Astrophysics of Galaxies
Variations of angular momentum $L_z$ as an indicator of orbital chaos of globular clusters in the central region of the Galaxy with a bar
A. T.~Bajkova, A. A.~Smirnov and V. V.~Bobylev
It is shown how the violation of the invariance of the $Z$-component of the orbital angular momentum $L_z$ in the axially symmetric potential of the
Galaxy with a bar can serve as an indicator of the degree of orbital chaos of globular clusters in the central region of the
Galaxy. In this case, the higher the variations of $L_z$ of the orbit over a certain period of time, the higher the chaos of the orbit. In essence, a new method for analyzing orbital dynamics – regular or chaotic – is proposed. A high level of correlation between the results of orbit classification by the proposed method and the results of classification by other methods is shown. As a result, a sample of 45 globular clusters in the central region of the
Galaxy with a radius of 3.5 kpc is divided into regular, chaotic, and weakly chaotic.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Did our Universe Tunnel out of the Wrong Higgs Vacuum?
Bibhushan Shakya
This paper explores various aspects and implications of the initial configuration of the Standard Model (SM)
Higgs field at the beginning of our Universe. It is well known that the SM
Higgs field features a deeper, more stable minimum at large field values. While it is possible that our Universe began and remained in the electroweak
vacuum at all times, this scenario is extremely fine-tuned from the point of view of initial conditions. This fine-tuning can be ameliorated by the exponential expansion of spacetime during inflation: intriguingly, this requires at least $\sim 40$ e-folds of inflation, tantalizingly close to the $50-60$ e-folds expected from horizon and flatness considerations. The
Higgs could thus provide the reason for a prolonged epoch of inflation in our
cosmic history. Otherwise, the most natural initial state corresponds to our Universe initialized in the more stable but "wrong"
Higgs vacuum, and subsequently driven dynamically to the weak scale
vacuum during reheating. An important, hitherto unexplored aspect of this dynamics is that the barrier between the two
vacua persists when the electroweak
vacuum becomes energetically favorable, becoming arbitrarily small as the temperature increases, and therefore triggers a first-order phase transition. This transition produces ultra-high (megahertz to gigahertz) frequency gravitational waves (GWs), serving as a challenging but unique SM target for GW experiments. Novel pathways for various beyond the Standard Model phenomena such as the production of dark matter and
baryon asymmetry also become possible in this configuration.
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Astrophysics of Galaxies
Gas excitation of post-starburst galaxies at 0.6 < z < 1.3
A. Zanella, S. Belli, F. M. Valentino et al. (+1 more)
Molecular gas traces the fuel for
star formation and the processes that regulate it. Observing its physical state (e.g. excitation) reveals when and why
galaxies quench. We observed the CO(5-4) emission of 8 post-starburst (SB)
galaxies at z~0.6-1.3. To our knowledge, this is the first time that high-J transitions are probed for quiescent
galaxies beyond the local Universe. All targets are detected in CO(2-1) or CO(3-2) and have gas fractions up to 20%. Using the ratio R52=L'CO(5-4)/L'CO(2-1) as a proxy for gas excitation, we distinguish among mechanisms responsible for the low SFE of post-SBs. In the first scenario, the molecular gas is predominantly diffuse and cold, implying a low fraction of dense
star-forming gas and low R52 values. In the second scenario, elevated gas temperatures at moderate densities, e.g. due to AGN activity, shocks, or
turbulence, produce high R52 values. On average our post-SBs have R52=0.28, comparable to high-
redshift galaxies. However, CO(5-4) non-detections, corresponding to
galaxies without signs of interaction, yield R52<0.10, 2 times lower than local
star-forming
galaxies. The average CO Spectral Line Energy Distribution (SLED) peaks at J=3, similar to the Milky Way. Three
galaxies show signs of ongoing mergers and have R52 = 0.40 and CO SLEDs peaking at J > 4-5, similar to high-
redshift galaxies. At least one requires additional mechanisms (AGN, shocks) to explain the rise of the SLED up to J=5. Our results favor a scenario in which most systems are dominated by low-density molecular gas with low excitation, consistent with quenching driven by gas stabilization, feedback regulation, or stripping. In interacting systems instead, enhanced excitation is likely driven by heating processes not related to
star-formation (e.g., AGN,
turbulence, shocks). Residual
star formation is insufficient to exhaust the remaining molecular gas in the majority of post-SBs.
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All authors A. Zanella, S. Belli, F. M. Valentino, A. Bolamperti
High Energy Astrophysical Phenomena
Detection Prospects for AGNs with the Cherenkov Telescope Array
Luana Passos-Reis, Elisabete M. de Gouveia Dal Pino, Tarek Hassan et al. (+9 more)
The Cherenkov
Telescope Array Observatory (CTAO) will enable detailed studies of Active
Galactic Nuclei (AGN) in the very-high-energy (VHE) regime, as the next-generation ground-based gamma-ray observatory, designed to enhance sensitivity and energy coverage (20 GeV – 300 TeV) over current Imaging Atmospheric Cherenkov
Telescopes (IACTs). In the context of the CTAO Science Collaboration, within the AGN Population working group, we developed a variability-based strategy to improve predictions of AGNs detectable by CTAO, using
Fermi-LAT data and normalized excess variance (NXS) as a tracer of flux variability. By extrapolating from 30-day to 3-day timescales, we expanded the sample of sources with short-timescale variability estimates from 87 to 407. This approach allows us to identify flaring and distant AGNs that are promising CTAO targets. The results are being used to support the CTAO extragalactic science program and will be included in an upcoming Consortium publication for the AGN Population collaboration.
