High Energy Astrophysical Phenomena
Magnetic reconnection with a 0.1 rate: Effective resistivity in general relativistic magnetohydrodynamics
B. Ripperda, M.P. Grehan, A. Moran et al. (+5 more)
Relativistic
magnetic reconnection is thought to power various multi-wavelength emission signatures from
neutron stars and black holes. Relativistic resistive magnetohydrodynamics (RRMHD) offers the simplest model of reconnection. However, a small uniform resistivity underestimates the reconnection rate compared to first-principles kinetic models. By employing an effective resistivity based on kinetic models - which connects the reconnection electric field to the charge-starved current density - we show that RRMHD can reproduce the increased reconnection rate of kinetic models, both in local current sheets and in global black hole magnetospheres.
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All authors B. Ripperda, M.P. Grehan, A. Moran, S. Selvi, L. Sironi, A. Philippov, A. Bransgrove, O. Porth
Cosmology and Nongalactic Astrophysics
Cosmic Collider Gravitational Waves sourced by Right-handed Neutrino production from Bubbles: Testing Seesaw, Leptogenesis and Dark Matter
Anish Ghoshal and Pratyay Pal
We study a minimal type-I seesaw framework in which a first-order phase transition (FOPT), driven by a singlet scalar, produces right-handed
neutrinos (RHNs) through bubble collisions, realizing a
cosmic-scale
collider that probes ultra-high energy scales. The resulting RHN distribution sources novel low-frequency gravitational-waves (GWs) in addition to the standard bubble-collision contribution. A stable lightest RHN can account for the observed dark matter (DM) relic abundance for masses as low as $M_{1} \equiv m_{\rm DM} \gtrsim 10^{6}\,\mathrm{GeV}$, with the associated novel GW signal accessible in LISA, ET and upcoming LVK detectors. If the RHNs are unstable, their CP-violating decays generate the observed
baryon asymmetry via leptogenesis for $M_{1} \gtrsim 10^{11}\,\mathrm{GeV}$ and phase transition temperatures $T_* \gtrsim 10^{6}\,\mathrm{GeV}$, for which the novel GW spectrum is detectable in ET, BBO and upcoming LVK. If RHN decays also populate a dark-sector
fermion with mass $m_{\chi} \in [10^{-4},10^{4}],\mathrm{GeV}$, successful co-genesis of
baryons and asymmetric dark matter occurs for $T_* \gtrsim 10^{7}\,\mathrm{GeV}$ and $M_{1} \gtrsim 10^{9}\,\mathrm{GeV}$, naturally explaining $\Omega_{\rm DM} \simeq 5\Omega_{\rm B}$. The corresponding GW signals are testable with LISA, ET, and BBO. Finally, we analyze a UV-complete multi-Majoron model, based on a global $U(1)_N \times U(1)_{\rm B-L}$ extension, motivated from the hierarchy of
lepton masses, which we dub as Mojaron
collider. The corresponding FOPT in this model leaves a distinctive GW signature arising from RHN production during $U(1)_N$
symmetry breaking detectable by BBO, ET and upcoming LVK. Successful leptogenesis is realized for heaviest RHN mass $M_3 \sim 10^{10}\,\mathrm{GeV}$ and a $U(1)_N$ breaking vev $v_2 \sim \mathcal{O}(\mathrm{TeV})$, which sets the seesaw scale.
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Instrumentation and Methods for Astrophysics
Validation of Satellite Lifetime Predictions at Leonid Space
Scott Shambaugh
This paper validates Leonid Space's satellite lifetime prediction pipeline through a backtesting campaign of 1283 deorbited satellites spanning six decades of spaceflight, showing that it accurately recreates their last year of flight. The pipeline combines a custom high-speed orbit propagator, ballistic coefficient estimation from on-orbit TLE data, atmospheric density corrections from data assimilation, custom space weather forecasts, and probabilistic Monte Carlo analysis. Validation proceeds in four steps that progressively remove the benefit of hindsight: starting from a "perfect knowledge" scenario using actual space weather data and ephemerides, we gradually replace historical data with contemporary predictions to arrive at a fully predictive scenario analogous to a deorbit prediction performed for a spacecraft flying today. These forecasts are scored using the continuously ranked probability score and root mean square calibration error, yielding a median one-year prediction accuracy of 2.4 days (0.7%) with perfect knowledge and 35.3 days (9.7%) in the fully predictive scenario.
Solar flux forecasts contribute 75% of the variance in our predictions, dominating all other sources of error. To our knowledge, this is the first comprehensive backtesting of long-term satellite lifetime predictions that reports quantitative results for the fully predictive case, and it establishes a new framework for scoring
solar cycle forecasts by grounding forecast accuracy in operationally-relevant satellite lifetime predictions.
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Instrumentation and Methods for Astrophysics
Experiments in binary evolution
Stephan Geier, Thomas Kupfer, Pierre Maxted et al. (+1 more)
The majority of
stars more massive than the Sun is found in binary or multiple
star systems and many of them will interact during their
evolution. Specific interactions, where progenitors and post-mass transfer (MT) systems are clearly linked, can provide yet missing observational constraints. Volume-complete samples of progenitor and post-MT systems are well suited to study those processes. To compile them, we need to determine the parameters of thousands of binary systems with periods spanning several orders of magnitude. The bottleneck are the orbital parameters, because accurate determinations require a good coverage of the orbital phases. The next generation of time-resolved spectroscopic surveys should be optimized to follow-up and solve whole populations of binary systems in an efficient way. To achieve this, a scheduler predicting the best times of the next observation for any given target in real time should be combined with a flexibly schedulable multi-object spectrograph or ideally a network of independent
telescopes.
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All authors Stephan Geier, Thomas Kupfer, Pierre Maxted, Veronika Schaffenroth
Cosmology and Nongalactic Astrophysics
An information-theoretic framework for quantifying coherence in the cosmic density field
Biswajit Pandey and Anindita Nandi
We introduce an information-theoretic framework for quantifying the coherence retained in the
cosmic density field across
cosmic time. Using mutual information between density fields at different
redshifts in cosmological $N$-body simulations, and subtracting an appropriate reference baseline, we isolate the excess statistical dependence generated by gravitational
evolution. Unlike conventional clustering statistics, this approach is sensitive to nonlinear and higher-order correlations and directly measures the shared information between different
cosmic epochs. The shared mutual information exhibits a strong dependence on spatial scale, increasing as the density field is progressively coarse-grained, reaching a maximum, and declining at larger scales. Through a series of tests involving different simulation volumes, discretization schemes, alternative baseline constructions, and subvolume analyses, we show that the location of this maximum is governed primarily by finite-sampling effects in the mutual information
estimator rather than by a fundamental physical coherence scale. The observed peak therefore provides an empirical indication of the range over which the present
estimator yields robust measurements. We further demonstrate that the mutual information is sensitive to
cosmic evolution and cosmological parameters. Our analysis shows that filamentary environments retain more statistically accessible shared information between
cosmic epochs than sheets and clusters. We also note that the shared information between the initial and present-day density fields is found to be positive but extremely small, reflecting the progressive redistribution of information during nonlinear structure formation. Our results establish mutual information as a powerful new tool for quantifying coherence,
memory, and information retention in the large-scale structure of the Universe.
