Astrophysics of Galaxies
Witnessing the rapid growth of disk galaxies over cosmic time using JWST and HST
Samane Raji, Mireia Montes, Ignacio Trujillo et al. (+3 more)
Measuring
galaxy sizes is fundamental to understanding how
galaxies grow and evolve. Traditional methods to measure sizes either trace the concentration of light (i.e., effective radius) or are limited by the depth of the survey (isophotal methods). With the advent of deep, wide surveys, a new physically motivated definition of size has emerged: the edge of the
galaxy, defined as the most distant location where
star formation has occurred or is still occurring. In this work, we take advantage of the extraordinary depth and spatial resolution of the Hubble and James Webb Space
Telescopes to perform an accurate study of
galaxy edges at $z=1$. Using 22 photometric bands, we derive radial age and
metallicity profiles for two disk
galaxies in the GOODS-South field with
stellar masses of around $4\times10^{10}\ M_\odot$. The age profiles display a characteristic U-shape, while the
metallicity profiles steadily decrease with galactocentric distance. The turnover in the age profile occurs near the
galaxy edge, suggesting that
stellar migration is responsible for the
stars beyond the edge of these
galaxies. Comparison with $z=0$ disk
galaxies suggests that
galaxies at $z=1$ grow inside-out, with little or no increase in mass within the inner 8 kpc, but a significant increase (approximately 300%) in the outer regions.
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All authors Samane Raji, Mireia Montes, Ignacio Trujillo, Fernando Buitrago, Carlos Marrero-de la Rosa, Andrés Asensio Ramos
Solar and Stellar Astrophysics
Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. III. SiO and SiS abundances
R. Unnikrishnan, E. De Beck, L.-Å. Nyman et al. (+9 more)
The present understanding of C-rich AGB chemistry largely relies on observations of the archetypal carbon
star IRC+10216. Current molecular abundance estimates for carbon
stars are based either on single-dish spectra sampling a range of excitation conditions, or on interferometric mapping of a few lines. We aim to estimate the circumstellar abundances of SiO, SiS, and their most abundant isotopologues ($^{29}$SiO, $^{30}$SiO, $^{29}$SiS, $^{30}$SiS, and Si$^{34}$S) for a sample of five carbon
stars. We derived molecular abundances using detailed 1D non-local thermodynamic
equilibrium (non-LTE) radiative transfer (RT) modelling, constrained by both morphological and excitation information obtained from spatially resolved ALMA maps and single-dish observations. We further compared the derived abundances to chemical modelling results. We obtain good fits to the SiO and SiS line profiles, and derived well-constrained abundance profiles and reliable isotopic ratios for all sources except AFGL 3068. While the SiS peak abundances are very similar across the sample (2.0$\times$10$^{-6}-4.7\times$10$^{-6}$), we find that the SiO peak abundances of the rest of the
stars are a factor of $\sim$5 larger than that of IRC+10216. The $e$-folding radii ($R_\mathrm{e}$) are in the range 1.3$\times$10$^{16}-7.0\times$10$^{16}$ cm for SiO and 6.0$\times$10$^{15}-1.0\times$10$^{17}$ cm for SiS. The $R_\mathrm{e}$ increases with gas density for both SiO and SiS. Chemical models reproduce the derived SiO abundance profiles well, while over-predicting the SiS $R_\mathrm{e}$ values. Our models highlight the necessity of having spatially resolved observations across a broad range of excitation conditions, while also making evident the limitations inherent in 1D RT modelling using simplified (circum)
stellar models. We find that the currently assumed SiS photodissociation rate in chemical models is underestimated.
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All authors R. Unnikrishnan, E. De Beck, L.-Å. Nyman, H. Olofsson, W. H. T. Vlemmings, M. Maercker, M. Van de Sande, T. J. Millar, T. Danilovich, M. Andriantsaralaza, S. B. Charnley, M. G. Rawlings
High Energy Astrophysical Phenomena
The Millimeter/X-ray Relation in Rapidly Accreting Supermassive Black Holes at $z < 0.16$
Sophie M. Venselaar, Claudio Ricci, Santiago Del Palacio et al. (+12 more)
A tight correlation between
nuclear millimeter and X-ray emission has recently been found in nearby ($z < 0.01$) and low-Eddington ratio ($\rm \lambda_{Edd} < 0.1$)
radio-quiet Active
Galactic Nuclei (AGN), suggesting a common origin in the hot X-ray corona. We test this relation in nine more distant RQ AGN ($z \sim 0.06-0.16$) with higher bolometric luminosities ($\log(L_{\rm bol}/\mathrm{erg\,s^{-1}})=45.3-46.3$), Eddington ratios ($\rm \lambda_{Edd} = 0.19-0.85$), and X-ray bolometric corrections ($\kappa_{2-10}=29-194$), selected from the Burst Alert
Telescope (BAT) survey. We obtained quasi-simultaneous observations with Swift at 2-10 keV and the Atacama Large Millimeter/submillimeter Array (ALMA) at 100 GHz and with high angular resolution ($<0.14$"). We find that these high-luminosity AGN lie above the millimeter/X-ray correlation defined by lower-luminosity sources. A joint fit to both samples yields a second-degree
polynomial with an intrinsic scatter of 0.32 dex. Furthermore, the millimeter emission correlates linearly with both the UV disk luminosity and $L_{\rm bol}$, with intrinsic scatters of 0.45 and 0.35 dex, respectively. We propose that the deviation from the linear millimeter/X-ray relation arises from a two-component coronal electron population: thermal electrons that produce X-rays, but become less efficient at higher luminosities, and nonthermal electrons that produce millimeter emission and remain tied to $L_{\rm bol}$. Additional millimeter emission from
outflow-driven shocks may also contribute, though spectral energy distribution modeling and spectral index studies favor a coronal origin.
