Solar and Stellar Astrophysics
On the origin of carbon- and oxygen-rich hot subdwarfs: an sdB merger scenario
Bo Tang, Xinyu Ji, Songyu Hu et al. (+2 more)
Carbon- and oxygen-rich hot subdwarfs (CO-sdO
stars) represent an extremely rare subclass of helium-rich hot subdwarfs. Recent observations of PG 1654+322, PG 1528+025, and UCAC4 108 reveal unusually large surface mass fractions of carbon and oxygen, which are difficult to explain within existing formation scenarios. We explore whether mergers involving sdB
stars can provide a viable formation channel for these objects. Using the stellar
evolution code MESA, we model the post-merger
evolution of two merger channels: mergers between two sdB
stars and mergers between a helium white dwarf and an sdB
star. Carbon and oxygen synthesized during core helium burning in sdB
stars may provide a natural chemical reservoir if efficient mixing occurs during the merger. The resulting evolutionary tracks are broadly consistent with the effective temperatures, surface gravities, and luminosities observed for the three
stars, suggesting remnant masses of about 0.8-1.0 M_sun. Our calculations suggest that mergers involving sdB
stars may represent a viable formation pathway for CO-rich hot subdwarfs.
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All authors Bo Tang, Xinyu Ji, Songyu Hu, Zhongyang Liu, Xianfei Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The alternative scalar field dark sector of the Universe: Cosmological inflation, quintessence and ekpyrotic model in the framework of scalar-tensor cosmology
Marcin Postolak
This dissertation investigates scalar field descriptions of the dark sector (of the Universe), with emphasis on scalar-tensor cosmology, inflationary effective field theory, quintessence, and ekpyrotic/cyclic alternatives to inflation. The thesis first reviews scalar-tensor theories of
gravity, starting from Brans-Dicke theory and extending to general non-minimally coupled scalar fields. Particular
attention is paid to the interpretation of the scalar field, the relation between the Jordan and Einstein conformal frames, and the role of conformal transformations in cosmology. This provides the theoretical basis for treating scalar fields either as modified matter or as additional gravitational degrees of freedom. The second part discusses cosmological inflation from the viewpoint of effective field theory. The spontaneous breaking of time translations, the Goldstone description of adiabatic perturbations, higher-dimensional operators, radiative corrections and Planck-suppressed terms are analyzed in the context of ultraviolet sensitivity and the eta problem. The third part is devoted to quintessence as the simplest dynamical dark energy model. 'Tracking', 'scaling', 'thawing' and 'freezing' behaviors are discussed, together with observational diagnostics such as the statefinder parameters, the $(\omega_{\phi},\omega'_{\phi})$ plane and the $Om(z)$ diagnostic. The DESI DR2 results are used as motivation for considering time-dependent effective dark energy beyond a strict cosmological constant. The final part studies ekpyrotic and cyclic cosmologies. The ekpyrotic phase is analyzed as a smoothing mechanism based on an ultra-stiff scalar field equation of state. Perturbations, non-Gaussianity, tensor modes, bounce conditions,
entropy production, geodesic incompleteness and phase-resolved field-space distance bounds are discussed.
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Earth and Planetary Astrophysics
Homogeneous Nucleation of Water Vapor Evidenced by Elongated Clouds on Mars
J. Hernandez-Bernal, A. Maattanen, A. Spiga et al. (+1 more)
It is widely accepted that water vapor forms clouds by heterogeneous nucleation (condensation on pre-existing dry
nuclei). Homogeneous nucleation (directly from water vapor, without a pre-existing
nuclei) is theoretically possible, but it requires high levels of supersaturation and so it is not considered a viable cloud formation process under real atmospheric conditions. Here, we show that introducing homogeneous nucleation in a meteorological model of Mars allows to successfully reproduce the unique characteristics of the Arsia Mons Elongated Cloud, a remarkable water ice cloud that occurs recurrently on Mars and which had remained impossible to model under conventional cloud microphysics. This finding demonstrates that homogeneous nucleation happens on Mars, provides the first evidence of homogeneous nucleation of water vapor in a planetary atmosphere, and challenges current assumptions about cloud formation processes, which is also relevant for certain clouds on Earth and potentially on other
planets.
