{\rm fit}\,\xi_{\rm mm}^{\rm lin}(r)$. Thus nonlinear and baryonic terms do not dominate the residual scale dependence isolated by this statistic. Halo-mass bias alone predicts lower amplitudes than measured, while fixed-mass shuffling strongly suppresses the signal; in TNG300 the amplitude is therefore dominated by galaxy assembly bias at fixed halo mass. Quenching, colour, and concentration share a common rescaled shape, whereas stellar-mass and halo-mass splits do not. These results suggest that galaxy assembly bias sets the amplitude of two-halo conformity, while the double-difference structure of the statistic suppresses nonlinear residuals when the compared populations have similar halo-mass and transition-scale structure.
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Earth and Planetary Astrophysics

Atmospheric characterization of six ultra-hot Jupiters from $K$-band high-resolution spectroscopy

Luke Finnerty, Michael P. Fitzgerald, Yinzi Xin et al. (+27 more)

We present new Keck/KPIC high-resolution spectroscopic detections of three ultra-hot Jupiters (UHJs) in the $K$ band: WASP-189b ($\rm SNR = 7.2$), MASCARA-1b ($\rm SNR = 8.6$), and TOI-1518b ($\rm SNR = 7.1$), as well as a tentative detection of KELT-9b ($\rm SNR = 5.0$). We perform a uniform set of atmospheric retrieval analysis on these objects, as well as previously reported KPIC observations of WASP-33b ($\rm SNR = 11.2$) and KELT-20b ($\rm SNR = 10.5$), We perform atmospheric retrievals for the pressure-temperature ($P-T$) profile, orbital velocity parameters, $v\sin i$, and abundances of CO, H$_2$O, OH, and Fe, with parameterized mixing profiles to account for the expected vertical abundance variations of H$_2$O and OH. We also perform a set of retrievals assuming chemical equilibrium, which are generally in good agreement with the free retrievals. Except for \knb, the retrieved spectra are dominated by CO emission features, with additional weak H$_2$O or OH features consistent with thermal dissociation of H$_2$O. \knb, which is significantly hotter, appears to have very weak molecular features. Dissociation limits our ability to reliably constrain H$_2$O or OH abundances from $K$ band data alone, resulting in poor constraints on the C/O ratio. For all objects, the atmospheric abundances from detected carbon and oxygen species are $1-10\times$ solar. These results highlight the importance of wide spectral coverage for high-resolution retrievals. Additional observations to expand phase and wavelength coverage are needed to better constrain oxygen species and possible spatial inhomogeneities from dissociation.
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All authors Luke Finnerty, Michael P. Fitzgerald, Yinzi Xin, Jerry W. Xuan, Julie Inglis, Shubh Agrawal, Ashley Baker, Randall Bartos, Geoffrey A. Blake, Benjamin Calvin, Sylvain Cetre, Jacques-Robert Delorme, Greg Doppmann, Daniel Echeverri, Katelyn Horstman, Chih-Chun Hsu, Nemanja Jovanovic, Joshua Liberman, Ronald A. López, Dimitri Mawet, Evan Morris, Jacklyn Pezzato-Rovner, Jean-Baptiste Ruffio, Ben Sappey, Tobias Schofield, Andrew Skemer, J. Kent Wallace, Nicole L. Wallack, Jason J. Wang, Ji Wang

Earth and Planetary Astrophysics

Photometry of Kuiper belt objects in inner and outer mean motion resonances with Neptune