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All authors Sophie M. Venselaar, Claudio Ricci, Santiago Del Palacio, Kriti K. Gupta, Chin-Shin Chang, Roberto Serafinelli, Macon A. Magno, Richard Mushotzky, Elena Shablovinskaya, Taiki Kawamuro, Ezequiel Treister, Jacob S. Elford, Susanne Aalto, George C. Privon, Michael J. Koss
Cosmology and Nongalactic Astrophysics
Introducing the Lumina project: large-volume radiation-hydrodynamic simulations of the epochs of hydrogen and helium reionization
Oliver Zier, Aaron Smith, Xuejian Shen et al. (+8 more)
Understanding how
galaxies and active
galactic nuclei (AGN) jointly drive the reionization of the intergalactic medium (IGM) across
cosmic time remains a major challenge in cosmology. We present Lumina, a large-volume radiation-hydrodynamic simulation that self-consistently follows the coupled
evolution of the intergalactic medium,
galaxies, and AGN through HI, HeI, and HeII reionization down to
redshift $z=3$. Lumina evolves a cosmological volume of comoving side length $L_{\mathrm{box}}=500\,\mathrm{cMpc}$ with $2\times 6000^{3}$ resolution elements, corresponding to baryonic and dark-matter mass resolutions of $3.6\times 10^{6}\,\text{M}_{\odot}$ and $1.9\times 10^{7}\,\text{M}_{\odot}$, respectively. The simulation uses the moving-mesh code AREPO, combining the IllustrisTNG
galaxy-formation model with a GPU-accelerated M1 radiation-transport solver in six frequency bins. The initial conditions employ separate transfer functions for
baryons and dark matter and include their relative streaming velocity. Lumina predicts a late, predominantly
stellar-driven hydrogen reionization, with the median sub-volume fully ionized by $z\approx 5.2$ and residual neutral HI patches persisting until $z\approx 4.75$. HeII reionization is driven self-consistently by AGN and is nearly complete by $z=3$. The simulation yields a Thomson-scattering optical depth in excellent agreement with Planck, an IGM thermal history and photoionization background broadly consistent with observational constraints, and a clear late-time thermal boost associated with HeII reionization. Its
galaxy population remains consistent with the original IllustrisTNG project, while the larger volume improves statistics for rare objects, large-scale environments, and
cosmic variance, enabling forward modelling of observables linking HI and HeII
topologies to the evolving
galaxy and AGN populations.
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All authors Oliver Zier, Aaron Smith, Xuejian Shen, Rongrong Liu, Rahul Kannan, Sonja M. Koehler, Volker Springel, Rüdiger Pakmor, Mark Vogelsberger, Teodora-Elena Bulichi, Lars Hernquist
High Energy Astrophysical Phenomena
Ultra high-energy cosmic rays from relativistic outflows in accretion induced collapse of white dwarfs
Mainak Mukhopadhyay and Shunsaku Horiuchi
When a rapidly-rotating, highly magnetized white
dwarf (WD) approaches the Chandrashekhar limit through mass
accretion, it can undergo an
accretion-induced collapse (AIC) to form a proto-
neutron star or protomagnetar. The protomagnetar can drive a magnetically-dominated relativistic
outflow, whose low
entropy can lead to efficient formation of heavy
nuclei. In this work, we propose that such relativistic
outflows from AIC of WDs can contribute as sources of ultra high-energy
cosmic rays (UHECRs). We model the acceleration of heavy
nuclei in these relativistic
outflows, and show that AICs can dominantly power the observed UHECRs, if a majority of them host relativistic
outflows. Accounting for uncertainties in the acceleration mechanisms and AIC rates, AICs can contribute $\sim$ a few $10^{43} - 10^{45}\ {\rm erg \ Mpc}^{-3} {\rm yr}^{-1}$ in UHECR energy generation rate density, assuming iron-like
nuclei.
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Cosmology and Nongalactic Astrophysics
Peculiar-velocity distribution functions and 21-cm fluctuations
Ryan Yuran Zhang and Marc Kamionkowski
Predictions for observables involving the cosmological 21-cm background require calculations of spatial correlations of
star formation rate densities (SFRDs) which have a nonlinear dependence on the
baryon-dark matter relative velocity. Prior work derived these SFRD correlations with a simplifying assumption that neglected the difference between the correlations of the components of the velocity parallel and perpendicular to the separation between the two points being correlated. Here we calculate the full joint PDF of the squares of the peculiar velocity at two different points. The error that arises in predictions for 21-cm fluctuations if this subtlety is overlooked is generally less than a few percent, but it can be larger for some values of wavenumber $k$ and
redshift $z$ if there are cancellations between different contributions to the total signal. The correct expression is easily implemented and increases the run time of the code by only a few percent.
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Astrophysics of Galaxies
The Simulated Oxygen Shortage (SOS): Mapping the Missing OVI in Simulated Dwarf Galaxies to Subgrid Physics
Daniel R. Piacitelli, Alyson M. Brooks, N. Nicole Sanchez et al. (+9 more)
Observations reveal extended \OVI\, reservoirs in the circumgalactic medium (CGM) of
dwarf galaxies, yet current simulations systematically underpredict \OVI\, column densities. Utilizing two suites run with different simulation codes, the \MM\, simulations (Marvelous Massive
Dwarfs and Marvel-ous
Dwarfs) and the publicly available FIRE-2 simulations, we explore the role of subgrid models and the resulting CGM phase in shaping \OVI\, production. By comparing observationally derived \OVI\, masses to the mass of oxygen produced over the
galaxies'
star formation history, we find evidence for an underproduction of oxygen for low-mass simulated
galaxies. Despite clear differences in feedback implementation, CGM structure, and metal mixing, we find that \OVI\, in both suites generally self-selects cool/warm ($\rm log\, T\,/K \sim 4.5$), diffuse ($\rm log\,n_{gas}\,/cm^{-3} \sim -5.0 $), and moderately metal-enriched ($\rm log\, Z/Z_{\odot} \sim -1 $) material at large radii from the
galaxy. We show that neither the choice of ultraviolet background nor plausible variations in CGM thermal structure can close the gap with observations. Taken together, our results point to a possible underproduction of oxygen in low-mass
galaxies. Feedback prescriptions contribute via insufficient metal transport to large radii. Hence, the \OVI\, deficit may motivate an investigation of current modeling choices for
supernova yields,
star formation, and feedback in low-
metallicity environments.
