Astrophysics of Galaxies
Untangling Similarities and Differences in Star Formation Histories Across Cosmological Simulations
Alicia M. Savelli, Matthew A. Kustec, Joshua S. Speagle et al. (+5 more)
How
galaxies assemble depends on processes ranging from small-scale baryonic physics to large-scale cosmological assembly, which are difficult to disentangle with observations alone. Using $\sim$63,000 simulated
galaxies from seven cosmological simulations spanning hydrodynamical, semi-analytic, and semi-empirical models, we explore how specific
star formation histories (sSFHs) vary across modelling assumptions. Using non-linear dimensionality reduction (UMAP), we find that sSFH shape variation organizes along a few smooth axes in a 2D
embedding, broadly corresponding to (1) peak timing, (2) peak sharpness, and (3) subsequent quenching rate. We identify sSFH shapes that many simulations share ("common"), well described to first order by dark matter
halo assembly, and a few tied to individual simulations ("unique"), which likely reflect subgrid and parametrization choices such as merger-triggered burst prescriptions. A notable exception is a common population of rapidly quenched
galaxies found across most simulations, likely driven by e.g., active galactic
nucleus (AGN) feedback, that
halo assembly alone cannot reproduce. The origin of the most distinctive unique shape, an Illustris-dominated history with an early peak and slow decline, remains unclear, but we test the effects of short-term variability. With a multi-objective auto-encoder neural network, we recover the simulation that a given sSFH is drawn from with $\sim$95% out-of-sample accuracy; ablation tests indicate this information is embedded in long-timescale sSFH morphology rather than short-term variability. These results provide avenues for theoretical and observational follow-up connecting
star formation histories to subgrid physical models.
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All authors Alicia M. Savelli, Matthew A. Kustec, Joshua S. Speagle, Kartheik G. Iyer, Eshal Ahmed, Zehao Peng, Norman Murray, Cissy Kuang
Astrophysics of Galaxies
Intermittency in the Multiphase ISM — I. Extreme Density, Velocity, and Magnetic Fluctuations
Yue Hu
Intermittency is a fundamental property of astrophysical
turbulence because it concentrates strong gradients, dissipation, and transport into rare, localized structures. In the multiphase interstellar medium (ISM), turbulent driving is especially important because the balance between compressive and solenoidal motions can regulate how extreme fluctuations are distributed among thermal phases. Yet conventional increment statistics quantify intermittency without identifying the structures that host it. We analyze three matched ideal-MHD simulations of a thermally multiphase neutral medium that differ only in the compressive fraction of the driving. Density, velocity, and
magnetic-field increments are non-Gaussian in every thermal phase. Increasing compressive driving redistributes density and
magnetic fluctuations preferentially into the cold gas rather than uniformly enhancing them across phases. We identify the structures associated with extreme increments using local, scale-matched diagnostics of compression, thermal gradients, vorticity, strain,
magnetic curl, and
magnetic tension. Extreme
magnetic increments preferentially occur where
magnetic curl and
magnetic tension are simultaneously enhanced, more strongly than extreme velocity increments are associated with their kinematic hosts. Extreme velocity increments show comparable enrichment in vorticity and strain, whereas extreme density increments preferentially trace converging flows and thermal gradients only in the unstable medium. These associations weaken beyond a phase-dependent coherence scale. Our results show that turbulent driving controls how intermittency is partitioned among thermal phases, while distinct physical structures host extreme density, velocity, and
magnetic fluctuations.
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Instrumentation and Methods for Astrophysics
Graph Learning with Multiplicative Aggregation for Solar Filament Fragment Association Modeling in Full-disk H$\alpha$ Images
GaoFei Zhu, GangHua Lin, Xiao Yang et al. (+4 more)
Solar filaments are prominent features in H$\alpha$ observations. During their
evolution, they often exhibit complex morphological and topological changes, which, due to line-of-sight projection effects, appear as fragmentation and merging. These phenomena make it difficult to reliably track solar filaments using automated methods, as the same structure may appear different over time. To address this issue, we formulate filament fragment association as a graph-based learning problem, where individual fragments are represented as nodes and candidate pairwise relationships are modeled as edges to infer whether fragments belong to the same filament. Furthermore, we propose a novel graph neural network (GNN) that incorporates multiplicative aggregation layers to enhance feature aggregation in the graph, replacing conventional additive aggregation with a multiplicative mechanism to better capture information between fragments. Experimental results demonstrate that the proposed method achieves reliable performance in filament fragment association, validating the effectiveness of the graph-based formulation and the proposed multiplicative aggregation mechanism.
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All authors GaoFei Zhu, GangHua Lin, Xiao Yang, Suo Liu, Yu Liu, ZhiSheng Gao, Cheng Zeng
Earth and Planetary Astrophysics
DEMOS. II. What the full Lupus demographics truly tell us about protoplanetary disc evolution
Lorenzo A. Malanga, Giovanni P. Rosotti, Giuseppe Lodato et al. (+7 more)
Assessing whether disc
evolution is driven by viscosity or MHD winds is crucial to determine the conditions in which
planets form. The rich statistical information encoded in nearby
star-forming regions provides an excellent opportunity to probe disc
evolution. In this paper, we apply the
Bayesian inference tool DEMOS, designed to exploit the statistical properties of disc populations and infer initial conditions and model parameters, to the Lupus disc population. We consider the observed distributions of stellar mass $M_\star$, disc mass $M$ (from continuum flux), mass
accretion rate $\dot{M}$ and CO disc size $R_{90%, CO}$. We constrain all parameters for both the viscous model, with internal photoevaporation, and the MHD winds model, with unprecedented precision. The inferred initial conditions suggest that positive correlations between initial disc properties and $M_\star$ must be present. Both models yield a typical $R_0$ of $3-5$ au for a disc around a $0.3\ \text{M}_\odot$
star, with positive stellar-mass dependence. We infer $\alpha$ (or $\alpha_\text{DW}$) of $3-4 \times 10^{-4}$ for discs around $0.3\ \text{M}_\odot$
stars, with an approximately quadratic dependence on $M_\star$. For the viscous-photoevaporative model, the typical wind mass-loss rate is $\dot{M}_\text{w} \sim 10^{-9}$ M$_\odot$ yr$^{-1}$, scaling with $M_\star$ with an exponent of $\sim 2.5$. The inferred mean age is 1.6 Myr for the MHD winds model and 0.9 Myr for the viscous-photoevaporative model. Despite a slight preference for the latter,
Bayesian evidence shows that both models reproduce the data comparably well, and neither can be ruled out. However, their best-fit synthetic populations predict substantially different evolutionary pathways. Applying DEMOS to multiple populations, especially evolved ones like Upper Scorpius, will allow to place stronger constraints on disc
evolution mechanisms.
