Instrumentation and Methods for Astrophysics
Event Reconstruction for Radio-Based In-Ice Neutrino Detectors with Neural Posterior Estimation
Nils Heyer, Christian Glaser, Thorsten Glüsenkamp et al. (+1 more)
The detection of ultra-high-energy (UHE)
neutrinos in the EeV range is the goal of current and future in-ice
radio arrays at the South Pole and in Greenland. Here, we present a deep neural network that can reconstruct the main
neutrino properties of interest from the raw waveforms recorded by the
radio antennas: the
neutrino direction, the energy of the particle shower induced by the
neutrino interaction, and the event
topology, thereby estimating the
neutrino flavor. For the first time, we predict the full posterior PDF for the energy and direction reconstruction via neural posterior estimation utilizing conditional normalizing flows, enabling event-by-event uncertainty prediction. We improve over previous reconstruction
algorithms and obtain a median resolution of 0.30 log(E) and 18 square degrees for a 'shallow' detector component and 0.08 log(E) and 28 square degrees for a 'deep' detector component for neutral current (NC) events at a shower energy of 1 EeV. This deep learning approach also allows us to reconstruct the more
stochastic $\nu_e$ - charged current (CC) events. We quantify the impact of different
antenna types and systematic uncertainties on the reconstruction and derive a goodness-of-fit score to test the compatibility of measured
neutrino signals with the Monte Carlo simulations used to train the neural network.
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All authors Nils Heyer, Christian Glaser, Thorsten Glüsenkamp, Martin Ravn
Solar and Stellar Astrophysics
Energy-dependent SEP Fe/O abundances during the May 2024 superstorm
G.D. Muro, C.M.S. Cohen, Z. Xu et al. (+16 more)
During mid-May 2024, active region (AR) 13664 produced a series of M- and X-class
flares along with several coronal mass ejections (CMEs) that resulted in exceptionally strong aurora at Earth. This study presents in-situ
solar energetic particle (SEP) ion composition data from
Solar Terrestrial Relations Observatory Ahead (STA), Advanced Composition Explorer (ACE), and Parker
Solar Probe (PSP) as their
magnetic connectivity to AR 13664 varied throughout the event period. Between 08 to 24 May, STA was separated by 12{\deg} in longitude from ACE at 0.96 AU. SEP intensities rose gradually due to merged CMEs from AR 13664. On 13 May, an M6
flare was followed by a rapid-onset SEP event at STA, although velocity dispersion analysis yielded no clear path length or release time. PSP, 95{\deg} longitudinally separated from Earth at 0.74 AU, observed gradually increasing SEP intensities beginning 11 May, followed by a jump in both SEP intensity and
magnetic field (>100 nT) on 16 May. These early event intervals display stepwise SEP increases, consistent with the passage of successive CMEs. On 20 May, an X16.5
flare from AR 13664 produced an Fe-rich SEP event observed at all three spacecraft despite their wide longitudinal separations. Throughout the period, Fe/O ratios ranged from <0.01 to >0.8 and increased with energy between 1 to 100 MeV/nuc. This trend deviates from the typical energy-dependent decrease expected from diffusive shock acceleration and suggests more complex scenarios, possibly involving variable suprathermal seed populations or species-dependent transport.
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All authors G.D. Muro, C.M.S. Cohen, Z. Xu, R.A. Leske, A.C. Cummings, S. Bale, G. D. Berland, E. R. Christian, M. E. Cuesta, M. I. Desai, F. Fraschetti, J. Giacalone, L. Y. Khoo, A. Labrador, D. J. McComas, J. G. Mitchell, M. Pulupa, N. A. Schwadron, M. M. Shen
Astrophysics of Galaxies
Stellar Evolution with Radiative Feedback in AGN Disks
Zheng-Hao Xu, Yi-Xian Chen and Douglas N. C. Lin
Stars embedded in the inner pc region of an active
galactic nucleus (AGN) experience extreme
accretion conditions that significantly alter their
evolution. We present one-dimensional MESA simulations of
stars growing and decaying within AGN disks, implementing radiative-feedback-regulated
accretion which limits
stellar growth near the Eddington luminosity, as well as wind-driven mass loss. Unlike stand-alone
stars in the field, these embedded
stars follow unique evolutionary tracks with well-determined mass
evolution and chemical yields. We distinguish two regimes: “immortal"
stars that indefinitely remain on the main sequence due to efficient hydrogen mixing; and “metamorphic"
stars that evolves off the main sequence, ultimately enriching the disk with heavy elements upon hydrogen and helium exhaustion in their cores. Results indicate that embedded
stars in AGN disks can attain large masses, but gas retention and limited mixing likely render the “immortal" track unsustainable. We show radiative feedback plays a critical role in preventing runaway growth, since it regulates the inflow to at most of order-unity the Eddington-limited mass-loss rate. Embedded metamorphic
stars significantly enrich AGN disks with helium and $\alpha$-elements, potentially explaining the observed high
metallicity in broad-line regions (BLR) without excessive helium enrichment. This study underscores the critical interplay between
stellar feedback and
accretion physics in shaping the
stellar populations and chemical
evolution within AGN disks.
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Solar and Stellar Astrophysics
Do Planets Affect the Behavior of the Long-term Solar Activity?