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Astrophysics of Galaxies
Figuring Out Gas & Galaxies in Enzo (FOGGIE). XV. Examining the Spatial and Kinematic Relationship between Circumgalactic Mg II and O VI
Mackenzie Ticoras, Brian W. O'Shea, Claire Kopenhafer et al. (+9 more)
Understanding the thermodynamic properties of the circumgalactic medium (CGM) is key to uncovering the
baryon cycle in
galaxies. Here we present spatial and kinematic relationships between Mg II and O VI as representatives for low and high ion-bearing gas, in the cosmological zoom-in
galaxy simulation suite FOGGIE, a set of Milky-way-like
galaxy simulations with high CGM resolution. We find the O VI-bearing gas exists as a diffuse
halo around the
galactic disk, while the Mg II-bearing gas is more centrally located. We investigate the covering fraction, probability of co-observation, co-kinematic correspondence of these ions using two different analysis methods. We make both mock sightlines using two-dimensional projections of our simulations treating these
cells as integrated lines of sight and we create one-dimensional ray objects and use the SALSA (Boyd et al. 2020) code to investigate individual gas structures that contribute most to the line of sight column densities, which we call mock absorbers. We explore the relative kinematics of these mock absorbers and find Mg II and O VI appear to have a co-kinematic relationship when looking at absorber pairs with the closest relative velocity like in Werk et al. (2016). However, this does not necessarily correspond with a close spatial separation meaning many O VI and Mg II absorber pairs only appear to be co-kinematic but are physically unrelated. Taking a more holistic look at Mg II and O VI absorber pairs reveals a much weaker correlation between these two ions.
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All authors Mackenzie Ticoras, Brian W. O'Shea, Claire Kopenhafer, Cassandra Lochhaas, Molly S. Peeples, Jason Tumlinson, Cameron Trapp, Vida Saeedzadeh, Ramona Augustin, Nicolas Lehner, Britton D. Smith, J. Christopher Howk
Earth and Planetary Astrophysics
Protoplanetary disk cavities with JWST-MIRI: a dichotomy in molecular emission
Patrick Mallaney, Andrea Banzatti, Colette Salyk et al. (+24 more)
The
evolution of
planet-forming regions in protoplanetary disks is of fundamental importance to understanding
planet formation. Disks with a central deficit in
dust emission, a "cavity", have long attracted interest as potential evidence for advanced disk clearing by protoplanets and/or winds. Before JWST, infrared spectra showed that these disks typically lack the strong molecular emission observed in full disks. In this work, we combine a sample of 12 disks with millimeter cavities of a range of sizes ($\sim2$-70 au) and different levels of millimeter and infrared continuum deficits. We analyze their molecular spectra as observed with MIRI on JWST, homogeneously reduced with the new JDISCS pipeline. This analysis demonstrates a stark dichotomy in molecular emission where "molecule-rich" (MR) cavities follow global trends between water, CO, and OH luminosity and
accretion luminosity as in full disks, while "molecule-poor" (MP) cavities are significantly sub-luminous in all molecules except sometimes OH. Disk cavities generally show sub-luminous organic emission, higher OH/H$_2$O ratios, and suggest a lower water column density. The sub-thermal excitation of CO and water vibrational lines suggests a decreased gas density in the emitting layer in all cavities, supporting model expectations for C$_2$H$_2$ photodissociation. We discover a bifurcation in infrared index (lower in MR cavities) suggesting that the molecular dichotomy is linked to residual $\mu$m-size
dust within millimeter disk cavities. Put together, these results suggest a feedback process between
dust depletion, gas density decrease, and molecule dissociation. Disk cavities may have a common evolutionary sequence where MR switch into MP over time.
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All authors Patrick Mallaney, Andrea Banzatti, Colette Salyk, Ilaria Pascucci, Paola Pinilla, Joan Najita, Klaus M. Pontoppidan, Sebastiaan Krijt, Geoffrey A. Blake, Benoit Tabone, Till Kaeufer, Ke Zhang, Feng Long, Jane Huang, Giovanni Rosotti, Karin I. Oberg, Maria Jose Colmenares, Andrew Lay, Lucas A. Cieza, L. Ilsedore Cleeves, Joe Williams, Chengyan Xie, Miguel Vioque, Mayank Narang, Nicholas P. Ballering, Minjae Kim, the JDISCS Collaboration
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The Sequential Monte Carlo goes NUTS: Boosting Gravitational-Wave Inference
Gabriele Demasi, Giulia Capurri, Massimo Lenti et al. (+9 more)
Sequential Monte Carlo (SMC) methods have recently been applied to gravitational-wave inference as a powerful alternative to standard sampling techniques, such as Nested Sampling. At the same time, gradient-based Markov Chain Monte Carlo
algorithms, most notably the No-U-Turn Sampler (NUTS), provide an efficient way to explore high-dimensional parameter spaces. In this work we present SHARPy, a
Bayesian inference framework that combines the parallelism and evidence-estimation capabilities of SMC with the state-of-the-art sampling performance of NUTS. Moreover, SHARPy exploits the local
geometric structure of the posterior to further improve efficiency. Built on JAX, a high-performance computing framework that enables automatic differentiation and hardware acceleration, SHARPy performs gravitational-wave inference on binary black-hole events in around ten minutes, yielding posterior samples and
Bayesian evidence estimates that are consistent with those obtained through Nested Sampling. This work sets a new milestone in Gravitational-Wave inference with likelihood-based methods and paves the way for model comparison tasks to be accomplished in minutes.
