Solar and Stellar Astrophysics · Cross-listed from physics.space-ph
Evolution of Coronal Mass Ejection Properties through Superposed Epoch Analysis from 0.2 to 2.2 au
Yakub Olufadi, Nada Al-Haddad, Florian Regnault et al. (+6 more)
Coronal mass ejections (CMEs) are explosive and energetic events consisting of strong
magnetic structures erupting from the
solar corona. We use superposed epoch analysis to investigate the general properties of CMEs as measured in situ from 0.2 to 2.2 au based on over 1600 events obtained from the HELIO4CAST catalog. We examine the dependence of the CME global properties on
solar cycle phase, and compare the CME parameters derived in the active phase (AP) with the quiet phase (QP). Our findings show that during the AP of the
solar cycle, the occurring CMEs are faster and have stronger
magnetic field strength than during the QP, which has denser but weaker
magnetic strength. These differences in
magnetic field strength and density remain even when controlling for the speed. This may indicate that the enhanced profiles observed during the AP are not only a consequence of the CME propagation speed but may also reflect intrinsic differences in the eruption mechanism during different
solar cycle phases. We also study how the
magnetic field strength and components of the CME
magnetic ejecta (ME) structure evolve with heliocentric distance. We find that the toroidal and poloidal ME
magnetic field components have a similar power law decrease with distance, indicating a comparable expansion behavior of CMEs in these dimensions. We further quantify the CME
magnetic field asymmetry %(often associated with CME aging) using the front-to-rear ratio of the toroidal component across heliocentric distance and find evidence of an increase of this ratio with heliocentric distance.
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All authors Yakub Olufadi, Nada Al-Haddad, Florian Regnault, Noé Lugaz, Bin Zhuang, Charles J. Farrugia, Christian Möstl, Emma E. Davies, Eva Weiler
High Energy Astrophysical Phenomena
The Role of Whistler and Ion Cyclotron Waves in Particle Escape from Mirror Modes in the Intracluster Medium
Petr Ugarov, Francisco Ley and Ellen Zweibel
Electron and ion-cyclotron waves are well known to exist in
solar system
plasmas but their existence and importance in
galaxy clusters is an open question. Guided by numerical simulations, (Ley et al. (2024)) argued that whistlers (electron-cyclotron) and ion-cyclotron (IC) waves are generated by trapped particles in mirror modes in the nonlinear stages of the mirror instability under ICM conditions. Building on this work, we construct a novel particle propagation simulation of the ICM
plasma based on the static electromagnetic field configuration from the fully kinetic particle-in-
cell (PIC) simulation of the nonlinear mirror instability by (Ley et al. (2024)). We study how the trapping rate of particles is related to the secondary waves driven by mirror modes. We observe that secondary whistlers and IC waves enhance trapped particle escape from mirror modes. We measure the particle-wave scattering rate by whistlers and IC waves, demonstrate that the scattering rates and wave amplitudes follow the proportionality relation expected from quasilinear theory, and show the existence of a significant correlation between scattering rates and the excitation of secondary instabilities.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Energy extraction from NED-deformed rotating black holes via the Comisso-Asenjo reconnection process
Marco Figliolia, Gaetano Lambiase, Ali Övgün et al. (+1 more)
We study rotating black holes in general relativity coupled to nonlinear electrodynamics (NED), focusing on an axisymmetric solution with deformation parameter $g$. On the spherical seed, weak-field
lensing via the Gauss-Bonnet method and the shadow radius yield a
spin-insensitive bound by enforcing a conservative $\sim 10\%$ tolerance on the Sgr A* ring size, namely $g/M \lesssim 1.26$. In the eikonal regime we derive analytic quasinormal-mode shifts, even in $g$, and obtain an independent ceiling consistent with the shadow constraint. For the rotating geometry, we provide closed-form ZAMO scalars, chart horizons and the ergoregion, and analyze equatorial geodesics (
photon orbits and ISCO). We then formulate the Comisso-Asenjo reconnection channel in the ZAMO frame, identify the negative-energy window, and integrate the extracted power over the allowed radii; from the tolerated fractional departure from the Kerr power we define a
spin-dependent extraction bound $g_\delta(a\mid\sigma_0,\xi)$. Taken together, the QNM/shadow ceiling and the extraction bound appreciably narrow the admissible region for $g/M$ in the $(a/M,g/M)$ plane, so even within our deliberately simplified, single-layer equatorial setup, the two complementary probes already provide informative constraints on NED deformations, testable with present data and upcoming horizon-scale and ringdown campaigns.
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All authors Marco Figliolia, Gaetano Lambiase, Ali Övgün, R. C. Pantig
Instrumentation and Methods for Astrophysics
A distributed resource-adaptive implementation of the widefield radio-interferometric measurement model for scalable image formation
Arwa Dabbech and Yves Wiaux
Modern image formation
algorithms in
radio interferometry rely on repeated applications of the operator {\Phi} modelling the measurement process and its adjoint {Phi^\dagger} to enforce consistency with the acquired data, specifically via their composite mapping {Phi^\dagger\Phi} encoding the array's point spread function (PSF). The large data volumes produced during wideband observations yield significant computational challenges for image formation. Moreover, for widefield imaging, the baseline components along the line of sight w complicate severely the measurement model beyond the conventional 2-dimensional non-uniform
Fourier transform (NUFFT), making the PSF highly position-dependent. We propose a distributed resource-adaptive implementation of the widefield measurement model, enabled by a hybrid w-stacking/w-projection approach, whereby the number of w-bins is set in a fully automated manner to minimise the computational cost under the compute system's
memory constraints. The resulting measurement model is naturally decomposed and distributed into low-dimensional operators specific to w-bins. Residual w-offsets are integrated as measurement-specific
Fourier kernels augmenting the sparse de-gridding
matrix of the basic NUFFT model. An optional data dimensionality reduction is also introduced, jointly encoding the sequential
Fourier de-gridding/gridding operations in {Phi^\dagger\Phi} into a
holographic matrix when required by
memory constraints. For further parallelisation, the sparse de-gridding or
holographic matrices are decomposed into blocks via
memory-controlled
Fourier partitioning. The approach has been validated in prior works through real data case studies for both monochromatic and wideband imaging of MeerKAT and ASKAP data. We provide herein a thorough analysis of its computational efficiency using simulated MeerKAT data. A MATLAB implementation is available in BASPLib.
