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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 8 September

Astrophysics of Galaxies

The environmental dependence of the circumgalactic medium in a high-resolution cosmological simulation

Georg Herzog, Rajeshwari Dutta and Michele Fumagalli

There is increasing evidence from observations that the circumgalactic medium (CGM) of galaxies depends on the large-scale structure in which they are embedded. When probing the CGM in absorption using quasar sightlines, studies find an enhanced sky coverage in the CGM of galaxies in overdensities compared to galaxies in isolation. However, the exact reason for this environmental dependence is still unclear. In this work we aim to model for the first time the influence of the large-scale structure on the cool and warm ($T\sim10^{4-5}$ K) gas phases of the CGM. We use a high-resolution ($m_{gas}\approx 4.5\times 10^4$ M$_{\odot}$, $m_{dm}\approx 2.4\times 10^5$ M$_{\odot}$) cosmological simulation based on the EAGLE model of galaxy formation. We select all galaxies at $z=0$ with stellar mass $M_*>10^8$ M$_\odot$ and split them into galaxies in overdensities (group galaxies) and galaxies in isolation using a Friends-of-Friends algorithm. For these two samples, we investigate how the large-scale structure influences the physical properties of the CGM and the measured covering fractions of the cool and warm gas phases. When the two samples of group and isolated galaxies are matched in stellar mass, halo mass, and we use only central galaxies, we do not find any significant difference in the physical properties of the CGM and the measured covering fractions. However, when satellite galaxies are included, we recover the observational trends in the difference of covering fractions with the environment. The difficulty of recovering the observational trends shows the complexity of capturing the multiphase CGM in simulations. However, since our results concerning the admixture of satellites are independent of the employed subgrid physics, this work shows that central galaxies and satellites need to be disentangled in observational studies to clearly discern the role of the environment on the CGM.
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Cosmology and Nongalactic Astrophysics

$\texttt{LensFactory.jl}$: A general-purpose strong lens modeling package

Ashish Kumar Meena

We present LensFactory.jl, an efficient, open-source, general-purpose strong lens modeling package written in Julia. It supports single- and multi-plane lensing with a wide range of analytic lens profiles, and its modular design, built on Julia's multiple dispatch, makes it straightforward to add new profiles or inference methods, while native multi-threading parallelizes the computationally expensive steps, enabling full cluster-scale lens reconstructions within hours on a desktop-class machine. We validate the mass-reconstruction pipeline of LensFactory.jl on two simulated galaxy clusters (Ares and Hera), recovering the convergence and magnification maps well where the lensing constraints lie, and on the JWST-observed cluster SMACS J0723.3-7327, obtaining a strong lens model (image-plane RMS of 0.46”) consistent with previously published results. In addition, we introduce singularity maps as a complementary diagnostic for comparing lens models, probing differences in the higher-order derivatives of the lensing potential, which remain largely unconstrained by standard observables such as image positions, time delays, and flux ratios. LensFactory.jl is accompanied by a set of worked examples covering all core functionality.
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Earth and Planetary Astrophysics

XUE. ProDiMo models of internally and externally irradiated planet-forming disks around 0.3-4.0 solar mass stars (The IRIS project I)

Jenny Frediani, Konstantin V. Getman, Peter Woitke et al. (+18 more)

Most stars and planets form in massive star-forming regions, where disks are exposed to external far-ultraviolet (FUV) radiation from nearby O- and B-type stars. The combined effects of stellar irradiation and external FUV fields on terrestrial planet-forming regions (< 10 au) across stellar masses remain unclear. We investigate how internal UV and X-ray irradiation and external FUV fields affect mid-infrared (mid-IR) gas emission and the atmospheric carbon-to-oxygen (C/O) ratios inferred in T Tauri and Herbig Ae/Be disks. We compute disk structures with ProDiMo and synthetic spectra with FLiTs, convolved to a representative JWST/MIRI-MRS resolution (R$\sim$2680). (1) We present the Internal and external irRadIation of diSks (IRIS) grid: four model sets spanning stellar masses of 0.3-4.0 solar masses, including stellar X-ray flares and an external FUV field of 1e4 G0 (Habing units). (2) We predict increasing flux densities with stellar mass for key atomic and molecular mid-IR tracers. (3) External FUV irradiation enhances CH3+ and H2 emission, whereas FUV-induced disk truncation yields inner disk chemistry resembling that of disks irradiated only by their host stars. (4) Mid-IR H2O, CO2, and C2H2 line ratios imply carbon-rich compositions (C/O$\sim$1-10) in the warm emitting layers of T Tauri and Herbig Ae/Be disks, primarily reflecting stellar irradiation, with little sensitivity to external FUV irradiation. The IRIS grid provides a flexible framework for interpreting JWST and future Extremely Large Telescope (ELT) infrared disk observations across a broad range of stellar properties and irradiation conditions. Future models should include FUV-driven photoevaporative winds, X-ray radiative transfer, and time-dependent X-ray irradiation.
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All authors Jenny Frediani, Konstantin V. Getman, Peter Woitke, Bayron Portilla-Revelo, Eric D. Feigelson, Christian Rab, Arjan Bik, María Claudia Ramírez-Tannus, Rens Waters, Thomas Henning, Inga Kamp, Germán Chaparro, Sebastián Hernández, Simón Rodríguez, Pablo Cuartas-Restrepo, Andrew Winter, Thomas J. Haworth, Thomas Preibisch, Sierk E. van Terwisga, Veronica Roccatagliata, Alexis Brandeker

Instrumentation and Methods for Astrophysics

A Missing Tool for Calculating Auto/Cross-correlation Function under Nonuniform Sampling Observations

Chen-Ran Hu, Yong-Feng Huang, Jin-Jun Geng et al. (+10 more)

Nonuniform sampling presents a long-standing challenge in astrophysical time-domain analysis, invalidating the standard autocorrelation and cross-correlation functions and forcing researchers to adopt ad-hoc methods like interpolation or binning, which introduce unquantified biases and lack rigorous error estimation. Here we introduce a new method for calculating the nonuniform autocorrelation function (NUACF) and nonuniform cross-correlation function (NUCCF) for irregularly sampled time series. Instead of relying on interpolation, it naturally evaluates the correlation function by incorporating time-interval weights and misalignment penalties. Monte Carlo simulations provide confidence bands for significance assessment and a complete error budget for the time delays that accounts for both flux uncertainties and sampling irregularity (essential but generally absent from existing methods). Through extensive simulations, we demonstrate our method outperforms traditional methods across various conditions, from strictly periodic to complex repeating variability patterns (e.g., intermittent but aperiodic). Its effectiveness is demonstrated via various real astrophysical data sets, revealing repetitive variability in stellar light curves, measuring time delays for multi-band disc reverberation in the AGN Fairall 9, and providing model-independent validation of time delays for the gravitationally lensed quasar HE 0435-1223. The method provides a rigorous and general solution to the ubiquitous problem of nonuniform sampling, positioning it as a useful tool for large-scale time-domain survey data analysis. The framework is also directly applicable to emerging time-domain phenomena such as fast radio bursts (FRBs), enabling, e.g., the study of correlations between persistent radio source luminosity and repeating FRB activity, or among the multi-parameter variability curves of FRB emission itself.
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All authors Chen-Ran Hu, Yong-Feng Huang, Jin-Jun Geng, Orkash Amat, Ze-Cheng Zou, Chen Deng, Fan Xu, Xiao-Fei Dong, Chen Du, Nurimangul Nurmamat, Pei Wang, Lang Cui, Cheng-Ming Li