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All authors J. Hernandez-Bernal, A. Maattanen, A. Spiga, F. Forget
Cosmology and Nongalactic Astrophysics
A halo-based intrinsic-alignment model for simulation-based inference
M. Gatti
Simulation-based inference and other field-level weak-
lensing analyses require intrinsic-
alignment (IA) models generating realistic intrinsic-ellipticity fields across two-point and non-Gaussian observables. We develop a
halo-based IA prescription with separate central and satellite components and test it against intrinsic
galaxy shapes in FLAMINGO. We jointly fit two-point and higher-order statistics involving the IA,
lensing, and density fields, including correlations between the intrinsic shapes of distinct
galaxies, and compare against field-level nonlinear-
alignment and density-weighted NLA prescriptions. We first evaluate the models at the positions of the original FLAMINGO
galaxies, fixing the
galaxy–matter connection and isolating the IA response. NLA and $\delta$NLA leave substantial discrepancies on nonlinear scales and across higher-order observables, whereas the
halo model provides a simultaneous description of all statistics. We then remove the FLAMINGO
galaxy catalogue and regenerate the source population from the
halo field using a low-dimensional
halo occupation model; the agreement is preserved even when the detailed occupation is only approximately reproduced. Much of this performance can be retained with a compact four-parameter portable model, and the same architecture transfers successfully to an independent
gravity-only N-body realization with different
halo definitions and shape measurements. These results show that nonlinear field-level IA modelling can be substantially improved over simple NLA-like prescriptions without introducing a large nuisance-parameter space. The
halo model therefore provides a promising route for incorporating intrinsic
alignments into simulation-based weak-
lensing inference, although further validation across
halo masses, hydrodynamical simulations, and realistic survey selections will be needed before application to data.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Gravitational-Wave Inference For Noise PSD Jumps Across Data Gaps
Jian-Ming Yan and Zong-Kuan Guo
Long-duration gravitational-wave (GW) inference inevitably encounters data gaps, which are often accompanied by abrupt, non-stationary changes in the detector noise power spectral density (PSD). Conventional practice typically analyzes the pre-gap and post-gap data separately, causing avoidable information loss and potentially degrading parameter inference. We build on
Bayesian gap augmentation in the Wilson–Daubechies–Meyer (WDM) time–frequency domain and focus on a practically important failure mode: short gaps with large PSD amplitude jumps. In this regime, the local diagonal (Whittle-like) approximation that underpins the WDM likelihood can no longer be relied upon in the time direction near the gap edges, which may lead to biased and/or less robust inference unless the local diagonal validity is restored without resorting to full segmentation. We propose a two-stage, validity-driven remedy. First, frequency-domain prior-predictive prewhitening (PW) incorporates endpoint-informed noise information to mitigate the dominant mismatch responsible for poor diagonal behavior, enabling a more favorable WDM representation while retaining computational tractability. Second, when a time-direction smoothness criterion still fails, we apply adaptive gap expanding (AGE), selectively enlarging only the minimal neighborhood around the gap boundaries needed to restore local diagonal validity. Toy-model simulations with chimeric PSD transitions show that WDM+PW+AGE yields substantially tighter and more accurate posteriors than single-sided pre-gap/post-gap analyses, while maintaining computational efficiency suitable for next-generation missions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The Irreversible Depletion of Dark Matter Spikes by Extreme-Mass-Ratio Inspirals
Charlie Sharpe, Yonadav Barry Ginat, Thomas F. M. Spieksma et al. (+2 more)
Dense dark matter spikes around massive black holes (MBHs) have been widely predicted to produce gravitational-wave dephasing in extreme-mass-ratio inspirals (EMRIs) that are potentially observable by LISA. We show that EMRIs, the very objects used to probe these spikes, also destroy them. Combining Fokker-Planck models of nuclear
star clusters with post-Newtonian three-body simulations of EMRI-dark matter encounters, we demonstrate that repeated gravitational slingshots irreversibly eject dark matter particles from the cluster's loss cone over gigayear time-scales. For MBHs at $z = 3$ with masses $\lesssim 10^5 \,M_\odot$, even conservative EMRI rates of $\mathcal{O}(1-10) \, \mathrm{Gyr}^{-1}$ suffice to deplete the spike density by orders of magnitude; for more realistic rates of $\mathcal{O}(100-300) \, \mathrm{Gyr}^{-1}$, the mass range extends to $\lesssim 10^6 \,M_\odot$. As a result, the gravitational-wave dephasing expected from such systems is greatly reduced, narrowing the prospects of detecting DM through this channel. Only heavy, high-
redshift systems with sufficiently low EMRI rates – for example, a $\sim 10^6 \,M_\odot$ MBH at $z \gtrsim 5$ with $\lesssim 100$ EMRIs per Gyr – can induce dephasing that exceeds one radian.
