Cosmology and Nongalactic Astrophysics
Cosmological inference with halo clustering reconstructed from the redshift-space galaxy distribution
Ryuichiro Hada and Teppei Okumura
Accurate modeling of small-scale
redshift-space clustering is crucial for full shape RSD analyses, where satellite
galaxies contribute to 1-
halo terms and Finger-of-God distortions. We investigate
halo reconstruction based on the cylinder grouping (CG) method of Okumura et al. (2017), which selects an effective
halo center tracer from the observed
galaxy distribution, and how it impacts cosmological parameter inference. Using DESI-like luminous red
galaxy mock catalogs from the AbacusSummit simulations at $z=1.1$, we perform effective field theory (EFT)-based full-shape modeling of the power spectrum of the reconstructed-
halo sample. We show that the dominant reconstruction-induced systematics can be described and incorporated within the standard EFT framework. In particular, a simple multipole-dependent rescaling inferred directly from the data on large scales captures the dominant effect, while residual small-scale changes are absorbed by the standard counterterm and
stochastic sector, without introducing additional reconstruction-specific parameters. The reconstructed-
halo sample yields unbiased constraints on cosmological parameters, including the growth rate $f\sigma_8$ and Alcock-Paczynski parameters. Compared to the
galaxy sample, it enables both improved robustness and increased statistical precision: the inferred $f\sigma_8$ remains stable when extending the fit beyond $k_{\max}\simeq 0.2\,h\,{\rm Mpc}^{-1}$, with its uncertainty reduced by more than $20\%$.
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Astrophysics of Galaxies
Do little red dots really form a distinct class of astronomical objects?
Jean-Baptiste Billand, David Elbaz, Maximilien Franco et al. (+8 more)
JWST observations have identified a class of enigmatic sources known as little red dots (LRDs), interpreted as a distinct class of active
galactic nuclei (AGNs) and host
galaxies, whose black hole masses, AGN emissivities,
stellar masses, and possible quasi-
stars or black hole
stars (BH*) suggest a previously unidentified class of extragalactic objects. However, two questions remain: is there a clear discontinuity between LRDs and field
galaxies at the same epochs, and do LRDs form a homogeneous population? We address these issues with a continuous metric of the "LRDness" of
galaxies, measuring their compactness (delta_compact), the sharpness of the V-shaped spectral energy distribution (delta_v-shape), and the strength of the broad Balmer emission. This approach, which avoids a binary "on-off" view, was applied to 48,000 (5,000)
galaxies with photometric (spectroscopic) data over 750 arcmin^2. V-shape prominence correlates strongly with morphology, with no clear transition at the usual LRD threshold: the compact fraction rises with V-shape intensity. Similarly, broad H-alpha strength increases with V-shape sharpness and compactness. The [N II] deficit is not exclusive to LRDs, but a global property of compact, metal-poor
galaxies. Only a minority of LRDs (the 3% most extreme) show a prominent Balmer break (greater than 3) of potentially non-
stellar origin. LRDs and non-LRDs follow a similar Balmer decrement versus V-shape trend, suggesting a common origin consistent with
dust attenuation, reinforced by the agreement between observed Balmer ratios and attenuated Case B predictions. The inferred
dust mass (4-7 x 10^4 M_sun) is low enough to explain ALMA non-detections. We conclude that most LRDs are not a separate class, but rather the extreme tail of a continuous distribution of
galaxies and broad H-alpha emitters, consistent with a classical broad-line region and
dust component.
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All authors Jean-Baptiste Billand, David Elbaz, Maximilien Franco, Fabrizio Gentile, Emanuele Daddi, Mauro Giavalisco, Dale D. Kocevski, Joseph S. W. Lewis, Benjamin Magnelli, Valentina Sangalli, Maxime Tarrasse
Solar and Stellar Astrophysics
Prominence signatures in the Fraunhofer G-band; Testing ionization memory with multi-line prominence diagnostics
A.G.M. Pietrow, H. Balthasar, P. Váradi Nagy et al. (+4 more)
The Fraunhofer G-band around 4304 Å is widely used as a photospheric diagnostic and is generally not expected to show signatures of chromospheric or coronal structures. However, recent amateur observations have suggested the presence of off-limb prominence emission in this spectral region. We investigate the origin of the prominence emission in the G-band to determine if this is caused by methylene (CH) or other lines in this band. We also aim to test these lines for the presence of ionization
memory effects in neutral lines. We present a case study of two prominences, one obtained with a
Solar Explorer (Sol'Ex) spectroheliograph and another with the high-resolution Fast Multi-Line Universal Spectrograph (FaMuLUS) camera system at the echelle spectrograph of the German
Vacuum Tower
Telescope (VTT). Line widths are measured for simultaneously observed neutral and ionized metal lines, allowing a comparison of thermal and non-thermal broadening components to see if these lines exhibit any ionization
memory effects. We report clear prominence emission in several metal lines within the G-band, primarily from Ti II and Ca I lines, while contributions from CH molecular lines are not observed. A comparison of the simultaneously observed ionized and neutral lines reveals no clear evidence for an ionization
memory effect. Since the prominence emission does not originate from CH lines, we will not call them "G-band prominences" but rather prominences in the G-band, as they are independent of the primary diagnostic in this spectral window. In addition, the absence of a clear ionization
memory effect suggests that such effects may be less pronounced for weak neutral lines.
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All authors A.G.M. Pietrow, H. Balthasar, P. Váradi Nagy, R. Kamlah, A. Stork, C. Denker, M. Verma
Solar and Stellar Astrophysics
Multi-fluid multi-species models for inverse FIP-effect
Juan Martínez-Sykora, Paola Testa, Deborah Baker et al. (+1 more)
The inverse First Ionization Potential (FIP) effect is rarely observed in the
solar atmosphere, and this anomaly poses a challenging problem in understanding physical processes driving this chemical fractionation. In this work, we investigate various scenarios where the inverse FIP effect could occur using simplified 1D multi-fluid MHD models. The model treats the full MHD equations with multi-fluid and multi-species effects, rather than using wave analysis to derive the ponderomotive force and semi-empirical 1D models. In the parametric study considered here, for upward Alfvén waves, one can achieve a negative (opposite) ponderomotive force when the
magnetic field strength and the
magnetic flux tubes' expansion with height counteract the dissipation and damping effects from multi-fluid interactions.
