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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 25 February

Cosmology and Nongalactic Astrophysics

Bulk and turbulent gas motions in the interacting galaxy cluster Abell 3395 South observed with XRISM

Naomi Ota, Angie Veronica, Jakob Dietl et al. (+8 more)

We investigate the gas motions in the core region of the Abell~3395 South subcluster (A3395S) using high-resolution X-ray spectroscopy with XRISM/Resolve. By analyzing the Fe~XXV He$\alpha$ emission line, we directly measure the line-of-sight bulk and turbulent velocities of the intracluster medium. We find that the one-dimensional turbulent velocity is low, at the level of $124\pm21~{\rm km\,s^{-1}}$, while a significant line-of-sight bulk velocity of $263\pm23~{\rm km\,s^{-1}}$ is detected. The coexistence of low turbulence and finite bulk motion suggests that A3395S has not yet reached a dynamically relaxed state. These results are consistent with the non-detection of a radio halo in A3395S, implying that turbulent particle reacceleration is currently inefficient in the cluster core. This study demonstrates that high-resolution X-ray spectroscopy with XRISM provides a powerful means to directly constrain intracluster medium dynamics in merging galaxy clusters, and it provides a reference for future comparative studies of A3395N and A3391 within the same large-scale structure.
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All authors Naomi Ota, Angie Veronica, Jakob Dietl, Anri Yanagawa, Thomas H. Reiprich, Veronica Biffi, Klaus Dolag, Marcus Brüggen, Esra Bulbul, Florian Pacaud, Yoshiki Toba

Astrophysics of Galaxies

Performance assessment of the gPLUTO code for the numerical modeling of radio galaxy evolution

Gourab Giri, Andrea Mignone, Alessio Suriano et al. (+2 more)

High-resolution tri-axial simulations are indispensable for realistically co-modeling the dynamical signatures and the radiative fingerprints of astrophysical jets, which are becoming increasingly important in modern computational studies of jet physics. However, such simulations impose extreme computational requirements that often exceed the capabilities of conventional CPU-based codes. GPU-accelerated simulations offer a transformative solution to mitigate these limitations. In this work, we present a detailed performance benchmarking of the recently developed GPU-enabled PLUTO code (gPLUTO), demonstrating runtime speed-ups ranging from an order of magnitude to (approximately) over 30 relative to CPU-only configurations. A direct comparison between computations of extragalactic jet propagation performed at different grid resolutions confirm the physical fidelity and production readiness of the gPLUTO code, while underscoring the importance of resolving the jet radius adequately to capture the jet dynamics accurately. Leveraging GPU-PLUTO's capabilities, we finally present an application by performing high-resolution simulations of giant radio galaxy jets (GRGs $\gtrsim 1$ Mpc), representing the first such well-resolved 3D study to our knowledge (resolving scales down to 500 pc). These simulations probe a range of environmental effects on GRG jets, clarifying their formation from central galaxies within host cosmic structures, rapid peripheral expansion, and the development of asymmetric cocoon morphologies.
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All authors Gourab Giri, Andrea Mignone, Alessio Suriano, Marco Rossazza, Stefano Truzzi

High Energy Astrophysical Phenomena

Constraints on neutrino emission and hadronic flux from 1LHAASO catalog $\gamma$-ray sources

Xue-Rui Ouyang, Yun-Feng Liang, Shi-Long Chen et al. (+2 more)

IceCube has detected neutrino emission from the Galactic Plane (GP) at a significance of $4.5\sigma$, though its origin remains uncertain. Utilizing ten years of IceCube muon-track data, we investigate potential correlations between the GP neutrinos and $\gamma$-ray sources in the first LHAASO catalog (1LHAASO). To avoid issues caused by spectral extrapolation, this analysis focuses on sources detected by the Water Cherenkov Detector Array (WCDA). We employ an unbinned likelihood analysis to search for neutrino emission and constrain the hadronic $\gamma$-ray component of these sources. Neither single-source searches nor stacking analyses reveal significant neutrino signals. The stacking analysis indicates that the 1LHAASO WCDA population contributes at most $\sim$20% to the diffuse GP neutrino flux measured by IceCube. The total hadronic contribution to the cumulative $\gamma$-ray emission from all WCDA sources is constrained to be at most $\sim$$60\%$, suggesting a predominantly leptonic origin for the $\gamma$-ray emission from the LHAASO source population. Even accounting for unresolved sources below the detection threshold, we estimate the total neutrino flux from all discrete sources (resolved plus unresolved) reaches at most about 40% of the observed GP neutrino flux. These results support that the bulk of the GP neutrino emission is mainly from truly diffuse processes, i.e., cosmic-ray interactions with the interstellar medium, rather than from unresolved point sources.
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All authors Xue-Rui Ouyang, Yun-Feng Liang, Shi-Long Chen, Rong-Lan Li, Ming-Xuan Lu

High Energy Astrophysical Phenomena

Short-duration GRB 250221A Afterglow Driven by Two-Component Jets from the merger of a compact star

Xiao Tian, Hou-Jun Lü, Xiao-Xuan Liu et al. (+4 more)

GRB 250221A is a short gamma-ray burst (GRB) at redshift $z=0.768$, with a duration of 1.8 s and no extended emission in either Swift/Burst Alert Telescope or Konus-Wind bands. A remarkable rebrightening feature in both optical and X-ray bands was observed at $\sim$0.6 days after the burst trigger, but no supernova or kilonova signature was detected. The burst properties and empirical correlations or distributions (e.g., duration, spectral hardness, location in the Amati correlation, $\varepsilon-$value, $f_{\rm eff}$ parameter, and physical offset) favor a compact binary merger origin. However, a dense circumburst medium with $n\sim 80\rm~cm^{-3}$, obtained by adopting the energy injection into a jet to interpret the late-time rebrightening is inconsistent with the compact binary merger origin. In this paper, we propose a two-component jet model to explain the multiwavelength afterglow observations of GRB 250221A, in which the relativistic narrow jet ($\rm \theta_{c} \sim 3.8^\circ$) produces the prompt and the early decay afterglow emission, while the mildly relativistic wide jet ($\rm \theta_{w} \sim 4.4^\circ$) dominates at later times, resulting in the observed rebrightening feature. If this is the case, one can obtain a lower medium density with $n\sim 0.72\rm~cm^{-3}$ which is a little bit higher than that of short GRBs in merger environments, but falls into the reasonable and acceptable range. Finally, a possible kilonova emission is also discussed within the scenario of compact star merger origin of GRB 250221A.
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All authors Xiao Tian, Hou-Jun Lü, Xiao-Xuan Liu, Xiao-Fei Dong, Jia Ren, Wen-Long Zhang, En-Wei Liang