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All authors Daniel R. Piacitelli, Alyson M. Brooks, N. Nicole Sanchez, Hetvi Khatri, Charlotte Christensen, Cameron Hummels, Nishant Mishra, Akaxia Cruz, Ben Keller, Thomas R. Quinn, Sijing Shen, James Wadsley
Astrophysics of Galaxies
A stellar bar hidden in an extreme gas-rich disk galaxy at z=4.055
Leindert A. Boogaard, Luca Costantin, Thor Tepper-García et al. (+14 more)
The classical picture for the formation of
stellar bars – key dynamical drivers of the
evolution of
galaxies – is through secular
evolution of instability in gas poor,
stellar-dominated disks. The detection with the James Webb Space
Telescope (JWST) of
stellar bars and spiral arms in
galaxies at early
cosmic times has thus challenged LambdaCDM-based expectations, which recent studies reconcile by suggesting that these
galaxies are
baryon-dominated and have already consumed most of their gas. Yet, a paradox arises, as early
galaxies are expected to be increasingly rich in gas, which is generally considered to prevent or slow down
stellar bar formation. Here, we show the detection of a
stellar bar in GN20, a gas-rich
star-forming disk
galaxy at a
redshift of z=4.055, only 1.5 billion years after the Big Bang. Simultaneous observations of the
stars, gas, and
dust reveal that GN20 is indeed
baryon-dominated (over dark matter; 72+/-34%), but the baryonic mass is largely in the form of gas (74+/-25%). This discovery demonstrates that gas-rich disks do support rapid
stellar bar formation in the early Universe, motivating a new theoretical perspective on bar formation in gas-rich systems, and providing a potential new mechanism for very early
galaxy assembly and quenching.
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All authors Leindert A. Boogaard, Luca Costantin, Thor Tepper-García, Joss Bland-Hawthorn, Jacqueline A. Hodge, Cheng-Lin Liao, Mahmoud Hamed, Luis Colina, Fabian Walter, Oscar Agertz, Arjan Bik, Alejandro Crespo Gómez, Emanuele Daddi, Georgios E. Magdis, Pablo G. Pérez-González, Hannah Übler, Axel Weiss
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Polarization Analysis of Ringdown Signals
Nicole Khusid, Will Farr and Maximiliano Isi
Merging binary black holes exhibit a ringdown phase in which they primarily emit gravitational waves in the shape of damped sinusoids corresponding to quasi-normal modes of the Kerr remnant. In general, each mode carries four degrees of freedom encoding amplitude and phase information. When the modes are excited with equatorial reflection
symmetry, as is the case for black hole mergers with
spins (anti)aligned to the orbital angular momentum, the
symmetry constrains two degrees of freedom. As a result, the relationship between polarization amplitudes and phases in each mode is fixed by the viewing (inclination) angle to the equatorial plane. We use such a constrained model to fit the ringdown signals of both non-precessing and precessing systems such as GW150914 and GW190521, respectively. We show that we can measure the degree of circular polarization and handedness of ringdown signals like those of GW150914, even if only the two LIGO detectors are available; such a polarization measurement can be translated into an inferred source inclination assuming the reflection
symmetry above, again using the ringdown signal alone. On the other hand, the constrained polarization model is insufficient to capture the polarization structure of signals from precessing systems, leading to biases in the inferred mode frequencies and amplitudes. We explore the magnitude of this effect by fitting GW190521-like injections with the restricted model, finding weaker predictive accuracy relative to the arbitrary-polarization model and potentially significant systematic biases. As our detectors continue to improve, using the correct polarization model is increasingly important to avoid biased ringdown measurements.
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High Energy Astrophysical Phenomena
Eccentric Stellar-mass Binary Black Holes: Population, Detectability, and Waveform Analysis in the LISA and LIGO Era
Zeyuan Xuan, Smadar Naoz, Kyle Kremer et al. (+3 more)
Eccentric binary black holes (BBHs) formed through dynamical interactions can significantly contribute to gravitational wave (GW) detections. In this work, we present a simulated catalog of dynamically-formed,
stellar-mass BBHs in the local universe, incorporating contributions from the
Galactic field (flyby interactions),
Galactic nucleus (eccentric Kozai-Lidov
evolution), and globular clusters (N-body interactions). Our results predict a wide, highly eccentric BBH population in the Milky Way (MW), with source counts of $\sim 36, 13, 4.7, 2.3, 1.0$ (for $\mathrm{SNR} > 1, 3, 8, 20, 50$, respectively) during a 10-yr LISA observation. Extending this model to cosmological populations, we show that different dynamical channels can produce distinct eccentricity distributions in the LVK band and can contribute hundreds of additional low-SNR mHz sources. Specifically, our model yields a merger rate of $\Gamma \sim 9 \mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ and $\sim 490$ extragalactic mHz BBHs with $\mathrm{SNR} > 1$. However, due to the lower mass and weaker GW signals of
stellar-mass BBHs, this number declines sharply at higher detection thresholds (e.g., $\sim 1$ for $\mathrm{SNR} > 8$). We further highlight the impact of eccentric BBH signals on the LISA global fit, showing that their individual harmonics can be independently detected in the Milky Way, and may mimic circular binaries with systematically biased chirp masses. Lastly, we show that post-Newtonian waveforms converge reliably for eccentric BBHs with masses of $\lesssim 10^3 M_\odot$ in the mHz band. Overall, eccentric BBHs represent a prevalent and promising target for future space-based GW observatories. The simulated catalog and the LISA Eccentricity Astrophysics Package (LEAP) developed in this work are publicly available at https://github.com/zeyuanxuan/lisa-leap/.