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All authors Luana Passos-Reis, Elisabete M. de Gouveia Dal Pino, Tarek Hassan, Santiago Pita, Jonathan Biteau, Jean-Philippe Lenain, Atreya Acharyya, Alberto Domínguez, Lucas Gréaux, Luiz Augusto Stuani Pereira, Edivaldo Moura Santos, Paolo Goldoni
Astrophysics of Galaxies
Stellar Populations with MaNGA: Iron Kink and Nitrogen Fuzz
Guy Worthey and Tathagata Pal
Recent analysis of 2968 MaNGA early type
galaxies has yielded two notable trends with velocity dispersion ($\sigma$) not previously discussed in the literature. First, Fe abundance rises with $\sigma$, but only until $\sigma\approx100$ km s$^{-1}$, after which it falls. This kink is reproduced by TNG100 simulations, implying that hierarchical merger processes might explain it. Second, astrophysical scatter in N is high for
galaxies with $\sigma < 100$ km s$^{-1}$. Due to the restricted list of nucleosynthetic sources for N, it is likely that asymptotic
giant branch
stars provide most of this N. A varied
star formation history (compared to that of massive
galaxies) along with variable retention and recycling of N-enriched gas might explain the fuzz of N abundance in low-$\sigma$
galaxies. Because a timescale argument seems necessary to explain the nitrogen fuzz, and an initial mass function argument is ruled out, similar timescale arguments for the [Mg/Fe] trend as a function of velocity dispersion are supported.
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Solar and Stellar Astrophysics
An axisymmetric shock breakout indicated by prompt polarized emission from the type II supernova 2024ggi
Yi Yang, Xudong Wen, Lifan Wang et al. (+18 more)
The death of massive
stars is triggered by an infall-induced bounce shock that disrupts the
star. How such a shock is launched and propagates through the
star is a decade-long puzzle. Some models assume that the shock can be reenergized by absorbing
neutrinos, leading to highly aspherical explosions. Other models involve jet-powered shocks that lead to bipolar explosions reflected in the geometry of the shock-breakout emission. We report measurement of the geometry of the shock breakout through unprecedentedly early spectropolarimetry of the nearby type II
supernova 2024ggi starting ~1.2 days after the explosion. The measurement indicates a well-defined
symmetry axis of the shock breakout, which is also shared by the hydrogen-rich envelope that emerged after the circumstellar matter was engulfed by the ejecta, revealing a persisting and prominent
symmetry axis throughout the explosion. These findings suggest that the physical mechanism driving the explosion of massive
stars manifests a well-defined axial
symmetry and acts on large scales.
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All authors Yi Yang, Xudong Wen, Lifan Wang, Dietrich Baade, J. Craig Wheeler, Alexei V. Filippenko, Avishay Gal-Yam, Justyn Maund, Steve Schulze, Xiaofeng Wang, Chris Ashall, Mattia Bulla, Aleksandar Cikota, He Gao, Peter Hoeflich, Gaici Li, Divya Mishra, Ferdinando Patat, Kishore C. Patra, Sergiy S. Vasylyev, Shengyu Yan
Cosmology and Nongalactic Astrophysics
Semi-Analytical Jeans Filtering Functions for Baryonic Density and Velocity Fields in Second-Order Cosmological Perturbation Theory
Diego Fernando Fonseca, Leonardo Castañeda and Luz Ángela García
Cosmological perturbation theory provides the framework for describing the
evolution of matter density fluctuations and the formation of large-scale structure in the $\Lambda$CDM paradigm. We present a semi-analytical approach for a mixed fluid composed of cold dark matter (CDM) and
baryons. Assuming General Relativity, we derive the equations of motion from the Vlasov equation, incorporating baryonic effects through the stress tensor and retaining only baryonic pressure. We introduce Jeans Filtering Functions (JFF) as a biasing tool to describe baryonic fluctuations using CDM as a tracer. First- and second-order solutions are obtained with a semi-analytical method based on a single iteration of the equations of motion. These solutions can be evaluated at low computational cost and allow us to study the shift of the filtering scale beyond linear order and its impact on the matter power spectrum without computing the spectrum explicitly. In contrast to approaches based directly on the power spectrum, we quantify baryonic effects through the fluctuation fields themselves. We derive semi-analytical expressions for baryonic density and velocity fluctuations, with the velocity divergence field providing the most significant result. The method offers a readily evaluable description of baryonic effects in large-scale structure and shows how pressure shifts the filtering scale, with implications for quantities such as the filtering mass and the temperature of pressure-supported components.
