Solar and Stellar Astrophysics
Extreme Ultraviolet Microflashes at Plume Bases: A Candidate for Powering the Corona and Solar Wind?
Navdeep K. Panesar, Sanjiv K. Tiwari, Meng Jin et al. (+4 more)
Solar plumes -
outflows of bright coronal
plasma - are a major component of the open-
magnetic-field corona and
solar wind, but their driving mechanism remains uncertain. Here we report on network microflashes, fine-scale bright bursts captured by
Solar Orbiters Extreme Ultraviolet Imager in 174A images encompassing
magnetic network at the base of plumes. Because they sit in evidently unipolar
magnetic flux, they are evidently a new, previously unidentified, kind of network event. Approximately 20 microflashes are ongoing within a plume base, with a new microflash starting every second. The energy for an average microflash is 1024 erg, in the range of nanoflares. A 3D data-driven global MHD model yields open
magnetic field with fast
solar wind for the investigated plumes. From our findings, we suggest that network microflashes result from fine-scale bursts of reconnection of crossed legs of unipolar
magnetic field, that the bursts are often triggered by 5-minute p-mode oscillations, and that the bursts are candidates for powering the open-field corona and
solar wind. That is, unipolar microflashes such as ours are plausibly from unipolar-network-field reconnection bursts that sustain the heliosphere.
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All authors Navdeep K. Panesar, Sanjiv K. Tiwari, Meng Jin, Ayla Weitz, Ronald L. Moore, V. Aparna, Alphonse Sterling
Solar and Stellar Astrophysics
Transformation of solar wind energy and helicity spectra in the frame of magnetohydrodynamics shell modeling
I. Dukanov, E. Yushkov, P. Frick et al. (+1 more)
Based on the data recorded during the Parker
Solar Probe mission, it can be suggested that there is no balance between kinetic and
magnetic energy in the vicinity of the Sun. The spectra collected at different radial distances show an energy transfer from one component to another, followed by a change in inertial range slope and large-scale break shifted towards lower wavenumbers. Using the shell (cascade) modeling approach, we attempt to explain and understand this observed spectra transformation, considering a free-decay
turbulence process and modeling a simple transition to a quasi-stationary
equilibrium between the
magnetic and kinetic energies. Varying the parameters of
turbulence mirror asymmetry (helicity), we numerically simulate changes in spectral indices, large-scale shift position, and inertial range transformations, comparing our model results with spacecraft observations of
solar wind
turbulence. We present and discuss the chaotic nature of the spectral
magnetic helicity distributions, as well as the fact that helicity can accumulate at large scales. The applicability of a simple MHD shell model to repeat the key features of
solar wind
turbulence dynamics offers wide possibilities for its further use.
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All authors I. Dukanov, E. Yushkov, P. Frick, D. Sokoloff
Earth and Planetary Astrophysics
Clustering SPH Debris into N-body Fragments: A Collisional Code for Planet Formation
Samuele Crespi, Mohamad Ali-Dib and Ian Dobbs-Dixon
Giant impacts among planetary embryos generate long-lived debris that feeds back on late-stage terrestrial
planet growth, yet most N-body models either assume perfect merging or treat fragments in ad hoc ways. We present SHARD, a collision-resolution framework that couples a hybrid integrator (REBOUND/mercurius) to a six-dimensional catalog of smoothed-particle hydrodynamics (SPH) outcomes spanning impact speed, geometry, total mass (up to 2 M_earth), mass ratio, and target/projectile water fractions. For each detected impact we multi-linearly interpolate to return the two largest remnants with self-consistent kinematics and volatile budgets, and we reconstruct the unresolved fragment population by aggregating nearby SPH debris snapshots and compressing them with mass-weighted k-means in velocity space into a tractable number of fragments above a tunable minimum mass. Exact conservation of total mass and water mass is enforced across survivors and debris, with immediate, energy-based reaccretion checks performed within the timestep. Debris interpolation is constrained to the tabulated SPH grid (no extrapolation), and special handling of hit-and-run and catastrophic regimes is included. We
benchmark our code against SyMBA in a Mercury-formation experiment and find broad qualitative agreement, though our final embryos distribution is dynamically hotter and more top-heavy in mass. The
benchmark outcome suggests that debris clustering is dynamically consequential: fragment resolution controls reaccretion, damping, and volatile retention. This SPH-anchored debris treatment provides a drop-in, compositionally aware alternative to perfect merging, enabling late-stage
accretion studies that retains fragment feedback without saturating the integrator.