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All authors Zeyuan Xuan, Smadar Naoz, Kyle Kremer, Michael L. Katz, Bence Kocsis, Erez Michaely
Astrophysics of Galaxies
Near-IR Weak-lensing (NIRWL) Measurements in the CANDELS Fields. II. Mass Mapping and Overdensity Characterization
Kyle Finner, Bomee Lee, Ranga-Ram Chary et al. (+4 more)
The Hubble Space
Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) fields offer an exceptional combination of depth, spatial resolution, and area for identifying a shear-selected sample of dark matter overdensities. We present the first near-infrared (NIR) weak-
lensing (WL) analysis of the 0.23 square degrees covered by the HST CANDELS fields: COSMOS, UDS, EGS, GOODS-N, and GOODS-S. Leveraging the high sensitivity of HST NIR imaging to distant
galaxies, we achieve a WL source
galaxy density of $\sim170$
galaxies arcmin$^{-2}$. Our analysis identifies 12 shear-selected overdensities spanning masses from $M_{200}=(0.2$–$2.2)\times10^{14}\ M_\odot$, with a median mass of $M_{200}=5.5\times10^{13}\ M_\odot$, demonstrating the strong capability of NIR WL for measuring low-mass systems. The systems lie in the
redshift range $0.22<z<0.9$, with a mean
redshift of $z=0.68$. We utilize multiwavelength data to confirm the nature of the overdensities. Seven of the overdensities have diffuse X-ray emission reported in the literature, with X-ray centroids that are spatially consistent with our WL peaks, confirming their nature as collapsed structures. We find that our WL detections broadly follow the expected X-ray luminosity–WL mass scaling relations. By stacking the tangential shear of all detections, we determine the average radial mass density profile and find that it is well fit by an NFW model with fitted concentration and mass of $4.9\pm2.1$ and $M_{200}=1.3\pm0.3\times10^{14}\ M_\odot$, respectively. These results serve as a precursor to NIR WL science with the Roman High Latitude Wide Area Survey.
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All authors Kyle Finner, Bomee Lee, Ranga-Ram Chary, Giuseppe Congedo, Kim HyeongHan, M. James Jee, Peter Taylor
Astrophysics of Galaxies
Quenching of X-ray emission in little red dots by both Compton-thick gas and high accretion rates
Albert Sneppen, Darach Watson, James H. Matthews et al. (+1 more)
Little red dots (LRDs) are candidate high-
redshift supermassive black holes accreting in dense gas. They remain undetected in X-rays. In previous work, we provided the first quantitative models that reproduce the optical and near-infrared spectra of LRDs with the \sirocco radiative transfer code, thereby constraining the properties of the surrounding gas. Here, we use these constraints to predict the X-ray attenuation produced by dense gas cocoons, and explore its dependence on Balmer-break strength,
metallicity, intrinsic X-ray spectral energy distribution, and observed bandpass as a function of
redshift. The X-ray constraints are very tight, requiring extinction by a Compton-thick gas column ($N_{\rm H}\sim10^{25}\,{\rm cm}^{-2}$) with moderate
metallicity $0.05$-$0.1\,Z_\odot$ and intrinsically weak X-ray emission (bolometric to X-ray luminosity ratio, $k_{\rm bol,X}\gtrsim 30$), as observed in narrow-line active
galactic nuclei with high
accretion rates, to make LRDs sufficiently faint to evade detection. Intrinsically bright X-ray emitters as seen in typical broad-line active
galactic nuclei would be detected even behind the typical Compton-thick gas columns with modest
metallicity that were inferred from the optical spectra. Very low
metallicity objects might be detected in X-rays even with low intrinsic X-ray luminosities, suggesting that LRDs are not (currently) chemically pristine.
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All authors Albert Sneppen, Darach Watson, James H. Matthews, Stuart A. Sim
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Damiano F. G. Fiorillo, Ángel Gil Muyor, Georg G. Raffelt et al. (+1 more)
Magnetic fields between a
supernova (SN) and Earth convert
axions into gamma rays. The absence of such a signal in coincidence with SN 1987A
neutrinos, using the coherent Milky Way field, provides well-studied constraints on $g_{ap}\times g_{a\gamma}$ (
axion-
proton times
axion-
photon couplings) and on $g_{a\gamma}$ alone. We show that the small-scale power of the turbulent
magnetic field component boosts
axion-
photon conversion and, crucially, extends sensitivity to larger masses. The turbulent field components of the Milky Way and of the Large Magellanic Cloud (hosting SN 1987A) yield improvements of up to two orders of magnitude in $g_{ap}\times g_{a\gamma}$.
Turbulence should likely impact the sensitivity of other searches based on other
axion-
photon conversion sites, such as starburst
galaxies.
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All authors Damiano F. G. Fiorillo, Ángel Gil Muyor, Georg G. Raffelt, Edoardo Vitagliano
High Energy Astrophysical Phenomena
Entity – Hardware-agnostic Particle-in-Cell Code for Plasma Astrophysics. III: Higher-order shape functions & generalized field stencils
Ludwig M. Böss, Arno Vanthieghem, Hayk Hakobyan et al. (+2 more)
Modern particle-in-
cell (PIC) codes have become an integral tool in
plasma astrophysics. As most
plasma phenomena grow from initially small instabilities, it is important to ensure PIC codes can suppress noise and ensure that any growing instability is indeed physical. Therefore, we introduce our efforts to implement higher-order methods for the current deposit and field interpolation as well as generalized field stencils for the field solver in the PIC code Entity. Our updated current deposit scheme allows for up to $11^\mathrm{th}$-order accurate interpolation, while the generalized stencils for the field solver can be tuned to suppress numerical dispersion. We perform extensive tests to ensure high accuracy of the implemented schemes for charge conservation, stabilization against numerical heating, improved energy conservation, and suppression of numerical Cherenkov effects. To supply a
benchmark on performance impact, we demonstrate the scaling of the higher-order current deposit and discuss the possible performance balance between higher-order interpolation, numerical resolution, and the inclusion of additional current filtering.
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All authors Ludwig M. Böss, Arno Vanthieghem, Hayk Hakobyan, Evgeny A. Gorbunov, Damiano Caprioli
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
TransitionListener v2.0 – Robust gravitational wave predictions for cosmological phase transitions
Jonas Matuszak and Carlo Tasillo
Gravitational wave backgrounds from strong first-order cosmological phase transitions are key observational targets predicted by many SM extensions and might be observed by current and future observatories like LISA, the Einstein
Telescope or
pulsar timing arrays (PTAs). Still, their precise forecast given a specific model remains a challenge. In this article, we present TransitionListener v2.0, a Python framework for precision studies of cosmological phase transitions and their associated gravitational wave (GW) signals. The code provides an end-to-end pipeline from a user-defined scalar potential to GW spectra and signal-to-noise ratios, enabling both
benchmark studies and large-scale parameter scans. Version 2 introduces a self-consistent treatment of the transition dynamics, including the
evolution of the true-
vacuum fraction and its backreaction on the Hubble expansion, as well as a consistent description of reheating during percolation. A direct computation of the mean bubble separation allows to faithfully map to the GW spectral templates from bubble collisions, sound waves, and
turbulence stemming from state-of-the-art simulations. TransitionListener includes built-in sensitivity curves for space- and ground-based detectors and PTAs, interfaces to PTA likelihoods, and wrappers for
Bayesian model inference and high-dimensional parameter scans. Compared to existing public tools, TransitionListener v2.0 improves the physical consistency and numerical stability of GW predictions across a wide range of models, with particular emphasis on the strongly supercooled and ultraslow transition regime where conventional approximations break down and the most promising GW signals are expected.
