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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 6 April

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

Galileon versus Quintessence: A comparative phase space analysis and late-time cosmic relevance

Mohd Shahalam

We perform a comparative phase space analysis of the light mass Galileon model and standard Quintessence in the context of late–time cosmic acceleration. Focusing on a spatially flat FLRW background, we consider a cubic Galileon interaction supplemented by a scalar potential and examine three representative choices of the potential: a generalized cosh potential, a simple cosh potential, and a linear potential. By introducing suitable dimensionless variables, the cosmological field equations are reformulated as an autonomous dynamical system, allowing a systematic investigation of the stationary points and their stability properties. For the light mass Galileon scenario, we find that although the phase space admits scalar field dominated solutions, all critical points are of saddle type for the potentials considered. In particular, no stable late-time accelerating attractor emerges, even in the presence of de-Sitter like configurations. In contrast, the Quintessence limit admits stable de-Sitter attractors for cosh potentials, providing a viable description of the observed late–time acceleration. Our results highlight a key qualitative distinction between Galileon and Quintessence cosmologies and indicate that, within the light mass Galileon framework, the higher-order Galileon interactions may be required to realize a stable accelerating Universe.
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Astrophysics of Galaxies

From NVSS to RACS: Identifying truly Compact Galactic and Extragalactic sources with Steep Spectra

Rajat Shinde, Yogesh Maan and Apurba Bera

Compact, steep-spectrum radio sources are key tracers of exotic astrophysical objects such as pulsars and high-redshift radio galaxies. All-sky radio surveys at different frequencies, like the TIFR-GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey (NVSS), have been usually exploited to identify such tracers. The more recent imaging survey, Rapid ASKAP Continuum Survey (RACS), with higher angular resolution and better sensitivity offers an avenue for a far better identification and characterisation of compact, steep-spectrum sources. In this work, using publicly available RACS images at 887 MHz and 1.4 GHz, we present an image-domain characterisation of 171 compact source candidates between declinations -40 degrees and +41 degrees, that were detected and appeared compact at 147 MHz in TGSS but not detected at 1.4 GHz in NVSS. Our detailed characterisation resulted in the identification of 66 compact sources, 87 non-compact, diffuse or resolved sources, and 18 sources that are not detected in either of the RACS or NVSS images, implying spectral indices steeper than -2.0. Out of the 66 compact sources, 38 have spectral indices steeper than -1.5. We demonstrate that a large fraction of the sources in our sample were earlier not detected and resulted in incorrect spectral index limits due to poor imaging quality of NVSS in the Galactic plane. We present the spectral indices and morphological classification of all the sources in our sample and discuss their usefulness in identifying and studying interesting sources such as radio pulsars, high-redshift radio galaxies, and other extragalactic sources.
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High Energy Astrophysical Phenomena

Recoil kicks from binary black hole mergers in GWTC catalogs: implications for retention and hierarchical mergers

Tousif Islam

We infer recoil (kick) velocities for both individual binary black hole (BBH) mergers and candidate intermediate-mass black hole events, as well as for the BBH populations inferred from GWTC catalogs up to GWTC-5. We obtain informative recoil constraints for several events, including GW231028-153006 ($v_{\rm kick}=839^{+1018}_{-681}\,\mathrm{km\,s^{-1}}$) and GW231123-135430 ($v_{\rm kick}=974^{+944}_{-760}\,\mathrm{km\,s^{-1}}$), while finding that the majority of event-level recoil posteriors remain broad and only weakly informative. We further infer consistent population-level recoil distributions across GWTC-3, GWTC-4, and GWTC-5, with median kick velocities of approximately $300$–$330\,\mathrm{km\,s^{-1}}$. Using both event-level and population-level recoil estimates, we find typical retention probabilities of $\sim2$–$3\%$ for globular clusters, $\sim28$–$32\%$ for nuclear star clusters, $\sim25$–$29\%$ for dwarf galaxies, and $\sim92$–$94\%$ for elliptical galaxies. We also compute recoil-induced displacements and dynamical-friction return times, finding that retained remnants in globular clusters and nuclear star clusters can remain displaced from their host cores for extended periods. Our results show that retention alone is not sufficient to determine the prospects for hierarchical mergers: hierarchical-merger efficiency depends on both remnant retention and post-kick re-centering.
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Solar and Stellar Astrophysics

A critical analysis of main-sequence fitting in open clusters to derive the helium-to-metal enrichment ratio $\Delta Y/\Delta Z$

G. Valle, N. Ricci, M. Dell'Omodarme et al. (+3 more)

We aim to investigate the feasibility of accurately determining the helium-to-metal enrichment ratio $\Delta Y/\Delta Z$ for open clusters using Gaia DR3 photometry. To test the reliability of this calibration, we performed a theoretical investigation using mock open clusters. We generated synthetic photometric data from isochrones calculated by five different stellar evolution codes (FRANEC, PARSEC 1.2s, PARSEC 2.0, BASTI, and MIST), for which the true $\Delta Y/\Delta Z$ is known. We then fitted these mock clusters with two sets of isochrones calculated with the FRANEC code, differing only in the implementation of bolometric corrections (BCs). The analysis focused on the G-band absolute magnitude range (4.3 to 6.5 mag) to minimise the impact of poorly constrained physics. Synthetic clusters were generated at [Fe/H] values from 0.0 to 0.15 dex, for different numbers of populating stars and different levels of photometric uncertainties. The Monte Carlo experiments revealed significant and code-dependent biases. Unbiased results were achieved only when the stellar models used for synthetic-cluster generation and fitting were identical. Using identical FRANEC stellar models but different BCs introduced a significant bias of up to 0.6. Furthermore, using different stellar models for synthetic cluster generations resulted in even larger biases: $\Delta Y/\Delta Z$ was underestimated by up to 0.8 for PARSEC target isochrones, while it was overestimated for BASTI and MIST isochrones by up to 0.6 and 1.5, respectively. The magnitude and the inconsistency of these biases strongly suggest that the photometric calibration of $\Delta Y/\Delta Z$ using open clusters is not reliably robust.
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All authors G. Valle, N. Ricci, M. Dell'Omodarme, P.G. Prada Moroni, S. Degl'Innocenti, S. Cassisi