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All authors Gabriele Demasi, Giulia Capurri, Massimo Lenti, Angelo Ricciardone, Barbara Patricelli, Adriano Frattale Mascioli, Lorenzo Piccari, Saulo Albuquerque, Gianluca M. Guidi, Francesco Pannarale, Giulia Stratta, Walter Del Pozzo
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Quantum dynamics of cosmological particle production: interacting quantum field theories with matrix product states
Evan Budd, Adrien Florio, David Frenklakh et al. (+1 more)
Understanding real-time dynamics of interacting
quantum fields in curved spacetime remains a major theoretical challenge. We employ tensor network methods to study such dynamics using interacting scalar and gauge theories in 1+1 spacetime dimensions, subject to a quench modeling a homogeneously expanding gravitational background. The models considered are the scalar $\lambda\phi^4$ theory and the Schwinger model, i.e. a Dirac
fermion coupled to a $U(1)$ gauge field which is equivalent via bosonization to a scalar field with a cosine self-interaction. In the free scalar limit, both theories reproduce known analytical results, providing a nontrivial numerical validation of bosonization in curved spacetime for the Schwinger model. Our central finding is that self-interactions lead to a suppression of gravitational particle production compared to the free-field case, as evidenced by two-point functions and the spectra of produced particles. We further examine the behavior of
entanglement generation and find that interactions suppress
entanglement growth in the $\lambda\phi^4$ theory, while in the Schwinger model, the interplay between suppressed particle production and enhanced inter-particle correlations leads to more complex
entanglement behavior. Our results pave the way for further explorations of nonperturbative
quantum real-time dynamics of interacting scalar and gauge theories in arbitrary gravitational backgrounds.
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All authors Evan Budd, Adrien Florio, David Frenklakh, Swagato Mukherjee
Earth and Planetary Astrophysics
Hunting for "Oddballs" with Machine Learning: Detecting Anomalous Exoplanets Using a Deep-Learned Low-Dimensional Representation of Transit Spectra with Autoencoders
Alexander Roman, Emilie Panek, Roy T. Forestano et al. (+3 more)
This study explores the application of autoencoder-based machine learning techniques for anomaly detection to identify
exoplanet atmospheres with unconventional chemical signatures using a low-dimensional data representation. We use the Atmospheric Big Challenge (ABC) database, a publicly available
dataset with over 100,000 simulated
exoplanet spectra, to construct an anomaly detection scenario by defining CO2-rich atmospheres as anomalies and CO2-poor atmospheres as the normal class. We benchmarked four different anomaly detection strategies: Autoencoder Reconstruction Loss, One-Class Support Vector Machine (1 class-SVM), K-means Clustering, and Local Outlier Factor (LOF). Each method was evaluated in both the original spectral space and the autoencoder's latent space using Receiver Operating Characteristic (ROC) curves and Area Under the Curve (AUC) metrics. To test the performance of the different methods under realistic conditions, we introduced Gaussian noise levels ranging from 10 to 50 ppm. Our results indicate that anomaly detection is consistently more effective when performed within the latent space across all noise levels. Specifically, K-means clustering in the latent space emerged as a stable and high-performing method. We demonstrate that this anomaly detection approach is robust to noise levels up to 30 ppm (consistent with realistic space-based observations) and remains viable even at 50 ppm when leveraging latent space representations. On the other hand, the performance of the anomaly detection methods applied directly in the raw spectral space degrades significantly with increasing the level of noise. This suggests that autoencoder-driven dimensionality reduction offers a robust methodology for flagging chemically anomalous targets in large-scale surveys where exhaustive
retrievals are computationally prohibitive.
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All authors Alexander Roman, Emilie Panek, Roy T. Forestano, Eyup B. Unlu, Katia Matcheva, Konstantin T. Matchev
High Energy Astrophysical Phenomena
Axions explain the formation of supermassive black holes at cosmic dawn
Pierre Sikivie and Yuxin Zhao
In a recent paper we pointed out that supermassive black holes, with masses ranging from $10^5$ to $10^{10} M_\odot$ form naturally at
cosmic dawn if the dark matter is QCD
axions or
axion-like particles with mass $m > 10^{-16}\, \mathrm{eV}/c^2$. No additional assumptions are required. Here we answer in detail the most commonly raised questions regarding our work.
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Astrophysics of Galaxies
The Polarization and Magnetic Field of the Radio Arc as Observed by ALMA at 100 GHz
Nora Salem, Dylan M. Paré, Paulo Cortes et al. (+2 more)
The unique
Galactic Center non-thermal filaments (NTFs) have been a focus of investigations for over 40 years. The most prominent manifestation of the NTFs is a bundle of parallel filaments known as the
Radio Arc.
Radio polarimetric observations made with the Very Large Array (VLA) at 10 GHz have revealed an alternating
magnetic field pattern in the
Radio Arc that could either be a result of multiple field systems being encountered along the line of sight or an intrinsic feature of the
Radio Arc. These VLA observations were not able to distinguish between these possibilities due to the large rotation measures encountered towards the source. We present ALMA 100 GHz observations of the
Radio Arc that are not impacted by significant Faraday effects. The observations reported here represent both the first time that ALMA has been used to study the NTFs and the first time 100 GHz polarimetric observations have been conducted on the
Radio Arc. We find a uniformly rotated
magnetic field with respect to the NTF filament orientation, with the angle of rotation being constant along the length of each filament. However, we find a systematically different
magnetic field orientation in different
Radio Arc filaments. We use this field pattern to update our understanding of the line-of-sight structures local to the
Radio Arc. We find that the
magnetic field inferred from our ALMA observations is likely a result either of confusion from multiple
magnetic field systems or because the polarization is centrally concentrated within the NTF filaments.
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All authors Nora Salem, Dylan M. Paré, Paulo Cortes, Mark R. Morris, Valentin J. M. Le Gouellec
Instrumentation and Methods for Astrophysics
Uncovering Hidden Systematics in Extreme-Precision Radial Velocity Measurements
Lily L. Zhao, Debra A. Fischer, Andrew E. Szymkowiak et al. (+2 more)
We identify and correct for small but coherent instrumental drifts in seven years of radial velocity data from the EXtreme PREcision Spectrograph (EXPRES). The systematics are most notable for the six months before and after 2022 January, when EXPRES experienced larger temperature variations, and we see a systematic trough-to-peak amplitude of 2.8 m/s in the radial velocities. This is large enough to mimic or obscure planetary signatures. To isolate and correct these effects, we develop a suite of diagnostics that track two-dimensional échellogram shifts, scalings, and rotation, as well as line bisector spans (LBS) derived from
laser frequency comb (LFC) lines. By combining these empirical tracers with instrument telemetry in a multi-dimensional regression, we reduce the EXPRES instrument trend traced with
solar RVs from an RMS of 1.32 m/s to 0.43 m/s, a 67% improvement, and the aggregate of twelve chromospherically quiet
stars show a 26% reduction in velocity scatter. Our injection-recovery simulations further demonstrate a doubling in sensitivity to low-amplitude planetary signals after correction. When applied to the
stellar time series of $\rho$ Coronae Borealis ($\rho$CrB), the correction removes a spurious
planet d signal, restoring the integrity of the data. These results highlight the need for long-term monitoring and multi-dimensional calibration diagnostics on the path toward true centimeter-per-second precision in next-generation EPRV instruments.