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All authors Juan Martínez-Sykora, Paola Testa, Deborah Baker, Bart De Pontieu
Earth and Planetary Astrophysics
Investigation of gravitational stability of protoplanetary disks based on statistical analysis of their masses
Sophia A. Drobchik and Sergey A. Khaibrakhmanov
We compiled a sample of $1155$ protoplanetary disks, combining data from ten surveys of
star-forming regions. Based on the sample, we constructed a power-law approximation of the disk mass distribution: $dN/dM \propto M^{-\beta}$, $\beta = 1.36 \pm 0.14$. We used the sample for a statistical analysis of the gravitational stability of protoplanetary disks. To analyze the stability of the disks, we calculated the Toomre parameter ($Q$) for each of them. In the calculations, it was assumed that the radial density distribution in the disks is described by a power-law profile. The calculations of the Toomre parameter show that only $1.2$ % of the disks in the sample are formally unstable ($Q < 1$), while $1.7$ % are in a state of marginal stability ($1 \leq Q \leq 2$). The low observed abundance of unstable disks contradicts theoretical expectations and may be explained by a systematic underestimation of disk masses due to limitations of observational methods. Considering the effects of optical depth, CO depletion, as well as uncertainty in the gas-to-
dust ratio, we conclude that the actual fraction of the gravitationally unstable systems may be significantly higher.
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High Energy Astrophysical Phenomena
Combining the Mass–Radius Posteriors of J0030+0451 Allowing for Unknown Model Systematics
Ryan O'Connor, Chun Huang and Alexander Y. Chen
The NASA
Neutron star Interior Composition Explorer (NICER) mission measures the X-ray pulse profiles of select millisecond
pulsars and uses sophisticated pulse profile modeling (PPM) techniques to constrain their masses ($M$) and radii ($R$), in order to probe the state of matter in their interiors. One of the most studied
pulsars, PSR J0030+0451, has been analyzed by multiple groups using different choices of hotspot models. The different choices of hotspot prescriptions to fit the same observational data led to different $M$–$R$ posteriors that do not completely agree with one another, resulting in a practical bottleneck for dense-matter equation-of-state (EoS) inference. In this paper, we adapt a robust
Bayesian combination framework to the published $M$–$R$ posteriors of PSR J0030+0451 while allowing for unknown systematic uncertainties that might have led to the apparently divergent results. Using this technique, we combine eight existing $M$–$R$ posteriors into a single conservative and reproducible posterior that incorporates unknown model systematics across the currently available analyses and is suitable for direct use in EoS studies. The resulting constraint is $M = 1.46^{+0.09}_{-0.08}\,M_\odot$, $R = 12.69^{+0.64}_{-0.55}\,\mathrm{km}$, and compactness $C = 0.172^{+0.006}_{-0.007}$ (68% credible interval). Incorporating this combined J0030+0451 constraint in an EoS-agnostic joint analysis with PSR~J0437–4715 and GW170817 yields $R_{1.4} = 11.98^{+0.58}_{-0.68}\,\mathrm{km}$ and $\Lambda_{1.4} = 320^{+216}_{-138}$. Our results provide a combined $M$–$R$ constraint for J0030+0451 and a practical framework for incorporating cross-model uncertainty into
neutron star EoS inference pipelines.
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High Energy Astrophysical Phenomena
Galactic Diffuse Gamma-Ray and Neutrino Emission from Cosmic-Ray Interactions in Stellar Atmospheres
Yanbo Wang, Zhenglong Wang, Rui Zhang et al. (+1 more)
The
Galactic diffuse gamma-ray emission is conventionally modeled as the product of
cosmic-ray interactions with the interstellar medium. However, the cumulative contribution of
stellar atmospheres acting as hadronic interaction targets remains an unexplored multi-messenger background. In this work, we present the first systematic evaluation of this
stellar diffuse emission by coupling MESA
stellar evolution profiles and
magnetic-field-modulated
cosmic-ray transport with a 3D
Galactic population synthesis framework. We find that the cumulative
stellar contribution to the
Galactic diffuse gamma-ray flux is negligible at 1 TeV, and the associated diffuse
neutrino flux ($\sim 10^{-16}\;\mathrm{TeV\;cm^{-2}\;s^{-1}\;sr^{-1}}$) remains orders of magnitude below current IceCube limits. Nevertheless, at ultra-high energies ($>10\;\mathrm{TeV}$), this emission establishes an irreducible local background that overtakes the strongly attenuated extragalactic isotropic gamma-ray background. Our results demonstrate that the
Galactic stellar ensemble is a strictly sub-dominant background, indicating that
stellar subtraction templates are not required for identifying
Galactic PeVatrons or constraining dark matter annihilation.
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All authors Yanbo Wang, Zhenglong Wang, Rui Zhang, Yi Zhang
Solar and Stellar Astrophysics
The magnetic sensitivity of the Ca II H and K lines
M. Kriginsky, J. Leenaarts, J. de la Cruz Rodriguez et al. (+2 more)
The
solar chromosphere is a transition layer between the cool, dense photosphere and the hot, rarefied corona. This boundary region plays a key role in regulating energy transport and structuring the
magnetic field throughout the
solar atmosphere. Understanding its thermodynamic and
magnetic properties is essential to model and interpret
solar phenomena. This study investigates the theoretical properties and diagnostic potential of the polarisation signals in the Ca II H and K lines, with particular emphasis on their capability to probe
magnetic fields in the upper chromosphere with the CHROMIS instrument at the Swedish 1-m
solar telescope. We combine semi-empirical atmospheric models with high-resolution
solar observations to model the formation of the Ca II H and K lines using non-local thermodynamic
equilibrium radiative transfer calculations. The sensitivity of the lines to the
magnetic field is examined through response functions and synthetic inversions, enabling an assessment of their diagnostic performance under realistic chromospheric conditions. For typical chromospheric field strengths, the linear polarisation of the Ca ii H & K lines is less than 1.7%, below the expected detection threshold of CHROMIS. However, their circular polarisation reaches more than 10% in strong-field regions, which is detectable by CHROMIS. Both lines are sensitive to
magnetic fields in the upper chromosphere, with the K line forming slightly higher due to its larger opacity, and the H line exhibiting a somewhat stronger Zeeman sensitivity owing to its higher effective Lande factor and longer wavelength. Using the weak-field approximation, the line of sight
magnetic field can be reliably inferred. These results confirm that the Ca II H & K lines constitute powerful diagnostics for studying the
magnetic structure of the upper
solar chromosphere.