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High Energy Astrophysical Phenomena
Armen Sedrakian
Binary
neutron star mergers provide a unique laboratory for studying matter under conditions that cannot be reproduced in terrestrial experiments. They probe dense matter at supranuclear density, finite temperature, rapid rotation, strong
gravity, and extreme
neutron excess, while producing observable signals in gravitational waves, electromagnetic radiation, and, in principle,
neutrinos. This review focuses on the
nuclear physics of binary
neutron star mergers. We discuss the dense-matter equation of state (EoS), the inspiral and merger dynamics, the structure and lifetime of the post-merger remnant, transport and dissipative processes, weak interactions and
neutrino transport, and the production of heavy elements through $r$-process nucleosynthesis. Particular emphasis is placed on the connection between microscopic physics and multimessenger observables, including
tidal deformability, post-merger gravitational-wave spectra, kilonova light curves, short gamma-ray bursts, and afterglows. We also review how observations of events such as GW170817, together with
neutron star mass and radius measurements, laboratory
nuclear experiments, and theoretical many-body calculations, constrain the EoS and the composition of dense matter. The goal is to summarize the current understanding of how
nuclear physics controls the dynamics and observable signatures of binary
neutron star mergers, and to identify the open questions that future multimessenger observations and improved
nuclear theory will address.
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Cosmology and Nongalactic Astrophysics
NuSTAR as an Axion Helioscope: probing axion-nucleon and axion-electron couplings
Tiziano Zanzarella, Francisco R. Candón, Maurizio Giannotti et al. (+5 more)
We investigate
solar X-ray observations as a probe of
axions and
axion-like particles. These particles can be produced in the interior of the Sun via the conversion of thermal
photons, as well as through processes involving
axion-electron and
axion-nucleon interactions. The resulting
axions can then reconvert into
photons in the Sun's atmospheric
magnetic field, generating a signal in the X-ray energy range. In this work, we derive new limits on
axions using X-ray observations with the
Nuclear Spectroscopic
Telescope Array (NuSTAR) during the 2020
solar minimum. In the regime where ALP production is dominated by couplings to electrons or nucleons, we obtain bounds on the product of couplings $g_{ae}\cdot g_{a\gamma}\lesssim 1.1\times10^{-24}\,\rm GeV^{-1}$ and $g_{aN}^{\rm eff}\cdot g_{a\gamma}\lesssim 2.3\times 10^{-19}\,\rm GeV^{-1}$ at 95% CL, for
axion masses $m_a\lesssim10^{-6}\,\rm eV$. These constraints strongly improve current ground-based experimental limits, establishing
solar X-ray observations as a powerful and robust method for
axion searches.
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All authors Tiziano Zanzarella, Francisco R. Candón, Maurizio Giannotti, Marco Regis, Jaime Ruz, Marco Taoso, Elisa Todarello, Julia K. Vogel
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Charging Across the Phantom Divide with Modified Gravity
Rodrigo Calderon and Eric V. Linder
Cosmology where the effective dark energy crosses $w=-1$ can be realized in Horndeski
gravity with shift symmetric terms plus a linear potential. We highlight the special role of the nearly conserved scalar charge. The theory is highly predictive for the early phantom behavior and we identify three ways to cross $w=-1$. None of them recreate conditions indicated by current data very well. The major lesson is that such modified
gravity with a potential lacking a cosmological constant and only crossing $w=-1$ once (hence the less elaborate models) has difficulty fitting current data. We provide an online interactive application solving the system of
evolution equations, for the reader to explore various scenarios at will.
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Astrophysics of Galaxies
Cosmic Ray Feedback in Galactic Disks: Star Formation, Cosmic Ray Transport, and Multiphase Outflows in TIGRESS++ Simulations
Chang-Goo Kim, Lucia Armillotta, Eve C. Ostriker et al. (+5 more)
We present new simulations of local
star-forming disks that self-consistently evolve
cosmic rays (CRs) and multiphase gas using TIGRESS++. To isolate the role of CRs, we conduct paired simulations under
solar-neighborhood conditions: a magnetohydrodynamics (MHD) model following the standard TIGRESS-classic framework with FUV heating and
supernova (SN) feedback from
star clusters formed via gravitational collapse; and a CRMHD model in which an additional 10% of each SN's energy is injected as CRs. These CRs are transported anisotropically along
magnetic field lines via a two-moment solver, with the CR scattering rate set by balancing Alfven-wave growth and damping based on the self-confinement paradigm. The CRMHD model develops a characteristic two-zone vertical CR profile: uniform pressure in the
diffusion-dominated, high-density midplane gas, and an exponential atmosphere shaped primarily by advection and streaming in low-density extraplanar gas. The CR pressure is comparable to the total thermal gas pressure in the midplane, but is too uniform to affect gas dynamics, leaving SFRs unchanged. In contrast, the vertical CR pressure gradient at |z| > 1 kpc accelerates warm outflowing gas, resulting in an approximately 4 times higher mass loading factor than in the MHD model. CR-gas interactions increase CR energy near the midplane through compressional work, while CR streaming heats low-density warm-hot gas. TIGRESS++ opens a path toward investigating CR transport and CR-regulated ISM and
outflow dynamics at high resolution across diverse
galactic environments.
