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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 25 September

High Energy Astrophysical Phenomena

Discovery of minute-scale polarization angle rotation in a supermassive black hole jet

Aristeidis Polychronakis, Ioannis Liodakis, Dmitry Blinov et al. (+7 more)

Relativistic jets from supermassive black holes oriented towards our line of sight called blazars have puzzled the astronomical community for decades. Their fast jets and preferential alignment creates a fog of relativistic effects that obscures their true properties. Optical polarimetry - tracing the uniformity, direction, and evolution of the magnetic field in the jets, has revealed a unique phenomenon to blazars; coherent changes of the magnetic field manifesting as rotations of the polarization angle ($\Psi$). The origin of those rotations has been debated for decades with several proposed models to explain them. We detected an extremely fast - minute time-scale - rotation in the polarization angle of $\sim136^\circ$ over the span of about 80 minutes, making it the fastest known rotation by almost an order of magnitude. Our optical polarization observations combined with radio very long baseline interferometry allow us to reject different models of particle acceleration and strongly point to relativistic effects and the interaction of standing and moving shock waves as the origin of the extreme polarization variations in jets.
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All authors Aristeidis Polychronakis, Ioannis Liodakis, Dmitry Blinov, Anastasia Glykopoulou, Sebastian Kiehlmann, Karan Pal, Georgios F. Paraschos, Lena Debbrecht, Swati Ravi, Herman L. Marshall

Astrophysics of Galaxies

$\textit{N\=ap\=owaw\=a`enakaulua}$: a close quasar pair at cosmic dawn in the Aether survey

Silvia Onorato, Emanuele Paolo Farina, Roberto Decarli et al. (+32 more)

We present the discovery and first characterization of $\textit{N\=ap\=owaw\=a`enakaulua}$: the most compact known quasar pair candidate in the Epoch of Reionization, with a projected separation of only $0.98^{\prime\prime}$ ($\approx 5.56$ pkpc at $z \sim 6.08$) and a velocity offset of $\Delta v \simeq 15 \text{ km s}^{-1}$. Using spectroscopy from JWST/NIRSpec IFU, as part of the $\textit{Aether survey}$, Gemini/GNIRS and GMOS we characterize the continuum and emission line properties of the two quasars, enabling constraints on their black hole masses ($M_{\text{BH}} \simeq 1.5 \times 10^9$ and $4.0 \times 10^8\,M_\odot$), accretion states ($\lambda_{\text{Edd}} \simeq 1.23$ and $1.07$), and systemic redshifts ($z_{\rm sys} \simeq 6.0781$ and $6.0785$). We place this pair in the cosmological context by comparing the chance of occurrence to extrapolations of high-$z$ quasar clustering measurements at larger scales, resulting in a $\sim 2-3$ order of magnitude excess with respect to expectations. This excess hints at an underlying population of merger-triggered quasar pairs at cosmic dawn or to a denser-than-average galactic environment. $\textit{N\=ap\=owaw\=a`enakaulua}$ thus represents a crucial signpost to investigate the mass assembly of the first massive galaxies and black holes.
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All authors Silvia Onorato, Emanuele Paolo Farina, Roberto Decarli, Klaudia Protušová, Elia Pizzati, Debora Pelliccia, Devin S. Chu, Larry Lindsey Kimura, Leinani Lozi, Emily Peavy, Fabrizio Arrigoni-Battaia, Eduardo Bañados, Aaron J. Barth, Silvia Belladitta, Manuela Bischetti, Sarah E. I. Bosman, Hyunseop Choi, Tiago Costa, Anna-Christina Eilers, Xiaohui Fan, Simona Gallerani, Thomas R. Geballe, Anniek J. Gloudemans, Eunchong Kim, Brian C. Lemaux, Weizhe Liu, Yoshiki Matsuoka, Chiara Mazzucchelli, Atsuko Nitta, Jan-Torge Schindler, Andrew W. Stephens, Hyewon Suh, Fabian Walter, Feige Wang, Jinyi Yang

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Neutrino Direct Simulation Monte Carlo: Accurate modeling of out-of-equilibrium decaying cosmological relics

Kensuke Akita, Miguel Escudero, Oleksii Ihnatenko et al. (+1 more)

We consider nonstandard cosmologies in which decaying relics inject energy at MeV temperatures, driving neutrinos out of equilibrium. The subsequent neutrino evolution shapes predictions for the cosmic radiation density and primordial light element abundances. Earlier work introduced Neutrino Direct Simulation Monte Carlo ($\nu$DSMC), which describes neutrino transport through Monte Carlo sampling of particle interactions. Here, we extend this method by jointly evolving the relic population, neutrino spectra, electromagnetic plasma, and cosmic expansion, and coupling this evolution to Big Bang nucleosynthesis. The framework includes direct and inverse decays of the relic, neutrino flavor conversion, quantum statistics, and pion production by energetic neutrinos. To reveal the physical impact of these effects and independently test $\nu$DSMC, we compare several approaches to neutrino evolution across a range of nonstandard cosmological scenarios. We find excellent agreement with independent solutions of quantum kinetic or quasi-classical Boltzmann equations. Compared with these calculations, $\nu$DSMC includes a broader range of physical processes and is substantially faster for strongly nonthermal neutrino populations. This makes broad, robust parameter scans for nonstandard cosmologies practical. We show that when departures from thermal equilibrium are large, approximations that average over neutrino momenta can give qualitatively incorrect predictions, including the wrong sign of the change in the effective number of neutrino species and substantially incorrect primordial nuclear abundances. We conclude that the extended $\nu$DSMC framework enables reliable cosmological tests of new physics by following neutrino thermalization and its observable consequences.
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All authors Kensuke Akita, Miguel Escudero, Oleksii Ihnatenko, Maksym Ovchynnikov

Astrophysics of Galaxies

Balmer Break Measurements Trace Departures from the Star-Forming Main Sequence at $1<z<4$ with JWST/NIRSpec

Suprabhas Narisetty, Yongda Zhu, Eiichi Egami et al. (+4 more)

We present JWST/NIRSpec PRISM observations of galaxies at $1<z<4$ to study the relation between Balmer-break strength ($D_{\rm Balmer}$) and recent star formation. Using NIRSpec spectra from the JADES Transient Survey in GOODS-S, we measure $D_{\rm Balmer}$ and hydrogen recombination-line equivalent widths, and infer galaxy properties through spectral energy distribution (SED) fitting of the accompanying photometry. We find a clear anti-correlation between $D_{\rm Balmer}$ and the rest-frame equivalent width of H$\alpha$+[\ion{N}{2}], such that galaxies with stronger breaks show weaker nebular emission and lower recent star formation activity. $D_{\rm Balmer}$ also correlates with mass-weighted stellar age, supporting its use as an empirical tracer of evolved stellar populations at these redshifts. Star formation rates inferred from H$\alpha$, Pa$\gamma$, and SED fitting are broadly consistent, with scatter likely driven in part by dust attenuation, line-measurement uncertainties, and the different timescales probed by each indicator. Galaxies with stronger $D_{\rm Balmer}$ also tend to lie further below the star-forming main sequence at fixed stellar mass, indicating that $D_{\rm Balmer}$ is linked to recent suppression of star formation. In contrast, we find only a weak relation between $D_{\rm Balmer}$ and SED-derived dust attenuation, suggesting that dust is not the main driver of the observed trends. These results show that $D_{\rm Balmer}$, combined with recombination-line measurements, is a useful empirical diagnostic of galaxies transitioning away from the star-forming population at cosmic noon.
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All authors Suprabhas Narisetty, Yongda Zhu, Eiichi Egami, Stefano Carniani, Francesco D'Eugenio, Christa DeCoursey, Christopher N. A. Willmer