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All authors M. Kriginsky, J. Leenaarts, J. de la Cruz Rodriguez, S. Danilovic, O. Andriienko
Cosmology and Nongalactic Astrophysics
Impact of Stochastic Pop~III X-ray Binaries on the Cosmological 21-cm Signal
Saswata Dasgupta, Boyuan Liu, Anastasia Fialkov et al. (+3 more)
High-mass X-ray binaries are one of the primary drivers of the 21-cm signal from
Cosmic Dawn and Reionization, playing a leading role in the thermal history of the intergalactic medium. In traditional semi-numerical simulations, a deterministic scaling relation between the total X-ray luminosity of high-mass X-ray binaries, $L_{\rm X}$, and
star formation rate (SFR) is usually adopted. However, this assumption is inaccurate for high-
redshift low-SFR regions hosting few sources. The spatial variation in the number and luminosity of these sources is expected to enhance fluctuations in the
Cosmic Dawn 21-cm signal. Here we quantify this effect by introducing a
stochastic $L_{\rm X}$ model sampled from a power-law X-ray luminosity function. Implementing this in 21cmSPACE, a large-scale simulation framework of
Cosmic Dawn and Reionization, and adopting a soft X-ray spectral energy distribution ($\beta=1.5$, $E_{\rm min}=0.1\,\mathrm{keV}$) that leads to a relatively strong
stochastic signature, we find that the stochasticity leads to enhanced fluctuations in X-ray heating rate fields, and affects the 21-cm power spectrum on small scales ($k>0.3~ \mathrm{cMpc^{-1}}$). The impact of stochasticity on the global 21-cm signal and on the large-scale power spectrum is found to be negligible. Our results suggest these effects will remain undetected by the upcoming Square Kilometer Array. However, large-scale lunar-based experiments may be sensitive to the signatures of
stochastic X-ray heating at $z\sim 25$. Quantifying these corrections is a vital step toward robust 21-cm modeling and ensuring that future precision data interpretation is free from astrophysical biases.
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All authors Saswata Dasgupta, Boyuan Liu, Anastasia Fialkov, Furen Deng, Jiten Dhandha, Rennan Barkana
Astrophysics of Galaxies
Global m=1 slow mode in near-Keplerian self-gravitating torus: applications to stellar nuclear disks and AGN molecular tori
Elena Bannikova, Volodymyr Akhmetov, Peter Berczik et al. (+3 more)
Global m=1 asymmetries are observed in many self-gravitating astrophysical systems and are often interpreted as large-scale slow modes in near-Keplerian potentials. Prominent examples include eccentric
nuclear disks in
galactic centres, such as the double
nucleus of M31. However, the origin and long-term stability of such modes remain unclear. We investigate the
evolution and stability of a collisionless, self-gravitating
torus orbiting a dominant central mass, aiming to determine whether a slow non-axisymmetric (m=1) mode can arise spontaneously. We perform direct N-body simulations exploring different
torus-to-central mass ratios and initial conditions. The calculations use the high-order Hermite GPU integrator ($\varphi$-GPU), allowing us to follow long-term
evolution with many particles. We find that a global slow m=1 mode forms spontaneously from initially axisymmetric configurations. The lopsided structure is sustained by coherent apsidal
alignment and persists over secular timescales. Its maintenance requires nonlinear coupling of low-order modes, including the m=3 component, as well as a sufficient vertical thickness of the
torus. As a result of the long-lived overdensity, the central mass is displaced from the system barycenter. These results provide a framework for understanding eccentric
nuclear disks, such as those in M31 and NGC4486B, as well as molecular
tori in AGNs, and suggest that such asymmetries may produce observable offsets of the central supermassive black hole.
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All authors Elena Bannikova, Volodymyr Akhmetov, Peter Berczik, Serhii Skolota, Massimo Capaccioli, Maryna Ishchenko
Earth and Planetary Astrophysics
The RoPES project with HARPS and HARPS-N III. Two candidate planets orbiting the G-type star HD 161098
N. Nari, A. Suárez Mascareño, J. I. González Hernández et al. (+9 more)
Context. The development of refined instruments and techniques for a detailed analysis of the radial velocities (RVs) of
stars other than the Sun allows the presence of planetary signals of amplitude below 1 ms$^{-1}$ to be investigated. Long-term RV surveys allow the detection of Earth-like and super-Earth-like
planets in the habitable zones of Sun-like
stars,
prime targets for future missions for the atmospheric characterization of
exoplanets. Aims. We present the analysis of the nearby G8 V-type
star HD 161098 (V = 7.68 mag, d = 29.75 pc). We searched for terrestrial
planets in the habitable zone. Methods. We combined historical
datasets with new data collected in an ongoing blind search program with HARPS, HARPS-N, and ESPRESSO. We utilized recently developed tools to extract RVs and to deal with the analysis of
stellar activity. We performed a joint analysis of RVs and activity indicators to separate the planetary signals from those related to activity. Results. We detected two sub-ms$^{-1}$ signals that we claim as candidate
planets. We are not able to confirm their nature with certainty. Candidate HD 161098 b has an orbital period of 72.578$_{-0.060}^{+0.059}$ d and a minimum mass of 3.63 $\pm$ 0.59 MEarth. HD 161098 c has an orbital period of 682.5$_{-9.9}^{+9.5}$ d and a minimum mass of 7.8$_{-1.4}^{+1.5}$ MEarth.If confirmed, candidate HD 161098 c would reside in the optimistic habitable zone of the
star. We find a
magnetic cycle of 4090$_{-130}^{+140}$ d period and a rotation period of 28.22$_{-0.35}^{+0.30}$ d. Our analysis sets the stage for future observing campaigns of the
star, finalized for the confirmation of our results. Conclusions. We are entering the sub-ms$^{-1}$ era at long orbital periods with a combination of
stellar activity treatment and long-term campaigns.