Instrumentation and Methods for Astrophysics

Conditional Image Diffusion with Interferometric Closure Invariants: Independent EHT Imaging of Centaurus~A and 3C~279

Samuel Lai, Nithyanandan Thyagarajan, O. Ivy Wong et al. (+1 more)

We present independent imaging analyses of Event Horizon Telescope (EHT) observations of the active galactic nuclei in radio galaxy Centaurus~A and quasar 3C~279 using Generative Deep learning Image Reconstruction with Closure Terms (GenDIReCT), a recently developed machine-learning framework built on conditional diffusion models that uses interferometric closure invariants as primary observables. For Centaurus~A, our reconstruction reveals two prominent emission ridges ($\simeq 80\,\mu$as each) along the jet sheath with a brightness ratio of $1.4\pm 0.1$ and an opening angle of $12.3\pm 0.3$~deg. For 3C~279, we identify three distinct components in the image, with the southern jet ejecta on sub-parsec scale exhibiting a proper motion of $4.6\pm 1.0\,\mu$as over $\approx 5.39$ days away from the northern components, corresponding to an apparent superluminal velocity of $\simeq 10\pm 2$ times light speed. These measurements are consistent with those reported by the EHT Collaboration. The results are significant because we demonstrate that: (1) imaging from interferometric aperture synthesis data, especially in VLBI and most acutely in extremely sparse arrays like the EHT, remains a severely ill-posed and challenging inverse problem, yet closure invariants preserve robust morphological information that can strongly constrain structural features, and (2) more importantly, closure-invariant imaging largely avoids calibration systematics, thus providing a fundamentally independent view of spatial structure with very high angular resolution. The generative nature of GenDIReCT further allows us to sample and characterise clusters of plausible image solutions for each dataset. As a calibration-independent, generative imaging approach, GenDIReCT offers a robust and truly independent blind-imaging tool for current and future VLBI experiments.
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All authors Samuel Lai, Nithyanandan Thyagarajan, O. Ivy Wong, Foivos Diakogiannis

Astrophysics of Galaxies

A Decade-Long Increasing Mid-Infrared Luminosity in Galaxy NGC6447: a Turning-On Candidate of Active Galactic Nucleus

Xinyu Dai, Nate Adams, Natalie Kovacevic et al. (+6 more)

It is widely expected that the obscured accretion stage can be the initial turning-on stage of active galactic nuclei from quiescent galaxies. We present mid-infrared light curves of NGC 6447 in 3.5$\mu$m and 4.6 $\mu$m bands observed by WISE/NEOWISE, which show an almost monotonic increasing trend of 1.2 mag over 14 years. The optical light curve from ASAS-SN during the same period is consistent with a constant showing no variability. The mid-infrared color evolution shows that the galaxy transitioned into an active galactic nucleus (AGN) in 2018. The SPHEREx spectrum reveals an increasing continuum resembling warm to hot dust emission from an AGN. NuSTAR detected an X-ray source with a 2-30 keV luminosity of $8.4\times10^{41}$ ergs/s at the lower boundary of AGN X-ray emission range, and a factor of >7 variability in one year compared to the Swift upper limit. NGC 6447 was classified as a quiescent galaxy in the literature. The multi-wavelength timing and spectral properties of NGC 6447 are consistent with the expected AGN turning on event, where the obscuring material around the AGN central engine is gradually dispersed, revealing the central engine. This example shows that long-term infrared variability can be a powerful tool to find similar sources. Based on the sample selection statistics, we estimate the duration of the episodes of AGN accretion (duty cycle) signified by the turning-on event as $10^4$-$10^6$ yr.
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All authors Xinyu Dai, Nate Adams, Natalie Kovacevic, Kaitlyn Parrinello, Marko Micic, Heechan Yuk, Zijun Gao, Lorelei Starling, Francesco Shankar

Astrophysics of Galaxies

Revisiting the Origin of the Star-Forming Main Sequence Based on a Volume-Limited Sample of ~25,000 Galaxies

Yang Gao, Shujiao Liang, Qinghua Tan et al. (+10 more)

We revisit the extensively debated star-forming main sequence (SFMS)-a tight correlation between the star formation rate and stellar mass in both kiloparsec-resolved and integrated galaxies. We statistically explore the fundamental drivers of star formation at global scales, using a large volume-limited sample of 24,954 local star-forming galaxies to overcome the limitations of previous works. Based on the mid-infrared 12 micron luminosity, stellar mass, and g-r color, we estimate the molecular gas mass for the considered sample. At galaxy-wide scales, we establish global relations between the surface densities of the star formation rate, stellar mass, and molecular gas mass . These global density relations are connected with and follow similar trends as the resolved SFMS, the Kennicutt-Schmidt (KS) relation, and the molecular gas main sequence (MGMS). Taking advantage of this large catalog, we show that the scatters in the global KS and MGMS relations are smaller than that of the global relation between the star formation rate surface density and stellar mass surface density, and their Pearson correlation coefficients are higher. More importantly, multivariate regression and partial correlation analyses demonstrate that the apparent correlation between the star formation rate surface density and stellar mass surface density is entirely mediated by the molecular gas surface density, with its best-fit parameters directly derivable from those of the KS and MGMS relations. Overall, our findings suggest that the correlation between stellar mass and molecular gas, as well as that between molecular gas and star formation, are more direct and fundamental. The star-forming main sequence thus appears to be a natural by-product of these two tighter relations.
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All authors Yang Gao, Shujiao Liang, Qinghua Tan, Enci Wang, Huilan Liu, Hongmei Wang, Tao Jing, Xiaolong Wang, Kaihui Liu, Ning Gai, Yanke Tang, Yifan Wang, Yutong Li