Astrophysics of Galaxies

MUSE spectroscopy of the compact dual AGN in the $z=3.273$ radio-loud gravitational lens MG B2016+112

Jianghao Huyan, Júlia M. Sisk-Reynés, Daniel A. Schwartz et al. (+4 more)

Dual active galactic nuclei (AGN) are unique laboratories for studying how galaxy mergers trigger accretion onto supermassive black holes (SMBHs). However, at redshifts $z>1$, only few dual AGN are confirmed at projected separations $\gtrsim$ 1 kpc for the two SMBHs. We present archival MUSE spectroscopy of the three resolved lensed images of the radio-loud system MG B2016+112. At z = 3.273 and at a projected separation of 175 pc, this the most compact confirmed dual AGN at z > 1. We detect Ly$\alpha$, C IV, N V, He II, and C III] emission across images A$--$C after correcting for ISM absorption at $z \sim 0$. We find that the Ly $\alpha$, C IV, N V lines are affected by saturated absorption at $z \sim 3.27$. The He II / C III] emission-line ratios are consistent between images A and B but differ significantly from image C. We fit the C IV emission regions of images A$--$C by allowing for up to two Gaussians and use broad component to place lower limits on their respective SMBH masses: $\gtrsim 2 \times {10}^{7} M_\odot$, $\gtrsim 2.3 \times {10}^{7} M_\odot$, and $\gtrsim 1.5 \times {10}^{7} M_\odot$. Correcting for their strong lensing magnifications suggests Eddington ratios of $\lesssim$ 0.47, 0.51, and 0.04, respectively. Together with previous VLBI and X-ray analyses, our results provide strong, independent spectroscopic evidence that MG B2016+112 hosts two AGN. Our findings motivate deep, spatially resolved near-IR spectroscopy to independently revisit our mass estimates and determine the physical conditions of the host galaxy, which has likely undergone a major merger.
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All authors Jianghao Huyan, Júlia M. Sisk-Reynés, Daniel A. Schwartz, Varsha P. Kulkarni, Anna Barnacka, Adi Foord, Charlotte A. Eades

Solar and Stellar Astrophysics

Measuring the Expansion of Solar Magnetic Fields with Multiline Inversions from Sunrise III

Juan Carlos Trelles Arjona, María Jesús Martínez González, Christoph Kuckein et al. (+34 more)

Magnetic fields in the solar atmosphere are expected to expand with height, forming magnetic canopies that couple the photosphere and chromosphere. Except for sunspots, direct measurements of this expansion remain scarce because they require simultaneous magnetic diagnostics over a broad range of atmospheric heights. We analyze four consecutive high-resolution spectropolarimetric raster scans of an emerging flux region observed with the Sunrise III/SCIP instrument. Simultaneous inversions of five photospheric Fe I lines and two chromospheric Ca II lines provide a quasi-continuous reconstruction of the magnetic field from the deep photosphere to the lower chromosphere. We apply a constant-flux method that follows the same magnetic flux through different atmospheric layers to quantify magnetic expansion. All three pores analyzed exhibit an overall increase in magnetic area with height, approximately doubling their cross section between the lower photosphere and the highest atmospheric layers sampled by the inversions. The expansion remains broadly stable throughout the 48-minute observing sequence. We further characterize the expansion with a quadratic parameterization and investigate its relation to pore properties. The three pores exhibit similar core magnetic field strengths but different expansion behaviors, indicating that the magnetic core strength alone does not determine the expansion. However, the present sample is too small to establish whether these differences are related to the thermodynamic or magnetic properties of the pores and their surroundings. These results demonstrate the potential of simultaneous multiline inversions for investigating the three dimensional magnetic topology of solar magnetic structures and provide the first direct measurements of the height-dependent magnetic expansion of solar pores.
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All authors Juan Carlos Trelles Arjona, María Jesús Martínez González, Christoph Kuckein, Sergio Javier González Manrique, Manuel Collados, Sami K. Solanki, Andreas Lagg, Achim Gandorfer, Jose Carlos del Toro Iniesta, Yukio Katsukawa, Pietro Bernasconi, Thomas Berkefeld, Alex Feller, Tino L. Riethmüller, Alberto Álvarez-Herrero, Masahito Kubo, H. N. Smitha, David Orozco Suárez, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hölken, Francisco A. Iglesias, Ryohtaroh T. Ishikawa, Yusuke Kawabata, Takuma Matsumoto, Takayoshi Oba, Azaymi L. Siu-Tapia, Hanna Strecker, Dušan Vukadinović, Hirohisa Hara, Toshifumi Shimizu

Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

Electric Potential Patterns Forecasting in the Southern Hemisphere with Deep Learning Techniques

Francesco Pio Ramunno, Simone Mestici, Igino Coco et al. (+5 more)

Space weather disturbances driven by the solar wind can degrade satellite navigation, disrupt radio communications, and threaten power infrastructure, making accurate forecasting of the high-latitude ionosphere's response a critical operational need. Existing approaches, empirical climatological models and physics-based magnetohydrodynamic simulations, either smooth out the ionosphere's time-dependent, non-linear response or are too computationally expensive for real-time use, while prior machine learning efforts have mostly targeted scalar indices rather than the full spatial structure of ionospheric convection. Here we train and compare three deep learning architectures, a probabilistic diffusion model conditioned on multi-variate solar wind and interplanetary magnetic field measurements at the L1 Lagrange point, an unconditioned diffusion ablation, and a deterministic U-Net baseline, to forecast Southern Hemisphere high-latitude electric potential maps derived from SuperDARN radar observations. Using five years (2020–2025) of SuperDARN data synchronised with DSCOVR L1 measurements, we evaluate the models under a single-pass regime, an extended autoregressive rollout of up to 350 frames, and an out-of-distribution case study on the intense March 2015 St.\ Patrick's Day storm, unseen during training. We find that the relative advantage of the deterministic and probabilistic approaches is not fixed: the deterministic model is competitive over short horizons and calm conditions, while the diffusion model's advantage grows and eventually dominates as the forecast horizon lengthens and the event becomes more dynamic, evidence that probabilistic, sample-based generative models are the more promising direction for operational, long-horizon space weather forecasting.
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All authors Francesco Pio Ramunno, Simone Mestici, Igino Coco, Maria Walach, Stefano Massetti, Maria Federica Marcucci, Brandon Panos, André Csillaghy