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All authors Lily L. Zhao, Debra A. Fischer, Andrew E. Szymkowiak, John M. Brewer, Joe Llama
High Energy Astrophysical Phenomena
Looking for observational signatures of early binary black hole systems
Peggy Varniere, Fabien Casse and Fabrice Dodu
Context. A lot of recent studies have focused on the observables associated with near merger binary black-holes (BBHs) embedded in a circumbinary disk (CBD) but we still we lack knowledge of observables of BBHs in their early stage. In that stage the separation between the two black holes is so large that both black holes could potentially retain their individual
accretion disk existing before the creation of the BBH. For such early BBH systems, it is interesting to look for observables originating in those individual disks whose structure is likely to differ from mini-disks often observed in simulations of later stages of BBHs. Aims. In a companion paper we presented a set of hydrodynamical simulations of an individual disk surrounding a primary black hole while being impacted by the presence of a secondary black-hole in an early BBH system, leading to the creation of three well-known characteristic features in the disk's structure. Here we explore the imprints of these three features on the observables associated with the thermal emission of the pre-existing black hole disk. The aim is two-fold, first to see which observables are best suited for detecting those early systems and, secondly, what could be extrapolated about these systems from observations. Methods. We used general relativistic ray-tracing in order to produce synthetic observations of the thermal emission emitted by early BBHs with different mass ratio and separations in order to search for distinctive observational features of early systems. Results. We found that in the case of early BBH with pre-existing disk(s) a necessary, although not unique, observational feature is the truncation of their disk(s). Conclusions. Such observable could be used for automated search of potential BBHs and discriminate some existing candidates.
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High Energy Astrophysical Phenomena
A comprehensive search for high-velocity X-ray sources: New compact object binary candidates in the Gaia era
Yue Zhao, Poshak Gandhi, Christian Knigge et al. (+6 more)
We perform a comprehensive search for high-velocity X-ray sources with large X-ray/optical flux ratios ($F_\mathrm{X}/F_\mathrm{G}$), identifying candidates for interacting black hole or
neutron star binaries potentially accelerated by
supernova natal kicks. We cross-match X-ray points sources from a variety of catalogues (Chandra, XMM-Newton, Swift and eROSITA) with
Gaia DR3. Using
Gaia coordinates, parallaxes, and proper motions, we compute peculiar velocities ($\upsilon_\mathrm{pec}$) relative to
Galactic disc rotation. Remaining agnostic about radial velocities (RVs), we vary RVs to find the minimum possible $\upsilon_\mathrm{pec}$ values ($\upsilon_\mathrm{pec, min}$). Uncertainties on $\upsilon_\mathrm{pec, min}$ are estimated via Monte Carlo resampling, and we select X-ray sources that have $1\,\sigma$ lower limits on $\upsilon_\mathrm{pec, min}\geq 200\,\mathrm{km~s^{-1}}$ and high $F_\mathrm{X}/F_\mathrm{G}$ values. We show that this velocity threshold excludes most contaminants (e.g., cataclysmic variables and active binaries) while retaining a sensible fraction of compact object binaries, demonstrating that $\upsilon_\mathrm{pec}$ could serve as an effective indicator for the presence of a
neutron star or black hole companion. Our selection yields a sample of 2372 sources, from which we construct a gold sample of 7 sources that have relatively well-constrained astrometry and confident optical counterparts. Follow-up is necessary to confirm and characterise their high-energy emission, as well as a
Galactic disc vs.
halo origin.
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All authors Yue Zhao, Poshak Gandhi, Christian Knigge, Phil Charles, Daniel Stern, Peter Boorman, Pornisara Nuchvanichakul, Cordelia Dashwood Brown, David A.H. Buckley
Cosmology and Nongalactic Astrophysics
Quintom Dark Energy: Future Attractor and Phantom Crossing in Light of DESI DR2 Observation
Phusuda Thanankullaphong, Prasanta Sahoo, Prajwal Hassan Puttasiddappa et al. (+1 more)
We study the late-time cosmological dynamics of a two-field dark energy model consisting of a canonical quintessence scalar field and a phantom scalar field in a spatially flat FLRW universe. The fields are minimally coupled to
gravity and uncoupled at the level of the potential, with the quintessence sector governed by an exponential potential and the phantom sector by an inverse power-law potential. By reformulating the background equations as a five-dimensional autonomous dynamical system, we identify and analyze the fixed points and their stability properties, revealing stable late-time attractors corresponding to phantom-dominated accelerated expansion. We confront the model with observations through a
Bayesian parameter estimation performed using the Cobaya framework, employing several combinations of recent cosmological data sets, including Pantheon+
supernovae, compressed
cosmic microwave background distance priors, DESI DR2
baryon acoustic oscillation measurements, and DES Year-5
supernova data. The observational constraints favor a dynamical dark energy sector moderately and are consistent with deviations from a cosmological constant at the present epoch. The regions of parameter space preferred by the data are compatible with the stable accelerating solutions identified in the dynamical analysis, establishing a direct connection between phase-space stability and observational viability. A notable feature of the model is that the effective dark energy equation of state undergoes phantom divide crossing in a gradual and asymptotic manner, rather than as a sharp transition.
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All authors Phusuda Thanankullaphong, Prasanta Sahoo, Prajwal Hassan Puttasiddappa, Nandan Roy
Astrophysics of Galaxies
The JWST EXCELS survey: Outflows in 1.5 < z < 5 quiescent and recently quenched galaxies are likely relics from episodic AGN activity
Elizabeth Taylor, Adam C. Carnall, David Maltby et al. (+24 more)
We investigate the presence and origin of neutral gas
outflows and inflows in 13 post-starburst (PSB) and quiescent
galaxies at
redshifts 1.8 $\leq$ z $\leq$ 4.6, using JWST NIRSpec spectroscopy from the EXCELS survey. NaD absorption profiles reveal that 3 out of 13 exhibit blueshifted absorption indicative of
outflows, and a further 2 objects show signs of inflowing gas.