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Solar and Stellar Astrophysics
JWST Reveals Carbon-rich Chemistry in a Transitional Disk
M. Volz, C. C. Espaillat, C. V. Pittman et al. (+6 more)
We present JWST-MIRI Medium Resolution Spectrometer (MRS) observations of the Classical T Tauri
stars GM Aur and RX J1615.3-3255 (J1615), both hosting transitional disks. Despite their similar
stellar and disk properties, the two systems differ strikingly in their carbon-bearing molecular emission. Using local thermodynamic
equilibrium (LTE) slab models to analyze spectral lines within the 13.6-17.7 micron wavelength range, we find that J1615 exhibits strong emission from H2O, HCN, C2H2, 12CO2, 13CO2, OH, and 13C12CH2, whereas GM Aur shows only H2O and OH. We measure the
accretion rates of both objects using contemporaneous optical spectra and find that J1615's
accretion rate is lower than that of GM Aur. We constrain the properties of the
dust in both disks using SED modeling and find elevated amounts of crystalline silicates and larger
dust grains in the disk of J1615. The enhanced carbon emission in J1615 may result from a combination of lower
accretion rate and larger and more processed
dust grains in the inner disk, conditions that together may allow carbon-rich gas to persist and be detected. These results expand the sample of protoplanetary disks around
solar-mass
stars with strong CO2 and C2H2 emission and identify J1615 as a carbon-rich transitional disk, providing new insights into the chemical diversity of
planet-forming environments.
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All authors M. Volz, C. C. Espaillat, C. V. Pittman, S. L. Grant, T. Thanathibodee, M. McClure, B. Tabone, N. Calvet, F. M. Walter
Astrophysics of Galaxies
Kinetic Theory and the Mechanics of Isothermal Gas Spheres: Derivation of the Classical Emden–Chandrasekhar Equation via the Vlasov–Poisson Formalism
Steven D Miller
We present a derivation of the mechanics of isothermal gas spheres directly from the Vlasov–Poisson equation. By extremising the Boltzmann
entropy, we obtain the Maxwell–Boltzmann distribution for a self-gravitating isothermal Newtonian gas, which is a stationary solution of the Vlasov–Poisson system. From this distribution, the corresponding Poisson–Boltzmann equation for the gravitational potential is deduced. The second variation of
entropy reproduces the classical Antonov instability criterion: the critical energy is $E_c \simeq -0.335\,\frac{G M^2}{R}$, below which no local
entropy maximum exists and the configuration becomes unstable (the so-called "gravothermal catastrophe"). In this work, we assume $E>E_c$, so all
equilibria lie on the stable branch, and the Antonov instability does not affect the analysis. Specializing to spherical
symmetry, we recover the classical equation for the isothermal gas sphere, as originally studied by Chandrasekhar, which has applications to the formation of red
giant stars. We also derive the fundamental equation of hydrostatic
equilibrium, the energy integral and the virial
theorem directly from the stationary Vlasov–Poisson solution, demonstrating also that an isothermal gas exhibits negative specific heat. Furthermore, we show that an isothermal gas sphere of strictly constant density is an impossibility. This exposition emphasizes some of the deep connections and self-consistency between kinetic theory, statistical mechanics, and
stellar structure, while highlighting some formal aspects of classical astrophysical models.
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Astrophysics of Galaxies
Model of super-Alfvénic MHD turbulence and structure functions of polarization
A. Lazarian, D. Pogosyan and Y. Hu
MHD
turbulence driven at velocities higher than the Alfvén velocity, i.e., super-Alfvénic
turbulence, is widely spread in astrophysical environments, including
galaxy clusters and molecular clouds. For statistical studies of such
turbulence, we explore the utility of the polarization angle structure functions $D^\phi(R)= \left\langle\sin^2(\phi_1-\phi_2) \right\rangle$, where $\phi$ denotes the polarization angle measured at points separated by a projected distance $\mathbf{R}$ on the plane of the sky. Lazarian, Yuen and Pogosyan, 2022, showed that in the case of super-Alfvénic
turbulence, the spectral slope of $D^\phi(\mathbf{R})$ differs from that of the underlying
magnetic fluctuations, limiting its applicability for field strength estimation with known techniques. In this work, we provide an analytical framework that explains the modification of the $D^\phi(R)$ spectral slope in super-Alfvénic
turbulence and validate our predictions with numerical simulations. We demonstrate that for super-Alfvénic
turbulence, the structure function $D^\phi (R)$ gets shallower with the increase of $M_A$. Our study makes $D^\phi (R)$ a valuable diagnostic of super-Alfvénic
turbulence and opens a way to obtain $M_A$ from observations. We also explore numerically the structure function of the polarization degree and the spectrum of the polarization directions, the latter being the
Fourier transform of $D^\phi$. We discuss the implications of our findings for
turbulence and
magnetic field studies in the intracluster and interstellar media.
