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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 13 November

Astrophysics of Galaxies

Extending the Frontier of Spatially-Resolved Supermassive Black Hole Mass Measurements to at $1\lesssim z\lesssim2$: Simulations with ELT/MICADO High-Resolution Mass Models and HARMONI Integral-Field Stellar Kinematics

Dieu D. Nguyen, Michele Cappellari, Tinh Q. T. Le et al. (+8 more)

Current spatially resolved kinematic measurements of supermassive black hole (SMBH) masses are largely confined to the local Universe (distances $\lesssim100$ Mpc). We investigate the potential of the Extremely Large Telescope's (ELT) first-light instruments, MICADO and HARMONI, to extend these dynamical measurements to galaxies at redshift $1\lesssim z\lesssim2$. We select a sample of five bright, massive, quiescent galaxies at these redshifts, adopting their Sérsic profiles from HST photometry as their intrinsic surface brightness distributions. Based on these intrinsic models, we generate mock MICADO images using SimCADO and mock HARMONI integral-field spectroscopic data cubes using HSIM. The HARMONI simulations utilize input stellar kinematics derived from Jeans Anisotropic Models (JAM). We then process these mock observations: the simulated MICADO images are fitted with Multi-Gaussian Expansion to derive stellar mass models, and stellar kinematics are extracted from mock HARMONI cubes with pPXF. Finally, these derived stellar mass models and kinematics are used to constrain JAM dynamical models within a Bayesian framework. Our analysis demonstrates that SMBH masses can be recovered with an accuracy of $\sim$10%. We find that MICADO can provide detailed stellar mass models with $\sim$1 hour of on-source exposure. HARMONI requires longer minimum integrations for reliable stellar kinematic measurements of SMBHs. The required on-source time scales with apparent brightness, ranging from 5-7.5 hours for galaxies at $z\approx1$ (F814W, 20-20.5 mag) to 5 hours for galaxies at $1<z\lesssim2$ (F160W, 20.8 mag). These findings highlight the ELT's capability to push the frontier of SMBH mass measurements to $z\approx2$, enabling crucial tests of SMBH-galaxy co-evolution at the top end of the galaxy mass function.
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All authors Dieu D. Nguyen, Michele Cappellari, Tinh Q. T. Le, Hai N. Ngo, Elena Gallo, Niranjan Thatte, Fan Zou, Tien H. T. Ho, Tuan N. Le, Huy G. Tong, Miguel Pereira-Santaella

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

Bubble Friction in Symmetry-Restoring Transitions

Andrew J. Long, Bibhushan Shakya and Julia Anabell Ziegler

In standard (symmetry-breaking) first-order phase transitions, the frictional pressure on expanding bubble walls can be dominated by transition radiation – the emission of a gauge boson with phase-dependent masses as particles present in the thermal plasma pass through bubble walls. This process is enhanced in the soft limit, and is known to produce a significant frictional effect that is proportional to the Lorentz factor $\gamma$ of the bubble wall, thereby prohibiting runaway behavior. We calculate the analogous pressure for phase transitions with symmetry restoration. In such transitions, we show that the pressure due to this process can be $\textit{negative}$, producing the opposite effect. However, when the Lorentz factor of the wall gets very large, the result approaches the same scaling as the standard scenarios. Therefore, phase transitions with symmetry restoration can feature an intermediate negative friction regime even in the presence of significant interactions with the plasma, and the bubble wall terminal Lorentz factor can be significantly larger (by more than an order of magnitude) than in the corresponding symmetry-breaking scenarios. This can carry important implications for various phenomenological applications, from gravitational waves to physics beyond-the-Standard-Model.
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Instrumentation and Methods for Astrophysics

Ginnungagap – a massively parallel cosmological initial conditions generator

Sergey Pilipenko, Gustavo Yepes, Stefan Gottlöber et al. (+1 more)

Ginnungagap is a fully parallel (MPI+OpenMP) code designed to generate cosmological initial conditions for simulations involving very large numbers of particles. It operates in several modes, including the creation of initial conditions with either uniform or spatially varying resolution (for "zoom-in" simulations). The initial conditions can be fully random or derived by extending the resolution of existing ones while preserving the large-scale structures. Ginnungagap is open source and modular, consisting of a collection of independent tools that can be used for a variety of tasks. In this paper, we describe the main features of Ginnungagap and present test results for different types of simulations prepared with it.
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All authors Sergey Pilipenko, Gustavo Yepes, Stefan Gottlöber, Steffen Knollmann

Solar and Stellar Astrophysics

A predictive framework for realistic star planet radio emission in compact systems

J. J. Chebly, C. K. Louis, A. Strugarek et al. (+2 more)

Radio emission from star planet interactions (SPI) beyond our solar system has yet to be firmly detected, primarily due to challenges such as weak signals, directional beaming effects, and low frequency emissions that are blocked by the ionosphere of Earth. Addressing these obstacles calls for strategic target selection. This proof of concept study aims to improve SPI target prioritization by simulating SPI induced radio emission frequencies and estimating associated radio power to identify systems most likely to produce detectable signals. We combine Zeeman Doppler Imaging (ZDI) maps with 3D magnetohydrodynamic (MHD) stellar wind simulations and use the ExPRES code to model SPI driven radio emissions. We also estimate the intensity of these emissions using the Radio Magnetic Scaling Law, based on the magnetic field and plasma density parameters from the 3D wind models. This approach is applied to systems such as Tau Boo, HD 179949, and HD 189733 to assess their detectability with current and future radio telescopes. This framework, tested on benchmark systems, is applicable to any star planet system with available ZDI maps and wind models. As magnetic field reconstructions and wind simulations improve, the method will become more robust. It provides a data driven approach to prioritize targets and optimize telescope scheduling. This shall enable systematic exploration of magnetic SPI radio emissions across a wide range of exoplanetary systems.
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All authors J. J. Chebly, C. K. Louis, A. Strugarek, J. D. Alvarado-Gómez, P. Zarka

