High Energy Astrophysical Phenomena
Faint supernovae and hyper-runaway white-dwarfs from single He-detonation in double HeCO-white-dwarf mergers
Hila Glanz, Hagai B. Perets and Aakash Bhat
We present three-dimensional hydrodynamical simulations of mergers between low-mass hybrid HeCO white
dwarfs (WDs), offering new insights into the diversity of thermonuclear transients. Unlike previously studied mergers involving higher-mass HeCO WDs and CO WDs, where helium detonation often triggers core ignition, our simulations reveal incomplete helium shell detonations in comparable-mass, lower-mass WD pairs. The result is a faint, rapidly evolving transient driven by the ejection of intermediate-mass elements and radioactive isotopes such as $^{48}$Cr and $^{52}$Fe, without significant $^{56}$Ni production. These transients may be detectable in upcoming wide-field surveys and could account for a subset of faint thermonuclear
supernovae. Long-term
evolution of the merger remnant shows that high-velocity PG-1159-type
stars might be formed through this scenario, similar to normal CO-CO white
dwarf mergers. This work expands our understanding of white
dwarf mergers and their implications for nucleosynthesis and
stellar evolution.
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Astrophysics of Galaxies
The LMC Corona Favors a First Passage
Scott Lucchini, Jiwon Jesse Han, Sapna Mishra et al. (+1 more)
We use constrained idealized simulations of the LMC/Milky Way interaction to determine if the size of the LMC's gaseous
halo (Corona) can be used to distinguish between first and second passage models $-$ an orbital trajectory for the LMC in which it has just recently approached the Milky Way for the first time (first passage), or one in which it has had a previous pericenter (second passage). Using live circumgalactic gas particles combined with analytic dark matter potentials evolved to follow previously published orbital trajectories, we find that the first passage model is able to reproduce the observed velocity profile and column density profile of the present day LMC Corona. On the other hand, in a second passage scenario the longer interaction time leads to the velocities and column densities around the LMC at the present day being significantly lower than observations. Based on this observed velocity profile, recent works have found that the LMC's Corona has been truncated to 17$-$20 kpc, and we find truncation radii of $16.6\pm 0.5$ kpc and $5.7^{+1.8}_{-2.2}$ kpc for the first and second passage models, respectively. Thus, based on the gas properties of the LMC's CGM at the present day, a second passage trajectory is strongly disfavored.
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All authors Scott Lucchini, Jiwon Jesse Han, Sapna Mishra, Andrew J. Fox
Astrophysics of Galaxies
Threading the Magellanic Needle: Hypervelocity Stars Trace the Past Location of the LMC
Scott Lucchini and Jiwon Jesse Han
Recent discoveries have shown that a population of hypervelocity
stars (HVSs) originate from the Large Magellanic Cloud (LMC). We use three such HVSs as dynamical tracers to constrain the past orbit of the LMC. Since each
star was ejected at a finite time in the past, it must intersect the past position of the LMC's central black hole at its ejection time. We model the LMC's orbit under the influence of dynamical friction and extended mass distributions for both the LMC and the Milky Way, generating a large ensemble of orbital realizations. By evaluating which orbits intersect the back-integrated HVS trajectories, we compute posterior distributions over the LMC's orbital history. This approach provides significantly tighter constraints on the past motion of the LMC than previously possible. We find two previously published orbital models that are consistent with these new constraints: a first-passage trajectory from a self-consistent hydrodynamic simulation, and a second-passage trajectory from a collisionless N-body simulation. In parallel, we infer the present-day ejection site of the HVSs – likely tracing the LMC's dynamical center and supermassive black hole – independent of conventional methods.
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High Energy Astrophysical Phenomena · Cross-listed from physics.chem-ph
Mixed Stochastic-Deterministic Density Functional Theoretic Decomposition of Kubo-Greenwood Conductivities in the Projector Augmented Wave Formalism
Vidushi Sharma, Lee A. Collins and Alexander J. White
Pairing the accuracy of Kohn-Sham density-functional framework with the efficiency of a
stochastic algorithmic approach, mixed
stochastic-deterministic Density Functional Theory (mDFT) achieves a favorable computational scaling with system sizes and electronic temperatures. We employ the recently developed mDFT formalism to investigate the dynamic charge-transport properties of systems in the warm dense matter regime. The optical conductivity spectra are computed for single- and multi- component mixtures of carbon, hydrogen, and beryllium using two complementary approaches: Kubo-Greenwood in the mDFT picture and real-time Time-Dependent mDFT. We further devise a decomposition of the Onsager coefficients leading up to the Kubo-Greenwood spectra to exhibit contributions from the deterministic,
stochastic, and mixed electronic state transitions at different incident
photon energies.
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Astrophysics of Galaxies
Robust magnetic field estimates in star-forming galaxies with the equipartition formula in the absence of equipartition
H.-H. Sandy Chiu, Mateusz Ruszkowski, Maria Werhahn et al. (+2 more)
The equipartition model is widely used to estimate
magnetic field strength from synchrotron intensity in
radio galaxies, yet the validity of its underlying assumptions remains uncertain. Using an Arepo simulation which incorporates a two-moment
cosmic ray (CR) transport scheme and a multiphase interstellar medium, we compare
magnetic fields inferred from synthetic synchrotron emission maps with the true fields in the simulation. Starting from the derivation of the equipartition formula, we find that the deviation between the equipartition
magnetic field and the true
magnetic field depends only weakly on the ratio of the
magnetic to the CR energy density. In practice, for both face-on and edge-on projections, the equipartition model slightly overestimates the total synchrotron-weighted
magnetic field with mean offsets of 32% (0.17 dex) and 36% (0.2 dex), even though the energy equipartition between CR
protons and
magnetic fields does not hold locally. Beyond these average offsets, a clear trend emerges in edge-on projections that the model underestimates the field in the disk and overestimates it in the
halo. Our results demonstrate that the validity of the equipartition model depends only weakly on the strict fulfillment of energy equipartition, and that the equipartition model remains a practical method for estimating
magnetic field strengths in face-on projection maps based on our CR-magnetohydrodynamics simulation.