Audrey Thirouin and Scott S. Sheppard

We present a time-resolved photometric survey of Kuiper Belt Objects (KBOs) trapped in the inner and outer Neptune resonances. Lightcurves and rotational properties provide constraints on the shapes, internal structures, collisional histories, and formation environments of these primitive bodies. Our survey was conducted using the Magellan-Baade telescope and the Lowell Discovery Telescope, allowing us to go fainter than past works and yielding lightcurve studies for 41 KBOs in the 1:1, 5:4, 4:3, 11:5, 7:3, 12:5, and 5:2 resonances. We obtained complete lightcurves for objects displaying large amplitudes, with two KBOs in the 5:2 resonance (2001 XQ$_{254}$, 2013 RZ$_{108}$), one object in the 7:3 (2013 TJ$_{159}$), and one object in the 12:5 (2015 AR$_{293}$). Their lightcurve amplitudes range from 0.26 to 0.46mag, with rotational periods between 5.35 and 11.63 h. 2013 TJ$_{159}$ has the fastest rotation, largest amplitude, and most asymmetric lightcurve in our sample. Combining our results with published studies, we find that inner and outer resonant KBOs generally display lower lightcurve amplitudes than the dynamically Cold Classical population and the 5:3 and 7:4 resonances. The absence of the amplitude–period trends observed in those populations, and their surface color distributions, further suggests that inner and outer resonances do not share the same origin or evolutionary history as the Cold Classicals and overlapping resonances. Based on the literature and our survey, only one nearly equal-sized contact binary, 2004 TT$_{357}$, is currently known among the surveyed populations, implying a lower limit to the contact binary fraction of $\sim$12-15% in the 5:2 resonance.
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Astrophysics of Galaxies

A Model Context Protocol Server for Astrophysical RAG: Unified Access to HI, Dwarf, Globular Cluster, IntZ, and ALPINE Kinematic Corpora with FAISS Semantic Search

David C. Flynn

We present the EPS Research Astro-RAG MCP Server v2.3.0, a cross-platform Model Context Protocol (MCP) implementation providing unified, machine-readable access to five astrophysical corpora spanning the local universe (z = 0) to z = 5.68 (the high-redshift frontier of the ALPINE survey). The server exposes a humanreadable browser query interface, a REST API, and an LLM-native MCP endpoint, enabling deterministic retrieval, metadata filtering, and structured analysis across 2,064 objects: galaxies spanning HI rotation curve surveys, dwarf and irregular systems, and high-redshift kinematic targets, together with Milky Way globular clusters. Version 2.3.0 introduces FAISS-accelerated natural-language similarity search using pre-built 384-dimensional MiniLM-L6-v2 vector indexes, enabling corpus-wide semantic queries without fine-tuning or API keys. We describe the server architecture, unified schema design, FAISS index construction pipeline, MCP toolset, and cross-epoch use cases including rotation-curve retrieval, metadata filtering, and semantic similarity exploration. The server is publicly deployed on HuggingFace Spaces (https://dflynn5656-astro-rag-mcp.hf.space), released under the MIT License, and fully reproducible from Zenodo (DOI: 10.5281/zenodo.21154451). The full platform is available at https://github.com/eps-research/rag-corpus-series.
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Astrophysics of Galaxies

Ultraviolet Interstellar Extinction toward High Galactic Latitudes

Ajay Mishra and Aigen Li

Nearby high Galactic latitude clouds provide a unique laboratory to study the physics and structure of the Galactic interstellar medium (ISM) and the properties of the interstellar dust. In this work, we select 32 sightlines toward reddened background stars at high Galactic latitudes with |b| > 20 degr, for which high-quality spectra from the International Ultraviolet Explorer are available. We utilize the "pair-method" to derive the ultraviolet interstellar extinction curves for these sightlines. We examine the extinction properties of these sightlines and find no systematic variations with the Galactic latitudes, although they do show appreciable sightline-to-sightline variations.
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Astrophysics of Galaxies

Widespread Detection of Aromatic and Aliphatic Emission in the Dual Quasar J0749+2255 at Cosmic Noon