High Energy Astrophysical Phenomena

Using the Cherenkov Telescope onboard EUSO-SPB2 for Target of Opportunity searches of very high energy neutrino sources

Tobias Heibges, Claire Guépin, Diksha Garg et al. (+4 more)

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) mission launched from Wanaka New Zealand on May 13, 2023. The mission ended after 36 h due to a balloon leak that resulted in the payload being lost in the Pacific Ocean. Over the course of the mission, the onboard Cherenkov Telescope (CT) was pointed just below the Earth's limb to search for optical signals from upward-moving extensive air showers that were induced by decaying tau-leptons that were generated by the conversion of $>10$ PeV tau-neutrinos in Earth. Such very-high energy (VHE) neutrinos may be produced in several classes of astrophysical sources that are suspected of possibly accelerating particles to ultra-high energies. In this contribution, we discuss the EUSO-SPB2 Target-of-Opportunity (ToO) campaign to search for VHE neutrino signals coming from astrophysical sources that crossed the CT's field of view ($6.4^\circ \times 12.8^\circ$). We also present a new software tool designed for scheduling observations, the Neutrino Target Scheduler, that we developed to support the ToO campaign. We also calculate upper limits on the neutrino fluences from sources observed during the ToO campaign. Our observations demonstrate the viability of conducting ToO follow-up observations from a near space environment with future balloon missions, such as the pathfinder mission POEMMA-Balloon with Radio.
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All authors Tobias Heibges, Claire Guépin, Diksha Garg, Luke Kupari, Mary Hall Reno, Tonia M. Venters, Lawrence Wiencke

Solar and Stellar Astrophysics

Alfven Waves in Partially Ionised Solar Steady-State Plasmas

Nada F. Alshehri, Istvan Ballai, Viktor Fedun et al. (+1 more)

Our study investigates the properties of Alfvén waves in partially ionised solar plasmas in the presence of steady, field-aligned, flows of charged and neutral particles. Our work aims to understand how such flows modify wave propagation and damping in environments where ion-neutral collisions are significant. We employ a two-fluid model that treats ions and neutrals as separate, colliding fluids and incorporates background steady flows for both species. Using a combination of analytical dispersion analysis and numerical solutions, we examine the impact of these flows on the behaviour of Alfvén waves. Our results show that steady flows lead to substantial modifications of wave properties, including Doppler shifts, propagation direction reversal, flow-dependent changes in damping rates, and the appearance of a new mode associated with neutral flow and collisional coupling. We also identify conditions under which flow-driven mode conversion can arise. Our results offer new insights into the interplay between plasma flows and particle collisions in the regions of the solar atmosphere where partial ionisation is relevant.
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All authors Nada F. Alshehri, Istvan Ballai, Viktor Fedun, Gary Verth

High Energy Astrophysical Phenomena

Curious Case of CGRaBS J0211+1051: Observational Evidence of Lepto-Hadronic Origin of High-Energy Emission?

Sunil Chandra, Pankaj Kushwaha, Pranjupriya Goswami et al. (+1 more)

We present an extensive analysis of the multi-wavelength data of the low-synchrotron-peaked BL Lac object CGRaBS J0211+1051, which has been gathered over more than ten years with many observatories. Two major gamma-ray flares have been observed during the Fermi era: one in January 2011 and other in June 2019. During these events, CGRaBS J0211+1051 was also bright in other energy bands. On the other hand, there are also examples of optical activity that do not exhibit any comparable gamma-ray variability. Here, we study the temporal and spectral characteristics of the object in an attempt to understand the emission mechanisms operating in this source. A peculiar feature in its spectrum is the X-ray domain, which is unusually soft considering its object class. Interestingly, the relatively soft UV and optical spectrum does not extrapolate well to the X-rays. To mimic the observed SEDs during quiescent and flaring periods, we use both a purely leptonic and a hadro-leptonic modeling approach to reproduce four broadband SEDs from various epochs. When taking into account the steep optical-UV spectrum, we find that the hadro-leptonic scenarios better explains the SEDs compared to the purely leptonic model. The hadro-leptonic interpretation of the two gamma-ray flares suggests that CGRaBS J0211+1051 could be both a potential neutrino emitter and TeV-bright (E>10 TeV). Thus, it may offer a unique test bed to check for hadro-leptonic contributions to the multi-messenger emission in blazar jets.
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All authors Sunil Chandra, Pankaj Kushwaha, Pranjupriya Goswami, Michael Zacharias

Cosmology and Nongalactic Astrophysics

A Dynamical Scalar Field Model for Dark Energy: Addressing the Hubble Tension and Cosmic Evolution