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All authors Chang-Goo Kim, Lucia Armillotta, Eve C. Ostriker, Sanghyuk Moon, Lachlan Lancaster, Jeong-Gyu Kim, Nora B. Linzer, Ronan N. Hix
High Energy Astrophysical Phenomena
Constraining Scattering Medium Geometry with Cyclic Spectroscopy
Jacob E. Turner
We use cyclic spectroscopy to infer the scintillation parameter $C_1$ for the millisecond
pulsar B1937+21. This marks the first time this parameter has been measured for any
pulsar without assuming a pulse broadening function shape prior to deconvolution from the intrinsic pulse profile, removing significant potential biases in scattering delay estimation and letting us consider a wider range of line-of-sight geometries. At 428 MHz, we find a weighted mean and standard deviation across multiple epochs and independent scintillation fluctuations of $C_1$=1.21$\pm0.01$, which, along with the consistent presence of diffuse scintillation arcs, favors a thick screen geometry spanning just over 10% of the Earth-
pulsar distance. The resulting precision in our weighted average allows us to rule out various thin screen geometries, as well as thick screen geometries comprising more than 30% of the Earth-
pulsar distance, with greater than $5\sigma$ certainty at this observing frequency. We also use our measured $C_1$ values to determine diffraction scales, which we find to be roughly 11$\times10^3$ km between 418 and 438 MHz, suggesting an inner scale on the order of $10^3$ km. Future implementations of our method to other lines of sight through the
galaxy may substantially improve efforts to understand structures that contribute to the majority of
pulsar emission scattering in the interstellar medium. As flagship instruments like the Green Bank
Telescope begin offering the use of cyclic spectroscopy backends, and other instruments begin exploration and commissioning of similar systems, demonstrations like these will be crucial for the widespread adoption of cyclic spectroscopy.
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Astrophysics of Galaxies
Bar-halo interaction: the role of orbital anisotropy
Paula Gherghinescu, Francesca Fragkoudi and Alis Deason
We investigate the dynamical response of dispersion-dominated
halo populations to a rotating
galactic bar, focusing on how the underlying
halo phase space distribution function (DF), and in particular the orbital anisotropy, shapes resonant structure formation. Using controlled test-particle simulations in a fixed Milky Way-like potential, we systematically vary the velocity anisotropy and net rotation of
halo-like components while keeping the
halo density profile, global potential, and bar properties fixed. We find that bar-induced resonances generate prominent substructure in energy-angular momentum space, but that the morphology, strength, and density contrast (i.e. overdensities versus underdensities) of these features depend sensitively on the
halo orbital anisotropy and how resonant transport aligns with gradients of the DF in action space. For instance, radially biased
halos tend to exhibit stronger responses and features across all main resonances. Our results also show that angular momentum exchange and the torque exerted on a
halo are governed not only by its density profile but crucially by its orbital anisotropy structure. This highlights the importance of
halo anisotropy when interpreting phase-space substructure in the
stellar halo of the Milky Way with current and future surveys, while also having implications in further understanding the DM
halo-bar coupling in disk
galaxies.
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Astrophysics of Galaxies
Limited imprint of high-mass IMF variations on sodium abundances in main-sequence galaxies
Ziyi Guo, Donatella Romano, Zhiqiang Yan et al. (+10 more)
Growing evidence suggests that the
stellar initial mass function (IMF) varies systematically across
galaxies, deviating from the canonical Milky Way form. Such variations would modify the integrated nucleosynthetic yields, and hence the abundance patterns used in
stellar population synthesis studies. How these could impact, in particular, the sodium abundance (and sodium-to-oxygen ratios) in
star-forming
galaxies is not well understood. In this work, we systematically study how high-mass IMF variations affect sodium enrichment using a one-zone
galactic chemical
evolution model. The model incorporates
star formation histories from semi-analytic simulations and is calibrated to match the observed
galaxy mass–
metallicity relation. We find that varying the IMF high-mass end (and the IMF slope) could only alter the sodium abundance by less than 0.1 dex, across
galaxies with
stellar masses from $10^9\,\mathrm{M}_\odot$ to $10^{11}\,\mathrm{M}_\odot$. This result is robust under different
stellar models and
galaxy evolution assumptions, primarily because sodium production is similar to that of oxygen. We conclude that sodium abundance is largely insensitive to changes in the high-mass IMF, unlikely to compromise the use of sodium indices as IMF diagnostics in
stellar population studies.