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All authors Lorenzo A. Malanga, Giovanni P. Rosotti, Giuseppe Lodato, Alice Somigliana, Benoît Tabone, Rossella Anania, Carlo F. Manara, Leonardo Testi, Claudia Toci, Francesco Zagaria
High Energy Astrophysical Phenomena
Discovery of 51 pulsars in a reanalysis of the Green Bank North Celestial Cap Survey and a revised pulsar census
R. Sengar, L. Vleeschower, D. L. Kaplan et al. (+13 more)
We present results from a reanalysis of the Green Bank North Celestial Cap (GBNCC) survey, conducted at 350 MHz with the Green Bank
Telescope between 2009 and 2020, covering the sky with declinations $\delta>-40^\circ$. We searched the survey data using an FFT-based periodicity search, with candidate selection extending to very low spectral signal-to-noise ratios and summing up to 32 harmonics. From the 60 promising candidates identified in this search, we confirmed 51 new
pulsars using the Green bank and CHIME. We also used a direct folding search method (DFSM) to search for slow
pulsars between 500 ms and 10 s. Of the 51
pulsars identified in the FFT search, 43 fall within this period range, all of which were found by the DFSM. The DFSM also found an additional
pulsar that had been missed during the inspection of the FFT candidates. Most of the new discoveries are canonical
pulsars, with
spin periods ranging from 299 ms to 4.4 s and dispersion measures from 10 to 192 $\rm pc \, cm^{-3}$. We also found a binary millisecond
pulsar with a
spin period of 3.2 ms in a 4.5-d orbit. We redetected 855
pulsars in the data, 825 of which were found in the FFT search. Within the effective parameter space of our periodicity search, the FFT search recovered $\sim$98 % of the known
pulsars within the survey sensitivity limits. After accounting for previously reported
pulsars whose observations were not processed or whose parameters lay outside our search range, the updated GBNCC census now includes 964
pulsars.
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All authors R. Sengar, L. Vleeschower, D. L. Kaplan, G. Y. Agazie, M. Bailes, A. Cassity, H. T. Cromartie, M. E. Decesar, T. Dolch, W. Fiore, E. Fonseca, R. S. Lynch, E. Parent, S. M. Ransom, I. H. Stairs, J. van Leeuwen
Astrophysics of Galaxies
Physical characteristics of the Galaxy defining the oscillation period of librating orbits near the OLR of the bar
A. M. Melnik and E. N. Podzolkova
We studied librating orbits of
stars near the Outer Lindblad Resonance (OLR) of the bar using the angle-action variables of
Hamiltonian dynamics. The librating orbits change the direction of their elongation relative to the major axis of the bar in a limited range of angles. To calculate orbits, we used the model of the
Galaxy with an analytical bar which reproduces well the distributions of the observed stellar velocities along the Galactocentric distance R derived from the Gaia DR3 data. We compared the values of the orbital oscillation period of a typical
star obtained from the theory and with the use of numerical simulation. Both values were found to be in good agreement and are equal to 2.0 Gyr. It was shown that the change in the average orbital radius, <R>, of a
star, calculated over the time interval of one radial oscillation, is regulated by the change in the direction of orbital elongation. As the orbit is tilted relative to the minor axis of the bar in the sense of Galactic rotation, the angular momentum of the
star, L, decreases, on average, causing a decrease in <R>. As the orbit is tilted in the opposite direction, <L> and <R> increase. We derived a general formula for the oscillation frequency, omega, of orbits captured by libration near the OLR of the bar. It turned out that the ratio of the frequency of orbit oscillations to the epicyclic frequency, omega/kappa, is determined by the parameters q_R and <p>, where the factor q_R is the ratio of the amplitude of the radial force generated by the bar to the average radial force produced by the entire
galaxy at the distance of the OLR, and the parameter <p> characterizes the average elongation of orbits captured by libration near the OLR.
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Earth and Planetary Astrophysics
DEMOS I. A Bayesian inference framework to constrain disc evolution from observed demographics
Lorenzo A. Malanga, Giovanni P. Rosotti, Giuseppe Lodato et al. (+3 more)
The mechanism driving the
evolution and dispersal of protoplanetary discs has a substantial impact on the theories of
planet formation. To date, neither the viscous paradigm nor the MHD wind-driven framework have been ruled out by the observations. The statistical richness of the observed samples provides a unique opportunity to test evolutionary models through population synthesis. However, comparisons between models and observations are normally carried out by eye, and a more statistically rigorous approach has not yet been implemented. We present DEMOS, a
Bayesian inference tool that aims to infer the model parameters and initial conditions that best reproduce the full distribution of global properties of disc populations. This framework relies on a comparison between observations and synthetic populations generated with the 1D disc population-synthesis code Diskpop. We tested the tool with both the MHD wind model and the viscous framework with internal photoevaporation. Applying DEMOS to synthetic populations, we find that, for both models, it accurately recovers the model parameters of disc populations and their associated uncertainties, including cases in which initial conditions are correlated with the stellar mass. In the optimal scenario in which disc masses,
accretion rates and disc sizes are available, the tool can also constrain the angular-momentum transport parameter. We show that, although parameter estimates are the most precise with samples of about 100 discs, the tool also yields meaningful constraints for smaller populations of 10-30 discs. We further find that the predictions obtained with DEMOS closely align with those found by previous works. We anticipate that DEMOS will be a valuable tool to infer the initial conditions of observed disc populations, to design observational programmes, and to assess which evolutionary model best reproduces the data.