M.M. Katsova, V.N. Obridko, D.D. Sokoloff et al. (+1 more)
Solar activity is a process driven by many independent but interconnected phenomena. Although the 11-year cycle is the result of operation of the dynamo mechanism, the cause of longer secular variations is not clear. In search of such a cause, it was proposed to take into account the influence of the planetary system. In order to verify the idea, we consider the action of all
planets in the
solar system reduced to the effect of a single barycenter. The
tidal force is decomposed into radial and meridional components. The radial
tidal force is too small compared to the powerful radial
gravity of the Sun. The meridional force is not compensated for by
solar gravity and depends on latitude. As the latitude of the barycenter changes quite slowly, the sign of this component changes over a characteristic time scale of about 5 years, during which the meridional acceleration constantly acts on the surface of the Sun. This could ultimately lead to speeds of several meters per second and, in principle, could significantly change the speeds of the meridional currents involved in generating the
magnetic field. However, it turned out that the calculated speed variation does not agree with the observed periodicity of
solar activity. Earlier, the relation was analyzed between the activity periods on
solar-type
stars and the rotation periods of
exoplanets, and no correspondence was observed either. Thus, the planetary hypothesis as a cause of long-term modulation of
solar activity is not confirmed.
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All authors M.M. Katsova, V.N. Obridko, D.D. Sokoloff, N.V. Emelianov
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Astrophysical Constraints on Charged Black Holes in Scalar–Tensor–Vector Gravity
Erdem Sucu, Kuantay Boshkayev, Yassine Sekhmani et al. (+2 more)
We explore charged black holes in Scalar-Tensor-Vector
Gravity (STVG), unveiling their distinctive features across multiple physical domains. Our topological analysis reveals that the STVG coupling parameter $\alpha$ bolsters thermal stability while electromagnetic charge $Q$ weakens it. Using the Gauss-Bonnet
theorem, we find that $\alpha$ amplifies light deflection and enlarges shadow silhouettes, with $Q$ generating opposite effects. Our
quantum-corrected models with exponential
entropy terms pinpoint phase transitions in the microscopic regime, modifying conventional thermodynamic relationships. Calculations of strong gravitational
lensing, shadow geometry, and Hawking emission show clear STVG signatures that diverge from Einstein's predictions. Notably, our
accretion disk analysis uncovers an intriguing phenomenon: specific combinations of $\alpha$ and $Q$ can produce radiation patterns resembling spinning Kerr black holes, creating potential identification challenges for observers. These findings establish concrete observational tests for STVG theory through next generation astronomical imaging and
lensing campaigns. By connecting theoretical predictions to measurable quantities, we outline specific pathways to confirm or constrain STVG using data from current and future space
telescopes.
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All authors Erdem Sucu, Kuantay Boshkayev, Yassine Sekhmani, İzzet Sakall{\i}, Mohsen Fathi
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
Quadrature-witness readout for backscatter mitigation in gravitational-wave detectors limited by back-action
Niels Böttner, Roman Schnabel and Mikhail Korobko
Disturbances in gravitational wave (GW) observational data are often caused by non-stationary noise in the detector itself, such as back-scattering of
laser stray light into the signal field. Unlike GW signals, non-stationary noise can appear in both the GW-signal quadrature and the orthogonal quadrature, which is usually not measured. Simultaneous sensing of this orthogonal quadrature provides a witness channel that can be used to reconstruct the disturbance in the signal quadrature enabling a subtraction of non-stationary noise. Here, we present the concept of quadrature witness that is compatible with frequency-dependent squeezing, which is already used to simultaneously reduce
photon shot noise and
photon radiation pressure noise. We demonstrate that implementing this approach in a GW detector could reduce noise caused by loud back-scatter events, thereby improving the overall sensitivity and robustness of GW observatories.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
On the Evidence for Violation of the Equivalence Principle in Disk Galaxies
Corey Sargent, William Clark, Antonia Seifert et al. (+5 more)
We examine the claimed observations of a gravitational external field effect (EFE) reported in Chae et al. We show that observations suggestive of the EFE can be interpreted without violating Einstein's equivalence principle, namely from known correlations between morphology, environment and dynamics of
galaxies. While Chae et al's analysis provides a valuable attempt at a clear test of Modified Newtonian Dynamics, an evidently important topic, a re-analysis of the observational data does not permit us to confidently assess the presence of an EFE or to distinguish this interpretation from that proposed in this article.
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All authors Corey Sargent, William Clark, Antonia Seifert, Alicia Mand, Emerson Rogers, Adam Lane, Alexandre Deur, Balša Terzić
High Energy Astrophysical Phenomena
Photon Orbit Signatures in Spectra of Black Hole Accretion Disks
Daniel C. M. Palumbo, George N. Wong and Angelo Ricarte
Light orbiting an accreting black hole may impact the disk or jet multiple times before escaping to the observer, at a variety of angles with respect to the local
magnetic field. In this letter, we characterize the imprints of these long path lengths and disparate
magnetic field impacts in synchrotron spectra of hot
accretion disks, as the strongly lensed “
photon ring” exhibits a higher synchrotron turnover frequency in each lensed sub-image. We apply tools of varying complexity: first, we develop a minimal, unlensed one-zone model that isolates the first two sub-images of the
accretion flow. By varying the
magnetic field geometry encountered by each sub-image, we show that distinctive spectral signatures emerge in both total intensity and fractional linear polarization. Second, we examine a semi-analytic radiatively inefficient
accretion flow (RIAF) model, in which we find that there is generally a frequency at which the first indirect image outshines the direct image even in total flux density. Lastly, we demonstrate that even general relativistic magnetohydrodynamic (GRMHD) simulation snapshots show this spectral character. We find a typical correction to the unresolved spectrum of order $10\%$ near the turnover frequency that grows with increasing viewing inclination, growing to order unity at higher frequencies. We predict sensitive spectral studies of the cores of Messier 87* and Sagittarius A* at frequencies exceeding $300$ GHz to constrain the existence of the
photon ring even without imaging, with prospects for
photon ring detection even in other sources with unresolved shadows.