C.E. Mentzer, Aigen Li and X.J. Yang

Based on JWST/MIRI integral field observations, we report a widespread detection of aromatic and aliphatic hydrocarbon emission at rest-frame 3.3 and 3.4 micron in SDSSJ074922.96+225511.7 (hereafter J0749+2255), a dual quasar at redshift z~2.17, corresponding to a cosmic age of ~3 billion years after the Big Bang, a time period known as the "cosmic noon" when star formation and black hole growth peak. With the 3.3 micron emission ascribed to aromatic C–H stretches of small PAH molecules and the 3.4 micron emission assigned to aliphatic C–H stretches of aliphatic sidegroups attached to PAHs, we utilize the observed intensities of the 3.3 and 3.4 micron emission bands to estimate the aliphatic fractions of PAHs and their variations across J0749+2255, which is, to our knowledge, the most distant object to date in which both aromatics and aliphatics have ever been detected. We find that both the 3.3 and 3.4 micron emission bands are pronounced and the aliphatic fractions are surprisingly high in the most luminous regions centered on the two quasar nuclei, suggesting that not only small PAHs (of ~20–30 carbon atoms) but also their attached aliphatic sidegroups survive in intense ultraviolet radiation arising from extreme starburst.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

Transformers with Physics-Informed Encodings and Simulation-Based Inference for Robust Detection of Eccentric Binary Black Holes in Pulsar Timing Array Data

Subhajit Dandapat and Alvin J. K. Chua

Pulsar timing arrays (PTAs) provide a unique window into nanohertz gravitational waves (GWs), but extracting astrophysical parameters from noisy, long-baseline timing residuals remains computationally challenging with traditional Bayesian techniques due to the high dimensionality of the parameter space, complex and correlated noise models, and the cost of repeated likelihood evaluations. We introduce a Transformer with a physics-informed positional-encoding framework for the efficient inference of eccentric binary black holes in relativistic orbits from PTA data. Our approach embeds analytical GW phase evolution directly into the model through structured positional encodings, enabling the network to learn physically meaningful representations from raw PTA timing residuals. We then use generative models, including discrete and continuous conditional normalizing flows, to infer posterior distributions within a simulation-based inference framework. Across a range of signal-to-noise ratios, the proposed method achieves improved accuracy, sharper posteriors, and faster inference compared to physics-agnostic baselines. While presented for deterministic white-noise signals, the modular framework readily generalizes to realistic PTA analyses incorporating red noise and additional components. This work highlights the potential of physics-aware deep learning models as scalable alternatives to conventional inference pipelines for next-generation PTA datasets.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Identifying lensed gravitational waves with physics-informed posterior learning

Tian-Yang Sun, Xiao Guo, Jing-Fei Zhang et al. (+1 more)

Gravitational lensing of gravitational waves can probe compact lenses, dark matter substructure, and cosmological distances, but identifying lensed events is difficult when unrelated binary mergers overlap in the same analysis window. We develop physics-informed posterior learning for ranking lensed multi-image signals against unrelated multiple-merger events. The method exploits the geometric-optics consistency that lensing can change amplitudes, arrival times, and Morse phase offsets while preserving the intrinsic phase evolution of the source. We infer a simulation-trained approximate posterior for the common detector-frame chirp mass and symmetric mass ratio, and fuse posterior samples with direct waveform features. Training uses generic multi-image simulations, while point-mass, singular-isothermal-sphere, singular-isothermal-ellipsoid, and shear-perturbed lenses are reserved for held-out lens-family evaluation. For the observationally motivated binary-black-hole population, the fusion ranking raises the detection efficiency from $20.8\%$ to $35.2\%$ at a $1\%$ reference false-positive-rate threshold calibrated on the corresponding unrelated multiple-merger sample. It lowers the network signal-to-noise ratio needed for $50\%$ detection efficiency from 45.3 to 33.5, which corresponds to a 1.35 times larger signal-to-noise-ratio-equivalent distance scale. The gain is limited by loud unrelated multiple-merger events that are partly source consistent, and by the need to calibrate the unrelated multiple-merger population. These results suggest that physical consistency can become a guiding principle for machine learning searches in dense gravitational-wave catalogs.
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All authors Tian-Yang Sun, Xiao Guo, Jing-Fei Zhang, Xin Zhang

High Energy Astrophysical Phenomena

Cross-validation of six dispersion measure estimation methods for FRB 20240114A

Tonglun Wang, Songbo Zhang, Yuanchuan Zou et al. (+11 more)