Earth and Planetary Astrophysics

Radial velocity follow-up of Gaia astrometric substellar companions: six confirmed brown dwarfs and 13 impostor binaries

Marcus L. Marcussen, Simon H. Albrecht, Kamil K. Kalinowski et al. (+7 more)

With microarcsecond precision, Gaia has made the astrometric discovery of substellar companions feasible. However, follow-up observations are needed to check on orbital solutions and rule out astrophysical false positives. We validate and characterise a sample of 20 Gaia Data Release 3 (DR3) astrometric candidates for substellar companions, with the dual goal of identifying false positives and deriving robust physical parameters for genuine companions. We performed high-resolution spectroscopy using FIES, NIRPS, and NEID at the Nordic Optical Telescope, the ESO 3.6m telescope, and the WIYN Telescope, respectively. Double-lined spectroscopic binaries were identified as false positives, and surviving systems were characterised through joint Gaia astrometry and radial velocity modelling. Thirteen of the candidates proved to be near-twin binary stars for which the astrometric motion of the center of light is small enough to mimic that of a single star in response to a substellar companion. We confirm that six companions are brown dwarfs with masses in the range ${\sim}26$–$68\,M_\mathrm{Jup}$, two of them for the first time. In contrast to earlier studies of lower-mass Gaia candidates, we find that the astrometric orbital solutions are generally reliable to within the stated uncertainties.
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All authors Marcus L. Marcussen, Simon H. Albrecht, Kamil K. Kalinowski, Joshua N. Winn, Gu{\dh}mundur Stefánsson, Jens Reersted Larsen, Julie Gadeberg, Evan Fitzmaurice, Kevin Schlaufman, Suvrath Mahadevan

Cosmology and Nongalactic Astrophysics

Harnessing stellar kinematics to constrain dark energy with the double-source-plane gravitational lens SDSS J0946+1006

Daniel J. Ballard, Wolfgang J. R. Enzi, Thomas E. Collett et al. (+6 more)

SDSS J0946+1006 is an attractive target for measuring cosmological parameters through lens modelling. It is the best-studied galaxy-scale strong gravitational lens with multiple sources whose redshift separations are well-suited to constraining the dark energy equation of state. However, multi-plane lens models with free cosmological parameters risk a multi-plane mass-sheet degeneracy, although this can be lifted by a non-lensing deflector density profile tracer. We simultaneously reconstruct near-infrared and near-ultraviolet HST imaging whilst including a velocity dispersion measurement from VLT-MUSE to constrain the foreground deflector. Imaging is reconstructed faithfully regardless of whether the inferred kinematics are realistic, though we find the kinematic constraint essential for shifting the preferred cosmology into a region not in significant tension with other dark energy probes. Deflector density profile perturbations, via substructure and multipolar halo shape deformations, have only a modest effect on inferred cosmology. Combining our fiducial model with Planck CMB data yields $w=-1.01^{+0.08}_{-0.13}$; or, combined with Pantheon SNe Ia, $w=-0.99^{+0.13}_{-0.15}$. We further show that this system proves a remarkably valuable complementary probe in the $w_{0}$-$w_{a}$ plane of an evolving dark energy model, and that the DESI BAO tension with $\Lambda$CDM seen when combined with other datasets is not reproduced when combined with this lens, yielding $(w_{0}, w_{a})=(-0.87^{+0.10}_{-0.11}, -0.22^{+0.28}_{-0.25})$. The system's third source, visible with MUSE, only weakly constrains $w$CDM but may strengthen $w_{0}w_{a}$CDM constraints, though further mass-model complexity along its line of sight is required. Overall, kinematics-informed multi-plane lens modelling is a robust route to competitive dark energy constraints, even with a single system.
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All authors Daniel J. Ballard, Wolfgang J. R. Enzi, Thomas E. Collett, Coleman M. Krawczyk, Giovanni Granata, Tian Li, Geraint F. Lewis, Karl Glazebrook, Huimin Qu

Earth and Planetary Astrophysics

MAD-LEO: A Maneuver-Annotated Orbital Dataset for LEO Satellites with Tiered Multi-Source Evidence

Zhixin Guo, Qi Shi, Xiaofan Xu et al. (+6 more)

With the rapid development of aerospace technology and the large-scale deployment of low Earth orbit (LEO) constellations, the risk of orbital collisions has increased, creating a growing demand for reliable observations of satellite maneuvers. However, public datasets containing real maneuver records remain scarce. We present MAD-LEO, a Maneuver-Annotated orbital Dataset for LEO satellites. The mission-reported subset contains 1,134 maneuver events from eleven geodetic and altimetry satellites spanning 1992 to 2026, with labels taken directly from mission-published maneuver histories. Each event is checked against two-line element (TLE) data, precise orbit products, and satellite laser ranging (SLR) observations, with evidence tiers assigned according to data availability. The operational subset pairs operator-published ephemerides for 6,785 Starlink satellites with cataloged TLE records over a continuous 107-hour period. Technical validation across seven machine-readable experiment suites confirms the cross-source consistency of the labels and the evidence products.
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All authors Zhixin Guo, Qi Shi, Xiaofan Xu, Linqiang Ge, Hua Zhu, Liyan Ben, Bendian Nie, Yuanrui Zhao, Xiaohan Li

Astrophysics of Galaxies · Cross-listed from cs.SC

Physical Law Ecology: mapping multi-mechanism ecologies as the zeroth step of data-driven scientific discovery

Xiongheng Bian, Xiangyu Cui, Ma Feng et al. (+1 more)

Every data-driven equation discovery method assumes (implicitly and without verification) that the target system obeys a single governing law ($K{=}1$). Here we show that this assumption is the primary bottleneck limiting scientific discovery in multi-mechanism systems, and introduce Physical Law Ecology, a framework that makes $K^*$ (the number of coexisting independent mechanisms) itself the first quantity to be determined from data. The framework automatically mines a pool of topologically distinct candidate equations, constructs a continuous dominance weight field across parameter space, and discovers analytic evolution laws governing mechanism succession—with optional monotonicity constraints encoding irreversible physics. Across four unrelated systems (elastomer mechanics, pool boiling, galactic dynamics, and droplet evaporation), BIC consistently identifies $K^*{=}3$ independent governing topologies. Applied to 163 SPARC galaxies (3,269 spatially resolved measurements), the framework autonomously recovers three gravitational laws whose coexistence provides evidence against the single-universal-acceleration hypothesis of MOND ($p<10^{-34}$). In engineering applications, multi-law weighted prediction reduces error by 67-72% over single-equation baselines while retaining full interpretability. By establishing the determination of $K^*$ as the zeroth step of scientific discovery-prior to and independent of equation search—this work opens a direction orthogonal to existing symbolic regression: not finding better equations, but mapping the ecology of mechanisms that govern complex systems.
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All authors Xiongheng Bian, Xiangyu Cui, Ma Feng, Xiaoyan Shen