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All authors Lorenzo A. Malanga, Giovanni P. Rosotti, Giuseppe Lodato, Benoît Tabone, Alice Somigliana, Leonardo Testi
Solar and Stellar Astrophysics
An upper limit on Galactic OB+black hole binaries from SDSS-V
J. Müller-Horn, H.-W. Rix, S. Shahaf et al. (+14 more)
Binaries composed of a luminous OB
star and a black hole (BH) are a key evolutionary link between massive stellar binaries and merging compact-object binaries, but only a handful are known and their occurrence fraction remains poorly constrained. We use multi-epoch spectroscopy from the SDSS-V Milky Way Mapper to place a first rigorous empirical upper limit on the fraction of Galactic massive ($\geq 10\,\mathrm{M}_\odot$) OB
stars with a close BH companion, $f_\mathrm{BH}$. Radial-velocity (RV) variability alone cannot distinguish BH companions from the far more numerous luminous binaries. We therefore combine the SDSS-V RV variability measurements of 3130 massive OB
stars with high-resolution follow-up and literature information to identify luminous companions among the RV-variable subset. Forward-modelling the detectability of OB+BH systems using BH masses and orbital parameters from binary-
evolution models, we find $f_\mathrm{BH} \lesssim 3\%$ at 95% credibility. This empirical upper limit approaches, but does not exclude, theoretical predictions for the OB+BH fraction. The constraint is primarily limited by the number of RV-variable systems that can be decisively classified, highlighting the importance of complete, high-quality follow-up for future searches.
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All authors J. Müller-Horn, H.-W. Rix, S. Shahaf, B. Pennell, E. Zari, M.C. Ramírez-Tannus, A. Farah, R. Essick, J.I. Villaseñor, M.R. Blanton, J.G. Fernández-Trincado, J.A. Kollmeier, C. Lam, K. Maltsev, A. Roman-Lopes, D.P. Schneider, A. Tkachenko
High Energy Astrophysical Phenomena
Scaling Up: A Global Optical/X-ray Correlation For Reprocessing Across Black Hole Masses
Changhyun Cho, David M. Russell, Aaryan Sharma et al. (+9 more)
This study extends the optical/X-ray correlation from black hole low-mass X-ray binaries (XRBs) to active galactic
nuclei (AGN), bridging scales from stellar-mass to supermassive black holes (SMBHs). In XRBs, optical emission predominantly originates from the thermal reprocessing of high-energy
photons on the surface of the geometrically thin, optically thick
accretion disk. The reprocessed optical luminosity follows a power-law relation of the form $L_{V} \propto L_{X}^{\beta} a$, with $\beta \sim 0.5$, where $L_X$ is the X-ray luminosity and the orbital separation $a$ serves as a proxy for the disk size. To test the universality of this relationship across all mass scales, we analyzed quasi-simultaneous X-ray and optical flux data from a sample of XRBs and AGN that have estimates of the radius of the optically emitting disk. To bridge the structural differences between these populations, we utilized the characteristic optical/X-ray time lag derived from reverberation mapping as a physical proxy for the reprocessing radius. Our analysis reveals a tight, global correlation across all black hole masses, described by $\log L_V = 0.48\log L_X + 0.96\log a_R + 6.5$ with a scatter of $\sim 0.20$ dex, where $a_R$ is the reprocessing radius derived from the lag. Incorporating a
geometric correction for the disk inclination angle ($\cos i$) slightly reduces this scatter to $0.18$ dex. These results suggest that X-ray reprocessing is scale-invariant across
accretion disks, from stellar-mass black holes to SMBHs. This scaling relation provides new constraints for models of X-ray emission regions in accreting black holes.
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All authors Changhyun Cho, David M. Russell, Aaryan Sharma, Payaswini Saikia, Maria Cristina Baglio, Kevin Alabarta, Sandeep K. Rout, Yi-Jung Yang, Eleonora Caruso, Mokhine Motsoaledi, Meriana Allah, Ian M. McHardy
High Energy Astrophysical Phenomena
Radio and Gamma-Ray Timing of a Newly Discovered Millisecond Pulsar
L. Vleeschower, R. Sengar, L. Nieder et al. (+17 more)
We report the discovery and timing of PSR J2147-3604, a fully recycled millisecond
pulsar with a
spin period of 3.2 ms, discovered in a reprocessing of the 350-MHz Green Bank North Celestial Cap (GBNCC) survey and later serendipitously confirmed by the MeerKAT TRAPUM UHF survey of Fermi-LAT unidentified sources. We followed up this
pulsar with Murriyang/Parkes
radio telescope and obtained a phase-connected timing solution spanning one year, revealing a 4.5-day binary orbit with very low eccentricity (e ~ 1.9 x $10^{-5}$). A follow-up search in LAT data revealed gamma-ray pulsations, allowing for a joint
radio and gamma-ray timing analysis. Assuming a
neutron-
star mass of 1.5 Msun, the inferred median companion mass (~0.2 Msun) is consistent with a helium white dwarf. The
pulsar has a low dispersion measure of 17.0 pc cm$^{-3}$ and shows strong scintillation, leading to it being detected in ~72% of the observations covering the 704-1174 MHz band with Murriyang. The
pulsar has a narrow duty cycle of ~6.5%, which leads to individual time of arrival (ToA) uncertainties of ~4.5 us for a 10 min integration with MeerKAT, suggesting this
pulsar is well suited for inclusion in PTA experiments.
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All authors L. Vleeschower, R. Sengar, L. Nieder, C. J. Clark, D. L. Kaplan, A. Anumarlapudi, R. Girgaonkar, T. Thongmeearkom, G. Y. Agazie, M. Bailes, E. D. Barr, R. P. Breton, M. E. Decesar, T. Dolch, M. Kramer, R. S. Lynch, E. Parent, S. M. Ransom, B. W. Stappers, J. van Leeuwen
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Universal relations for hybrid stars and their quark cores: a systematic scan of the quark-matter parameter space
J. P. Carlomagno, G. A. Contrera, A. G. Grunfeld et al. (+1 more)
Universal, equation-of-state (EOS) insensitive relations among the global properties of compact
stars are well established for hadronic
neutron stars and for self-bound strange
stars. We ask whether analogous relations hold for the
quark core of a hybrid
star, and whether the core can be constrained from the surface. Describing
quark matter with the three-flavor MIT bag model with repulsive vector interactions, matched to the hadronic DD2 EOS through a Maxwell construction, we scan the full $(B^{1/4},G_V)$ plane and obtain 1112 hybrid EOSs with maximum masses above $2\,M_\odot$, broadly compatible with current multimessenger constraints. For every stable configuration we evaluate the mass, radius, moment of inertia, and tidal deformability both at the stellar surface and at the boundary of the
quark core. Global quantities follow the relations of hadronic
stars—the $I$–Love relation to within $0.5\%$—while core quantities follow those of self-bound strange
stars with median deviations of $6$–$9\%$. We explain the latter by expanding the structure of the core in powers of its compactness: to first order, the core mass, baryon mass, moment of inertia, and tidal deformability depend only on the compactness and on the properties of the
hadron–
quark interface, chiefly the ratio $\xi=p_{\rm tr}/\varepsilon_+$ of transition pressure to
quark energy density. The strange-
star relations are the $\xi\to0$ member of this family, and the deviations from them measure $\xi$. The fractional core mass and radius of all configurations follow the normalized mass profile of the
star, and no global observable allows the core size to be inferred. Evanescent cores dominate the viable parameter space, while sizable cores require low bag constants and strong vector couplings.