Cosmology and Nongalactic Astrophysics

Resurgence and Hyperasymptotics in Wave Optics Astronomy

Job Feldbrugge, Samuel Crew and Ue-Li Pen

With the discovery of gravitational waves and fast radio bursts, wave optics has become increasingly relevant in astrophysics. This paper studies the behaviour of random gravitational and plasma lenses, presenting the refractive and diffractive expansions, with higher-order terms that allow error estimates and embody the counterintuitive resurgence phenomenon. Specifically, we show that the diffractive expansion converges for a broad class of bounded lens models and provides an efficient description of interference patterns across frequency regimes. Next, building on Picard-Lefschetz techniques, we derive the full refractive expansion to arbitrary order, organising it into a transseries. Near caustics, the standard transseries is supplemented with uniform asymptotics. We study this transseries, with both Borel and hyperasymptotic resummation yielding systematic approximations to lensing integrals at all frequencies. Our results give a framework for modelling wave optics lensing near caustics and beyond the geometric optics approximation and thereby illustrate how tools from resurgence and asymptotic analysis can be applied to practical problems in astrophysics. Near caustic singularities, the post-refractive corrections diverge, while the uniform asymptotic expansion becomes accurate. We use the leading uniform approximation to derive the strong wave optics suppression of off-axis caustics, which clarifies their subdominant role.
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Tuesday 24 February

Astrophysics of Galaxies

Constraining the Lifespan of Intelligent Technological Civilization in the Galaxy

Sohrab Rahvar and Shahin Rouhani

In this work, we explore constraints on the emergence and longevity of technologically intelligent civilizations in our Galaxy, considering the Fermi paradox. We argue that under optimistic assumptions about the probability of life and intelligence emerging on Earth-like planets, the absence of contact with extraterrestrial civilizations imposes limits on their lifespan. Our analysis suggests that if intelligent life is common, technological civilizations must be relatively short-lived, with lifetimes constrained to $\lesssim 5\times10^3$ years under our most optimistic scenario. Considering electromagnetic communication, we note that our current light cone encompasses the entire Galactic history over the past $\sim 10^5$ years, making the lack of detected signals particularly puzzling for long-lived civilizations. We emphasize that these results should be interpreted as upper bounds derived from the Fermi paradox, not as predictions of actual lifespans.
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Cosmology and Nongalactic Astrophysics

Intracluster Medium Fluctuations on Scales up to 1 Mpc: A Combined eROSITA and SPT/Planck Analysis of Abell 3266

H. Saxena, A. Heinrich, J. Sayers et al. (+22 more)

Galaxy clusters form through hierarchical assembly, where smaller substructures merge to build the largest gravitationally bound objects in the universe. These mergers, combined with feedback from AGN, filamentary accretion, and other energy injection processes, generate turbulence and perturbations within the intra-cluster medium (ICM). X-ray and Sunyaev-Zel'dovich (SZ) observations can be utilized to measure these ICM density and pressure inhomogeneities, in turn providing constraints on the effective Equation of State (EOS) of the perturbations and ICM velocities. In this work, we analyze deep SRG-eROSITA and Planck/SPT observations of Abell 3266 (A3266), a dynamically complex merging cluster with elongated morphology and significant substructure. We measure pressure and density fluctuations, and compute the power spectra and deprojected 3D amplitudes of these perturbations. We estimate the ratio of pressure-to-density fluctuation amplitudes as $1.00 \pm 0.55$ and non-thermal pressure support $0.068 \pm 0.050$. Density fluctuations are found to be stronger in the northern sector of the cluster compared to the south, consistent with ongoing accretion along a filamentary structure revealed by eROSITA. Further, we find the amplitude of density fluctuations increases with radius, qualitatively consistent with the trend found in cosmological simulations. Uncertainties in our results are dominated by the relatively low sensitivity of current Planck/SPT data, suggesting that improvements in SZ data quality could substantially improve our understanding of ICM energy injection, transport, and dissipation from this technique.
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All authors H. Saxena, A. Heinrich, J. Sayers, I. Zhuravleva, E. Bulbul, J. Sanders, C. Avestruz, R. Basu Thakur, E. Battistelli, A. Botteon, F. Cacciotti, F. Columbro, A. Coppolecchia, S. Cray, P. de Bernardis, M. De Petris, L. Lamagna, E.T. Lau, S. Masi, A. Paiella, F. Piacentini, E. Rapaport, L. Rudnick, D. White, J. ZuHone

Solar and Stellar Astrophysics

On the Importance of the Convective Urca Process in 3D Simulations of a Simmering White Dwarf

Ferran Poca-Amorós, Brendan Boyd, Dean M. Townsley et al. (+1 more)

Type Ia supernovae are bright thermonuclear explosions that are important to numerous areas of astronomy. However, the origins of these events are poorly understood. One proposed setting is that of a near Chandrasekhar mass white dwarf that undergoes runaway carbon burning in the core. During the thousand years leading up to the explosion, the white dwarf undergoes a simmering phase where slow carbon burning heats the core and drives convection. A poorly understood aspect of this phase is the convective Urca process, which links convection with weak nuclear reactions. We use the low Mach number code MAESTROeX to perform full 3D simulations as is required to accurately capture the turbulent convection. We present simulations with and without the A=23 convective Urca process, which have relaxed to a steady state. We characterize the effects of the convective Urca process on the neutrino losses, the nuclear energy generation, and the convective boundary. We find that the size of the convection zone is substantially reduced by the convective Urca process, though convection still extends past the Urca shell. Our findings on the structure of the convective zone and the compositional changes can be used to inform 1D stellar models that track the longer-timescale evolution.
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All authors Ferran Poca-Amorós, Brendan Boyd, Dean M. Townsley, Alan Calder

Solar and Stellar Astrophysics

Calibration of the [C/N] and [Y/Mg] chemical clocks with asteroseismic ages from the TESS space mission