Astrophysics of Galaxies

Random gas motions inside sub-parsec scale supercritical filaments

Chao Zhang, Tie Liu, Mika Juvela et al. (+12 more)

Supercritical gas filaments in molecular clouds host the dense cores in which new stars form. The mechanisms governing their formation and subsequent gas accretion remain poorly understood. In this study, we conduct a statistical analysis of a large sample of sub-parsec supercritical filaments using H13COp J=1-0 data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) Survey. We identified velocity-coherent filaments in position-position-velocity (PPV) space and systematically examined velocity gradients both along and perpendicular to their skeletons. Our analysis uncovers a remarkable result: at scales of ~ 0.1-1 pc, the local velocity gradients within these supercritical filaments show no preferred alignment with the filament skeletons and exhibit no correlation with the local gravitational field. This random orientation suggests the presence of chaotic gas motions deep inside these dense structures. These findings may indicate that turbulence-rather than gravity-dominates gas dynamics and structural evolution at small scales, even in regions on the verge of star formation, challenging the paradigm of gravity-dominated structure formation within molecular clouds. This scenario should be further tested by more state-of-the-art simulations. This study offers key observational insights into the roles of turbulence and gravity in establishing the initial conditions for star formation.
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All authors Chao Zhang, Tie Liu, Mika Juvela, Paolo Padoan, Hong-Li Liu, Di Li, Guido Garay, Neal J. Evans, Fengwei Xu, Paul F. Goldsmith, Qizhou Zhang, Kee-Tae Kim, Yankun Zhang, Zhiyuan Ren, Mengke Zhao

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Multi-field oscillons/I-balls in the Friedberg-Lee-Sirlin model

Kai Murai, Tatsuya Ogawa and Fuminobu Takahashi

We study oscillon/I-ball solutions in a real scalar version of the Friedberg-Lee-Sirlin (FLS) model. Using the multiple-scale analysis, we derive the conditions for oscillon solutions and explore multi-field oscillon configurations. In these configurations, the two fields form co-located oscillons that oscillate with frequencies set by their respective masses. These multi-field oscillons can be viewed as a bound state of two oscillons due to attractive interactions between the fields. We confirm these analytical predictions through numerical lattice calculations. This work extends the standard picture of single-field oscillons and may be relevant for cosmological scenarios involving multiple interacting real scalar fields.
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Cosmology and Nongalactic Astrophysics

Directional Tests of the Cosmic Distance Duality Relation using Pantheon+ and BAO

Pushty Shrimankar and Gopal Kashyap

We present a model-independent test of anisotropy in the cosmic distance duality relation (CDDR), $D_L=(1+z)^2 D_A$, using the Pantheon+ type Ia supernova sample and baryon acoustic oscillation (BAO) data. The angular diameter distance is reconstructed via Gaussian Processes, enabling an estimate of $\eta(z)=D_L/[D_A(1+z)^2]$ without assuming a background cosmology. We also allow for a possible isotropic evolution, parameterized as $\eta(z)=1+\eta_1 z$, and find a redshift-dependent deviation whose significance depends on the assumed supernova calibration. Anisotropy is modeled through a dipole modulation and constrained using a full covariance-based likelihood. To assess statistical significance, we construct null realizations that preserve both the redshift distribution and the survey selection function. We find that the observed dipole amplitude is consistent with isotropic expectations and lies below the levels induced by statistical fluctuations and survey geometry. We obtain a robust 95% upper bound $A_{95}=0.025$, stable across different supernova calibration choices. We find no evidence for intrinsic anisotropy in the CDDR. Our results highlight the importance of accounting for survey selection effects in anisotropy searches and provide a viable framework for testing directional deviations in cosmological relations.
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Cosmology and Nongalactic Astrophysics

Information-Geometric Perspective on the Hubble Tension: Eigenmode Rotation and Curvature Suppression in wCDM

Seokcheon Lee

The Hubble tension is shaped not only by shifts between early- and late-time parameter estimates, but also by the stiffness of the constraints that define them. In this work, we analyze this geometric structure in the wCDM model by separating the discrepancy into two components: a parameter displacement and a directional Fisher curvature. Within the local Gaussian approximation, the quadratic tension along a given direction factorizes into the squared shift and the combined directional curvature contributed by the datasets. Applying this framework to Planck, DESI DR2, and SH0ES, we show that extending \LambdaCDM to wCDM primarily reshapes the Fisher geometry of the CMB constraint rather than opening a genuinely new route to concordance. Allowing the dark-energy equation-of-state parameter w to vary suppresses the leading Planck Fisher eigenvalue to only \sim 2.7 % of its \LambdaCDM value, while producing only a modest rotation of the dominant acoustic-scale eigenmode. The net effect is a strong softening of the effective acoustic rigidity. At the same time, high-precision late-time data, especially from DESI DR2, inject substantial curvature along the expansion-rate direction. This added stiffness acts as a geometric wall, closing off phantom-like escape routes and sharply limiting tension relief within the extended parameter space. Our results indicate that changes in the inferred H_0 tension under model extension are best understood as a reconfiguration of the constraint manifold rather than as evidence for new physical agreement. The shift-curvature decomposition thus offers a simple, fast, and physically transparent way to diagnose cosmological tensions.
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Cosmology and Nongalactic Astrophysics