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Solar and Stellar Astrophysics
Effects of density stratification on Rossby waves in deep atmospheres
Catherine C. Blume and Bradley W. Hindman
Though Rossby waves have been observed on the Sun, their radial eigenfunctions remain a mystery. The prior theoretical work either considers quasi-2D systems, which do not apply to the
solar interior, or only considers fully radiative or fully convective atmospheres. This project calculates the radial eigenfunctions for Rossby waves in a deep atmosphere for a general stratification. Here, we use the $\beta$-plane approximation to derive a vertical equation in terms of the Lagrangian pressure fluctuation $\delta P$, and we then calculate radial eigenfunctions for Rossby waves in a standard
solar model, Model S. We find that working in the Lagrangian pressure fluctuation results in cleaner wave equations that lack internal singularities that have been encountered in prior work. The resulting radial wave equation makes it abundantly clear that there are two wave cavities in the
solar interior, one in the radiative interior and another in the convection zone. Surprisingly, our calculated radial vorticity eigenfunctions for the radiative interior modes are nearly constant throughout the convection zone, raising the possibility that they may be observable at the
solar surface.
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Astrophysics of Galaxies
Making the most of pure parallels: Machine learning augmented photometric redshifts for sparse JWST filter sets
Kenneth J. Duncan
Photometric
redshifts (photo-$z$s) are an essential tool for
galaxy evolution science with JWST. However, for deep surveys with more limited filter sets (i.e. $N_{\text{filt}} \sim6$) such as large pure parallel surveys, the most commonly used template-fitting based photo-$z$ approaches can yield highly confident but spurious results for high-$z$ populations of interest. The utility and legacy value of these
datasets could therefore be negatively impacted. To address this challenge, we present an application of machine learning (ML) based photo-$z$ techniques to deep JWST photometric
datasets. We employ two different ML
algorithms, using Gaussian processes and nearest-neighbour estimates, alongside a more standard template fitting approach. We show that simple nearest-neighbour based estimates can provide more accurate photo-$z$s than template fitting out to $z\sim8$, as well as reducing the fraction of catastrophic outliers by a factor of $\sim2-3$. Additionally, `hybrid' estimates combining template and ML can yield further improvements in overall accuracy and reliability while retaining some ability to predict photo-$z$ out to $z > 10$. The nearest-neighbour only or hybrid estimates can achieve photo-$z$s with robust scatter of $\sigma_{\text{NMAD}}\sim0.03-0.04$ and outlier fractions of $\sim3-10\%$ between $0 < z \lesssim 8$ from just 6 NIRCam bands, with negligible additional computational costs compared to standard template fitting. Our methodology is easily adaptable to alternative
datasets, filter combinations or training samples. Overall, our results highlight the potential for even simple ML techniques to enhance the scientific return of JWST pure parallel and wide-area surveys.
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Solar and Stellar Astrophysics
Dark Matter in White Dwarfs: Implications for Their Structure
Sílvia P. Nunes, José D. V. Arbañil, Juan M. Z. Pretel et al. (+1 more)
White
Dwarfs (WDs), the final evolutionary stage of most
stars, are frequently modeled considering only a dense
plasma matter. However, their potential interaction with dark matter (DM), especially in
galactic halos where DM is expected to be prevalent, may lead to significant consequences. This work proposes a novel EoS (EoS) that consistently incorporates both hot dense
plasma and cold dark matter (CDM) contributions in hot WDs. The hot dense
plasma EoS is extended to include thermal and radiative contributions. At the same time, the CDM component is modeled as a linear fluid, with the coupling constant $\alpha$ determined self-consistently within the
star. A smooth phase transition between hot dense
plasma and CDM regimes is introduced via a
hyperbolic mixing function that depends on local energy density and
stellar temperature. Our results show that the inclusion of CDM leads to an increase in the WD radius by approximately $12\%$ and a total mass enhancement of $0.7\%$, compared to standard hot WD models without
lattice effects. These results highlight the importance of considering CDM in
stellar modeling and suggest that WDs may serve as indirect probes for the astrophysical properties of dark matter.
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All authors Sílvia P. Nunes, José D. V. Arbañil, Juan M. Z. Pretel, Sérgio B. Duarte
Astrophysics of Galaxies
Hot accretion onto spiral galaxies: the origin of extended and warped HI discs
Sriram Sankar, Jonathan Stern, Chris Power et al. (+6 more)
Gas
accretion, hot ($\sim 10^6$ K) atmospheres, and a tilt between the rotation axes of the disc and the atmosphere are all common predictions of standard
galaxy evolution theory for massive
star-forming
galaxies at low
redshift. Using idealised hydrodynamic simulations, we demonstrate that the central regions of hot
galaxy atmospheres continuously condense into cool ($\sim 10^4$ K) discs, while being replenished by an inflow from larger scales. The size and orientation of the condensed disc are determined by the angular momentum of the atmosphere, so the condensed disc is expected to often be tilted and more extended than the
stellar disc. Continuous
accretion from hot atmospheres can thus explain the ubiquity of extended and warped HI discs around local spirals, and also potentially provide the necessary fuel for
star formation. This hot
accretion scenario predicts the absence of significant HI from
galaxy halos, consistent with recent 21 cm constraints on nearby spirals (the so-called `HI desert'). Moreover, our analysis indicates that observations of HI warps can be used to constrain the angular momentum,
accretion rate, and gas
metallicity of hot
galaxy atmospheres, important parameters for disc
galaxy evolution that are hard to determine by other means.