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Astrophysics of Galaxies
Probing the Molecular Hearts of Extreme Bipolar Planetary Nebulae with ALMA
Paula Moraga Baez, Joel H. Kastner, Jesse Bublitz et al. (+6 more)
We present results from a program of Atacama Large Millimeter Array (ALMA) 1.3 mm (Band 6) molecular line mapping of a sample of nearby, bipolar/pinched-waist, molecule-rich PNe (NGC 6302, Hubble 5, NGC 2440, NGC 6445, NGC 2899, and NGC 2818). Maps of $^{12}$CO(2$-$1) and $^{13}$CO(2$-$1) emission as well as emission lines of HCN, HNC, HCO$^+$, CN, and CS $-$ many of these detected in these PNe for the first time $-$ reveal the molecular mass distributions, compositions, and velocity fields of the equatorial and, in some cases, polar regions of the sample PNe. In each case, the bulk of the molecular gas traces an expanding equatorial
torus, with
torus expansion velocities ranging from $\sim$15 to $\sim$50 km s$^{-1}$ and molecular masses from $\sim$0.002 to $\sim$0.1 $M_\odot$. The inferred molecular
torus dynamical ages, which span the range $\sim$500 yr (Hb 5) to $\sim$11000 yr (NGC 2818), provide support for a model wherein molecular
torus ejection precedes bipolar lobe formation. Collectively, these ALMA survey results provide insight into the rapid structural
evolution as well as the zones of irradiated molecular gas within bipolar PNe that are descended from relatively massive progenitors, likely residing in interacting binary systems, over $\sim$10 kyr of the post-AGB
evolution of such systems.
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All authors Paula Moraga Baez, Joel H. Kastner, Jesse Bublitz, Javier Alcolea, Miguel Santander-Garcia, Thierry Forveille, Pierre Hily-Blant, Bruce Balick, Rodolfo Montez Jr
High Energy Astrophysical Phenomena
Symbolic Regression Is All You Need: From Simulations to Scaling Laws in Binary Neutron Star Mergers
P. Darc, Clecio R. Bom, Charles Kilpatrick et al. (+2 more)
Gravitational wave sources with electromagnetic counterparts have highlighted the need for predictive, interpretable models linking the parameters of compact binary systems to post-merger remnants and mass
outflows. In this work, we explore AI-driven symbolic regression (SR) frameworks to derive updated analytical relations for disk ejecta mass in binary
neutron star mergers, trained on state-of-the-art numerical relativity simulations. Our method reveals a set of compact equations that outperform existing fitting formulae across multiple statistical metrics while remaining physically interpretable. Notably, SR also enables alternative predictor sets (e.g., $\{M_1,M_2,\tilde{\Lambda}\}$) that match or exceed the accuracy of models relying solely on compactness of the lightest
neutron star ($C_1$), enabling new parameter constraints from electromagnetic observations. Unlike traditional black-box machine learning models, these closed-form expressions generalize robustly to regions of the parameter space not represented in the training data, offering a physics-informed tool for multimessenger observations and constraints on the
neutron star equation of state.
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All authors P. Darc, Clecio R. Bom, Charles Kilpatrick, Bernardo M. O. Fraga, Gabriel S. M. Teixeira
Earth and Planetary Astrophysics
WATSON-Net: Vetting, Validation, and Analysis of Transits from Space Observations with Neural Networks
M. Dévora-Pajares, F.J. Pozuelos, J.C. Suárez et al. (+2 more)
Context. As the number of detected transiting
exoplanet candidates continues to grow, the need for robust and scalable automated tools to prioritize or validate them has become increasingly critical. Among the most promising solutions, deep learning models offer the ability to interpret complex diagnostic metrics traditionally used in the vetting process. Aims. In this work, we present WATSON-Net, a new open-source neural network classifier and data preparation package designed to compete with current state-of-the-art tools for vetting and validation of transiting
exoplanet signals from space-based missions. Methods. Trained on Kepler Q1-Q17 DR25 data using 10-fold cross-validation, WATSON-Net produces ten independent models, each evaluated on dedicated validation and test sets. The ten models are calibrated and prepared to be extensible for TESS data by standardizing the input pipeline, allowing for performance assessment across different space missions. Results. For Kepler targets, WATSON-Net achieves a recall-at-precision of 0.99 (R@P0.99) of 0.903, ranking second, with only the ExoMiner network performing better (R@P0.99 = 0.936). For TESS signals, WATSON-Net emerges as the best-performing non-fine-tuned machine learning classifier, achieving a precision of 0.93 and a recall of 0.76 on a test set comprising confirmed
planets and false positives. Both the model and its data preparation tools are publicly available in the dearwatson Python package, fully open-source and integrated into the vetting engine of the SHERLOCK pipeline.