Probing cosmic anisotropy with galaxy clusters and supernovae

Shubham Barua, Sujit K. Dalui and Shantanu Desai

Using $\Lambda$CDM and Padé-(2,1) cosmography, we study directional variations in the Hubble constant, $H_0$, using galaxy clusters (GC) and Type Ia Supernovae (SNe), from the PantheonPlus compilation, employing the hemisphere decomposition method. Since there is a degeneracy between $H_0$ and absolute magnitude $M_B$ for SNe, Cepheid-host calibration is usually required to constrain $H_0$. To complement the Cepheid-host calibration in the SNe analysis, we use GC X-ray scaling relations as a complementary probe of anisotropy. We consider five redshift bins on the full SNe sample $[z_\mathrm{min}, 0.5]$ where $z_\mathrm{min}= \{0.015, 0.03, 0.05, 0.1, 0.2\}$. Our results show that the combined GC sample is consistent with statistical isotropy and that there is a $\sim 2.5 \sigma$ anisotropy preference in the lowest-redshift bin in the SNe-only case. This preference weakens when low-redshift SNe are progressively removed. In the SNe$+$GC analysis, we find that any anisotropy preference is driven by how the $H_0-M_B$ and the $H_0-k$ (where $k$ is the normalization parameter in the GC scaling relation) degeneracies are treated. The low-redshift bin anisotropy preference in the SNe-only analysis persists in the SNe$+$GC case when Cepheid-host calibration is used while the results are consistent with statistical isotropy when $k$ is fixed. Overall, our results do not provide compelling evidence for a statistically significant anisotropy in the local expansion rate. Our findings highlight the importance of combining complementary cosmological probes and examining the dependence of anisotropy constraints on calibrations and parameter degeneracies when assessing claims of cosmic anisotropy.
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Solar and Stellar Astrophysics

Speckle Interferometry of 25 Gaia Two-Parameter Potential Binaries

Paul McCudden, Russell Genet, John Major et al. (+20 more)

Gaia two-parameter (G2P) stars have cumulative errors in parallax and proper motion so great that only their mean positions were reported in DR3. One potential cause of these high errors is another star as indicated by two intensity peaks in the scans. Speckle interferometry astrometric measurements of 25 G2P stars with high multi-peak percentages were obtained with the 1.5m telescope at Mt. Wilson Observatory. Of the 25 observed G2P stars, seven had no reported Gaia companions within 5.0". We found nearby companions for all seven. The 18 other G2P stars had known Gaia companions within 2.0". Of these, 13 had separations that agreed closely with the speckle measurements but with some discrepancy in position angles, three stars did not agree in either separation or position angle and no companion was detected for the remaining two. Although some of these issues may be resolved in DR4 or DR5, others may be inherent limitations of Gaia capabilities that speckle interferometry observations may be able to fill.
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All authors Paul McCudden, Russell Genet, John Major, Zachary Hartman, A. U. Kovic, Rick Wasson, Michael-James Ellis, Lou Jackson, Bradley Brungardt, Zaida Weems, Astrid Wehlitz, Evan Wille, Leon Bewersdorff, Nick Hardy, Rachel Freed, David Rowe, Thomas C. Smith, Reed Estrada, Thomas Meneghini, Reggie Jones, Tom Mason, Dwight Collins, Mark Copper

High Energy Astrophysical Phenomena

A comparison of three neodymium atomic data sets for kilonova modeling

Christopher J. Fontes, Nicholas Vieira, Chris L. Fryer et al. (+4 more)

We examine the impact of input neodymium (Nd) atomic data on the light curves and spectra of kilonovae, probing the sensitivity of kilonova observables to the atomic physics of this important lanthanide element. We use the SuperNu Monte Carlo radiative transfer code, simulating a simple semi-analytic 1D kilonova with a pure Nd atmosphere, fixing the radiative transfer method while using input atomic data generated by three different codes: the LANL suite of atomic physics codes, HULLAC, and Autostructure. We see that the choice of atomic data significantly shapes the resulting light curves and spectra. Peak bolometric luminosities differ by a ratio of nearly 1.5 between HULLAC/Autostructure and LANL data sets. Moreover, we observe significant near- to mid-IR differences in the structure of the spectra. We specifically attribute these differences to the choice of atomic data for neutral Nd I. Many of the results here have been adapted from a presentation at "Radiative Transfer and Atomic Physics of Kilonovae" in Stockholm, 2023. We additionally present a LANL data set with energies calibrated to available values in the NIST Atomic Spectra Database, and demonstrate that this calibration also significantly affects IR spectral structure at late time. The substantial differences in kilonova observables that arise from tuning the atomic data of just one lanthanide element highlight the special attention that must be paid to atomic physics uncertainties when modeling kilonovae, from AT2017gfo to beyond.
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All authors Christopher J. Fontes, Nicholas Vieira, Chris L. Fryer, Adithan Kathirgamaraju, Oleg Korobkin, Marko Ristić, Ryan T. Wollaeger

Cosmology and Nongalactic Astrophysics

Replacing Gaussian Processes with Neural Networks in Pulsar Timing Array Inference of the Gravitational-Wave Background

Shreyas Tiruvaskar and Chris Gordon

Bayesian inference of nanohertz gravitational-wave background models in pulsar timing array analyses often relies on Gaussian-process interpolators to avoid repeated, computationally expensive strain-spectrum calculations. However, Gaussian-process training becomes a bottleneck for large training sets. We test whether probabilistic neural networks can replace Gaussian processes in this role for both a self-interacting dark matter model and a phenomenological environmental model. We find that neural networks recover consistent posteriors while significantly reducing both training and Markov chain Monte Carlo runtime, with the largest gains for the more computationally demanding model.
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Sunday 5 April