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All authors Sriram Sankar, Jonathan Stern, Chris Power, Barbara Catinella, Drummond Fielding, Claude-André Faucher-Giguère, Imran Sultan, Michael Boylan-Kolchin, Joss Bland-Hawthorn
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
The future ability to test theories of gravity with black-hole shadows
Akhil Uniyal, Indu K. Dihingia, Yosuke Mizuno et al. (+1 more)
The horizon-scale images of supermassive black holes (BHs) by the Event Horizon
Telescope Collaboration (EHT) have provided new opportunities to test general relativity and other theories of
gravity. In view of future projects, such as the next-generation Event Horizon
Telescope (ngEHT) and the Black-Hole Explorer (BHEX), having the potential of enhancing our ability to probe extreme
gravity, it is natural to ask: how much can two black-hole images differ? To address this question and assess the ability of these projects to test theories of
gravity with black-hole shadows, we use general-relativistic magnetohydrodynamic and radiative-transfer simulations to investigate the images of a wide class of accreting BHs deviating from the Kerr solution. By measuring the mismatch between images of different BHs we show that future missions will be able to distinguish a large class of BHs solutions from the Kerr solution when the mismatch in the images exceeds values between $2\%$ and $5\%$ depending on the image-comparison metric considered. These results indicate future horizon-scale imaging with percent-level image fidelity can place meaningful observational constraints on deviations from the Kerr metric and thereby test strong-field predictions of general relativity.
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All authors Akhil Uniyal, Indu K. Dihingia, Yosuke Mizuno, Luciano Rezzolla
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Boson Stars Hosting Black Holes
Amitayus Banik, Jeong Han Kim and Xing-Yu Yang
We study a self-gravitating ultralight dark matter condensate (a
boson star) hosting a central black hole, in the nonrelativistic limit, which we refer to as a
boson star black hole (BS-BH) system. We numerically solve the equations of hydrostatic
equilibrium, consistently incorporating the gravitational potential of the black hole, to obtain all possible configurations of this BS-BH system for different
boson star masses, interaction types, and black hole masses. We also propose an analytic expression for the density profile and compare it with the numerical results, finding good agreement for attractive interactions and for a finite range of mass ratios between the black hole and
boson star. Finally, considering the inspiral of this BS-BH system with a second, smaller black hole, we study the dephasing of gravitational waves due to the presence of the dark matter environment. A Fisher
matrix analysis reveals the regions of parameter space of the dark matter mass and self-coupling that future gravitational wave observatories such as LISA can probe.
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Astrophysics of Galaxies
Probing the dawn of galaxies: star formation and feedback in the JWST era through the GAEA model
Sebastiano Cantarella, Gabriella De Lucia, Fabio Fontanot et al. (+4 more)
The James Webb Space Telecope (JWST) opened a new window for the study of the highest
redshift ($z>7$) Universe. This work presents a theoretical investigation of the very-high
redshift Universe using the state-of-the-art
GALaxy Evolution and Assembly (GAEA) model, run on merger trees from the Planck-Millennium $N$-body simulation. We show that GAEA successfully reproduces a wide range of high-$z$ observational estimates including: the
galaxy stellar mass function up to $z\sim13$ and the total (
galaxies and AGN) UV luminosity function (LF) up to $z\sim10$. We find that the AGN UV emission represents an important contribution at the bright end of the UVLF up to $z\sim8$, but it is negligible at higher
redshift. Our model reproduces well the observed mass-
metallicity relation at $z\leq4$, while it slightly overestimates the normalization of the relation at earlier
cosmic epochs. At $z\geq11$, current UVLF estimates are at least one order of magnitude larger than model predictions. We investigate the impact of different physical mechanisms, such as an enhanced
star formation efficiency coupled with a reduced
stellar feedback or a negligible
stellar feedback at $z>10$. In the framework of our model, both the
galaxy stellar mass and UV luminosity functions at $z\geq10$ can be explained by assuming feedback-free starbursts in high-density molecular clouds. However, we show that this model variant leads to a slight increase of the normalization of the $z\geq10$ mass-
metallicity relation, strengthening the tension with available data. A model with negligible
stellar feedback at $z>10$ also predicts larger numbers of massive and bright
galaxies aligning well with observations, but it also overestimates the
metallicity of the interstellar medium. We show that these model variants can in principle be discriminated using the relation between the
star formation rate and
galaxy stellar mass.
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All authors Sebastiano Cantarella, Gabriella De Lucia, Fabio Fontanot, Michaela Hirschmann, Lizhi Xie, Maximilien Franco, Adèle Plat
Astrophysics of Galaxies
Igniting galaxy formation in the post-reionization universe
Jorge Moreno, Coral Wheeler, Francisco J. Mercado et al. (+9 more)
It is widely believed that the ultraviolet background produced during the epoch of reionization conspires against the formation of low-mass
galaxies. Indeed, this mechanism is often invoked as a solution to the so-called `missing satellites problem.' In this paper we employ FIREbox, a large-volume cosmological simulation based on the Feedback In Realistic Environments (FIRE-2) physics model, to characterize the mechanisms governing
galaxy ignition in the post-reionization era. By carefully matching recently-ignited
halos (with
stellar ages below $100$ Myr at the time of selection) to
halos that failed to form any
stars, we conclude that the presence of cold-dense gas and
halo concentration help incite the process of
galaxy formation. Concretely, we find that $100\%$ of recently-ignited
halos experience cold-dense gas enhancements relative to their matched failed counterparts. Likewise, approximately $83\%$ display enhancements in both cold-dense gas and Navarro-Frenk-White concentration ($c_{\rm NFW}$), while the remaining $\sim17\%$ exhibit enhanced cold-dense gas content and suppressed $c_{\rm NFW}$ values. Lastly, our simulation suggests that
galaxy ignition can occur as late as $z=2$, potentially allowing us to observationally catch this process `in the act' in the foreseeable future.