E. Pakštienė, G. Tautvaišienė, V. Bagdonas et al. (+8 more)

Context. Stellar ages are typically very difficult to estimate for field stars. New empirical methods, based on abundance ratios of chemical elements, are emerging and need to be calibrated. Aims. Our main aim is to contribute to revealing relations between [C/N] and [Y/Mg] ratios and stellar ages by determining astroseismic ages and non-local thermodynamic equilibrium (NLTE) abundances, and accounting for stellar evolutionary stages and birth places in the Galaxy. Methods. We searched for solar pulsations in a sample of 1250 bright F, G, and K giants using data from the TESS space telescope and determined asteroseismic ages using the BASTA and PARAM codes. For the [Y/Mg] relations with age, we determined abundances accounting for deviations from the local thermodynamic equilibrium. For the [C/N] relations with age, we separated stars according to their evolutionary stages. Results. We determined asteroseismic ages for 218 giants and derived [Y/Mg] and [C/N] relations with age for subsamples of stars in three regions of the Galactic thin disc and the thick disc. Conclusions. The [Y/Mg]-age relation exhibits a clear radial dependence across the Galactic disc, with a steeper trend in the outer disc, progressively flatter relations towards the inner disc, and a very flat trend in the thick disc. NLTE abundances of Mg and especially of Y have to be used in order to obtain a more precise stellar age evaluation from [Y/Mg] ratios. When using [C/N] abundance ratios as stellar age indicators, evolutionary stages of stars have to be taken into account.
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All authors E. Pakštienė, G. Tautvaišienė, V. Bagdonas, H. Kjeldsen, M.L. Winther, A. Drazdauskas, C. Viscasillas Vázquez, Y. Chorniy, Š. Mikolaitis, R. Minkevičiūtė, E. Stonkutė

High Energy Astrophysical Phenomena

Complex Analysis of Askaryan Radiation: UHE-$\nu$ Identification and Reconstruction using the Hilbert Envelope of Observed Signals

J. C. Hanson and R. Hartig

The detection of ultra-high energy neutrinos (UHE-$\nu$), with enegies above 10 PeV, has been a long-time goal in astroparticle physics. Autonomous, radio-frequency (RF) UHE-$\nu$ detetectors have been deployed in polar regions that rely on the Askaryan effect in ice for the neutrino signal. The Askaryan effect occurs when the excess negative charge within a UHE-$\nu$ cascade radiates in a dense medium. UHE-$\nu$ can induce cascades that radiate in the RF bandwidth above thermal backgrounds. To identify UHE-$\nu$ signals in data from Askaryan-class detectors, analytic models of the Askaryan electromagnetic field have been created and matched to simulations and laboratory measurements. These models describe the Askaryan electromagnetic field, but leave the effects of signal propagation through polar ice and RF channel response to simulations. In this work, a fully analytic Askaryan model that accounts for these effects is presented. First, formulas for the observed voltage trace and its Hilbert envelope are calculated. Second, the analytic model is compared to UHE-$\nu$ signals at 100 PeV from NuRadioMC, a key Monte Carlo toolset in the field. Correlation coefficients between the analytic signal envelope and MC data in excess of $0.94$ are found, and 99.99% of UHE-$\nu$ signals pass a correlation threshold of $\rho\geq 0.4$. Analysis of RF thermal noise reveals that just 0.2 background events have $\rho\geq 0.4$ in 5 years at a 1 Hz thermal trigger rate. Finally, we describe future work related to the measurement of the logarithm of the UHE-$\nu$ cascade energy.
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Astrophysics of Galaxies

The turbulence driving mode in NGC7793 and NGC1313

Lewis J Miller, Kathryn Grasha and Christoph Federrath

We present spatially resolved measurements of turbulence driving modes across entire extragalactic discs of NGC7793 and NGC1313, using Atacama Large Millimetre/submillimetre Array (ALMA) CO(J=2-1) observations at 13pc resolution. By applying a kernel-based analysis of density and velocity fluctuations, we map the turbulence driving parameter, b, which characterises the balance between solenoidal ($b\sim0.3$) and compressive ($b\sim1$) turbulent driving regimes. b is quantified as the ratio of the turbulent density fluctuations relative to the turbulent sonic Mach number, M. Both galaxies show predominantly solenoidal driving on average for the regions where we find valid results ($b\geq 0.33(\pm 0.05)^{+0.14}_{-0.10}$ in NGC7793; $b\geq 0.24(\pm 0.03)^{+0.10}_{-0.07}$ in NGC1313), noting that this is without including the influences of magnetic fields, making these measurements lower limits. We find substantial spatial variation of b, including localised regions of strongly compressive driving. NGC1313 exhibits higher turbulent Mach numbers and density dispersions than NGC7793, consistent with the disturbed morphology and recent satellite interaction in NGC1313. The turbulence in both NGC7793 and NGC1313 is supersonic ($3\lesssim M\lesssim 20$), and NGC1313 shows a radially decreasing trend of M with galactocentric radius. Radial trends indicate more solenoidal driving in the galaxy centres, potentially reflecting enhanced shear, and increasingly compressive modes in the outskirts. These results demonstrate that turbulence driving varies systematically with galactic environment and cannot be assumed uniform across discs. Our study applies a previously established method to larger scales and new data, linking local turbulence physics to global star formation regulation in galaxies, providing a new avenue for testing theoretical models with future integral field units and ALMA surveys.
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Earth and Planetary Astrophysics

Formation of Water-rich Giant Planet Satellites at Decretion Disk Ice Lines

Teng Ee Yap and David J. Stevenson

The volatile budgets of giant planet satellites are critical to unraveling the origin of their building blocks within the circumplanetary disks that hosted them. The Galilean moons Ganymede and Callisto, as well as the Saturnian moon Titan, are known to be anomalously water rich on the basis of their mean densities and interior models informed by gravity data from Galileo and Cassini, characterized by ice-to-rock ratios around unity. Here, we show that the water-ice sublimation line in a decreting circumplanetary disk lends itself to the formation of a water-rich solid reservoir, serving as a natural site for the birthplace of icy satellites. Fundamentally, this reflects how interior to the ice line, water vapor is advected outward, while beyond it, water ice drifts inward as pebbles. Using a semi-analytic model for dust and vapor evolution, we simulate vapor and ice accumulation at the ice line, showing that solids just beyond it achieve steady-state ice-to-rock ratios a factor of a few higher than elsewhere in the disk. For typical disk parameters, this ice buildup occurs within a timescale of a few thousand years. We propose this as a first-order process that explains, at least to some extent, the compositions of three aforementioned satellites. We explore the impact of uncertain turbulence parameters on our results, namely the turbulent Schmidt number and Shakura-Sunyaev alpha, before discussing them in the context of icy satellite D/H ratios. We conclude by evaluating alternative scenarios for explaining water-rich satellites, based on the conversion of CO to CH4, with water as a by-product.
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Astrophysics of Galaxies

