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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 24 April

Astrophysics of Galaxies

Spatially resolved metallicity and ionization in the merging system Gz9p3 at z=9.3

Arjan Bik, Javier Álvarez-Márquez, Alejandro Crespo Gómez et al. (+26 more)

Studying the interstellar medium (ISM) in merging high-redshift galaxies is crucial for understanding early galaxy assembly, star formation, and black hole growth, predicted by hierarchical $\Lambda$CDM models. Deep imaging and spatially resolved spectroscopy with JWST enable unprecedented insight into these processes, even for galaxies in the Epoch of Reionization. We present NIRSpec and MIRI integral field spectroscopy and MIRI imaging of the merging galaxy Gz9p3 at z=9.3 of the UV and optical rest-frame showing a clumpy morphology in the continuum as well as line emission covering the entire galaxy over a range of 5 kpc from the central clump to the tail region. We analyze the integrated spectrum as well as different apertures in the galaxy allowing a spatially resolved characterization of the ionized ISM of this galaxy. We compare our measurements with archival NIRCam imaging and ALMA data. We measure a total star formation rate of 13.4 $\pm$ 1.8 Msun yr$^{-1}$, a metallicity of 12+log(O/H) = 7.84 $\pm$ 0.05 and $\xi_{ion}$= 25.4 $\pm$ 0.1 erg$^{-1}$ Hz and a burstiness parameter of 0.9 $\pm$ 0.1 for the integrated spectrum. We find large spatial differences in these parameters between the central clump and the tail region. The optical [OIII] emission peaks in the main galaxy, the far-infrared [OIII] emission peaks towards the tail, indicating different physical conditions in the ISM of the tail and main galaxy. This study presents the spatially resolved ISM analyses of a galaxy at z>9, revealing nebular line emission and strong spatial variations in star formation, metallicity, physical conditions, and ionizing efficiency. The results indicate a recent, metal-poor starburst in a tail alongside a more evolved, enriched central clump with evidence for extreme excitation. This demonstrates the power of spatially resolved JWST spectroscopy of galaxies in the Epoch of Reionization.
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All authors Arjan Bik, Javier Álvarez-Márquez, Alejandro Crespo Gómez, Luis Colina, Pablo G. Pérez-González, Göran Östlin, Carmen Blanco Prieto, Jens Melinder, Danial Langeroodi, Gillian Wright, Hiddo S. B. Algera, Leindert A. Boogaard, Karina Caputi, Steven Gillman, Thomas Greve, Jens Hjorth, Edoardo Iani, Sarah Kendrew, Alvaro Labiano Ortega, Michele Perna, Carlota Prieto Jimenez, John Pye, Pierluigi Rinaldi, Paul van der Werf, Fabian Walter, Florian Peißker, Andreas Eckart, Thomas Henning, Manuel Güdel

High Energy Astrophysical Phenomena

How lonely are the Binary Compact Objects Detected by the LIGO-Virgo-KAGRA Collaboration?

Devesh Giri and Suvodip Mukherjee

Gravitational-wave (GW) observations of compact binary coalescences (CBCs) are traditionally interpreted under the assumption that the binary evolves in isolation. However, in realistic astrophysical environments, brief three-body encounters may perturb the binary's orbital evolution and imprint deviations on the emitted GWs. We develop a physically motivated model for such interactions, retaining Newtonian three-body dynamics supplemented by leading-order ($2.5$PN) radiation-reaction within the binary. We show that such encounters produce a distinctive morphology of dephasing and amplitude modulation in GWs. We search for this kind of distortion from the LIGO–Virgo–KAGRA (LVK) GW catalog GWTC-4 on three events: GW170817, GW190814, and GW230627\_015337, chosen based on high SNR and in-band duration $\gtrsim 10~\mathrm{s}$. We find no statistically significant deviation in the data, which translates into constraints on the absence of any intermediate-mass black hole in the mass range above $\sim 10^2$ M$_\odot$ in the vicinity of these binaries of radius approximately $10^{-1}~\mathrm{AU}$. This arises from robust exclusions arising from fly-by interactions that would dynamically disrupt the binary and are directly ruled out independent of waveform modelling, placing the first upper bound on intermediate-mass black holes near these GW events. In future, with the availability of long-duration GW signals, this new avenue can probe encounters of the binary GW sources with compact objects of lighter masses at distances farther away than 1 AU and hence opens a new window to probe the population of individual compact objects of both astrophysical and primordial origin in astrophysical systems of dense environments ranging from galactic centers to dense globular clusters.
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Astrophysics of Galaxies

Quiescent fractions in high-redshift galaxy groups reflect their hot-or-cold state of gas accretion

Guillaume Elias, Emanuele Daddi, Chiara D'Eugenio et al. (+15 more)

Cold accretion and quenching are closely related aspects of galaxy evolution, as sustained gas supply is required to maintain star formation. High-redshift galaxy groups therefore provide a valuable laboratory for testing how the thermal state of accreting gas relates to the emergence of quiescence. We measure quiescent fractions in a sample of 16 spectroscopically confirmed galaxy groups at $1.6<z<3.6$, spanning halo masses from $10^{12.8},{\rm M_\odot}$ to $10^{13.9},{\rm M_\odot}$, by fitting the SEDs of candidate member galaxies selected from the COSMOS2020 catalog and using a membership-probability approach to estimate group quiescent fractions. We compare these quiescent fractions to the expected cold or hot accretion state of each halo and find evidence for a correlation: quiescent fractions reach about 50 percent in groups in the hot-accretion regime and are consistent with zero in groups in the cold-accretion regime. In mature hot-accreting groups, massive quiescent galaxies are preferentially found in the inner regions ($R<0.5R_{\rm vir}$), with a 4.4-sigma excess relative to the outskirts. Most groups lack a clearly established brightest group galaxy and instead show small stellar-mass gaps, typically $M_{*,1}/M_{*,2}<3$, indicating that they remain in an active assembly phase rather than being dynamically evolved systems. Consistently, the stellar-mass excess of the dominant galaxy, measured relative to the SHMR expectation, does not predict the group quiescent fraction. Taken together, our results support a picture in which the cold-to-hot transition in gas accretion contributes to the onset of quiescence, possibly through inside-out starvation associated with filament disruption in shock-heated intra-group gas, and suggest that environment plays a greater role than internal processes in shaping the quiescent galaxy population in these structures.
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All authors Guillaume Elias, Emanuele Daddi, Chiara D'Eugenio, David Elbaz, Maximilien Franco, Fabrizio Gentile, Raphael Gobat, Sicen Guo, Shuowen Jin, Clotilde Laigle, Shiying Lu, Georgios E. Magdis, Benjamin Magnelli, Nikolaj B. Sillassen, Veronica Strazzullo, Maxime Tarrasse, Tao Wang, Luwenjia Zhou