Arpit Kottur, Jui Mahajan and Raka Dabhade

We propose a dynamical dark energy model based on a canonical scalar field with a hybrid potential of the form $V(\phi) = V_{0}e^{-\lambda\phi} + V_{1}\phi^{n}$. We constrain the model's 11-dimensional parameter space using a comprehensive combination of cosmological data, including the Planck 2018 Cosmic Microwave Background (CMB) power spectra, Baryon Acoustic Oscillations (BAO), the Pantheon+ supernova sample, SH0ES and the matter power spectrum from SDSS. The model provides an excellent fit to the data, with a reduced chi-squared of $\chi^2_{\text{red}} = 0.989$, while successfully alleviating the Hubble constant tension. Our analysis yields a Hubble constant of $H_0 \approx 72.820$ km/s/Mpc, reducing the discrepancy between early and late-universe measurements. We find that the data favors a 'thawing' quintessence scenario, characterized by a potential slope parameter $\lambda \approx 0.056$. This small but non-zero slope drives a late-time deviation from $\Lambda$CDM ($w(z=0) \approx -0.85$) while preserving the standard expansion history at high redshifts. A model comparison using the Bayesian Information Criterion finds that the standard $\Lambda$CDM model is still slightly preferred ($\Delta\text{BIC} = 2.178$) due to its fewer parameters. Nevertheless, our results demonstrate that this hybrid potential model is a compelling, physically motivated alternative to a cosmological constant.
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Earth and Planetary Astrophysics

True spin-orbit obliquities distribution: data-driven confirmation of no clustering of misaligned planets

Alessandro Matteo Rossi, Monica Rainer, Francesco Borsa et al. (+1 more)

Context. True spin-orbit obliquities {\Psi} offer valuable insights into the evolutionary history of exoplanetary systems. Previous studies have suggested that exoplanets tend to occupy either aligned or perpendicular orbits. However, recent research has indicated potential biases caused by the low sample, questioning whether this dichotomy would persist with a larger dataset. Simultaneously, a similar dichotomous behavior has been suggested for Neptune-sized planets. Aims. We aim to investigate the distribution of true spin-orbit obliquities {\Psi} with an enlarged sample, looking for confirmation of the disputed dichotomy previously found, with a focus also on the obliquities of Neptunes. Methods. Starting from a sample of 264 projected obliquities {\lambda}, we homogeneously compute true obliquities {\Psi} for 116 planets using the rotation period method. We combine them with 4 further values gathered from literature and we then study their distribution, also as a function of various star-planet system parameters. Results. Our data-driven work based on 120 true obliquities {\Psi} - the largest sample to date - strongly confirms the presence of a single cluster of aligned planets, followed by an isotropic distribution of misaligned planets with no preferred misalignment. This result is based on a uniform distribution of stellar inclinations {i_\star} , for which non-uniformity could have biased previous interpretations of the arrangement of true obliquities. We confirm that Neptunians show a tentative dichotomous distribution with data available today, but its veracity needs confirmation with an enlarged sample, also because an anisotropic distribution of stellar inclination may be one of the factors hindering the real distribution.
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All authors Alessandro Matteo Rossi, Monica Rainer, Francesco Borsa, Stefano Facchini

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

Probing thermal leptogenesis and dark matter through primordial gravitational waves from a supercooled universe

Peter Athron, Satyabrata Datta and Zhao-Yang Zhang

We explore the cosmological dynamics of a supercooled first-order phase transition in the classically conformal $U(1)_{B-L}$ extension of the Standard Model, where radiative symmetry breaking simultaneously generates the right-handed neutrino (RHN) masses, and a strong stochastic gravitational-wave (GW) background. The slow decay of the scalar field into RHNs can induce an early matter-dominated (EMD) era whose duration is sensitive to the RHN mass and gauge coupling $g^\prime$. This non-standard cosmological phase reshapes the GW spectrum and leaves a distinctive RHN-mass-dependent spectral distortion that correlates with the flavour regime of thermal leptogenesis. Within this framework, one RHN can serve as a dark matter candidate produced nonthermally from scalar decays, while the remaining states generate the baryon asymmetry via thermal leptogenesis. For $g^\prime=0.5$, we identify such a parameter region, and show that with singlet extensions, even with a smaller gauge coupling, one can realise this mechanism for the three-flavour regime. The resulting GW signals, amplified by supercooling and modified by EMD, provide a unique window to probe the scale and flavour structure of leptogenesis in future high-frequency GW observations.
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Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

Electron Heat Flux and Whistler Instability in the Earth's Magnetosheath

Ida Svenningsson, Emiliya Yordanova, Yuri V. Khotyaintsev et al. (+4 more)

Despite heat flux's role in regulating energy conversion in collisionless plasmas, its properties and evolution in the magnetosheath downstream of the Earth's bow shock are scarcely explored. We use MMS in situ measurements to quantify and characterize the electron heat flux in the magnetosheath. We find that the heat flux is shaped by the magnetosheath magnetic field as it drapes around the magnetosphere. While it is affected by solar wind upstream conditions and increases with magnetic field strength, it is not substantially changed by local magnetosheath processes. Also, the heat flux is limited by whistler instability thresholds.
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All authors Ida Svenningsson, Emiliya Yordanova, Yuri V. Khotyaintsev, Mats André, Giulia Cozzani, Alexandros Chasapis, Steven J. Schwartz