High Energy Astrophysical Phenomena

A Multidimensional General-Relativistic Boltzmann Solver for Neutrino Transport: Implementation, Discretization and Optimization

Arthur Offermans, Harry Ho-Yin Ng, Patrick Chi-Kit Cheong et al. (+2 more)

We present the implementation of a multidimensional general-relativistic Boltzmann solver for neutrino transport using the finite volume method. We extend the general-relativistic magnetohydrodynamics solver Gmunu to discretize the full $6$D phase space. We discretize the momentum space in spherical coordinates in the comoving frame, and the position space in the lab frame in Cartesian, cylindrical or spherical coordinates. As in the M1 scheme, we expand the interaction kernels up to first order in a Legendre series. We present a discretization scheme that ensures consistency between the number-conservative and non-conservative formulations in empty flat spacetime, multiple dimensions and coordinate systems, conserves energy to $\sim 1\%$ with $20$ energy bins in 1D tests. We discuss optimizations of the implicit solver for stiff source terms to minimize its computational cost. In particular, we introduce a method that leverages the Legendre expansion of the kernels to reduce the dimensionality of the problem. In a 1D core-collapse supernova snapshot, our method yields a speed-up factor of $300$ compared to a full-matrix LU method for $14$ angular bins when including energy- and species-coupling interactions. Finally, we validate our implementation on standard test cases and report quadratic convergence in space, energy and propagation angles. We compare our solver to the M1 scheme in simplified 1D configurations and find differences of about $10\%$ in the free-streaming luminosities in relaxation test cases, which we attribute primarily to the M1 closure relation. The average energies, on the other hand, agree between the two methods. We compare both methods on a core-collapse supernova test case and find an overall good agreement in the fluid variables' profiles at the time of core bounce for $20$ energy bins.
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All authors Arthur Offermans, Harry Ho-Yin Ng, Patrick Chi-Kit Cheong, Anthony Mezzacappa, Tjonnie Guang Feng Li

Earth and Planetary Astrophysics

Inclination of Miranda as a Constraint on the Tidal Dissipation of Uranus

Maryame El Moutamid and Matija Ćuk

The five major moons of Uranus record a complicated geological history characterized by both tectonic resurfacing and heavy impact cratering, connecting their evolution to dynamical processes in the Solar System. Miranda, the smallest and closest major moon to Uranus, has an unusually large orbital inclination ($4.3^\circ$) and an remarkable surface geology dominated by coronae and tectonic structures. In this paper we explore whether Miranda's inclination and geological history can be explained through past orbital resonances within the Uranian satellite system. Using direct $N$-body integrations with the code SIMPL, we explore the tidal and dynamical evolution of the five major moons while assuming a fast tidal dissipation of Uranus and varying the internal responses of the satellites. Our simulations confirm that Miranda's inclination can be excited through resonant interactions involving Ariel and Umbriel, even when Miranda mean motion is not involved in that resonance. The Ariel-Umbriel 5:3 mean-motion resonance appears to be the most recent major dynamical event capable of driving Miranda's inclination to its current value. We compute the tidal heating associated with these resonance encounters and show that, for a strongly dissipative Uranus ($Q_U\sim600$), the resonance could cause heat fluxes in Miranda approaching those required to form its coronae. These results could provide new constraints on Uranus's tidal dissipation.
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Solar and Stellar Astrophysics

A Comprehensive Study of the Magnetic White Dwarfs in DESI DR1

Adam Moss, Pierre Bergeron, Mukremin Kilic et al. (+2 more)

As the end point of stellar evolution for most stars, white dwarfs offer powerful insight into stellar magnetism. Multiple formation channels are required to explain the observed properties of magnetic white dwarfs, and the mechanisms that produce unusual objects have potential to unlock new realms of physics. The large samples made possible by spectroscopic surveys enable study of these processes on an unprecedented level. Here we perform a detailed model atmosphere analysis of the magnetic white dwarfs in DESI Data Release 1. We identify 833 magnetic systems, 762 of which we fit using an offset dipole model. Of these, 127 targets require more in-depth analysis as they possess shallower or sharper absorption features than predicted by the offset dipole model. For these we use a patchy offset dipole atmosphere model in which the magnetic field only contributes to the line opacities at certain regions of the visible stellar disk. We compare the observed distribution of magnetic white dwarfs to the mechanisms that generate magnetic fields. We find that a core-convective dynamo that forms on the main-sequence matches the parameters of many of the magnetic systems, while a dynamo that fills the radiative interior on the giant branch reproduces many of the lower mass objects that the core-convective dynamo cannot. This sample is the largest single data release of magnetic white dwarfs to date. The diversity of formation channels and the frequency of objects with unusual field geometries highlight the power of multiplexed surveys to advance our knowledge of stellar magnetism.
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All authors Adam Moss, Pierre Bergeron, Mukremin Kilic, Warren R. Brown, Jamie Tayar

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Mind the second gap: The impact of gaps on noise and signal parameter inference

Ollie Burke, Federico Pozzoli, Martina Muratore et al. (+1 more)

Gravitational-wave data is never analysed without some conditioning: filtering and tapering act multiplicatively on the noise, destroying the stationarity on which the Whittle likelihood — the backbone of nearly all gravitational-wave inference — rests. The problem is particularly evident for LISA, where gaps are expected to overlap almost all signals and the noise must be estimated jointly with those astrophysical signals. We provide an analytical and numerical framework to assess the impact of noise mis-modelling when signal and noise parameters are inferred jointly in the presence of gaps. From a Fisher-matrix formalism verified against Bayesian inference, we obtain closed forms for the model uncertainties, their maximum-likelihood estimates and the true scatter in the latter, for various approximations to the likelihood. The Fisher-based linear formalism is extended through the Godambe–White curvature to the non-linear regime that severe mis-modelling produces. We survey gap families from long, well-tapered interruptions to short, high-rate ones, injecting massive black-hole binaries. Except in the case of frequent gaps, we show that the windowed covariance is well approximated by its leading diagonal — the window convolved with the power spectral density — for the estimation of both signal and noise parameters. By omitting the convolution, the signal sector remains unbiased but the noise parameters, in particular the optical-metrology noise which is dominant at high frequency, is displaced by over an order of magnitude in power. At the highest glitch rates the diagonal approximation stays accurate yet loses an order of magnitude in precision. To remedy this, we propose an exact time-domain likelihood of the surviving samples which can be efficiently (and accurately solved) via preconditioned conjugate gradient methods.
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All authors Ollie Burke, Federico Pozzoli, Martina Muratore, Jonathan R. Gair