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All authors Jorge Moreno, Coral Wheeler, Francisco J. Mercado, M. Katy Rodriguez Wimberly, Jenna Samuel, Pratik J. Gandhi, Elia Cenci, Robert Feldmann, Michael Boylan-Kolchin, Andrew Wetzel, James S. Bullock, Philip F. Hopkins
Astrophysics of Galaxies
Dynamical Friction Constraints on the Dark Matter Hypothesis Across Astronomical Scales
X. Hernandez and Pavel Kroupa
Dynamical friction implies a consistency check on any system where dark matter particles are hypothesised to explain orbital dynamics requiring more mass under Newtonian
gravity than is directly detectable. Introducing the assumption of a dominant dark matter
halo will also imply a decay timescale for the orbits in question. A self-consistency constraint hence arises, such that the resulting orbital decay timescales must be longer than the lifetimes of the systems in question. While such constraints are often trivially passed, the combined dependencies of dynamical friction timescales on the mass and orbital radius of the orbital tracer and on the density and velocity dispersion of the assumed dark matter particles leads to the existence of a number of astronomical systems where such a consistency test is failed. Here, we review cases from
stars in ultrafaint
dwarf galaxies,
galactic bars, satellite
galaxies, and, particularly, the multi-period mutual orbits of the Magellanic Clouds, as recently inferred from the
star formation histories of these two
galaxies, as well as the nearby M81 group of
galaxies, where introducing enough dark matter to explain observed kinematics leads to dynamical friction orbital decay timescales shorter than the lifetimes of the systems in question. Taken together, these observations exclude dark matter
halos made of particles as plausible explanations for the observed kinematics of these systems.
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Instrumentation and Methods for Astrophysics
The Real-Time Data Processor Framework for Data Handling and Analysis of High-Energy Instruments
A. Bulgarelli, N. Parmiggiani, L. Castaldini et al. (+5 more)
We implemented a real-time data processor (rta-dp) framework that can be used to develop real-time analysis pipelines and data handling systems to manage high-throughput data streams with distributed applications in the context of ground and space astrophysical projects and high-energy instruments. The rta-dp is based on the ZeroMQ in-
memory communication framework to receive input data, share data between distributed processes, and send or receive commands and pipeline configuration. The rta-dp framework has a flexible architecture that allows the implementation of distributed analysis systems customized to the requirements of several scenarios. The rta-dp framework also provides monitoring capabilities for the running processes and sends housekeeping, logging, alarms, and informative messages that a monitoring process can acquire. We are using the rta-dp in several contexts, such as acquiring and processing data from X-ray detectors to the data quality system of the ASTRI Project, as well as reprocessing and archiving data.
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All authors A. Bulgarelli, N. Parmiggiani, L. Castaldini, R. Falco, A. Di Piano, V. Fioretti, G. Panebianco, A. Rizzo
Solar and Stellar Astrophysics
Echoes of the First Stars: Massive Star Evolution in Extremely Metal-Poor Environments with the Habitable Worlds Observatory
Peter Senchyna, Calum Hawcroft, Miriam Garcia et al. (+3 more)
A remarkable span of frontier astrophysics, from gravitational-wave archaeology to the origin of the elements to interpreting snapshots of the earliest
galaxies, depends sensitively on our understanding of massive
star formation and
evolution in near-pristine, relatively enriched gas. From the surprisingly massive black holes detected by LIGO/Virgo to highly ionized nebulae with peculiar enrichment patterns observed in
galaxies at
Cosmic Dawn, evidence is mounting that our understanding of massive-
star populations at very low
metallicity remains critically incomplete. The fundamental limitation is the hand nature has dealt us: only a few
star-forming
galaxies within $\lesssim$1 Mpc can currently be resolved into individual
stars, and none reach the extreme
metallicities and
star-formation intensities that characterized the early Universe. With an ultraviolet integral-field spectrograph aboard the Habitable Worlds Observatory (HWO), this barrier will finally be broken. HWO will bring rare, actively
star-forming, extremely metal-poor
dwarf galaxies at $\sim$10-20 Mpc such as I Zw 18 within reach of resolved UV-optical spectroscopy, providing our first direct, statistical view of individual massive
stars and the feedback they drive at $>$30 $M_\odot$ and $<$10% $Z_\odot$. This science is deeply synergistic with many next-generation facilities, yet requires the unique combination of spatial resolution and UV/optical sensitivity that only HWO can provide. The massive
star science enabled by HWO within the Local Volume represents a transformational advance in our ability to probe the earliest
stellar populations - those that seeded the Milky Way and other
galaxies with the first heavy elements, and paved the way for life in the transparent, reionized Universe we inhabit today.
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All authors Peter Senchyna, Calum Hawcroft, Miriam Garcia, Aida Wofford, Janice C. Lee, Chris Evans
High Energy Astrophysical Phenomena
Is The Trace Anomaly at its Minimum Value at Neutron Star Centers?