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Simulation-based Inference for Gravitational Waves from Binary Neutron Stars: Application of Summary Data from Heterodyning

Masaki Iwaya, Vivien Raymond, Soichiro Morisaki et al. (+1 more)

Gravitational-wave parameter estimation for binary neutron star (BNS) systems poses severe computational challenges due to the extended signal duration, which can reach several minutes in current detectors. Neural posterior estimation (NPE), a simulation-based inference approach, offers dramatic speedups but requires effective dimensionality reduction of the high-dimensional input data. We present a novel compression strategy based on likelihood-oriented summary statistics derived from the relative binning formalism of Zackay et al. (2018), which compresses raw frequency-domain data into the summary data. The summary data is based on a polynomial approximation of the waveform ratio using frequency banding grounded in post-Newtonian approximation, and directly evaluated with only $O(1000)$ sample points of the waveform. As a result, both the training and storage cost become more efficient than previously reported networks for BNS inference. We train a set of NPE networks on these summary statistics and validate a network against traditional nested sampling over 1024 BNS injections. The network produces well-calibrated posteriors across all source parameters we consider, with Jensen-Shannon divergences (JSD) consistent with numerical noise for most parameters. Although we find that the median JSD for the most inconsistent parameter exceeds $10^{-2}$ bits with current configurations, our results show potential for rapid parameter estimation of the BNS signal.
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All authors Masaki Iwaya, Vivien Raymond, Soichiro Morisaki, Kazuki Takada

Cosmology and Nongalactic Astrophysics

Testing $\Lambda$CDM with ANN-Reconstructed Expansion History from Cosmic Chronometers

Yuki Hashimoto, Kazuharu Bamba and Sanjay Mandal

In modern cosmology, the rapid growth of high-precision observational data, along with significant theoretical advances, has intensified the challenge of identifying a robust, model-independent framework to probe the expansion history of the Universe. In this work, we propose a novel artificial neural network (ANN)-based framework for the non-parametric reconstruction of the late-time cosmic expansion. The framework is trained and validated through a three-stage screening pipeline prior to its application to real observational data. As a demonstration of its effectiveness, we reconstruct the Hubble parameter $H(z)$ using the latest cosmic chronometer measurements. Our results show that the reconstructed expansion history aligns with the predictions of the $\Lambda$CDM model within observational uncertainties, thereby supporting the robustness and reliability of the proposed approach.
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Astrophysics of Galaxies

A study of the spatial evolution of the Radcliffe wave in a sample of young open star clusters

Vadim V. Bobylev, Anisa T. Bajkova and Nazar R. Ikhsanov

A sample of 139 young open star clusters closely associated with the Radcliffe wave is considered. Modeling their spatial distribution and kinematics over a time interval of 30 Myrs ago and 30 Myrs into the future revealed that they exhibit the main properties characteristic of a Radcliffe wave over the past 10-15 Myr. They are distributed on the galactic XY plane as a long and narrow chain inclined to the Y axis, and exhibit a wave-like behavior of their vertical coordinates up to 15 Myr in the past. This behavior of their vertical coordinates will persist over the interval of 15-20 Myr in the future. A new finding is the presence of vertical perturbations with an amplitude of deviation from the galactic symmetry plane of up to 200 pc over the entire time interval considered in the past, up to -30 Myr. This result calls into question the possibility of using a scenario in which the initial disturbance of the interstellar medium is assumed to be the Parker instability of the galactic magnetic field.
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Instrumentation and Methods for Astrophysics

Thermal background reduction for mid-infrared imaging by low-rank background and sparse point-source modelling

R.A.R. Moens, A.G.M. Pietrow, B. Brandl et al. (+1 more)

Mid-infrared astronomy from the ground faces critical challenges in accurately detecting and quantifying sources due to the dominant spatially and time-variable background noise. Moreover, chopping and nodding, the traditional methods for dealing with these background issues, will not be technically feasible on the next generation of extremely large telescopes. This limitation requires the development of novel computational methods for a robust background reduction. We present and evaluate a novel method named LOw-RAnk Background ELimination (LORABEL) to improve the sensitivity of mid-infrared astronomical observations, without the need for classical telescope nodding, source masking, or other overheads in observing time. We applied a low-rank background-reduction strategy to (1) data taken on the ground with the VISIR with synthetically injected sources, and (2) airborne data from SOFIA. We compared the performance of our new method to classical chopping and nodding techniques, and analysed the effect on source photometry and detection precision for different observational scenarios. In regimes with a low signal-to-noise ratio (S/N $<5$) in the ground-based VISIR data, LORABEL reduces variation in the photometric error with respect to chopping differences alone and even the classical chop-nod sequence, at the cost of introducing a bias. Secondly, we demonstrate that LORABEL increases detection precision in comparison to traditional background-reduction methods. For the SOFIA dataset, we achieve a $20-100$ fold decrease in mean background flux with respect to the traditional chop-nod method while preserving most of the source flux. Our findings suggest that LORABEL is applicable to a wider range of instrumental observation, that is, both ground-based and airborne, and it is a suitable tool in the context of faint-source detection.
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All authors R.A.R. Moens, A.G.M. Pietrow, B. Brandl, R. Van de Plas