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Cosmology and Nongalactic Astrophysics
Primordial Black Hole from Tensor-induced Density Fluctuation: First-order Phase Transitions and Domain Walls
Utkarsh Kumar and Anish Ghoshal
Gravitational waves generated by violent processes in the early Universe necessarily couple to scalar perturbations beyond linear order. We show that tensor perturbations produced by first-order phase transitions and by annihilating domain-wall networks source density fluctuations at second order, thereby opening a distinct channel for
primordial-black-hole (PBH) formation. We compute the tensor-induced density spectrum for both sources and map the resulting PBH abundance onto the macroscopic parameters $(\alpha,\beta/H,T_\star)$ of a first-order phase transition and $(\alpha_{\rm ann},V_{\rm bias},\sigma)$ of a domain-wall network. Existing PBH limits therefore impose complementary constraints on early-Universe sources of
stochastic gravitational waves. We find viable regions where one can have an observable gravitational-wave background and an appreciable abundance of asteroid-mass PBHs, including
benchmark points that saturate the dark-matter abundance. Our results establish a direct, testable correlation among the source scale, the gravitational-wave spectrum, and the PBH mass function, distinguishing this tensor-induced channel from PBHs formed through delayed
vacuum decay or direct defect collapse. We also discuss viable particle physics origin of such FOPT and DW, and therefore, constraints on such microphysics, either in the visible, or in dark sector models.
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Cosmology and Nongalactic Astrophysics
Isocurvature-Free QCD Axion Dark Matter from Inflaton-Driven Early QCD: the Necessity of Inflationary Plateaus
Katherine Freese, Evangelos I. Sfakianakis and Barmak Shams Es Haghi
A direct coupling between the inflaton and Standard Model
gluons can dynamically raise the QCD confinement scale during inflation, making the
axion temporarily heavy and suppressing
axion isocurvature perturbations. As inflation proceeds, the confinement scale relaxes, the
axion becomes light, and late-time de Sitter fluctuations can generate the observed dark matter abundance. We analyze this mechanism without specifying an inflationary potential, instead parametrizing the background by $\epsilon(N) \propto 1/N^p$, where $N$ is the number of $e$-folds before the end of inflation. The single parameter $p$ distinguishes monomial models ($p=1$), standard plateau models ($p=2$), and ultra-flat plateau or hilltop-like models ($p\ge 3$). We analytically show that the mechanism selects plateau-like ($p\ge 2$) inflation: monomial models generically cause the confinement scale to grow too rapidly, while plateau models keep the QCD sector under perturbative control. In the minimal scenario, reheating occurs through the same inflaton-
gluon coupling, and viable
axion dark matter production is obtained when deconfinement occurs after the CMB window. The early-confinement sector also generically shifts the scalar spectral index to smaller, redder values. Because ultra-flat ($p \ge 3$) models inherently predict overly red spectra, this shift exacerbates their tension with CMB data, leaving $p=2$ plateau models as the phenomenologically viable parameter space (in this parametrization).
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Cosmology and Nongalactic Astrophysics
Strong Gravitational Lensing with the James Webb Space Telescope
Adi Zitrin
The theory of General Relativity predicts that, since massive bodies curve spacetime, light from a distant source would be deflected by a foreground massive object – a phenomenon known as Gravitational
Lensing. Historically, the strength of deflection of light from background
stars by the sun, during the 1919
solar eclipse, supplied one of the first proofs for the theory of General Relativity. However, it is only in the last few decades, with the advent of the Hubble Space
Telescope and other large, ground-based facilities, that
lensing has become a principal tool in modern astronomy.
Lensing allows us to study both the matter content of the
lensing bodies such as
galaxies or clusters of
galaxies, mainly dominated by the otherwise-invisible dark matter, and the distant background sources that are being lensed by them. Strong gravitational
lensing, where sources are substantially magnified and multiply imaged, is particularly useful to that end. The substantial magnification enables a high-resolution view of the sources and the detection of fainter and farther objects than would otherwise be possible; and image multiplicity helps in verifying the distance to them, and in studying variable or transient sources. Paired with the unprecedented capabilities of the James Webb Space
Telescope (JWST),
lensing now allows us to observe, detect, and study distant sources like never before. I summarise recent advances in strong-
lensing applications and near-future prospects with JWST.
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High Energy Astrophysical Phenomena
Detecting the Axion-Photon Conversion Background
Felix Weber and Vikram Ravi
The potential to detect
axion dark matter through astrophysical processes has shown high promise in recent years. We therefore expand on previous work studying the
axion-to-
photon conversion efficacy of
neutron stars and the interstellar medium (ISM) in this endeavor, respectively. For
neutron stars (NS), we examine the possibility of a background signal emanating from all NS magnetospheres in the
galaxy. Using a heuristic
Galactic model, we find a significant background signal emanating from such magnetospheres in the Milky Way. This signal, while weak in absolute power ($\gtrsim 1$ mJy sr$^{-1}$ from the
Galactic Center, at 2 GHz), can be detected through new statistical techniques with current instrumentation like the Atacama Large Millimeter Array (ALMA) at high
radio frequencies (200 - 950 GHz). These techniques make use of higher order statistics like spectrally-limited ($\sim 300$ km s$^{-1}$) increases in confusion noise levels and kurtoses of survey images, and also show promise for general population estimation techniques. For the ISM, we consider Primakoff processes between free electrons and
axions, and derive typical signal strengths of $10^{-15}$ Jy sr$^{-1}$ $\cdot$ $m_a$/eV, with a local, cosmological upper bound of $10^{-8}$ Jy sr$^{-1}$ $\cdot$ $m_a$/eV. Hence, we find that any diffuse
axion signal from the ISM and other, large-scale, astrophysical
plasmas to be too weak to be detected with modern technologies. We therefore find that the best avenue towards detecting a potential
quantum chromodynamics (QCD)
axion dark-matter particle is through the
radio imaging of large swaths of the
Galactic Center and other regions where we expect large numbers of
pulsars and
neutron stars.