Cosmology and Nongalactic Astrophysics

Evolving dark energy and a younger Universe from cosmic inhomogeneity

Jacky David Yang and Hans-Otto Carmesin

Joint analyses of baryon acoustic oscillations, type Ia supernovae and the cosmic microwave background show a preference for an evolving dark-energy equation of state, and recent studies suggest that cosmic inhomogeneities can produce an apparent evolution of dark energy within general relativity. Here we examine this effect within a framework in which the possibility that matter can be unevenly distributed enters the expansion dynamics directly. The framework yields redshift-dependent effective values of the Hubble constant and of the dark-energy density parameter without introducing a new free parameter. Using CMB-inferred parameters to fix the homogeneous limit, we find that the dark-energy density parameter increases by about eight percent toward the present, from 0.679 to 0.735, while the inferred Hubble constant shifts from the Planck value toward the range obtained from local measurements. Both trends are broadly consistent with published estimates from supernovae, baryon acoustic oscillations, X-ray clusters and gravitational waves, although a joint analysis of the underlying data is left for future work. Integrating the resulting expansion history gives a present-day cosmic age of 13.521 Gyr, compared with 13.827 Gyr for the homogeneous model; we interpret the difference of 0.306 Gyr as a global time dilation between the two descriptions. The framework also yields the homogeneous-limit dark-energy density parameter, two thirds, from the formation of volume alone. The predicted redshift dependences can be tested against forthcoming measurements of cosmic distances and expansion rates.
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Solar and Stellar Astrophysics

The 91T/99aa-like Type Ia Supernova 2019vrq, Part I: Photometry, Spectroscopy, and Spectropolarimetry of a Nearly Standard Candle

Yi Yang, Peter Hoeflich, J. Craig Wheeler et al. (+16 more)

Among the various major subtypes of Type Ia supernovae (SNe), the luminous 1991T-like (Filippenko et al. 1992; Phillips et al. 1992) and 1999aa-like (Krisciunas et al. 2000; Garavini et al. 2004) events stand out as particularly important for constraining the explosion mechanism. Their white dwarf (WD) progenitors are thought to have masses close to or exceeding the Chandrasekhar limit. We present spectrophotometric and polarimetric time-series observations of the overluminous Type Ia SN2019vrq. Between -9 and +12 days relative to the light-curve peak, its continuum polarization is consistent with zero, as seen in most normal-bright SNeIa and despite a possible rise up to 0.2% toward longer wavelengths as seen in subluminous SNeIa. Polarization across major spectral features is marginal ($\lesssim$0.3%) with the exception of the high-velocity CaII near-infrared triplet, which reaches $\sim$0.5%. This low polarization indicates a substantially spherically symmetric electron-scattering photosphere and minimal large-scale ejecta asymmetry. Early-time spectra reveal hot, doubly ionized ejecta dominated by SiIII and blended iron-group features. Intermediate-mass-element lines, such as CaII and SiII, are more clearly seen than in 91T-like events, though these lines remain weaker than in normal SNeIa. The intrinsically higher peak luminosity of overluminous 91T/99aa-like SNeIa (Yang et al. 2022; Phillips et al. 2024), their comparatively short formation timescale for a massive WD progenitor - a channel that becomes more common toward high redshift, and the moderate viewing-angle dependence of their spectrophotometric properties as inferred from their persistently low polarization, together suggest that this subclass may serve as a promising standard candle at high redshift.
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All authors Yi Yang, Peter Hoeflich, J. Craig Wheeler, Dietrich Baade, Lifan Wang, Aleksandar Cikota, D. Andrew Howell, Curtis McCully, Alexei V. Filippenko, Ferdinando Patat, Chris Ashall, Mattia Bulla, Avishay Gal-Yam, Melissa. L. Graham, Daichi Hiramatsu, Divya Mishra, Estefania Padilla Gonzalez, Craig M. Pellegrino, Steve Schulze

Solar and Stellar Astrophysics

Physics-induced impact on the properties of Kepler/K2 solar analogs in the light of PLATO's requirements

Saniya Khan, Gaël Buldgen, Jérôme Bétrisey et al. (+2 more)

Solar analogs are useful laboratories for tests of stellar structure and evolution, particularly in the context of the upcoming PLATO mission. Our study focuses on six seismic solar analogs observed by Kepler and K2. We investigate the impact of the model physical ingredients on these six targets in order to evaluate how well one can satisfy the PLATO precision requirements for stellar parameters with the data quality that is currently available to us. We used as reference values the stellar mass, age, and chemical composition obtained with the Forward and Inverse COmbination (FICO) procedure, based on OPAL opacities and a combination of NACRE II and Solar Fusion II (SFII) nuclear reaction rates. The efficiency of macroscopic transport is calibrated on lithium abundances derived from the analysis of HERMES spectra. From there, we carried out extensive tests of the physical ingredients with the help of a Levenberg-Marquardt local minimisation method using both classical and seismic constraints. In particular, we investigated the impact induced by the use of OPLIB opacities and SFIII nuclear reaction rates on the stellar fundamental properties, as well as the use of various seismic constraints. We quantify the potential differences that changes in the modelling input physics may lead to, and compare their extent with the requirements expected for the PLATO mission (15% in mass, 2% in radius, and 10% in age), providing crucial constraints on the accuracy and robustness with respect to systematics of the determination of fundamental properties for PLATO. For our sample of solar analogs, we are able to accurately retrieve stellar masses within 2.5%. As for stellar ages, we quantify systematics of the order of 10-14% at most, but there are also very promising cases for which deviations remain within 4% depending on the stars and constraints considered.
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All authors Saniya Khan, Gaël Buldgen, Jérôme Bétrisey, Rafael A. García, Savita Mathur

High Energy Astrophysical Phenomena

Neutron Economy and Freeze-out Dynamics in the Late-Time Cold r-Process

Mengke Li and Bradley Meyer

Standard r-process models often treat the freeze-out phase as a passive, uniform smoothing of the global abundance pattern. We demonstrate, however, that the final pattern is instead actively sculpted by a dynamic “neutron economy” that operates well after the free neutron source is exhausted. By analyzing cold neutron star merger outflows, we identify a distinct neutron exporter-importer relationship: the second-peak region ($A \sim 130$) transitions early into a $\beta$-decay dominated regime, acting as a net exporter, while the third-peak ($A \sim 195$) and Rare Earth ($A \sim 164$) regions remain capture-dominated neutron importers. Targeted simulations reveal that the final peak structures emerge from a competition between two opposing forces: a global “push” driven by neutron capture shifting mass toward heavier nuclei, and a local “pull” from beta delayed neutron emission returning material back toward lighter masses. We identify $^{136}\text{Pd}$, $^{135}\text{Ag}$, and $^{130}\text{Ru}$ as the primary exporters driving this economy, while third-peak fine structure is governed by $N=126$ isotones (Sm to Tb). Physically, this transport reflects a fundamental drive toward shell closure, where nuclei that overshoot the $N=82$ closed shell shed mass to migrate back toward this stable configuration, while nuclei in the third peak capture these redistributed neutrons to anchor themselves at the $N=126$ shell. Crucially, our models overproduce the odd-even staggering in the third peak compared to solar data. This discrepancy suggests current models likely overestimate the $\beta$-delayed neutron emission probabilities ($P_n$) for these $N=126$ nuclei, highlighting them as high-priority targets for theoretical refinement and future FRIB experiments.
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High Energy Astrophysical Phenomena