Astrophysics of Galaxies

A Morphological Identification and Study of Radio Galaxies from LoTSS DR2. I. The "Winged” Radio Galaxies

Soumen Kumar Bera, Taotao Fang, Tapan K. Sasmal et al. (+3 more)

We conducted an extensive identification and analysis of various morphological classes and subclasses of radio galaxies using the latest high-resolution data from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS DR2). This paper presents the first results of our large-scale investigation: a new catalog of “winged" radio galaxies (WRGs). These objects represent a fascinating class of irregular radio galaxies, characterized by a pair of secondary radio lobes (“wings") in addition to the primary active lobes. We identified and cataloged 621 new WRGs and 403 additional candidates. Among the confirmed winged sources, 382 are classified as “X"-shaped radio galaxies (XRGs), while the remaining 239 are “Z"-shaped radio galaxies (ZRGs). We also estimated several basic parameters for these winged sources and performed a Fanaroff-Riley (FR) classification. Our results show that the majority of the sources ($\sim$88%) exhibit edge-brightened radio lobes and high average radio power ($\rm log_{10}[P_{144MHz} / W Hz^{-1}]$ = 26.25), consistent with an FR-II classification. The average spectral index between 144 MHz and 1.4 GHz is –0.84, which is steeper than that found for previously identified winged sources based on higher-frequency data from the VLA Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. This indicates that our study is capable of detecting fainter sources. The median linear size of the winged sources, 498 kpc, confirms that these are large-scale structures, with approximately 16% having sizes exceeding 0.7 Mpc, making them potential candidates for giant radio galaxies.
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All authors Soumen Kumar Bera, Taotao Fang, Tapan K. Sasmal, M. Kunert-Bajraszewska, Xuelei Chen, Soumen Mondal

Instrumentation and Methods for Astrophysics

The Leiden/ESA Astrophysics Program for Summer Students (LEAPS)

S. Bellotti, A. D. Sellek, P. Sharda et al. (+3 more)

International student mobility plays a critical role in shaping future research careers, particularly in highly globalized fields such as astrophysics. The Leiden/ESA Astrophysics Program for Summer Students (LEAPS) offers a 10-week, fully funded research program at Leiden Observatory and the European Space Agency's ESTEC centre for undergraduate and master's students. Designed to foster early research involvement, LEAPS supports students from diverse academic and cultural backgrounds. Since its inception in 2013, LEAPS has hosted 194 students from over 40 countries. Data collected for 165 participants reveal that over 50% have progressed to Ph.D. studies, with some members of earlier cohorts already securing competitive international fellowships in astronomy. LEAPS participants have collectively contributed to at least 25 peer-reviewed publications and 13 international conference presentations. LEAPS has contributed successfully in preparing undergraduates for research careers in astrophysics through hands-on experience, mentorship, and scientific exposure. By addressing barriers related to financial means and promoting diversity, the program not only enhances individual career trajectories but also contributes to the broader goal of inclusive academic mobility. Continued efforts are needed to further increase global representation and assess long-term impacts on participants' scientific careers.
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All authors S. Bellotti, A. D. Sellek, P. Sharda, K. M. Dutkowska, A. Chrimes, H. Röttgering

High Energy Astrophysical Phenomena

Signature of iron line profile from a Kerr-like wormhole

Cheng Liu, Hoongwah Siew, Hong-Xuan Jiang et al. (+2 more)

Broad, skewed iron K$\alpha$ emission lines in the X-ray spectra of accreting black holes encode key information about the spacetime geometry of the innermost disk. While the Kerr metric is standard for spin measurements, horizonless alternatives like traversable "Kerr-like" wormholes can mimic many black hole signatures, challenging current data interpretations. We develop a relativistic reflection framework incorporating Kerr-like wormhole geometries to predict iron line distortions and assess the feasibility of distinguishing event horizons from wormhole throats.Using a custom ray-tracing subroutine, we implement two XSPEC modules: kwline for $\delta$-function profiles and kwconv for full reflection spectra, parameterized by spin, throat radius, and shape-function coefficients. We compute a dense grid of line profiles and generate synthetic NuSTAR spectra with realistic response matrices. By fitting these simulations with canonical Kerr models, we quantify deviations attributable to wormhole geometries.We find that Kerr-like wormholes produce narrower Fe K$\alpha$ lines with suppressed red wings as the throat parameter $\lambda$ increases. In 50 ks NuSTAR simulations ($\lambda=0.9, a_*=0.998$), simple convolutional models (kerrconv) can mimic the wormhole spectrum. However, self-consistent models like relxillCp result in statistical failure, yielding structured residuals and unphysical parameter pegging (e.g., emissivity $q_{\rm in} \to 10$). We conclude that large-throat wormholes are detectable in high-quality X-ray spectra if analyzed with fully consistent reflection models rather than post-processing approximations.
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All authors Cheng Liu, Hoongwah Siew, Hong-Xuan Jiang, Yosuke Mizuno, Tao Zhu

Solar and Stellar Astrophysics

Quiescent and flaring states of three active stars: V834 Tau, LQ Hya, and BY Dra

Gurpreet Singh, Jeewan C. Pandey and Subhajeet Karmakar

We present a detailed X-ray study of the quiescent and flaring coronae of three active main-sequence K-type stars, V834 Tau, LQ Hya, and BY Dra, using XMM-Newton observations. The quiescent coronae are well described by two-temperature thermal plasma models, with cool and hot components at 0.26-0.30 keV and 0.93-1.01 keV, respectively. Despite similar coronal temperatures, X-ray luminosities (10$^{29.18\mbox{--}29.75}$ erg s$^{-1}$) and overall abundances, the relative emission measures of the cool and hot components differ among the stars. High-resolution spectroscopy reveals significant iron depletion by factors of 5-10 relative to photospheric values, and an inverse first-ionisation-potential effect in all three stellar coronae. Six energetic flares are detected, with peak temperatures of 30 – 133 MK and released energies of $0.6\mbox{--}4.2\times$10$^ {33}$ erg, classifying them as superflares. Most flares exhibit decay times roughly twice their rise times, although one event shows a decay phase nearly twenty times longer than its rise. Time-resolved spectroscopy and loop scaling laws yield flare parameters consistent with previous studies of active stars. LQ Hya displays recurrent superflares at the same rotational phase across observations separated by six months, suggesting a long-lived, complex magnetic field structure. These results provide insights into the magnetic activity and flare energetics in active stars, and their implications for stellar and exoplanetary environments.
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Solar and Stellar Astrophysics