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Earth and Planetary Astrophysics
The Role of Formation Location in Shaping Sulfur-, Nitrogen-, and Carbon-Bearing Species in Super-Earth and Sub-Neptune Atmospheres
Aaron Werlen, Remo Burn, Caroline Dorn et al. (+2 more)
Atmospheric compositions of sub-Neptunes and super-Earths are often interpreted as tracers of formation location relative to volatile ice lines. However, prolonged magma oceans can chemically equilibrate with
primordial atmospheres and modify accreted volatile signatures. In this study, we couple a synthetic
planet population from the Bern Generation III formation model to an extended global chemical
equilibrium framework including sulfur and nitrogen chemistry, and compare accreted and equilibrated compositions for $\sim$ 1200 young
planets shortly after formation ($\sim$ 4 Myr) formed inside and outside the water ice line. We find that interior-atmosphere equilibration systematically alters elemental ratios and molecular abundances. The atmospheric C/O ratio shifts relative to the accreted state and remains systematically higher for
planets formed outside the ice line. Nitrogen-bearing species NH$_3$, N$_2$ are strongly depleted through dissolution into the silicate melt, while minor amounts of HCN are produced, leading to low atmospheric nitrogen abundances. Sulfur-bearing species remain more abundant than nitrogen-bearing species; during equilibration, accreted H$_2$S partitions into the interior and small amounts of SO$_2$ form, but overall sulfur abundances depend only weakly on formation location. Silicon-bearing gases (SiH$_4$, SiO) are generated in substantial amounts, with narrower distributions for
planets formed outside the ice line. We identify atmospheric C/O, SiH$_4$, and H$_2$O as potential indicators of formation location, while nitrogen depletion emerges as a generic outcome of magma ocean equilibration. Comparison with characterized sub-Neptunes such as TOI-270 d, K2-18 b, and GJ 3470 b shows broad consistency with oxygen-dominated, metal-rich atmospheres shaped by interior-atmosphere exchange.
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All authors Aaron Werlen, Remo Burn, Caroline Dorn, Lukas Felix, Annika Salmi
High Energy Astrophysical Phenomena
Polarization Signatures from GRMHD Simulations of Black Hole Accretion
P. Chris Fragile, Maciek Wielgus and Cora Prather
This chapter tells the still-unfolding story of extracting polarization signatures from general relativistic magnetohydrodynamics simulations of
accretion disks. In some sense, this effort is premature as there are still very few results of this kind. Much more abundant are phenomenological models. Nevertheless, we feel now is the time to rally the community to this cause. Since the focus of this book is on X-ray polarimetry, we focus exclusively on simulations of
accretion onto compact objects. Most of the relevant work so far has been on black hole
accretion disks, though
neutron stars are also viable targets for X-ray polarimetry. The focus of our chapter is on how X-ray polarimetry coupled with
accretion simulations might help us better understand properties of the disks, coronae, and jets that are the dominant components of accreting compact sources. We briefly illustrate the promise of this technique by demonstrating how it has already been used in the case of the Event Horizon
Telescope (using
radio polarimetry). We also speculate about where this field may be heading in the near future.
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High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph
Axion magnetohydrodynamics and reconnection-driven axion bursts
H. Terças
We formulate
axion magnetohydrodynamics beyond the ideal limit, retaining
axion inertia and the essential physics of non-ideal
plasmas from first principles. In this framework, regions where
magnetic flux freezing breaks down acquire a new physical role: whenever $\mathbf{E} \cdot\ \mathbf{B} \neq 0$,
magnetic dissipation acts as a localized source of
axion radiation. We show that
magnetic reconnection naturally excites mixed Alfvén-
axion modes, enabling coherent energy exchange between
magnetic fields and
axions in magnetically dominated environments. In
neutron stars and magnetars, this mechanism leads generically to transient
axion bursts powered by reconnection–driven Alfvénic dissipation. We connect this production process to observational prospects and derive a characteristic sensitivity to the
axion–
photon coupling, complementary to searches based on static
magnetic fields.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Matter Flavor Conversion Mediated by Pseudo-Sterile States as the Possible Origin of Neutrino Oscillation Anomalies
Sabya Sachi Chatterjee and Antonio Palazzo
Neutrino oscillation experiments present anomalous results across a vast range of baselines and energies. Here we show that a 3+1 scenario in which sterile
neutrinos feel a novel matter potential $V_s$ proportional to background density of ordinary or (asymmetric) dark matter is able to explain several anomalies. At low-energies ($E\lesssim$ 1 TeV) the model behaves as an effective 3-
flavor NSI-like scheme among active
flavors and eliminates the tension between the two LBL experiments NOvA and T2K provided that the potential is negative and the two sterile mixing angles $\theta_{14}$ and $\theta_{24}$ are non-zero. A further indication in favor of a negative non-zero potential comes from the anomalous excess of $\nu_e$-like events observed in Super-Kamiokande atmospheric
neutrinos, which, in the new scenario is explained by a modification of the 3-
flavor resonance at few GeV. A high energies ($E\gtrsim $ 1 TeV) the new framework reveals its 4-
flavor nature and produces a resonant behavior at $E \simeq$ 10 TeV as hinted at by IceCube. We identify an irreducible 3-level dynamics generating a new resonance in the $(\nu_e, \nu_\mu)$ sector intertwined with two conventional resonances in the $(\nu_e, \nu_s$) and $(\nu_\mu, \nu_s)$ systems. The novel amplification mechanism manifests with the emergence of effective mixing angles in matter ($\theta_{12}^m$ or $\theta_{13}^m$) involving active
neutrinos. The scenario requires values of $f = V_s/|V_{NC}| \sim -20 $, $\Delta m^2_{41} \sim 60 $ eV$^2$, $|U_{e4}|^2\simeq \sin^2\theta_{14} \simeq 0.01-0.03$ and $|U_{\mu4}|^2 \simeq \sin^2\theta_{24}\simeq 10^{-4}-10^{-3}$. Such a very small size of $|U_{\mu4}|^2$ eliminates the tension between IceCube and the other $\nu_\mu$ disappearance searches. The model can be directly probed by KATRIN, which is very sensitive to the electron-sterile
neutrino admixture in the region of high $\Delta m^2_{41}$.