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All authors H.-H. Sandy Chiu, Mateusz Ruszkowski, Maria Werhahn, Christoph Pfrommer, Timon Thomas
Astrophysics of Galaxies
Inferring Stellar Densities with Flexible Models I: The Distribution of RR Lyrae in the Milky Way with $\textit{Gaia}$ DR3
Madeline Lucey, Cecilia Mateu, Adrian Price-Whelan et al. (+3 more)
Understanding the formation and evolutionary history of the Milky Way requires detailed mapping of its
stellar components, which preserve fossil records of the
Galaxy's assembly through
cosmic time. RR Lyrae
stars are particularly well-suited for this endeavor, as they are old, standard candle variables that probe the
Galaxy's earliest formation epochs. In this work, we employ a hierarchical
Bayesian Gaussian Mixture Model (GMM) to characterize the three-dimensional density distribution of RR Lyrae
stars in the Milky Way over the galactocentric radius ($R$) of $\approx 0.2-120~\rm{kpc}$. This approach provides a flexible framework for modeling complex
stellar distributions, particularly in the inner
Galaxy where the bulge, disk, and
halo components overlap. Our analysis reveals that the inner
Galaxy ($R\lesssim10~\rm{kpc}$) is dominated by a distinct prolate
stellar population with axis ratio $q$=1.31. Consistent with previous work, we find the
halo follows a $r^{-4}$ power-law profile that flattens within 12 kpc of the
Galactic center. We also confirm the outer
halo ($R\gtrsim10~\rm{kpc}$) is oblate $q$=0.70 with a tilt angle of $18^{\circ}$. We report for the first time that this tilt aligns the
halo major axis in the direction of the Sagittarius
dwarf galaxy. These results establish GMMs as an effective and flexible tool for modeling
Galactic structure and provide new constraints on the distribution of old
stars in the inner
Galaxy.
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All authors Madeline Lucey, Cecilia Mateu, Adrian Price-Whelan, David Hogg, Hans-Walter Rix, Robyn Sanderson
Instrumentation and Methods for Astrophysics
Advancing the Concept Maturity Level of the Servicing Architecture for Habitable Worlds Observer
Jonathan W. Arenberg
This paper advances the concept maturity level (CML) of the Habitable Worlds Observatory (HWO) servicing architecture. Since servicing has occurred on other missions, this paper argues that the current CML is 2. To advance to CML 3, option spaces must be established for trade studies. We introduce the three space ages and the argument that we are on the cusp of a new revolutionary era. Servicing is only part of that coming change and the other elements of the future space age are introduced. The challenge of designing a flagship mission such as HWO is discussed. The value proposition for the adoption of a new technology, such as servicing HWO, is established. In the latter portion of the paper it is shown that these elements have promise of being beneficial to HWO and should be included in any trade space.
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Earth and Planetary Astrophysics
An Open-Access Web Tool for Light Curve Simulation and Analysis of Small Solar System Objects
J. L. Rizos, J. L. Ortiz, P. J. Gutierrez et al. (+2 more)
We present a web-based application designed to simulate rotational light curves of small airless
Solar System bodies under user-defined geometrical and physical conditions. The tool integrates both physical and empirical photometric models and enables users to input custom shape models, surface properties, and viewing geometries. A dedicated module also computes projected silhouettes at the epoch of
stellar occultations, allowing direct comparison with observed chords. The application, developed in Python and Django, has been validated using well-characterized targets such as (136108) Haumea, (101955) Bennu, and (433) Eros, showing excellent agreement between synthetic and observed light curves and silhouettes. Beyond standard light curve simulations, the tool supports scenarios including surface heterogeneity, non-principal axis rotation (tumbling), and phase-angle effects. This flexible and accessible platform provides a powerful resource for interpreting photometric data, supporting ongoing observation campaigns, and aiding future mission planning.
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All authors J. L. Rizos, J. L. Ortiz, P. J. Gutierrez, I. M. Navajas, L. M. Lara
High Energy Astrophysical Phenomena
HESS J1831$-$098 – Exploring a pulsar halo scenario with H.E.S.S. data
Karim Sabri, Yves Gallant, Justine Devin et al. (+1 more)
Pulsar halos are a class of extended very-high-energy (VHE) sources highlighted by the HAWC observatory towards the Geminga
pulsar and PSR B0656$+$14. These VHE sources are interpreted as the inverse Compton emission from electrons and positrons diffusing in the interstellar medium at an inhibited rate, having escaped the
pulsar wind nebula. Our aim is to search for new
pulsar halos using H.E.S.S. data and to constrain their physical properties. Using a physically-motivated model of
pulsar halos, we created template-based models of the spatial and energetic distributions of the expected gamma-ray emission using the Gammapy library. A promising candidate source to which this model can be effectively applied is HESS J1831$-$098, an extended VHE source spatially coincident with two energetic
pulsars, which also exhibits spectral continuity and morphological compatibility with the ultra-high-energy source 1LHAASO J1831$-$1007u*. It could be powered by the
radio pulsar PSR J1831$-$0952 with a characteristic age of 128 kyr. We present a spectro-morphological analysis of this source with H.E.S.S. data, revealing that the emission is well described with a
pulsar halo model, although we cannot reject a simple 2D Gaussian morphology. We discuss the implication of the derived physical parameters of the model.