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All authors N. Nari, A. Suárez Mascareño, J. I. González Hernández, A. K. Stefanov, R. Rebolo, J. M. Mestre, X. Dumusque, M. Cretignier, V. M. Passegger, L. Mignon, F. Manni, R. G. S. B. De Amorim
Astrophysics of Galaxies
Scale-dependent surface and volume density properties of filaments in molecular clouds
Guo-Yin Zhang, Alexander Men'shchikov and Jin-Zeng Li
We present a systematic analysis of scale-dependent properties of filamentary structures in seven nearby molecular clouds $-$ Taurus, Ophiuchus, Perseus, Orion A, California, IC 5146, Vela C $-$ using the multiscale extraction method $getsf$. Alongside the usual surface density profiles $\Sigma(r)$, we derived volume density profiles $\rho(r)$ for a large sample of filaments, providing new observational constraints on their three-dimensional structure. The half-maximum widths $H$ and $h$ of the surface and volume density profiles, respectively, systematically increase with the spatial scale, following power laws $\tilde{H} \propto Y^{0.50}$ and $\tilde{h} \propto Y^{0.37}$, with distributions spanning $\sim 0.01 - 1 $ pc across all scales, challenging the notion of a universal filament width of $\sim 0.1$ pc. The median volume density slopes $\tilde{\beta} \approx 2.1 - 2.4$ are systematically lower than the value $\beta = 4$ expected for an isothermal cylinder in hydrostatic
equilibrium. For shallow profiles with $\beta \lesssim 1$, the volume density width $h$ falls below the surface density width $H$ by one to two orders of magnitude, demonstrating that surface density widths overestimate the true physical extent of filaments with shallow profiles. Volume density contrasts are substantially higher than surface density contrasts ($\tilde{C}_{\rho} \approx 17 - 52$ versus $\tilde{C}_{\Sigma} \approx 1.1 - 2.7$), confirming that filaments are substantially more prominent in three dimensions than their projected appearance suggests. Measured filament widths and slopes systematically depend on the angular resolution and distance, highlighting the importance of accounting for resolution bias in comparative filament studies.
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Cosmology and Nongalactic Astrophysics
Emergence of Complex Web Structures
Francisco-Shu Kitaura
Complex structures often emerge from initially homogeneous or weakly correlated states. We address the apparent tension between this ordering and
entropy growth through a unified framework combining semi-microscopic phase-space dynamics, transport geometry, information theory, and coarse-grained effective modeling. The key point is that
entropy depends on the level of description: a coarse-grained spatial field may become more ordered as structure forms, even while the full phase-space description becomes more complex through shell crossing, multistreaming, and the activation of velocity degrees of freedom. Using a Lagrangian–Eulerian transport map, we show how density amplification is governed by the Jacobian of the deformation and how anisotropic collapse arises from the
eigenvalues of a hierarchy of deformation tensors. Long-range interaction or information flow is encoded in the displacement field, so that nonlocality enters directly through transport. We connect this
geometric description to a maximum-
entropy Gaussian baseline and show how nonlinear transport and nonlocal coupling generate scale coupling, higher-order correlations, and non-Gaussianity. We then formulate a Landau–Ginzburg description in which the growth of seed anisotropies is interpreted as the activation of lower effective free-energy branches, providing a coarse-grained realization of self-organization. Applied to generated cosmological fields, this framework indicates that the nonlocal
tidal level becomes relevant already at moderate overdensity. Although cosmological structure formation is the main realization considered here, the framework is intended more broadly as a mesoscopic
language for systems in which transport, anisotropy, nonlocality, and self-organization are central.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Helicity-supported stationary spacetimes: A class of finite-energy, horizonless, axisymmetric solutions
Francisco S. N. Lobo and Tiberiu Harko
We construct a class of stationary, axisymmetric, horizonless spacetimes whose
curvature is generated entirely by smooth, localised differential rotation $\Omega(r)$, while the spatial geometry remains exactly flat. Despite vanishing ADM mass, these helicity-supported configurations exhibit non-trivial
curvature, finite
tidal forces, and a gravitomagnetic field arising from the radial shear of the rotation. The twisted stationary Killing congruence produces global frame-dragging, including a gravitational Sagnac effect, and the effective potential admits stable circular orbits for null and timelike particles. The
tidal tensor gives oscillatory restoring forces, ensuring stability against radial perturbations. Linearising the Einstein equations yields a wave equation for axisymmetric perturbations of $\Omega(r)$; the effective potential is positive and localised, the operator is self-adjoint and positive definite, and the frequency spectrum is real, implying linear stability. Perturbations propagate as shear waves analogous to Alfvén waves. These results show that differential rotation alone can sustain a regular, asymptotically flat gravitational field with rich dynamics. This class of spacetimes provides a tractable platform for exploring gravitomagnetism,
tidal and wave phenomena in smooth rotating backgrounds, with direct applications to rotating astrophysical structures.
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Astrophysics of Galaxies
The environmental imprint on molecular layering in the dusty streamer of M512
M. De Simone, L. Cacciapuoti, D. Capela et al. (+7 more)
Protostellar streamers are elongated structures that channel material from larger scale onto disks, influencing their physical and chemical
evolution. The M512 protostar in Orion/Lynds 1641 hosts one of the most massive and extended streamer discovered so far, offering a unique opportunity to study these processes. We investigate the morphology, chemistry, and origin of this streamer,and its potential impact on the protostellar disk. Using archival ALMA observations of C18O, DCO+, N2D+, and HCO+, we compare their spatial distributions through moment maps and spatial profiles. The streamer shows clear chemical stratification: C18O lies on the western side of the protostar, N2D+ is farther out to the east, and DCO+ is in the middle. This suggests that the structure has been shaped by environmental effects rather than tracing a single coherent infalling flow, with only the densest gas near the protostar likely to accrete onto the disk. Overall, the bulk of the streamer reflects the physical and chemical imprint of the surrounding cloud, highlighting the importance of environmental shaping in interpreting streamer-disk connections and their role in disk growth.