Astrophysics of Galaxies

The Identification of Asymmetric Barred Galaxies in Illustris TNG-50

Junwoo Jung, Minjin Kim and Taehyun Kim

Most barred galaxies exhibit symmetric structures. However, recent studies have shown that a subset of barred galaxies exhibit lopsided morphologies. To quantify their occurrence and investigate their physical origins, we analyze barred galaxies in the IllustrisTNG TNG50 simulation. We select 519 clearly barred galaxies in their stellar mass maps out of 770 barred galaxies from the TNG50-1 catalog. We classify the bar morphologies into four subgroups - `Lopsided', `Perturbed', `Symmetric', and `Indeterminate' - and perform a comparative analysis of their physical properties. We find that galaxies hosting asymmetric bars (`Lopsided' and `Perturbed') tend to have higher gas densities around the bar region, enhanced star formation activity, and more recent bar-formation epochs than galaxies with symmetric bars. However, the factor that most consistently distinguishes the four subgroups is the stellar mass distribution of the host galaxy, and there appears to be no physical correlation with bar size. These findings suggest that asymmetric bars form preferentially in less massive galaxies and may evolve into symmetric bars over time through secular processes. However, this conclusion should be considered with caution, as the fraction of asymmetric bars in the TNG50 simulation is systematically higher than that observed in the local universe.
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Astrophysics of Galaxies

MIDIS: Strong H$\beta$+[OIII] Line Emitters at $z \geq 9$

Thomas R. Greve, Steven Gillman, Pierluigi Rinaldi et al. (+24 more)

We present a search for strong H$\beta$+[O III] emitters at $z=9.4-11.3$ in the HUDF using ultra-deep JWST/MIRI F560W imaging from the MIDIS survey. Three galaxies are identified via pronounced F560W flux excesses, consistent with strong rest-frame optical line emission. SED modelling yields rest-frame H$\beta$+[O III] equivalent widths of $\sim 600-1300$AA (median $\simeq 1260$AA), placing these sources among the most extreme known at these epochs. Combining these with a literature sample of 16 spectroscopically confirmed galaxies at $z\geq 9$, we find a median ${\rm EW}^{\rm H\beta+[O III]}_{\rm rest}\simeq 1300$AA, similar to values at $z\sim6-9$. We find no evidence for either a strong increase or decline in EW beyond $z\sim9$. A tentative trend of higher EW with increasing UV luminosity is observed, while no statistically significant anti-correlation with stellar mass is found. We place a first constraint on the H$\beta$+[O III] luminosity function at $z\simeq9-11$ ($\Phi\sim10^{-3.4}\,{\rm Mpc^{-3}\,dex^{-1}}$ at $\log( L_{\rm H\beta+[OIII]}/{\rm erg\,s^{-1}})=42.5$), consistent with a decline relative to $z\sim7-8$. The MIDIS sources have $\log(\xi_{\rm ion}/{\rm Hz\,erg^{-1}})=25.1-25.4$. We find significant correlations between $\xi_{\rm ion}$ and EW and $\beta$, but not with UV luminosity, consistent with trends at lower redshift. These results suggest that the physical conditions governing nebular emission and ionising efficiency are already in place at $z\sim9-11$, extending trends established at $z\sim6-9$.
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All authors Thomas R. Greve, Steven Gillman, Pierluigi Rinaldi, Iris Jermann, Jens Melinder, Göran Östlin, Pablo G. Pérez-González, Luis Colina, Fabian Walter, Javier Álvarez-Márquez, Martin J. Ward, Alejandro Crespo Gómez, John P. Pye, Tuomo V. Tikkanen, Edoardo Iani, Roman A. Meyer, Leindert A. Boogaard, Jens Hjorth, Danial Langeroodi, Paul van der Werf, Sarah E. I. Bosman, Karina I. Caputi, Luca Costantin, Marianna Annunziatella, Arjan Bik, Álvaro Labiano, Thomas Henning

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

Fast Magnetosonic Turbulence in Two-Dimensional Relativistic Plasmas

Petr Ugarov, Vladimir Zhdankin and Giuseppe Arrò

We present fully kinetic simulations of driven 2D turbulence in a relativistic plasma, designed for the first time to induce a fast magnetosonic cascade. As the driving strength increases, turbulence transitions from a weak wave-dominated regime to strong shock-driven dynamics. Using spatiotemporal Fourier analysis, we identify fast modes, finding that the weak turbulence regime exhibits spectral properties that are in excellent agreement with theoretical expectations. Our results are relevant for the modeling of turbulence in high-energy astrophysical plasmas.
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Astrophysics of Galaxies

Detection of High-Velocity Na$\;$I Absorption Toward the Stellar Remnant of SN 1181 AD

Peter Garnavich and Robert A. Fesen

We report the detection of weak high-velocity Na$\;$I absorption at V$_{\odot}$ = $-61.0\pm0.2$ km s$^{-1}$ in the spectrum of the stellar remnant at the center of the Galactic supernova remnant of 1181 AD. This velocity is not unlike that seen in old, more evolved SN remnants, but is much less than the remnant's $\simeq10^{3}$ km s$^{-1}$ expanding optical nebula. We briefly discuss its possible nature and origin.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

A Conformal Boundary Ansatz for Warm Inflation Initialization: A Toy Model

Somnath Das and Rizwan ul Haq Ansari

We present a theoretical framework demonstrating a deterministic initialization mechanism for Warm Inflation via classical conformal boundary conditions. A persistent challenge in dissipative inflationary models is the "cold start" paradox: initializing the requisite thermal bath to generate the dissipative friction that subsequently sustains radiation production. Postulating an idealized, asymptotically scale invariant pre-inflationary phase, we mathematically prove that a conformal Weyl mapping to the emergent metric furnishes a finite, analytically derived initial radiation density. Implementing a spontaneous conformal symmetry-breaking ansatz, an emergent inflaton field is subjected to this inherited thermal bath. We analytically derive the initial kinematics of this framework, demonstrating that for strict sub-Planckian temperatures, the universe naturally initializes in the weak dissipative regime (Q << 1). The initial Hubble friction provided by the boundary radiation enables a smooth, deterministic kinematic handoff to the warm slow-roll steady-state attractor. As a mathematical proof-of-concept, this mechanism provides a fully realized framework to bypass the bootstrap problem of warm inflation.
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Astrophysics of Galaxies