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All authors Karim Sabri, Yves Gallant, Justine Devin, Kirsty Feijen
High Energy Astrophysical Phenomena
Mapping the Nearest Ancient Sloshing Cold Front in the Sky with XMM-Newton
Sheng-Chieh Lin, Yuanyuan Su, Iraj Vaezzadeh et al. (+8 more)
The Virgo Cluster is the nearest cool core cluster that features two well-studied sloshing cold fronts at radii of $r \approx 30$ kpc and $r \approx 90$ kpc, respectively. In this work, we present results of XMM-Newton mosaic observations of a third, southwestern, cold front at a radius of $r \approx 250$ kpc, originally discovered with Suzaku. All three cold fronts are likely to be parts of an enormous swirling pattern, rooted in the core. The comparison with a numerical simulation of a binary cluster merger indicates that these cold fronts were produced in the same single event $-$ likely the infall of M49 from the northwest of Virgo and it is now re-entering the cluster from the south. This outermost cold front has probably survived for $2-3$ Gyr since the disturbance. We identified single sharp edges in the surface brightness profiles of the southern and southwestern sections of the cold front, whereas the western section is better characterized with double edges. This implies that
magnetic fields have preserved the leading edge of the cold front, while its western side is beginning to split into two cold fronts likely due to Kelvin-Helmholtz instabilities. The slopes of the 2D power spectrum of the X-ray surface brightness fluctuations, derived for the brighter side of the cold front, are consistent with the expectation from Kolmogorov
turbulence. Our findings highlight the role of cold fronts in shaping the thermal dynamics of the intracluster medium beyond the cluster core, which has important implications for cluster cosmology. Next-generation X-ray observatories, such as the proposed AXIS mission, will be ideal for identifying and characterizing ancient cold fronts.
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All authors Sheng-Chieh Lin, Yuanyuan Su, Iraj Vaezzadeh, William Forman, Elke Roediger, Charles Romero, Paul Nulsen, Scott W. Randall, John ZuHone, Ralph Kraft, Christine Jones
Earth and Planetary Astrophysics
Eclipse Mapping with Ariel: Future Prospects for a Population-Level Mapping Survey
Daniel Valentine, Hannah R. Wakeford, Mark Hammond et al. (+4 more)
Eclipse mapping is a powerful tool for measuring 3D profiles of
exoplanet atmospheres. To date, only JWST has been capable of widely applying this technique, but as a general observatory, it is too time-limited to conduct population-level mapping studies. Ariel, on the other hand, is a dedicated
exoplanet mission set to observe 1000 transiting
exoplanets, making it a natural candidate for this. To assess Ariel's mapping potential, we quantitatively
benchmark its abilities against those of JWST using a simulation-and-
retrieval framework with existing JWST eclipse maps as test cases. We find that for high-ranking targets, Ariel will be able to derive qualitatively similar maps to JWST using the same amount of observations; for mid-ranking targets, Ariel will be able to compete using as few as 3x as many observations; and for lower-ranking targets, the use of phase curves overcomes the need for an impractical number of repeated eclipse observations. We find that while Ariel is unlikely to have extensive latitudinal mapping abilities, it will have wide-ranging longitudinal abilities, from which the first-order atmospheric dynamics can be constrained. Using an analytically-derived metric, we determine the best eclipse mapping targets for Ariel, finding that it will be able to map nearly 100 targets using full phase curves in only quarter of its lifetime. This would be the largest mapping survey to date, and have enormous ramifications for our demographic understanding of
exoplanet atmospheric dynamics. Finally, we rank all the best mapping targets for both JWST and Ariel in order to encourage future eclipse mapping studies.
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All authors Daniel Valentine, Hannah R. Wakeford, Mark Hammond, Ryan C. Challener, Billy Edwards, Theresa Lüftinger, Maximillian N. Günther
Solar and Stellar Astrophysics
Far beyond the Sun: III. The magnetic cycle of $\boldsymbol\iota$ Horologii
Julián D. Alvarado-Gómez, Gaitee A. J. Hussain, Eliana M. Amazo-Gómez et al. (+6 more)
We present a comprehensive investigation of the
magnetic cycle of the young, active
solar analogue $\iota$ Horologii ($\iota$ Hor) based on intensive spectropolarimetric monitoring using HARPSpol. Over a nearly three-year campaign, the technique of Zeeman-Doppler Imaging (ZDI) was used to reconstruct 18 maps of the large-scale surface
magnetic field of the
star. These maps trace the
evolution of the
magnetic field morphology over approximately 139
stellar rotations. Our analysis uncovers pronounced temporal
evolution, including multiple polarity reversals and changes in field strength and geometry. We examine the
evolution of the poloidal and toroidal field components, with the toroidal component showing strong modulation in concert with the chromospheric activity. Furthermore, for the first time, we reconstruct
stellar magnetic butterfly diagrams which are used to trace the migration of large-scale
magnetic features across the
stellar surface, determining a
magnetic polarity reversal timescale of roughly 100 rotations ($\sim773$ d). In addition, by tracking the field-weighted latitudinal positions, we obtain the first estimates of the large-scale flow properties on a
star other than the Sun, identifying possible pole-ward and equator-ward drift speeds for different field polarities. These results provide critical insights into the dynamo processes operating in young
solar-type
stars and offer a direct comparison with the
solar magnetic cycle.