The MeerKAT 1.3 GHz Survey of the Large Magellanic Cloud

W. D. Cotton, N. Rajabpour, M. D. Filipović et al. (+11 more)

We present a radio-continuum survey of the LMC using the MeerKAT telescope, describe the full-Stokes products included in the first data release, and highlight some initial results. The observations are centred at 1.3 GHz with a bandwidth of 0.8 GHz. The imaging products comprise six fields of view, each encompassing $\sim$5$^\circ$ $\times$ 5$^\circ$ with the resulting images achieving a resolution of 8". The median broad-band Stokes~I image root-mean-square noise value is $\sim$11 $\mu$Jy beam$^{-1}$. The survey enables a variety of astrophysical studies, which we showcase with the presentation of a few findings. Within the LMC we identify a new supernova remnant candidate; present planetary nebulae and Wolf-Rayet stars without previous radio detections; and show the MeerKAT view of the well-known star-forming region 30 Doradus. We also present some examples of interesting foreground and background sources in the field, including the AB~Dor multiple-star system, a radio ring galaxy, a possible Odd Radio Circle, and a remarkable bent-tail radio galaxy.
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All authors W. D. Cotton, N. Rajabpour, M. D. Filipović, F. Camilo, R. Z. E. Alsaberi, L. H. Bester, A. C. Bradley, E. J. Crawford, M. Ghavam, O. K. Khattab, Z. J. Smeaton, O. M. Smirnov, J. Th. van Loon, V. Velović

Earth and Planetary Astrophysics

Rattle-and-Break: the Impact of Planetesimal Scattering on Super-Earth Resonant Chains

Sam Hadden and Yanqin Wu

The spacings of super-Earths in multi-transiting systems exhibit a distribution that is broad and mostly featureless, with the exception of notable excesses of planet pairs situated a few percent wide of first-order mean motion resonances (MMRs). In this work, we extend the so-called "breaking-the-chains" model to account for both of these characteristics. Assuming that super-Earths are settled into stable chains of resonances after disk-driven migration, we show that scattering a planetesimal population that contains only a few percent of a system's mass can reorganize primordial chains in remarkable ways. The planetesimal scattering "rattles" the chains by repelling adjacent planet pairs wide of their initial MMRs. Some chains remain rattled but otherwise intact and make up the observed excesses wide of MMRs. In other systems, however, this initial rattling sows the seeds of later orbital instabilities that break the chains entirely. If individual planetesimals' masses are of order a Pluto mass or so, the onset of these instabilities can occur tens or hundreds of Myr after birth, naturally explaining the apparent disappearance of near-resonant pairs on this timescale. The origin of such Pluto-mass debris is currently unknown.
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Astrophysics of Galaxies

Probing the magnetic fields and dust properties in the young embedded star-forming region AFGL 6366S using Near Infrared and Optical linear polarimetry

Samrat Biswas, Biman J Medhi, Motohide Tamura et al. (+2 more)

We present Near-Infrared (NIR) and Optical linear polarimetry towards the partially embedded cluster AFGL 6366S. The polarization ranges from 0.44-10.3 per cent in NIR and 0.16-11.22 per cent in Optical bands. The position angle spans $1^\circ - 179^\circ$ in both NIR and Optical bands. About 22 stars exhibit intrinsic polarization signatures. A polarization hole is evident towards the densest ($\sim 3.4 \times 10^{23} \mathrm{cm}^{-2}$) and warmest ($\sim 28.8 \mathrm{K}$) central cluster region. It is attributable to depolarization induced by Radiative Torque Disruption (RAT-D) of large grains and a modest contribution from magnetic-field tangling. The local magnetic field towards the cluster's central region is significantly misaligned with both the large-scale Galactic field and the long axis of the filament present in the region. The field morphology wraps around two dense molecular clumps of radii 0.34 pc and 0.22 pc and $\mathrm N(\mathrm H_2)$ = $(7.9 \pm 1.1) \times 10^{22}$ cm$^{-2}$ and $(4.3 \pm 0.5) \times 10^{22}$ cm$^{-2}$, respectively. The clumps are embedded in the filamentary structure and represent locally accelerated stages of mass accumulation. Gravitationally driven mass flows, largely perpendicular to the local magnetic field, produce a U-shaped field curvature across the filament axis. The plane-of-sky magnetic field strengths towards the two clumps are $ 447.91 \pm 83.81 \mu\mathrm{G}$ and $396.66 \pm 73.64 \mu\mathrm{G}$. The corresponding mass-to-flux ratios ($\lambda \sim 1.34$ and $0.82$) indicate that one clump is magnetically supercritical and the other is subcritical. The Alfven Mach numbers ($\mathcal{M}_A$) $\sim$ 0.395 and 0.393 indicate that both the clumps are in sub-Alfvénic state.
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All authors Samrat Biswas, Biman J Medhi, Motohide Tamura, H.S Das, Jungmi Kwon

Astrophysics of Galaxies

FRESCO: Constraining Dust Attenuation and Star-Formation Rates of $z\sim 2$ Star-Forming Galaxies with JWST Paschen and Ground-Based Balmer Emission Line Observations

Michael A. Wozniak, Naveen A. Reddy, Pascal A. Oesch et al. (+7 more)