Wings of little dots: Exponential broad lines from a stratified BLR

Piero Madau, Roberto Maiolino, Jan Scholtz et al. (+1 more)

We investigate the origin of the broad exponential wings seen in the Halpha profiles of many JWST-discovered little red dots (LRDs) and little blue dots (LBDs). Recent studies show that exponential broad-line profiles are not unique to LRDs, are common in LBDs too, and need not imply that electron scattering is the dominant broadening mechanism in every source. Motivated by our unification picture, in which LRDs are dust-reddened, high-inclination counterparts of compact blue broad-line AGNs, we model the broad Balmer emission with a virialized, radially stratified broad-line region (BLR). In this framework, the observed profile is the luminosity-weighted superposition of clouds spanning a range of radii, and hence virial velocities. We show that a stratified BLR reproduces the exponential-like wings observed in three representative LRDs and one LBD, without requiring electron scattering as the dominant broadening mechanism. For the LBD GS-3073, the same BLR – calibrated only to Halpha – predicts, parameter-free, that He II 4686 and Hbeta should be broader than Halpha, consistent with observations and offering an independent test of BLR ionization stratification. Our results support a picture in which wings and cores encode different physics: the wings arise primarily from virial BLR stratification, while the cores retain imprints of absorption and radiative transfer in dense gas. The fits further suggest that the cloud radial distribution peaks near the dust sublimation radius, with the exponential wings shaped by the inner, line-emitting BLR shells whose higher virial velocities produce the high-velocity tails. This offers a simple physical explanation for the exponential wings of little dots, without invoking exotic new components or scenarios.
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All authors Piero Madau, Roberto Maiolino, Jan Scholtz, Francesco D'Eugenio

Cosmology and Nongalactic Astrophysics

Gaussian-Process Emulation of the Redshift-Space Halo Power Spectrum Monopole in Cosmologies with Massive Neutrinos

Jixin Gan, Yonghao Feng and Gong-Bo Zhao

We present a Gaussian-process (GP) emulator for the monopole of the redshift-space halo power spectrum in $\Lambda$CDM cosmologies with massive neutrinos. The emulator is trained on 1000 COLA simulations distributed in a Latin-hypercube design over the six-dimensional cosmological parameter space $\{\Omega_m h^2,\Omega_b h^2,\Omega_\nu h^2,\sigma_8,h,n_s\}$, with outputs at 11 snapshots spanning $0.5 \le z \le 2.0$. From redshift-space halo catalogues we measure shot-noise-subtracted monopole spectra over $0.01 \le k \le 0.50\,h\,\mathrm{Mpc}^{-1}$. We also generate 1000 fixed-cosmology realizations to estimate the covariance matrix and to construct synthetic data vectors for likelihood tests. On held-out cosmologies, the emulator reproduces the simulated spectra to typically better than $2\%$ across the scales and redshifts considered. Combined with its GP-based estimate of interpolation uncertainty, this speed and accuracy make the emulator well suited to repeated likelihood evaluations in Markov Chain Monte Carlo analyses. The resulting framework provides an efficient route toward neutrino-mass inference from DESI-motivated redshift-space clustering measurements.
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Solar and Stellar Astrophysics

Stellar Parameters and Orbital Period Estimates for Composite-Spectrum sdB+MS Binaries from LAMOST

Jiangdan Li, Jianping Xiong, Jiao Li et al. (+5 more)

Hot subdwarf (sdB) stars in binary systems with main-sequence (MS) companions provide valuable insights into mass transfer and envelope ejection processes in binary evolution. Their mass ratios, orbital periods, and stellar properties encode key information about their evolutionary histories. In this work, we analyze a sample of 123 composite-spectrum sdB+MS binaries identified from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope Low-Resolution Survey (LAMOST-LRS) Data Release (DR) 8. We adopt atmospheric parameters from spectral decomposition and estimate stellar masses and radii using theoretical evolutionary tracks. Radial velocities for both the hot subdwarfs and cool companions are measured independently through cross-correlation with synthetic templates. Orbital periods are statistically estimated using single-epoch RV separations and a Monte Carlo method that accounts for random inclination and orbital phase. We find that sdB masses are narrowly distributed around 0.5 Msun, consistent with expectations for core helium-burning stars, while MS companion masses span 0.6-1.9 Msun, with most falling between 1.0 and 1.4 Msun. The inferred orbital-period distribution shows a clear concentration toward long periods, broadly consistent with expectations for binaries formed through stable Roche-lobe overflow. Given that our sample consists of composite-spectrum sdB binaries, mainly sdB+FGK systems, the prevalence of long periods is largely driven by observational selection effects rather than the intrinsic period distribution of the sdB binary population. This study provides one of the largest uniform catalogs of composite spectrum sdB binaries to date, offering new observational constraints on their physical properties and formation channels.
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All authors Jiangdan Li, Jianping Xiong, Jiao Li, Hai-Liang Chen, Hongwei Ge, Mingkuan Yang, Xuefei Chen, Zhanwen Han

High Energy Astrophysical Phenomena

Revisiting the X-ray Variability Plane of AGNs: The Significant Role of the Photon Index

Ruisong Xia, Hao Liu, Yongquan Xue et al. (+9 more)