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Earth and Planetary Astrophysics
High-Eccentricity Tidal Migration Driven by Secular Chaos in Wide-Binary Systems
Yurou Liu, Hareesh Gautham Bhaskar, Xian-Yu Wang et al. (+1 more)
High-eccentricity
tidal migration driven by a distant
stellar companion offers a natural pathway for producing some hot Jupiters; yet, most theoretical work has relied on an idealized three-body configuration whose simplicity makes the problem especially tractable. In reality, many cold-Jupiter systems may host additional
planets or substellar objects, whose interactions can dramatically alter the pathways to secularly excite extreme eccentricities. We investigate how secular chaos can drive high-eccentricity
tidal migration in hierarchical “3+1” systems–
stellar binaries hosting a
planet and an additional intermediate companion orbiting the primary
star. We show that the onset of secular chaos is regulated by the ratio of the von-Zeipel-Lidov-Kozai (ZLK) timescales of the inner and outer orbits $\mathcal{R}$. When $\mathcal{R}\sim 0.5-2$, most systems can undergo migration even when their mutual inclinations remain modest–below the $39.2^\circ$ critical angle for ZLK oscillations–with
diffusion timescales spanning a broad range, up to thousands of inner orbit ZLK timescales. For larger mutual inclinations, secular migration operates over a much broader region of parameter space with $\mathcal{R} \sim 0.05-100$, but most evolutionary pathways become non-secular and potentially unstable–behavior recently identified as an alternative pathway to
tidal migration. Our model predicts hot Jupiters in nearly polar orbits relative to both the host
star's
stellar equator (
stellar obliquities $\sim 60^\circ-120^\circ$) and the orbits of the outer two companions. Future
Gaia releases and long-term radial velocity campaigns are likely to uncover additional “3+1” systems, providing valuable opportunities to test this migration pathway.
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All authors Yurou Liu, Hareesh Gautham Bhaskar, Xian-Yu Wang, Cristobal Petrovich
Earth and Planetary Astrophysics
Unraveling the Mystery of the Peculiar and Young Hot Jupiter CoRoT-2b II: Phase Resolved Emission Spectroscopy with VLT/CRIRES+ and Gemini-S/IGRINS
Aurora Y. Kesseli, Siddharth Gandhi, Lisa Dang et al. (+8 more)
Hot Jupiters are expected to be tidally locked and synchronously rotating due to their short orbital periods. These conditions create large day-night temperature contrasts and are thought to drive eastward super-rotating jets. Indeed, the majority of hot Jupiters are observed to have the hottest region of the
planet either at the substellar point or offset in the eastern direction. However, the full phase curve of CoRoT-2b, observed with the Spitzer Space
Telescope, exhibits robust evidence of a western hotspot offset. To determine the origin of this peculiar hotspot offset, we present phase-resolved high-resolution observations of CoRoT-2b from the CRIRES+ spectrograph on the Very Large
Telescope (VLT) and the IGRINS spectrograph on Gemini South, covering both pre- and post-eclipse phases (0.34–0.63). We detect the signal from the
planet (S/N$>$4) in both pre- and post-eclipse phases separately, and therefore perform separate cross-correlation and
retrieval analyses at the two epochs. The phase-resolved
retrievals show highly consistent abundances and C/Os, but prefer a hotter and more isothermal temperature-pressure profile at post-eclipse phases, consistent with the phase curve observations that indicated a western hotpsot offset. By testing multiple hypotheses invoked to drive a western hotspot offset, we find the most likely explanation to be sub-synchronous planetary rotation. We measure the
planet's rotational broadening to be $2.24\substack{+0.81\\-0.77}$ km s$^{-1}$, whereas the expectation from tidally locked rotation is $4.37\pm0.13$ km s$^{-1}$ (2.6-$\sigma$ discrepant). Other observations, such as high precision phase curves or eclipse mapping, would help to further confirm the western hotspot offset and sub-synchronous rotation.
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All authors Aurora Y. Kesseli, Siddharth Gandhi, Lisa Dang, Alexis Lavail, Alejandro Sanchez-Lopez, Ying Shu, Emily Rauscher, Hayley Beltz, Romain Allart, Stefan Pelletier, Vatsal Panwar
Solar and Stellar Astrophysics
Pre-nova Observations of T CrB: A view from the CHARA Array
Ryan Norris, Narsireddy Anugu, Thomas Gaudin et al. (+38 more)
T CrB is a symbiotic recurrent nova consisting of a red
giant and white
dwarf with recent eruptions in 1866 and 1946 and an anticipated eruption in the mid 2020s. We report CHARA Array observations obtained with MIRC-X (H -band) and MYSTIC (K-band) in 2022-2025. We fit limb darkened disk models constrained with literature limb darkening coefficients to the squared visibilities as only the first visibility lobe is sampled. The average limb darkened diameter of the
star across these epochs is $0.70\pm0.04$ mas in H-band and $0.72\pm0.07$ mas in K-band. Adopting a distance of $914^{+24}_{-22}$ pc, the
stellar radius is $69\pm5~R_{\odot}$ in H-band and $71\pm8~R_{\odot}$ in K-band. This is consistent with filling a Roche lobe volume radius of $71~R_{\odot}$ inferred from published orbital solutions. These measurements provide a pre-eruption angular diameter and support a Roche lobe filling donor.