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All authors M. Dévora-Pajares, F.J. Pozuelos, J.C. Suárez, M. González-Penedo, C. Dafonte
Solar and Stellar Astrophysics
3D MHD simulations of coronal loops heated via magnetic braiding II. Automatic detection of reconnection outflows and statistical analysis of their properties
Gabriele Cozzo, Paola Testa, Juan Martinez-Sykora et al. (+5 more)
Recent observations of fast and bursty “nanojets” suggest novel diagnostics of nanoflare heating in the
solar corona. The aim of this work is to investigate the presence and properties of reconnection
outflows, similar to observed nanojets, in numerical simulations, and explore their relationship with the nanoflare properties. This work explores their potential as diagnostics for nanoflare heating in observations. We developed an
algorithm of Reconnection
Outflows Automatic Detection (ROAD) in 3D MHD simulations of coronal loops. We applied the
algorithm to a 3D MHD stratified coronal loop model heated by
magnetic reconnection and analyzed the statistical properties of the jets produced at reconnection sites, over about one
solar hour. The
magnetic structure is maintained at high temperature and for an indefinite time by intermittent episodes of local
magnetic energy release due to reconnection.
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All authors Gabriele Cozzo, Paola Testa, Juan Martinez-Sykora, Paolo Pagano, Fabio Reale, Franco Rappazzo, Viggo Hansteen, Bart De Pontieu
Solar and Stellar Astrophysics
3D MHD simulations of coronal loops heated via magnetic braiding I. Continuous driving
Gabriele Cozzo, Paola Testa, Juan Martinez-Sykora et al. (+13 more)
The nature and detailed properties of the heating of the million-degree
solar corona are important issues that are still largely unresolved. Nanoflare heating might be dominant in active regions and quiet Sun, although direct signatures of such small-scale events are difficult to observe in the highly conducting, faint corona. The aim of this work is to test the theory of coronal heating by nanoflares in braided
magnetic field structures. We analyze a 3D MHD model of a multistrand flux tube in a stratified
solar atmosphere, driven by twisting motions at the boundaries. We show how the
magnetic structure is maintained at high temperature and for an indefinite time, by intermittent episodes of local
magnetic energy release due to reconnection. We forward-modelled optically thin emission with SDO/AIA and MUSE and compared the synthetic observations with the intrinsic coronal
plasma properties, focusing on the response to impulsive coronal heating. Currents build up and their impulsive dissipation into heat are also investigated through different runs. In this first paper, we describe the proliferation of heating from the dissipation of narrow current sheets in realistic simulations of braided coronal flux tubes at unprecedented high spatial resolutions.
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All authors Gabriele Cozzo, Paola Testa, Juan Martinez-Sykora, Fabio Reale, Paolo Pagano, Franco Rappazzo, Viggo Hansteen, Bart De Pontieu, Antonino Petralia, Edoardo Alaimo, Federico Fiorentino, Fabio D'Anca, Luisa Sciortino, Michela Todaro, Ugo Lo Cicero, Marco Barbera
Cosmology and Nongalactic Astrophysics
How to evaluate the sufficiency and complementarity of summary statistics for cosmic fields: an information-theoretic perspective
Ce Sui, Yi Mao, Xiaosheng Zhao et al. (+2 more)
The advent of increasingly advanced surveys and
cosmic tracers has motivated the development of new inference techniques and novel approaches to extracting information from
cosmic fields. A central challenge in this endeavor is to quantify the information content carried by these summary statistics in
cosmic fields. In particular, how should we assess which statistics are more informative than others and assess the exact degree of complementarity of the information from each statistic? Here, we introduce mutual information (MI) that provides, from an information-theoretic perspective, a natural framework for assessing the sufficiency and complementarity of summary statistics in cosmological data. We demonstrate how MI can be applied to typical inference tasks to make information-theoretic evaluations, using two representative examples: the
cosmic microwave background map, from which the power spectrum extracts almost all information as is expected for a Gaussian random field, and the 21~cm brightness temperature map, from which the scattering transform extracts the most non-Gaussian information but is complementary to power spectrum and bispectrum. Our results suggest that MI offers a robust theoretical foundation for evaluating and improving summaries, thereby enabling a deeper understanding of
cosmic fields from an information-theoretic perspective.
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All authors Ce Sui, Yi Mao, Xiaosheng Zhao, Tao Jing, Benjamin D. Wandelt
Earth and Planetary Astrophysics
Conservation laws in non-inertial frames and non-conservation of energy of relative motion in two-body problem
Roman R. Rafikov
The dynamics of systems of multiple gravitationally interacting bodies is often studied in a frame attached to one of the objects (e.g. a central
star in a planetary system). As this frame is generally non-inertial, indirect forces appear in the equations describing the motion of bodies relative to the reference object. According to the convention adopted in celestial mechanics, the associated indirect acceleration is defined to be different for every object under consideration, whereas the gravitational coupling between each body and the reference object is described via the effective two-body potential, which does not obey the equivalence principle. Here we point out that a slightly different and more physically motivated definition of the indirect acceleration provides significant benefits when interpreting relative motion in a non-inertial frame. First, the indirect acceleration ends up being the same for all objects in the system. Second, the non-conservation of momentum, angular momentum, and energy of the whole system in a non-inertial frame naturally follow from the action of the indirect acceleration on the system as an external force. We also argue that the vis viva integral of the classical two-body problem should not be interpreted as a statement of energy conservation in a non-inertial frame attached to one of the bodies. The energy of relative motion is not conserved in this frame due to the work done on the two-body system by the indirect force. These results can be useful for interpreting dynamics in various astrophysical contexts, in particular the physics of disc-
planet coupling.