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All authors Ziyi Guo, Donatella Romano, Zhiqiang Yan, Zhi-Yu Zhang, Xiaoting Fu, Lizhi Xie, Tereza Jerabkova, Gabriella De Lucia, Michaela Hirschmann, Fabio Fontanot, Eda Gjergo, Alice Concas, Xiaodong Tang
High Energy Astrophysical Phenomena
Strong Constraints on Millisecond Pulsar Injection Spectra from Fermi-LAT Observations of the Galactic Center
Jordan Koechler, Pedro De la Torre Luque and Mattia Di Mauro
Millisecond
pulsars (MSPs) are a leading explanation of the
Galactic Center excess (GCE) observed in
Fermi-LAT data. We constrain this scenario by jointly modeling
prompt and inverse-Compton $\gamma$ rays from MSP-injected $e^\pm$ on the
Galactic bulge, using recent
Fermi-LAT GCE spectra from state-of-the-art interstellar emission models and data analysis. Current data place strong upper limits on the efficiency ratio $\eta_e/\eta_\gamma$ across broad $e^\pm$ injection scenarios, surpassing those from globular-cluster observations with MAGIC and competitive with projected CTAO sensitivities toward the
Galactic bulge.
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Earth and Planetary Astrophysics
Dynamical Stability and Habitability in the HD 20794 System
Stephen R. Kane
The Keplerian orbit of a terrestrial
planet can be a significant driver in the
evolution of surface conditions, as well as influencing the overall dynamics of the system. The HD 20794 system harbors three confirmed
planets orbiting a nearby G-type
star, including HD 20794 d, a $\sim$5.82 $M_\oplus$ (minimum mass)
planet on a highly eccentric ($e = 0.45$) orbit that passes through the Habitable Zone (HZ). Here, we present a dynamical analysis of the HD 20794 system. We calculate the HZ boundaries and quantify the fraction of the orbital period that
planet d spends within the conservative and optimistic HZ limits. Using N-body simulations, we explore the long-term orbital stability across inclinations spanning $\sim$5–90\degr. The system remains dynamically stable over the full $10^7$ year integration for all tested inclinations, including $i = 5\degr$ ($M_d \approx 67$ $M_\oplus$). The secular eccentricity oscillations share a common eigenperiod that scales inversely with the total system mass, consistent with Laplace-Lagrange secular theory. We examine the origin of the eccentricity of
planet d, including
planet-
planet scattering and secular excitation from an unseen eccentric outer companion. HD 20794 d is the lowest-mass confirmed
planet with $e > 0.4$ whose orbit crosses the HZ of its host
star, and its periastron passage deep within the HZ makes it a likely dynamical disruptor for additional terrestrial
planets, reinforcing its status as the dominant habitability prospect in the system. The proximity of HD 20794 and its inclusion on the Habitable Worlds Observatory precursor target list make this a high-priority system for understanding the interplay between orbital dynamics and planetary habitability.
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Earth and Planetary Astrophysics
The Persistent Missing Mass Problem in Planet Formation
Eve J. Lee, William DeRocco, Sam Hadden et al. (+1 more)
Recent ground-based microlensing surveys suggest that our
Galaxy may abound with small free floating
planets, potentially up to $\sim$21 such
planets per
star. We explore the implication of such possibility on the mass budget for
planet formation. When the microlensing
planets, both bound and free-floating, are taken into account, along with the short-period
planets, T Tauri disks have insufficient mass to source the mass of known
planets, even if all the solids convert into planetary bodies. Younger Class 0/I disks can help resolve the problem but generally fall short of the required mass when variable
planet formation efficiency from pebble or planetesimal
accretion is taken into consideration. If the free-floating
planet mass function is as bottom-heavy as reported, heavier Class 0/I disks may be necessary. Alternatively, free-floaters may preferentially form in the most massive disks around massive
stars consuming the majority of the mass budget, leading to a decrease in the bound
planet occurrence rate for higher mass
stars, which is observed. Precise constraints on the bottom of
planet mass function are necessary: a peaked mass function may eliminate the missing mass problem; by contrast, verifying a bottom-heavy function could spell a crisis in
planet formation.
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All authors Eve J. Lee, William DeRocco, Sam Hadden, B. Scott Gaudi
Astrophysics of Galaxies
NISER-IUCAA New Simulations of JWST GAlaxies and Quasars(NINJA): Properties of galaxies at $5 \leq z \leq 10$
Ranit Behera, Raghunathan Srianand, Nishikanta Khandai et al. (+1 more)
We present the NINJA suite of cosmological hydrodynamical simulations developed to investigate
galaxy formation and
evolution at $z \gtrsim 5$ in the era of JWST. Using our fiducial simulation, we explore a range of spectral synthesis prescriptions and
dust attenuation models, demonstrating that suitably chosen parameters can reproduce the observed UV luminosity functions (UVLFs) over $5 \leq z \leq 10$. In all cases, the inferred
dust-to-metal ratio evolves with
redshift, although its normalization at fixed
redshift varies by a factor of $\sim 7$, depending on the adopted
dust–
metallicity scaling and attenuation curve. These model variations introduce substantial scatter in predictions for the $B$-band luminosity function, the H$\alpha$ luminosity function, the UV slope–UV magnitude relation, the
stellar mass–Balmer ratio relation, and the relation between
stellar and nebular colour excesses. Simultaneously reproducing these observables across multiple
redshifts will therefore be essential for constraining
dust models at high
redshift with forthcoming observations. Observations of
galaxies spanning a broad range of
stellar masses with the Atacama Large Millimeter/submillimeter Array (ALMA) will provide particularly strong and independent constraints on
dust properties. Our fiducial models underpredict the UV luminosity function at $z \geq 10$ relative to current observations, even when adopting a top-heavy IMF and neglecting
dust attenuation. We find that
galaxy properties are not fully converged at these
redshifts in our simulation, indicating that higher-resolution simulations are required to robustly model
galaxies at $z > 10$. We further emphasize that degeneracies between feedback prescriptions used in our simulation and
dust properties must be carefully addressed when interpreting high-
redshift observations and calibrating
galaxy formation models.