High Energy Astrophysical Phenomena

Nuclear equation-of-state effects on the two-dimensional post-outburst thermal evolution of magnetized neutron-star crusts

Wei-Feng Zhang, Zhi-Fu Gao, Wen-Qi Ma et al. (+2 more)

We present a controlled two-dimensional study of nuclear-equation-of-state (EOS) effects on the post-outburst thermal relaxation of magnetized neutron-star crusts. Six EOS models are evolved at a fixed gravitational mass of $1.4 M_{\odot}$ with EOS-specific TOV backgrounds, crust compositions, and transport inputs under identical magnetic-field and heating prescriptions. Our analysis combines self-consistent multi-EOS evolution with a BSk-family factorization that separates structural, microphysical, and interaction contributions, together with an accepted-step energy ledger and a numerical-sensitivity budget. The models show EOS-dependent changes in both the early response and the later redistribution of heat between the surface, crust, and inner boundary; light-curve crossings near $10^2$ days demonstrate that the EOS effect is not a simple luminosity rescaling. By 1000 days the cumulative surface-photon energy fraction differs by less than one percentage point, whereas the internal energy partition differs much more strongly. The updated sensitivity tests show that the late-time luminosity differences and the largest peak contrasts exceed the corresponding BSk24 numerical-sensitivity scales, while the smallest early peak contrast remains less securely resolved. The calculations are intended as a reproducible EOS-sensitivity benchmark rather than an observational fit.
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All authors Wei-Feng Zhang, Zhi-Fu Gao, Wen-Qi Ma, Na Wang, Yan-ling Liu

Astrophysics of Galaxies

J023721.13$-$010528.5: A Giant $S$-shaped Radio Galaxy Showing Four Episodes of Jet Activity

Pavan Vijay Khadekar, Dharam Vir Lal and Ramana Athreya

We present high-sensitivity, high-resolution radio observations of J023721.13$-$010528.5 using the upgraded Giant Metrewave Radio Telescope in band-3 (250–500\,MHz) and band-4 (550–950\,MHz), along with MeerKAT (1280\,MHz) and VLA (3\,GHz) survey images. The radio source, hosted by a bright cluster galaxy at redshift $z=0.372$, is a giant radio galaxy with a projected linear size between the outermost hotspots of 1.2~Mpc and is one of the largest $S$-shaped radio sources known. Its radio morphology revealed four pairs of components straddling the radio core, which were also local maxima in profiles of radio flux densities and equipartition energy density measured along the radio lobes. Spatially resolved multi-frequency spectral analysis showed progressively older emission from the inner to the outer components, spanning approximately 4–21 Myr. The high degree of symmetry of the inner three component-pairs with respect to the radio core makes it improbable that these are randomly located knots in the radio jet. Therefore, we present J023721.13$-$010528.5 as the prototype of a new class of radio galaxies with four episodes of jet activity — a quadruple-double radio galaxy. We suggest that giant $S$-shaped radio sources may be among the most promising targets for identifying and studying multi-epoch radio jet activity, since their large linear sizes and jet-axis evolution can spatially separate hotspots from successive episodes, making them easier to detect and analyse.
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Solar and Stellar Astrophysics · Cross-listed from hep-ph

A distance-independent constraint on the axion-electron coupling from RGB stars

Thomas Levasseur, Oscar Straniero and Andrea Caputo

Interest in axions and axion-like particles has resurged, driven by their role in solving the strong CP problem and their appeal as dark matter candidates. The luminosity of the tip of the red giant branch (TRGB) offers a key observable for probing these particle properties. This work aims to improve existing bounds on the axion-electron coupling by adopting a differential observable that is less sensitive to distance, interstellar extinction, the zero-point of bolometric corrections (BCs), and other systematic uncertainties. We use the bolometric magnitude difference between the TRGB and the RGB bump (RGBB) as a distance-independent constraint, applied to three globular clusters of intermediate-to-high metallicity: NGC 104 (47 Tuc), NGC 362, and NGC 5904 (M5). Using photometric catalogs of RGB stars, we determine V- and I-band magnitudes of both features and convert them to bolometric values. After validating that our stellar models reproduce the observed RGBB luminosity, we perform a maximum likelihood analysis with Monte Carlo simulations to propagate uncertainties and derive new bounds on the coupling. A combined analysis of the three clusters yields a maximum likelihood at $g_{13} = g_{ae}/10^{-13} = 0.8$ and a 95% C.L. upper limit of 1.49. Although slightly less stringent than recent bounds from larger multi-cluster samples, this limit is substantially more robust. Under reasonable mass-loss assumptions, $g_{13} \gtrsim 7.5$ is ruled out, as it predicts the disappearance of the HB and AGB phases routinely observed in globular clusters, a limit more than an order of magnitude stronger than current direct experimental bounds such as XENONnT. We demonstrate the effectiveness of this differential, distance-independent method for constraining physics beyond the Standard Model. Applying it to a wider sample of globular clusters would further refine the constraint on $g_{ae}$.
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Solar and Stellar Astrophysics

Magnetic Signatures in Merger Products

Nicolas Muntean, Lisa Bugnet, Lynn Buchele et al. (+5 more)

Asteroseismic estimates of the magnetic field strength in the radiative interior of red giant stars depend strongly on the internal stellar structure derived from models. Since red giant branch merger products have been shown to be able to possess a different core structure than single stars of the same mass, we investigate how a mass-gain history influences our estimates of an internal magnetic field strength. We construct stellar models with and without a mass-gain event after the onset of the RGB evolutionary phase with masses of $1.1\,M_\odot \le M \le 2\,M_\odot$. First, by assuming a weak magnetic field, we investigate the influence of a mass-gain event on the global sensitivity of the oscillation frequencies to the magnetic field. We find that mass-gain models can be several times more sensitive to the field than single-star models of identical total mass at masses above $1.6\,M_\odot$. Therefore, considering a mass-gain evolutionary history for merger candidates allows a significant correction to the magnetic field strength. In the presence of strong magnetic fields, we also show that the critical field strength needed to suppress mixed dipole modes is significantly lower if a mass-gain event has occurred (for stars with masses $M\gtrsim1.6\,M_\odot$). The massive end of the suppressed stars' distribution is therefore strongly favored by a merger origin. We conclude that properly constraining the stellar evolutionary history is essential when aiming to constrain internal field strength estimates from asteroseismic observations.
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All authors Nicolas Muntean, Lisa Bugnet, Lynn Buchele, Debasish Dutta, Lukas Einramhof, Paul G. Beck, Lucas Barrault, Bastien Liagre

Cosmology and Nongalactic Astrophysics

Vacuum Decay and Baryogenesis Associated with Primordial Black Holes at Finite Temperature