Outflow velocities range from $\approx$ 300 - 1200 kms$^{-1}$, and we find gas flows are detected exclusively in objects that quenched $\lt$ 600 Myr ago. This result holds when we include comparable objects from recent literature. We derive mass
outflow rates over two orders of magnitude higher than current levels of
star formation in our sample, indicating that the winds are unlikely to be driven by
supernovae, and likely play a significant role in keeping the
galaxies quenched. The majority of the
outflow sample have anomalously high energy and momentum
outflow rates compared to those predicted for current levels of
star formation or AGN activity. We conclude that we are likely observing fossil
outflows driven by previous, more luminous AGN activity which has since faded. We then compare with the EAGLE simulation to explore a potential '
outflow cycle', finding that our observations are consistent with a model in which z $\sim$ 3 quiescent
galaxies undergo short $\simeq$ 5 Myr periods of AGN activity strong enough to drive
outflows, which occur every $\simeq$ 40 Myr on average. This AGN activity drives observable
outflows that persist for up to $\simeq$ 10 Myr after the AGN fades, followed by a $\simeq$ 20 Myr lull, and a subsequent short inflow, which eventually re-ignites AGN activity, and the cycle repeats.
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All authors Elizabeth Taylor, Adam C. Carnall, David Maltby, Omar Almaini, Ho-Hin Leung, Struan D. Stevenson, Andrea Negri, Fergus Cullen, Vivienne Wild, Ross J. McLure, Alice E. Shapley, Karla Z. Arellano-Córdova, Ryan Begley, Cecilia Bondestam, Thomas de Lisle, Callum T. Donnan, James S. Dunlop, Richard Ellis, Guillaume Hewitt, Anton M. Koekemoer, Feng-Yuan Frey Liu, Derek J. McLeod, Kate Rowlands, Ryan L. Sanders, Dirk Scholte, Maya Skarbinski, Thomas M. Stanton
Solar and Stellar Astrophysics
The Stellar Winds Atlas I: Current uncertainties in mass-loss rates
Amedeo Romagnolo, Floor S. Broekgaarden, Konstantinos Antoniadis et al. (+1 more)
Stellar winds are a major source of uncertainty in understanding the life and deaths of massive
stars. Across studies in the field, prescriptions for
stellar winds differ substantially in both their physical assumptions and implementation, making them a dominant contributor to model-to-model variation. In this work, we present a systematic analysis of the physical assumptions underlying commonly adopted wind prescriptions for optically thin and optically thick winds of hot
stars, as well as the winds of cool supergiants. Our analysis reveals substantial discrepancies across all regimes: predicted mass-loss rates for optically thin winds differ by more than an order of magnitude, while rates for cool supergiants vary by several orders of magnitude, with even wider uncertainties arising in extrapolation regimes beyond the Humphreys-Davidson limit. These disparities introduce significant ambiguity into the predicted formation of Wolf-Rayet (WR)
stars, a problem further compounded by the inconsistent application of transition criteria. A central issue is the "cool Wolf-Rayet problem", a temperature regime where the classical electron-scattering Eddington factor ($\Gamma_{\rm e}$) loses physical consistency. Because this factor is widely used to determine WR mass-loss rates, its failure forces models to rely on uncertain extrapolations and ad-hoc corrections. We conclude that the dominant
stellar wind uncertainties arise from a mismatch between the physical assumptions in
stellar wind models and the structure of the
stars to which they are applied. Our framework clarifies the origins of current theoretical discrepancies and identifies the key physical bottlenecks that must be addressed to improve mass-loss modeling for massive
stars.
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All authors Amedeo Romagnolo, Floor S. Broekgaarden, Konstantinos Antoniadis, Alex C. Gormaz-Matamala
Solar and Stellar Astrophysics
A 500 pc volume-limited sample of hot subluminous stars II. Atmospheric parameters, mass distribution, and kinematics
H. Dawson, M. Dorsch, S. Geier et al. (+30 more)
We present a quantitative spectroscopic and kinematic analysis of a volume-complete sample of hot subluminous
stars within 500 pc of the Sun, assembled using accurate parallax measurements from
Gaia Data Release 3 (DR3). In total, 3226 spectra of 253 hot subdwarf
stars were analysed to derive atmospheric parameters (effective temperature, surface
gravity, and helium abundance) and radial velocities. Spectral energy distributions (SEDs) combined with
Gaia parallaxes were used to measure
stellar radii, luminosities, and masses. The derived atmospheric parameters reveal a consistent
alignment between sdB and sdO
stars in the Kiel diagram when compared to theoretical evolutionary models. We identify a population (about 10%) of hot subdwarfs located below the 0.45 Msun zero-age EHB in both the Kiel and Hertzsprung-Russell diagrams, which likely originate from intermediate-mass progenitors (1.8-8 Msun). The overall mass distribution peaks at 0.48 pm 0.12 Msun, while hot subdwarfs below the EHB peak at 0.43 pm 0.10 Msun, supporting non- or semi-degenerate helium ignition characteristic of intermediate-mass
stars. Interpolation of EHB and post-EHB tracks yields mass distributions consistent with those derived from SEDs and parallaxes. Assuming a mass range between 0.40 and 0.50 Msun, we find that the post-EHB birthrate is 2-3 times higher than the EHB birthrate, suggesting overestimated EHB lifetimes or contamination from additional formation channels. Our kinematic analysis shows that 86 pm 2% of the
stars belong to the
Galactic thin disk, with 13 pm 1% and 1 pm 1% associated with the thick disk and
halo. The below-EHB population is found exclusively in the thin disk, the only
Galactic component young enough to host intermediate-mass progenitors. Its absence from other large samples suggests that non-degenerate formation channels play a more prominent role in the
Galactic disk.