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All authors Ryan Norris, Narsireddy Anugu, Thomas Gaudin, Magdalena Otulakowska-Hypka, Fabian Kaczmarek, Cameron Caruso, Cody Gustafson, Andrew Kotowski, Rebecca Proni, Nirupam Roy, Fabien Baron, Dipankar P.K Banerjee, Dana K. Baylis-Aguirre, Michelle J. Creech-Eakman, Justin Linford, Alexandre Gallenne, Joanna Mikołajewska, John D. Monnier, Denis Mourard, Ulisse Munari, Nicolas Nardetto, Rachael M. Roettenbacher, Jennifer L Sokoloski, Montana Williams, C. E. Woodward, Stefan Kraus, Jean-Baptiste Le Bouquin, Sorabh Chhabra, Isabelle Codron, Jacob Ennis, Tyler Gardner, Mayra Gutierrez, Noura Ibrahim, Cyprien Lanthermann, Benjamin R. Setterholm, Christopher D. Farrington, Olli Majoinen, Norm Vargas, Douglas R. Gies, Gail H. Schaefer, Theo ten Brummelaar
Astrophysics of Galaxies
Black Hole Stars Across the Universe: Identifying Central Engine Dominated Little Red Dots at $z\sim1.5-9.5$
Andrea Weibel, Rohan P. Naidu, Pascal A. Oesch et al. (+16 more)
Photometric selections of Little Red Dots (LRDs) largely rely on identifying their “V-shaped” spectral energy distribution (SED). Recent work suggests this V-shape stems from a combination of a central engine – also referred to as a Black Hole
Star (BH*) – and a
star-forming host
galaxy. We present a new and highly complementary photometric selection that is based on incorporating BH* templates in the eazy
redshift fitting code. Selecting compact sources where a BH* template contributes $>80$% to the best fitting SED in the rest-optical, we compile a sample of 241 BH*-dominated candidates from $\sim1000\,{\rm arcmin}^2$ of legacy and pure parallel JWST imaging. Our selection does not require a blue UV-component, and it successfully identifies objects that resemble the paradigmatic sources “MoM-BH*-1” and “The Cliff”. We find that BH*-dominated sources exist across a wide range of
redshifts ($z\sim1.7-9.3$) and optical luminosities (log$(L_{5100}/{\rm erg}\,{\rm s}^{-1})\sim42-44.5$), and we measure a median Balmer break strength of $\sim3$, with some breaks reaching values $>10$. We estimate bolometric luminosities in the range log$(L_{\rm bol}/{\rm erg}\,{\rm s}^{-1})\sim42-45$, which, assuming
accretion at the Eddington-limit, would translate to black hole masses of $M_{\rm BH}\sim10^4-10^7{\rm M_\odot}$, spanning the intermediate mass black hole to the
quasar regime. The number density of BH*-dominated candidates peaks at $z\sim5-6$ ($\sim10^{-5}\,{\rm Mpc}^{-3}$) and it declines by an order of magnitude down to $z\sim2$. Tentatively, comparing to V-shaped LRD samples suggests that the fraction of BH*-dominated sources among the broader LRD population does not decrease towards lower
redshift. Crucially, our work demonstrates that BH*-dominated sources are not merely an early-Universe phenomenon but rather persist at least until
cosmic noon.
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All authors Andrea Weibel, Rohan P. Naidu, Pascal A. Oesch, Anna de Graaff, Raphael E. Hviding, Zhaoran Liu, Jorryt Matthee, Christina C. Williams, Gabriel Brammer, Alba Covelo Paz, Jenny E. Greene, Christian Kragh Jespersen, Zhiyuan Ji, Michael V. Maseda, David J. Setton, Wendy Q. Sun, Alberto Torralba, Callum Witten, Mengyuan Xiao
Astrophysics of Galaxies
Dust in the Average Galaxy: Attenuation, Emission, and Opacity from $0<z<7$
Caitlin M. Casey, Hollis B. Akins, Andrew J. Battisti et al. (+43 more)
We present constraints on the
dust emission and attenuation properties of
galaxies across 0<z<7 using JWST imaging from the COSMOS-Web Survey combined with deep FIR/(sub)millimeter data from Spitzer, Herschel, SCUBA-2, NIKA-2 and ALMA. We analyze over 500,000
galaxies to independently constrain attenuation in the rest-frame UV/optical as well as
dust emission from stacked FIR SEDs, enabling a direct comparison between the two. We find UV/optical attenuation systematically underpredicts IR luminosity by a factor of ~3x at 0.5<z<7 and up to an order of magnitude for $M_\star>10^{10.5}M_\odot$. We derive empirical relationships for the effective attenuation,
dust temperature, fraction of
star formation that is unobscured, and
dust-to-
stellar mass ratio as functions of
redshift and
stellar mass. We separate the first order effect of
star/
dust geometry from
dust grain properties by combining constraints on the IR SED, UV SED, and
dust mass surface density. Importantly, we measure over an order of magnitude decrease in $\kappa_{UV}/\kappa_{FIR}$–the ratio of
dust mass absorption coefficients in the UV at 1600Å\ and FIR at 500$\mu$m–from z~0 to z~7. A depressed $\kappa_{UV}/\kappa_{FIR}$ is consistent with a deficit of small
dust grains, possibly attributable to the intense radiation fields of high-$z$
star formation; indeed, we find a
redshift-invariant inverse relationship between $\kappa_{UV}/\kappa_{FIR}$ and $\Sigma_{SFR}$. Most
evolution in the
dust-to-
stellar ratio is at $z<1$, the product of mild downward
evolution in the
dust-to-gas ratio combined with steep
evolution in the gas-to-
stellar ratio. The significant
evolution and dynamic range of $\kappa_{UV}/\kappa_{FIR}$ and prevailing disconnect between the UV/optical and FIR regimes emphasize that direct
dust constraints are irreplaceable for the majority of
star-forming
galaxies at z<7, not just the most extreme
star-formers.