Qi Sun and Ligong Bian

Within finite-temperature effective potential framework, we study the effects of PBHs on vacuum decay, the associated gravitational wave spectrum, and the baryon asymmetry. For the PBHs considered, the Hawking temperatures are below the ambient temperature, and their dominant effect is taken to be the gravitational distortion of the Higgs field configuration. Relative to flat spacetime, the PBH background reduces the vacuum decay exponent, enhances the gravitational wave peak amplitude, and shifts the peak frequency downward. For PBH masses of roughly $10^{11}~{\rm g}-10^{13}~{\rm g}$, the sphaleron energy is reduced, while the small PBH abundance renders the associated washout negligible. Additionally, over roughly the same mass range, PBH-emitted BSM particle decays generate a baryon asymmetry too small to spoil the agreement between the baryon abundances inferred from BBN and CMB.
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Cosmology and Nongalactic Astrophysics

Finding the distribution of matter using lenses - II: deconvolution-based reconstruction with 3x2pt measurements

Jun-Qian Jiang, Ajoy Dawn, Dhiraj Kumar Hazra et al. (+2 more)

We present a deconvolution-based framework for testing scale-dependent departures of the late-time matter power spectrum from a fiducial cosmological model using $3\times2$pt measurements. We introduce a free-form scale-dependent modulation $A(k)$ of the fiducial nonlinear matter power spectrum and construct the linear response of binned galaxy-clustering, galaxy-galaxy-lensing, and cosmic-shear spectra to the discretized modulation $A(k)$. The response is evaluated with full-sky, beyond-Limber kernels including density, redshift-space-distortion, gravitational-shear, and intrinsic-alignment contributions. We reconstruct $A(k)$ using a regularized modified Richardson-Lucy algorithm, with weak diffusion in $\ln k$ and selection of the minimum-$\chi^2$ solution along the iteration history. Using Rubin/LSST Year 10-like synthetic data, we find that oscillatory modulations with amplitudes $\gtrsim1\%$ can be recovered over $0.1\lesssim k\lesssim0.5\,{\rm Mpc}^{-1}$, provided the oscillation frequency $f\lesssim10$ on $\log_{10}[k/(0.2\,{\rm Mpc}^{-1})]$. We further introduce a posterior-weighted consistency statistic calibrated with posterior-predictive null mocks, thereby accounting for cosmological and nuisance-parameter uncertainties without relying on Wilks' theorem. The null case is consistent with $A(k)=1$, while a $1\%$ oscillatory modulation is detected at $\sim 2.6\sigma$. These results demonstrate the potential of regularized deconvolution as a model-independent consistency test of the matter power spectrum in future $3\times2$pt surveys.
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All authors Jun-Qian Jiang, Ajoy Dawn, Dhiraj Kumar Hazra, Benjamin L'Huillier, Arman Shafieloo

Cosmology and Nongalactic Astrophysics

Finding the distribution of matter using lenses - I: deconvolution-based reconstruction with CMB lensing

Ajoy Dawn, Jun-Qian Jiang, Dhiraj Kumar Hazra et al. (+2 more)

The matter power spectrum is one of the primary statistical descriptors of the large-scale distribution of matter in the Universe and provides a powerful probe of cosmic structure formation. Measurements of cosmic microwave background (CMB) lensing offer an integrated view of the matter distribution over a wide range of redshifts, enabling the reconstruction of the underlying matter power spectrum. In this work, we reconstruct the reference linear matter power spectrum $ P_\text{lin}(k,0)$ from the baseline joint CMB lensing measurements of Planck PR4, ACT DR6, and SPT-3G using a covariance-weighted modified Richardson-Lucy(MRL) deconvolution algorithm. The reconstructed spectrum is found to be consistent with the fiducial linear prediction on large scales, while exhibiting a systematic enhancement for $k \gtrsim 0.1\,{\rm Mpc}^{-1}$, where nonlinear gravitational evolution becomes important. To investigate this behavior, we introduce a scale-dependent correction factor, $A(k)$, defined through $P(k)=A(k)\,P_{\rm nl}(k),$ where $P_{\rm nl}(k)$ is the fiducial nonlinear matter power spectrum obtained from 2LPT simulations. The reconstructed correction factor remains consistent with unity within $2\sigma$ confidence over the reconstructed range, indicating that the observed enhancement is well explained by the standard nonlinear evolution of the matter power spectrum. In addition, the reconstruction shows agreement with the fiducial BAO template around the BAO feature at $k\sim(0.04-0.06)\ {\rm Mpc}^{-1}$, indicating that some BAO-scale information survives the lensing projection.
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All authors Ajoy Dawn, Jun-Qian Jiang, Dhiraj Kumar Hazra, Benjamin L'Huillier, Arman Shafieloo

High Energy Astrophysical Phenomena

Sharpening the Mass Measurement of PSR J1048+2339 via High-Cadence Photometry

Kwan-Lok Li, Ka-Yui Au, Lupin C. C. Lin et al. (+3 more)

Neutron stars are among the densest objects in the universe, and the mass measurements are crucial to the understanding of their equation of state. Pulsars in tight binaries can be weighed dynamically, but accurate mass estimates are often hampered by uncertainties in orbital inclinations. In this paper, we report on multi-epoch optical monitoring of the pulsar binary, PSR J1048+2339, using the 0.5-m RIFT telescope at Lulin Observatory. Our observations reveal frequent optical flares with eclipses caused by the companion. Using the eclipse duration with archival photometric data and orbital ephemeris in the literature, we constrain the inclination to 78.0+/-1.0 degrees and the pulsar mass to 1.79 (+0.09, -0.08) solar masses. This measurement is among the most precise for any redback system to date, demonstrating a novel way to improve the pulsar mass measures with small aperture optical telescopes. Furthermore, the optical eclipse duration is significantly shorter than that measured in M/GeV gamma-rays, possibly suggesting that a fraction of the eclipsed gamma-ray emission originates from the apex of the intrabinary shock. Based on these constraints, we estimate the magnetic field strength of the companion to be 30-170 G. This is consistent with the high field strength implied by the X-ray orbital modulation observed.
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All authors Kwan-Lok Li, Ka-Yui Au, Lupin C. C. Lin, C. Y. Hui, Albert K. H. Kong, Jumpei Takata