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All authors H. Dawson, M. Dorsch, S. Geier, J. Munday, M. Pritzkuleit, U. Heber, F. Mattig, D. Benitez-Palacios, M.Vuckovic, I. Pelisoli, K. Deshmukh, A. Bhat, L. Kufleitner, M. Uzundag, V. Schaffenroth, N. Reindl, R. Culpan, R. Raddi, L. Antunes Amaral, A. G. Istrate, S. Justham, R. H. Ostensen, J. H. Telting, T. Steinmetz, N. Rodriguez-Segovia, P. Fernandez-Schlosser, A. Duran-Reyes, E. Arancibia-Rojas, M. Latour, G. T. Jones, M. O'Brien, S. Sahu, A. Elms
Astrophysics of Galaxies
The NIRISS PASSAGE Spectroscopic Redshift Catalog in COSMOS
Mason S. Huberty, Kalina V. Nedkova, Zahra Sattari et al. (+34 more)
We present the Parallel Application of Slitless Spectroscopy to Analyze
Galaxy Evolution (PASSAGE) spectroscopic
redshift catalog in the COSMOS field. PASSAGE is a JWST Cycle 1 Near Infrared Imager and Slitless Spectrograph (NIRISS) wide-field slitless spectroscopy (WFSS) pure-parallel survey, obtaining near-infrared spectra of thousands of extragalactic sources. 15 out of 63 PASSAGE fields fall within the Hubble Space
Telescope (HST) COSMOS footprint, of which 11 overlap with COSMOS-Web, a JWST treasury survey providing additional space-based photometry. We present our custom line-finding
algorithm and visual inspection effort used to identify emission lines and derive the spectroscopic
redshifts for line-emitting sources in PASSAGE. The line-finding
algorithm identifies between ~200 and 950 line-emitting candidates per field, of which typically 47% were identified as true emission lines post visual inspection. We identify 2183 emission line sources at 0.08<z<4.7, 1896 of which have available COSMOS photometric
redshifts. We find excellent
redshift agreement between the COSMOS photometric
redshifts and the PASSAGE spectroscopic
redshifts for strong (S/N>5), multi-line emitting sources. This agreement weakens for PASSAGE single-line emitters with ambiguous identities. These single-line emitters are likely mis-identified around 18% of the time based on comparisons to photometric
redshifts. We derive
stellar masses using PASSAGE photometry and spectroscopic
redshifts, in broad agreement with existing COSMOS-Web
stellar masses, but with some discrepancy driven by
redshift disagreements. We publicly release this spectroscopic
redshift catalog, which will enable community-led science in
prime extragalactic fields and serve as a crucial
dataset for validating Euclid and Roman spectroscopy.
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All authors Mason S. Huberty, Kalina V. Nedkova, Zahra Sattari, Vihang Mehta, Claudia Scarlata, Marc Rafelski, Matthew J. Hayes, Peter J. Watson, Ayan Acharyya, Jacob Levine, Benedetta Vulcani, Alexandra Le Reste, Farhanul Hasan, James Colbert, Michele Trenti, Xin Wang, Axel Runnholm, Matthew A. Malkan, Andrew J. Bunker, Anahita Alavi, Hakim Atek, Andrew J. Battisti, Y. Sophia Dai, Keunho Kim, Alaina Henry, Michael J. Rutkowski, Hollis Akins, Caitlin M. Casey, Maximilien Franco, Santosh Harish, Jeyhan S. Kartaltepe, Anton Koekemoer, Daizhong Liu, Henry McCracken, Jason Rhodes, Brant Robertson, Marko Shuntov
Solar and Stellar Astrophysics
Spectral signatures of bright grains determine chromospheric heating
Elias R. Udnæs and Tiago M.D. Pereira
Chromospheric heating is an important ingredient in the energy budget of the
solar atmosphere, which is challenging to quantify from observations. By using 3D radiative magnetohydrodynamic simulations of the
solar atmosphere combined with non-LTE spectral synthesis, we estimated chromospheric heating from synthetic spectra and studied the spectral and temporal signatures of heating events. We performed k-means clustering on the Mg II h, Ca II H, and Ca II 8542 Å lines to identify representative profiles associated with elevated chromospheric heating and studied their atmospheric stratification. We find that locations with the strongest chromospheric heating show spectral signatures with strong emission. Profiles with strong emission in the blue wing of the lines (blue grains) are created by upward-propagating shock waves and have an order of magnitude higher heating in the chromosphere than the ambient heating. Profiles with strong emission in the red wing (red grains) also display heating that is an order of magnitude stronger than the baseline, but these spectra do not show a characteristic atmospheric stratification. Spectra classified as blue grains have a consistent temporal
evolution, which is an oscillating sawtooth pattern in the line core and emission in the blue wing. However, spectra classified as red grains did not show a consistent temporal signature: Red wing emission from the simulations can appear spontaneously or be associated with an oscillation. While red and blue grain profiles account for around 3% of our synthetic spectra, they account for more than 12% of the total chromospheric heating in these simulations. By comparing two quiet Sun simulations, we find that the prevalence of bright grains is influenced by the
magnetic field configuration, with a unipolar configuration showing fewer bright grains and consequently a lower share of heating from such events.
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High Energy Astrophysical Phenomena
Complex dynamical regimes of the Tayler-Spruit dynamo
Paul Barrüre, Jérôme Guilet, Basile Gallet et al. (+1 more)
Astrophysical dynamos feature various spatial structures and dynamical regimes, ranging from hemispherical
magnetic fields to the random reversals of the geodynamo. The Tayler-Spruit dynamo, recently confirmed in direct numerical simulations, has been invoked to explain angular momentum transport in
stellar radiative zones and magnetar formation in a proto-
neutron star spun up by fallback
accretion. Whether this dynamo mechanism can lead to different dynamical regimes remains an open question. Using three-dimensional direct numerical simulations, we model the dynamics of a stably stratified spherical Couette flow, with the outer sphere rotating faster than the inner one. While the generation of strong stationary and hemispherical dynamos has been observed in our previous studies, we report for the first time the existence of reversals and complex temporal dynamics. We observe that the dynamics is strongly correlated with the equatorial
symmetry breaking of the flow. Focusing on a fiducial dynamo simulation, we propose an interpretation of its dynamics that consists in the coupling of two large-scale
magnetic modes with opposite equatorial
symmetries by the flow
symmetry breaking. While this interpretation captures the simplest observed dynamics, the nonlinear interaction between a higher number of
magnetic modes is certainly required to describe more complex regimes. The wide diversity of dynamical regimes generated by the Tayler-Spruit dynamo may have interesting implications for the geometry of the
neutron star magnetic fields, and therefore
neutron star emissions.
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All authors Paul Barrüre, Jérôme Guilet, Basile Gallet, Raphaël Raynaud
Earth and Planetary Astrophysics
Vetting and False Positive Analysis of TOI 864.01: Evidence for a Likely Hierarchical Eclipsing Binary Masked by Dilution
Biel Escolà-Rodrigo
We present a detailed vetting analysis of the TESS candidate TOI 864.01, initially identified as a potential ultra-short-period (P ~ 0.52 d) Earth-sized
planet orbiting an M-
dwarf. Using 12 sectors of TESS photometry spanning a multi-year baseline, we recover a robust periodic transit-like signal. While the recovered transit depth is attenuated by detrending (~ 158 ppm), the SPOC pipeline reports an undiluted depth of ~ 640 ppm.