We present new constraints on dust attenuation and star-formation rates (SFRs) for 77 galaxies at redshifts $z=1.43-2.65$, using Paschen emission line detections from the JWST FRESCO survey and ground-based Balmer line measurements from the MOSDEF survey. Using nebular and continuum emission maps, we find that Paschen emission covers a smaller area than continuum emission observed in the F210M (2.1 $\mu$m; rest-frame optical) and F444W (4.4 $\mu$m; rest-frame near-IR) bands, and is preferentially located toward galaxy outskirts. These results suggest that current star formation is concentrated in regions farther from galaxy centers than older stellar populations traced by the continuum, indicative of inside-out star formation. With a careful accounting of slit-loss corrections for ground-based measurements, we calculate nebular reddening and dust-corrected SFRs using the Balmer decrement (H$\alpha$/H$\beta$) and Paschen-to-Balmer line ratios (Pa$\alpha$/H$\alpha$ and Pa$\beta$/H$\alpha$), assuming the Milky Way extinction curve. On average, Paschen-derived reddening and SFRs agree with Balmer-derived values; however, two galaxies exhibit significantly higher Paschen reddening and four show significantly higher Paschen SFRs. We find that non-unity dust covering fractions bias the Balmer decrement toward less reddened OB associations, while decrements involving the Paschen lines are less affected by this bias. These results highlight the enhanced sensitivity of the Paschen lines to the most heavily obscured OB associations in $z\sim2$ galaxies, particularly in galaxies with patchy dust geometries. Future studies using Paschen lines exclusively to measure nebular reddening will yield more robust constraints on the dustiest star-forming regions.
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All authors Michael A. Wozniak, Naveen A. Reddy, Pascal A. Oesch, Ivan Kramarenko, Jorryt Matthee, Chloe Neufeld, Irene Shivaei, Bahram Mobasher, Alice E. Shapley, Brian Siana

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

Beam tube boundary effects in stray light modeling of long Fabry-Perot arm cavities for third-generation gravitational-wave detectors

M. Andrés-Carcasona and M. Evans

Next-generation gravitational-wave detectors such as Cosmic Explorer and the Einstein Telescope will operate 10-40 km Fabry-Perot arm cavities inside vacuum beam tubes. FFT-based paraxial tools treat propagation in free space and therefore do not explicitly enforce beam tube boundary conditions. We introduce a waveguide-like mode description of the optical field that incorporates an imposed beam tube boundary condition and enables an independent benchmark of free-space FFT tools We derive the associated modal-mixing matrices for mirrors and baffles, including a closed-form series for axisymmetric circular apertures. We quantify the strain-equivalent couplings from baffle miscentering and from a localized near-wall tube defect, and show that they are suppressed as baffle density increases. In the relevant regime of densely baffled cavities and small perturbations, beam tube boundary effects are subdominant, which supports the continued use of FFT-based codes to guide the design of 3G detectors.
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Astrophysics of Galaxies

Galaxy and black hole coevolution in dark matter haloes not captured by cosmological simulations

Hassen M. Yesuf and Connor Bottrell

Star formation in galaxies is governed by internal and environmental processes, yet their relative roles are not well understood. In particular, uncertainties in measurements of active galactic nuclei (AGN) host galaxies, combined with modeling limitations, obfuscate the impact of supermassive black hole feedback across environments and over time. Here we address this with a comprehensive analysis of ~60,000 nearby AGNs (z < 0.15 and new environment and halo-mass measurements for ~500,000 AGN and non-AGN host galaxies. This benchmark enables unified comparisons with three prominent cosmological simulations–SIMBA, TNG, and EAGLE–and reveals major, contrasting shortcomings. Simulations fail to reproduce observed trends linking star formation, quiescence, AGN luminosity, stellar mass, and halo mass. While simulations qualitatively capture that AGNs are more common in low-mass halos than in rich groups or clusters, detailed host demographics diverge strongly from observations. Partial agreement exists in the stellar mass distribution within large-scale structures, yet all simulations overproduce quenched low-mass satellites in massive halos, while misrepresenting quenched fractions of massive central galaxies and those in low-density environments, which are sensitive to feedback implementation. Improved AGN physics and modeling of multi-phase gas cooling and flows are required to capture the observed interplay between black holes, galaxies, and halos.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Lepton asymmetry leading to baryogenesis by primordial black holes

Mriganka Dutta, Banibrata Mukhopadhyay, Abhishek Kumar Jha et al. (+2 more)

Baryogenesis remains an unresolved problem in cosmology, with existing mechanisms facing significant caveats. We show that the effects of primordial black holes (PBHs) on neutrinos produce the lepton asymmetry $\sim 10^{-10}$ which subsequently produces the baryon asymmetry. We consider the Dirac Lagrangian in curved spacetime in local coordinates exhibiting Hermitian pseudo-vector and non-Hermitian vector terms. These terms lead to energy splitting between weakly interacting neutrinos and antineutrinos, resulting in their unequal number densities and hence a lepton asymmetry. While the non-Hermitian effect leads to a non-conserved total probability of neutrinos, the leptogenesis due to gravitational effects of a PBH could be significant until the nucleosynthesis era. This in turn produces baryon asymmetry from the symmetry of lepton and baryon numbers via the sphaleron process in the electro-weak era. We show that in the most conservative scenario, the PBHs of mass $\sim 10^{12}$ g and spin $\sim 0.01$ produce the observed baryogenesis at temperature 130 GeV, when such PBHs are available abundantly. However, massive PBHs also could produce the observed asymmetry, assuming the non/anti-Hermitian vector couplings for neutrino and anti-neutrino get canceled from the Lagrangian, leading the system to be Hermitian.
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All authors Mriganka Dutta, Banibrata Mukhopadhyay, Abhishek Kumar Jha, Mayank Pathak, Siba Prasad Das

Cosmology and Nongalactic Astrophysics

Implications for Primordial Black Hole Dark Matter from a Single Subsolar Mass Gravitational-wave Detection in LVK O1–O4