Fast Radio Bursts (FRBs) are important cosmological probes, but their applications depend critically on accurate dispersion measure (DM) determinations. We present a systematic comparison of six DM estimation methods using 2,874 bursts from FRB20240114A, the most active repeating FRB currently known, observed by FAST during a single 4.4-hr session on 2024 March 12. This large, homogeneous sample over a short timescale, during which the propagation environment is expected to be nearly static, provides an ideal benchmark for isolating algorithmic effects on DM determination. We investigate the dependence of inter-method consistency on signal-to-noise ratio (S/N), burst morphology, and radio frequency interference (RFI). Low-S/N bursts exhibit significantly larger inter-method deviations, while single-component bursts produce highly consistent DM values across methods. In contrast, complex double- and multiple-component bursts with drifting substructures lead to substantial inter-method scattering, indicating that DM discrepancies are primarily driven by algorithmic responses to burst morphology. RFI does not significantly alter the global statistical behavior of DM deviations, but it affects density-filtering methods through morphology distortion caused by frequency-channel masking. Even after imposing strict inter-method consistency constraints, FRB20240114A still exhibits notable apparent DM fluctuations spanning $\sim$528-534~pc~cm$^{-3}$ over 15,780s. For morphologically simple bursts these variations far exceed the measurement uncertainty and, on second-to-minute timescales, cannot arise from any plausible change in the line-of-sight electron column, pointing instead to a frequency-dependent emission-time structure intrinsic to the bursts that mimics dispersion.
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All authors Tonglun Wang, Songbo Zhang, Yuanchuan Zou, Xuan Yang, Pei Wang, Di Xiao, Xianghan Cui, Ye Li, Hao Qiu, Yingze Shan, Junyi Shen, Ya Zeng, Longxuan Zhang, Wenlong Zhang

Solar and Stellar Astrophysics

Star Planet Interactions

Arghyadeep Paul, Kristina Kislyakova, Manuel Güdel et al. (+13 more)

Star-planet interactions (SPIs) describe the continuous exchange of energy, momentum, and mass between exoplanets and their host stars through radiative, tidal, magnetic, and particle-driven processes. Together, these interactions shape the structure, evolution, and observable properties of exoplanetary systems. In this review, we bring together current theoretical and observational understanding of SPIs, highlighting how stellar radiation, winds, and magnetic activity influence planetary atmospheres, interiors, and orbital evolution, while using the Solar System as a valuable reference for interpreting these processes. High-energy stellar radiation, particularly in the far- and extreme-ultraviolet and X-ray bands, drives atmospheric heating, photochemistry, ionisation, and escape. These effects are further influenced by stellar winds and magnetic interactions, which can either protect planetary atmospheres or accelerate their loss over time. Tidal interactions redistribute energy and angular momentum, producing internal heating and driving orbital migration and circularisation. Magnetic star-planet coupling provides additional pathways for energy transfer through reconnection and current systems, potentially enhancing atmospheric escape, heating planetary ionospheres and interiors, and generating observable signatures such as radio emission and enhanced stellar activity. We discuss how these processes work together, emphasising that their long-term impact depends on stellar evolution, planetary properties, atmospheric structure, and magnetic field strength. By presenting radiative, tidal, and magnetic interactions within a unified framework, this review highlights the physical mechanisms that shape planetary environments and identifies the key observational signatures that will complement future studies of exoplanet evolution and habitability.
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All authors Arghyadeep Paul, Kristina Kislyakova, Manuel Güdel, Rim Fares, Judy Chebly, Sergio Joya, Miljenko Čemeljić, Katja Poppenhäger, Julian Alvarado-Gomez, Silva Järvinen, Cesar Bertucci, Dibyendu Nandy, Antonio García Muñoz, Antoine Strugarek, Mayank Narang, Shyama Narendranath

Earth and Planetary Astrophysics

Interpreting ALMA Multiwavelength Continuum Observations of PDS 70 c: An Optically Thick Dust Ring in the Circumplanetary Disk