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All authors Caitlin M. Casey, Hollis B. Akins, Andrew J. Battisti, Jed McKinney, Ezequiel Treister, Jorge A. Zavala, Hiddo Algera, Manuel Aravena, Yingjie Cheng, Nicole E. Drakos, Andreas L. Faisst, Maximilien Franco, Seiji Fujimoto, Ghassem Gozaliasl, Ali Hadi, Santosh Harish, Michaela Hirschmann, Olivier Ilbert, Kohei Inayoshi, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Claudia del P. Lagos, Erini Lambrides, Ronaldo Laishram, Daizhong Liu, Arianna S. Long, Georgios E. Magdis, Sinclaire M. Manning, Crystal L. Martin, Felix Martinez III, Richard Massey, Jacqueline E. McCleary, Henry Joy McCracken, Lauro Moscardini, Desika Narayanan, Louise Paquereau, Jason Rhodes, Brant E. Robertson, Rasha M. Samir, Claudia Scarlata, Marko Shuntov, Laura Sommovigo, Aswin P. Vijayan, Wuji Wang, Can Xu, Dhruv Zimmerman
Astrophysics of Galaxies
Dust-Embedded Star Formation: Bridging Magellanic Cloud Studies of Massive Young Stellar Objects to Nearby Spiral Galaxies
M. Jimena Rodríguez, Rémy Indebetouw, Janice C. Lee et al. (+13 more)
We use JWST NIRCam and MIRI imaging at 2, 4, 10, and 21 um to study young, dusty compact sources in four nearby
galaxies at distances of ~ 1-5Mpc (M33, NGC300, NGC7793, and NGC5068). This work bridges well-characterized massive young
stellar objects (MYSOs) in the Magellanic Clouds from the Spitzer SAGE survey to new studies of embedded clusters in more distant
galaxies with JWST. Guided by the SAGE-LMC catalog, we define JWST color-magnitude selection criteria (F1000W versus F1000W-F2100W) and test them using resolution-degradation experiments. We identify 216, 32, 80 and 139 dusty young objects in the four
galaxies, respectively. The selected population spans sources from systems dominated by a single MYSO to compact marginally resolved sources hosting multiple MYSOs. The color selection remains stable across 1-5 Mpc, and the 10um luminosity function retains a slope of alpha~ -2. However, blending and surface-brightness dilution remove fainter sources, leading to incompleteness of up to ~ 50% at 5.2 Mpc and biasing the sample toward brighter objects (F1000W < 19 mag). The sample spans approximate
stellar masses of ~10-2 X 10^5 Mo. Spatial resolution affects the interpretation of mid-infrared emission: clustering increases the fraction of emission attributed to compact sources in active regions, while blending into diffuse emission dominates in quiescent environments. Comparisons with PAH-selected young clusters in the PHANGS
galaxy NGC5068 show that our selection recovers ~ 80% of the PAH-selected sources. We show that the practical limit for studying individual MYSOs with JWST is ~3 Mpc. The resulting catalog provides a foundation for future resolved studies of
star formation rates and early cluster
evolution.
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All authors M. Jimena Rodríguez, Rémy Indebetouw, Janice C. Lee, Bradley C. Whitmore, David A. Thilker, J. Peltonen, Erik Rosolowsky, Thomas G. Williams, Eric W. Koch, Bruce Elmegreen, Ralf S. Klessen, Roberta Paladini, Sumit Sarbadhicary, Daniel A. Dale, Kelsey E. Johnson, Aida Wofford
High Energy Astrophysical Phenomena
Can a slow and strong phase transition in neutron stars relieve major compact-star observation tensions?
Chen Zhang
Recent anomalous compact-
star observations challenge the conventional
neutron-
star interpretation in complementary ways: HESS J1731–347 and XTE J1814–338 favor unusually small radii at low mass, while the secondary component of GW190814 appears too massive for an ordinary
neutron star under GW170817-based maximum-mass inferences. We examine whether
neutron stars with a strong first-order
hadron-
quark phase transition can address these tensions via the extended stable hybrid branches that arise when the phase conversion is slow compared to radial oscillations, while remaining consistent with GW170817 and NICER constraints. Using a piecewise-polytropic (PP)
benchmark, supplemented by an independent speed-of-sound (CS) parametrization comparison, we find two viable scenarios after a general parameter scan over both the hadronic and hybrid branches. Scenario 1 realizes an all-at-once solution: the same equation of state has a pure hadronic branch compatible with both the GW190814-scale mass and HESS J1731–347, while its slow stable hybrid branch reaches XTE J1814–338. Scenario 2 retains the GW190814-scale hadronic branch but reaches XTE J1814–338 and HESS J1731–347 on slow stable hybrid branches in very different transition-strength regimes.
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High Energy Astrophysical Phenomena
The properties of tidal disruption event infrared counterparts produced by dust rings and inference of the observing angle
Rob A. J. Eyles-Ferris
A substantial fraction of
tidal disruption events (TDEs), resulting from a black holes's disruption and
accretion of a
star, exhibit infrared (IR) counterparts thought to arise from spherical shells of
dust reprocessing the TDE emission. Some modelling of TDEs also predicts an angular dependence in their observed properties with more X-ray emission on-axis and more optical emission at higher angles. However, there is growing evidence that X-ray rich TDEs are more likely to exhibit IR counterparts, contradicting the spherical shell model that predicts no significant variation in IR luminosity with angle. Here, I demonstrate that this result naturally follows for
dust arranged in a ring instead of a spherical shell. I present a toy model of this scenario and show that on-axis angles result in a brighter counterpart. I also show that on-axis angles result in a delay in the initial rise and off-axis angles may display a double-peaked structure. Crucially, this model also allows the observing angle of the TDE to be constrained. Finally, I demonstrate that this model reproduces the properties of two IR counterparts, including constraining their observing angles and independently inferring an optical plateau, and briefly comment on its application to quasi-periodic eruption counterparts.