Earth and Planetary Astrophysics

Fundamentals of interior modelling and challenges in the interpretation of observed rocky exoplanets

Philipp Baumeister, Francesca Miozzi, Claire Marie Guimond et al. (+7 more)

Most our knowledge about rocky exoplanets is based on their measure of mass and radius. These two parameters are routinely measured and are used to categorise different populations of observed exoplanets. They are also tightly linked to the planet's properties, in particular those of the interior. As such they offer the unique opportunity to interpret the observations and potentially infer the planet's chemistry and structure. Required for the interpretation are models of planetary interiors, calculated a priori, constrained using other available data, and based on the physiochemical properties of mineralogical phases. This article offers an overview of the current knowledge about exoplanet interiors, the fundamental aspects and tools for interior modelling and how to improve the contraints on the models, along with a discussion on the sources of uncertainty. The origin and fate of volatiles, and their role in planetary evolution is discussed. The chemistry and structure of planetary interiors have a pivotal role in the thermal evolution of planets and the development of large scale properties that might become observables with future space missions and ground-based surveys. As such, having reliable and well constrained interior models is of the utmost importance for the advancement of the field.
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All authors Philipp Baumeister, Francesca Miozzi, Claire Marie Guimond, Marie-Luise Steinmeyer, Caroline Dorn, Shun-Ichiro Karato, Emeline Bolmont, Alexandre Revol, Alexander Thamm, Lena Noack

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Confronting dark energy in Harada's Conformal Killing Gravity with observational data

Mohsen Khodadi, Gaetano Lambiase and Javad. T. Firouzjaee

Based on a comprehensive analysis of recent observational data-a combination of DESI DR1, Planck CMB, and Pantheon+ SN Ia-this study critically evaluates the two dark energy (DE) proposals within Harada's Conformal Killing Gravity (CKG) model. The model in question predicts either a dominant phantom-type effective DE component with EoS $\omega = -5/3$ or a hybrid scenario combining a cosmological constant ($\omega = -1$) with a subdominant $\omega = -5/3$ fluid (around $5\%$) to address the Hubble tension (HT) and late-time acceleration. An analysis based on the Trans-Planckian Censorship Conjecture (TCC) demonstrates that the pure CKG fluid scenario $\omega = -5/3$ is excluded, whereas the hybrid model remains only marginally compatible. Our Markov Chain Monte Carlo (MCMC) analysis constrains the effective DE density parameter to $\Omega_{\text{eff}} = 0.009^{+0.006}_{-0.007}$ ($68\%$ CL), consistent with zero and ruling out the around $5\%$ contribution required by Harada's CKG. The resulting Hubble expansion history $H(z)$ and effective EoS $\omega_{\text{eff}}(z)$ are indistinguishable from those of $\Lambda$CDM. Bayesian model comparison via the Akaike Information Criterion (AIC) shows no statistical preference for CKG over $\Lambda$CDM ($\Delta \text{AIC} = +2.6$), disfavoring the additional complexity of the CKG model. The key output of this study is that both DE proposals in Harada's CKG are ruled out by current cosmological data, and HT remains unresolved.
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Astrophysics of Galaxies

Systematic Analysis of Changing-look AGN Variability Using ZTF Light Curves

Huimei Wang, Xue-Bing Wu, Nanyu Yao et al. (+5 more)

Changing-look active galactic nuclei (CLAGNs) are a unique population of AGNs that exhibit the appearance (turn-on) or disappearance (turn-off) of broad emission lines. This study aims to explore the intrinsic mechanisms of CLAGNs by investigating their photometric variability using data from the Zwicky Transient Facility (ZTF), which has provided high-cadence observations over the past five years. By visual inspections, we construct a sample of 152 CLAGNs from the literature, all of which show spectral transitions and large optical variability in their ZTF light curves. By analyzing 90 of these CLAGNs and the control samples of Type 1 AGNs, Type 2 AGNs, and extremely variable quasars (EVQs), matched in redshift ($0.2<z<0.8$) and supermassive black hole mass, we compare the color variability, structure function (SF), and variability metric $\sigma_{\mathrm{QSO}}$, which quantifies how closely the light curves resemble a damped random walk (DRW) model. We find that while CLAGNs and EVQs differ from typical Type 1 and Type 2 AGNs in bolometric luminosity and Eddington ratio, the on/off-state CLAGNs share similar variability patterns with the overall CLAGN population, and distinct from EVQ, Type 1 and Type 2 AGNs. This suggests that 'on' and 'off' CLAGNs are not simply equivalent to Type 1 and Type 2 AGNs, respectively. Instead of undergoing genuine transitions between two AGN types, CLAGNs may inhabit a critical state where moderate fluctuations in accretion rate lead to the temporary spectral changes.
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All authors Huimei Wang, Xue-Bing Wu, Nanyu Yao, Bing Lyu, Yuxuan Pang, Yuming Fu, Rui Zhu, Qian Yang

High Energy Astrophysical Phenomena

Probing AGN Disks Density Profiles through Gravitational Wave Observations

Xiangyu Lyu, En-Kun Li, Changfu Shi et al. (+1 more)