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All authors Julián D. Alvarado-Gómez, Gaitee A. J. Hussain, Eliana M. Amazo-Gómez, Yu Xu, Katja Poppenhäger, Judy Chebly, Jean-François Donati, Beate Stelzer, Jorge Sanz-Forcada
Astrophysics of Galaxies
SIGNALS of Giant HII Regions: A Spatially Resolved Analysis of NGC 604
Ray Garner III, Robert C. Kennicutt Jr, Laurent Drissen et al. (+6 more)
Observing
giant HII regions at fine spatial scales uncovers detailed structures and reveals variations in ionization, abundance, and dynamical properties of ionized gas and the effect of
stellar feedback. Using emission line data of M33 observed with SITELLE as part of the
Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey (SIGNALS), we present maps of the principal optical emission line ratios for NGC 604, the most luminous HII region in M33. The excitation maps align well with the H$\alpha$ morphology and are clearly related to the location of the central
stellar cluster and secondary
stellar groups. The maps of ionization-sensitive line ratios show substantial variations across the face of NGC 604. We demonstrate that these variations are unlikely to be due to chemical inhomogeneities but are primarily caused by changes in ionization, which in turn affect the observed line ratios. We present the H$\alpha$ kinematics of the region and connect it to the excitation structure, showing how the dynamic motions influence the spatial distribution of ionized gas. We note two distinct sources identified in these excitation maps: a known
supernova remnant and a previously unknown planetary nebula. Such parsec-scale features contribute only a small percentage to the overall light and would remain undetected without the use of high-resolution spatial data. Throughout the paper, we make comparisons to and raise concerns about single-aperture and long-slit spectroscopic measurements of
giant HII regions, highlighting the limitations and potential inaccuracies of such methods.
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All authors Ray Garner III, Robert C. Kennicutt Jr, Laurent Drissen, Carmelle Robert, Laurie Rousseau-Nepton, Christophe Morisset, Philippe Amram, R. Pierre Martin, Emma Jarvis
Solar and Stellar Astrophysics · Cross-listed from physics.flu-dyn
Nonmodal growth and optimal perturbations in magnetohydrodynamic shear flows
Adrian E. Fraser, Alexis K. Kaminski and Jeffrey S. Oishi
In astrophysical shear flows, the Kelvin-Helmholtz (KH) instability is generally suppressed by
magnetic tension provided a sufficiently strong streamwise
magnetic field. This is often used to infer upper (or lower) bounds on field strengths in systems where shear-driven fluctuations are (or are not) observed, on the basis that perturbations cannot grow in the absence of linear instability. On the contrary, by calculating the maximum growth that small-amplitude perturbations can achieve in finite time for such a system, we show that perturbations can grow in energy by orders of magnitude even when the flow is sub-Alfvénic, raising the possibility that shear-driven
turbulence may be found even in the presence of strong
magnetic fields, and challenging inferences from the observed presence or absence of shear-driven fluctuations. We further show that
magnetic fields introduce additional nonmodal growth mechanisms relative to the hydrodynamic case, and that 2D simulations miss key aspects of these growth mechanisms.
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High Energy Astrophysical Phenomena
Optimising the MeerKAT Pulsar Timing Array and towards precision pulsar timing with SKA-mid
Pratyasha Gitika, Ryan M. Shannon, Matthew Bailes et al. (+4 more)
Pulsar timing arrays (PTAs) are
Galactic-scale nanohertz-frequency gravitational wave (GW) detectors. Recently, several PTAs have found evidence for the presence of GWs in their
datasets, but none of them have achieved a community-defined definitive (> 5$\sigma$) detection. Here, we identify limiting noise sources for PTAs and quantify their impact on sensitivity to GWs under different observing and noise modelling strategies. First, we search for intrinsic pulse jitter in a sample of 89 MSPs observed by the MeerKAT
Pulsar Timing Array and obtain new jitter measurements for 20 MSPs. We then forecast jitter noise in
pulsars for the future SKA-Mid
telescope, finding that the timing precision of many of the best-timed MSPs would be dominated by jitter noise. We then consider dispersion measure variations from the interstellar medium and find that their effects are best mitigated by modelling them as a stationary Gaussian process with a power-law spectrum. Improving upon the established hasasia code for PTA sensitivity analysis, we assess the timing potential of the lower frequency UHF-band (544$-$1088\,MHz) of MeerKAT and find a potential increase in GW background sensitivity by $\approx 8$%, relative to observing at L-band. We show that this improvement relies on assumptions on the propagation through the interstellar medium, and highlight that if observing frequency-dependent propagation effects, such as scattering noise, are present, where noise is not completely correlated across observing frequency, then the improvement is significantly diminished. Using the multi-frequency receivers and sub-arraying flexibility of MeerKAT, we find that focussed, high-cadence observations of the best MSPs can enhance the sensitivity of the array for both the continuous GWs and
stochastic GWB. These results highlight the role of MeerKAT and the MPTA in the context of international GW search efforts.