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All authors Ranit Behera, Raghunathan Srianand, Nishikanta Khandai, Prakash Gaikwad
Cosmology and Nongalactic Astrophysics
Field-level multi-tracers simulation-based inference of cosmological parameters from 3D maps
Giulio Scelfo, Satvik Mishra, Mauro Rigo et al. (+2 more)
Extracting maximum cosmological information from current and upcoming large-scale structure data requires going beyond summary statistics as currently used in likelihood-based inference. Simulation-Based Inference (SBI) promises to enable the exploitation of field-level information and the rich physics of modern hydrodynamical simulations. We develop a proof-of-concept SBI pipeline to explore its potential to constrain the cosmological parameters $\{\Omega_{\rm m}, \sigma_8\}$ from
galaxy number counts, neutral hydrogen (HI) intensity mapping and their combination. We use neural emulators trained on full hydrodynamical simulations to generate
galaxy and HI maps from fast, approximate dark matter simulations. Combined with neural posterior estimation, this enables the estimation of cosmological parameters while marginalizing over astrophysical effects. We perform inference both on the power spectrum and on representations derived from field-level 2D or 3D maps, comparing results from each probe and the combination of both tracers, and assessing the impact of data compression and multi-tracers information on cosmological constraints. Combining
galaxy and HI fields improves constraints with respect to single-tracer cases by a factor 2 to 7 in terms of a Figure of Merit describing the joint precision on cosmological parameters, depending on the tracer/configuration. Moving from summary statistics to field-level inference leads to a consistent gain in constraining power of about a factor 3, with 3D maps providing the most precise and well-calibrated posteriors. This gain in precision is robust even when astrophysical parameters are marginalized over. Further developments (including realistic survey effects and improvements in emulators' faithfulness) will enable the application of this analysis pipeline to upcoming surveys.
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All authors Giulio Scelfo, Satvik Mishra, Mauro Rigo, Roberto Trotta, Matteo Viel
Astrophysics of Galaxies
How galaxies acquire their stellar mass at high redshift: High star formation efficiencies and the relative roles of dust and initial mass function
Hao Fu, Francesco Shankar, Fabio Fontanot et al. (+9 more)
JWST has measured an unprecedented abundance of
galaxies above $z\gtrsim 4-5$, whose formation and
evolution are still difficult to reconcile within traditional
galaxy evolution models in a $\Lambda$CDM framework. Here, we present a study on the
star formation histories of these high-
redshift galaxies between $z\simeq5-12$ via a data-driven semi-empirical model that uses the observed UV LFs as input to retrieve SFRs, naturally bypassing any uncertain modelling of cooling, feedback and/or
stochastic processes.
Galaxy stellar masses are progressively built in time by integrating their SFRs assigned along their progenitor
haloes via the SFR-
halo accretion rate relation, derived from abundance matching between the input observed UV LFs with the dark matter
halo accretion rate distributions at each
redshift. This makes the SFEs a full prediction of the model rather than a tuned input, serving as a natural baseline to test burstiness,
dust attenuation, or IMF variations. Our approach naturally reproduces the total
stellar mass function, the large-scale clustering, and the
star-forming main sequence. We find that massive
galaxies grew their
stellar mass with a bursty
star formation at $z\sim9-10$, broadly in agreement with the
star formation histories inferred from spectral energy distribution fitting, with the SFE reaching high peaks of $0.8-0.9$ at $z>9$ and lowering to standard values of $0.2-0.3$ below $z\lesssim9$. We find that the presence of
dust could enhance the predicted SFRs at $z\lesssim8$, better reproducing the observed SFRs of massive dusty
galaxies, and increase the SFEs to values close to or even above unity at $z \gtrsim 8$. Finally, switching to top-heavy IMFs reduces the SFEs by a factor of $2-3$, highlighting the need for a variable IMF as an inevitable ingredient in the
evolution of
galaxies at high
redshifts to avoid unphysical SFEs, especially in the presence of
dust.