Massive black holes surrounded by a gaseous disk have been a prevailing model to explain a wide spectrum of astrophysical phenomena related to active galactic nucle (AGNs). However, direct and precise measurements of the disk density profiles remain elusive for current telescopes. In this work, we demonstrate that it is possible to pinpoint the gas density if an inspiralling stellar mass binary black hole is embedded in the AGN disk. Furthermore, if the barycenter of the pair follows an eccentric orbit around an AGN, then space-borne gravitational wave detectors can measure the density of the surrounding disk with multi-year observations by tracking the gravitational wave evolution. The error between the inferred density profile and the injected truth can be constrained to below $2\times10^{-11}\rm g/cm^3$. Our work opens up an exciting new channel to investigate the very center of galaxies, where disk gas density distributions $\rho(r)$ can be recovered by analyzing time-dependent environmental imprints in gravitational waveforms.
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All authors Xiangyu Lyu, En-Kun Li, Changfu Shi, Yi-Ming Hu

Astrophysics of Galaxies

Estimating accretion times of halo substructures in the Milky Way

Hefan Li, Masashi Chiba, Xiang-Xiang Xue et al. (+1 more)

To unravel the formation history of the Milky Way, we estimate the accretion times of six phase-space substructures in the stellar halo, using the orbital frequencies toward two spatial directions ($r, \phi$) in spherical coordinates. These substructures, identified in our previous studies, are located in the solar neighbourhood and therefore have high-precision astrometry from Gaia. The uncertainties of the results are determined using the Monte Carlo method, and the significance is established through comparison with random halo samples. The results for the substructure GL-1 in both directions show good consistency and high significance ($4.3\sigma$ and $3.9\sigma$), yielding a combined accretion time of $5.6 \pm 0.1$ Gyr ago, where the uncertainties quoted are statistical only. The substructures GL-4 and GR-1, with smaller pericenters, exhibit higher significance in the less massive potential of the Milky Way, implying that the more massive potential may overestimate the central mass, especially the bulge. The accretion times of GL-4 and GR-1 are $6.9 \pm 0.3$ Gyr with a confidence of $3.7\sigma$, and $2.0 \pm 0.1$ Gyr with a confidence of $4.4\sigma$, respectively. Further constraints on the accretion times of phase-space substructures require more precise astrometric data, e.g., by Gaia DR4, China Space Station Survey Telescope and Roman space telescope.
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All authors Hefan Li, Masashi Chiba, Xiang-Xiang Xue, Gang Zhao

Solar and Stellar Astrophysics

Analysis of the magnetic fields in massive young stellar objects with masers

P.I. Pavlova, S.A. Khaibrakhmanov and A.M. Sobolev

We analyze observational data on methanol masers in the disks of young massive stellar objects in the massive star formation regions: NGC6334I, G33.641-0.228, G12.89+0.49. Special attention is paid to analysis of the magnetic fields and their possible connection with maser flares. For this purpose, we estimate the distance from star to maser, the magnetospheric radius and magnetic field strength in the region of this radius. The distances from stars to masing regions lie in range from 380 to 620 au. Stellar and disk's magnetic field strengths are comparable at the magnetosphere boundary and lie in the range from 590 to 1880 G for considered objects. Our estimates show that the magnetic fields may play an important role in the considered regions. In particular, observed luminosity bursts and maser flares may be related to magnetic reconnection events near the stars.
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High Energy Astrophysical Phenomena

Synchrotron radiation from NGC 470 HLX1 - a hidden hyperluminous accreting neutron star?

Tanuman Ghosh, Shiv Sethi, Gulab Chand Dewangan et al. (+3 more)

We present the first broadband spectral analysis of NGC 470 HLX1, a hyperluminous X-ray source that exhibits significant flux variability over different epochs. We investigate the feasibility of synchrotron radiation with varying latitude from a magnetized neutron star to explain the source's spectra. Although the statistical quality of the data does not allow us to rule out simple phenomenological models, it is adequate to constrain the parameter space for this more physically motivated model. We also shed light on the particle acceleration mechanisms and maximum Lorentz factor of electrons within the neutron star magnetospheric plasma under super-Eddington accretion conditions. In our broadband spectral modeling, the detection of a blackbody-like component suggests the presence of a disk near the corotation radius or an outflow ejected from the disk. The viability of synchrotron emission in an HLX system offers new insights about the nature of these sources, motivating further sample studies to assess whether most of these sources are powered by accreting neutron stars.
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All authors Tanuman Ghosh, Shiv Sethi, Gulab Chand Dewangan, Matteo Bachetti, Vikram Rana, Ranjeev Misra

Solar and Stellar Astrophysics

Fast Rotating Blue Straggler Stars in the globular cluster NGC 1851

Alex Billi, Lorenzo Monaco, Francesco R. Ferraro et al. (+4 more)