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Astrophysics of Galaxies
Michal Zajaček
It is of a general interest to look for signatures of
stellar bodies orbiting supermassive black holes (SMBHs) in
galactic nuclei other than the
Galactic center. Previously
stellar transits were analyzed in UV, optical, and X-ray domains as well as potential microlensing signatures due to more compact bodies orbiting SMBH
accretion disks. Here we complement previous studies by considering nearby ($z=0.001$) millimeter-bright active
galactic nuclei targeted by different facilities in the millimeter domain. At these wavelengths the jet base and the
nuclear ring are sufficiently compact so that they can be occulted by large evolved
stars in dense
nuclear star clusters. We find that in the millimeter domain evolved
stars with
stellar radii of $\gtrsim 500\,R_{\odot}$ can cause eclipses with the relative depth of $\sim 10-40\%$. Typical recurrence timescales are at least 10 years and the eclipse durations are $\sim 10$ days. Towards lower frequencies the eclipse temporal profiles become shallower and broader while towards higher frequencies they are deeper and narrower. Although expected to be rare due to selection effects and evolved
stars being prone to
tidal disruption, eclipses of millimeter
radio cores can be applied to estimate the distance of the extragalactic
star from the SMBH and its
stellar radius. In case the eclipse is recurring, we provide a relation for estimating the SMBH mass.
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High Energy Astrophysical Phenomena
Significant or Not? The Impact of Randomisation During Data Reduction on Confirming a New Pulsating Ultraluminous X-ray Source Candidate in Centaurus A
Amy H. Knight, Timothy P. Roberts, Callum Potter et al. (+2 more)
We report the discovery of a new candidate pulsating ultraluminous X-ray source (PULX) in NGC 5128 (Centaurus A). The candidate, 4XMM J132542.2-425943, is a transient source, identifiable as a clear X-ray point source for $\sim 8$ months in 2014, during its only major recorded outburst. The source flux exceeded $10^{-12}$ erg cm$^{-2}$ s$^{-1}$ at the peak of the outburst. The long-term light curve of 4XMM J132542.2-425943 shows two further, less luminous detections in 2017 and 2024, but was otherwise in quiescence. This behaviour is similar to the class of pulsating transients with outbursts that reach the ultraluminous regime, which includes the well-studied
Galactic PULX, Swift J0243.6+6124. However, 4XMM J132542.2-425943 displays a soft X-ray spectrum, making this source distinct from the existing population of PULXs, which typically show hard spectra below $10$ keV. We searched the 2014 XMM-Newton observations for X-ray pulsations, revealing coherent, sinusoidal X-ray pulsations at a frequency of $1.27$ Hz in one XMM-Newton observation (ObsID 0724060801), at a marginal significance. For this signal we measure a pulsed fraction, PF$\approx~15 - 17~\%$ and $\dot{f}~\sim~4~\times~10^{-9}$ Hz s$^{-1}$. However, we find that the intrinsic randomisation employed by XMM-Newton's Science Analysis Software, XMM-SAS, during the data reduction procedure introduces considerable uncertainty in the strength of our marginal pulsations, which varies significantly between consecutive data reduction iterations. We explore the impact of this randomisation and demonstrate that it can generate widespread false positives and false negatives, which, in the context of PULX searches, may cause viable candidates to be unnecessarily discarded or vice versa.
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All authors Amy H. Knight, Timothy P. Roberts, Callum Potter, Alistair T. Pagan, Dominic J. Walton
Solar and Stellar Astrophysics
Analysing the highly irregular boundaries of solar pores
T. J. Duckenfield, D. B. Jess, S. Jafarzadeh et al. (+3 more)
Solar pores possess irregular and evolving boundaries that are often far from the ideal circular flux tubes assumed in many magnetohydrodynamic (MHD) oscillation models. To tackle this irregularity in a consistent way for wave analysis, we introduce a framework that employs the convex hull of the pore boundary - derived from intensity minimum error thresholding - as the domain to perform further analysis. Using the modal assurance criterion, we find the range of pore shapes for which this approximation is valid. We demonstrate the usefulness of this framework by applying it to multi-height, high-cadence observations (4170 angstrom continuum, G-band, Na~i, and Ca~ii~K) of a
solar pore, and apply Proper Orthogonal Decomposition of the convex hull to determine wave modes. The fundamental sausage ($m=1$) and kink ($m=2$) mode is found to remain reliable, while higher-order fluting modes ($m\ge3$) are strongly degraded by small-scale boundary irregularity. As expected, sausage-like modes dominate the variance at all heights and exhibit a systematic upward shift in frequency, consistent with freely propagating compressive waves. In contrast, the kink-like motions appear weak, confined to a persistent low-frequency peak, and most plausibly interpreted as a forced response to granular buffeting rather than a propagating mode. Together, these results establish a practical methodology for boundary-mode analysis in real, highly structured pores and provide new constraints on the nature and height
evolution of MHD waves in the lower
solar atmosphere.
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All authors T. J. Duckenfield, D. B. Jess, S. Jafarzadeh, L. A. C. A. Schiavo, S. S. A. Silva, S. D. T. Grant
Astrophysics of Galaxies
Impact of stellar population models on the estimated physical properties of galaxies
Bozhidara Stoyanova, Médéric Boquien, Paola Santini et al. (+5 more)
Accurate estimates of fundamental physical properties of
galaxies, such as
star formation rates (SFRs) or
stellar masses, are essential for testing and constraining models of
galaxy formation and
evolution. Spectral energy distribution (SED) modeling has become the standard method for deriving these quantities. However, the influence of the underlying
stellar population synthesis (SPS) models on the inferred parameters remains poorly quantified. This work investigates how the choice of SPS models affects the estimation of SFRs and
stellar masses derived from SED modeling. Four widely used SPS models are applied to a sample of 17 230
galaxies with spectroscopic
redshifts, selected from recently published Hubble Space
Telescope and James Webb Space
Telescope photometric catalogs. SEDs are modeled using the Code for Investigating
GALaxy Emission. The analysis is performed in two steps: (i) estimating
galaxy properties with each SPS model, and (ii) employing synthetic catalogs to assess the relative impact of model choice on the recovered parameters. Systematic differences are found among the models, with
stellar mass estimates varying by up to ~ 0.6 dex and SFRs by up to ~ 0.4 dex between certain model pairs. The choice of
stellar population model introduces significant systematic uncertainties in derived
galaxy properties. This dependence should be accounted for when interpreting SED-based measurements and comparing results across different studies of
galaxy evolution.