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All authors Charlie Sharpe, Yonadav Barry Ginat, Thomas F. M. Spieksma, Alexander Heger, Bence Kocsis
High Energy Astrophysical Phenomena
Multi-wavelength polarization degree dependence of Mrk 421 for different particle energy distributions
Hritwik Bora, Ranjeev Misra and Rupjyoti Gogoi
We report on the constraints obtained from the multi-wavelength polarization degree and energy spectra measurements for the High Synchrotron Peaked Blazar (HBL) source Mrk 421 using different forms of the electron energy distribution. We find that the optical and X-ray data are consistent with the electron energy distribution being a broken power-law (BPL) or other distributions, with all electrons experiencing the same
magnetic field configuration. This is in contrast to other HBL sources like the Mrk 501, where, for the BPL distribution, the X-ray producing higher energy electrons need to exist in a more ordered
magnetic field environment than the optical producing lower energy ones. This is because the break energy of the spectrum produced by the BPL distribution for Mrk 421 lies below the IXPE energy band. We discuss the implications of the findings.
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Astrophysics of Galaxies
MEGATRON: Dwarf Galaxy Quenching in the Epoch of Reionization
David Attard, Ilian T. Iliev, Martin P. Rey et al. (+3 more)
Low-mass
galaxies during the Epoch of Reionization are expected to form
stars in short bursts separated by periods of inactivity, but what regulates this cycle, and how sensitive it is to the modelling of stellar feedback, remains unclear. We use the MEGATRON high-
redshift zoom simulation suite, in which four
star-formation and stellar-feedback prescriptions are evolved from identical initial conditions, to study the regulation of stellar mass growth in
galaxies with $M_{*} \sim 10^{4} - 10^{8} M_{\odot}$ at $z = 8.5$. We classify
galaxies as
Star-Forming, Mini-Quenched (no significant
star formation over the last 10 Myr), or Quenched (no significant
star formation over the last 100 Myr). The feedback prescription controls both how often
galaxies are quiescent and how this depends on mass. Models with stronger or more clustered feedback yield larger quiescent fractions compared to the fiducial and Varying IMF models. Duty cycles at fixed mass also differ by factors of several between models. The cold gas profiles of Quenched
galaxies are consistent with two physically distinct modes of quenching: mechanical gas evacuation, producing compact, cold gas-poor systems, and thermodynamic suppression, retaining a cold but
star-formation-inactive reservoir. At these masses, quiescent
galaxies fall below un-lensed JWST/NIRCam detection limits, whereas
star-forming
galaxies of the same mass do not, and consequently flux-limited samples will be biased towards active phases. Measuring the quiescent fraction as a function of stellar mass in
lensing fields would provide a direct test of stellar-feedback models at
Cosmic Dawn.