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Astrophysics of Galaxies
Identification of Candidate Halos Hosting Massive Black Hole Seeds in the $\textit{Renaissance}$ Simulations with Support Vector Machines
Brandon Pries and John H. Wise
The nature of the origins of supermassive black holes remains uncertain. Multiple possible seeding pathways have been proposed across a variety of mass scales, each with their own strengths and weaknesses. One such channel is a direct collapse black hole (DCBH), thought to form from the deaths of supermassive
stars in pristine atomic cooling
halos in the early universe. In this work, we investigate the ability to identify
halos likely to form a DCBH based on their properties using a support vector machine (SVM). We implement multiple methods to improve the accuracy of the model, including selecting subsets of critical features and optimizing SVM hyperparameters. We find that our best model requires quantities relevant to
star formation, such as the
metallicity, incident flux of Lyman-Werner radiation, and
halo stellar mass. The SVMs produced from this work can serve as probabilistic and holistic seeding prescriptions for DCBHs in cosmological simulations.
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Earth and Planetary Astrophysics
Isolating the gravitational influence of Uranus's winds requires close passages inward of the rings
Christopher R. Mankovich, Marzia Parisi, Damon F. Landau et al. (+1 more)
Close orbits by a Uranus Orbiter and Probe (UOP) could be used to deduce Uranus's multipolar
gravity field to higher precision and angular degree than the J2 and J4 currently measured from ground-based ring occultations and the Voyager 2 flyby. We examine Jn sensitivity limits obtained from simulations of candidate UOP trajectories, pairing these with Uranus interior and wind models to perform
retrievals from the
gravity moments. We consider zonal wind profiles derived from recent feature-tracking data, assuming that zonal winds extend into the
planet along cylinders, with a radial decay function similar to those that explain Jupiter and Saturn
gravity. Present knowledge of J2 and J4 permits a fairly wide range of possible wind depths in Uranus, up to 1,800 km or 7% by radius. Measuring additional
gravity moments is essential to separate this unknown wind depth from other interior properties of interest, but J6 is found to be too dominated by bulk rotation to be a useful probe of the wind depth. Odd moments arising from Uranus's observed north-south asymmetric flow are strong functions of the wind depth, but the usefulness of J3 is hindered by its sensitivity to present uncertainties in the wind profile. The even moment J8, or the odd moments J5 and J7, are the best probes of the depth of Uranus's winds. J8, and most likely J5 and J7, are measurable in a highly inclined orbit making >~10 pericenter passages inward of the $\zeta$ ring, approximately 1,000-2,500 km above Uranus's cloud tops.
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All authors Christopher R. Mankovich, Marzia Parisi, Damon F. Landau, Janosz W. Dewberry
Cosmology and Nongalactic Astrophysics
Gravity-Selected Galaxy Clusters: a Tight Mass-Richness relation and an unclear Compton $Y$-richness trend
S. Andreon and M. Radovich
This paper, the third in a series, investigates the scaling relations between optical richness, weak-
lensing mass, and Compton $Y$ for a sample of
galaxy clusters selected purely by the effect of their gravitational potential on the shapes of background
galaxies. This selection method is uncommon, as most cluster samples in the literature are selected based on signals originating from cluster
baryons. We analize a complete sample of 13
gravity-selected clusters at intermediate
redshifts (with $0.12 \leq z_{phot} \leq 0.40$) with weak-
lensing signal-to-noise ratios exceeding 7. We measured cluster richness by counting red-sequence
galaxies, identifying two cases of line-of-sight projections in the process, later confirmed by spectroscopic data. Both clusters are sufficiently separated in
redshift that contamination in richness can be straighforwardly dealt because the two red sequences do not blend each other. We find an exceptionally tight richness–mass relation using our red-sequence-based richness
estimator, with a scatter of just $\sim0.05$ dex, smaller than the intrinsic scatter of Compton Y with mass for the same sample. The lower scatter highlights the effectiveness of richness compared to Compton $Y$. No outliers are found in the richness-mass scaling, whether or not one cluster with a mass likely affected by projection effects is included in the sample. In the Compton $Y$-richness plane, the data do not delineate a clear trend. The limited sample size is not the sole reason for the unclear relation between Compton $Y$ and richness, since the same sample, with identical richness values, exhibits a highly significant and tight mass-richness correlation.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Excitation factors for horizonless compact objects: long-lived modes, echoes, and greybody factors
Romeo Felice Rosato, Shauvik Biswas, Sumanta Chakraborty et al. (+1 more)
We present an analytical and numerical investigation of the quasinormal excitation factors of ultracompact horizonless objects. These systems possess long lived quasinormal modes with extremely small imaginary parts, originating from the effective cavity between the
photon sphere and the object's interior. We show that the excitation of such modes is strongly suppressed, scaling with the imaginary part of their frequency, and therefore they contribute to the waveform only at very late times. This hierarchy naturally explains the structure of echo signals: the
prompt ringdown is dominated by standard light ring modes, the early echoes arise from moderately damped cavity modes, and only the latest echoes are governed by long lived modes. Based on this, we propose a practical ringdown waveform model based on a superposition of ordinary black hole quasinormal modes and cavity modes, which captures the complexity of the ringdown of horizonless ultracompact objects. We further demonstrate that the combination of small excitation factors and weak damping enhances the robustness of long lived modes against localized perturbations, in contrast to the spectral instabilities affecting standard black hole quasinormal modes. Finally, we extend the analysis of greybody factors to exotic compact objects and wormholes, showing that they remain stable under small deformations of the effective potential and thus represent robust observables. Our results provide a unified framework for understanding excitation, stability, and echoes in ultracompact horizonless objects, with direct implications for their spectral properties and gravitational wave signatures.