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All authors J. P. Carlomagno, G. A. Contrera, A. G. Grunfeld, G. Lugones
Instrumentation and Methods for Astrophysics
Estimating the spectral resolution of a radio data cube from its noise properties
P. Serra, G. Mulas, K. M. Hess et al. (+4 more)
We present a new method to estimate the spectral resolution of a
radio data cube from its noise properties. We assume that the data cube is the result of the convolution of a spectrally-uncorrelated cube with a constant convolution kernel K. We demonstrate that K and the resolution, defined as K's integral, can be estimated thanks to the analytical relation between the autocorrelation of the noise spectra extracted from the cube and the power spectrum of the kernel. We discuss a number of
algorithms that make this method robust in the realistic case of a finite number of spectra and channels, real signal and artefacts, and we present the results obtained for a number of
datasets from the literature. We further highlight that this method is applicable to any data cube that meets our assumptions independently of the observing frequency or the exact nature of the cube's "third" axis, e.g., it could be used to measure the time resolution of transient-search data cubes. We make this method available as part of the open-source software tool spectre.
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All authors P. Serra, G. Mulas, K. M. Hess, P. Kamphuis, T. Westmeier, Y. Ascasibar, J. M. van der Hulst
Earth and Planetary Astrophysics
High-resolution transmission spectroscopy of KELT-18b Metastable helium detection at 1083 nm
M. Chella, M. Monticelli, F. Biassoni et al. (+5 more)
We present the first high-resolution transmission spectroscopy of the ultrahot Jupiter KELT-18b, probing its escaping atmosphere by analyzing a single transit obtained with the CARMENES spectrograph. Transmission spectroscopy and Doppler
tomography were utilized to isolate the planetary signal. To mitigate contamination from the strong telluric OH lines overlapping the region of interest, two distinct data analysis procedures were applied: a standard Molecfit and OH-masking approach as well as a PCA-based method. By combining the two complementary approaches, we successfully detect a He\,I triplet absorption feature of $1.10 \pm 0.22\%$ ($5.1\sigma$). The signal exhibits a velocity shift consistent with zero and is attributed to the exoplanetary atmosphere. An injection test reveals that the PCA-based method significantly suppresses the retrieved signal. Additionally, using the ATES and TPM codes, we modeled the atmospheric photoevaporation and the helium triplet profile for different He/H ratios and stellar XUV fluxes, accounting for instrument and planetary rotational broadening. From our simulations we derive a mass-loss rate and an evaporation efficiency for KELT-18b of $10.47 \leq \log_{10}(\dot{M}) \leq 11.68$ and $0.153 \leq \eta \leq 0.321$, demonstrating that the atmosphere of KELT-18b is undergoing photoevaporation. Furthermore, our simulations show good agreement with the observed transmission spectrum, allowing us to exclude very low He/H ratios at a $3\sigma$ confidence level for XUV fluxes up to approximately twice the nominal reconstructed value. Our result expands the known parameter space of
exoplanets with confirmed helium absorption, establishing KELT-18b as the most massive
planet orbiting the hottest host
star with such a detection.
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All authors M. Chella, M. Monticelli, F. Biassoni, F. Borsa, M. Rainer, G. Guilluy, M. Basilicata, L. Cabona
Solar and Stellar Astrophysics
From Giant Envelopes to Rapidly Contracting Cores in Rotating Population III Stars from $500$ to $1000 \, M_\odot$
Devesh Nandal, John Chisholm, Daniel J. Whalen et al. (+4 more)
Population III (Pop III)
stars link the chemical enrichment of the early Universe to the formation of the first massive black holes, yet their
evolution remains poorly understood at extreme masses. Using GENEC, we evolve rotating zero
metallicity models from $500$ to $1000\,M_\odot$ at $v/v_{\rm crit}=0.1$ through core Si burning, and a $1000\,M_\odot$, $v/v_{\rm crit}=0.4$ model evolved through He exhaustion. In the fiducial $1000\,M_\odot$ model, convection and rotational transport carry freshly synthesized C and O into H burning layers, producing $62.1\,M_\odot$ of primary N by He exhaustion. Surface mass loss removes $20.2\,M_\odot$, including $1.8\times10^{-3}\,M_\odot$ of N, with $\log(\mathrm{N}/\mathrm{O})=0.68$, $\log(\mathrm{N}/\mathrm{C})=1.48$, and $\log(\mathrm{C}/\mathrm{O})=-0.80$. By the final hydrostatic model, the inner $100\,M_\odot$ is confined within $0.088\,R_\odot$ while the photosphere remains several thousand solar radii away. As C, Ne, O, and Si burning accelerate, chemical mixing freezes out and advanced products remain buried beneath the envelope. At core Si exhaustion, the central angular velocity reaches $4\times10^{-3}\,{\rm s^{-1}}$ while the surface rotates at $5.25\times10^{-8}\,{\rm s^{-1}}$, a contrast of $7.6\times10^4$. Contraction drives this
spin up, while inner specific angular momentum changes by less than $1\%$. The maximum $j_{\rm eq}/j_{\rm ISCO}$ is $0.313$, limiting disk formation in our inside out estimate. These models show that Pop~III
stars can produce strong primary N signatures and rapidly rotating black hole progenitors while their envelopes determine which products enrich the early Universe.