Non-LTE corrections for determinations of europium abundances in F-G-K stars in a broad metallicity range

L. I. Mashonkina and S. A. Yakovleva

Europium plays a key role in studies of nucleosynthesis in the rapid (r-) process of neutron capture nuclear reactions and the evolution of the r-process element abundances in galaxies. We refine the method for analyzing the Eu~II lines in stellar spectra by updating the Eu~II model atom with recent data on the rate coefficients for inelastic processes in the Eu II + H I collisions. The method was tested by deriving abundances from the Eu~II 4129 A and 6645 A lines in the Sun and five reference stars with well determined atmospheric parameters and high-resolution spectra available. It was shown that abandoning the local thermodynamic equilibrium (LTE) assumption allows the abundances from the two lines to be matched within the error bars, while the difference in the LTE abundances amounts to -0.09 dex for the Sun and -0.07 dex to -0.18 dex for the metal-poor stars. Accounting for the departures from LTE (non-LTE effects) for Eu~II leads to reducing the statistical errors of the derived stellar Eu abundances. The non-LTE abundance corrections for 11 lines of Eu~II were calculated for a grid of the plane-parallel MARCS model atmospheres with effective temperatures, surface gravities, and metallicities relevant to F-G-K type stars. They are publicly available and can be applied for improving stellar Eu abundances in studies of the galactic chemical evolution.
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Solar and Stellar Astrophysics

Asteroseismic rotation rates of hot subdwarf B stars hint at transient accretion from leftover common envelope matter

Facundo D. Moyano, Hongwei Ge, Zhanwen Han et al. (+6 more)

Asteroseismology enabled measuring the rotation rate in the deep stellar interiors of stars across several evolutionary phases, advancing the theory of angular momentum transport in single stars from the main sequence to the white dwarf phase. However, binary stellar evolution products have not yet been studied in the context of angular momentum transport constrained by asteroseismology. Hot subdwarf B (sdB) stars can pulsate in non-radial modes, enabling probing of their internal rotation. Those in binary systems form through mass transfer, thus they can be used to probe theories of internal rotation in post-mass transfer stars. Here, we interpret observed asteroseismic core and envelope rotation rates of sdB stars in unsynchronised binary systems that formed through the common-envelope channel, using stellar evolution models of rotating sdB stars with internal magnetic fields. We find that when sdB stars form with the angular momentum content of red giant cores prior to common-envelope ejection, their predicted core rotation rates are two to ten times lower than measured asteroseismic rotation rates, and their envelope rotation rates are lower by two to five orders of magnitude. This suggests that the angular momentum content of sdB stars increases during their formation. Since sdB stars in close binary systems may host circumstellar matter from a past common-envelope ejection, we show that if they accrete a small amount of matter, the combination of internal magnetic fields with angular momentum transfer through accretion spins up both the core and envelope to match their measured asteroseismic rotation rates.
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All authors Facundo D. Moyano, Hongwei Ge, Zhanwen Han, Beatriz Bordadágua, Murat Uzundag, Philipp Podsiadlowski, Veronika Schaffenroth, Xuefei Chen, Zhengwei Liu

Solar and Stellar Astrophysics

The circumstellar environment of the young, low-mass dipper star JH 223. Accretion and large-scale magnetic field topology

T. P. Freitas, J. Bouvier, B. Zaire et al. (+11 more)

Studies of magnetospheric accretion and magnetic field topology in T Tauri stars have advanced over the years, but their applications to fully convective, very-low-mass T Tauri stars remain relatively unexplored. We aim to analyze the circumstellar environment of the very-low-mass dipper-like star JH 223 by investigating the accretion process and characterizing its large-scale magnetic field topology. We analyzed the photometric variability of JH 223 using observations from multiple telescopes, including K2, TESS, and LCOGT. Additionally, we used Gemini/GRACES spectroscopic and CFHT/SPIRou spectropolarimetric data to investigate the star-disk interaction and characterize the large-scale stellar magnetic field using Zeeman-Doppler imaging. JH 223 is a fully convective classical T Tauri star with an age of about 3 Myr and a mass of 0.4 M$_{\odot}$. The large-scale surface magnetic field is predominantly poloidal, with a 250 G dipolar component. The dipole field strength and mass accretion rate indicate that the disk truncation radius is near the corotation radius. The star-disk interaction, combined with the inclined dipole, generates accretion columns that warp the inner disk. As the star rotates, this warp periodically obscures the stellar surface every 3.31 days, producing dipper light curves. The same period is also detected in radial velocity and longitudinal magnetic field variability. The accretion columns, traced by redshifted absorption in H$\alpha$ and He I 1083 nm, are associated with the inner disk warp at the same rotational phase. The accretion process in JH 223 is dynamic, transitioning from an unstable to a stable regime over a few weeks, consistent with magnetohydrodynamic simulations of star-disk interaction. Results from multi-technique observations suggest that the magnetospheric accretion model remains valid for fully convective very-low-mass young stars.
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All authors T. P. Freitas, J. Bouvier, B. Zaire, S. H. P. Alencar, A. P. Sousa, L. Rebull, A. Bayo, A. Frasca, J. Alonso-Santiago, K. Grankin, C. Contreras Peña, A. M. Cody, L. A. Hillenbrand, A. Carmona

Cosmology and Nongalactic Astrophysics

Caustic Skeleton and the Local Cosmic Web: the Coma Cluster node and the Pisces-Perseus ridge