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All authors Hao Fu, Francesco Shankar, Fabio Fontanot, Andrea Lapi, Feng Yuan, Mohammadreza Ayromlou, Daniel Roberts, Lumen Boco, Nicola Menci, Emiliano Merlin, Laura Pentericci, Mengyuan Xiao
Astrophysics of Galaxies
A framework for modelling Population III stars in cosmological simulations
Bipradeep Saha, Rahul Kannan and Giovanni M. Mirouh
Population III (Pop III)
stars are the first generation of
stars to form in the universe, emerging from
primordial gas composed mainly of hydrogen and helium. They play a crucial role in ending the
cosmic dark ages and initiating reionization. In this work, we present a comprehensive framework for modelling Pop III
stars in cosmological simulations. This includes three key components: (1) an enhanced thermochemical network that tracks the
equilibrium abundances of key catalytic species such as $\rm{H_2^+}$ and $\rm{H^-}$, which are crucial for forming molecular hydrogen in
primordial gas; (2) detailed
stellar spectra of Pop III
stars computed from MESA evolutionary tracks and TLUSTY atmosphere models; and (3) comprehensive
supernova feedback, including both Core-Collapse and Pair-Instability
supernovae, with detailed elemental yields. We implement these improvements in AREPO-RT and test them using cosmological zoom-in simulations of a $1.95 \times 10^9$ $\rm M_\odot$
halo at $z=3$. Our results show that Pop III
stars form at $z > 13$ and continue forming until $z \sim 5$, significantly affecting early
galaxy evolution through radiation and energetic
supernova feedback. The enhanced thermochemistry enables more efficient gas cooling, while Pop III feedback creates photo-heated diffuse gas and drives distinct metal enrichment patterns at $10 < z < 6$. The choice of IMF for Pop III
stars critically determines the balance between radiative and mechanical feedback, with top-heavy choices producing stronger feedback and more metals but retaining less metal-enriched gas within the
halo. Finally, we show that high-energy radiation from Pop III
stars is necessary to explain the recent high-equivalent-width observations of the $\rm HeII$ line from a
galaxy at $z\sim11$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Electromagnetic Signatures From Primordial Black Holes in the Solar System
Alexandra P. Klipfel and David I. Kaiser
Primordial black holes (PBHs) in the asteroid-mass range, with typical masses $10^{17}\,{\rm g}\lesssim M \lesssim 10^{23}\,{\rm g}$, have drawn significant recent
attention as a viable dark matter candidate. The peak frequencies of
photons emitted via Hawking radiation from asteroid-mass PBHs range from infrared to $\gamma$-ray bands. We calculate expected local transit rates for extended PBH mass distributions which could comprise all the dark matter. We evaluate prospects for detecting Hawking-radiated
photons from local PBH transits through the inner
Solar System and from PBH explosions in the far outer edges of the
Solar System. We consider several existing and proposed ground-based and space-based instruments sensitive to
photons from the
radio band to ultrahigh energy $\gamma$-rays. We find that proposed instruments, such as the AMEGO-X satellite, could reliably detect PBH transits within ${\cal O} (0.1 \, {\rm AU})$ of the Earth, while the HAWC and LHAASO observatories are both sensitive to PBH explosions out to ${\cal O}(0.1 \, {\rm pc})$ and ${\cal O}(0.5 \, {\rm pc})$ respectively. We conclude by specifically considering potential companion electromagnetic signatures in the case of a PBH explosion about $10^3\,{\rm AU}$ from Earth, which has been suggested as a potential source for the $\sim 220 \, {\rm PeV}$ ultrahigh-energy KM3-230213A
neutrino event observed by the KM3NeT collaboration in 2023. Whereas we find that the recent KM3NeT event would not have yielded detectable electromagnetic signals – due to its location on the sky, proposed distance from Earth, and the offline status of the HAWC observatory at that time – we demonstrate that future PBH explosions at comparable distances could yield measurable electromagnetic signals at Earth, depending on
alignment of the PBH burst with detector fields of view.
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Solar and Stellar Astrophysics
Bimodality in Rotational Modulation of Planet-Hosting Stars
Alexandre Araújo and Adriana Valio
Stellar magnetic activity is governed by the interplay between rotation, convection, and the
evolution of surface
magnetic structures, yet the role of planetary systems in shaping these processes remains uncertain. Here, we analyze Kepler photometry of more than 1,300
stars to investigate rotational modulation in
stars with and without confirmed
exoplanets. Using a time–frequency analysis, we measure the photometric proxy of rotational modulation dispersion, $S_{\rm phot}$, tracing the temporal coherence of surface
magnetic features.
Stars hosting confirmed
exoplanets exhibit systematically enhanced $S_{\rm phot}$ values compared to
stars without detected
planets ($\Delta S_{\rm phot}=0.17 \pm 0.01$ rad d$^{-1}$; $p<10^{-25}$). More importantly, the $S_{\rm phot}$ distribution of
planet hosts is bimodal, with peaks at $0.12$ and $0.44$ rad d$^{-1}$ (Hartigan's Dip Test $p<10^{-6}$; $\Delta \mathrm{BIC}=188.7$), a feature absent in the control sample. We interpret $S_{\rm phot}$ as a proxy for rotational modulation dispersion, reflecting spot
evolution rather than true differential rotation. The two regimes correspond to stable
magnetic coherence with long-lived active regions and rapidly evolving activity patterns. The presence of these distinct regimes exclusively among
planet-hosting
stars suggests that planetary systems may influence the temporal organization of
stellar magnetic activity and indirectly affect
stellar dynamos.
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Cosmology and Nongalactic Astrophysics
Unifying Early and Late Dark Energy: Dynamical Requirements and Obstructions
William Giarè and Jeremy Sakstein
We investigate whether early- and late-time dark energy could arise from a single scalar field. Adopting a bottom-up perspective, we first identify the sequence of dynamical regimes that any unified scenario must traverse to account for both an early dark energy phase relevant for pre-recombination solutions of the Hubble tension and the late-time acceleration of the Universe. We derive the corresponding requirements on the scalar energy density and equation of state. We then adopt a complementary top-down perspective and translate these requirements into constraints on the phase-space structure of minimally coupled scalar fields with tracking-like dynamics. We show that satisfying all requirements necessitates a potential with three distinct slopes, arranged in a steep-steeper-shallow hierarchy. This conclusion remains unchanged in the presence of conformal couplings to dark matter. These results place strong constraints on attempts to construct unified models of early- and late-time dark energy. We discuss implications for model-building.