High Energy Astrophysical Phenomena

Near-Horizon Tidal Disruption Events

Yang Yang and Xian Chen

Tidal disruption events (TDEs) offer a unique dynamical probe of the spacetime geometry around supermassive black holes (SMBHs). While conventional TDEs occur around SMBHs of $M_\bullet \sim 10^6 - 10^7 M_\odot$, where stars are disrupted far from the event horizon, here we identify a special class of TDEs around rapidly spinning SMBHs with masses $M_\bullet \gtrsim 10^8 M_\odot$, where the tidal-disruption radius approaches the gravitational radius. We term these events "near-horizon TDEs" and, by calculating geodesics in Kerr spacetime, investigate how the proximity of the horizon modifies the debris evolution and subsequent fallback. We find that for stars encountering the SMBH on parabolic orbits, up to $\sim (90 \%-95 \%)$ of the stellar debris either plunges directly into the SMBH or escapes the system. Bound orbits, by contrast, retain a substantially larger fraction of the debris. Using the resulting debris distribution, we calculate the fallback rates and find that bound orbits produce intrinsically higher peak fallback rates and shorter decay timescales, by factors of $\sim 10^3$ relative to parabolic orbits. However, when the stellar orbital angular momentum is particularly low, the peak fallback rate can be substantially suppressed by debris lost to plunge orbits. This combination of rapid fallback and a mass deficit naturally explains overluminous TDEs such as ASASSN-15lh, which standard TDE models have struggled to reproduce. Our work establishes near-horizon TDEs as a new probe of strong-field gravity and a promising tool for identifying massive, rapidly spinning SMBHs.
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Astrophysics of Galaxies

The Impact of Circumgalactic Rotation on Ly$\alpha$ Radiative Transfer

Hee-Gyeong Kym, Seok-Jun Chang, Max Gronke et al. (+1 more)

Hydrogen Lyman-alpha (Ly$\alpha$) is a prominent emission line from the circumgalactic medium (CGM). Due to its resonant nature, Ly$\alpha$ carries imprints of the physical properties and kinematics of the cold CGM. In particular, CGM rotation can modify the Ly$\alpha$ peak separation, which is often interpreted as a tracer of H I column density. We present 3D Monte Carlo Ly$\alpha$ radiative-transfer simulations in a CGM-like rotating medium and examine how the emergent spectra depend on rotational velocity ($V_{\rm rot}$), H I column density ($N_{\rm HI}$), viewing angle, clumpiness, and intrinsic source width. We find that rotation broadens the integrated spectra and increases the peak separation, with the strongest viewing-angle dependence when rotational Doppler shifts dominate over frequency diffusion. At high $N_{\rm HI}$, numerous scatterings reduce the sensitivity of integrated spectra to rotation, producing a degeneracy between $V_{\rm rot}$ and $N_{\rm HI}$. Consequently, Ly$\alpha$ peak separation alone can overestimate $N_{\rm HI}$ in a rotating medium. Spatially resolved halo spectra provide a clearer diagnostic: opposite sides of the rotating medium show systematic redshifted and blueshifted asymmetries associated with the line-of-sight velocity of the last-scattering gas. Such rotation-driven signatures can also contribute to velocity-map patterns often interpreted in terms of inflow or outflow, highlighting the need to consider rotation in spatially resolved Ly$\alpha$ observations. We further show that the main signatures persist in simple clumpy media, while the halo signatures are largely insensitive to the intrinsic source width. Our results demonstrate that spatially resolved Ly$\alpha$ observation is essential for disentangling CGM rotation from radiative-transfer effects.
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All authors Hee-Gyeong Kym, Seok-Jun Chang, Max Gronke, Kwang-Il Seon

Astrophysics of Galaxies

Series of core collapse numerical simulations (SOLANUM) I: Modelling the early and late infall in a sun-like protostar

D. Navarro-Almaida, B. Commerçon, U. Lebreuilly et al. (+5 more)

Magnetohydrodynamical simulations and interferometric observations toward young stellar objects reveal the accretion of gas that may alter the physical properties and chemical composition of protostellar disks. Our goal is to constrain the physical history and properties of late infalling gas, and assess its potential to change the physical and chemical properties of the disk. We carried out a core collapse simulation of 5 M$_{\odot}$ of gas endowed with tracer and sink particles during $\sim 3.6\times 10^{5}$ yr. We analyzed the properties of the rotationally supported disk, and the origin and physical history of the gas from which it is initially formed. We also selected the tracer particles that describe the late infall to analyze their origin and physical history, and compare them to the information obtained from the disk. The final mass of the sink reaches 1.02 M$_\odot$, while the mass of the disk stays fairly constant around 0.02 M$_\odot$. Throughout its evolution, the disk radius increases up to $\sim 40$ au and its density is reduced by a factor of $\sim 8$. Filaments that channel gas from the envelope to the disk and sink appear as a result of the magnetic interchange instability. Tracer particles can identify late infalling gas, whose physical properties resemble that of observed streamers and are only accreted in the final snapshots of the simulation. The origin and physical history of the late infalling gas are different from those of the gas that initially forms the disk. Core collapse simulations predict the appearance of filaments that connect the envelope to the disk. The late accretion of gas through these channels has properties similar to those of streamers and brings gas to the disk with a different physical history that could translate into a different chemical composition.
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All authors D. Navarro-Almaida, B. Commerçon, U. Lebreuilly, P. Hennebelle, A. Ahmad, A. Fuente, P. Rivière-Marichalar, J. E. Pineda

High Energy Astrophysical Phenomena

SN 2025fhm: A central-engine powered Ic-BL supernova associated with X-ray transient EP250304a

Cui-Ying Song, Nan Jiang, Xiaofeng Wang et al. (+32 more)

We present X-ray, optical, and radio follow-up observations of EP250304a, an extragalactic fast X-ray transient (EFXT) discovered by the Einstein Probe. Its X-ray light curve exhibits two broad pulses with comparable peak fluxes within the first $\sim$1~ks, a feature rarely seen among low-luminosity gamma-ray bursts or EFXTs. Optical follow-up observations were carried out using the Korea Microlensing Telescope Network, the Thai Robotic Telescope, the Las Cumbres Observatory 1~m global network, the Gemini Multi-Object Spectrograph on Gemini south telescope, and the Global Supernova Network. The fast-cooling phase (within 3 days) of optical data can be well fitted by a shocked cocoon model. However, during the supernova phase (SN 2025fhm, from 3 to 88 days), the late-time light curve cannot be explained solely by radioactive $^{56}$Ni decay, as demonstrated by a grid of simulations using the one-dimensional Lagrangian radiation hydrodynamics code SNEC, which reveals a significant energy excess at late epochs. To account for this excess, a central engine like a rapidly spinning, highly magnetized neutron star is needed to provide additional energy injection. This model yields a best-fit spin period of $\sim$12.60~ms and magnetic field strength of $\sim 3.52\times10^{15} \rm G$, and it successfully explains both the late-time bolometric light curve and the early X-ray pulse structures. Our results indicate that EP250304a/SN 2025fhm is likely powered by a central magnetar rather than by radioactive decay alone, offering new insights into the energy budget and physical origin of EFXTs and their associated supernovae.
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All authors Cui-Ying Song, Nan Jiang, Xiaofeng Wang, Yi-Han Iris Yin, Lingzhi Wang, Wenxiong Li, Shengyu Yan, Dae-Sik Moon, Tao An, Aleksandar Cikota, Samaporn Tinyanont, Liang-Duan Liu, Cui-Yuan Dai, Christopher D. Matzner, Bin-Bin Zhang, Lixin Yu, Qinyu Wu, Hong Soo Park, Sang Chul Kim, Youngdae Lee, Yu-Hao Zhang, Haowei Peng, Franz E. Bauer, Joseph R. Farah, Moira Andrews, Kathryn Wynn, Yuan Qi Ni, D. Andrew Howell, Curtis McCully, Ning-Chen Sun, Danfeng Xiang, Yuan Liu, Wenxin Wang, Yijia Zhang, Wei Chen