Amelie Read, Job Feldbrugge, Celine Boehm et al. (+2 more)

We apply caustic skeleton theory to the Manticore-Local simulations, which are Bayesian constrained reconstructions of the Local Universe from the 2M++ galaxy catalogue, and extract the three-dimensional multi-scale caustic skeleton of two canonical weblike structures in our Local Universe, namely the Coma Cluster and the Pisces-Perseus ridge as they represent the most prominent cluster node and filamentary artery in the nearby Universe. We show that the Caustic Skeleton network of caustic singularities accurately reproduces the observed large-scale organisation of galaxies in redshift space for one of the Manticore realisations. The hierarchy of caustic features allows us to establish a multi-scale classification of the large-scale environment in which observed 2M++ galaxies reside. One of the most interesting aspects of the theory is that it predicts two topologically distinct classes of filaments (A_4 swallowtail and D_4 umbilic caustics) that form through fundamentally different folding histories yet appear morphologically similar enough, on the surface, to be overlooked by conventional structure identifiers. We find that the influence of D_4 filaments only becomes increasingly relevant towards smaller scales, and the Pisces-Perseus Supercluster in particular is revealed to be a distinctly D_4-dominated structure compared to the extended Stickman structure around the Coma Cluster. In other words, caustic skeleton theory enables a novel topological characterisation of one of the most studied filamentary complexes in the nearby Universe. [Shortened]
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All authors Amelie Read, Job Feldbrugge, Celine Boehm, Rien van de Weygaert, Benjamin Hertzsch

Astrophysics of Galaxies

Joint State-and-Dynamics Inference for Galaxy Population Evolution on an Effective Manifold

Tsutomu T. Takeuchi and Ryusei R. Kano

Galaxy surveys provide noisy, incomplete, selection-affected population snapshots rather than complete evolutionary histories. We formulate galaxy evolution as joint inference of effective physical states, their population intensity, and cross-epoch dynamics. An effective state is a coarse-grained description defined by predictive adequacy and distinguished from measured variables and learned representations. The intrinsic population is a finite non-negative measure evolving through one-galaxy transport, source and removal terms, and nonlocal two-to-one merger jumps. A sub-probability observational kernel maps this population to survey catalogs and supplies the likelihood for state inference. Projected luminosity and stellar-mass functions generally do not obey closed dynamics and cannot identify the underlying channels alone. In a restricted IllustrisTNG proof of concept, a finite-time non-merger kernel and reduced merger operator are calibrated on training root merger trees and evaluated on held-out lineages. Dynamical propagation improves the normalized later mass–sSFR distribution relative to a static baseline, while the merger channel captures number loss from disappearing secondary progenitors. Under noisy and censored mock observations, the propagated prior improves posterior-stacked reconstruction of the latent population relative to a frozen-static prior. The framework provides an observation-directed, simulation-assisted route to galaxy state-and-dynamics inference.
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Earth and Planetary Astrophysics

The science from asteroid sample return missions

Elizabeth J. Tasker, Harold C. Connolly Jr and Shogo Tachibana

To date, three samples from near-Earth asteroids have been delivered to Earth by Japan's Hayabusa (2010) and Hayabusa2 (2020) missions, and the United States OSIRIS-REx mission (2023). Free from terrestrial contamination, these pristine materials provide new opportunities to investigate planetary formation processes, the delivery of organics and water to the early Earth, and the nature of potentially hazardous asteroids. As analysis of the asteroid samples proceeds in laboratories around the world, we visit each of the missions, review the initial scientific findings, and explore the value of sample return in understanding our origins and protecting our future.
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Solar and Stellar Astrophysics

Repeated Sunspot Light Bridge Jets Associated with Slipping Base Brightenings

Yadan Duan, Xiaoli Yan, Yuhang Gao et al. (+3 more)

Light bridge (LB) jets offer a unique window into small-scale eruptive phenomena within sunspots, the Sun's strongest magnetic environments; however, their generation mechanism remains a subject of debate. Using high-resolution observations from the New Vacuum Solar Telescope (NVST), we investigated six recurrent light bridge jets and the slipping motions of their jet base points (JBPs). Analogous to coronal jets, our observations show that these LB jets are characterized by a preceding JBP followed by a collimated jet spire. The JBP of each repeated jet along the LB displays apparent slipping motion at velocities of 0.6-1.5 km/s, which is temporally correlated with quasi-periodic enhanced photospheric horizontal motion of 1.3-6.5 km/s. Following the slipping JBPs, the resulting jet spires' fronts display similar slipping behaviors within the upper solar atmosphere. The Chinese Ha Solar Explorer (CHASE) reveals Ellerman-bomb-like spectral signatures at the JBPs, confirming that magnetic reconnection is operating at the jet base. Based on these results, we propose that repeated 3D reconnection occurring between the horizontal LB field and the ambient vertical umbral field may drive these LB jets. This process appears to be driven and/or modulated by quasi-periodic horizontal motion fueled by convective upflows and the transport of magnetic flux along the light bridge. This work suggests that some LB jets share a common reconnection-driven mechanism with coronal jets and provides direct evidence of slipping reconnection occurring along the sunspot light bridge.
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All authors Yadan Duan, Xiaoli Yan, Yuhang Gao, Jincheng Wang, Zhe Xu, Yongyuan Xiang

Astrophysics of Galaxies

Short timescale variation in the submillimeter flux of Sagittarius A*

Makoto Miyoshi, Yoshiaki Kato, Yoshiharu Asaki et al. (+8 more)