Bao-Jun Cai, Bao-An Li and Yu-Gang Ma
While the equation of state (EOS) $P(\varepsilon)$ of
neutron star (NS) matter has been extensively studied, the EOS-parameter $\phi = P/\varepsilon$ or equivalently the dimensionless trace anomaly $\Delta = 1/3 - \phi$, which quantifies the balance between pressure $P$ and energy density $\varepsilon$, remains far less explored, especially in NS cores. Its bounds and density profile carry crucial information about the nature of superdense matter. Physically, the EOS-parameter $\phi$ represents the mean stiffness of matter accumulated from the
stellar surface up to a given density. Based on the intrinsic structure of the Tolman–Oppenheimer–Volkoff equations, we show that $\phi$ decreases monotonically outward from the NS center, independent of any specific input NS EOS model. Furthermore, observational evidence of a peak in the speed-of-sound squared (SSS) density-profile near the center effectively rules out a valley and a subsequent peak in the radial profile of $\phi$ at similar densities, reinforcing its monotonic decrease. These model-independent relations impose strong constraints on the near-center behavior of the EOS-parameter $\phi$, particularly demonstrating that the mean stiffness (or equivalently $\Delta$) reaches a local maximum (minimum) at the center.
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Astrophysics of Galaxies
Only Nitrogen-Enhanced Galaxies Have Detectable UV Nitrogen Emission Lines at High Redshift
Peixin Zhu, Lisa J. Kewley, Tiger Yu-Yang Hsiao et al. (+1 more)
The detections of bright UV nitrogen emission lines in some high-
redshift galaxies suggest unexpectedly high nitrogen-to-oxygen ratios ($\log(\rm N/O)\gtrsim-1.0$) compared to local values ($\log(\rm N/O)\gtrsim-1.5$) at similar
metallicities ($12+\log(\rm O/H)\lesssim8.0$). Although the presence of these `N-enhanced'
galaxies indicates signatures of atypical chemical enrichment processes in the early universe, the prevalence of nitrogen enhancement in high-$z$
galaxies is unclear. So far, only $\sim$10 $z>5$
galaxies have nitrogen abundance measurements, and they all suggest elevated N/O ratios. Do all high-
redshift galaxies exhibit elevated N/O ratios, or are we simply missing `N-normal'
galaxies whose nitrogen abundances follow the local N/O scaling relation? To tackle these questions, we calculate the detection limits of UV NIII] or NIV] lines in current JWST surveys CEERS and JADES, and compare them to predictions from both `N-enhanced' and `N-normal' AGN narrow-line region and H II region photoionization models. We find that CEERS can only detect
galaxies with significant nitrogen enhancement ($\log(\rm N/O)\gtrsim-0.4$), while JADES can only detect
galaxies with moderately elevated N/O ratios compared to local values ($\log(\rm N/O)\gtrsim-1.0$). Even for the deepest exposure in JADES, UV nitrogen lines produced by `N-normal'
galaxies at $z>5$ are too faint and thus not detectable, making their nitrogen abundance unmeasurable. Our results suggest that the existing sample of
galaxies with measurable nitrogen abundances at $z\gtrsim5$ is incomplete and biased toward
galaxies with significantly elevated N/O ratios. Deep ($t_{\rm exp}\sim40-500\,$hours) spectroscopic surveys will be crucial for building a complete sample to study nitrogen enrichment mechanisms in the early universe.
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All authors Peixin Zhu, Lisa J. Kewley, Tiger Yu-Yang Hsiao, James Trussler
Instrumentation and Methods for Astrophysics
Addressing prior dependence in hierarchical Bayesian modeling for PTA data analysis I: Methodology and implementation
Luigi D'amico, Eleonora Villa, Fatima Modica Bittordo et al. (+4 more)
Complex inference tasks, such as those encountered in
Pulsar Timing Array (PTA) data analysis, rely on
Bayesian frameworks. The high-dimensional parameter space and the strong interdependencies among astrophysical,
pulsar noise, and nuisance parameters introduce significant challenges for efficient learning and robust inference. These challenges are emblematic of broader issues in decision science, where model over-parameterization and prior sensitivity can compromise both computational tractability and the reliability of the results. We address these issues in the framework of hierarchical
Bayesian modeling by introducing a reparameterization strategy. Our approach employs Normalizing Flows (NFs) to decorrelate the parameters governing hierarchical priors from those of astrophysical interest. The use of NF-based mappings provides both the flexibility to realize the reparametrization and the tractability to preserve proper probability densities. We further adopt i-nessai, a flow-guided nested sampler, to accelerate exploration of complex posteriors. This unified use of NFs improves statistical robustness and computational efficiency, providing a principled methodology for addressing hierarchical
Bayesian inference in PTA analysis.