4FHL: The Fourth Catalog of Hard Fermi-LAT Sources

The Fermi-LAT Collaboration

We present a catalog of sources detected above 50 GeV by the Fermi Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope using 16 years of observations. This is the Fourth Catalog of Hard Fermi-LAT Sources (4FHL), containing 673 objects detected in the 50 GeV-2 TeV energy range. The sensitivity and localization are improved by factors of $\sim$2 relative to the previous LAT catalog at the same energies (i.e. the 2FHL catalog). The increased photon statistics, nearly doubling the number of detections relative to 2FHL, enables more detailed population studies, including the identification of fainter sources detected above 50 GeV. The majority of the sources (84.7%) are associated with extragalactic counterparts, primarily BL Lacertae objects, including 36 objects at redshift $z>1$. Galactic sources account for 10% of the sample, mainly pulsar wind nebulae and supernova remnants, while $\sim$5% remain unassociated or of uncertain classification. Twenty sources are reported with no counterpart in previous LAT catalogs. The 4FHL catalog provides the deepest all-sky survey above 50 GeV to date. By focusing on this high-energy regime, it provides a fundamental link between space-based gamma-ray observations and the TeV range probed by current and future ground-based observatories. It serves as a useful reference for guiding future observations, including new potential targets for follow-up with Cherenkov telescopes.
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Cosmology and Nongalactic Astrophysics

Kruglov-entropy cosmology from apparent-horizon thermodynamics: background dynamics and observational constraints

Candrasyah Muhammad, Burin Gumjudpai, Nandan Roy et al. (+1 more)

We investigate two late-time cosmological models generated by Kruglov's nonadditive entropy at the apparent horizon. Model I, originally derived by Kruglov, follows the Cai–Kim thermodynamic construction and leads to an implicit modified Friedmann equation, whereas Model II, proposed and derived in this work, is obtained from an entropy-integral prescription and contains an effective vacuum contribution. We formulate both models in terms of the dimensionless Hubble parameter, include radiation, impose exact present-day closure, and evolve the physical branch using analytic derivatives of the implicit Friedmann equations. We constrain the models with DESI DR2 baryon acoustic oscillations and a compressed CMB likelihood, with and without DES-Y5 Type-Ia supernovae. Model I is driven to a markedly lower Hubble constant, $H_0\simeq62.4,\mathrm{km,s^{-1},Mpc^{-1}}$ for the combined data, and remains non-phantom with $w_{\rm DE,0}\simeq-0.814$; it is strongly disfavoured relative to flat $\Lambda$CDM. Model II stays close to $\Lambda$CDM in the standard cosmological parameters and gives $w_{\rm DE,0}\simeq-1.003$, while its two entropy-sector parameters remain strongly degenerate. Its best-fit likelihood is comparable to $\Lambda$CDM, but the additional parameters are not supported by information criteria. These results show that the two thermodynamic realizations of the same nonadditive entropy have sharply different phenomenological consequences at the homogeneous-background level. In summary, the observational plausibility of entropy-based cosmology hinges critically on how the generalized horizon entropy is incorporated into the Friedmann dynamics.
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All authors Candrasyah Muhammad, Burin Gumjudpai, Nandan Roy, Pornrad Srisawad

Solar and Stellar Astrophysics

The Molecular Circumstellar Environments of Red Supergiants in Galactic Open Clusters

Mark A. Siebert, Elvire De Beck, Guillermo Quintana-Lacaci et al. (+4 more)

We aim to expand the sample of RSGs with direct measurements of circumstellar gas through millimeter observations of two of the largest coeval RSG populations in the Galaxy: the open clusters RSGC1 and RSGC2. We present an interferometric molecular line study of 28 RSGs in RSGC1 and RSGC2 with ALMA. The primary targeted emission is CO $J=2-1$ and continuum, with additional thermal and maser SiO lines observed for RSGC2 targets. We measure terminal expansion velocities, systemic velocities, emission-region sizes, and provide updated dust models and luminosities using the new long-wavelength constraints. Finally, we perform 1D radiative transfer modeling of CO rotational-line emission to estimate mass-loss rates. We detect $^{12}$CO toward six RSGs in RSGC2 and five in RSGC1. Except for DFK 52, the spatial distribution of all $^{12}$CO emission is relatively compact or unresolved. The obtained mass-loss rates range from $\log(\dot{M}/M_\odot\,\mathrm{yr}^{-1})=-5.5$ to $-3$, but are highly uncertain due to a lack of stringent constraints on the envelope sizes and temperatures. The lower-limit $\dot{M}$-values we obtain are high compared to standard empirical prescriptions and favor dust models assuming a radiatively driven wind. DFK 49 is a clear outlier: its revised luminosity is the lowest in both clusters, yet it harbors a strong wind with $\dot{M}>10^{-5}\,M_\odot\,\mathrm{yr}^{-1}$. The CO emission regions are much smaller than expected from nearby RSGs and theoretical models, and suggest a unique phase structure for the CSM around RSGs in cluster environments. This work demonstrates the mutual utility of molecular line and dust observations for constraining RSG winds, while highlighting the need for future spatially resolved, multi-tracer observations of RSGC targets to establish the physical structure of their circumstellar environments and improve mass-loss determinations.
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All authors Mark A. Siebert, Elvire De Beck, Guillermo Quintana-Lacaci, Theo Khouri, Maryam Saberi, Matthias Maercker, Wouter H. T. Vlemmings

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Natural Saturation Of The Sterile Neutrino Dark Matter Resonant Production By a High Lepton Flavor Asymmetry In Primordial Plasma

Dmitry Gorbunov and Dmitry Kalashnikov

Sterile neutrinos remain a well-motivated dark-matter candidate whose cosmological abundance can be enhanced by resonant active–sterile conversion in the presence of a lepton asymmetry in primordial plasma. In the standard picture, a larger initial asymmetry increases the matter potential and can therefore promote resonant production. However, the same increase also shifts the resonance to later stages of the cosmological evolution when the plasma temperature is lower. We show that this delayed production epoch can overlap with the onset of active neutrino oscillations, which redistribute the flavor asymmetries and may substantially reduce, or in some cases nearly erase, the lepton asymmetry needed for a successful resonant sterile-neutrino production. This interplay provides a natural saturation mechanism for the final sterile-neutrino abundance: beyond a certain range of initial asymmetries, increasing the primordial asymmetry no longer leads to a proportional increase in the produced dark-matter density. We identify this effect as an additional constraint on resonant sterile-neutrino production at large lepton asymmetry and discuss its dependence on the flavor structure of the initial asymmetry and on the background cosmological evolution. Our numerical results reveal two order of magnitude range in sterile-active neutrino mixing parameter $\sin^2(2\theta)$ presently consistent with the resonant mechanism of the dark matter sterile neutrino production. It must be investigated by the next generation X-ray telescopes to fully explore this mechanism and corresponding minimal models suggesting sterile neutrinos as viable dark matter. We also consider pion condensation at large flavor lepton asymmetries, which may lead to a first-order QCD phase transition and associated gravitational-wave production in the early Universe.
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High Energy Astrophysical Phenomena