X-ray variability provides a powerful probe of the innermost regions of active galactic nuclei (AGNs), offering valuable insights into the accretion process and the structure of the corona. Previous studies have established a correlation between the X-ray variability timescale, black hole mass, and luminosity, forming the AGN X-ray variability plane. A possible link between the X-ray spectral photon index and X-ray variability was noted in early studies but has rarely been incorporated into subsequent analyses of the variability plane. Moreover, the limited sample sizes in earlier works have limited the robustness and universality of the X-ray variability plane. In this work, we compile a sample of 112 AGNs with 399 exposures from the 4XMM-DR14 catalog and constrain the correlations between X-ray variability timescale, black hole mass, luminosity, and photon index using the recently developed fitting method, BADDAT {(Baseline-Aware Dependence fitting for DAmping Timescales)}, which enables a robust exploration of an extended parameter space. Our analysis confirms the dependence of the rest-frame variability timescale ($\tau_{\rm rest}$) on black hole mass ($M_{\rm BH}$) and further incorporates the photon index ($\Gamma$) into the variability plane, yielding a best-fit relation of $\log (\tau_{\rm rest}/{\rm s}) = 1.22\log (M_{\rm BH}/M_\odot) - 0.24\Gamma - 3.53$, which is strongly favored over the model with $M_{\rm BH}$ alone. In contrast, the inclusion of luminosity does not produce a comparable improvement. The correlation with $\Gamma$ likely reflects the effects of Comptonization and the geometry of the corona.
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All authors Ruisong Xia, Hao Liu, Yongquan Xue, Jialai Wang, Guowei Ren, Mouyuan Sun, Shifu Zhu, Mengqiu Huang, Qingwen Wu, Xian-Liang Lu, Zhen-Bo Su, Shuying Zhou

Astrophysics of Galaxies

The Distribution of Cosmic Ray Electrons in Star-Forming Galaxies

Anvar Shukurov and Charles Jose

We derive explicit, algebraic expressions for the steady-state number density of cosmic ray electrons as a function of position and energy using Green's function of the diffusion equation with energy losses for an axisymmetric distributions of the particle sources in the galactocentric radius $r$ and distance to the mid-plane $z$. The solution is obtained for a Gaussian distribution of the particle sources in $r$ and $z$ but we show that it can be used for an arbitrary spatial distribution of the sources. The accuracy of our results is about 10% or better in wide ranges of $r$, $z$ and particle energies. These solutions can be used in the interpretation of radio astronomical observations of galaxies, particularly in the studies of the radio luminosities for large galaxy samples, and represent a physically justifiable and efficient alternative to the assumption of the energy equipartition between cosmic rays and interstellar magnetic fields.
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Cosmology and Nongalactic Astrophysics

Reconstruction of the Quintessence Scalar Field Potential Using Gaussian Processes

Redouane El Ouardi, Amine Bouali, Ahmed Errahmani et al. (+3 more)

Recent cosmological observations, including the latest Dark Energy Spectroscopic Instrument (DESI) data releases DR1 and DR2, have renewed interest in the possibility that dark energy may exhibit dynamical behavior rather than being a strict cosmological constant. In this work, we perform a fully model-independent reconstruction of the quintessence scalar field potential using Gaussian Process regression and current Hubble measurements. Instead of assuming a specific functional form for the scalar field potential, we reconstruct the quintessence potential and the corresponding kinetic energy directly from observational data. Our analysis is based on Hubble parameter measurements obtained from cosmic chronometers and the latest high-precision DESI DR2 baryon acoustic oscillation (BAO) data, together with Type Ia supernova data from the Pantheon+ compilation. Gaussian Processes provide a nonparametric and model-independent framework that allows the data to guide the reconstruction. We employ two covariance functions, namely the squared exponential and the Matern ($\nu = 9/2$) kernels, in order to assess the sensitivity of the reconstruction to the kernel choice. We further explore the impact of background cosmological assumptions by considering different priors on the matter density and spatial curvature. Finally, we compare the reconstructed scalar field potential with two theoretically motivated benchmark models: a power law potential and an exponential potential. We find that both models remain consistent with the reconstructed potential within the inferred confidence intervals.
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All authors Redouane El Ouardi, Amine Bouali, Ahmed Errahmani, Ryan E. Keeley, Arman Shafieloo, Taoufik Ouali

Solar and Stellar Astrophysics

The PLATO Science Calibration and Validation Plan: Targets for the First Long-pointing Field

Konstanze Zwintz, Conny Aerts, Andrew Tkachenko et al. (+56 more)