High Energy Astrophysical Phenomena

Radio Emission with Dust: A Bow-Shock Interpretation for the TDE Candidate AT 2019avd

Shuyuan Wei, Yanan Wang, Guobin Mou et al. (+5 more)

Forward shocks produced by interactions between a single ejected blob and the circumnuclear medium (CNM) around a supermassive black hole are widely invoked to explain radio emission from tidal disruption events (TDEs). However, recent observational evidence such as rapidly rising radio emission, double-peaked broadband spectral energy distributions, and declining shock energies at late times poses challenges to this picture. Alternative scenarios have therefore been proposed, including bow shocks arising from outflows colliding with dense clouds, the production of new ejecta at late times, and variations in microphysical parameters. To investigate the roles of these factors, we analyze the long-lived radio flare of the TDE candidate AT 2019avd, for which dust has been identified through mid-infrared observations, using a radio dataset spanning more than five years. We find that a bow-shock scenario can account for the majority of the observed radio emission, while a forward shock, or an additional bow shock involving different clouds, may begin to dominate at late times. However, a forward-shock scenario remains viable when allowing for evolving microphysical parameters and more complex CNM structures. We discuss the remaining tensions in both the outflow-CNM and outflow-cloud interaction scenarios.
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All authors Shuyuan Wei, Yanan Wang, Guobin Mou, Linhui Wu, Santiago del Palacio, Ranieri D. Baldi, Xiaolong Yang, Yang Huang

Solar and Stellar Astrophysics

Detection of resonant nodes in a pore chromosphere

T. Felipe, H. Kumar and E. G. Broock

Active region atmospheres host many oscillatory phenomena. The chromosphere is delimited by steep temperature gradients at the photosphere and transition region, where magnetoacoustic waves are trapped and can form standing oscillations within this resonant cavity. We aim to detect the signature of the resonant nodes of standing waves, which are expected to produce sudden jumps in the oscillatory phase and power dips. Spectroscopic temporal series of H$\alpha$ in a pore were acquired with the Swedish Solar Telescope. The velocity and temperature fluctuations at multiple atmospheric heights were inferred from the analysis of the intensity at many spectral positions along the line wings. Wavelet analysis was employed to characterize the phase differences and the power at different heights. The phase shift between velocity and temperature shows a $\pm90^{\circ}$ value, which is consistent with standing oscillations. Robust evidence of the presence of a nodal layer in the temperature at around the height probed by the intensity at H$\alpha\pm0.30$ Å\ is found, such as the detection of 180$^{\circ}$ jumps in the phase of the temperature oscillations and remarkable power dips at the same atmospheric layer. The exact height of the resonant nodes depends on the spatial location and time. We generally find a mixture of standing and propagating waves. This is consistent with a leaky resonator where waves are partially reflected at the transition region, while some of them are able to propagate into the corona. For the first time, we report the detection and characterization of resonant nodes in the solar chromosphere. This result provides strong observational support for the chromospheric resonant cavity model and paves the way for the development of new seismological techniques to investigate the structure of active region chromospheres.
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Astrophysics of Galaxies

Low-Redshift Interlopers in the SDSS DR16 $z > 5$ Quasar Catalogue

Vivek Kumar Jha, Harikumar N and Yogesh Wadadekar

High-redshift quasars ($z>5$) are crucial for studying early black hole growth and reionisation. SDSS Data Release 16 catalogues 655 such sources with multiple redshift estimators. We systematically examined this subsample and found 480 sources (73.2%) where pipeline redshift (Z\_DR16Q) disagrees with the derived estimate (Z\_FIT) significantly. Visual inspection confirms that 125 of these (19.1% of the total) are actually low-redshift active galactic nuclei. In 114 cases, broad Mg\,ii with C\,iii and C\,iv was misidentified as Ly$\alpha$; in 11 cases, H$\alpha$ was misidentified as Ly$\alpha$. This error is immediately revealed by the absence of Gunn–Peterson trough blueward of Ly$\alpha$. Crucially, Z\_FIT recovers correct redshift in the affected sources where emission lines are prominent, indicating the algorithm is sound; the issue lies in community preference for Z\_DR16Q or Z\_SPEC. We urge caution against uncritical use of pipeline redshifts for $z>5$ DR16Q sources and recommend Z\_FIT as the preferred estimator.
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Astrophysics of Galaxies

AEON-z5: A Candidate AGN-driven Outflow Enriching the Circumgalactic Medium at $z\simeq5.23$

Xiaoyang Wei, Zheng Cai, Shiwu Zhang et al. (+6 more)

The dispersal of chemically enriched gas from galaxies into their surroundings is a key process in galaxy evolution, yet direct observational evidence at z>5 remains scarce. We present AEON-z5, a galaxy at z~5.23 in the COSMOS field comprising a compact continuum-emitting core surrounded by an extended, line-dominated ionized nebula. JWST/NIRCam imaging shows that H$\alpha$+[N II] and H$\beta$+[O III] emission extends to projected radii of >4 kpc - 2-2.5 times the typical effective radius at the host stellar mass - reaching the outer ISM and the inner CGM. F444W grism data reveal a highly asymmetric H$\alpha$+[N II] profile, which we interpret as a bipolar outflow and decompose into three kinematic components. The dominant component has a flux-weighted velocity offset of ~+489 km/s and FWHM~630 km/s, with a wing reaching $v_{84}$~792 km/s. A tentative detached feature at $\Delta v_{LOS}$~2800 km/s, detected at 1.5$\sigma$ in the 1D spectrum (2.4$\sigma$ in the 2D fit), may trace an outflow clump. These kinematics are most coherently explained by an AGN in the core. For the extended nebula, we derive a velocity curve shifting redward with radius, reaching 200-400 km/s at $r_p$~1.3-2.5 kpc - a trend that may reflect an accelerating outflow, corotating gas, or recycled inflow viewed in projection. Crucially, the measured [N II]/H$\alpha$ ratios imply near-solar N2-based abundances (0.7-1.0 $Z_\odot$), remaining >0.37 $Z_\odot$ after allowing for AGN excitation and calibration systematics. The combination of large extent, enrichment, and extreme kinematics identifies AEON-z5 as a candidate snapshot of feedback-driven metal transport, offering a direct view of how early AGN activity may redistribute chemically processed gas into the CGM within the first ~1.1 billion years.
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All authors Xiaoyang Wei, Zheng Cai, Shiwu Zhang, Fujiang Yu, Yunjing Wu, Shuaiyi Li, Xiaojing Lin, Mingyu Li, Xuelun Mei

High Energy Astrophysical Phenomena

Revisiting EBL Constraints from Gamma-Ray Observations: A Critical Assessment and Methodological Improvements