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All authors M. De Simone, L. Cacciapuoti, D. Capela, E. Macias, L. Podio, A. Miotello, A. Gupta, J. Bae, S. Grant, C. Espaillat
Earth and Planetary Astrophysics
Compact Hydrogen Sulfide Emission Indicates Sulfur-bearing Ice Sublimation in the Inner Disk of HD 163296
Yoshihide Yamato, Yuri Aikawa, Kenji Furuya et al. (+8 more)
The sulfur chemistry in protoplanetary disks directly affects the composition and potential habitability of nascent
planets, but its volatile inventory remains highly uncertain. Here, we present deep Atacama Large Millimeter/submillimeter Array (ALMA) observations of hydrogen sulfide (H$_2$S) along with SO and SO$_2$ in the disk around HD 163296 at an angular resolution of $\approx0.\!\!^{\prime\prime}3$ (or $\approx$30 au). We detect unresolved, compact emission of H$_2$S and SO (and tentatively SO$_2$) at the disk center with a broad line width of $\sim$40 km s$^{-1}$, suggesting that the emission is originating from the innermost regions. By fitting line profiles with a geometrically-thin Keplerian-rotating disk model, we constrain the emitting radii and gas temperatures of these molecules to be $\approx$3-5 au and $\gtrsim$90-120 K, respectively, consistent with sublimation of sulfur-bearing molecules along with water ice in the inner warm region. While the higher or comparable column density of H$_2$S with respect to SO and SO$_2$ indicates that H$_2$S is an important volatile sulfur reservoir in the disk, the limited constraints mean that we cannot rule out significantly depleted volatile sulfur as also commonly inferred in other
planet-forming disks. Further observations are needed to better constrain disk sulfur inventory, unravel how sulfur compounds are reprocessed in disks, and shed light on the nature of less-volatile species, such as salts and sulfide minerals, which may occupy a significant portion of sulfur budget.
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All authors Yoshihide Yamato, Yuri Aikawa, Kenji Furuya, Charles J. Law, Karin I. Öberg, Chunhua Qi, Cataldi Gianni, Romane Le Gal, Shota Notsu, Viviana V. Guzmán, Jane Huang
Earth and Planetary Astrophysics
From Dust to Planets – A Chemical Perspective
Klaus Mezger, Jonas Pape, Aryavart Anand et al. (+3 more)
Chemical and chronological information preserved in meteorites permits the reconstruction of events and processes in the
solar nebula from the formation of the first solids to the
accretion of planetary bodies and their subsequent differentiation. The path from a gas-
dust cloud to differentiated
planets includes intervals of steady
evolution interrupted by singular events that dramatically altered this steady path, leading to planetary bodies with distinct chemical compositions and different degrees of internal differentiation. The dominant continuous process in the early
Solar System was the cooling of the gas-
dust cloud, which caused a steady condensation of elements into solid compounds and a continuous increase in the
dust/gas ratio. Planetesimal formation started within less than 1 Ma of
Solar System formation and continued for ca. 3 Ma apparently in random regions within the disk. The first planetesimals most likely formed due to streaming instabilities and created gaps in the gas-
dust disk that prevented significant element exchange. Later planetesimals formed by
accretion of chondrules that had developed in the
dust rings by bow shocks. The Earth formed by early
accretion of volatile-poor material and a later collision with a Mars-sized volatile richer body after proto-Earth had formed a metal core. This chance event provided the chemical conditions that transformed the Earth into a habitable
planet.
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All authors Klaus Mezger, Jonas Pape, Aryavart Anand, Pascal M. Kruttasch, Hauke Vollstaedt, Jan Hoffmann
Astrophysics of Galaxies
Extragalactic microlensing through Ultra Diffuse Galaxies
Sung Kei Li, Thomas Broadhurst, Jose M. Diego et al. (+4 more)
Stellar microlensing is a powerful method to constrain compact dark matter models, uncover binary
stars, and
exoplanets during caustic crossing events. At cosmological distances, James-Webb Space
Telescope (JWST) is routinely detecting microlensed
giant stars in highly magnified
galaxies behind massive
lensing clusters. Here, we explore for the first time microlensing in modest
redshift galaxies commonly seen through local Ultra Diffuse
Galaxies (UDGs). Using the UDG NGC1052-DF2 as a proof-of-concept, we find that detecting microlensing events through UDGs is possible. Euclid is ideal for identifying samples of low-
redshift star-forming
galaxies seen through local
galaxies for deeper cadenced follow-up, where our zeroth-order calculation estimates that $\mathcal{O}(1-10)$ events per year are expected over the whole sky under the monitoring of LSST, assuming all UDGs share similar distance and
stellar content as NGC1052-DF2. Such measurements can help settle the DM issue for UDG
galaxies by providing a
stellar mass estimate weighted more by the low end of the
stellar initial mass function (IMF) than standard
stellar synthesis estimates. Note, lower efficiency is estimated for JWST of $\sim 5.6\times10^{-2}\,\textrm{yr}^{-1}$ over its five background
galaxies is expected for typical JWST$\sim29$\,mag visits, and a low Vera Rubin Legacy Survey of Space and Time (LSST) detection rate of$\sim 0.03\,\textrm{yr}^{-1}$ such that NGC1052-DF2 might not be a
prime target given its lack of low-
redshift background
galaxies.
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All authors Sung Kei Li, Thomas Broadhurst, Jose M. Diego, Jeremy Lim, Jose M. Palencia, James Nianias, Jiashuo Zhang
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Emulator-Assisted Nuclear DFT Inference and Its Consequences for the Structure of Neutron Stars
Pietro Klausner, Marco Antonelli, Gianluca Colò et al. (+3 more)
Nuclear density functional theory provides a unified description of finite
nuclei and bulk
nuclear matter, and is widely used to model the
neutron star equation of state. However, extrapolations to supra-saturation densities require a quantified treatment of uncertainties arising from parameter estimation and functional choices. We present an updated
Bayesian inference of a Skyrme energy density functional augmented by a flexible meta-model density dependence at high density.
Nuclear observables are computed using a Gaussian emulator of the publicly available Milano HFBCS-QRPA code, enabling efficient exploration of a high-dimensional parameter space. Relative to previous analyses, we extend the calibration set with isospin-sensitive data, including masses and charge radii along selected Ca and Sn isotopic chains, and updated constraints from
giant monopole resonances. The resulting posteriors are further constrained by ab initio
neutron-matter calculations and astrophysical observations, including recent NICER measurements, yielding consistent crust and core properties of catalyzed NS compatible with current constraints. Bulk
nuclear-matter parameters are well approximated by a multivariate Gaussian with covariance
matrix provided for direct reuse, while several finite-
nucleus parameters exhibit pronounced non-Gaussianity.