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All authors David Attard, Ilian T. Iliev, Martin P. Rey, Harley Katz, Corentin Cadiou, Nicholas Choustikov
Solar and Stellar Astrophysics
On the frequency-dependent time lags of the intermediate polar V709 Cas
Zackery A. Irving, Noel Castro Segura, Diego Altamirano et al. (+9 more)
Cataclysmic variables (CVs) are binary systems in which a white dwarf (WD) primary accretes material from a late-type secondary, typically via a disc. To date, only six CVs, all of which are non-
magnetic, have been found to exhibit lags (delayed variability in one band with respect to another). In all six cases, these lags are “red” (i.e., red lags blue) with a time lag of order seconds. While there is no generally accepted mechanism for producing red lags in CVs, current theories suggest reprocessing in the disc, either on the thermal or recombination time-scales, or inside-out shocks propagating through the disc. Using $g$-, $r$-, and $i$-band data from the OPtical TIming CAMera (OPTICAM), we report the discovery of frequency-dependent red lags from V709 Cas: a
magnetic CV of the intermediate polar (IP) subclass. These red lags reach a maximum of $\sim$4–6 s on time-scales of 7.4–13.0 min, similar to previously-reported lags in non-
magnetic CVs. The detection of lags in an IP is significant as the WD's
magnetic field truncates the
accretion disc, limiting disc-based lag mechanisms to large radii; as a result, characteristic
accretion disc time-scales cannot explain the observed lags. However, recombination can occur on second time-scales, even in systems with truncated discs. For example, we show that recombination in the disc's bright spot, where overflowing material from the secondary meets the outer-edge of the disc, plausibly explains V709 Cas's optical spectrum, the prominence of optical
spin-orbit beat pulsations, and the red lags found in this work.
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All authors Zackery A. Irving, Noel Castro Segura, Diego Altamirano, Martina Veresvarska, Mariano Mendez, Federico Garcia, Domitilla de Martino, Simone Scaringi, Federico Vincentelli, Angel Castro, Federico Soto, Raul Michel
Earth and Planetary Astrophysics
Chondrule size averaging in two and three dimensions
Emmanuel Jacquet
Chondrule sizes are an important discriminant of chondrite groups and chondrule formation theories. Yet most studies report 2D sizes without attempting the somewhat tedious corrections to 3D proposed in the past literature. I show here that 3D size averages can be simply calculated directly from 2D averages of appropriate powers of sizes (and vice-versa), without having to reconstruct 3D distributions, although explicit formulas to that end are also provided. This illuminates the comparison between 3D and 2D arithmetic size averages, which are confirmed to be little different for the published
datasets. Yet I suggest another type of average, the "sphere-weighted average" (i.e. weighted by the chondrule equal-volume sphere area), a measure of the surface/volume ratio of the chondrule population, which is more robust against omission of small chondrules. While larger than the arithmetic averages, it is best in line with previous literature estimates based on less exhaustive surveys of chondrules.
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Earth and Planetary Astrophysics
Astrometric Evidence for Outer Giant Planets in Known Exoplanet Systems
Clarissa R. Do Ó, William Thompson, Dori Blakely et al. (+19 more)
Outer giant
planets can influence the formation and dynamical
evolution of their planetary systems. However, their long orbital periods make them difficult to detect using transit and radial velocity (RV) techniques. Measurements from Hipparcos, Gaia DR2 and DR3 (G23H) can detect the stellar reflex motion induced by distant companions before the release of Gaia DR4 epoch astrometry. Using the G23H catalogue, we identify 29 outer companion candidates ($a_{median}$ $>$ 8.4 AU) in known transiting and RV systems. Starting from 170
exoplanet hosts with $P(\mathrm{companion})>0.75$ and posterior support for $0.3$–$13\,M_{\rm J}$ companions, we retain 29 systems where each selected component has a median semi-major axis beyond the outermost known
planet with every known
planet outside its 95% highest posterior density region in mass and semi-major axis. We incorporate published RV and imaging data from the literature to further constrain the outer candidate's mass and semi-major axis. In eight systems present in the sample, an RV variation or trend has already been reported in the literature. The reported candidates could potentially explain these RV variations, but joint astrometric and RV fits are needed to establish whether the same companions produce both signals. These results provide a set of high priority targets for further RV monitoring and joint orbit analysis with Gaia DR4. If these companions are confirmed, their orbital constraints will provide a starting point for studies of their influence on the dynamical
evolution of the known inner
planets.