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All authors Luigi D'amico, Eleonora Villa, Fatima Modica Bittordo, Aldo Barca, Francesco Alì, Massimo Meneghetti, Luca Naso
Astrophysics of Galaxies
3D Full Spectrum Fitting: Algorithm Comparison
Prashin Jethwa, Simon Hubmer, Ronny Ramlau et al. (+1 more)
Full spectrum fitting is the prevailing method for extracting
stellar kinematic and population measurements from 1D
galaxy spectra. 3D methods refer to analysis of Integral Field Spectroscopy (IFS) data where spatial and spectral dimensions are modelled simultaneously. While several 3D methods exist for modelling gas structures there has been less investigation into the more computationally demanding problem of 3D full spectrum fitting for
stellar recoveries. This work introduces and compares two
algorithms for this task: the Projected Nesterov Kaczmarz Reconstruction method (PNKR) and a version of the Bayes-LOSVD software which has been modified to account for spatial correlations. We aim to understand strengths and weaknesses of both
algorithms and assess the impact of 3D methods for
stellar inferences. We apply both recovery
algorithms to a mock IFS data over a signal-to-noise ratio (SNR) range from 20-200 and evaluate the quality of the recoveries compared to the known ground truth. Accounting for spatial correlations in Bayes-LOSVD significantly improved the accuracy and precision of kinematic recoveries. 3D modelling with PNKR did not provide any significant improvement over 1D fits however, for SNR>40, PNKR did recover the most accurate kinematics overall. Additionally, by modelling the joint distribution over kinematics and populations, PNKR could successfully infer trends between these quantities e.g. inferring local
metallicity-velocity trends, albeit with a significant bias on the absolute
metallicity. Having demonstrated advantages of (i) 3D modelling with Bayes-LOSVD, and (ii) joint kinematic-population analyses with PNKR, we conclude that both methodological advances will prove useful for detecting and characterising
stellar structures from IFS data.
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All authors Prashin Jethwa, Simon Hubmer, Ronny Ramlau, Glenn Van de Ven
Astrophysics of Galaxies
ALMA and JWST Imaging of $z\ >\ 6$ Quasars: No Spatial Position Offset Observed Between Quasars and Their Host Galaxies
Aurora Wilde, Marcel Neeleman, Romain Meyer et al. (+4 more)
We present a study determining the spatial offset between the position of the supermassive black hole (as traced through their broad line regions) and the host
galaxy in six $z > 6$
quasars. We determined the host
galaxy's position from $\lesssim$$0.1^{\prime\prime}$ ($\lesssim$ 600 pc) resolution Atacama Large Millimeter/sub-millimeter Array (ALMA) [CII] 158 $\mu m$ and corresponding
dust continuum imaging. We determined the
quasar's position from $\lesssim$ 400 pc resolution James Webb Space
Telescope Near-Infrared Camera (JWST NIRCam) imaging. We estimated the observational uncertainties on the
quasar's position using astrometric data from the Global Astrometric Interferometer for Astrophysics (
GAIA) of field
stars within the NIRCam images. We find that all six
quasars are found within the central $\sim 400$ pc of their host
galaxy dust continuum and [CII] emission. Apparent offsets seen in rest-frame optical JWST observations are not detected in our ALMA data, suggesting they likely result from
dust obscuration rather than a true physical separation between the SMBH and its host
galaxy. Kinematic modeling of these data further reveals that none of the
galaxies show evidence for recent merger activity, and most of the
galaxies can be accurately modeled using a simple disk model. The lack of an offset supports theoretical models that predict that positional offset within these
galaxies are either short-lived or intrinsically rare.
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All authors Aurora Wilde, Marcel Neeleman, Romain Meyer, Roberto Decarli, Fabian Walter, Brenda Frye, Xiaohui Fan
Cosmology and Nongalactic Astrophysics · Cross-listed from cond-mat.stat-mech
Burgers dynamics for Poisson point process initial conditions
Patrick Valageas
We investigate the statistical properties of one-dimensional Burgers dynamics evolving from
stochastic initial conditions defined by a Poisson point process for the velocity potential, with a power-law intensity. Thanks to the geometrical interpretation of the solution in the inviscid limit, in terms of first-contact parabolas, we obtain explicit results for the multiplicity functions of shocks and voids, and for velocity and density one- and two-point correlation functions and power spectra. These initial conditions gives rise to self-similar dynamics with probability distributions that display power-law tails. In the limit where the exponent $\alpha$ of the Poisson process that defines the initial conditions goes to infinity, the power-law tails steepen to Gaussian falloffs and we recover the spatial distributions obtained in the classical study by Kida (1979) of Gaussian initial conditions with vanishing large-scale power.
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Solar and Stellar Astrophysics
Moderate Nesting and Cross-Equatorial Asymmetry of Active Regions in Solar Cycle 24
Aimee Norton, Alex Mendez, Ruizhu Chen et al. (+2 more)
Solar Cycle 24 data are used to determine how often the Sun emerges sunspots in `activity nests', i.e., regions where sunspots and active regions (ARs) repeatedly emerge. We use the
Solar Photospheric Ephemeral Active Region (SPEAR) catalog created from Helioseismic and
Magnetic Imager (HMI) data as well as the HMI Carrington Rotation maps of radial
magnetic field, $B_r$. The Sun shows moderate nesting behavior with 41% (48%) of AR
magnetic flux found in Northern (Southern) hemispheric nests that are short-lived (average lifetimes $\sim$3.3 - 4.0 months). Different rotation rates are used to search for nests that may not be evident `by eye'. The maximum number of nests are found with slightly prograde rotational velocities, with significant nest flux also found at synodic 451–452 nHz prograde and 409–411 nHz retrograde frequencies. Nest patterns show strong hemispheric asymmetry, indicating that the physical origin of nests identified herein must also be asymmetric or antisymmetric across the equator.
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All authors Aimee Norton, Alex Mendez, Ruizhu Chen, Mausumi Dikpati, S. Aswin Amirtha Raj
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
High-$Q$ Superconducting Lumped-Element Resonators for Low-Mass Axion Searches
Roman Kolevatov, Saptarshi Chaudhuri and Lyman Page
Low-frequency superconducting lumped-element resonators have recently attracted significant
attention in the context of
axion dark matter searches. Here we present the design and implementation of a fixed-frequency superconducting resonator operating near 250 kHz, possessing an inductor volume of approximately 1 liter and achieving an unloaded quality factor $Q \approx 2.1\times10^{6}$. This resonator represents a significant improvement over the state of the art and informs the design of searches for low-mass
axions.