A statistical hardness classification of ultraluminous X-ray sources using long-term Swift/XRT monitoring

Sinan Allak, Wei Yu, Menglei Zhou et al. (+2 more)

We characterize long-term hardness behavior in 29 ultraluminous X-ray sources (ULXs) using over 3500 archival Swift/XRT observations. We classify observations as soft-band dominated, hard-band dominated, or uncertain from the hardness ratio (HR; 1.5–10/0.3–1.5 keV count rates) and its confidence bounds. We derive $f_{\rm soft}$ and $f_{\rm hard}$ and define the Crossing Index (CI) as the fraction of consecutive confidently classified observations on opposite sides of $HR=1$. We analyze these descriptors with rule-based classification and unsupervised hierarchical clustering. The rule-based analysis identifies eight soft-band-dominated, five hard-band-dominated, and 16 mixed-band systems; clustering yields a similar three-group structure. Known or candidate accretor types tend to occupy band-dominated groups, whereas unknown accretors are more common in the mixed-band group. All four sources with reported long-term X-ray modulation discussed in an orbital or super-orbital context are classified as mixed-band. The three-cluster solution is preferred in 25 of 29 leave-one-out trials, while bootstrap tests find the band-dominated groups more stable than the mixed-band group. As the classification uses observed count rates, the groups represent Swift/XRT signatures rather than intrinsic spectral states. Response-folding tests show that modeled HR depends on absorption column density and photon index. Bayesian reanalysis of a representative low-count source reduces CI from 56.3% to 38.5% while preserving its mixed-band classification. Random downsampling produces no systematic shift in CI; halving the observations changes median CI by at most $\sim10\%$ across four sources. Larger samples with independent absorption constraints can test links among these observational classes, accretor type, long-term periodic modulation, and other X-ray properties.
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All authors Sinan Allak, Wei Yu, Menglei Zhou, Honghui Liu, Andrea Santangelo

Astrophysics of Galaxies

SQuIGG$\vec{L}$E: Ubiquitous Cool Gas Outflows with Large Mass-Loading Factors in $z\sim0.7$ Post-starburst Galaxies

Yuanze Luo, Justin S. Spilker, David J. Setton et al. (+13 more)

While recent James Webb Space Telescope studies have highlighted cool gas outflows as an important mechanism for rapid quenching at $z\gtrsim2$, such space-based spectroscopic samples remain limited in size. In this work, we search for and characterize cool gas outflows traced by Fe II $\lambda\lambda$2586,2600 and Mg II $\lambda\lambda$2796,2803 absorption in post-starburst galaxies (PSBs) at $0.5<z<0.9$, which are accessible to ground-based spectroscopy. Utilizing the SQuIGG$\vec{L}$E survey containing over 1300 PSBs, we stack spectra in bins of stellar mass, (specific) star formation rate, burst mass, burst mass fraction, and time since quenching. We observe blueshifted line centroids indicative of outflows in all stacks except the one containing galaxies that quenched more than 260 Myr ago. Outflow velocities decline with increasing time since quenching, while showing little correlation with other galaxy properties. The inferred outflows have large mass loading factors of 1 – 120, maximum velocities above the interstellar medium escape velocities of their host galaxies, and energy and momentum fluxes exceeding those expected from the current star formation. Our results suggest that cool gas outflows are ubiquitous in intermediate-redshift PSBs and are likely relic outflows launched by previous starburst or AGN activity. These outflows have the potential to quench star formation by transporting gas into the galactic halos, consistent with outflows playing an important role in rapid quenching from intermediate to high redshift.
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All authors Yuanze Luo, Justin S. Spilker, David J. Setton, Timothy Heckman, Rachel Bezanson, Vincenzo R. D'Onofrio, Alex Geiger, Andy D. Goulding, Jenny E. Greene, Kate Rowlands, Katherine A. Suess, Elizabeth Taylor, Margaret E. Verrico, Andrew Weldon, Vivienne Wild, Pengpei Zhu

Astrophysics of Galaxies

SQuIGG$\vec{L}$E: Spatially resolved NIRSpec Pa$\alpha$ reveals that the most CO-luminous, $z\sim0.7$ post-starburst galaxies exhibit falling—but still active—star formation behind optically thick dust

David J. Setton, Jenny E. Greene, Rachel Bezanson et al. (+13 more)

One of the fundamental uncertainties in the study of galaxies at the interface between star formation and quiescence–post-starburst galaxies–is their instantaneous star formation rate. While these galaxies appear quiescent in the rest UV-optical, many of the youngest systems are highly CO luminous, implying dense molecular gas, and potentially star formation. However, their instantaneous star formation rates have proved elusive, as measurements with rest-optical emission lines or UV-to-IR SED fitting yield order-of-magnitude uncertainty. Here, we present JWST/NIRSpec G395M/170LP integral field spectroscopy of the three most CO-luminous massive galaxies in the SQuIGG$\vec{L}$E survey, spatially resolving Pa$\alpha$/Br$\gamma$/Br$\beta$ to map the dust-corrected star formation rate. We find that these galaxies host star formation rates of $27-80$ $M_\odot \ \mathrm{yr^{-1}}$, though $\sim30-40\%$ of the emission may arise from non-star-forming ionization (AGN or shocks), implied by high [FeII]/Pa$\alpha$ in central spaxels. We also find effective $A_{\mathrm{Pa}\alpha}\sim1$ and individual $\sim700$ pc spaxels with $A_{\mathrm{Pa\alpha}}\sim2$, implying significant dust obscuration of nebular regions that contribute little to the rest-optical lines. These galaxies are not consistent with total quiescence; the measured star formation rates place these galaxies on or above the main sequence. However, their star formation rates are significantly lower ($\sim0.5-1$ dex) than the peak star formation rates inferred from spectrophotometric fitting. We propose that the CO luminous post-starburst phase represents the last gasp of star formation in galaxies on the rapid quenching pathway, and that dust-obscured star formation, outflows, and (speculatively) an uncertain CO-to-H2 conversion reconcile their gas exhaustion with observed timescales of fading.
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All authors David J. Setton, Jenny E. Greene, Rachel Bezanson, Katherine A. Suess, Justin S. Spilker, Vincenzo R. D'Onofrio, Elia Cenci, Robert Feldmann, Alex J. Geiger, Andy D. Goulding, Mariska Kriek, Anika Kumar, Yuanze Luo, Desika Narayanan, Margaret E. Verrico, Pengpei Zhu

Astrophysics of Galaxies

A solution to the paradox of youth in the Galactic centre

Rodrigo P. Silva, Alexandre C. M. Correia, Tjarda C. N. Boekholt et al. (+1 more)