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All authors Clarissa R. Do Ó, William Thompson, Dori Blakely, Aniket Sanghi, Jerry W. Xuan, Dimitri Mawet, Jessica Speedie, Sarah Blunt, Simon Blouin, Jingwen Zhang, Doug Johnstone, Jean-Baptiste Ruffio, Eric Nielsen, Brendan P. Bowler, Alexandre Bouchard-Côté, Kyle Franson, William Roberson, Ryan Cloutier, Andre Fogal, Kaitlyn Hessel, Christian Marois, Alexandra Rochon
Instrumentation and Methods for Astrophysics
First laboratory demonstration of iEFC for high-contrast imaging at small angular separation on ELT scales
Charles Sallard, Patrice Martinez, Alain Spang et al. (+7 more)
Implicit electric field conjugation (iEFC) is an efficient, model-free wavefront control technique for dark hole creation. Its model-free nature, relying on calibration with real data rather than a synthetic model of the instrument, makes it uniquely versatile and highly attractive. It has been successfully demonstrated in a variety of environments, both in the laboratory and on-sky, using different experimental platforms and coronagraphs. A common characteristic of these demonstrations is that the resulting DHs exhibit moderate to large inner working angles and wide fields of view, often extending over several tens of $\lambda/D$. Here, we report the first demonstration of iEFC at small angular separations, achieving a DH spanning 1 to 4 $\lambda/D$ on a segmented pupil in H-band under laboratory conditions. This combination of aggressive IWA and reduced FoV highlights the uniqueness of the SPEED facility (segmented pupil experiment for
exoplanet detection). SPEED is a high-contrast imaging testbed designed for extremely large
telescopes (ELTs), developed in the context of the ELT/PCS instrument (planetary camera and spectrograph), currently in pre-phase A. Its small-IWA coronagraph, an APCMC (apodized pupil complex mask coronagraph), and its multi- and out-of-pupil-plane deformable mirror (DM) architecture are specifically optimized for DHs at very small IWAs, down to the diffraction limit. Our results demonstrate (i) that widely separated out-of-pupil DMs are well suited to generating DHs with IWAs down to 1 $\lambda/D$, and (ii) the effectiveness of iEFC, when combined with the SPEED wavefront control architecture, for high-contrast imaging with segmented
telescopes. Ultimately, these results pave the way toward meeting the stringent high-contrast requirements of ELT-class instruments, opening new opportunities for
exoplanet detection at unprecedented angular resolutions.
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All authors Charles Sallard, Patrice Martinez, Alain Spang, Kian Milani, Lyu Abe, Mathilde Beaulieu, Carole Gouvret, Aurélie Marcotto, Julien Dejonghe, Olivier Preis
High Energy Astrophysical Phenomena
Re-interpreting the GRS 1915+105 observations within the variable TADAF scenario
Chun Xu
The Galactic microquasar GRS 1915+105 is one of the most interesting X-ray binary systems, exhibiting an exceptionally diverse range of observational phenomena. It displays the most complicated and variable X-ray light curves and carries superluminal
radio jets. Its X-ray and
radio fluxes change on very different timescales, from seconds to minutes to days and even longer. In recent years, its jet has also displayed large position angle shifts. We find that most of the observational phenomena can be well explained within our newly developed variable turbulent ADAF (TADAF) model. The
accretion disk is composed of an outer thin disk and an unstable inner TADAF
torus whose size is variable. The previously suggested 'disappearance' and regain of the inner disk is understood as the transition between the thick TADAF and the thin disk. Some types of QSOs are understood in terms of the radius change of the TADAF
torus. The jet position angle shift is understood as the direct sideways frame-dragging on the jet by the Lense-Thirring effect from a tilted, spinning black hole. The slower the outshooting jet, the larger the angle shift. We note that such an effect also applies to other sources, such as V404 Cygni and the AGN M87. This mechanism may also be applicable to the famous 'precessing' jet in SS 433.
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Earth and Planetary Astrophysics
Detecting Extragalactic Exoplanets With Fast Radio Burst Nanolensing
Kenneth F. Olibrice and Dylan L. Jow
Fast
Radio Bursts (FRBs) are spatially and temporally compact sources at cosmological distances. As background sources, they will be uniquely sensitive to the gravitational
lensing of
exoplanets outside of our own
galaxy. We present a method to detect extragalactic
exoplanets using planetary echo nanolensing-periodic, nanosecond-scale variations in the relative time of arrival (ToA) between an initial FRB and its microlensed echo as the
planet orbits its host
star. For a simple binary lens model, we demonstrate that measuring the amplitude and period of these ToA fluctuations enables a determination of the
exoplanet mass and orbital parameters. FRBs will be most sensitive to echo nanolensing by lenses within ten megaparsecs of the Milky Way as well as within ten megaparsecs of the FRB host, opening the door to detections of
planets at a range of
redshifts. We estimate that at least one in a million FRBs will exhibit this phenomenon (i.e. an optical depth of $\tau_l = 10^{-6}$). While current burst rates and low repeating-FRB fractions make a detection challenging in the immediate term, upcoming high-volume surveys and next-generation arrays (such as the SKA Phase 2) will bring the unambiguous detection of extragalactic
exoplanets across cosmological
redshifts into possibility.