In this work we study the rotational velocities of a sample of blue straggler stars (BSSs) and reference stars belonging to the Galactic globular cluster NGC 1851, using high-resolution spectra acquired with FLAMES-GIRAFFE at the ESO/VLT. After field decontamination based on radial velocities and proper motions, the final sample of member stars is composed of 15 BSSs and 45 reference stars populating the red giant and horizontal branches of the cluster. In agreement with previous findings, the totality of reference stars has negligible rotation (lower than 15 km/s). In contrast, we find high values of rotational velocity (up to $\sim$ 150 km/s) for a sub-sample of BSSs. By defining the threshold for fast rotating BSSs at 40 km/s, we found 4 fast-rotating BSSs out of 15, corresponding to a percentage of 27 $\pm$ 14 %. This results delineates a monotonically decreasing trend (instead of a step function) between the percentage of fast spinning BSSs and the central concentration and density of the host cluster, supporting a scenario where recent BSS formation preferentially occurs in low-density environments from the evolution of binary systems.
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All authors Alex Billi, Lorenzo Monaco, Francesco R. Ferraro, Alessio Mucciarelli, Barbara Lanzoni, Mario Cadelano, Israel Trangolao

Astrophysics of Galaxies

Impact of selection criteria on the structural parameters of the Galactic thin and thick discs

Simon Alinder, Thomas Bensby and Paul McMillan

Context: The Milky Way contains a thick and a thin disc that differ in chemical, kinematic, structural, and spatial properties. There is significant overlap in the distributions of these properties, especially so at higher metallicities. Distinguishing between these major structural components is crucial for understanding the formation and evolution of the Galaxy. Multiple selection methods exist to classify stars as thin or thick disc stars, each with its own advantages and limitations. Aims: We investigate how different classification methods for categorising stars into the thick and thin disc populations influence the determination of structural properties of the two discs. Methods: We apply five different selection methods. Two methods use cuts in the [$\alpha$/Fe]-[Fe/H] and [Mg/Mn]-[Al/Fe] planes; one uses a dynamical separation in $J_\phi$ -$J_Z$ space; one uses an age-based cut; and the last one uses a kinematic likelihood method. For each method, we derive relative density profiles of each component as functions of height above the Galactic plane and Galactocentric radius, and fit these to a simple two-exponential disc model. We use red giant stars from APOGEE DR17 and stellar ages from astroNN. Results: Methods based on abundance or age data produce the cleanest separations, while kinematic and dynamical methods suffer higher contamination due to difficulties in separating well-mixed populations. The thin disc scale heights show a clear flaring as they increase with radius, while the thick disc stays approximately constant at around 1 kpc over most radii for all methods. All methods find the thin disc to have a longer scale length than the thick disc, with the difference being greatest for the chemical selection methods. A scale length of the thick disc of 2.0 kpc leads to one of between 2.3 and 3.0 kpc for the thin disc.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Trapped and Unstable: Axion-like particle fragmentation at finite temperature

Nicklas Ramberg and Daniel Schmitt

We investigate the emergence of a resonant behavior in axion-trapped misalignment models featuring finite-temperature potential barriers. As the temperature decreases and the field is released from its trapped configuration, inhomogeneities are exponentially amplified through an instability in their equation of motion, leading to the fragmentation of the axion field. We show that this process constitutes a novel source of gravitational waves (GWs), analogous to those generated in zero-temperature axion fragmentation, but with distinct characteristics. We quantify the resulting GW spectrum, identifying the peak frequency and amplitude associated with the inhomogeneous axion dynamics. Our results indicate that the GW signal can be enhanced by up to two orders of magnitude compared to the standard fragmentation scenario, while exhibiting a markedly different spectral shape. The parameter space featuring both strong GW signals and reproducing the correct dark matter abundance is, however, limited.
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Cosmology and Nongalactic Astrophysics

Composite Dissipation in Warm Inflation: Implications for the Primordial Power Spectrum

Ayush Sahu, Richa Arya, Sergio E. Jorás et al. (+1 more)

Warm inflation is a well-motivated and generalized framework of inflation, describing a coupled inflaton-radiation bath. In this work, we investigate a warm inflation model with a quartic potential and a composite dissipation coefficient $\Upsilon(\phi, T) = C_1 \frac{T^3}{M_{\text{Pl}}^2} + C_2 \frac{T^3}{\phi^2}.$ The two terms in $\Upsilon$ dominate at different scales: the first term governs the early inflationary dynamics at large (CMB) scales, while the second term becomes significant at smaller scales. The model features two distinct stages of inflation: an initial phase where strong dissipation ($Q \gg 1$) generates a red-tilted primordial spectrum consistent with CMB observations (from ACT), followed by a second phase producing a blue-tilted spectrum with a significant amplification of power at small scales, leading to primordial black hole formation. We analyze the effects of key parameters – like the duration of each inflationary phase, the slow-roll parameter at the end of the first phase, the dissipation strength at the pivot scale, and the choice of the growth function – on the primordial power spectrum and its spectral index. Additionally, we examine the consistency of the model with the swampland distance conjecture and trans-Planckian conjecture, needed for embedding these models with some UV complete theories. This work highlights the potential of warm inflation with a composite dissipation coefficient to reconcile large-scale CMB measurements with small-scale structure formation.
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All authors Ayush Sahu, Richa Arya, Sergio E. Jorás, Karim H. Seleim

Cosmology and Nongalactic Astrophysics

Where Galaxies Point: First Measurement of the Large-Scale Axial Intrinsic Alignment

Pedro da Silveira Ferreira, Rafael Oliveira Ramos, Paula S. Ferreira et al. (+5 more)