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All authors Pratyasha Gitika, Ryan M. Shannon, Matthew Bailes, Daniel J. Reardon, Matthew T. Miles, David J. Champion, Kathrin Grunthal
Solar and Stellar Astrophysics
Statistical framework for nuclear parameter uncertainties in nucleosynthesis modeling of r- and i-process
S. Martinet, G. Goriely, A. Choplin et al. (+1 more)
Propagating
nuclear uncertainties to nucleosynthesis simulations is key to understand the impact of theoretical uncertainties on the predictions, especially for processes far from the stability region, where
nuclear properties are scarcely known. While systematic (model) uncertainties have been thoroughly studied, the statistical (parameter) ones have been more rarely explored, as constraining them is more challenging. We present here a methodology to determine coherently parameter uncertainties by anchoring the theoretical uncertainties to the experimentally known
nuclear properties through the use of the Backward Forward Monte Carlo method. We use this methodology for two nucleosynthesis processes: the intermediate
neutron capture process (i-process) and the rapid
neutron capture process (r-process). We determine coherently for the i-process the uncertainties from the (n,$\gamma$) rates while we explore the impact of
nuclear mass uncertainties for the r-process. The effect of parameter uncertainties on the final nucleosynthesis is in the same order as model uncertainties, suggesting the crucial need for more experimental constraints on key
nuclei of interest. We show how key
nuclear properties, such as relevant (n,$\gamma$) rates impacting the i-process tracers, could enhance tremendously the prediction of
stellar evolution models by experimentally constraining them.
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All authors S. Martinet, G. Goriely, A. Choplin, L. Siess
Cosmology and Nongalactic Astrophysics
BaBy Cosmic Tension
Christophe Ringeval
We show that the recently released B-mode polarisation data from the South Pole
Telescope (SPT) favour a non-vanishing contribution of
primordial gravitational waves of inflationary origin which is in tension with the previous BICEP-Keck (BK) measurements. Our analysis uses the third-order slow-roll
primordial power spectra, with theoretically motivated priors, on the multifrequency SPT likelihoods complemented by the latest Planck satellite data products. The SPT measurements provide 1.0 bit of information gain on the first slow-roll parameter, which is higher than the 0.9 bit provided by BK even though the SPT sensitivity is five times lower. Moreover, the
Bayesian dimensionality on the same parameter exceeds 1.5 for SPT versus 0.3 for BK showing that it is overconstrained by the SPT data. Even if this BB-tension could be the result of a yet to be understood foreground, our findings should motivate for a closer analysis of this unexpected B-modes excess.
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Astrophysics of Galaxies
On the origin of counterrotating stellar disks in TNG50. I
M. C. Bugueño, Facundo A. Gómez, Arianna Dolfi et al. (+1 more)
Understanding
galaxy evolution is key to explaining the structures we observe in the present-day Universe. Counterrotating
stellar disks (CRDs), i.e. co-spatial
stellar disks rotating with opposite angular momentum, have been proposed as signatures of past
accretion events. Therefore, they constitute potentially valuable tracers of
galactic assembly. We aim to investigate the properties, formation, and significance of CRDs in a sample of Milky Way mass
galaxies using the IllustrisTNG cosmological simulations. We select 260 central late-type
galaxies (i.e. $M_{\rm tot} \approx 10^{12}$, $D/T>0.5$, $N_{\rm star}>10^5$). For each
galaxy, we measure the circularity of its
stellar particles and define the CRD by considering all particles with circularity $\epsilon < -0.7$, which are located within the spatial extension of the main disk. We then characterize the mass fraction, spatial extent, and
star formation history of the CRDs. Out of the 260
galaxies, we find that 26 host significant CRDs (i.e. contributing at least 1% of the total
stellar mass of the disk). This means that CRDs are rare, consistent with the results from observations. We also find that the most of the CRDs are compact (i.e. 88%), in-situ dominated (i.e.73%), and exhibit bursty SFHs whose peaks often coincide with external perturbations. This means that external perturbations are able to catalyze
star formation, even when a majority of the CRD's
star population is in-situ. Finally, we find that a variety of formation pathways can lead to CRDs, including interaction-induced in-situ bursts and smooth
accretion of misaligned gas. Overall, our results suggest that CRDs are rare but diverse in origin. In most cases, their formation is linked to the
accretion of retrograde gas, either through mergers or environmental inflow, suggesting that these structures are sensitive tracers of the
galaxy's past
accretion history.
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All authors M. C. Bugueño, Facundo A. Gómez, Arianna Dolfi, Patricia B. Tissera
Astrophysics of Galaxies
Deciphering the radio-star formation correlation on kpc scales. IV. Radio halos of highly-inclined Virgo cluster spiral galaxies
B. Vollmer, M. Soida and V. Heesen
In addition to the
radio continuum emission of the thin
galactic disk, vertically extended emission is ubiquitous in starforming disk
galaxies. This
halo emission can represent an important fraction of the total emission of the
galaxy The
cosmic ray electrons (CRe) responsible for the
radio continuum emission are produced within the thin disk and transported into the
halo. We made an attempt to reconstruct the radial properties of
radio continuum
halos in nearly edge-on
galaxies where the
star formation rate (SFR) distribution can be deprojected and the vertical
radio continuum emission is well distinct from the disk emission. The deprojected SFR distribution is convolved with a Gaussian kernel to take CRe
diffusion within the
galactic disk into account and a vertical profile of the
radio continuum emissivity is added to the disk emission. The three-dimensional emission distribution is then projected on the sky and compared to VLA
radio continuum observations at 20 and 6 cm. We found that overall the
halo emission contains information on the underlying distribution of the
star formation rate. The majority of our
galaxies show flaring
radio continuum
halos. Except for one
galaxy, our Virgo
galaxies follow the trend of increasing effective height with increasing
radio continuum size found by the CHANG-ES collaboration. We confirm that
radio continuum
halos can represent a significant fraction of the total
radio continuum emission of a starforming spiral
galaxy. At 20 cm and 6 cm between 30 and 70 of the total
radio continuum emission originate in the
halo. We propose a
halo classification based on the height ratio and SI between 20 and 6cm. If we interpret the vertical structures of the large-scale
magnetic field within the disk-
halo and
halo types as a sign of a
galactic outflow or wind, all
galaxies except one most probably harbor an advection-dominated
halo.