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Solar and Stellar Astrophysics
LISA Double White Dwarfs in Triple Systems
Zhijun Wang, Guoliang Lü, Chunhua Zhu et al. (+5 more)
Double white dwarfs (DWDs) in the
Laser Interferometer Space
Antenna (LISA) band are major Galactic gravitational-wave sources, but many tight DWD progenitors may reside in hierarchical triples. Triple
evolution can alter both the production rate and parameter distributions of LISA DWDs. Using the Multiple
Star Evolution (MSE) code, we study how the adiabatic mass-loss model (Ge model) and the SCATTER formalism for triple common-envelope (TCE)
evolution affect triple-channel LISA DWD formation. Our main model evolves 10^5 triples with both ingredients. Three control models, each with 10^4 triples, vary the mass-transfer stability criterion to the original MSE polytropic model, remove SCATTER, or adopt low
metallicity (Z=0.001). We also evolve 10^6 isolated binaries with the same framework as a binary-channel reference. Systems that are dynamically unstable under the polytropic model can instead undergo stable Roche-lobe overflow under the Ge model. This sustained mass transfer modifies the donor envelope, reduces its binding energy, and helps the subsequent common-envelope phase form a close DWD rather than a merger. The Ge model increases the triple-channel LISA DWD yield by about 60% relative to the polytropic model, while SCATTER changes the integrated yield by only about 3%. After residence-time weighting, triples contribute about 1.3e7 LISA-band DWDs, including 1.4e4 individually resolvable systems. In the combined triple-plus-binary normalization, the binary channel contributes 3.1e6 LISA-band DWDs and 4.7e3 resolvable systems; these are the binary share of the combined population, not the binary-only Galactic estimate. The main triple model has a flatter, higher-q mass-ratio distribution than the polytropic-model triples, is dominated by He-CO and He-He binaries, and produces rare eccentric systems only when a tertiary
star remains bound.
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All authors Zhijun Wang, Guoliang Lü, Chunhua Zhu, Xizhen Lu, Sufen Guo, Helei Liu, Renyu Luo, Tian Huang
Cosmology and Nongalactic Astrophysics
Weak Lensing Measurements from the Lyman-$\alpha$ Forest
Anže Slosar
We attempt to measure the weak
lensing of the Lyman-$\alpha$ forest by projecting a quadratic
estimator of the forest-forest and
quasar-forest pair correlations, built from the DESI DR1 data, onto deflection templates constructed from low-
redshift galaxies and
quasars from DESI and BOSS. After validating deflection templates against the ACT DR6 and Planck PR4 CMB
lensing maps and testing the
estimator with injected displacements we measure the
lensing amplitude $A_L$ on the data. Consistent with predictions in the literature, the current generation of public data does not have sufficient signal-to-noise to measure this effect unequivocally: we find the
lensing amplitude $A_L=0.42\pm0.43$ from the forest auto-correlation and $0.87\pm0.48$ from the
quasar–forest cross-correlation. These two nearly independent measurements combine to $A_L=0.62\pm0.33$, consistent with both the fiducial value $A_L=1$ and with no
lensing.