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Earth and Planetary Astrophysics
Transit Timing Variations in TESS: A Catalog from the First Five Years
Emma Nabbie, Chelsea X. Huang, Robert A. Wittenmyer et al. (+1 more)
We present the first catalog of transit timing variations (TTVs) in TESS systems with multiple TESS Objects of Interest (TOIs) using data from Sector 1 to Sector 69, spanning the first five years of mission operations. With an initial sample of 175 multi-TOI systems, we find significant TTVs in 20 systems, 13 of which had not been previously detected. Our results are generally consistent with the findings of previous Kepler TTV catalogs, with compact systems more likely to have detectable TTVs. However, the TTV systems in TESS exhibit a pile-up at the 2:1 orbital period resonance, in contrast to the pile-up near the 3:2 resonance from previous Kepler catalogs. This provides a tentative indicator that there may be different disk migration recipes that Kepler systems favor versus TESS systems. This catalog is a vital first step in determining which orbital resonances migrating
planets tend to occupy at the end of formation, and aims to provide a list of high-impact targets for future in-depth follow up.
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All authors Emma Nabbie, Chelsea X. Huang, Robert A. Wittenmyer, George Zhou
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
CASPER: Interpretable ResNet based Classifier with FastShap Explainer for Gravitational Wave Detection
R. Rai, R. Verma and Somya
Traditional matched filtering has been the standard for Gravitational waves (GW) detection ever since LIGO was established, even though it requires pre-computed waveform templates and provides no accounts of information about which signal drove the decision of classification. Deep-learning alternatives showed competitive sensitivity, but system biasesincluding class overlap, imbalanced class weighting, limited sample variation, and traintest mismatchcontinue to cause problems with generalisation in real detector noise. We introduce CASPER-Classification with Attribution via ShaPlEy in Residual neural networks, an end-to-end pipeline combining residual convolutional neural network (CNN) classifier with a FastSHAP explainer. 260 distinct events from the Gravitational Wave open Science Centre were fetched across SNR range of 7-42 from both H1 and L1 detectors with no synthetic augmentation. The classifier achieves AUC (Area Under Curve) of 91% across the model with a low false alarm rate. Focal Loss and Platt Calibration were used to improve decision boundary and generalisation. FastSHAP attribution maps recover the complete chirp morphology and provides detailed maps for a visual interpretation of the decision. The complete pipeline contains fewer parameters than standard deep learning models and requires no hardware except a standard CPU making our model an effective lightweight pipeline for Gravitational Wave Detection under real life conditions.
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Astrophysics of Galaxies
Testing masking effectiveness using multi-line image cubes based on COSMOS2020 for [CII] line intensity mapping at $z_{[CII]} > 3.5$
J. Clarke, C. Karoumpis, A. Dev et al. (+5 more)
We created line intensity mapping intensity cubes for CO and [CII] emission lines using the COSMOS2020
galaxy catalogue, forming predictions based on empirical data, for observations from
Prime-Cam mounted on the Fred Young Submm
Telescope. We also included simulated noise including white and correlated components, and tested masking techniques to recover [CII] signal at $3.5<z<8.2$. We applied line luminosity models to the COSMOS2020
galaxy catalogue, spanning 1.44deg$^2$, to estimate the [CII] and CO J=1-0 emission, with other CO transitions derived using Spectral Line Energy Distribution templates. From these we made cubes for four 40 GHz bands in the EoR-Spec frequency range (205-420GHz), as well as a potential future upgrade to EoR-Spec including bands at 150 and 90GHz. Given the incompleteness of the empirical catalogue, these predictions are conservative lower limits, which we subsequently extrapolated from. We applied masks to recover the [CII] power spectra, using bright
galaxies of COSMOS2020 as a foreground catalogue to target CO at low z (targeted masking), and matching bright voxels across frequency bands to eliminate those associated with CO emission (blind masking). Our CO intensity cube predictions are consistent with ALMA, VLA and NOEMA observations, indicating that this method gives realistic CO estimates for E-COSMOS. In ideal conditions, masking can recover [CII] above 300GHz, with targeted masking requiring a complete foreground catalogue of bright CO sources to prevent them from contributing to contaminant emission, and blind masking needing additional lower frequency ranges to be effective. However, noise will hinder [CII] recovery above 300 GHz until near the end of the currently planned 2000 hour observing period, as $S/N<5$ without extra observing time. Whilst CO can be recovered below 300GHz, [CII] will be unavailable without cross correlation techniques.