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All authors Devesh Nandal, John Chisholm, Daniel J. Whalen, Andreas A.C. Sander, Volker Bromm, Peixin Zhu, Lisa J. Kewley
Cosmology and Nongalactic Astrophysics
MeV dark matter decay forecasts for the COSI mission
Robin Anthony-Petersen, Orion Ning, Yu Watanabe et al. (+21 more)
The decay of dark matter (DM) is a generic prediction of many particle physics models, producing distinctive monochromatic signatures in environments such as the Galactic
halo. Searches for decaying DM in the elusive 'MeV gap' have remained conspicuously under-explored, despite well-motivated models including
axion-like particles, sterile
neutrinos, and hidden-sector scenarios predicting signatures in this energy range. The upcoming Compton Spectrometer and Imager (COSI)
telescope will help bridge this gap. Designed to probe this energy band with high spectral resolution, low background, and wide field of view, COSI is well-suited for DM line searches at the MeV scale. In this work, we make projections for COSI's 2-year sensitivity for DM decay in the Milky Way
halo using dedicated all-sky simulations incorporating COSI's predicted instrument response. We conclude that COSI will improve the sensitivity to the DM lifetime by more than an order of magnitude over the DM mass range 0.4 to 10 MeV.
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All authors Robin Anthony-Petersen, Orion Ning, Yu Watanabe, Benjamin R. Safdi, Maíra Dutra, Francesca Calore, Savitri Gallego, William Guan, Christopher M. Karwin, Alexander Kusenko, Israel Martinez-Castellanos, Shigeki Matsumoto, Michela Negro, Uwe Oberlack, Field R. Rogers, Thomas Siegert, Tadayuki Takahashi, Haoyu Xie, Hiroki Yoneda, Andreas Zoglauer, Steven E. Boggs, Dieter H. Hartmann, Carolyn A. Kierans, John A. Tomsick
Astrophysics of Galaxies
Yue Samuel Lu, Dušan Kereš, Philip F. Hopkins et al. (+1 more)
Over the last decade,
magnetic fields (B-fields) have become a common ingredient in
galaxy formation simulations. Although seemingly unimportant in matching observational constraints such as the $M_*-M_{\rm halo}$ relations, the B-field influences the circumgalactic medium (CGM) gas and determines
cosmic ray (CR) propagation, making it an indispensable non-thermal component. Nevertheless, the intricate physics of B-fields, particularly how they evolve to the observed $\mu$G-level field, remains largely elusive. In this work, we systematically address the
evolution of B-fields over
cosmic time using the FIRE-2 (Feedback In Realistic Environments) magnetohydrodynamics (MHD) simulations. We present results for both Milky Way (MW)-mass and dwarf
galaxies, with and without CRs. We find that CRs have little impact on B-field properties, while the
halo mass controls the saturated B-field strength at $z\sim 0$. However, all runs reach a
halo-independent
magnetic-to-turbulent ratio of $f_{\rm B}\sim 1-10\%$, though the methods used to measure
turbulence could affect this value. We identify a three-stage evolutionary course for the B-field in tandem with
galaxy formation: i. expansion, ii. amplification, and iii. saturation. The feature is universal, though the timings depend on the initial location and
star formation history of the gas. Flux-freezing is the predominant driver for the first and last stages, exhibiting power relations $B\sim \rho^{2/3}$ and $\rho^{1/2}$, although the latter could also be explained by dynamical and energetic
equilibria. The intermediate amplification stage, potentially driven by “dynamos”, is fuelled by structure formation, feedback, and gas
turbulence. We
conjecture a numerically triggered,
turbulence-driven amplification process to explain this phenomenon.
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All authors Yue Samuel Lu, Dušan Kereš, Philip F. Hopkins, Sam B. Ponnada
High Energy Astrophysical Phenomena
MRI Turbulence versus $\alpha$-Viscosity in Circumbinary Disks: Implications for Gravitational-Wave Dephasing and Accretion Variability
Mudit Garg and Yan-Fei Jiang
Our understanding of gas torques on massive black hole binaries (MBHBs) relies on hydrodynamical (HD) simulations of circumbinary disks (CBDs) in which an $\alpha$-viscosity models angular momentum transport. However, CBDs around MBHBs near merger are hot, magnetized
plasmas where transport is driven by magnetohydrodynamical (MHD)
turbulence sustained by the magnetorotational instability (MRI). We test how well an $\alpha$-viscosity captures MRI
turbulence with 3D global Athena++ simulations of a locally isothermal CBD around an equal-mass, circular MBHB, run in HD and MHD from the same initial
torus on identical grids, so that only the transport mechanism differs. Excising the region within twice the binary separation, $r<2~a_{\rm bin}$, allows $1000$ orbits of
evolution, several times longer than previous MHD simulations. Both disks deliver the same
accretion rate, and the gas beyond $2~a_{\rm bin}$ exerts a positive torque in both, yet the MHD torque is $3.5$ times larger and $3$ times more variable. Near the midplane, transport is similar in the disk body but three times weaker in MHD at the cavity edge, where $2$-$3$ times more mass piles up in a more eccentric cavity, raising the torque. The
accretion rate is modulated mainly at twice the binary frequency in HD, but by a persistent lump at the cavity edge and its beat with the binary in MHD. The outer-disk torque therefore implies a contribution to the gas-induced phase shift in the gravitational-wave signal of LISA binaries $3.5$ times larger than in $\alpha$-disk models, and a different variability signature for LSST and Roman.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Dark Matter Stability from residual flavour symmetries
Giacomo Landini, Simone Marciano and Federico Mescia
We propose a model-independent framework in which Dark Matter stability emerges naturally from residual discrete $\mathbb{Z}_N$
symmetries left unbroken by the spontaneous breaking of continuous flavour
symmetries, both Abelian and non-Abelian. No ad hoc stabilizing
symmetry is required, as Dark Matter stability is an inherent consequence of the underlying flavour dynamics. As an explicit example, we construct a prototype model based on a $\text{SU}(2)_\text{F} \otimes \text{U}(1)_\text{F}$ Froggatt-Nielsen
symmetry, which successfully reproduces the observed charged lepton mass spectrum and the PMNS mixing
matrix, while identifying the lightest sterile
neutrino as a stable Dark Matter candidate. Furthermore, we study the Dark Matter phenomenology within our model in the freeze-in regime, including production channels mediated by higher-dimensional operators suppressed by the cutoff scale $\Lambda$. Our analysis shows that continuous flavour
symmetries can provide a unified, self-consistent framework addressing both the flavour puzzle and the origin, stability, and production of Dark Matter.