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Instrumentation and Methods for Astrophysics · Cross-listed from stat.AP
Neural Posterior Estimation with Autoregressive Tiling for Detecting Objects in Astronomical Images
Jeffrey Regier
Upcoming astronomical surveys will produce petabytes of high-resolution images of the night sky, providing information about billions of
stars and
galaxies. Detecting and characterizing the astronomical objects in these images is a fundamental task in astronomy – and a challenging one, as most of these objects are faint and many visually overlap with other objects. We propose an amortized variational inference procedure to solve this instance of small-object detection. Our key innovation is a family of spatially autoregressive variational distributions that partition and order the latent space according to a $K$-color checkerboard pattern. By construction, the conditional independencies of this variational family mirror those of the posterior distribution. We fit the variational distribution, which is parameterized by a convolutional neural network, using neural posterior estimation (NPE) to minimize an expectation of the forward KL divergence. Using images from the Sloan Digital Sky Survey, our method achieves state-of-the-art performance. We further demonstrate that the proposed autoregressive structure greatly improves posterior calibration.
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High Energy Astrophysical Phenomena
Self-consistent model of cosmic ray penetration into molecular clouds: Effect of energy losses
D. O. Chernyshov, A. V. Ivlev and V. A. Dogiel
The theory of
cosmic-ray (CR) penetration into dense molecular clouds developed recently for relativistic particles by Chernyshov et al. (2024) is extended to non-relativistic CRs. Interstellar CRs streaming into the clouds are able to resonantly excite MHD waves in diffuse cloud envelopes. This leads to the self-modulation, such that streaming particles are scattered at the self-generated waves. In contrast to relativistic CRs, transport of lower-energy particles in the envelopes is generally heavily affected by ionization losses; furthermore, both CR
protons and electrons contribute to wave excitation. We show that these effects have profound impact on the self-modulation, and can dramatically reduce CR spectra even for clouds with moderate column densities of a few times $10^{21}$ cm$^{-2}$.
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Instrumentation and Methods for Astrophysics
Focal-plane wavefront sensing with moderately broadband light using a short multi-mode fiber
Auxiliadora Padrón-Brito, Natalia Arteaga-Marrero, Ian Cunnyngham et al. (+1 more)
We propose a focal-plane wavefront sensor (FPWFS) based on a short multimode fiber (MMF) capable of operating under moderately broadband illumination. By coupling the aberrated focal-plane field into an MMF of length <1 cm, we preserve modal interference over a 10 nm bandwidth at near-infrared wavelengths. The resulting output intensity pattern encodes pupil phase information, enabling wavefront recovery via a neural network. Our approach resolves the inherent sign ambiguity of even pupil-phase aberrations and operates on millisecond timescales using readily available computing hardware, suitable for real-time adaptive optics. Unlike traditional pupil-plane sensors, the proposed FPWFS shares the optical path with the science beam, eliminating non-common-path aberrations by enabling simultaneous wavefront and focal-plane intensity
retrieval. Its simplicity, compactness, sensitivity, and low cost make it an attractive candidate for next-generation astronomical instruments.
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All authors Auxiliadora Padrón-Brito, Natalia Arteaga-Marrero, Ian Cunnyngham, Jeff Kuhn
Astrophysics of Galaxies
Probing the formation of megaparsec-scale giant radio galaxies II. Continuum & polarization behavior from MHD simulations
Gourab Giri, Christian Fendt, Joydeep Bagchi et al. (+4 more)
The persistence of radiative signatures in
giant radio galaxies remains a frontier topic of research, with contemporary
telescopes revealing intricate features that require investigation. This study aims to examine the emission characteristics of simulated GRGs, and correlate them with their underlying 3D dynamical properties. Sky-projected continuum and polarization maps at 1 GHz were computed from five 3D-RMHD simulations by integrating the synthesized emissivity data along the line of sight, with the integration path chosen to reflect the GRG
evolution in the sky plane. The emissivities were derived from these RMHD simulations, featuring FR-I and FR-II jets injected from different locations of the large-scale environment. The jet-cocoon morphologies are strongly shaped by the triaxiality of the environment, resulting in features like wings and asymmetric cocoons, thereby making morphology a crucial indicator of GRG formation mechanisms. The decollimation of the bulk flow in GRG jets gives rise to intricate cocoon features, most notably filamentary structures-magnetically dominated threads with lifespans of a few Myr. High-jet-power cases frequently display enhanced emission zones at mid-cocoon distances (alongside warmspots around the jet-head), contradicting the interpretations of the GRG as a restarting source. In such cases, examining the lateral intensity variation of the cocoon may reveal the source's state, with a gradual decrease in emission suggesting a low-active stage. This study highlights that applying a simple
radio power-jet power relation to a statistical GRG sample is unfeasible, as it depends on growth conditions of individual GRGs. Effects such as inverse-Compton CMB cooling and matter entrainment significantly impact the long-term emission persistence of GRGs. The diminishing fractional polarization with GRG
evolution reflects increasing
turbulence in the cocoon.