Stellar characterization based on
Gaia DR3 astrometry yields a nominally single-
star solution (RUWE = 1.18), highlighting the limitations of astrometric vetting for tight companions. We performed a statistical validation analysis using TRICERATOPS, aggregating data from all 12 available sectors. The analysis yields a False Positive Probability (FPP) of 0.25 and a Nearby False Positive Probability (NFPP) of < 10^-4. While these metrics ostensibly classify the target as a viable planetary candidate based on
Gaia-resolved sources, they fail to account for sub-pixel companions. Crucially, archival high-resolution imaging from the TESS Follow-up Observing Program (TFOP SG1) reveals a
stellar companion at a separation of 0.04", unresolved by both
Gaia and TESS. When this companion is considered, the signal is best interpreted as a Hierarchical Eclipsing Binary (HEB) on the companion.
Bayesian model comparison yields an inconclusive result (Delta ln Z ~ 0.25), consistent with the degeneracy introduced by unresolved blending. Ground-based follow-up photometry further supports significant dilution, with a measured transit depth (~ 0.37 ppt) shallower than predicted (~ 0.64 ppt) and a timing offset of 6.3 minutes. Taken together, we classify TOI 864.01 as a probable False Positive and recommend its retirement from planetary candidate lists.
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Earth and Planetary Astrophysics
JWST/MIRI coronagraphic search for planets in systems with gapped exoKuiper belts and proper motion anomalies
R. Bendahan-West, S. Marino, A. L. Carter et al. (+17 more)
Over the past decade, ALMA has uncovered a range of substructures within exoKuiper belts, pointing to a population of undetected
planets. With JWST's sensitivity, we now have the opportunity to identify these
planets thought to be responsible for the observed substructures in debris discs. We present Cycle 1 JWST/MIRI 11.4 {\mu}m coronagraphic observations of three exoKuiper belts that exhibit gaps in their radial structures: HD 92945, HD 107146, and HD 206893, to determine whether
planets are responsible for carving these structures, as seen in our
Solar System with the gas
giants. We reduce the JWST/MIRI data using spaceKLIP, and introduce new routines to mitigate the Brighter-Fatter effect and persistence. We do not detect any
planet candidates, and all detected objects in the field-of-view are consistent with background
stars or
galaxies. However, by combining JWST mass limits, archival observational constraints, and astrometric accelerations, we rule out a significant portion of
planet parameter space, placing tight constraints on the
planets possibly responsible for these gaps. To interpret these results, we explore multiple gap-carving scenarios in discs, either massless or with non-zero mass, including clearing by in-situ
planet(s), as well as shaping by inner
planets through mean-motion or secular apsidal resonances. Finally, we conclude that the
planets causing the proper motion anomaly in these systems must reside within the inner 20 au.
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All authors R. Bendahan-West, S. Marino, A. L. Carter, V. Squicciarini, A. D. James, A. A. Sefilian, T. D. Pearce, M. F. Friebe, C. Lazzoni, B. Lakeland, S. Ray, M. C. Wyatt, L. Matrà, J. Milli, V. C. Faramaz, Th. Henning, S. Hinkley, G. M. Kennedy, D. Mesa, A. Zurlo
Solar and Stellar Astrophysics
Can instrumental effects obscure the true photospheric wave spectrum?
M. Berretti, M. Stangalini, D. B. Jess et al. (+6 more)
Optical aberrations and instrument resolution can affect the observed morphological properties of features in the
solar atmosphere. However, little work has been done to study the effects of spatial resolution on the dynamical processes occurring in the Sun's atmosphere. In this work, owing to the availability of high-resolution observations of a
magnetic pore captured with the Interferometric BIdimensional Spectrometer mounted at the Dunn
Solar Telescope, we studied the impact of the diffraction limit and the sampling of an instrument on line-of-sight Doppler velocity oscillations. We reported a noticeable shift in the dominant frequency band from $5$ to $3$ mHz, as both the angular and detector resolutions of the instruments were degraded. We argue that the observed behaviour is a result of the increased contamination of straylight from neighbouring quiet Sun regions, masking the true behaviour of umbral oscillations. These results suggest that the wave energy contributions reported in the literature and based on low-resolution instrumentation may be fundamentally underestimated. As we move into the era of high-resolution instrumentation such as DKIST and MUSE, this work will offer a critical baseline for interpreting new observations, especially in terms of distinguishing true dynamic behaviours from artefacts introduced by instrument-related limitations.
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All authors M. Berretti, M. Stangalini, D. B. Jess, S. Jafarzadeh, S. D. T. Grant, G. Verth, V. Fedun, G. Chambers, F. Berrilli
Solar and Stellar Astrophysics
Constraints on sunspot group lifetimes from far-side Sun-as-a-star helioseismology with BiSON
William J. Chaplin, Rachel Howe, Sarbani Basu et al. (+5 more)
Frequencies of low-degree
solar p modes are sensitive to activity over the entire Sun, including the unobservable far-side hemisphere. When frequency shifts extracted from week-long BiSON
datasets are fitted to a linear combination of observed near-side activity and a far-side proxy made from the near-side measures shifted by half the
solar rotation period, the solution favours a slightly higher weighting from the far-side contribution. Here, we demonstrate that this unphysical mismatch is due to the inherent inaccuracy of the far-side proxy, which fails to capture active regions that evolve fully on the
solar far side, or that evolve (or have evolved) significantly as they rotate off (or onto) the visible disc. By simulating the
evolution of sunspot group areas over time, which act as a suitable measure of
solar activity, we show that the solution is sensitive to the lifetime of the activity. Assuming an underlying mapping from maximum group areas $A_{\rm max}$ (measured in millionths of the
solar hemispheric area, MSH) to group lifetimes $\tau$ (measured in days) of the form $\tau = \alpha A_{\rm max}$, we find that $\alpha \simeq 0.025^{+0.055}_{-0.016}\,\rm d\,MSH^{-1}$ gives results consistent with the BiSON finding. This is to be compared with the value of $\alpha = 0.1\,\rm d\,MSH^{-1}$ implied by the well-known Gnevyshev-Waldmeier rule. While our best-fitting $\alpha$ maps to an average group lifetime of $\tau \simeq 5^{+10}_{-3}\,\rm d$, the best-fitting distribution includes a reasonable fraction of groups with lifetimes longer than the
solar rotation period, which is essential to reproducing the mismatch.