In order to meet the science goals of the PLATO space mission, an extensive science calibration and validation plan has been designed. This paper describes this plan, as well as the methodology adopted to select the science calibration and validation stars that have entered its input catalogue. This is the so-called scvPIC, which is part of the general PLATO Input Catalogue (PIC) for the first selected long pointing field in the Southern Hemisphere known as LOPS2. While many of PLATO's science requirements needed dedicated stars as calibrators as discussed here, its most stringent requirement is the delivery of the age of the host stars of exoplanetary systems with an accuracy better than 10% for a G0V star of V = 10 mag, i.e. a nearby Sun-like star. This is presently not within reach for large populations of dwarfs and subgiants in the Milky Way as it requires the models of their stellar interiors to be improved. We discuss how this ambitious age requirement led to the selection of tens of thousands of red giants, and of thousands of main-sequence early F-type gravity-mode pulsators in order to deduce their internal rotation profile across stellar evolution. This asteroseismic observable will then be imported as key information into improved models of dwarfs and subgiants in the Milky Way as optimal modelling tools for ever better age-dating of the exoplanet hosts as the PLATO mission moves along. Additional calibrators and validators included in the scvPIC are a few thousands of binaries, a few hundreds of legacy and benchmark stars, a few hundred photometrically stable stars, and six transiting brown dwarfs.
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All authors Konstanze Zwintz, Conny Aerts, Andrew Tkachenko, Juan Cabrera, Orlagh Creevey, Rene Heller, Nicholas Jannsen, Chen Jiang, Oleg Kochukhov, Antonino Francesco Lanza, Pierre F. L. Maxted, Sergio Messina, Andrea Miglio, Thierry Morel, Benoi{\i}t Mosser, Rhita Ouazzani, John Southworth, Matthias Ammler van-Eiff, Jeroen Audenaert, Paul G. Beck, Kevin Belkacem, Aaron Birch, Diego Bossini, Angela Bragaglia, Lorenzo Briganti, David Brown, Anko Börner, Cristina Chiappini, Cilia Damiani, Patrick Gaulme, Pablo Heise Huijse, Ulrike Heiter, Krysztof G. Helminiak, Mykyta Kliapets, Mikkel N. Lund, Paola Marrese, Thibault Merle, Nicola Miller, Josefina Montalban, Dinil Bose Palakkatharappil, Carsten Paproth, Isabel Rebollido Vazquez, Nena Scheller, Sophia Sulis, Amaury H. M. J. Triaud, Marica Valentini, Mathieu Vrard, Magali Deleuil, Laurent Gizon, Ana M. Heras, J. Miguel Mas-Hesse, Hugh Osborn, Isabella Pagano, Giampaolo Piotto, Don Pollacco, Roberto Raggazoni, Gavin Ramsay, Heike Rauer, Stephane Udry

Solar and Stellar Astrophysics

Effects of Various Bipolar Approximations of Active Regions on Solar Surface Magnetic Field Simulations

Yukun Luo, Jie Jiang and Ruihui Wang

The evolution of solar surface magnetic fields is essential for understanding solar activity and the underlying dynamic process. The surface flux transport (SFT) model is a widely used and effective tool for simulating this evolution. Active regions are incorporated as magnetic flux sources of the SFT model, but their configurations are usually simplified as symmetric or asymmetric bipolar magnetic regions (BMRs). Here, we aim to quantitatively and systematically assess how such flux source approximations affect SFT results and explore improved approximation methods using our recently developed SFT code. By comparing simulations that incorporate realistic active region configurations from solar cycle 23 through the ongoing cycle 25, we show that approximating active regions as symmetric BMRs leads to a systematic overestimation of the axial dipole strength at solar minimum. This result is independently confirmed using an algebraic quantification that evaluates the axial dipole contribution of individual active regions. The overestimation can be partially reduced by monotonically decreasing the size of the approximated BMRs, but it cannot be fully eliminated. When active regions are instead represented by morphologically asymmetric BMRs, the simulated axial dipole strength exhibits a strong and nearly linear negative dependence on the size ratio between the following and leading polarities. Based on these results, we propose a combination of BMR size and polarity size ratio that yields an axial dipole evolution comparable to that obtained with fully incorporated realistic active region configurations. This study provides a new quantitative constraint for improving future simulations with approximated BMRs.
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High Energy Astrophysical Phenomena

Extraction method for response functions from X-ray light curves of AGN by optimization algorithm

Sanhanat Deesamutara, Tirawut Worrakitpoonpon, Poemwai Chainakun et al. (+4 more)

We introduce a numerical optimization method to extract the X-ray reverberation response functions from the multi-band light curves of the active galactic nuclei. This approach does not require prior assumptions about the accretion disc and corona geometry, provided that the light curves result from the superposition of direct and singly-convolved signals, consistently across all bands. By reformulating the light curve equations into the matrix form, the optimal response matrix is derived by minimizing the squared difference between the observed and reconstructed light curves using a gradient-based optimization algorithm. We demonstrate that the method can robustly accommodate up to two convolution processes, such as the reverberation and the propagation, simultaneously. When tested on the synthesized light curves, the method demonstrates robustness of the solutions to variations in the relative contributions of each light curve component as the recovered response kernel remains acceptably close to the ground truth, as evaluated by both the response geometry and the reconstructed light curves. The method's tolerance to random noise was also assessed. With appropriate denoising, the response kernel can be reliably recovered when the signal-to-noise ratio is at least $100$. We show, as a proof of concept, that the proposed method is geometrical-model independent and has the potential to offer a flexible complement to traditional approaches.
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All authors Sanhanat Deesamutara, Tirawut Worrakitpoonpon, Poemwai Chainakun, Wasutep Luangtip, Jiachen Jiang, Francisco Pozo Nuñez, Andrew J. Young

Solar and Stellar Astrophysics

A Few Years Later: Revisiting Period Variations of Eclipsing Binaries in the Northern Continuous Viewing Zone of TESS

T. Borkovits, T. Mitnyan, D. R. Czavalinga et al. (+1 more)

In our previous analysis of the eclipse timing variation patterns of eclipsing binaries located in and near the Northern Continuous Viewing Zone (NCVZ) of the TESS space telescope, 135 hierarchical triple star candidates were found. Now, two additional years of TESS observations are available and, hence, we have extended the former analysis with the use of the new observational data. We now detect 168 triple star candidates in the updated and reanalyzed sample. The majority ($\sim74\%$) of them are identical to the former triples candidates. For many of them, our new solutions are more certain than the original ones. Therefore, we can now conclude that we have identified at least 66 short-period hierarchical triple stellar systems in the NCVZ with full confidence. In the case of the majority of the remaining systems in our sample, the presence of a close third stellar component appears to be very likely. We also identify additional, longer timescale period variations in 34 systems ($20\%$ of the total sample) and conclude that in at least three systems the presence of a fourth stellar component is quite plausible. Finally, we report the complete disappearance of the eclipses in two former EBs and detect eclipse depth variations in seven other EBs as well. We interpret this effect as the consequence of changing orbital inclination caused by a non-coplanar third body.
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All authors T. Borkovits, T. Mitnyan, D. R. Czavalinga, S. A. Rappaport