The supermassive black hole at the Galactic centre, Sgr A*, is surrounded by an S cluster of young stars. These stars are predominantly B-type stars, but their origin remains uncertain. Unlike massive stars in the Galactic field, which exhibit a binary fraction of about $70\%$, those in the S cluster show a significantly lower fraction. It is key to understand this discrepancy for constraining their formation. We show that the binary deficit arises naturally from dynamical interactions between stellar binaries and Sgr A* in an in situ formation scenario. Using K-amplitude data, we derived an observational binary fraction of $f_{\mathrm{obs}} = 0.43 \pm 0.09$ for the S-cluster stars. Our dynamical modelling predicts that interactions with Sgr A* cause $18\%$ of the binaries to merge, $20\%$ to be disrupted, and $62\%$ to survive, yielding a theoretical binary fraction of $f_{\mathrm{theo}} = 0.38 \pm 0.10$. The predicted binary fraction with distance from Sgr A* is also consistent with independent observational constraints. These results show that the decline in binarity towards the Galactic centre is driven by stronger tidal forces, and they support an in situ origin of the S cluster in the same event that produced the Fermi bubbles.
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All authors Rodrigo P. Silva, Alexandre C. M. Correia, Tjarda C. N. Boekholt, Paulo J. V. Garcia

Astrophysics of Galaxies

H2 emission in the Orion Bar, NGC7023 and the Horsehead Nebula observed with the James Webb Space Telescope

M. Zannese, A. Sidhu, A. Guerras et al. (+25 more)

Molecular hydrogen (H2), the most abundant molecule in the interstellar medium, is a handy tool to study Photodissociation Regions. The JWST, with its high spatial resolution, sensitivity, and wavelength coverage, provides unique access to the detection and spatial morphology of the H2 rotational and rovibrational lines. Our goal is to analyze H2 line emission detected with JWST in several PDRs (the Orion Bar, NGC7023, and the Horsehead Nebula) to constrain the physical structure of dissociation front, and compare the impact of the ultraviolet field and the gas density across different regions. The analysis of H2 spatial morphology reveals similar filamentary structures across all regions. Spatial shifts between H2 lines (0.5") are observed and linked to differences in excitation mechanisms (thermalized vs FUV-pumped lines) and the temperature gradient. Despite differences in incident irradiation conditions, analysis of H2 rotational excitation yields high gas temperatures that are similar across the three PDRs. This is expected for a certain regime of excited PDRs (such as Orion and NGC7023), where the G0 at the DFs and the density are similar. However, it is surprising for less excited PDRs like the Horsehead Nebula. OPRs in the rotational and rovibrational levels differ across the three PDRs. We also used H2 rovibrational lines and the 0-0 S(3) line to estimate the visual extinction across the field of view, yielding markedly different results that constrain both the geometry and the grain composition. Due to the complex 3D geometry, H2 emission is observed throughout the FOV and is dominated by the thin UV illuminated layer, making H2 an unreliable tracer of gas temperature in deeper and coolers molecular layers of the PDR. Therefore, H2 emission is not sufficient to trace the possible temperature and density gradient across PDRs and must therefore be associated with other tracers.
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All authors M. Zannese, A. Sidhu, A. Guerras, M. Pound, M. Wolfire, A. G. G. M. Tielens, E. Peeters, E. Habart, A. Abergel, M. Baes, O. Berné, C. Boersma, E. Bron, J. Cami, R. Chown, E. Dartois, P. Dell'Ova, J. R. Goicoechea, K. D. Gordon, P. Guillard, O. Kannavou, K. Misselt, N. Monnier, A. Noriega-Crespo, T. Onaka, D. Van de Putte, L. Verstraete, A. N. Witt

Instrumentation and Methods for Astrophysics

MATISSE-py: a high-level Python interface for efficient, automated VLTI/MATISSE data reduction

A. Soulain, A. Matter, P. Berio et al. (+4 more)

The Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) at the Very Large Telescope Interferometer (VLTI) delivers rich mid-infrared interferometric datasets that are reduced through a robust, multi-stage ESO pipeline. In its native form, however, the reduction relies on command-line calls to esorex, hand-edited set-of-files (SOF) and configuration files, and manual iterations that are difficult to automate, reproduce, or integrate into modern Python workflows. We present MATISSE-py, a modular Python interface that wraps the official ESO esorex recipes behind a single, user-friendly matisse command. It automates discovery, reduction, calibration, and inspection of the data, and ships as a tested, open-source package built on industry-standard practices. Beyond convenience, MATISSE-py introduces science-grade improvements developed over seven years of MATISSE operations: visibility- and photometry-factor (V-factor and P-factor) corrections derived from the GRAVITY fringe tracker to mitigate residual visibility losses, per-baseline data filtering, beam-commuting-device (BCD) "magic-number" corrections, and an absolute spectrophotometric flux calibration using state-of-the-art reference spectra. On faint targets observed under degraded conditions, the V-factor correction recovers up to a few percent of lost visibility and reduces the statistical uncertainties by nearly 20%, while yielding calibrator diameters that are consistent across BCD modes. MATISSE-py thus consolidates the consortium's expertise into a maintainable package and shortens the reduction-to-science loop for the community.
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All authors A. Soulain, A. Matter, P. Berio, F. Millour, B. Lopez, R. Petrov, S. Lagarde

Earth and Planetary Astrophysics

N-Body Dynamics as a Mechanism for Mean Motion Resonance Formation in the Post-Gas Era

Kai Sun, Sheng Jin, Dong-Hong Wu et al. (+1 more)

Mean motion resonances (MMRs) are traditionally thought to form during the gas-rich phase of protoplanetary disks via disk-driven migration. Whether MMRs can form solely through collisional damping after disk dispersal has not been systematically investigated. To study MMR formation in the post-gas-disk era, we perform a large suite of N-body simulations, each containing 10,000 planetesimals around an M-dwarf star and evolving over 10 Myr. We compare two groups of simulations that differ only in their initial mass distributions. Each group consists of 10 runs with statistically identical initial planetesimal orbital distributions, generated using different random seeds. One group adopts a uniform planetesimal mass distribution, whereas the other features a bimodal distribution with massive embryos embedded in a swarm of smaller planetesimals. At 1 Myr, 40% of systems (8/20) exhibit near-resonant period ratios, but this fraction drops to 25% (5/20) by 10 Myr as higher-order commensurabilities dissolve. Resonant-angle tracking shows that all persistent systems have circulating resonant angles at 10 Myr, although one system undergoes a transient libration phase between about 2 and 7 Myr before returning to circulation. These results demonstrate that collisional merging can drive MMR formation even without a gas disk, although in this scenario near-resonant configurations are strongly favored over true resonances. Furthermore, this mechanism produces similar MMR fractions in both groups, suggesting that MMR formation is insensitive to the initial mass distribution, although the latter may modulate the formation pathway to a limited extent.
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All authors Kai Sun, Sheng Jin, Dong-Hong Wu, Meijuan Wang