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All authors J. Clarke, C. Karoumpis, A. Dev, D. Riechers, T. Oak, Y. Okada, K. Narita, F. Bertoldi
Solar and Stellar Astrophysics
Wildly Oscillating Stars – Unexplained dense ridge-like frequency agglomerations in A and F type pulsators
V. Antoci, J. Labadie-Bartz, M. Swiech et al. (+14 more)
We investigate the origin of the dense, ridge-like frequency clusters observed in a subset of A and F type pulsating
stars, which we refer to as `wildly oscillating'
stars (WOS). These agglomerated frequency regions occupy a confined part of the frequency spectrum, typically below the fundamental radial mode, and are not explained by pulsation theory. We analyse Kepler and TESS data, construct echelle diagrams, and perform searches for combination frequencies. We determine the fundamental radial mode in order to place the agglomerated regions in a seismic context. Rotational modulation is examined through phase-folded light curves and amplitude-phase analysis, and binarity and
geometric modulation scenarios are tested. The WOS phenomenon is confined to a narrow region near the overlap of the delta Sct and gamma Dor instability strips. The observed ridge morphology and mode density cannot be reproduced by simple asymptotic g-mode behaviour, low-order p modes, binarity, or typical rotational splitting. In at least two
stars, a significant fraction of peaks in the agglomerated region can be explained as nonlinear combination frequencies involving high-order g modes. However, these combinations require parent modes located within the agglomerated frequency band itself, indicating that intrinsic pulsation modes must be present there. Non-adiabatic stability calculations reproduce the classical instability domains but do not predict unstable modes with the observed density or organised ridge structure in the agglomerated region. The WOS appear to represent a pulsational regime not captured by current models of mode excitation or rotational modulation. The agglomerated frequency phenomenon requires a mechanism that selects or excites a confined intermediate-frequency band and produces organised ridge structures within a narrow region of
stellar parameter space (abridged for arXiv).
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All authors V. Antoci, J. Labadie-Bartz, M. Swiech, O. Deurfeldt-Pedros, S.J. Murphy, D.W. Kurtz, T.R. Bedding, G. Handler, J. Fuller, R.-M. Ouazzani, H. Kjeldsen, L. Fellay, M. Gade Pedersen, E. Niemczura, D.M. Bowman, M. Deal, P. Mani
Astrophysics of Galaxies
Exploring the Relationship Between Bars, Star Formation Activity, and Host Galaxy Properties from $\mathbf{z \sim 0}$ to $\mathbf{z \sim 2}$
Eden Wise, Shardha Jogee, Yuchen Guo et al. (+20 more)
We present the most comprehensive study to date of the relationship between bars,
star formation, and
galaxy properties from $z \sim$ 0 to $z \sim$ 2. We use a mass-complete sample of 1,171
galaxies from the JWST CEERS survey with $M_\star > 10^{10} M_\odot$ and repeat the analysis using COSMOS-Web data. Our results are: 1) At high
redshift ($z \sim$ $1-2$) barred
galaxies tend to have high sSFRs and low Sérsic indices ($n \leq 2$), while at low
redshifts barred
galaxies emerge with both low sSFR and higher $n$, suggestive of quiescent
galaxies with bulges. 2) The fractional contribution of barred quiescent
galaxies to the bar fraction rises steeply from $z \sim$ 2 to $z \sim$ 0, while that of barred actively
star-forming
galaxies falls. 3) The fraction of quiescent
galaxies that are barred rises steeply over the last 10 Gyr. 4) Our empirical results show good agreement with the TNG50-1 simulations for bars with $a_{\mathrm{bar}}$ $>$ 1.5 kpc. Our results allow for the possibility that bar-driven secular
evolution may lead to quiescence and/or that bars are more likely to persist and grow in gas-poor, quiescent
galaxies. The steep rise in the quiescent bar fraction over 10 Gyr may represent an evolutionary sequence whereby gas-rich disks at high
redshift first develop short, dynamically young bars and over time, repeated bar-driven gas inflows lead to central starbursts and declining gas fractions that strengthen the bar as the
galaxy transitions toward quiescence.
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All authors Eden Wise, Shardha Jogee, Yuchen Guo, Steven L. Finkelstein, Micaela B. Bagley, Marc Huertas-Company, Kartheik G. Iyer, Elizabeth J. McGrath, Natalia C. Villanueva, Tommaso Zana, Anton M. Koekemoer, Eric F. Bell, Jean-Baptiste Billand, Yingjie Cheng, Alexander de la Vega, Elena D'Onghia, Tobias Géron, Mauro Giavalisco, Benne W. Holwerda, Ray A. Lucas, Fabio Pacucci, Maxime Tarrasse, L. Y. Aaron Yung
Cosmology and Nongalactic Astrophysics
Tracing Ultra Light Axions in Post-reionization, Lyman-$\alpha$ and CMB Missions
Debarun Paul, Sourav Pal, Amit Dutta Banik et al. (+1 more)
Ultra-light
axions (ULAs) are dark matter candidates proposed to resolve the small scale anomalies of the standard cosmological model. Due to their inherent
quantum pressure, ULAs result in a distinct, scale-dependent suppression on the matter power spectrum, which can leave imprints on the upcoming observations. We explore such possibilities by
forecasting on the post-reionization large scale structure (LSS) surveys and next-generation
cosmic microwave background (CMB) missions. By utilizing the cross-correlation between 21-cm intensity mapping (SKA1-MID and PUMA) and the Lyman-$\alpha$ forest (DESI-like), we explore possible signatures of ULAs in post-reionization surveys while mitigating instrument-specific systematics. The Fisher
matrix analysis projects uncertainties on the fractional ULA abundance across a wide ULA mass range of $10^{-30}\text{ eV} \le m_a \le 10^{-20}\text{ eV}$, revealing an optimal detection sensitivity at intermediate masses around $m_a \sim 10^{-25}\text{ eV}$. Furthermore, while next-generation CMB mission alone can yield small projected errors on the ULA fraction compared to future LSS missions, a joint analysis of the DESI-like and PUMA cross-spectrum alongside CMB-S4-like missions estimates an error on the ULA fraction to be $\mathcal{O}(10^{-4})$ for $m_a\lesssim 10^{-28}$ eV, highlighting a significant improvement over standalone LSS and CMB missions.