K. Abe, S. Abe, J. Abhir et al. (+185 more)

The extragalactic background light (EBL), ranging from the infrared to the ultraviolet bands, is the second most intense photon field in the universe, surpassed only by the cosmic microwave background (CMB). It is primarily generated by starlight in galaxies, either directly or through absorption by dust and re-emission at longer wavelengths. Very high energy (VHE, $E$ > $100\,$GeV) photons can be absorbed via $\gamma \gamma$ interactions with the EBL during their propagation across cosmological distances, providing an indirect method to probe the EBL by studying its impact on the energy spectra of distant VHE sources. This paper examines the robustness of EBL constraints derived from gamma-ray data, critically assessing the assumptions made in previous studies about the intrinsic source spectra, the uncertainties of the observations and the validity of the analysis tools. We find that earlier studies likely underestimated the uncertainties in the EBL intensity constraints, underscoring the need to account for systematic uncertainties comprehensively. By employing a Monte Carlo (MC) simulation and a plausible model for unknown systematic errors, we compute more realistic uncertainties. Additionally, we discuss possible alternatives to set EBL constraints, relaxing the assumptions on the intrinsic spectra of gamma-ray sources, with the goal of achieving more robust constraints.
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All authors K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, A. Aguasca-Cabot, I. Agudo, I. Albanese, T. Aniello, S. Ansoldi, A. Arbet Engels, C. Arcaro, T. T. H. Arnesen, A. Babić, C. Bakshi, U. Barres de Almeida, J. A. Barrio, I. Batković, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, O. Blanch, G. Bonnoli, Ž. Bošnjak, E. Bronzini, I. Burelli, A. Campoy-Ordaz, A. Carosi, R. Carosi, M. Carretero-Castrillo, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, A. Cerviño, Y. Chai, G. Chon, A. Cifuentes Santos, J. L. Contreras, J. Cortina, S. Covino, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, M. Delfino, J. Delgado, C. Delgado Mendez, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsaesser, L. Foffano, L. Font, F. Frías García-Lago, S. Fröse, Y. Fukazawa, S. García Soto, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, T. Gradetzke, R. Grau, J. G. Green, P. Günther, D. Hadasch, A. Hahn, G. Harutyunyan, T. Hassan, J. Herrera Llorente, D. Hrupec, D. Israyelyan, J. Jahanvi, I. Jiménez Martínez, J. Jiménez Quiles, S. Kankkunen, T. Kayanoki, G. W. Kluge, J. Konrad, P. M. Kouch, H. Kubo, J. Kushida, M. Láinez, A. Lamastra, E. Lindfors, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, L. Lulić, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, G. Maneva, M. Manganaro, S. Mangano, K. Mannheim, M. Mariotti, M. Martínez, P. Maruševec, D. Mazin, S. Menchiari, J. Méndez Gallego, S. Menon, D. Miceli, J. M. Miranda, R. Mirzoyan, M. Molero González, E. Molina, H. A. Mondal, A. Moralejo, C. Nanci, A. Negro, V. Neustroev, M. Nievas Rosillo, C. Nigro, L. Nikolić, K. Nilsson, S. Nozaki, A. Okumura, J. Otero-Santos, S. Paiano, D. Paneque, R. Paoletti, J. M. Paredes, M. Peresano, M. Persic, M. Pihet, F. Podobnik, P. G. Prada Moroni, E. Prandini, W. Rhode, M. Ribó, J. Rico, A. Roy, N. Sahakyan, F. G. Saturni, F. Schiavone, K. Schmitz, F. Schmuckermaier, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, M. Takahashi, R. Takeishi, J. Tartera Barberà, P. Temnikov, T. Terzić, A. Tutone, S. Ubach, M. Vazquez Acosta, S. Ventura, G. Verna, I. Viale, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, M. Vorbrugg, I. Vovk, R. Walter, C. Walther, F. Wersig

Astrophysics of Galaxies

The Roman eXtreme Deep Field (RXDF)

Haojing Yan, Anton M. Koekemoer, Yue Shen et al. (+127 more)

The Roman eXtreme Deep Field (RXDF) program is one of the five General Astrophysics Survey (GAS) programs approved for observing time with the Nancy Grace Roman Space Telescope in Cycles 1 and 2. It has been allocated 386.41 hours to carry out an imaging survey to AB = 30 mag (5-sigma) over ~140x larger area than the Hubble eXtreme Deep Field (HXDF) full-depth area (ACS+WFC3/IR). The RXDF will cover the full Roman wavelength range with 7 bands, reaching AB = 30 mag in RZYJH, 29 mag in F, and 28 mag in K, over a full-depth area of 678.75 arcmin^2 embedded in a total area of 1,243 arcmin^2, and far exceeding the depths of the Roman Core Community Surveys (CCS). The RXDF is within the Euclid Ultra Deep Field (EUDF) near the North Ecliptic Pole (NEP), a strategic long-term field for generational space facilities, with a wealth of multi-wavelength data including extensive coverage from the James Webb Space Telescope (JWST) NEXUS Treasury program. The observations will cover 3 epochs at a 1-year cadence, each epoch divided into 3 sub-epochs ~10 days apart, enabling time-domain studies on time baselines from ~10 days to over ~2 years. The RXDF is uniquely positioned to address critical questions in reionization, large scale structure (LSS), growth of supermassive black holes (SMBHs), little red dots (LRDs), and high-z supernovae (SNe); the volumes probed by HST+JWST are too small at these extreme depths, and even the deepest CCS tiers are too shallow. In addition to our key objectives, a wealth of additional science will be enabled by engaging the community with our rapidly released datasets, revolutionizing a wide range of science for a lasting legacy. This short document, which is converted from the approved RXDF proposal, aims to provide the community with a summary of the program.
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All authors Haojing Yan, Anton M. Koekemoer, Yue Shen, Bangzheng Sun, Norman A. Grogin, Zihao Wu, Christian Kragh Jespersen, Rachel Somerville, Kyoung-Soo Lee, Dale D. Kocevski, Adam J. Burgasser, Pedro H. Bernardinelli, Yicheng Guo, Charles Steinhardt, Xiaohui Fan, Duncan Farrah, Gisella De Rosa, Feige Wang, Jinyi Yang, Lifan Wang, Fengwu Sun, Christopher N. A. Willmer, John David Silverman, Steven L. Finkelstein, Seth H. Cohen, Rolf A. Jansen, Rogier A. Windhorst, Brent M. Smith, Stefano Casertano, Anthony H. Gonzalez, Michael A. Strauss, Ray A. Lucas, Katherine E. Whitaker, Mingyang Zhuang, Rodrigo Angulo, Chloe Aurin, Micaela Bagley, Franz E. Bauer, Jessica M. Berkheimer, Rachel Bezanson, Alejandro S. Borlaff, Rebecca A. A. Bowler, Larry D. Bradley, W. N. Brandt, Denis Burgarella, Timothy Carleton, Delondrae D. Carter, Caitlin M. Casey, Christopher J. Conselice, Kyle W. Cook, Jeff Cooke, David A. Coulter, Tyler Desjardins, Tim Dewachter, Nicole E. Drakos, Simon P. Driver, Qiao Duan, Eiichi Egami, Andreas Faisst, Travis C. Fischer, Adriano Fontana, Ori Fox, Brenda Frye, Yoshinobu Fudamoto, Eric Gawiser, Mauro Giavalisco, Yuichi Harikane, Thomas Harvey, Nimish P. Hathi, Benne W. Holwerda, Taylor Hutchison, Olivier Ilbert, Akio K. Inoue, Lucy R. Ivey, Kartheik Iyer, Mathilde Jauzac, Ignas Juodzbalis, Jeyhan S. Kartaltepe, Daichi Kashino, Susan Kassin, Patrick Kelly, Kotaro Kohno, Stephanie LaMassa, Erini Lambrides, Rebecca Larson, Junyao Li, Zhiyuan Ma, Sangeeta Malhotra, Elizabeth McGrath, Peter Melchior, Marcio Melendez, Hironao Miyatake, Bahram Mobasher, Mireia Montes, Thomas Moore, Takahiro Morishita, Takashi Moriya, Leonidas Moustakas, Rohan Naidu, Rosalia O'Brien, Pascal A. Oesch, Masafusa Onoue, Rafael Ortiz III, Masami Ouchi, Robert G. Pascalau, Molly Peeples, Andreea O. Petric, Sara Petty, Justin Pierel, Marc Rafelski, Eniko Regos, Armin Rest, Mitchell Revalski, James Rhoads, Pierluigi Rinaldi, Aaron Robotham, Kate Rowlands, Pablo M. Sanchez-Alarcon, Paola Santini, Alice E. Shapley, Raymond C. Simons, Swara Ravindranath, Takahiro Sumi, Takumi S. Tanaka, Masayuki Tanaka, Scott Tompkins, Christina C. Williams, Edward J. Wollack, John F. Wu, L. Y. Aaron Yung