Earth and Planetary Astrophysics · Cross-listed from physics.geo-ph

From Image Morphology to Multiphysics Earth Posteriors

Ziye Yu, Xin Liu and Yuqi Cai

Structural learning and physical-property inference can draw on different sources of knowledge. We learn morphology from 33,140 natural, satellite, and texture images, without geological training models, then infer Earth properties from physical observations. Identical frozen weights map 128 coordinates into each $256\times256$ compressional-velocity, shear-velocity, or density field. Fixed adapters assign physical meaning; observation-specific likelihoods determine new posteriors without retraining. Across 256 unseen Earth models, image coordinates reduce projection error fourfold relative to a dimension-matched cosine basis. Matched inversions favor image coordinates for the tested curved-velocity targets and a smooth radial basis for the tested faulted targets. A simplified 2.5-dimensional application with 915 measured observations along one 120.9-km southern-California profile constrains a velocity–density contrast. Grouped arrival-time and gravity errors fall by 43% and 44% relative to the pretrained image prior, although the matched smooth radial basis predicts better. Direct layered-Rayleigh updating reduces blind phase-velocity error by 28% at five sites, whereas P-and-gravity-only sharing worsens it, distinguishing reusable morphology from beneficial cross-property coupling. These results establish a practical separation: images supply structural alternatives, and heterogeneous physical observations determine their experiment-specific posterior probabilities.
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Astrophysics of Galaxies

ATLASGAL: The HCN-IR Star Formation Relation for the Milky Way

I. I. Grozdanova, J. S. Urquhart, W.-J. Kim et al. (+8 more)

We examine the relation between star formation and dense gas, traced by HCN(1-0), using a sample of 343 Galactic clumps spanning the full range of evolutionary stages representative of high-mass and cluster formation, including quiescent, protostellar, young stellar object (YSO), and HII regions. Earlier Galactic studies, based primarily on luminous HII regions, reported a linear correlation between infrared (IR) and HCN luminosities, consistent with extragalactic surveys, and interpreted it as a universal star formation law. Our larger evolutionary sample yields a significantly steeper slope of $1.80\pm0.08$, inconsistent with extragalactic trends. However, we find that each of the star-forming evolutionary stages individually has a shallower slope ($\sim$1.2) than that of the full sample, with quiescent clumps showing no correlation. We estimate the Milky Way's total IR and HCN luminosities from dense clumps by integrating the bolometric luminosities and clump masses of Hi-GAL sources. Both fall significantly below extragalactic values, demonstrating that clumps alone cannot account for the IR-HCN relation. Only $\sim$5-25 per cent of Galactic HCN luminosity arises from dense clumps, implying that most extragalactic HCN traces gas that is not involved in star formation. Additionally, dense clumps contribute only $\sim$2-3 per cent of the Milky Way's IR luminosity, which is dominated instead by extended HII regions and PDRs tracing longer star formation timescales. As a result, the observed linear relation in nearby galaxies reflects a nearly constant star formation efficiency averaged over large areas and long timescales, rather than a direct link between SFR and dense gas mass.
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All authors I. I. Grozdanova, J. S. Urquhart, W.-J. Kim, F. Wyrowski, T. Csengeri, A. Karska, A. Giannetti, D. Colombo, D. Eden, M. A. Thompson, T. J. T. Moore

Earth and Planetary Astrophysics

JWST detection of methane emission from a young brown dwarf

K. L. Luhman, C. Alves de Oliveira, J. K. Faherty et al. (+1 more)

In recent studies, we have used low-resolution spectroscopy (R~100) with the James Webb Space Telescope (JWST) to uncover low-mass brown dwarfs (2-10 MJup) in the young cluster IC 348 that exhibit the so-called 3.4um absorption band from aliphatic hydrocarbons. Atmospheric models have not predicted the presence of that band in brown dwarfs at any age. Instead, methane absorption was expected in the coolest newborn brown dwarfs, but it was not detected. We have performed JWST spectroscopy at higher resolution (R~1000) on one of the brown dwarfs in IC 348, LRL 11001 (~6 MJup). The new measurement of the 3.4um band is fit well with four Gaussians that represent the CH stretching modes of CH2 and CH3 groups, indicating that the carrier is a large alkane (CnH2n+2). In addition, the spectrum contains emission lines at 3.324 and 3.333um, which we attribute to Q branches of CH4 hot bands between the octad and dyad regions (primarily nu3+nu4->nu4) and the tetradecad and pentad regions. This is the first detection of 3.33um CH4 emission from a young brown dwarf. The emission probably arises from the photosphere rather than a circumstellar disk given that no disks around stars or brown dwarfs are known to exhibit emission in these transitions. Modeling of the emission is needed to constrain the excitation mechanism, which could be either thermal (e.g., an accretion shock) or pumping by external radiation (e.g., neighboring cluster members). We speculate that vertical mixing has suppressed CH4 and enhanced large alkanes in the photosphere, but CH4 survives in the upper atmosphere, where it is available to experience the observed emission.
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All authors K. L. Luhman, C. Alves de Oliveira, J. K. Faherty, B. C. Smith

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Architecture Acceleration of Machine Learning Gravitational Waveform Surrogate Models

Adriano Frattale Mascioli, Lorenzo Piccari, Saulo Albuquerque et al. (+9 more)

Accurate and computationally efficient waveform models of compact binary coalescences are a fundamental requirement for gravitational wave data analysis. This work presents differentiable and hardware-accelerated implementations of the machine-learning surrogate models mlgw and mlgw-bns within the JAX ecosystem. The proposed framework enables JIT compilation, vector paralellization, native GPU acceleration, and automatic differentiation, while preserving the original surrogate training infrastructure and its applicability to arbitrary non-precessing waveform approximants. Benchmarks are performed in the binary black hole case with a newly trained surrogate of the SEOBNRv5HM approximant; on CPU, they show speed-ups in waveform evaluation time with respect to the original mlgw implementation that exceed one order of magnitude; further, when exploiting GPU acceleration and large-batch vectorization these reach approximately two orders of magnitude. The benchmarks performed in the case of binary neutron stars with a TEOBResumSPA surrogate model achieve similar gains on GPU. Our JAX-based surrogate modeling framework can be integrated into Bayesian parameter estimation pipelines through GWgpu-jax, an open-source package that connects JAX-compatible gravitational waveform generators to JAX-native sampling algorithms. We demonstrate this capability with a nested-sampling pipeline built upon BlackJax-NS, performing parameter estimation analyses of the GW150914 and GW170817 events with mlgw and mlgw-bns. The analyses require approximately twelve and seventeen minutes, respectively, on a single GPU and yield posterior distributions consistent with those reported by the LIGO-Virgo-KAGRA Collaboration. Beyond nested sampling, JAX automatic differentiation provides efficient gradient and Hessian evaluations of the waveform models, enabling integration with gradient-based Bayesian inference methods.
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All authors Adriano Frattale Mascioli, Lorenzo Piccari, Saulo Albuquerque, Gabriele Demasi, Giulia Capurri, Massimo Lenti, Angelo Ricciardone, Barbara Patricelli, Gianluca M. Guidi, Giulia Stratta, Walter Del Pozzo, Francesco Pannarale