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All authors Debarun Paul, Sourav Pal, Amit Dutta Banik, Supratik Pal
High Energy Astrophysical Phenomena
Discovery of a Supernova Following the Einstein Probe Transient EP250302a at z = 1.131
Brendan O'Connor, Malte Busmann, James Freeburn et al. (+7 more)
We present a multi-wavelength analysis of the Einstein Probe (EP) fast X-ray transient (FXT) EP250302a located at
redshift $z=1.131$. Despite its luminous
prompt X-ray emission, the event was not detected in gamma-rays. Multi-wavelength follow-up identified a bright optical and X-ray source that displayed rapid chromatic flaring before returning to the standard decay of a gamma-ray burst afterglow. We interpret the chromatic
flare as either due to a refreshed shock caused by a discrete shell collision or as reverse shock emission. Using the early optical data, we place constraints on the Lorentz factor of the
outflow, requiring an ultrarelativistic jet with $\Gamma_0>25$. We additionally obtained deep late-time imaging with the Gemini North
Telescope that reveals the presence of an optical excess at $20-30$ d post-explosion. We interpret this as
supernova (SN) emission and find good agreement with the canonical broad-lined Ic SN 1998bw with a flux-scaling factor of $k_\textrm{98bw}>0.3$. This adds to the growing evidence that the majority of EP FXTs are associated with the deaths of massive
stars.
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All authors Brendan O'Connor, Malte Busmann, James Freeburn, Lei Hu, Noel Klingler, Daniel Gruen, Igor Andreoni, Julius Gassert, Xander J. Hall, Antonella Palmese
High Energy Astrophysical Phenomena
QPO-like Signatures and Hydrodynamical Variability in Accretion around a JNW-type Compact Spacetime in Freund-Nambu Scalar-Tensor Gravity
Orhan Donmez, M. Yousaf and G. Mustafa
Scalar tensor theories of
gravity provide a broad as well as physically rich extension of general theory of relativity by allowing the gravitational interaction to be mediated not only by the spacetime metric but also by scalar degrees of freedom. In this manuscript, we present a new exact solution in the Freund-Nambu scalar-tensor (FNST)
gravity scenario, representing a nontrivial scalar-tensor generalization of the Janis-Newman-Winicour naked-singularity geometry, characterized by an additional coupling parameter q in the scalar sector. We also numerically solve the general relativistic hydrodynamic equations in order to investigate the shock-cone mechanism formed by Bondi-Hoyle-Lyttleton
accretion around this compact spacetime on the equatorial plane. We show that stronger scalar-tensor deviations modify the shock-cone morphology, significantly increase the amount of matter accumulated near the central compact object, and enhance the oscillatory behavior of the shock cone. The Lorentzian-like peaks obtained from the numerically computed power spectral density are interpreted as hydrodynamically generated QPO-like modes. These modes are driven by shock cone oscillations and by the compression and rarefaction of the
plasma trapped inside the cone. Finally, for a compact object with mass parameter M = 10M_sun, the numerically extracted frequencies are found mainly in the range from a few Hz up to approximately 100 Hz. These frequencies overlap with the QPO ranges reported in
stellar-mass black-hole-candidate systems. In particular, the frequencies obtained for the FNST2-FNST4 models fall within the range of timing features reported for the source GRS 1915+105. These results suggest that the exterior hydrodynamical variability of FNST compact spacetimes may provide phenomenological diagnostics of scalar-field-induced deviations from the Schwarzschild reference case.
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High Energy Astrophysical Phenomena
Optical polarization variability and its relation to gamma-ray activity in blazars
Styliana Grigoriou, Anastasia Glykopoulou and Ioannis Liodakis
Optical polarization can be an important probe of particle acceleration and high-energy emission processes in relativistic jets from supermassive black holes. We combined publicly available observations from three past blazar monitoring programs to produce densely sampled light curves for 15 blazars in order to explore the relation of gamma-ray activity to the polarization variability as well as discover new rotations of the polarization angle. We find that the polarization degree does not correlate with the gamma-ray flux for individual sources nor different subsamples of blazars, potentially indicating multiple emission mechanisms. In the combined
dataset, we identified a total of 64 rotations in 12 sources, 39 of which are newly identified rotations. We confirm the trend found in previous works for the whole sample: lower polarization degrees during periods of polarization angle rotations. However, looking at the individual sources, we identified cases where the rotation and non-rotation polarization degree distributions are indistinguishable, providing further evidence for the multiple emission mechanism hypothesis.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Freeze-in and ultra-relativistic freeze-out during general reheating scenarios
Kuldeep Deka
The dark-matter relic abundance can depend sensitively on the thermal history before radiation domination. We derive a general analytic framework for dark-matter production from the Standard Model bath during a non-instantaneous reheating era, unifying freeze-in, ultra-relativistic freeze-out and the approach to ordinary non-relativistic freeze-out. The reheating background is described by an effective equation-of-state parameter $\omega$ and a cooling index $\alpha$, while the dark-matter interaction rate is parametrised by an effective scale $\Lambda$ and a leading temperature power $n$. We show that the production history is organised by two critical temperature exponents: one controls whether a thermalised relativistic species decouples during reheating or after radiation domination begins, and the other controls whether post-decoupling production is infrared dominated, ultraviolet dominated or logarithmic. We derive analytic relic yields in the main regimes, including both the
entropy-diluted freeze-out contribution and the post-freeze-out production term. These results explain the scaling of relic-density contours and are checked against numerical Boltzmann solutions. For matter-like reheating our framework reproduces the known IR/UV ultra-relativistic freeze-out structure, while more general reheating histories can shift the same microscopic interaction between freeze-in, ultra-relativistic freeze-out and ordinary freeze-out regimes.