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All authors Gourab Giri, Christian Fendt, Joydeep Bagchi, Kshitij Thorat, D. J. Saikia, Roger P. Deane, Jacinta Delhaize
Astrophysics of Galaxies
The intracluster light analysis of the most evolved systems of galaxies: fossil groups
Nícolas O. L. de Oliveira, Yolanda Jiménez-Teja, Renato A. Dupke et al. (+7 more)
We present the analysis of the intracluster light (ICL) in three fossil groups (FG), RXJ085640.72+055347.36, RX J1136+0713, and RX J1410+4145, at z ~ 0.1. We used two optical broad-band filters, F435W and F606W, observed with the Hubble Space
Telescope and spectroscopic data obtained with the Gemini Multi-Object Spectrograph to generate the ICL maps and measure the ICL fraction using CICLE, an
algorithm developed to disentangle the ICL from the light of
galaxies. We found ICL fractions of 9.9% - 14.4%, 3.8% - 6.1%, and 4.7% - 10.7% for RXJ0856, RXJ1136, and RXJ1410, respectively. This behavior is not consistent with the presence of the ICL fraction excess previously observed in merging clusters and also inconsistent with the constant ICL fraction distribution characteristic of relaxed systems, although the values found are within the typical range expected for the latter. Instead, they show a significantly increasing trend with wavelengths over ~ 3800 - 5500A, indicating that fossil groups are indeed old and undisturbed systems, even compared with regular relaxed clusters.
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All authors Nícolas O. L. de Oliveira, Yolanda Jiménez-Teja, Renato A. Dupke, Eleazar R. Carrasco, Anton M. Koekemoer, Yuanyuan Su, Jose Manuel Vilchez, Jimmy A. Irwin, Eric D. Miller, Lucas E. Johnson
High Energy Astrophysical Phenomena
Fluorescent Fe K line emission of gamma Cas stars II. Predictions for magnetic interactions and white-dwarf accretion scenarios
Gregor Rauw
About 12 percent of the early-type Be
stars, so-called gamma Cas
stars, exhibit an unusually hard and bright thermal X-ray emission that could result from
accretion onto a white
dwarf companion or from
magnetic interactions between the Be
star and its decretion disk. Exploring the full power of high-resolution X-ray spectroscopy of gamma Cas
stars requires comparison of observations of the fluorescent Fe Kalpha emission lines near 6.4 keV with synthetic profiles of this line complex computed in the framework of the
magnetic interaction and the accreting WD scenarios. For the latter, we further distinguish between
accretion onto a non-
magnetic and a
magnetic WD. Our models account for different reservoirs of reprocessing material: the Be circumstellar decretion disk, the Be photosphere, an
accretion disk around the WD companion, a magnetically channelled
accretion flow and the WD photosphere. We find considerably different line properties for the different scenarios. For a non-
magnetic accreting WD, the global Fe Kalpha complex is extremely broad, reaching a full width of 140 eV, whilst it is ~ 40 eV for the
magnetic star-disk interaction and the
magnetic accreting WD cases. In the
magnetic star-disk interaction, the line centroid follows the orbital motion of the Be
star, whereas it moves along with the WD in the case of an accreting WD. For gamma Cas, given the 15 times larger amplitude of the WD orbital motion, the shift in position for an accreting WD should be easily detectable with high-resolution spectrographs such as Resolve on XRISM, but remains essentially undetectable for the
magnetic star-disk interaction. Upcoming high-resolution spectroscopy of the fluorescent Fe Kalpha emission lines in the X-ray spectra of gamma Cas
stars will thus allow to distinguish between the competing scenarios.
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High Energy Astrophysical Phenomena
Search for dark matter around intermediate mass black holes with the H.E.S.S. experiment
Jann Aschersleben, Dieter Horns, Emmanuel Moulin et al. (+1 more)
Intermediate mass black holes (IMBHs), with masses ranging from a hundred and a million
solar masses, are hypothesised to be surrounded by dense regions of dark matter known as dark matter spikes, where the annihilation of dark matter particles could produce detectable gamma rays. The detection of dark matter annihilation around IMBHs therefore offers a promising approach for probing the nature of dark matter. In this work, we search for dark matter annihilation around IMBHs using data from the
Galactic Plane Survey, the Extragalactic Survey and a selection of satellite
galaxies observed by the H.E.S.S. gamma-ray experiment in Namibia. Since no evidence for a gamma-ray signal from dark matter annihilation around IMBHs has been found, we set upper limits on the velocity-weighted annihilation cross section for dark matter masses between 800 GeV and 100 TeV. Our analysis obtains limits on the velocity-weighted annihilation cross section below the thermal relic cross section for dark matter masses between 10 and 100 TeV.
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All authors Jann Aschersleben, Dieter Horns, Emmanuel Moulin, Manuela Vecchi
Solar and Stellar Astrophysics
An analysis of the solar differential rotation in solar cycle No. 19 (1954-1964) determined using Kanzelhoehe sunspot group positions
Ivana Poljancic Beljan, Luka Sibenik, Tomislav Jurkic et al. (+7 more)
We study
solar differential rotation (DR) for
solar cycle No. 19 (1954-1964) by tracing sunspot groups on the sunspot drawings of Kanzelhoehe Observatory for
Solar and Environmental Research (KSO). Our aim is to extend previous DR analysis from the KSO data (1964-2016) to the years prior to 1964 to create a catalog of sunspot group positions and DR parameters from KSO sunspot drawings and white light images. Synodic angular rotation velocities were first determined using the daily shift (DS) and robust linear least-squares fit (rLSQ) methods, then converted to sidereal velocities, and used to derive
solar DR parameters. We compare the DR parameters obtained from different sources and analyse the north-south asymmetry of rotation for
solar cycle No. 19. It has been shown that our results for the equatorial rotation velocity (parameter A) and the gradient of DR (parameter B) coincide with earlier results from the KSO data (performed with a different method), as well as with results from the Kodaikanal
Solar Observatory (KoSO) and the Yunnan Observatories (YNAO). In contrast, the values of parameter A from three different earlier studies based on the Greenwich Photoheliographic Results (GPR) exhibit statistically significant differences when compared to the values of parameter A derived from KSO, KoSO and YNAO. These findings suggest that the GPR data have the largest inconsistency compared to the other three data sources, highlighting the need for further analysis to identify the causes of these discrepancies. The analysis of the north-south asymmetry in the
solar rotation profile using two different methods shows that the DR parameters of the hemispheres coincide, indicating a rotational
symmetry around the equator. This is consistent with previous results from KSO and YNAO data. However, all sources indicate slightly higher equatorial rotation velocities in the southern hemisphere.