Alberto Magaraggia and Nico Cappelluti

The detection of sub-solar mass black holes is a milestone of modern astrophysics as it would open a window either onto new stellar physics or could potentially unveil the nature of Dark Matter as Primordial Black Holes (PBHs). On November 12, 2025, the LIGO-Virgo-KAGRA (LVK) collaboration reported the compact binary merger candidate S251112cm, a system with no obvious electromagnetic counterpart, consistent with binary black hole merger with a chirp mass in the range $0.1-0.87 \, M_\odot$. The probability that at least one component has mass $<$1 $M_{\odot}$ is $>99\%$. Inspired by this trigger, we tested if a population of PBHs formed at Quantum Chromodynamics epoch with a broad mass function could account for a signal of this type. Our results, corresponding to a predicted event rate of $0.8 \,\text{yr}^{-1}$ as seen by LVK O3b, suggest that the observed merger rate of $0.23^{+0.86}_{-0.218}\,\text{yr}^{-1}\;(95\%\;\text{C.L.})$ if the trigger is confirmed as an astrophysical event would be compatible with such a model. Our predicted detection rate is also in agreement with current LVK expectations for stellar-mass binaries, remaining consistent with a scenario in which a non-negligible fraction of the $3-200 \;M_\odot$ mergers observed by LVK originate from Primordial Black Holes. If confirmed, this detection would place a lower limit to the PBH abundance $f_{PBH}>0.04$ for our adopted model.
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High Energy Astrophysical Phenomena

Shock-induced chiral magnetic effect

Steven P. Harris and Srimoyee Sen

Weak-interaction-mediated chiral imbalance generation in idealized massless electrons during core-collapse supernovae was once proposed to be the source of strong magnetic fields found in neutron stars. The effect goes by the name of chiral plasma instability (CPI). However, it was found that a finite electron mass damps out this process, inactivating the instability and preventing magnetic field growth. In this work we show that the instability can survive in the presence of abrupt density and temperature perturbation that drives the system sufficiently far out of weak equilibrium. As an example, we work with such perturbations generated by shockwaves which are common during both core collapse as well as neutron star mergers. We find that the chiral imbalance resulting from shock waves, under the right conditions of density and temperature, can sustain the chiral plasma instability despite the damping from the electron mass. Additionally, in an already magnetized medium, the chiral magnetic effect resulting from shock wave density and temperature perturbation can generate substantial ohmic heating. Our results imply that shockwaves generated in core-collapse supernovae and merging neutron stars can act as a source of strong heating in a magnetized medium as well as CPI.
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Cosmology and Nongalactic Astrophysics

Evolution of Cosmic Voids: Structure, Galaxies, and Dynamics

Saeed Tavasoli

We investigate the structural, photometric, and dynamical evolution of cosmic voids and their galaxy populations from $z=2.09$ to the present, focusing on void size as a key evolutionary parameter. Using void catalogs from four Millennium Simulation snapshots and SDSS data at $z<0.04$, we perform a unified analysis of void demographics, galaxy properties, and internal kinematics. Our analysis reveals clear evidence that cosmic voids exhibit a significant evolutionary trend of becoming progressively emptier toward low redshift, accompanied by a marked decline in the brightness and clustering of their galaxy populations. The void galaxy luminosity function evolves significantly: $M^{*}$ fades and $\alpha$ flattens with time, with large voids hosting brighter, more rapidly evolving galaxies than small voids. Stacked density profiles exhibit a universal shape when scaled by void radius, deepening and building more pronounced walls toward $z=0$. Galaxy spatial distributions reveal persistent size-dependent segregation, with galaxies in large voids lying farther from the center and more strongly clustered. Dynamical analysis of simulations shows coherent outward flows in all voids, with amplitudes decreasing toward $z=0$, providing a physical basis for observed redshift-space distortions. Comparison with SDSS broadly confirms these evolutionary trends but uncovers a non-zero central galaxy population in observed voids – absent in $\Lambda$CDM predictions – that may challenge current galaxy formation models in extreme underdensities. Future comparisons with additional simulations and deeper high-redshift surveys will provide stronger tests of $\Lambda$CDM in the most underdense regions.
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High Energy Astrophysical Phenomena

Collapse of Magnetized White Dwarfs as site of Heavy Element Formation and Kilonova Signal

Tetyana Pitik, David Radice, Daniel Kasen et al. (+3 more)

We present the first end-to-end calculation connecting the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf to observable kilonova signatures, combining 2D general-relativistic neutrino-magnetohydrodynamic simulations, followed by radiation hydrodynamics with in-situ nuclear network and 2D Monte Carlo radiative transfer with spatially resolved heating rates. Unlike all previous unmagnetized AIC models - which predicted proton-rich, $^{56}$Ni-dominated ejecta - strong magnetic fields eject ${\sim 0.2 M_\odot}$ of neutron-rich material $(\langle Y_e \rangle \sim 0.24)$ on dynamical timescales, before neutrino irradiation can raise the electron fraction, enabling strong $r$-process nucleosynthesis up to and beyond the third peak. The resulting kilonova is lanthanide-rich $(X_{\rm lan} \approx 8\%)$ and dominated by near-infrared emission. We compute synthetic light curves in the LSST and JWST bands and find striking agreement, without parameter tuning, between the observations of AT 2023vfi/GRB 230307A and our broadband light curves for polar viewing angles. These results establish magnetized AIC as a viable channel for heavy $r$-process element production and a compelling progenitor candidate for long-duration gamma-ray bursts with kilonova signatures.
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All authors Tetyana Pitik, David Radice, Daniel Kasen, Fabio Magistrelli, Patrick Chi-Kit Cheong, Sebastiano Bernuzzi

High Energy Astrophysical Phenomena

Global Magnetohydrodynamic Simulations of Monster Shocks in Neutron Star Magnetospheres

Michael P. Grehan, Bart Ripperda, Andrei M. Beloborodov et al. (+2 more)

Waves launched from the neutron star surface or inner magnetosphere propagate through the magnetosphere as small perturbations, but can grow relative to the background magnetic field and steepen into “monster shocks” – ultra-relativistic magnetized shocks which can power high-energy emission. Such shocks can develop around isolated magnetars, merging binaries, and collapsing neutron stars. They occur in magnetically dominated plasma and are described by relativistic magnetohydrodynamics (MHD). We present global relativistic MHD simulations of monster shocks in unperturbed and perturbed (“wrinkled”) backgrounds with a global dipolar geometry. Our simulations confirm analytical predictions for equatorial shocks and provide new insight into the behavior of oblique shocks off the equator. Simulations where the shock is formed through Alfvén mode to fast mode conversion are also presented, demonstrating the generic nature of the monster shock mechanism. We explore how the presence of additional modes in the magnetosphere modifies the shock behavior. Modes of comparable amplitude can fragment the shock front, substantially reduce the magnetization, produce localized enhancements in the Lorentz factor relative to an unperturbed dipole background, and intermittently generate additional shocks along a line of sight.
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All authors Michael P. Grehan, Bart Ripperda, Andrei M. Beloborodov, Christopher Thompson, Elias R. Most