We report evidence for large-scale axial intrinsic alignment (LAIA): a coherent axis shared by galaxies and cosmic-web filaments. Applying an orientation-field estimator to Dark Energy Survey (DES) Y3 shape data, we identify a preferred axis in galaxy orientations. Ellipticals' semi-major and spirals' semi-minor axes align with it, producing a $4.7\sigma$ signal whose pattern and amplitude hierarchy are consistent with morphology-dependent tidal-alignment and tidal-torquing expectations. Independently, Sloan Digital Sky Survey (SDSS) filament catalogues yield a compatible axis: northern and southern Galactic samples agree within $\simeq1\sigma$, the combined signal reaches $12.6\sigma$, and the axis lies within $\simeq2\sigma$ of the high-redshift galaxy sample direction. Because DES and SDSS footprints overlap marginally, this agreement is unlikely to arise from direct galaxy–filament alignment. It therefore provides a multi-survey, multi-observable test of a large-scale orientation field, stable under redshift and systematics tests. $N$-body mocks based on an isotropic $\Lambda$CDM cosmology with standard intrinsic-alignment prescriptions, including Euclid Flagship 2 and MICECAT v2, do not reproduce the pattern. LAIA provides a new statistical-isotropy probe linking galaxy morphology, cosmic-web structure and large-scale tidal fields.
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All authors Pedro da Silveira Ferreira, Rafael Oliveira Ramos, Paula S. Ferreira, Arianna Cortesi, Fabricio Ferrari, Valerio Marra, Clécio R. Bom, Renyue Cen

Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

Rediscovering the Lunar Equation of the Centre with AI Feynman via Embedded Physical Biases

Saumya Shah, Zi-Yu Khoo, Abel Yang et al. (+1 more)

This work explores using the physics-inspired AI Feynman symbolic regression algorithm to automatically rediscover a fundamental equation in astronomy – the Equation of the Centre. Through the introduction of observational and inductive biases corresponding to the physical nature of the system through data preprocessing and search space restriction, AI Feynman was successful in recovering the first-order analytical form of this equation from lunar ephemerides data. However, this manual approach highlights a key limitation in its reliance on expert-driven coordinate system selection. We therefore propose an automated preprocessing extension to find the canonical coordinate system. Results demonstrate that targeted domain knowledge embedding enables symbolic regression to rediscover physical laws, but also highlight further challenges in constraining symbolic regression to derive physics equations when leveraging domain knowledge through tailored biases.
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All authors Saumya Shah, Zi-Yu Khoo, Abel Yang, Stéphane Bressan

Astrophysics of Galaxies

New ASKAP radio-continuum surveys of the Small Magellanic Cloud

O. K. Khattab, M. D. Filipovic', Z. J. Smeaton et al. (+5 more)

We present two new radio continuum images from the ASKAP POSSUM survey in the direction of the Small Magellanic Cloud. The two new source lists contain 36,571 radio continuum sources detected at 944 MHz and 15,227 sources at 1367 MHz, with beam sizes of approximately 14.5 by 12.2 arcsec and 8.7 by 8.2 arcsec, respectively. We used the Aegean software package to generate these point source catalogues, and together with the previously published MeerKAT catalogue, we estimated spectral indices for the full set of matched radio point sources. By cross-matching our ASKAP catalogues with the MeerKAT data, we identified 21,442 and 12,654 common point sources at 944 MHz and 1367 MHz, respectively, using a 2 arcsec matching radius. These new catalogues improve our understanding of the Small Magellanic Cloud and demonstrate the capability of current radio telescopes such as ASKAP to investigate diverse galactic source populations
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All authors O. K. Khattab, M. D. Filipovic', Z. J. Smeaton, R. Z. E. Alsaberi, E. J. Crawford, D. Leahy, S. Dai, N. Rajabpour

Cosmology and Nongalactic Astrophysics

Slow neutrinos: non-linearity and momentum-space emulation

Amol Upadhye and Yin Li

Recent cosmological bounds on the sum of neutrino masses, M_nu = sum m_nu, are in tension with laboratory oscillation experiments, making cosmological tests of neutrino free-streaming imperative. In order to study the scale-dependent clustering of massive neutrinos, we develop a fast linear response method, FAST-nu f, applicable to neutrinos and other non-relativistic hot dark matter. Using it as an accurate linear approximation to help us reduce the dynamic range of emulator training data, based upon a non-linear perturbation theory for massive neutrinos, we improve the emulator's accuracy at small M_nu and length scales by a factor of two. We significantly sharpen its momentum resolution for the slowest neutrinos, which, despite their small mass fraction, dominate small-scale clustering. Furthermore, we extend the emulator from the degenerate to the normal and inverted mass orderings. Applying this new emulator, Cosmic-Enu-II, to large halos in N-body simulations, we show that non-linear perturbation theory can reproduce the neutrino density profile in the halo outskirts, 2R_vir < r < 10R_vir , to better than 10%.
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Astrophysics of Galaxies

JWST View of the Supernebula in NGC 5253. II. Nebular Lines

Sara C. Beck, Jean L. Turner, Elm Zweig et al. (+7 more)