High Energy Astrophysical Phenomena

From DAMPE to LHAASO: Rigidity Scales and Composition Changes in Galactic Cosmic Rays

Ruo-Yu Liu and Zhen Cao

This commentary briefly reviews recent measurements from DAMPE and LHAASO on cosmic rays to explore why the spectra of different species change shape across the TeV-PeV energy range. DAMPE finds that several primary nuclei show spectral softening at a similar magnetic rigidity, while the combined proton and helium data from DAMPE and LHAASO reveal a more complex evolution at higher energies. By comparing these spectral features and composition changes, we discuss what they may tell us about the sources of Galactic cosmic rays and how these particles propagate through the Galaxy.
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Cosmology and Nongalactic Astrophysics

Probing Projection Effects in Optically-Selected Clusters with Velocity Dispersions Outliers

K. Graham, T. E. Jeltema, C.-H. To et al. (+8 more)

The evolution of galaxy cluster abundance is a powerful probe of cosmology, but its efficacy depends on our ability to understand and control for systematics in the selection and mass estimation of clusters. We study redMaPPer-selected clusters in the Cardinal simulation, which simulates the DES Y3 observational conditions. Specifically, we investigate the line-of-sight velocity distributions of cluster member galaxies in 12,272 simulated clusters. We find that a significant fraction of clusters, 35%, have velocity dispersions that are high compared to their richness with an offset of $\sim 400$ km s$^{-1}$ between the outliers and the main population. A similar population of velocity dispersion outliers was found in the DES Y3 data. Nearly all of the outliers (98%) in a low-richness subsample have non-Gaussian velocity distributions, and they are more likely than the main population to have significant velocity substructure. These clusters also tend to have higher redshifts than clusters with typical velocity dispersions, and they show a larger scatter between halo mass and richness. Overall, our results point to a significant contamination of redMaPPer-selected samples from line of sight structure, particularly at high redshifts and low richness. Comparison to the Buzzard simulations shows similar results.
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All authors K. Graham, T. E. Jeltema, C.-H. To, V. Wetzell, Kyle W. Davis, Conghao Zhou, H.-Y. Wu, E.S. Rykoff, J. DeRose, Michel Aguena, R.H. Wechsler

Solar and Stellar Astrophysics

Multi-Height Spectropolarimetric Signatures of Magnetoacoustic Waves in Solar Plage

Taylor Sitterson, João M. da Silva Santos, Joshua Bentley et al. (+5 more)

We analyze high-cadence spectropolarimetric observations of solar plage obtained with the Visible Spectro-Polarimeter (ViSP) on the Daniel K. Inouye Solar Telescope (DKIST) to investigate low-chromospheric waves sampled by the Na I D1 5896 Angstrom and Ca II 8542 Angstrom lines. Observations were taken at an oblique viewing angle, providing sensitivity to transverse motions. Magnetic oscillations within plage elements exhibit significant line-of-sight (LOS) RMS amplitudes of approximately 9 G on average in the Na I D1 line, whereas the corresponding Ca II oscillations are only marginally above the noise level. Adaptive profile tracking provided line-core intensities and Doppler velocities, the weak-field approximation provided LOS magnetic fields, and non-LTE inversions provided mass densities and formation heights. Cross-spectral analysis shows velocity-intensity phase distributions coupled at -90 degrees, consistent with compressive oscillations. The velocity phases in Na I-Ca II indicate upward propagation and the phase speeds are predominantly sub-Alfvenic, consistent with slow magnetoacoustic waves. Although the slit geometry prevents a definitive identification of the tube eigenmode, the differing magnetic phase relationships suggest a height-dependent sausage-like behavior in the coupling between the magnetic and compressive perturbations. Additionally, our inferred wave fluxes are insufficient to heat active-region plage.
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All authors Taylor Sitterson, João M. da Silva Santos, Joshua Bentley, Tom Schad, Momchil Molnar, Bart De Pontieu, Juan Martinez-Sykora, Alexander G. M. Pietrow

Instrumentation and Methods for Astrophysics

CTree: Branch-wise compatible merger tree builder

Jinsu Rhee, Christophe Pichon and Yohan Dubois

We introduce a merger tree builder, CTree. Its key feature is the identification of progenitors using the evolutionary information encoded in object branches, rather than relying solely on the instantaneous particle membership in a single snapshot. In this sense, CTree can be described as a branch-wise merger tree builder. Specifically, CTree extracts particles associated with objects over a defined timescale and uses this information to compute the merit functions employed in the progenitor search across multiple snapshots. During this process, CTree requires only the identifiers of particles and objects. This ensures high compatibility with different halo and galaxy catalogues and also with pre-existing merger trees. To identify `core' particles that remain bound to the host halo over extended physical timescales, CTree employs a simple and efficient algorithm that does not rely on explicit radial or binding-energy information. The timescale adopted for core particle extraction and the number of snapshots used in the progenitor search can be user-configured. Basic validation tests using suites of dark matter-only simulations demonstrate that CTree produces stable and physically consistent halo merger trees, particularly in high-density regions or in simulations with high output cadence. The code is written in C++ and employs a hybrid message passing interface and OpenMP parallelization, making it well-suited for high-resolution cosmological simulations. The code is publicly available and actively maintained to improve performance, reliability, and compatibility.
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