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Cosmology and Nongalactic Astrophysics
Quantifying Weighted Morphological Content of Large-Scale Structures via Simulation-Based Inference
M. H. Jalali Kanafi and S. M. S. Movahed
We perform a simulation-based
forecasting analysis to compare the cosmological constraining power of higher-order summary statistics of the large-scale structure, the Minkowski Functionals (MFs) and a class weighted morphological measure known as the Conditional Moments of Derivatives (CMD), with that of the
redshift-space
halo power spectrum multipoles (PS), with a particular focus on their sensitivity to nonlinear and anisotropic features in
redshift space. Our analysis relies on
halo catalogs from the Big Sobol Sequence simulations at
redshift $z=0.5$, employing a likelihood-free inference framework implemented via neural posterior estimation. At the fiducial Quijote cosmology and for a Gaussian smoothing scale of $R=15\,h^{-1}\mathrm{Mpc}$, CMD provide systematically tighter constraints than MFs. Combining MFs and CMD into a joint
estimator improves the precision by $27\%^{+9\%}_{-5\%}$ for $\sigma_8$ and $26\%^{+7\%}_{-5\%}$ for $\Omega_{\mathrm{m}}$ relative to MFs alone, highlighting the complementary anisotropy-sensitive information captured by the CMD in contrast to the scalar morphological content encapsulated by the MFs. We compare the combined statistic MFs+CMD with the PS at matched effective scales ($k_{\max}\simeq0.16\,h\,\mathrm{Mpc^{-1}}$) under three
halo-selection conditions: all
halos, fixed number density, and mass-selected ($M>3\times10^{13}\,h^{-1}M_\odot$). In the mass-selected configuration, the (weighted) morphological
estimator outperforms the power spectrum by $45\%^{+20\%}_{-9\%}$ for $\sigma_8$ and $43\%^{+10\%}_{-7\%}$ for $\Omega_{\mathrm{m}}$. We also extend the simulation-based forecast analysis across a continuous range of cosmological parameters and multiple smoothing scales for morphological measures.
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Earth and Planetary Astrophysics
Tidally Torn: Why the Most Common Stars May Lack Large, Habitable-Zone Moons
Shaan D. Patel, Billy Quarles, Nevin N. Weinberg et al. (+1 more)
Earth-like
planets in the habitable zone (HZ) of M-
dwarfs have recently been targeted in the search for exomoons. We study the stability and lifetime of large (Luna-like) moons, accounting for the effects of 3-body interactions and
tidal forces using the N-body simulator rebound and its extension library reboundx. We find that those moons have a notably different likelihood of existence (and, by implication, observability). Large moons orbiting Earth-like
planets in the HZs of M4 and M2
dwarfs become unstable well before $10^7$ and $10^8 \textrm{ yr}$, respectively, and in most cases, those orbiting M0-
dwarfs become unstable in much less than $10^9 \textrm{ yr}$. We conclude that HZ
planets orbiting M-
dwarfs are unlikely to harbor large moons, thus affecting the total number of possible moons in our
galaxy and the Universe at large. Since moons may help enhance the habitability of their host
planet, besides being possibly habitable themselves, these results may have notable implications for exolife, and should also be considered when seeking solutions to the Drake equation and the
Fermi paradox.
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All authors Shaan D. Patel, Billy Quarles, Nevin N. Weinberg, Manfred Cuntz
Solar and Stellar Astrophysics
Modelling the Solar Cycle Nonlinearities into the Algebraic Approach
Mohammed H. Talafha
Understanding and predicting
solar-cycle variability requires accounting for nonlinear feedbacks that regulate the buildup of the Sun's polar
magnetic field. We present a simplified but physically grounded algebraic approach that models the dipole contribution of active regions (ARs) while incorporating two key nonlinearities: tilt quenching (TQ) and latitude quenching (LQ). Using ensembles of synthetic cycles across the dynamo effectivity range $\lambda_R$, we quantify how these mechanisms suppress the axial dipole and impose self-limiting feedback. Our results show that (i) both TQ and LQ reduce the polar field, and together they generate a clear saturation (ceiling) of dipole growth with increasing cycle amplitude; (ii) the balance between LQ and TQ, expressed as $R(\lambda_R) = \mathrm{dev(LQ)}/\mathrm{dev(TQ)}$, transitions near $\lambda_R \approx 12^\circ$, with LQ dominating at low $\lambda_R$ and TQ at high $\lambda_R$; (iii) over $8^\circ \leq \lambda_R \leq 20^\circ$, the ratio follows a shallow offset power law with exponent $n \approx 0.36 \pm 0.04$, significantly flatter than the $n=2$ scaling assumed in many surface flux–transport (SFT) models; and (iv) symmetric, tilt-asymmetric, and morphology-asymmetric AR prescriptions yield nearly identical $R(\lambda_R)$ curves, indicating weak sensitivity to AR geometry for fixed transport. These findings demonstrate that nonlinear saturation of the
solar cycle can be captured efficiently with algebraic formulations, providing a transparent complement to full SFT simulations. The method highlights that the LQ\–TQ balance is primarily controlled by transport ($\lambda_R$), not by active-region configuration, and statistically disfavors the SFT-based $1/\lambda_R^{2}$ dependence.
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