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Photon Propagation through Axion Clouds around Magnetized Compact Objects: Time Delays and Polarimetric Signatures

M. M. Chaichian, B. A. Couto e Silva and B. L. Sánchez-Vega

Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos probe propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to strongly magnetized compact objects, such as canonical pulsars. Working within the Euler–Heisenberg effective theory extended by the axion sector, we derive the photon dispersion relations in a strong magnetic background permeated by an oscillating axion field. The magnetized vacuum is birefringent already at the Euler–Heisenberg level and the axion cloud superimposes density-dependent, time-dependent, and parity-odd structure on this baseline. The resulting geometry-dependent deviations from luminal propagation yield kinematic time delays reaching $\Delta t_{\perp} \simeq 9.3 \times 10^{-12}$ s for $\mathbf{k} \perp \mathbf{B}$, far too small to account for macroscopic multimessenger offsets, so that propagation through such environments cannot, by itself, rule out Lorentz-invariance violation as an explanation for GRB offsets. In the polarization sector, we show that the axion-induced circular birefringence is an endpoint effect and therefore does not produce a leading net rotation for a complete vacuum-to-vacuum transit through a localized cloud. For configurations with a nonzero axion-field endpoint contrast, the same parity-odd phase defines a conditional environmental sensitivity benchmark. We find that this mechanism is optimally sensitive in the ultralight regime, yielding a benchmark reach of $g_{a\gamma\gamma} \lesssim 2.5 \times 10^{-10}\,\mathrm{GeV}^{-1}$ for canonical pulsar fields and axion masses near $m_a \sim 10^{-9}$ eV, and we identify the parity-odd (chiral) birefringence induced by the oscillating cloud as the signature that distinguishes the axion contribution from the calculable QED baseline.
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Cosmology and Nongalactic Astrophysics

Intracluster Light as a Probe for Dark Matter: Exploring Self-interacting Dark Matter and Cold Dark Matter with C-EAGLE Sims

Jaewon Yoo, Ellen L. Sirks, Cristiano G. Sabiu et al. (+5 more)

We assess whether intracluster light (ICL) can serve as an observational discriminator of dark matter physics. The self-interacting dark matter (SIDM) model has gained increasing attention as a possible resolution to small-scale discrepancies between collisionless cold dark matter (CDM) simulations and observations, predicting distinct tidal interaction histories within galaxy clusters. We analyze Cluster-EAGLE zoom-in galaxy clusters re-simulated from identical initial conditions in both CDM and SIDM frameworks. The morphological similarity between dark matter and multiple baryonic tracers – gas, all stars, galaxies, and the combined brightest cluster galaxy plus ICL (BCG+ICL) – is quantified using the Weighted Overlap Coefficient, a contour-overlap statistic. We find that dark matter is traced most accurately by BCG+ICL, followed by gas, all stars, and galaxies. The BCG+ICL component remains a robust tracer even at high redshift, while gas initially traces dark matter poorly but improves over time, eventually approaching the performance of BCG+ICL. Notably, in the SIDM case the gas distribution more closely resembles dark matter than in CDM. This reflects the underlying physics: in CDM, collisionless dark matter behaves similarly to the collisionless BCG+ICL, whereas in SIDM, self-interactions introduce an effective collisionality, making dark matter evolve more like the gas component. We also find that dwarf and satellite galaxies are more sensitive to the underlying dark matter model, despite their poorer overall tracing performance. Our results demonstrate the potential of ICL as a novel observational probe of dark matter physics and provide a first step toward using diffuse cluster light to constrain the nature of dark matter.
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All authors Jaewon Yoo, Ellen L. Sirks, Cristiano G. Sabiu, Changbom Park, Jaehyun Lee, Ankit Singh, Juhan Kim, Jongwan Ko

Saturday 4 April

Instrumentation and Methods for Astrophysics

Storm-Driven Suppression and Post-Storm Enhancement of Photographic Plate Transient Detections at Geosynchronous Altitude: Empirical Evidence and a Candidate Dusty Plasma Mechanism

Kevin Cann

The VASCO project has identified over 100,000 sub-second optical transients on photographic plates from the First Palomar Observatory Sky Survey (1949-1957), all predating artificial satellites. Cann (2026a) established that transient detection rates are dose-dependently suppressed during geomagnetic storms (Z = -3.391, p = 0.0007), ruling out emulsion defects and confirming the transients as real, magnetospherically coupled phenomena. Villarroel et al. (2022) constrained the source altitude to ~42,000 km (geosynchronous orbit) through an Earth-shadow deficit. This paper presents two results. First, a pre-registered empirical test reveals the full temporal recovery profile: transient rates remain suppressed at 55% of baseline during days 7-21 post-storm, then rise to 309% of baseline during days 25-45 (p = 0.00066, Wilcoxon rank-sum; all robustness checks significant). Combined with the dose-response staircase, the overall significance reaches 3.6-4.7 sigma (Fisher's method, range reflecting sensitivity to the independence assumption). Second, we propose a candidate physical mechanism: storm-enhanced electromagnetic trapping of charged micrometeoroid dust at L ~ 6.6, followed by aggregation of icy cometary grains under restored cold plasmaspheric conditions. A flux dilution analysis demonstrates that specular reflection from a partially reflective icy aggregate only 1-4 m in diameter suffices to produce the observed plate magnitude at 42,000 km. This mechanism connects the VASCO transients to independently observed magnetospheric dust swarms correlated with geomagnetic activity (Sommer 2024) and explains the extinction of the transient population following the onset of the space age. Multi-site replication is required to confirm these results.
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