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All authors Pietro Klausner, Marco Antonelli, Gianluca Colò, Francesca Gulminelli, Xavier Roca-Maza, Enrico Vigezzi
Solar and Stellar Astrophysics
Ultra-fast simulations of the solar dipole and open flux
Ismo Tähtinen, Timo Asikainen and Kalevi Mursula
Context.
Solar dipole captures important information about the large-scale
solar magnetic field. The
evolution of the
solar magnetic field including the
solar dipole can be simulated with a surface flux transport (SFT) model, but these simulations are more extensive than is necessary to produce the
evolution of the dipole alone. Aims. We present a dipole flux transport (DFT),
matrix method that combines the classic SFT model with dipole vector representation of the
solar magnetic field, allowing significantly faster simulations of the
solar dipole. Methods. By simulating the
evolution of basis vectors of a synoptic map, we constructed propagator
matrices that produce the time
evolution of the
solar magnetic field by means of
matrix multiplication. The computational speedup is achieved by compressing the propagator
matrices to very small fraction $(< 10^{-4}$) of their original size with a recent vector sum method. Results. Depending on time resolution, the DFT performs 100-1000 times faster than a 4-year SFT simulation of a single active region while producing equivalent results. For multiple source regions, daily propagation
matrices are sufficient to produce results that agree within 1% with the SFT simulation of
solar cycle 24, while performing 80 times faster. If the
evolution of individual active regions is needed, the DFT performs 50000 times faster than the SFT model. Conclusions. DFT makes
solar dipole simulations extremely fast, making it possible to run thousands of simulations in a few minutes with a basic laptop setup. As the magnitude of the dipole vector closely matches with open
solar flux (OSF) from the potential field source surface model, the DFT can be used to study the development of OSF in various scenarios extremely efficiently.
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High Energy Astrophysical Phenomena
A Falsifiable Timing Test for the Double-White-Dwarf Model of Long-Period Transients
Yejing Zhan, Di Wang and Fa-Yin Wang
Long-period transients (LPTs) are a newly identified class of
radio sources with burst recurrence times from minutes to hours, and their diversity suggests multiple physical origins. CHIME/ILT J1634+44, with a short period of 841 s, a long-period modulation of 4206 s, and a significant negative period derivative, strongly suggests a binary origin. For such a short-period source, Roche-lobe constraints strongly favor an ultra-compact companion, motivating a double-white-
dwarf (WD–WD) interpretation. In this Letter, we show that the WD–WD channel makes a sharp timing prediction: if the burst period is the orbital clock and the long-period modulation is a
spin-orbit beat, then the modulation period is not a free timescale. Instead it must evolve jointly with the orbital clock and the
spin clock through gravitational-wave losses,
magnetic dissipation, and
tidal interaction. For CHIME/ILT J1634+44-like parameters, we find that the beat clock drift $|\dot P_b|\sim 10^{-10} \text{ s s}^{-1}$, implying an observed-minus-calculated drift of tens of seconds in one year. Joint measurements of the burst period, modulation period, and their derivatives provide a minimal and falsifiable timing test of an ultra-compact binary origin.
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High Energy Astrophysical Phenomena
A Ring of Fire Orphan {\gamma}-Ray Flare in the Neutrino Candidate 3C 120
E. Traianou, G. Bruni, J. Rodi et al. (+7 more)
We present 43\,GHz VLBI observations of the
radio galaxy 3C~120 during its brightest $\gamma$-ray outburst (March 2018), recently associated with the IceCube
neutrino alert IC-180213A. Despite reaching $L_\gamma = 3.7 \times 10^{44}$\,erg\,s$^{-1}$, contemporaneous X-ray monitoring from INTEGRAL/ISGRI, MAXI/GSC, and Swift/XRT revealed no variability across 0.3-200\,keV, nor in B, V, R, and I band optical observations or 37 & 235\,GHz observations, establishing an orphan
flare. High-cadence VLBI imaging identified a new jet disturbance (N) propagating at $\beta_{\rm app} = (2.8 \pm 1.3)$ through quasi-stationary features C1-C3. The $\gamma$-ray peak coincided spatially and temporally with N crossing C3 ($r \sim 0.38$\,mas), where we measured a factor-of-5 increase in fractional polarization ($m = 16\%$) and $\Delta\chi \sim 24^\circ$ EVPA rotation, indicating localized
magnetic field compression. The extreme Compton dominance ($L_\gamma / L_{\rm syn,blob} \approx 160$) is naturally explained by the Ring of Fire scenario, in which N ($\Gamma_{\rm blob} = 6$, $B_{\rm blob} = 0.023$\,G) inverse-Compton scatters synchrotron
photons from C3, reproducing the observed $\gamma$-ray luminosity for physically reasonable parameters. Unlike the 2014-2015 orphan
flares attributed to rapid spine reorientation near the BLR, the 2018 event represents a distinct physical mechanism, a propagating disturbance interacting with stationary jet structure at $\sim10\times$ the BLR radius.This work provides the first direct observational link between VLBI-resolved jet dynamics and orphan $\gamma$-ray emission in a
radio galaxy.
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All authors E. Traianou, G. Bruni, J. Rodi, G. F. Paraschos, S. G. Jorstad, A. P. Marscher, A. Lähteenmäki, M. Tornikoski, J. Tammi, I. Agudo
High Energy Astrophysical Phenomena
GeV gamma-ray emission in the field of the shell-type supernova remnant Vela Jr revisited
Ting-Ting Ge, Qi-Hang Wu, Pak-Hin Thomas Tam et al. (+4 more)
We present an updated analysis of the gigaelectronvolt (GeV) gamma-ray emission from the shell-type
supernova remnant (SNR) RX J0852.0-4622 (Vela Jr) using 15 yr of
Fermi Large Area
Telescope (
Fermi-LAT) data. We quantitatively model the GeV morphology and find that it is best described by the masked H.E.S.S. shell template, indicating that the embedded
pulsar wind nebula (PWN) contributes little to the GeV flux. The 0.1-500 GeV spectrum is well fitted by a hard power law with a
photon index of $1.77 \pm 0.03$ and connects smoothly to the teraelectronvolt (TeV) spectrum, confirming previous results with improved precision. We further construct an independent eROSITA shell template and derive the 1-5 keV X-ray spectral energy distribution (SED) of the whole remnant, which provides new constraints on the synchrotron emission. We model the multi-wavelength (MWL) SED with a pure leptonic model and a hybrid
lepton-
hadron model. While the pure leptonic model reproduces the overall broadband shape, the hybrid model provides a better statistical description of the same
dataset, supporting a mixed-origin picture in which the hadronic contribution is mainly relevant in the GeV band and the TeV emission remains predominantly leptonic.