We study short-timescale 340 GHz flux-density variability of Sgr A* using ALMA Cycle 3 observations. Careful self-calibration enabled 10 s snapshot imaging with very high effective image-domain SNR, allowing high-cadence monitoring of Galactic Center sources. To reduce atmospheric and instrumental effects, we measured Sgr A* relative to multiple non-variable sources in the same field and corrected apparent variability caused by time-dependent u-v coverage and PSF changes using simulations with a static input model. We then searched for characteristic timescales over 20 s < tau < Tobs/3 using structure functions, the Lomb–Scargle method, and state-space-model autoregressive spectral analysis. No dominant narrow periodicity is found. Instead, the data show a short-timescale flat, white-noise-like regime at tau below about 2.3–6.3 min, followed by red-noise-like behavior at longer timescales. This flat regime appears in both active and quiescent phases, suggesting statistically independent fluctuations on these timescales. We interpret its upper boundary as an empirical transition timescale between decorrelated short-timescale fluctuations and longer-timescale correlated variability. The physical origin of this flat component remains uncertain, since previous theoretical and numerical studies more commonly report red-noise-like or broken-power-law variability.
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All authors Makoto Miyoshi, Yoshiaki Kato, Yoshiharu Asaki, Masato Tsuboi, Kenta Uehara, Tomoharu Oka, Masaaki Takahashi, José K. Ishitsuka, Takahiro Tsutsumi, Atsushi Miyazaki, Ryoji Matsumoto

Instrumentation and Methods for Astrophysics

FPGA-based Matched Filter Group Optimisation for SKA Pulsar Search Engine

Haomiao Wang, Ben Stappers, Prabu Thiagaraj et al. (+1 more)

Pulsar search is one of the main tasks for the Square Kilometre Array (SKA), implemented in the central signal processor (CSP) sub-element. As most the characteristics of undiscovered pulsars are unknown by definition, exhaustive searches over a multi-dimensional parameter space are employed. One main compute-intensive task of the pulsar search modules in the CPS is the matched filter group, which convolves the input signals with a group of large FIR filters. High-performance designs on FPGAs have been proposed that can process multiple large filters efficiently. But given that in many applications, including the here targeted pulsar search, FIR filters have many different sizes, there is further potential for optimisation. This paper investigates the optimisation of matched filtering designs. While the results are tranferable to other domains, we are motivated by the needs of the SKA pulsar search engine. The influence of changing number of filters and the difference in sizes is analysed. The generic design in time-domain (TD) is optimised by employing the longest processing time (LPT) first rule to distribute filter templates across filter processing pipelines. For the Fourier-domain (FD), the relationship between the required off-chip memory space and speedup over the generic design is investigated. To put the results into relation with with GPU design, we compared with a well-optimised design for top-end GPUs (NVIDIA Tesal P100). While a mid-range Intel Arria 10 is up to 7.5x slower than the P100, the performance per watt is slightly better on the Arria 10.
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All authors Haomiao Wang, Ben Stappers, Prabu Thiagaraj, Oliver Sinnen

Thursday 23 April

Cosmology and Nongalactic Astrophysics

Backlighting the Cosmic Web with Fast Radio Bursts: An Anthology of Dispersion Measure Cross-Correlations with Large-Scale Structure and Baryon Tracers

Kritti Sharma, Elisabeth Krause, Vikram Ravi et al. (+11 more)

Fast Radio Bursts (FRBs) probe baryons permeating the cosmic web through their dispersion measures (DMs), which encode the integrated electron density along cosmological sightlines. Using 3,455 unique FRB sources from CHIME/FRB with $\sim 15$ arcmin localizations, we present an anthology of DM correlations with tracers of large-scale structure and baryonic matter at redshifts $z \lesssim 1.5$. We measure statistically significant correlations at $2.6-5\sigma$ with ten probes, including galaxies ($2.8\sigma$), weak gravitational lensing ($2.6\sigma$), cosmic infrared background ($4.0\sigma$), cosmic microwave background (CMB) lensing ($3.3\sigma$), thermal Sunyaev Zel'dovich (tSZ) effect ($3.8\sigma$), X-ray emission tracing galaxy clusters ($5.0\sigma$) and superclusters ($3.3\sigma$), soft X-ray background (SXRB, $4.1\sigma$), and radio continuum emission ($3.2\sigma$). These measurements reveal a consistent picture in which FRB sightlines intersecting overdense environments carry systematically larger DMs. Correlations with hot-gas tracers provide additional leverage on the strength of feedback, as they are strongly weighted towards the dense, bound gas. The measured amplitude of tSZ$\times$DM and SXRB$\times$DM correlations are consistent with theoretical predictions of baryon distribution from a DM-$z$ relation-inferred model with moderate feedback at $\sim 0.5\sigma$ level. Weaker feedback scenario is ruled out at $\sim 3.5\sigma$ by the SXRB$\times$DM correlation. Taken together, these measurements constitute a quantitative multi-tracer foundation for a new era in which FRBs from next generation facilities, such as BURSTT, CHORD, DSA, and SKA, in harmony with other probes, will map the baryon content of the full extent of the cosmic web.
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All authors Kritti Sharma, Elisabeth Krause, Vikram Ravi, Dhayaa Anbajagane, Liam Connor, W.L. Kimmy Wu, Simone Ferraro, Sebastian Grandis, David Alonso, Yi-Kuan Chiang, Casey J. Law, Pranjal R. S., Samuel McCarty, Shivam Pandey

Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics

Wavelength-Dependent Evolution of Full-Field Transfer Matrices in Photonic Lanterns

Caleb Dobias, Miguel Römer, Swati Bhargava et al. (+10 more)