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High Energy Astrophysical Phenomena
GRB 260310A / SN 2026fgk: A Multi-Wavelength Study of a Nearby Underluminous Long GRB and SN with a Complex Afterglow
Ramandeep Gill, Rosa L. Becerra, Antonio de Ugarte Postigo et al. (+54 more)
We present a comprehensive multi-wavelength study of GRB 260310A / SN 2026fgk, a nearby ($z=0.153$), long-duration gamma-ray burst (GRB) with an exceptionally underluminous
prompt $\gamma$-ray emission and a Comptonized spectrum. The burst occurred at the edge of a blue host
galaxy at a projected distance of 15 kpc, which is one of the largest offsets reported for a long GRB. The bright optical afterglow, with dense coverage from COLIBRÍ, likely peaked at a few to several hours post-burst, followed by a shallow decay not expected from canonical afterglow models. Both the optical and X-ray light curves show a brief chromatic plateau from $4-7$ days. We show that the subsequent rebrightening observed at $\sim20$ days is best explained by the combined contribution of the associated Type Ic-BL
supernova, identified in GTC spectra, and a late-time refreshed shock. The broadband optical to X-ray spectral energy distribution is well described by synchrotron emission from the forward shock, while the
radio observations demand an additional emission component. We model the afterglow using (a) an on-axis uniform jet from a dirty fireball with late-time energy injection and (b) a misaligned jet with power-law angular structure, both having material emitting along our line-of-sight (LOS) moving with an initial Lorentz factor of $\Gamma_0\sim20-35$. We conclude that at more typical GRB distances ($z\gtrsim0.5$) the
prompt $\gamma$-ray emission from this source would likely have escaped detection, whereas its optical afterglow would have remained observable, making the event appear as an orphan afterglow or a gamma-ray quiet fast X-ray transient.
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All authors Ramandeep Gill, Rosa L. Becerra, Antonio de Ugarte Postigo, Christina C. Thöne, Alan M. Watson, Noémie Globus, Jean-Grégoire Ducoin, Peter Veres, Stanley E. Kurtz, Asuka Kuwata, Antonio Martín-Carrillo, Luca Izzo, Christophe Adami, Enrique Moreno Méndez, Nikos Mandarakas, Camila Angulo-Valdez, Stéphane Basa, William H. Lee, Edilberto Aguilar-Ruiz, Dalya Akl, Margo F. Aller, Miguel Ángel Aloy, Jie An, Sarah Antier, Jean-Luc Atteia, Nathaniel R. Butler, Krittapas Chanchaiworawit, Philipe V. De La Parra, Damien Dornic, Francis Fortin, Shaoyu Fu, Johan P. U. Fynbo, Lluis Galbany, Leonardo García-García, Stefan Geier, Marion Guelfand, Linbo He, Shuaiqing Jiang, Emeric Le Floc'h, Massimiliano Lincetto, Xing Liu, Gianluca Lombardi, Diego López-Cámara, Daniele Bjørn Malesani, Francesco Magnani, Kanthanakorn Noysena, Margarita Pereyra, Ny Avo Rakotondrainibe, Anthony C. S. Readhead, Delphine Russeil, Fredd Sánchez-Álvarez, Benjamin Schneider, Tirth D. Surti, Nial R. Tanvir, Samaporn Tinyanont, Dong Xu, Zipei Zhu
Solar and Stellar Astrophysics
Understanding hydrodynamical wave-driven shear mixing in stellar radiation zones. Looking in the mirror of the dyapicnal oceanic mixing
Stéphane Mathis
Stellar radiation zones play a key role in the long-term magneto-rotational and chemical
evolution of
stars. As parts of the oceans and of the atmosphere of the Earth, their dynamics is controlled by the Archimedean buoyancy force and the Coriolis acceleration. They are the seat of an efficient extraction of angular momentum and of a mild mixing of chemicals. In this context, particle tracing in recent nonlinear hydrodynamical equatorial numerical simulations of
stellar radiation zones where internal
gravity waves (hereafter IGWs) are propagating led to the measurement of an effective diffusivity following the prescriptions derived by Garcia-Lopez & Spruit and by Zahn for the inflectional instability of the vertical shear of low-frequency IGWs. However, the associated instability criteria are not fullfiled. This effective diffusivity is found to scale as the squared velocity of IGWs for every rotation rates. Other dependences have also been derived in the literature, for instance in the case of the Stokes displacement. To interpret these results, we propose to explore the parameterisation for the mixing of particles, which has been proposed for the oceans. A foundation stone in physical oceanography is the so-called Osborn & Cox energetic balance that leads to an effective dyapicnal diffusivity for the transport of matter that scales as the ratio of the dissipation of the fluctuating flows over the squared Brunt-Väisälä stratification frequency. We demonstrate that this diffusivity is equivalent to the eddy diffusivity derived by Zahn for the inflectional instability of the vertical shear applied to low-frequency IGWs. This allows us to characterize the corresponding energetic balance where the power extracted by the waves from the mean flows is balanced by their dissipation and by the power produced by their buoyancy flux, which triggers mixing, for any rotation rate.
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High Energy Astrophysical Phenomena
X-ray Polarization Signatures from Comptonization by Magnetic Reconnection Plasmoids
John Groger, Kun Hu and Henric Krawczynski
Emission from X-ray binaries in the hard spectral state is dominated by high-energy radiation attributed to the Compton scattering of seed
photons. The prevalent model of the Comptonization by hot electrons or pairs faces the problem of rapid radiative cooling of the emitting particles. A proposed alternative mechanism is the Comptonization by scattering off fast plasmoids formed during
magnetic reconnection. In this work, we simulate a simplified model of the plasmoid chain with Monte Carlo radiation transport and report on spectropolarimetric properties. We find that the Comptonization off trans-relativistic bulk plasmoids is not only able to reproduce the 100 keV spectral cutoff, but furthermore produces X-rays that are above 1 keV strongly polarized perpendicular to the reconnection layer. The polarization is stronger than that from the Comptonization by an isotropic hot
plasma owing to the confinement of the motion of the scattering plasmoids in the plane of the reconnection layer. The dependence of polarization on azimuthal viewing angle is discussed, along with possible locations for the plasmoid chain in an equatorial current sheet or the sheath of the black hole's relativistic jet.