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All authors Ting-Ting Ge, Qi-Hang Wu, Pak-Hin Thomas Tam, Jie Feng, Hai-Feng Zhou, Kai Wang, Su-Jie Lin
Earth and Planetary Astrophysics
Compact CO emission and no evidence of radial drift. ALMA observations of the faintest planet-forming disks in Lupus
Giulia Ricciardi, Francesco Zagaria, Anna Miotello et al. (+13 more)
A large fraction of
planet-forming disks observed with ALMA show faint CO emission, often interpreted as strong CO depletion. However, faint emission may also arise from spatially unresolved disks, whose sizes are overestimated, making them appear intrinsically faint. The limited sensitivity of previous observations has prevented testing this scenario, hindering our understanding of disk
evolution and
planet formation. We present new ALMA Band 7 observations of 12CO (J=3-2) and 13CO (J=3-2) in 17 of the faintest disks in Lupus, aiming to assess whether compact disk structure can explain their weak CO emission. The data reach an angular resolution of 0.25arcsec (about 20 au at 160 pc) and are an order of magnitude deeper than archival observations. We apply line stacking to enhance sensitivity and compare the derived CO luminosities with physical-chemical models of compact and extended disks, also estimating gas and
dust sizes. We detect both isotopologues in 10 disks, only 12CO in 4, and neither in 3. Several disks are consistent with being intrinsically compact and optically thick in both lines, providing an alternative to the CO depletion scenario. The inferred gas radii (Rco less than 40 au) support this interpretation and suggest that a significant fraction of disks may be born compact, in line with recent Class 0/I results. Gas-to-
dust size ratios show no clear evidence for
dust evolution, indicating these disks are not drift-dominated.
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All authors Giulia Ricciardi, Francesco Zagaria, Anna Miotello, Carlo F. Manara, Giovanni Rosotti, Luigi Zallio, Sean Andrews, Richard Booth, John Carpenter, Ilse Cleeves, Stefano Facchini, Viviana V. Guzmán, Claudia Toci, Miguel Vioque, David Wilner, Jonathan P. Williams
Astrophysics of Galaxies
The high-altitude, inner-disc, and chemically peculiar open cluster UBC 1052
Judit Donada, Laia Casamiquela, Friedrich Anders et al. (+8 more)
Out of all the discovered open clusters (OCs) that are located in the inner part of the
Galaxy, only a small fraction has been observed with high-resolution spectroscopy. An intriguing population of inner-disc OCs at relatively high altitudes ($Z$) from the
Galactic plane remains poorly studied. There are few reliable detections of such OCs, and their occurrence rate, dynamical origin and survival mechanism remain uncertain. We perform a detailed spectroscopic analysis of UBC 1052, located at a cylindrical galactocentric radius $R_{GC} = 6.1$ kpc and $Z = 340$ pc, which stands out as the oldest and highest-|$Z$| inner-disc OC studied at high resolution to date. We used FLAMES/VLT to acquire high signal-to-noise ratio UVES spectra of four red clump (RC) members ($G\sim14$ mag). From them we derived high-precision radial velocities ($v_{r}$) and local thermodynamic
equilibrium chemical abundances for 23 elements through a strict line-by-line differential analysis, achieving a median precision in [X/H] of $\simeq0.06$ dex for each
star. The four RC
stars have fully compatible chemical abundances, with [X/H] dispersions among them <$0.03$ dex for 20 elements. We also acquired GIRAFFE spectra of other candidate members and derived their $v_{r}$. We find that UBC 1052 has an age of $2.25\pm0.25$ Gyr, a distance of $3.11\pm0.07$ kpc, an extinction $A_{V} =1.23$ mag, a mean radial velocity of $34.0\pm0.6$ $km$ ${s}^{-1}$, and a slightly super-
solar [Fe/H] = $0.05\pm0.01$ dex. Such relatively low [Fe/H] at its $R_{GC}$ suggests that UBC 1052 is a rare candidate for an inward-migrated OC in the inner disc. Its detailed abundance pattern (e.g. [Ba/Zr] and [Nd/Y]) shows some interesting features that appear to be unique in the current census of OCs studied at high resolution, making it an interesting object for potential strong chemical-tagging searches for already dispersed member
stars. [Abridged]
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All authors Judit Donada, Laia Casamiquela, Friedrich Anders, Lola Balaguer-Núñez, Sergi Blanco-Cuaresma, Xavier Luri, Ditte Slumstrup, Carme Jordi, Alfred Castro-Ginard, Ricardo Carrera, Josep Manel Carrasco
Solar and Stellar Astrophysics
Stars on the ascending helium giant branch I. From white dwarf merger to helium giant: the evolutionary state of the rapidly rotating hot subdwarf HE 1518-0948
M. Pritzkuleit, M. Dorsch, M. M. Miller Bertolami et al. (+3 more)
Hot subdwarf
stars with masses above $0.8 M_\odot$ ascend the helium
giant branch after the end of core helium burning, before entering the white
dwarf cooling track or exploding as type Ib/c
supernovae. Such massive helium
stars are typically expected to form through the stripping of an intermediate mass
star by a binary companion after which some hydrogen is still expected to be retained. However, the subclass of extreme helium rich hot subdwarfs (He-sdOs) shows no or very weak hydrogen traces, and their low binary fraction suggests that they are either created through single-
star evolution triggered by a late hot flash in a low-mass red
giant or the merger of two helium white
dwarfs. Most He-sdOs are located close to the helium zero-age main sequence, while a small number exhibit much lower surface gravities, indicating inflated radii. Whether these objects are evolutionarily connected to the main He-sdO population remains unclear. In this work, we analyse the luminous, extreme helium-rich, low-surface-
gravity sdO HE 1518-0948 (HE 1518) through a detailed spectroscopic study of optical and ultraviolet data. A comparison with evolutionary models indicates that HE 1518 is the product of a massive double helium white
dwarf merger and is currently undergoing helium shell burning while ascending the helium
giant branch. This makes HE 1518 one of only a few known objects located in this sparsely populated region of the Hertzsprung-Russell diagram. Such
stars provide valuable laboratories for studying the
evolution of massive hot subdwarfs beyond core helium burning, and their high luminosities allow them to be detected at large distances.