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All authors William J. Chaplin, Rachel Howe, Sarbani Basu, Yvonne Elsworth, Steven J. Hale, Emily J. Hatt, Eleanor Murray, Martin B. Nielsen
Astrophysics of Galaxies
Converging on the eccentricity of massive black hole binaries in galactic mergers
Alessia Gualandris, Justin Read, Federica Fastidio et al. (+4 more)
Binaries of supermassive black holes (MBHBs) represent the primary sources of the gravitational wave background (GWB) detectable by
Pulsar Timing Arrays (PTAs). The eccentricity with which binaries form in
galactic mergers is the key parameter determining their evolutionary timescale from pairing to coalescence. However, accurately determining the binary eccentricity at formation is difficult in simulations due to
stochastic effects. We present a numerical study of the formation and
evolution of MBHBs that are potential PTA sources. We simulate mergers of equal-mass
galaxies on different initial orbits and follow the dynamics of the MBHBs through the hardening phase. We find that low-resolution simulations are affected by stochasticity due to torques from the
stellar distribution acting at pericentre passages. The dispersion in binary eccentricity decreases with increasing central resolution, as expected for a Poisson process. We provide a fitting formula for the resolution requirement of an N-body simulation of MBHB formation and
evolution as a function of the initial eccentricity of the merger, e0, and the required accuracy in the binary eccentricity, eb. We find that binaries experience a torque at first pericentre that is approximately independent of initial eccentricity, producing a general trend in which the binary eccentricity decreases above sufficiently large initial orbital eccentricities. While this behaviour is generic, the precise cross-over eccentricity (e0~0.97 in our models) and the sharpness of the drop-off depend on the
galaxy initial conditions. We provide a fitting formula for eb(e0) that can be used in semi-analytical models to determine the merger timescales of MBHBs as well as the amplitude and slope of the GWB.
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All authors Alessia Gualandris, Justin Read, Federica Fastidio, Julian Chan, Thibaut François, Nader Khonji, Walter Dehnen
Solar and Stellar Astrophysics
Coexisting Tayler instability-driven dynamos in radiative zones: New dynamo solution and its impacts on stellar physics
Paul Barrère, Alexis Reboul-Salze, Patrick Eggenberger et al. (+3 more)
Recent asteroseismic observations constitute a great challenge for rotating
stellar evolution models, which predict overly fast internal rotation rates when only hydrodynamic processes are included. This suggests the absence of one or several unidentified angular momentum (AM) transport processes in these models. Transport by large-scale and strong
magnetic fields in the radiative zone is a promising candidate to explain the observations. While these fields might be characterised by a fossil origin, the Tayler-Spruit dynamo constitutes a primary mechanism to form the necessary
magnetic fields. Despite recent numerical studies, this mechanism remains poorly known. Motivated by this scenario, we investigated the Tayler-Spruit dynamo through a new set of 3D numerical simulations. We modelled the radiative zone as a Boussinesq stably stratified fluid whose differential rotation is maintained by a volumetric body force. Here, we report, for the first time, the coexistence of two dynamo solutions, which mainly differ by the
magnetic field location (near the equator and the polar axis). While the equatorial dynamo is driven by an instability sharing both characteristics of the magnetorotational and Tayler instabilities, we focus mainly on the newly identified polar dynamo, which is driven by the standard Tayler instability. We show that this dynamo can still operate and transport AM efficiently in a strong stratification regime, with a Brunt-Väisälä frequency that is 130 times larger than the rotation rate. We extracted new scaling laws for the
magnetic field, AM transport, and the minimum shear to trigger the dynamo. Finally, we were able to roughly constrain the signature of the generated
magnetic fields on asteroseismic modes propagating in main sequence and evolved
stars.
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All authors Paul Barrère, Alexis Reboul-Salze, Patrick Eggenberger, Sébastien Deheuvels, Carolina Rodríguez, Maxime Marchand
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Resonant photon-axion conversion driven by axion dark matter oscillations
Run-Min Yao, Xiao-Jun Bi, Peng-Fei Yin et al. (+1 more)
Wave propagation in periodically time-dependent media can exhibit driven mode conversion that is absent in static or adiabatic descriptions. We show that coherent
axion dark matter provides an intrinsic realization of this dynamics for
photons propagating in a
magnetic field. The background's periodic birefringence continuously rotates the
photon polarization and thereby drives
magnetic photon–
axion mixing. Using Floquet theory, we derive resonant
photon–
axion conversion when integer harmonics of the
axion oscillation frequency compensate the dispersion mismatch, $\Delta_\gamma-\Delta_a\approx n m_a$ with $n\in\mathbb{Z}$. This resonance enables efficient mixing far from conventional level crossing and is lost when the periodic drive is averaged out of the propagation
Hamiltonian. The resulting conversion is bounded and
unitary, distinct from parametric instability or
axion decay. Our framework describes
photon propagation in coherent oscillating
axion backgrounds and predicts characteristic polarization signatures, which we illustrate in a blazar environment.
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All authors Run-Min Yao, Xiao-Jun Bi, Peng-Fei Yin, Qing-Guo Huang
Cosmology and Nongalactic Astrophysics
Bondi-Hoyle-Lyttleton accretion onto ultra dense dark matter halos and direct collapse black holes
Kandaswamy Subramanian and Bikram Phookun
We suggest a formation scenario of black holes with intermediate mass $\sim 10^3 M_\odot$, by post recombination Bondi-Hoyle-Lyttleton
accretion into ultra dense dark matter
halos (UDMH) of $\sim 10^5 M_\odot$, which have formed around the recombination epoch. Such UDMH can result from rare
curvature fluctuations on small scales whose amplitude is still well below the current
Cosmic Microwave Background (CMB) spectral distortion limits. Gas accreted by the UDMH is heated to virial temperatures above which atomic cooling is efficient, cools rapidly to about $\sim 8000$ K and collapses on the free fall time of few $10^4$ yr to the
halo core, until supported by rotation. Further fragmentation due to molecular cooling is prevented by the suppression of $H_2$ molecule formation by the CMB
photons at
redshifts $z> 200-400$. We find that the rotationally supported gas disk will be compact and massive enough to undergo self-gravitational instability in some cases, plausibly where
accretion is into a nearly spherical UDMH which has formed from a rare peak in the density field. This results in a further, rapid transfer of mass inwards due to viscous forces and gravitational torques leading to the formation of a supermassive
star and/or black hole of about $10^3 M_\odot$ at
redshifts of a few hundred. Such intermediate mass black holes formed at high
redshifts can have a large-enough abundance to seed the first super massive black holes and help explain the abundance of active
galaxies detected now at increasingly larger
redshifts by the James Webb Space
Telescope.
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