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All authors Romeo Felice Rosato, Shauvik Biswas, Sumanta Chakraborty, Paolo Pani
Earth and Planetary Astrophysics
No TiO detected in the hot Neptune-desert planet LTT-9779 b in reflected light at high spectral resolution
Sophia R. Vaughan, Jayne L. Birkby, Natasha E. Batalha et al. (+12 more)
LTT-9779 b is an inhabitant of the hot Neptune desert and one of only a few
planets with a measured high albedo. Characterising the atmosphere of this world is the key to understanding what processes dominate in creating the hot Neptune desert. We aim to characterise the reflected light of LTT-9779 b at high spectral resolution to break the degeneracy between clouds and atmospheric
metallicity. This is key to interpreting its mass loss history which may illuminate how it kept its place in the desert. We use the high resolution cross-correlation spectroscopy technique on four half-nights of ESPRESSO observations in 4-UT mode (16.4-m effective mirror) to constrain the reflected light spectrum of LTT-9779 b. We do not detect the reflected light spectrum of LTT-9779 b despite these data having the expected sensitivity at the level 100 ppm. Injection tests on the post-eclipse data indicate that TiO should have been detected for a range of different
equilibrium chemistry models. Therefore this non-detection suggests TiO depletion in the western hemisphere however, this conclusion is sensitive to temperature which impacts the chemistry in the upper atmosphere and the reliability of the line list. Additionally, we are able to constrain the top of the western cloud deck to $P_{\text{top, western}}<10^{-2.0}$ bar and the top of the eastern cloud deck $P_{\text{top, eastern}}<10^{-0.5}$ bar, which is consistent with the predicted altitude of MgSiO$_3$ and Mg$_2$SiO$_4$ clouds from JWST NIRISS/SOSS. While we do not detect the reflected light spectrum of LTT-9779 b, we have verified that this technique can be used in practice to characterise the high spectral resolution reflected light of
exoplanets so long as their spectra contain a sufficient number of deep spectral lines. Therefore this technique may become an important cornerstone of
exoplanet characterisation with the ELT and beyond.
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All authors Sophia R. Vaughan, Jayne L. Birkby, Natasha E. Batalha, Luke T. Parker, Haochuan Yu, Julia V. Seidel, Michael Radica, Jake Taylor, Laura Kreidberg, Vivien Parmentier, Sergio Hoyer, James S. Jenkins, Annabella Meech, Ricardo Ramírez Reyes, Lennart van Sluijs
Astrophysics of Galaxies
Kinematic scaling relations of disc galaxies from ionised gas at $z\sim1$ and their connection with dark matter haloes
Pavel E. Mancera Piña, Enrico M. Di Teodoro, S. Michael Fall et al. (+3 more)
We derive the Tully-Fisher (TFR, $M_\ast-V_{\rm circ,f}$) and Fall (FR, $j_\ast-M_\ast$) relations at
redshift $z = 0.9$ using a sample of 43 main-sequence disc
galaxies with H$\alpha$ IFU data and JWST/HST imaging. The strength of our analysis lies in the use of state-of-the-art 3D kinematic models to infer
galaxy rotation curves, the inclusion and morphological modelling of NIR bands, and the use of SED modelling applied to our photometry measurements to estimate
stellar masses. After correcting the inferred H$\alpha$ velocities for asymmetric drift, we find a TFR of the form $\log(M_\ast / M_\odot) = a \log(V_{\rm circ,f} / 150~\mathrm{km\,s^{-1}}) + b$, with $a=3.82^{+0.55}_{-0.40}$ and $b=10.27^{+0.06}_{-0.07}$, as well as a FR of the form $\log(j_\ast / \mathrm{kpc\,km\,s^{-1}}) = a \log(M_\ast / 10^{10.5} M_\odot) + b$, with $a=0.44^{+0.06}_{-0.06}$ and $b=2.86^{+0.02}_{-0.02}$. Compared with their $z=0$ counterparts, we find moderate
evolution in the TFR and strong
evolution in the FR over the past 8 Gyr. We interpret our findings in the context of the
galaxy-to-
halo scaling parameters $f_{\rm M}=M_\ast/M_{\rm vir}$ and $f_{\rm j}=j_\ast/j_{\rm vir}$. We infer that $f_{\rm j}$ shows little
redshift evolution and depends very weakly on $M_\ast$, with typical values around $f_{\rm j}\sim0.8$. As for $f_{\rm M}$, we find it to be higher and less dependent on $M_\ast$ at $z=0.9$ than at $z=0$. Interpreting our observed $f_{\rm M}-M_\ast$ relations within the Cold Dark Matter framework implies necessarily that the
galaxy populations at $z=0.9$ and $z=0$ are not the progenitor/descendant of one another. The alternative scenario is that the $z=0.9$ relations are incorrect due to strong selection effects, unidentified systematics, or the possibility that H$\alpha$ kinematics may not be a reliable dynamical tracer. Such problems would also affect previous studies on the same subject.