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All authors M. Pritzkuleit, M. Dorsch, M. M. Miller Bertolami, S. Geier, C. W. Bradshaw, H. Dawson
Solar and Stellar Astrophysics
Statistical Study of Balmer Continuum Enhancement in Solar Flares
Pranjali Sharma, Lucia Kleint and Jonas Zbinden
Identifying the physical mechanisms of continuum emission in
solar flares is important to improve our understanding of the transport of energy in the chromosphere. This study aims to quantify the occurrence statistics and spatial and temporal characteristics of near-ultraviolet (NUV) continuum enhancements across various classes of
solar flares. We analyzed 234 IRIS
flare observations and developed two independent detection pipelines. Both pipelines initially extract candidate enhancement events from pixel-level NUV time series and subsequently eliminate false positives by making use of the temporal and spatial correspondence between NUV and FUV continuum enhancement. We detected NUV continuum enhancements in 80 out of 234
flares. The enhancements occurred predominantly on the
flare ribbon edges and during the GOES impulsive phase but also after the GOES peak flux. In a few cases (4 pixels), NUV and FUV continuum enhancement was detected 7-15 minutes before the GOES start or more than 20 minutes after the peak, appearing as indistinct bright points in the active regions. Despite large uncertainties for C-class events, enhancement magnitude increase with
flare class, with X-class
flares showing the strongest enhancement. Our analysis reveals that the enhancements are confined to localized regions on the
flare ribbon edges. In terms of
flare energetics, this suggests the possibility of enhancement occurring preferably in the regions with freshly reconnected
magnetic field lines, or the ribbon fronts with gradual and modest high-energy flux injection of the non-thermal electrons. Enhancements found significantly after the
flare peak in strong
flares further suggest multiple heating episodes. The enhancement strengths of
flare events as weak as C1.1 from this study serve as an important constraint for
flare simulation models.
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High Energy Astrophysical Phenomena
A Comparative Study of TeV Gamma-Ray Sources with Various Objects
Xin Zhou, Ji Yang, Yang Su et al. (+5 more)
We investigate the relationships between LHAASO TeV gamma-ray sources and various kinds of objects, including
pulsar wind nebulae (PWNe),
supernova remnants (SNRs), HII regions, microquasars, and OB associations. We propose a Randomization-Adjusted Overlap Correlation (RAOC) method to statistically assess association probabilities and evaluate association proportions across catalogs. The results reveal statistically significant overlaps between LHAASO sources and SNRs, PWNe, and microquasars, supporting their role as important contributors to TeV gamma-ray emission. The estimated association proportions of LHAASO sources are 0.19$\pm$0.08 with SNRs, 0.20$\pm$0.04 with PWNe, and 0.027$\pm$0.008 with microquasars. The proportion of the gamma-ray sources associated with the subsample of shell-type SNRs is ~0.1. While HII regions also show potential association, particularly with the KM2A component, their large self-overlap ratio complicates precise estimation. In contrast, OB associations exhibit a high probability of chance coincidence, suggesting their limited contribution to TeV gamma-ray emission. Our analysis of TeV gamma-ray emission capabilities shows that ~60% of PWNe are gamma-ray bright in both the WCDA and KM2A energy ranges. For SNRs and microquasars, the TeV gamma-ray bright fraction is ~10%. The subsample of PWNe associated with molecular clouds (MCs) shows enhanced gamma-ray emission. Furthermore, positional analysis reveals a systematic offset of the gamma-ray sources overlapping with PWNe toward the associated MCs. These findings imply a role for MCs in PWN gamma-ray production. Additionally, self-correlation analysis indicates that about 70% of the WCDA and KM2A gamma-ray components share a common origin. The study also identifies selection effects in existing SNR catalogs and notes clustering among approximately 30% of HII regions within larger
star-forming regions.
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All authors Xin Zhou, Ji Yang, Yang Su, Xuepeng Chen, Yang Chen, Yan Sun, Qing-Zeng Yan, Shaobo Zhang
Earth and Planetary Astrophysics
Streaming instabilities in weakly ionized protoplanetary discs: the Ambipolar Streaming Instability (AmSI)
Arnaud Pierens and Min-Kai Lin
The regions of protoplanetary discs where
planets can form are believed to be weakly ionised, suggesting thereby that non-ideal magneto-hydrodynamics (MHD) effects play an important role in the disc dynamics and in the
planet formation process. In particular, the combined effect of ohmic resistivity and ambipolar
diffusion can be responsible for launching MHD-driven disc winds. In this context, we focus on the effect of ambipolar
diffusion (AD) and examine the stability of a dusty, magnetized disc by employing both linear stability analyses and numerical simulations. We show that
dust feedback tends to stabilize the MRI oblique modes involved in the ambipolar-shear instability. We also find that ambipolar
diffusion leads to the onset of a strong resonant drag instability (RDI), in which an Alfvén wave is destabilized by the relative drift between the gas and
dust components. The main impact of AD is to modify the Alfvén wave frequency, resulting in a large resonance width. The instability is found to have significant growth rates even in
dust-poor discs and for tightly coupled particles, which may help to bridge the gap between growth of
dust grains through coagulation and planetesimal formation.
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Cosmology and Nongalactic Astrophysics
A First Observational Assessment of Cosmic Backreaction Over an Extended Redshift Range
S. M. Koksbang
In the recent preprint arXiv:2604.07244v1, the authors introduce a novel combination of
redshift, distance, and expansion rate observables for constraining
cosmic backreaction observationally. The current work presents a first application of the method, in principle yielding the first direct constraints on the total
cosmic backreaction in our universe over a significant
redshift range. However, we find that current data are not yet sufficient to place tight constraints on backreaction. Thus, neither vanishing nor significant backreaction can be ruled out with the presented constraints. Nonetheless, the results suggest that forthcoming survey data will enable enlightening constraints on
cosmic backreaction using this method.
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