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Cosmology and Nongalactic Astrophysics
Interpreting the stacked kinetic SZ signal II: the degeneracy between satellite galaxies and baryonic feedback
Lurdes Ondaro-Mallea, Boryana Hadzhiyska and Raul E. Angulo
The kinetic Sunyaev-Zel'dovich (kSZ) signal stacked around a
galaxy sample traces the gas around
halos and is a powerful probe of baryonic feedback. Its interpretation, however, depends on the satellite
galaxies in the sample. Using the FLAMINGO hydrodynamical simulations and DESI-like samples of luminous red
galaxies (LRGs), bright
galaxies survey (BGS), and emission-line
galaxies (ELGs), we show that satellites and feedback have similar effects: both suppress the small-scale signal. This degeneracy arises because stacking on satellites, which are offset from the centre of their host
haloes, mimics the extended gas distribution produced by feedback. Although satellites make up only 20-30% of each sample, they account for 50-80% of the signal because they occupy more massive
halos than centrals; thus their imprint on the stacked profiles can be as large as that of feedback. At the precision of current DESI$\times$ACT data, neglecting satellites in the modelling biases the inferred gas fractions low, by up to a factor of two, and overestimates the feedback strength, particularly for the LRG and BGS samples. Remaining agnostic about the satellite population avoids this bias but reduces the constraining power, so robust constraints would require knowing the satellite fraction to better than 10%, for instance from
lensing and clustering data of the same
galaxy samples. Finally, a further contribution from satellites will become statistically significant with upcoming surveys: satellites trace the anisotropic gas distribution around their host
haloes, an effect that contributes 10% of the signal, and will likely require simulation-based models to capture.
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Cosmology and Nongalactic Astrophysics
Beyond the Kullback–Leibler divergence: the likelihood-ratio distribution as a detectability measure
Amirhossein Samandar, Mikel Martin Barandiaran, Linn Htat Lu et al. (+13 more)
The Kullback–Leibler (KL) divergence is the expectation value of the log-likelihood ratio between two specified models, evaluated with respect to one of the two models. It provides an average measure of the distinguishability of the models. We examine its connection to discovery potential and the accuracy of parameter estimates when one model represents a null hypothesis, and the alternative is a family of models characterized by one or more continuous parameters. For data drawn from a multivariate Gaussian distribution, we derive the log-likelihood-ratio distribution and its cumulants under two such hypotheses. We then search over the alternative model's parameter space and use peak prominence, the height of a likelihood-profile peak above its surrounding baseline, as an operational detection statistic. Repeating this search on simulated data drawn from the null model allows us to calibrate the prominence threshold for a specified false-positive rate. We study a toy Gaussian model as well as three cosmological examples involving
cosmic topology, the tensor-to-scalar ratio, and dark energy. In all these cases, detectability of a particular model depends not only on KL divergence, but also on the size of the model parameter space, the likelihood-ratio distributions, and the distance of the model from any parameter space boundaries. The relationship between KL divergence, discovery potential, and parameter estimation must therefore be calibrated for each family of models and detection statistic under consideration.
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All authors Amirhossein Samandar, Mikel Martin Barandiaran, Linn Htat Lu, Andrew H. Jaffe, Deyan P. Mihaylov, Glenn D. Starkman, Cynthia Trendafilova, Yashar Akrami, Stefano Anselmi, Javier Carrón Duque, Craig J. Copi, Fernando Cornet-Gomez, Arthur Kosowsky, Anna Negro, Ricardo G. Rodrigues, Andrius Tamosiunas
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Vanishing Love Numbers of Kerr-Newman Black Holes
Sumanta Chakraborty, Takuya Katagiri, Paolo Pani et al. (+1 more)
Tidal Love numbers characterize the conservative response of compact objects to external perturbations and provide a powerful probe of their nature. While the static Love numbers of Schwarzschild, Kerr, and Reissner–Nordström black holes remarkably vanish, the tidal response of a generic Kerr–Newman black hole has remained unexplored due to the intrinsic coupling between gravitational and electromagnetic perturbations. Exploiting a recent breakthrough in the separability of these perturbations, we analytically determine the static tidal response of the most general stationary black hole in four-dimensional Einstein–Maxwell theory. For arbitrary multipole order, charge, and
spin, we show that the entire
matrix of conservative Love numbers vanishes, including the mixed gravito-electromagnetic couplings. We also compute the nonvanishing static dissipative response induced by frame dragging.
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All authors Sumanta Chakraborty, Takuya Katagiri, Paolo Pani, Jun-Xi Shi
Instrumentation and Methods for Astrophysics
OASIS: On-the-fly ASynchronous Image Stream classification – Transformer-based models for the early detection of strongly lensed supernovae
Satadru Bag, Raoul Canameras, Sherry H. Suyu et al. (+4 more)
Time-domain surveys often produce asynchronous image sequences across irregular observation times and photometric bands. In many applications, predictions are needed after each new observation, particularly when transient sources must be identified early to trigger follow-up. Strongly lensed
supernovae (LSNe), for which follow-up is particularly time-critical, provide a useful example. We formulate this setting as On-the-fly ASynchronous Image Stream (OASIS) classification and explore reusable
transformer architectures for causal, on-the-fly classification. We demonstrate these architectures on the lensed-transient classification problem studied by Bag et al. (2026a,b), distinguishing LSNe Ia from unlensed astrophysical transients. We compare them with the recurrent baseline adopted by Bag et al. (2026b), which combines a ConvLSTM branch for image processing with a separate LSTM branch for encoding observation times. The baseline maps asynchronous observations onto a fixed band-by-observation grid, filling unobserved bands with zeros. Using a common training setup, we compare two
transformer-based approaches to modeling interactions among spatio-temporal
tokens: factorized
attention, which separates spatial and temporal interactions, and joint
attention, which models them together. On the demonstration
dataset, factorized architectures achieve mean losses of $0.095$–$0.100$, compared with $0.128$ for the recurrent baseline and $0.107$ or higher for joint architectures. A selective readout further reduces the best loss to $0.089$ for a factorized model. These results suggest that factorized
attention suits this
dataset better, without implying universal architectural superiority. We release the architectures as reusable foundations for time-domain astronomy and other applications involving evolving spatial features that require on-the-fly predictions.