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Cosmology and Nongalactic Astrophysics
Early- and Late-Time Modifications to $\Lambda$CDM: Implications for the Hubble Tension
Rahul Dhyani, Purba Mukherjee, Arindam Chatterjee et al. (+1 more)
We investigate an extension of $\Lambda$CDM in which a fraction of cold Dark Matter (DM) decays into invisible dark radiation (DR) around the radiation-matter equality epoch, together with a non-standard dark energy (DE) equation of state characterized by $w_0$. The decaying DM component modifies the early expansion history and reduces the sound horizon at
baryon drag, while the DE alters the expansion rate at the late times. A comprehensive analysis combining Planck 2018+ACT DR6+DESI DR2+CMB
lensing datasets has been carried out to explore the viability of this framework in addressing the $H_0$ tension. This model yields a Hubble constant of $H_0 = 69.83 \pm 0.98~\mathrm{km\,s^{-1}\,Mpc^{-1}}$, reducing the discrepancy with SH0ES measurement to ${\sim}2.2\sigma$ and local distance network measurement (H0DN) to ${\sim}2.9\sigma$. Further, considering SH0ES and Pantheon+, the inferred value of the Hubble constant becomes $H_0 = 70.20 \pm 0.66~\mathrm{km\,s^{-1}\,Mpc^{-1}}$. The
Bayesian evidence suggests that this framework offers a fit to the relevant cosmological
datasets at a statistically similar level as $\Lambda$CDM. It is observed that correlated early- and late-time modifications to the cosmological expansion history provide a more effective route to reducing the $H_0$ tension than either class of modification alone.
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All authors Rahul Dhyani, Purba Mukherjee, Arindam Chatterjee, Anjan A Sen
Astrophysics of Galaxies
Interstellar extinction, polarization efficiency, and grain alignment in the direction towards bright-rimmed clouds and cometary globules
Saikhom Pravash
The polarization of starlight and thermal
dust emission, resulting from non-spherical grains aligned with the interstellar
magnetic field (B-field), act as a powerful tool to trace the B-field morphologies and strengths in molecular clouds and constrain the grain
alignment mechanisms and grain properties. The exact
alignment mechanisms of grains is not yet fully clear. However, the leading theory is the
alignment induced by RAdiative Torques (RATs), known as RAT theory. In this work, we use optical polarization observations of background
stars projected towards nine of Bright-Rimmed Clouds (BRCs) and Cometary Globules(CGs) to study the polarization efficiencies and the
alignment mechanisms of the grains in the direction towards the outer diffuse envelopes of these clouds. We use distance and extinction data of the
stars from
Gaia EDR3 and StarHorse 2 Catalogue. We study the variations of the degree and position angle of polarization, and the extinction, as functions of distance of the
stars. For some of the clouds, we find discrete enhancement of the extinction at certain distances along with an increase in polarization degree, signifying the presence of polarizing
dust layers. We estimate the polarization efficiency of grains towards each of the clouds. We find that it decreases with increasing extinction, and also shows a slight increase with
dust temperature for some clouds associated with more ordered
magnetic field orientations, providing an implication for the
alignment of grains by RATs. Whereas, for some other clouds, the decrease in the polarization efficiency with extinction may be caused by more fluctuations in the
magnetic field orientations.
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High Energy Astrophysical Phenomena
Compactness Peaks and Subpopulations: Probing Stellar Physics and Formation Channels of Merging Binary Black Holes
Shanika Galaudage
The growing catalog of gravitational-wave detections from the LIGO-Virgo-KAGRA (LVK) collaboration reveals structure in the binary black hole (BBH) mass distribution, including peaks near m1 = 10
solar masses and m1 = 35
solar masses, a high-mass suppression consistent with the pair-instability
supernova gap, and a possible dearth of systems near chirp mass M = 10-12
solar masses. We apply Compactness Peaks + Channels, a stripped-
star-motivated five-component population model, to 152 BBH mergers from GWTC-4.0. The model is decisively preferred over the LVK Broken Power Law + 2 Peaks baseline, with log10 Bayes factor = 7.69, and decomposes the population into isolated first-generation (1G), dynamical 1G, and hierarchical second-generation (2G) channels with fractions 0.75 (+0.11/-0.16), 0.22 (+0.16/-0.11), and 0.02 (+0.03/-0.01), respectively. The low-mass isolated component sharply localizes the 10
solar mass feature, with narrow masses, near-equal mass ratios, and low partially aligned
spins, consistent with stripped-
star binary
evolution. The 35
solar mass feature is primarily captured by the high-mass dynamical 1G component. The hierarchical component is consistent with 2G+1G mergers, with elevated primary
spins, mu_chi = 0.65 (+0.30/-0.22), and asymmetric mass ratios. We localize the compactness-peak edges at 12.3 (+2.4/-1.3) and 16.1 (+5.7/-5.3)
solar masses, consistent with, but not yet requiring, a compactness-driven dearth between them. These results support a multi-component description of the BBH population and motivate further tests of compactness-driven isolated
evolution.
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