The nearby dwarf starburst NGC 5253 is dominated by a compact radio-infrared supernebula powered by a very young and bright embedded Super Star Cluster (SSC) of $\sim 10^9 L_\odot$. We observed this source and its surroundings over the 5-25$\mu$m range with MIRI/MRS on JWST and in Paper I presented the JWST view of the region and its continuum features. We now present the more than 70 emission lines of HI, $H_2$ and metal ions detected by MIRI/MRS. We derive the extinction by comparing HI recombination to the free-free radio continuum and find that it is very flat, i.e., almost independent of wavelength, over this spectral range. Nebular conditions are consistent with young ($\lesssim5\times10^6$ years) and very massive stars. All regions show high excitation, but the spatial distribution of the high excitation lines suggests that photons with energies close to 50eV are escaping the supernebula core in spite of 35 magnitudes of visual extinction.
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All authors Sara C. Beck, Jean L. Turner, Elm Zweig, John H. Black, Paul T. P. Ho, David S. Meier, Sergiy Silich, Daniel P. Cohen, S. Michelle Consiglio, Nicholas G. Ferraro

Astrophysics of Galaxies

JWST View of the Supernebula in NGC 5253. I. Overview and Continuum Features

Jean L. Turner, Sara C. Beck, Elm A. Zweig et al. (+7 more)

We present 5-28$\mu$m imaging spectroscopy of the "supernebula" in the dwarf galaxy NGC 5253 made with the JWST MIRI-MRS integral field spectrometer. NGC 5253 hosts a luminous ($L\sim 10^9~\rm L_\odot$) HII region, powered by a giant young star cluster, a possible local analogue to super star cluster formation at Cosmic Dawn and Noon. In this paper, the first in a series about the mid-infrared line and continuum emission in the center of NGC 5253, we present an overview and continuum spectra. The mid-infrared images reveal four continuum sources that we identify as hot dust emission from luminous HII regions. The dominant source is the pc-scale supernebula core seen at radio wavelengths. We find that the MIR to radio continuum flux ratio is identical to that of Galactic HII regions. The 9.7$\mu$m silicate feature is present and strongest in absorption toward the supernebula. PAH features at 6.2, 6.8, 7.7, 8.6, and 11.2$\mu$m are detected across the region, although weakly, particularly in the supernebula. Unusual PAH line profiles are seen, including a broad 6$\mu$m feature, likely in part aliphatic, from the extended starburst region and strong 11.0$\mu$m emission from the supernebula. These observations suggest dust processing by intense radiation fields and possible dust production and dispersal by Wolf-Rayet stars within the region.
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All authors Jean L. Turner, Sara C. Beck, Elm A. Zweig, L. Barcos-Muñoz, John H. Black, Daniel P. Cohen, S. Michelle Consiglio, Nicholas G. Ferraro, Paul T. P. Ho, David S. Meier

Astrophysics of Galaxies

findAbar: how astronomers may perceive the bar in galaxies differently

Elizabeth J. Iles, Joss Bland-Hawthorn, Courtney Crawford et al. (+18 more)

Bars are ubiquitous morphological features in the observed distribution of galaxies. There are similarly many methods for classifying these features and, without a strict theoretical definition or common standard practice, this is often left to circumstance. So, we were concerned whether astronomers even agree on the bar which they perceive in a given galaxy and whether this could impact perceived scientific results. As an elementary test, we twenty-one astronomers with varied experience in studying resolved galaxies and circumstances, have each assessed 200 galaxy images, spanning the early phase of bar evolution in two different barred galaxy simulations. We find variations exist within the classification of all the standard bar parameters assessed: bar length, axis-ratio, pitch-angle and even whether a bar is present at all. If this is indicative of the wider community, it has implications for interpreting morphological trends, such as bar-end effects. Furthermore, we find that it is surprisingly not expertise but gender, followed by career stage, which gives rise to the largest discrepancies in the reported bar parameters. Currently, automation does not seem to be a viable solution, with bar classifications from two automated bar-finding algorithms tested and failing to find bars in snapshots where most astronomers agree a bar must exist. Increasing dependence on machine learning or crowdsourcing with a training dataset can only serve to obfuscate any existing biases if these originate from the specific astronomer producing the training material. On the strength of this small sample, we encourage an interim best practice to reduce the impact of any possible classification bias and set goals for the community to resolve the issue in the future.
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All authors Elizabeth J. Iles, Joss Bland-Hawthorn, Courtney Crawford, Scott Croom, Hillary Davis, May Gade Pedersen, Anne Green, Madusha Gunawardhana, Miguel Icaza-Lizaola, Helen Johnston, Emily F. Kerrison, Yifan Mai, Benjamin T. Montet, Kovi Rose, Tomas Rutherford, Manasvee Saraf, Ellen L. Sirks, Eckhart Spalding, Sujeeporn Tuntipong, Jesse van de Sande, Pavadol Yamsiri

Instrumentation and Methods for Astrophysics

fiDrizzle-MU: A Fast Iterative Drizzle with Multiplicative Updates

Shen Zhang, Lei Wang, Huanyuan Shan et al. (+3 more)

We propose fiDrizzleMU, an algorithm for co-adding exposures via iterative multiplicative updates, replacing the additive correction framework. This method achieves superior anti-aliasing and noise reduction in stacked images. When applied to James Webb Space Telescope data, the fiDrizzleMU algorithm reconstructs a gravitational lensing candidate that was significantly blurred by the pipeline's resampling process. This enables the accurate recovery of faint and extended structures in high-resolution astronomical imaging.
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All authors Shen Zhang, Lei Wang, Huanyuan Shan, Ran Li, Xiaoyue Cao, Yunhao Gao