Solar and Stellar Astrophysics

Testing models for fully and partially stripped low-mass stars with Gaia: Implications for hot subdwarfs, binary RR Lyrae, and black hole impostors

Pranav Nagarajan, Kareem El-Badry, Alexey Bobrick et al. (+4 more)

When low-mass ($\lesssim 2$ $M_{\odot}$) red giants lose their envelopes to a companion just before the helium flash, the resulting mass transfer can produce binaries hosting hot subdwarfs, horizontal branch stars, and undermassive red clump stars. Recent work predicts a continuum of such products, from fully stripped hot subdwarfs to partially stripped horizontal branch and red clump stars, and suggests that young, metal-rich RR Lyrae can form when partial stripping leaves a helium-burning star in the instability strip. To enable direct comparison with observations, we model these binaries in a simulated Milky Way-like galaxy with a realistic metallicity-dependent star formation history and 3D dust map, generate epoch astrometry using Gaia's scanning law, and fit it with the cascade of astrometric models applied in Gaia DR3. We compare the simulated population to DR3 observations of hot subdwarfs, RR Lyrae, and red giants with high astrometric mass functions. The model significantly overpredicts the number of hot subdwarfs with astrometric binary solutions, partly because the predicted flux ratios are more unequal than observed. It also predicts $\gtrsim 100$ RR Lyrae with DR3 astrometric orbital solutions, while none are observed. We conclude that RR Lyrae in au-scale binaries may be substantially rarer than predicted. In contrast, the model plausibly explains the population of red clump stars with high astrometric mass functions, which we interpret as potential black hole impostors. We predict that $\sim 10 \times$ more stripped-star binaries will be detectable in DR4, whose sensitivity to longer periods will more strongly test wide-orbit systems.
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All authors Pranav Nagarajan, Kareem El-Badry, Alexey Bobrick, Giuliano Iorio, Francisco Molina, Joris Vos, Maja Vučković

Astrophysics of Galaxies

NOCTURNE. III. Unidentified variable emission in the nuclear regions of PKS 2153-69

Miguel Coloma Puga, Marco Berton, Pierpaolo Condò et al. (+4 more)

Historically, the study of the central regions of Type 1 AGN has been limited by the combination of the host galaxy spectrum with strong emission from the accretion disk and NLR/BLR, which prevented us from accurately probing the galactic and AGN properties in the central regions. Integral field spectroscopy allows us to correct for this effect and study both the unobscured cores of AGN host galaxies as well as the uncontaminated spectra of their central engines with unprecedented precision. Using MUSE WFM observations, in this work, we present a combined method for modelling and subtracting QSO light in type-1 AGN alongside results for one such source, PKS 2153-68 (z=0.028), both jetted and gamma-ray emitting. After separating the host galaxy and AGN spectra, we discuss the discovery of an unresolved and yet-to-be-identified high-velocity ($\sim$25000 km/s) short timescale ($\leq$1 yr) variable emission, unlike anything observed in other variable AGN.
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All authors Miguel Coloma Puga, Marco Berton, Pierpaolo Condò, Abigail García-Pérez, Emilia Järvelä, Anne Lähteenmäki, Swayamtrupta Panda

Astrophysics of Galaxies

The DECam MAGIC Survey: Uncovering the Tidal Tails of the Crater II Dwarf Galaxy

Kaia R. Atzberger, Andrew B. Pace, Nitya Kallivayalil et al. (+27 more)

Crater II (CraII), a large and low-density dwarf spheroidal galaxy, has unusual observed properties that are difficult to reproduce in cold dark matter simulations. Ongoing tidal disruption may help explain the discrepancies, as evidenced by the recent discovery of tidal tails. Here we present metallicity-sensitive narrowband photometry of the Ca II H and K lines from the Dark Energy Camera, covering $128$ deg$^2$ across the center and identified tidal tails of CraII as part of the Mapping the Ancient Galaxy in CaHK (MAGIC) survey. Our combined photometric metallicity, color-magnitude, proper motion, and parallax selections identify 162 CraII candidates. Of these, 37 candidates are located in the tidal tails which extend at least $7^\circ$ ($\sim 95$ kpc) from the center of CraII, suggesting it has lost $\gtrsim 25$% of its initial stellar mass. We confirm low contamination rates with dedicated control fields and highlight the extremely low surface brightness stellar features that can be uncovered with CaHK data, as faint as $\sim 36$ mag arcsec$^{-2}$. We also make the first detection of a metallicity gradient ($-0.34\pm0.17~{\rm dex}~{\rm deg}^{-1}$) in the center of the galaxy and infer a stream width of $w\sim 0.8^\circ$, roughly 50% larger than the CraII half-light radius. The detection of candidates in the most distant CraII pointings from its center implies that the tidal tails extend beyond our footprint. We compare the CraII stream to $N$-body models with "cored" and "cuspy" dark matter halo progenitors, determining that CraII's density profile is still ambiguous and warrants further modeling.
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All authors Kaia R. Atzberger, Andrew B. Pace, Nitya Kallivayalil, Anirudh Chiti, Denis Erkal, William Cerny, Guilherme Limberg, Vinicius M. Placco, Deepthi S. Prabhu, Guy S. Stringfellow, A. Katherina Vivas, Astha Chaturvedi, Peter S. Ferguson, Alexander H. Riley, David J. Sand, Jeffrey L. Carlin, Yumi Choi, Denija Crnojević, Alex Drlica-Wagner, Alexander P. Ji, Ting S. Li, Clara E. Martínez-Vázquez, Gustavo E. Medina, Noelia E. D. Noël, Alistair R. Walker, Julio A. Carballo-Bello, David J. James, Burçin Mutlu-Pakdil, Mahdieh Navabi, Joanna D. Sakowska