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Astrophysics of Galaxies
Chemical hints of Population III stars from silicon abundances in massive galaxies
E. Eftekhari, A. Ferré-Mateu, A. Vazdekis et al. (+4 more)
The formation of massive
galaxies remains a fundamental question in astrophysics, with recent JWST observations suggesting that intense
star formation occurred earlier than previously expected. We used the prototypical massive relic
galaxy NGC 1277 as a fossil record to probe the chemical signatures of early
star formation. With a
stellar mass of $1.2 \pm 0.4 \times 10^{11}M_\odot$ and a compact structure (half-light radius of 1.2 kpc), NGC 1277 is representative of massive relic
galaxies-systems that formed rapidly at high
redshifts ("red nuggets" at $z>2$) and have since undergone largely passive
evolution, preserving the imprint of their earliest
stellar populations. Using deep near-infrared spectroscopy, we identified unusually strong silicon (Si) absorption features in this
galaxy. We measure $[\mathrm{Si}/\mathrm{Fe}]=1.05^{+0.45}_{-0.27}$ and $[\mathrm{Mg}/\mathrm{Fe}]=0.36^{+0.27}_{-0.24}$, corresponding to a significantly enhanced silicon-to-magnesium ratio ($[\mathrm{Si}/\mathrm{Mg}]=0.67^{+0.45}_{-0.27}$) which cannot be reproduced by current
stellar population models or typical core-collapse
supernova yields. This enhancement suggests a contribution from very massive, metal-poor progenitors during the earliest phases of
star formation. Such conditions are consistent with nucleosynthetic yields from pair-instability
supernovae or other enrichment channels associated with extremely massive
stars, whose chemical signatures are expected to remain less diluted in systems like NGC 1277 due to their rapid formation timescales and minimal late-time
accretion. This result provides rare chemical evidence of early massive-
star enrichment preserved in a local relic
galaxy and opens a new observational window into the chemical
evolution of the Universe.
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All authors E. Eftekhari, A. Ferré-Mateu, A. Vazdekis, F. La Barbera, M. A. Beasley, J. P. V. Benedetti, M. Kriek
Astrophysics of Galaxies
Hector Galaxy Survey: Optical IFU and Chandra Reveal a Low-Luminosity AGN Behind Extended LINER Emission
Kyuseok Oh, Gabriella Quattropani, Pratyush Kumar Das et al. (+25 more)
We present evidence that the Hector
Galaxy Survey
galaxy C901005481609968 ($z_{\rm cl}=0.0553$), which exhibits spatially extended LINER-like emission in optical integral-field spectroscopy (IFS), hosts a low-luminosity active
galactic nucleus (LLAGN) that contributes substantially to its ionization budget. Although the
galaxy is not selected as an AGN by mid-infrared AGN color criteria, archival Chandra data reveal a compact
nuclear X-ray source with $\log L_{\rm X}\approx41.46$ erg/s, supporting the presence of an LLAGN. Spatially resolved emission-line diagnostics show LINER-like line ratios across most spaxels with $\mathrm{S/N} \geq 3$, while spatially resolved $\tau$ maps ($\tau \equiv Q_{\rm pAGB}/Q_{\rm req}$) indicate a widespread
photon deficit ($\log\tau<0$ over most of the mapped region), even under the most optimistic pAGB normalizations, the
nuclear region remains at $\tau < 1$. Line-ratio–kinematic tests find no evidence for shock-dominated excitation as the primary driver of the extended emission, although a localized or sub-dominant shock contribution cannot be ruled out with the present data. We use this
galaxy as a pilot case because the combination of Hector IFS and an independent
nuclear X-ray constraint provides a stringent validation of the spatially resolved
photon-budget framework. Our results indicate that evolved
stellar populations alone cannot account for the observed emission, that an additional
nuclear ionizing source is required at least in the inner region, and that a weak LLAGN likely contributes to the ionizing budget, particularly in the inner region. Our results demonstrate that extended LINER-like emission can conceal a substantial LLAGN contribution even when traditional optical and infrared AGN indicators are weak, and that spatially resolved
photon-budget tests combined with X-ray constraints can effectively reveal such hidden activity.
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All authors Kyuseok Oh, Gabriella Quattropani, Pratyush Kumar Das, Minje Beom, Joon Hyeop Lee, Oğuzhan Çak{\i}r, Andrei Ristea, Hyunjin Jeong, Jiwon Chung, Michael J. Koss, Scott M. Croom, Mina Pak, Matt S. Owers, Sarah M. Sweet, Jong Chul Lee, Julia J. Bryant, Sree Oh, Jesse van de Sande, Peixin Zhu, Stefania Barsanti, Madusha L. P. Gunawardhana, Sujeeporn Tuntipong, Robert Content, Jon Lawrence, Ayoan Salim Sadman, Will Saunders, Barnaby Norris, Gurashish Singh Bhatia