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All authors Ivana Poljancic Beljan, Luka Sibenik, Tomislav Jurkic, Klaudija Loncaric, Rajka Jurdana-Sepic, Damir Hrzina, Werner Poetzi, Roman Brajsa, Astrid M. Veronig, Arnold Hanslmeier
Solar and Stellar Astrophysics
Photometric Analysis of 30 Contact Binaries in M31
Xiang Gao, Kai Li, Li-Heng Wang et al. (+3 more)
M31, as the largest
galaxy in the Local Group, is of significant importance for the study of
stellar formation and
evolution. Based on the data of 5,859 targets observed in M31 by Gu et al (2024), we selected 30 contact binaries by visual inspection for further study. Using the PHOEBE software and employing
Bayesian optimization and Markov Chain Monte Carlo sampling, we determined the physical parameters of these 30 systems. The results show that 10 systems exhibit the O'Connell effect, which is well explained by introducing a dark spot on the primary
star. 11 systems have mass ratios below 0.15, classifying them as extremely low mass ratio contact binaries, making them promising candidates for binary mergers. Six systems have primary
star temperatures exceeding 10,000 K, classifying them as early-type contact binaries. The absolute physical parameters reveal that two contact binary systems contain massive
stellar components, which may eventually evolve into compact binary
star systems. To compare the effects of different
galactic environments on the
evolution of contact binaries, we constructed evolutionary diagrams for these 30 targets and for contact binaries in the Milky Way. The results show that, at the same mass, our targets have larger radii, higher luminosities, and lower orbital angular momenta than contact binaries in the Milky Way, indicating that they are at more advanced evolutionary stages. This may be attributed to the higher
metallicity in M31 compared to the Milky Way.
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All authors Xiang Gao, Kai Li, Li-Heng Wang, Hai-bo Yuan, Hong-rui Gu, Ya-Ni Guo
High Energy Astrophysical Phenomena
Likelihood-based reconstruction of muon lateral distribution function using combined integrator and binary detector modes
A.D. Supanitsky, D. Ravignani and V.V. Kizakke Covilakam
The origin of ultra-high-energy
cosmic rays, with energies $E \geq 10^{18}$ eV, remains unknown. Among the key observables used to investigate their nature are the energy spectrum, the arrival direction distribution, and the composition as a function of energy. The composition of the primary
cosmic ray is inferred from properties of the extensive air showers they initiate, particularly from parameters sensitive to the primary mass. The most sensitive parameters to the primary mass are the atmospheric depth of the shower maximum, typically measured with fluorescence
telescopes, and the
muon content of the shower, measured using dedicated
muon detectors. A commonly used observable in composition studies is the
muon density at a fixed distance from the shower axis, derived by evaluating the reconstructed
muon lateral distribution function (MLDF) at a reference distance. A specific type of
muon detector features two acquisition modes: binary and integrator (commonly referred to as ADC mode, for Analog-to-Digital Converter). The binary mode allows for direct
muon counting, while the ADC mode infers the
muon number from the integrated signal of the detector response. Existing methods reconstruct the MLDF using data from either acquisition mode individually, or by combining both, but usually assigning a single mode per detector station in a given event. This work presents a novel method to reconstruct the MLDF based on a likelihood approach that simultaneously incorporates data from both acquisition modes at each detector station. We apply our method to the underground
muon detectors of the Pierre Auger Observatory as a case study. However, this general approach can be applied to future detectors with dual acquisition capabilities. Our results demonstrate that the combined method outperforms traditional techniques that rely solely on either binary or ADC mode data.
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Instrumentation and Methods for Astrophysics
Multi-faceted light pollution modelling and its application to the decline of artificial illuminance in France
Rolf Buhler, Philippe Deverchère, Christophe Plotard et al. (+1 more)
Artificial Light At Night (ALAN) has been increasing steadily over the past century, particularly during the last decade. This leads to rising light pollution, which is known to have adverse effects on living organisms, including humans. We present a new software package to model light pollution from ground radiance measurements. The software is called Otus 3 and incorporates innovative ALAN
diffusion models with different atmospheric profiles, cloud covers and urban emission functions. To date, light pollution modelling typically focused on calculating the zenith luminance of the skyglow produced by city lights. In Otus 3 we extend this and additionally model the horizontal illuminance on the ground, including the contributions from skyglow and the direct illumination. We applied Otus 3 to France using ground radiance data from the Visible Infrared Imaging Radiometer Suite (VIIRS). We calibrated our models using precise sky brightness measurements we obtained over 6 years at 139 different locations and make this
dataset publicly available. We produced the first artificial illuminance map for France for the periods of 2013-2018 and 2019-2024. We found that the artificial ground illuminance in the middle of the night decreased by 23 % between these two periods, in stark contrast to the global trend.
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All authors Rolf Buhler, Philippe Deverchère, Christophe Plotard, Sébastien Vauclair