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All authors Satadru Bag, Raoul Canameras, Sherry H. Suyu, Stefan Schuldt, Stefan Taubenberger, Irham Taufik Andika, Alejandra Melo
Solar and Stellar Astrophysics
The nearby Type II supernova 2024ggi beyond 600 days: circumstellar interaction and dust formation
L. Ferrari, G. Folatelli, C. P. Gutiérrez et al. (+16 more)
The Type II SN 2024ggi is one of the nearest core-collapse SNe to have exploded in recent decades. Its proximity has enabled extensive multiwavelength monitoring from early times through the nebular phase. Signatures of late-time interaction between the SN ejecta and hydrogen-rich circumstellar material (CSM) have recently been reported. Here we extend its study using late-time optical photometry and spectroscopy from 570 to 820 d after explosion. We investigate the emergence and
evolution of late-time ejecta-CSM interaction and constrain the geometry of the interaction region and the properties of newly formed dust. Comparisons with other interacting SNe II and with synthetic spectra are presented. We model the H$\alpha$ profile with the Monte Carlo radiative-transfer code Damocles, including both gas and dust components. Spectroscopic signatures of interaction precede the photometric flattening. The spectra evolve from ejecta-dominated to interaction-dominated as H$\alpha$ develops a broad, boxy profile. The optical light curves subsequently flatten relative to the $^{56}$Co decay rate at approximately 650-670 d. The emission lines show a systematic blue-to-red asymmetry that requires a dust component newly formed within the ejecta. The inferred dust mass formed in the ejecta is $10^{-6}-10^{-5}$ M$_\odot$ if the grains are amorphous carbon or a carbon-silicate mixture, but can reach up to $10^{-3}$ M$_\odot$ for pure silicates.
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All authors L. Ferrari, G. Folatelli, C. P. Gutiérrez, A. Méndez, C. Ashall, K. Medler, K. Ertini, H. Kuncarayakti, N. Morrell, M. Stritzinger, W. Hoogendam, E. Hueichapán, R. Cartier, J. P. Anderson, M. Bersten, L. Galbany, J. L. Prieto, C. Cárdenas Uribe, S. Vazhayil
Earth and Planetary Astrophysics
JWST Imaging of Edge-on Protoplanetary Disks. V. Flux Ratio Reversal and Disk-edge Structure in the Flying Saucer
Jie Ma, Karl R. Stapelfeldt, Marion Villenave et al. (+8 more)
We present near- and mid-infrared broadband imaging observations of the edge-on protoplanetary disk 2MASS J16281370-2431391, a.k.a. the 'Flying Saucer', obtained with NIRCam and MIRI on board JWST. These data are combined with archival optical and near-IR broadband imaging from HST, millimeter dust continuum emission from ALMA, and optical lightcurves from the K2 and TESS for a comprehensive multi-wavelength study. The JWST observations reveal a reversal of the flux ratio between the two reflection nebulae at near-infrared wavelengths (2-3 $\mu m$), which can be explained by a misaligned inner disk. For the first time, JWST reveals the bright lining along the disk edge at 2 and 3 $\mu m$, arising from forward scattering of background
photons by dust grains near the $\tau\approx 1$ layer. By combining the dust lane thickness measured with HST and JWST, we find the dust grains up to at least $\sim$3$\mu$m are vertically mixed throughout the disk and have undergone significant growth. In addition, comparison of earlier HST/NICMOS J and K band images with those from JWST/NIRCam reveals variability in the scattered-light morphology, as well as measurable proper motion of the system with respect to the background
stars, confirming that the Flying Saucer is co-moving with the young
star population of $\rho$ Ophiuchi.
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All authors Jie Ma, Karl R. Stapelfeldt, Marion Villenave, Gaspard Duchêne, François Ménard, Ryo Tazaki, Youcef I. Bouarour, Greta Guidi, Laurine Martinien, Maxime Roumesy, Christophe Pinte
Instrumentation and Methods for Astrophysics · Cross-listed from cs.HC
Particle Selection in Virtual Reality
Boaz Keren-Gil, James Gain, Lucia Marchetti et al. (+2 more)
Point-cloud representations of 3D data are used in many fields, from astronomical surveys of
galaxies to medical imaging and
laser scans of buildings. A task common to all of these is interactive selection: picking out a meaningful subset of points for closer analysis. The data is inherently 3D, yet the traditional workflow uses a 2D mouse on a 2D projection and inherits the limitations of a flat screen. This paper compares Virtual Reality (VR) and desktop environments for 3D particle selection, asking whether VR's six-degree-of-freedom hand interaction yields measurable gains in accuracy, speed, usability, workload and flow. In a counterbalanced within-subjects experiment (N = 34), participants selected 90 target
galaxies from a catalogue of 16,816
galaxies, using mouse-driven selection with keyboard camera control on the desktop and a hand-held spherical brush that adds or removes particles in VR. We measured task accuracy, completion time, and three standard questionnaires: the System Usability Scale (SUS), the NASA Task Load Index (NASA-TLX) and the Flow State Scale (FSS). Accuracy was comparable (91.6% VR vs. 93.1% desktop; p = 0.858), but every other measure favoured VR. Tasks were 23% faster (p = 0.001, d = 0.93), usability was higher (SUS 84.6 vs. 54.0; d = -1.78), workload was lower (NASA-TLX 20.4 vs. 34.7; d = 0.90), and flow was higher (FSS 83.2 vs. 70.2; d = -1.23). Because the underlying problem, making a 3D selection through a 2D interface, is not specific to astronomy, we expect the pattern to carry over to point-cloud selection in other fields.
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All authors Boaz Keren-Gil, James Gain, Lucia Marchetti, Patrick Marais, Alexander Sivitilli
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Decay-Assisted Leptogenesis during Preheating
Wenbin Zhao
We revisit the non-thermal leptogenesis mechanism during preheating using the
quantum Boltzmann equations. This framework allows us to study the production and decay of heavy right-handed
neutrinos in a consistent manner. Due to their fermionic nature, right-handed
neutrino production can saturate after a few inflaton oscillations when their occupation numbers approach unity. Right-handed
neutrino decays can deplete their occupation numbers, allowing more particles to be produced and generating a larger lepton asymmetry. Compared with the case where right-handed
neutrinos decay only after production has finished, we find that the final baryon asymmetry can be enhanced by two orders of magnitude.