A fiber-based photonic lantern can couple an array of single-mode optical fibers to the guided modes of a multimode fiber, with the mapping between the single-mode fibers and guided modes fully described by a complex-valued transfer matrix. Recent experimental studies have reported strong wavelength-dependent evolution of this matrix in non-mode-selective photonic lanterns, yet a quantitative physical explanation for this behavior has not previously been demonstrated. Here, we present direct measurements of the wavelength-dependent encoding transfer matrix of a photonic lantern across the range 1525 nm to 1575 nm using off-axis holographic imaging, enabling high-fidelity recovery of both amplitude and phase. Beyond measurement, we introduce a physically grounded propagation model and numerical simulation that quantitatively reproduces the observed wavelength evolution and provides a unified physical explanation for behavior reported in prior experimental work. The model identifies differential modal phase accumulation in the multimode section as the dominant mechanism governing spectral evolution and shows that increasing the length of the multimode end systematically accelerates the phase evolution of the transfer matrix with wavelength. These results establish a direct and predictive link between photonic lantern geometry and spectral response, providing a design framework for tailoring lanterns either to enhance sensitivity to closely spaced wavelengths or to enforce uniform response over broad bandwidths for spectroscopic and imaging applications.
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All authors Caleb Dobias, Miguel Römer, Swati Bhargava, Tara Crowe, Liza F. Quinn Reyes, David Smith, Matias Barzallo, Daniel Cruz-Delgado, Sergio Leon-Saval, Stephanos Yerolatsitis, Miguel A. Bandres, Stephen S. Eikenberry, Rodrigo Amezcua-Correa

High Energy Astrophysical Phenomena

Downward ultra-high-energy neutrino detection in the air with radio antennas at ground-based observatories

Baobiao Yue, Karl-Heinz Kampert and Julian Rautenberg

Ultra-high-energy (UHE) neutrinos are unique cosmic messengers that can traverse cosmological distances unattenuated, providing direct insight into the most energetic processes in the universe. Radio detection offers significant advantages for detecting highly inclined air showers induced by UHE neutrinos. This is due to a larger exposure range compared to particle detectors, which is a result of minimal atmospheric attenuation of radio signals combined with good reconstruction precision. Furthermore, this technique improves the air shower longitudinal reconstruction, which can be used to identify neutrinos with their first interaction far below the top of the atmosphere. In this work, we present a method for identifying UHE neutrinos using ground-based radio antennas. A reconstruction algorithm is introduced based on the radio emission maximum ($X^{\text{radio}}_{\text{max}}$), which demonstrates its power in distinguishing deeply developing neutrino-induced showers from background cosmic rays. Using simulations of $\nu_e$-CC-induced air showers, we evaluate the trigger efficiency, reconstruction performance, and resulting effective area and aperture prediction for a reference array. Our results show that radio detection significantly enhances the sensitivity to very inclined showers above 1 EeV, complementing traditional surface detectors. This technique is highly scalable and applicable to future radio observatories, such as GRAND. The proposed reconstruction and identification strategy provides a pathway toward achieving the sensitivity required to detect UHE neutrinos.
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Instrumentation and Methods for Astrophysics

CCAT: Silicon-Platelet Feedhorns for Submillimeter Wavelengths

Jason Austermann, James Beall, James R. Burgoyne et al. (+12 more)

Silicon-platelet feedhorn arrays are an established technology at millimeter wavelengths that, for some applications, can provide significant advantages over traditional direct-machined metal feedhorns. The Prime-Cam focal planes operating in the 350 GHz ($\sim$860 $\mathrm{\mu}$m) and 850 GHz ($\sim$350 $\mathrm{\mu}$m) bands are anticipated to carry the first silicon-platelet feedhorn arrays to operate fully at submillimeter wavelengths, representing a significant step forward in the application of this technology. In particular, the feedhorns designed for operation in the 850 GHz band represent a 3x increase in frequency compared to previously demonstrated and deployed devices of this type. Here we present a demonstration of silicon-platelet feedhorns at these submillimeter wavelengths, including in-lab performance characterization. We present fabrication metrology, room-temperature beammaps, and cryogenic optical efficiency measurements where the feedhorns are coupled to prototype CCAT Prime-Cam detectors. We show that feedhorn performance measurements are well matched to simulation and compare that performance directly to traditional, direct-machined metal feedhorns.
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All authors Jason Austermann, James Beall, James R. Burgoyne, Scott Chapman, Steve Choi, Cody J. Duell, Anthony I. Huber, Johannes Hubmayr, Matthew A. Koc, Michael D. Niemack, Joel N. Ullom, Jeffrey van Lanen, Anna Vaskuri, Michael Vissers, Jordan Wheeler

Instrumentation and Methods for Astrophysics

Large language models are not the problem

Hiranya V. Peiris

If a Large Language Model (LLM) can replicate your scientific contribution, the problem is not the LLM. What does it say about our field that so much of the anxiety about AI comes down to the fear that a machine could do what we do? Perhaps it says we should be doing something better.
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High Energy Astrophysical Phenomena

Electromagnetic Precursors to Binary Neutron Star Mergers: Kinetic Simulations of Magnetospheric Flaring

Jasmine Parsons, Anatoly Spitkovsky, Alexander Philippov et al. (+1 more)

We present the first 3D global kinetic simulations of the interacting magnetospheres of pre-merger binary neutron stars. The stars, whose magnetic moments are anti-aligned, twist the field lines connecting them, leading to periodic eruptions. Each eruption consists of an expanding magnetic flux tube with a reconnecting current sheet trailing behind it, topologically analogous to coronal mass ejections. We predict two novel classes of electromagnetic precursor signals powered by the efficient dissipation of magnetic energy in these periodically forming trailing current sheets. First, particles accelerated in the sheets produce nonthermal gamma-ray signals peaking at $\sim16\,\mathrm{MeV}$, which escape minutes to seconds before merger while the sheets are still optically thin to pair production, with modest characteristic luminosities of $L_\mathrm{obs}\gtrsim 10^{42}\,\mathrm{erg/s}$, detectable only for nearby mergers. Second, merging plasmoids in the sheets could produce fast radio burst-like transients in the final seconds before merger, with characteristic luminosities $L_\mathrm{radio}\sim 10^{38-40}\,\mathrm{erg/s}$. These coherent radio precursors would be detectable by upcoming instruments, either in untargeted surveys by wide-field instruments such as CHORD, or through targeted follow-up of gravitational-wave early-warning alerts with instruments such as DSA or SKA-mid.
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All authors Jasmine Parsons, Anatoly Spitkovsky, Alexander Philippov, Hayk Hakobyan

Instrumentation and Methods for Astrophysics

Differentiable Forward Modeling for Efficient and Accurate Shear Inference

Ismael Mendoza, Axel Guinot, Matthew R. Becker et al. (+6 more)