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All authors Pavel E. Mancera Piña, Enrico M. Di Teodoro, S. Michael Fall, Antonino Marasco, Mariska Kriek, Marco Martorano
High Energy Astrophysical Phenomena
Radiation-mediated shocks in gamma-ray bursts: spectral evolution
Filip Alamaa and Frédéric Daigne
Radiation-mediated shocks (RMSs) occurring below the photosphere in a gamma-ray burst (GRB) jet could play a crucial role in shaping the
prompt emission. In this paper, we study the time-resolved signal expected from such early shocks. We model an internal collision using a 1D special relativistic hydrodynamical simulation, and we follow the
photon distributions in the resulting forward and reverse shocks as well as in the common downstream region to well above the photosphere using a designated RMS simulation code. We compute the light curve and time-resolved spectrum of the resulting single pulse taking into account the emission at different optical depths and angles to the line of sight. For the specific case considered, we find a light curve consisting of a short pulse lasting $\sim 0.1~$s for an assumed
redshift of $z = 1$, which could constitute a whole short GRB or be a building block within a highly variable longer GRB light curve. The efficiency is large, with $\approx 23$% of the total burst energy being radiated. The spectrum has a complex shape at very early times, after which it settles into a more generic shape with a smooth
curvature below the peak energy, $E_p$, and a clear high-energy power law that cuts off at $\sim 5~$MeV in the observer frame. The spectrum becomes narrower and softer at late times with $E_p$ steadily decreasing during the pulse decay from $E_p \approx 250~$keV to $E_p \approx 100~$keV. The low-energy index, $\alpha$, decreases during the bright part of the pulse from $\alpha \approx -0.5$ to $\alpha \approx -1$, although the low-energy part is better fit with a broken power law when the signal-to-noise ratio is high. The high-energy power law is generated by the reverse shock at low optical depths ($\tau < 30$) and has an index that decreases from $\beta \approx -2$ to $\beta \approx -2.4$.
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Astrophysics of Galaxies
Bridging scales: Modeling suppressed Bondi accretion on black holes and its impact on galaxy growth
Antonio J. Porras-Valverde, Priyamvada Natarajan, Angelo Ricarte et al. (+4 more)
The
accretion and feedback processes governing supermassive black hole (SMBH) growth span an enormous range of spatial scales, from the Event Horizon to the circumgalactic medium. Recent general relativistic magnetohydrodynamic (GRMHD) simulations demonstrate that strong
magnetic fields can substantially suppress Bondi
accretion by creating magnetically arrested disk (MAD) states, reducing inflow rates by up to two orders of magnitude relative to classical Bondi predictions. We incorporate this
magnetic suppression prescription from Cho et al. (2023, 2024) into the Dark Sage semi-analytic model (SAM), which tracks SMBH and
galaxy co-
evolution within hierarchical merger trees derived from the IllustrisTNG cosmological simulation. Implementing the suppression across different Eddington-ratio regimes, we explore its impact on black hole mass functions (BHMFs),
stellar mass functions (SMFs), and AGN luminosity functions. Restricting suppression to sub-Eddington accretors ($f_{\rm Edd} < 3 \times 10^{-3}$) and rescaling AGN feedback efficiencies gives simultaneous agreement with observed $z = 0$ SMFs and BHMFs, as illustrated by Case D in this work. At $z > 6$, super-Eddington growth episodes dominate in the SAM, reproducing JWST-inferred luminous AGN number densities. Our results highlight the critical sensitivity of
galaxy assembly to the coupling between small-scale
accretion physics and large-scale feedback regulation.
Magnetic suppression of hot gas
accretion can reconcile low-
redshift constraints while preserving the rapid black hole growth required at early
cosmic epochs, thereby providing a physically motivated bridge between horizon-scale GRMHD simulations and cosmological
galaxy-formation models.
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All authors Antonio J. Porras-Valverde, Priyamvada Natarajan, Angelo Ricarte, Kung-Yi Su, Hyerin Cho, Ramesh Narayan, Ben S. Prather