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All authors Bozhidara Stoyanova, Médéric Boquien, Paola Santini, Francesco Tombesi, Emiliano Merlin, Pietro Bergamini, Véronique Buat, Denis Burgarella
Cosmology and Nongalactic Astrophysics
KiDS+VIKING-450 cosmology with Bayesian hierarchical model redshift distributions
George T. Kyriacou, Arrykrishna Mootoovaloo, Alan F. Heavens et al. (+3 more)
Tomographic
redshift distributions from photometric data are crucial ingredients in
cosmic shear analysis, since they are required for the theoretical calculation of the signal based on the
redshift distribution of the
galaxies where the shear field is sampled. In this paper, we develop as a proof of concept Leistedt et al.'s template-based
Bayesian Hierarchical Model framework into an application to weak
lensing data by sampling the
redshift distributions of the
galaxies in the KiDS+VIKING-450 survey. We also use a principal component analysis to provide a set of representative templates drawn from a large superset. For computational tractability, subsets of $10^5$
galaxies are chosen to determine the
redshift distributions, and we test the sensitivity of the cosmological inference to the subset chosen, finding it to be subdominant compared to the statistical error. We marginalise over the inferred
redshift distributions and find that the
Bayesian method increases the clustering parameter compared with previous studies, alleviating the $S_8$ tension with Planck, where $S_{8}\equiv\sigma_{8}\sqrt{\Omega_{\tm{m}}/0.3}=0.756\pm 0.039$, assuming flat $\Lambda$CDM. The tension with Planck for this survey is reduced from $2.3\sigma$ to $1.9\sigma$. We also infer a value for the matter density, $\Omega_{\tm{m}}=0.31\pm 0.10$.
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All authors George T. Kyriacou, Arrykrishna Mootoovaloo, Alan F. Heavens, Andrew H. Jaffe, Florent Leclercq, Konrad Kuijken
Astrophysics of Galaxies
Probing the IMF in the Early Universe – Direct measurements in the Boötes I UFD with JWST/NIRCam
Keyi Ding, Mario Gennaro, Roberto J. Avila et al. (+20 more)
The dependence of the
stellar initial mass function (IMF) on
star-formation environment, particularly at low
metallicities and high
redshifts, remains poorly constrained. Ultra-faint
dwarf galaxies (UFDs) are local fossils of high-
redshift galaxies hosting old, metal-poor populations, and their resolved
stellar populations provide unique pathways to constrain the sub-
solar IMF. We investigate the low-mass IMF in the Boötes I (Boo I) UFD with JWST/NIRCam, leveraging its capability to resolve over 10,000
stars reaching $\lesssim$0.15\msun, obtaining one of the largest, deepest resolved
stellar samples for UFDs. We explore three different functional forms of the IMF with machine learning and statistical techniques, combining forward modeling of synthetic color-magnitude diagrams with simulation-based inference. We find that a single power-law IMF provides a poorer description of the observed luminosity function and yields a slope inconsistent with the canonical Salpeter IMF. Our best-fit broken power-law and lognormal IMF parameters are consistent with the Milky Way within 68% confidence level, providing evidence that
star formation at
metallicities as low as $\mathrm{[Fe/H]}\approx-2.4$ follows a similar IMF as in the Milky Way. By treating Boo I as a local relic analogous to a high-
redshift galaxy with a
stellar mass of $\lesssim10^5\msun$ at $z\gtrsim6$, our results provide evidence for the universality of the IMF across both local and high-
redshift environments.
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All authors Keyi Ding, Mario Gennaro, Roberto J. Avila, Massimo Ricotti, Rachael L. Beaton, Martha L. Boyer, Thomas M. Brown, Annalisa Calamida, Santi Cassisi, Vedant Chandra, Roger E. Cohen, Matteo Correnti, Denija Crnojević, Kareem El-Badry, Marla Geha, Puragra Guhathakurta, Nitya Kallivayalil, Evan N. Kirby, Kristen. B. W. McQuinn, Alessandro Savino, Cheyanne Shariat, Joshua D. Simon, Daniel R. Weisz
Solar and Stellar Astrophysics
The Role of Magnetic Reconnection in Energizing Protons and Heavier Ions at the Heliospheric Current Sheet
Giulia Murtas, Xiaocan Li, Fan Guo et al. (+3 more)
During near-Sun crossings of the heliospheric current sheet (HCS), Parker
Solar Probe (PSP) observed populations of high-energy
protons and heavier ions indicating possible energization by
magnetic reconnection up to 10s – 100s keV nucleon$^{-1}$. Here we study ion acceleration by
magnetic reconnection at the HCS. To estimate ion energization, we solve the Parker transport equation coupled to a large-scale 2D MHD reconnection simulation. We find that multiple ion species develop power-law distributions with both spectral index and high-energy cutoff $E_{\text{max}}$ consistent with in-situ data. By accounting for the injection physics determined by kinetic simulations, we confirm that the charge-to-mass ratio scales as $E_{\text{max}} \propto (Q/M)^{\alpha}$ with $\alpha \sim 0.8-1.1$, approximately consistent with PSP measurements in the broader range $\alpha \sim 0.6-1.7$. In the limit where ions are injected at the same energy per nucleon, $\alpha$ can be as low as $\sim 0.3$. These findings further support the role of
magnetic reconnection in producing high-energy heavy ions at the HCS.
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All authors Giulia Murtas, Xiaocan Li, Fan Guo, Giuseppe Arrò, Jeongbhin Seo, Colby Haggerty