Forthcoming Stage-IV dark energy optical surveys, such as LSST, have the ambitious goal of measuring cosmological parameters at sub-percent precision. Realizing their full scientific potential requires very precise measurement of the cosmic shear signal and control of corresponding systematics. In this work, we present a modern implementation of the Bayesian shear inference framework in Schneider et al. (2015), in the case that the PSF and sky background are known. This framework automatically propagates the pixel-noise measurement error from each galaxy into the final shear estimate, and thus requires no external calibration to handle noise bias. As a first application of this new implementation, we infer the cosmic shear posterior from simulated images consisting of isolated exponential galaxies with semi-realistic noise levels. In this simplified scenario, we estimate the absolute multiplicative bias $|m|$ of our approach to be below $0.9 \times 10^{-3}\,[3\sigma]$ when the intrinsic distribution of galaxy properties is known, and below $1.3 \times 10^{-3}\,[3\sigma]$ when these distributions are inferred alongside shear. Additionally, we make progress towards the algorithm's computational feasibility in the context of modern wide-field surveys, where billions of galaxies must be processed, by leveraging differentiable forward models of galaxies, gradient-based samplers, and GPUs. Our final galaxy-fitting MCMC produces $300$ effective samples of galaxy properties in $0.45$ seconds per galaxy using a single A100 GPU. In the future, we seek to generalize our algorithm to handle selection, detection, and model shear biases so it can be applied to real survey data.
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All authors Ismael Mendoza, Axel Guinot, Matthew R. Becker, Camille Avestruz, Jean-Eric Campagne, Natalia Porqueres, Michael Schneider, Eleni Tsaprazi, the LSST Dark Energy Science Collaboration

Instrumentation and Methods for Astrophysics

Understanding HWO's Field of Regard and Characterization Requirement Trade Space with a Dynamic Observation Scheduling Algorithm

Corey Spohn, Christopher C. Stark, Dmitry Savransky et al. (+1 more)

The Habitable Worlds Observatory (HWO) aims to image and characterize at least 25 ExoEarth candidates (EECs). Achieving this goal requires a detailed understanding of the observatory's design trade space, including the operational efficiency of the EEC survey. This study quantifies the impact of two critical parameters: the instantaneous field of regard (FoR) and the number of characterization observations required per EEC ($N_\text{char}$). We introduce a novel dynamic scheduling algorithm implemented within the EXOSIMS framework that models information gain during the mission. The scheduler models the orbital information known about each planet and forecasts detection probabilities to make scheduling decisions. We explore a multi-dimensional trade space, varying aperture size (6.5 m and 8.0 m), dedicated EEC survey time (2.5, 5.0, 7.5 years), $N_\text{char}$ (1 to 4), and FoR ($15^\circ$ to $135^\circ$). Our results demonstrate that the FoR is a major driver of the mission yield, with the yield decreasing significantly when the FoR is less than $90^\circ$. We find that increasing $N_\text{char}$ imposes a significant cost to mission yield, as each additional characterization required reduces yield by approximately 22%. The cumulative impact of requiring four characterizations instead of one lowers the yield by approximately 52%. This harsh penalty can be partially mitigated by increasing the survey duration. The relative yield loss when increasing $N_\text{char}$ from 1 to 2 is 38% for a 2.5 year survey and 14% for a 7.5 year survey. Our results highlight the complex interactions between HWO's engineering constraints and science requirements, and emphasize that the EEC survey efficiency is a critical component of HWO's design space.
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All authors Corey Spohn, Christopher C. Stark, Dmitry Savransky, Natasha Latouf

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

Data-Driven Acceleration of Eccentricity Reduction for Binary Black Hole Simulations

Vittoria Tommasini, Nils L. Vu, Mark A. Scheel et al. (+1 more)

Reducing orbital eccentricity in numerical relativity simulations of binary black holes is essential for producing astrophysically relevant gravitational wave models, as many of these systems are expected to be near-circular in nature. Standard eccentricity reduction procedures rely on iterative schemes, often requiring four or more trial simulations to achieve desired thresholds. This approach is computationally expensive because each trial simulation adds ~10% to the total simulation run time of multiple weeks to months. We introduce a data-driven approach that accelerates this process by learning the values of the initial orbital frequency, Omega_0, and radial velocity, adot_0, that yield an evolution with small eccentricity. This is done using a Gaussian Process Regression model trained on an archive of previously eccentricity-reduced numerical relativity simulations. For all configurations tested, using the trained model consistently reduces the number of required eccentricity reduction iterations to just zero or one, significantly lowering computational costs relative to post-Newtonian initial guesses. These results demonstrate the power of data-driven methods in accelerating expensive numerical relativity simulations.
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All authors Vittoria Tommasini, Nils L. Vu, Mark A. Scheel, Saul A. Teukolsky

Astrophysics of Galaxies

An Extended Parametric Model for Self-interacting Dark Matter Halos

Siddhesh Raut, Ethan Nadler and Andrew Benson

We improve upon the parametric model for the evolution of the density profiles of self-interacting dark matter (SIDM) halos introduced in Yang et al. (2024b), by considering the effects of mass accretion on a SIDM halo's gravothermal evolution. The original parametric model accurately predicts parameters $V_{\max}$ and $R_{\max}$, but with a tendency to overpredict $V_{\max}$ at $z=0$ for a subset of field halos. This discrepancy results from the parametric model predicting a faster rate of gravothermal evolution for these field halos compared to that measured in cosmological zoom-in simulations. We propose that the effects of mass accretion on the evolution of SIDM halos are not fully captured by the original parametric model. Our extended parametric model assumes that smooth mass accretion delays core-collapse by driving the SIDM halo back toward a Navarro-Frenk-White (NFW) profile (as it would have in the case of cold dark matter). We find that this extended model is able to substantially reduce the error in predicted $V_{\max}$ for halos compared to the original model, providing a more accurate model of SIDM halo evolution.
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