Yuhito Shibaike, Satoshi Okuzumi, Takahiro Ueda et al. (+2 more)

Giant planets form small gas disks, called circumplanetary disks (CPDs), during gas accretion. The CPD of PDS 70 c has been detected by the Atacama Large Millimeter/submillimeter Array (ALMA) in (sub)millimeter continuum emission, which is interpreted as thermal emission from dust in the CPD. The resulting spectral index suggests that the disk is optically thick over a wide range of wavelengths. However, this is inconsistent with previous CPD dust models, which predict that the disk is optically thin because of radial dust drift. Here, we present a new interpretation of the multiwavelength observations: the CPD hosts an optically thick dust ring, whose existence has been discussed in the context of satellite formation. We demonstrate that a dust-ring model that incorporates gas accretion, dust evolution, and dust thermal emission, is consistent with the observations under reasonable conditions, whereas a conventional ring-less model requires more stringent conditions. We also show that the dust ring inferred from the observations potentially satisfies the conditions for exomoon formation via streaming instability and subsequent gravitational instability.
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All authors Yuhito Shibaike, Satoshi Okuzumi, Takahiro Ueda, Kiyoaki Doi, Misato Fukagawa

High Energy Astrophysical Phenomena

Long-period radio transient PSR J0901-4046 is not an Isolated White Dwarf Pulsar

Maxim Lyutikov, Mukremin Kilic, Alexander Wolszczan et al. (+1 more)

We report the Chandra non-detection of PSR J0901$-$4046, a $P=75.89 $ seconds long-period radio transient (LPT). For a distance of 467 pc, the upper limit on X-ray luminosity is $L_X \leq$ few $\times 10^{28}$ erg s$^{-1}$. For the measured $P$ and $\dot{P}$, this upper limit, approximately 50 times lower than the previous Swift observations, is comparable to the spin-down luminosity of a neutron star, but would be approximately four orders of magnitude smaller than the spindown power of a white dwarf. Our results disfavor isolated WDs as the central star in PSR J0901$-$4046. We suggest that the isolated LPTs are powered by magnetic dissipation (not rotation), in a way similar to magnetars' radio emission.
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All authors Maxim Lyutikov, Mukremin Kilic, Alexander Wolszczan, Craig Heinke

High Energy Astrophysical Phenomena

Neutron stars with an agnostic Dark sector: Core and Halo configurations from a two-fluid approach

Asit karan, Asim Kumar Saha, Tuhin Malik et al. (+2 more)

The study of dark matter admixed neutron stars has the potential to advance our understanding of dark matter particle candidates. However, the large parameter space of dark matter particle masses restricts a systematic, model-independent study. In this analysis, we employ agnostic hadronic and dark matter equations of state to construct dark-matter-admixed neutron stars within a two-fluid formalism. Dark matter is characterised solely by its low-density equation of state and mass, and is modelled as a Fermi gas, while hadronic matter is anchored at low and high densities by chiral effective field theory and perturbative quantum chromodynamics calculations. A speed-of-sound parametrisation covers the intermediate density region for hadronic matter and the high-density region for dark matter, so the dark matter equation of state is constrained only by thermodynamic consistency, free from bias toward a softer or stiffer equation of state. Within this agnostic framework, we find that dark matter does not generically compactify the star: light dark matter forms extended halos that raise the tidal deformability, while heavy dark matter forms compact cores that lower it. Consequently, the dominant observational constraint shifts from gravitational-wave tidal deformability for light, halo-dominated models to NICER mass–radius data for heavy, core-dominated models. Using current data at $1\sigma$, we constrain the dark matter fraction to $f_{\mathrm{DM}} \lesssim 0.11$ for light dark matter. Being almost independent of any assumed dark-sector microphysics, our framework yields conservative, broadly applicable bounds on the dark-matter content of neutron stars. Neutron stars with similar masses but very different tidal deformabilities could be a smoking-gun signature of dark matter in Neutron stars.
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All authors Asit karan, Asim Kumar Saha, Tuhin Malik, Constança Providência, Ritam Mallick