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Instrumentation and Methods for Astrophysics
Extinction by non-spherical particles with the Nanoparticle Transition Matrix Code: perspectives for interstellar medium and exoplanetary atmospheres
G. La Mura, G. Mulas, M. A. Iatì et al. (+4 more)
The Transition
Matrix formalism (T-
matrix) offers an optimal solution to the problem of radiation scattering and absorption by particles characterized by a high degree of chemical and structural complexity. However, its application to particle models composed by large numbers of constituents has been classically limited by the substantial computational burden of the method. As a consequence, the investigation of light scattering and absorption processes, in cases where particle asymmetry and non-homogeneity play an important role, typically need to rely on simplifying assumptions which affect the correct interpretation of transmission spectra and extinction curves. This problem has a huge impact on many fields of scientific application. In particular, it has a critical role in astrophysics, because the ability to model highly non homogeneous particles is a fundamental requirement to understand the role of extinction in different phases of the interstellar medium (ISM), as well as to probe the physics of light transmission in planetary atmospheres within the Solar System and beyond. In this work we describe the application of a new implementation of the T-
matrix formalism, based on the framework originally developed by Borghese, Denti & Saija and named Nano-particle Transition
Matrix code, which leverages the power of modern hardware architectures to reduce the computational costs related to the solution of relevant particle models for the investigation of dust in the ISM and of hot-Jupyter class
planets atmospheric aerosols. This new implementation of the T-
matrix formalism can handle calculations of increasing complexity with a direct impact in the interpretation of the transmission spectra of transiting
exoplanets produced by the James Webb Space
Telescope (JWST) and of those expected from the Atmospheric Remote-sensing Infrared
Exoplanet Large survey (ARIEL).
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All authors G. La Mura, G. Mulas, M. A. Iatì, C. Cecchi-Pestellini, G. Aresu, S. Rezaei, R. Saija
Astrophysics of Galaxies
R(V) parameter of the dust extinction curve: mapping based on hot stars and connections to diffuse interstellar bands
R. Lallement, J.L. Vergely and N.L.J. Cox
Favored carriers of the Diffuse Interstellar Bands (DIBs) are carbonaceous molecules whose constituents have been presumably expelled by dying
stars along with those of dust grains. The parallel
evolution of DIB carriers and grains and their potential interplay are unknown. We assembled published R(V) measurements of 505 hot
stars. We inverted a catalog of extinction data based on Gaia XP spectra and NIR photometry, and used the resulting new 3D extinction map to locate the opaque areas responsible for R(V) for each
star. Using archived spectra, we measured their 5780, 5797 and 8620 A DIBs. In parallel, we compared local and line-of-sight (LOS) R(V)s from recent 3D maps with local and LOS Gaia DIB strengths from our recent map. Results: R(V)s from hot
stars reveal variations on large spatial scales, confirming with independent data the published 3D pattern. Gaia DIB strength maps show large spatial scale variations similar to those of R(V) maps, with higher abundance of DIB carriers corresponding to higher R(V). LOS Gaia DIB strengths and R(V)s from 3D maps also correlate positively in the R(V) range 2.3-3.4, but there is no connection for higher R(V), likely due to the disappearance of DIB carriers in dense clouds. Despite averaging effects along the LOS to hot
stars, we find differences in R(V)-DIB relationships among the three DIBs, with an
evolution from negative to positive correlation from the zeta- to the sigma-type DIBs. This can be understood in the frame of the bimodal
evolution of R(V) with the extinction, with the zeta (resp. sigma) DIB carrier disappearance in the decreasing (resp. increasing) phase of R(V). Various combinations of DIB strengths and DIB ratios may allow to define the range of R(V), but the relationship between DIBs and R(V) also appears to depend on the wavelength range used to determine R(V).
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Cosmic Colliders in Binary Blazars Probing Ultra-High-Energy Particle Physics
Giorgio Galanti
While terrestrial
colliders and fixed-target
cosmic-ray interactions are bounded at center-of-mass (CM) energies $\sqrt{s} \lesssim \mathcal{O}(10^5)\,\text{GeV}$, we demonstrate that bound sub-parsec binary blazars form broad-band, beam-beam hadronic “
Cosmic Colliders”, overcoming such limitation. Driven by modest jet misalignments ($\theta_{\rm mis} \sim 1^\circ - 6^\circ$), co-streaming
proton beams collide at CM energies reaching $\sqrt{s} \sim 10^{10}\,\text{GeV}$ - six orders of magnitude above the Large
Hadron Collider. Operating in a strictly optically thin regime ($\tau_{pp} \ll 1$), the system performs a continuous CM energy scan, probing asymptotic QCD scaling, gluon saturation, and Froissart unitarity, while opening a possible high-sensitivity window into physics beyond the Standard Model. Secondary PeV-EeV
neutrinos and sub-TeV $\gamma$-rays fall directly within reach of current and planned observatories such as LHAASO, CTAO, IceCube, and GRAND, establishing binary blazars as laboratories for physics at the ultimate energy limit.
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Cosmology and Nongalactic Astrophysics
The Cosmic Radio Dipole and Observer Effects in SKA all-sky surveys
D. Bertacca, L. Böhme, B. Bottazzi Baldi et al. (+13 more)
The Square Kilometre Array (SKA) will observe our Universe on the largest scales and so enable the study of fundamental assumptions in cosmology, such as
cosmic homogeneity and isotropy. Observations over recent years have reaffirmed an unexpected challenge to the Cosmological Principle first seen in measurements of the
cosmic radio dipole. This dipole anisotropy is thought to be caused by our local observer motion, however, it is observed to be about three times larger than predicted, with significances exceeding 5$\sigma$. The SKA is in a unique position to shed light on this anomaly by measuring this and other effects related to our observer motion. To quantify this, we forecast the capability of large-angle HI and continuum surveys of the SKA to constrain the kinematic matter dipole in
galaxy number counts, the modulation of the matter power spectrum by a kinematic dipole, and kinematic spectral distortions of diffuse
radio emission.
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All authors D. Bertacca, L. Böhme, B. Bottazzi Baldi, C. Burigana, M. Y. Elkhashab, C. L. Hale, S. von Hausegger, H. R. Klöckner, M. Land-Strykowski, G. F. Lewis, V. Mittal, O. T. Oayda, D. J. Schwarz, P. Tiwari, T. Trombetti, J. D. Wagenveld