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Cosmology and Nongalactic Astrophysics
Cross-correlating Squared kSZ and HI Intensity Fields: A Map-level ACT–MeerKAT Forecast
Yu-Er Jiang, Yun Liu, Yan Gong et al. (+5 more)
The kinetic Sunyaev–Zel'dovich (kSZ) effect probes the line-of-sight momentum of free electrons, but its blackbody spectrum and velocity-dependent sign make it difficult to isolate and cause conventional cross-correlations with density tracers to vanish. In this work, we investigate the cross-correlation of the squared kSZ field with the projected squared HI intensity field using mock ACT and MeerKAT observations constructed from a Jiutian-1G simulation lightcone. We generate
halo-based kSZ maps and MeerKAT-like HI brightness-temperature cubes over a $13.5^\circ\times13.5^\circ$ field. The simulations incorporate ACT beam smoothing and effective internal-linear-combination noise, together with the frequency-dependent MeerKAT beam, scanning strategy, map-making, and inhomogeneous thermal noise. We analyze signal-only, idealized amplitude-reconstructed, and Wiener-filtered kSZ maps. The resulting squared-field cross-correlations have diagnostic cumulative signal-to-noise ratios of approximately $3$-$4$. Our map-level results demonstrate the detectability of the ${\rm kSZ}^2\times {\rm HI}^2$ correlation in future joint ACT–MeerKAT observations.
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All authors Yu-Er Jiang, Yun Liu, Yan Gong, Zi-Yan Yuwen, Yin-Zhe Ma, Furen Deng, Xuelei Chen, Qi Guo
Instrumentation and Methods for Astrophysics
LUMA: A CNN for Strong Gravitational Lens Searches in Astronomical Imaging
Giovanni Vincenzo Donatiello, Achille A. Nucita, Francesco De Paolis et al. (+2 more)
We present LUMA, a convolutional neural network (CNN) pipeline for the automated detection of strong gravitational lenses in simulated astronomical imaging. The method combines a physically motivated preprocessing stage, which enhances faint arc and ring features, with a compact three-block CNN trained using class reweighting and modern learning-rate scheduling. On simulated data, the model reaches test accuracies of about $96$% and receiver operating characteristic (ROC) area-under-the-curve (AUC) values of $\simeq 0.99$ for the non-trivial classes, while confusion-
matrix analysis shows high completeness and purity for lens candidates. These results demonstrate that relatively lightweight CNN architectures can provide a competitive baseline for strong-lens searches, and they motivate future extensions toward real survey images and
transformer-based models.
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All authors Giovanni Vincenzo Donatiello, Achille A. Nucita, Francesco De Paolis, Antonio Franco, Francesco Strafella
Astrophysics of Galaxies
Morphological Identification of Dynamical Regimes in MHD Turbulence with ScaleAware-JEPA
Mengke Zhao, Guang-Xing Li and Keping Qiu
The morphology of turbulent interstellar gas reflects the coupled action of
turbulence,
magnetic fields, and self-
gravity, but density amplitude alone does not uniquely specify dynamical state. We use ScaleAware-JEPA to learn multiscale structural coordinates from density alone and test whether these learned coordinates organize dynamical states more clearly than density-based conditioning. Clump-like, filament-like, and diffuse-like latent neighborhoods show an ordered progression in turbulent velocity scaling that is not reproduced by density-selected populations. Velocity and
magnetic fields are withheld during training and used afterward as post-training physical diagnostics: MHD states occupy ordered but overlapping regions of the learned representation, and dimensionless dynamical balances vary coherently across the full latent atlas. These results show that a representation learned from density morphology can acquire a geometry that is systematically organized by established MHD diagnostics. Multiscale morphology therefore provides a useful coordinate for dynamical state beyond density amplitude alone.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Does the High Energy LUX-ZEPLIN Event Suggest Hyperfine Atomic Dark Matter?
Prolay Chanda, Bhaskar Das and Sagnik Mukherjee
The LUX-ZEPLIN (LZ) Collaboration has reported a nuclear-recoil candidate at $248\pm23~({\rm stat})\pm23~({\rm sys})~{\rm keV}$ in an extended high energy search window. We investigate whether this event can arise from the hyperfine excitation of hydrogen-like atomic dark matter. For a TeV-scale dark atom, a hyperfine splitting near $340~{\rm keV}$ places xenon scattering close to the observed value by naturally selecting the high-velocity tail of the Galactic
halo while suppressing the leading low-energy elastic response. The resulting endothermic kinematics predict a pronounced target hierarchy: the
benchmark transition is inaccessible on Ar and Ge, lies close to threshold on Xe, and remains open on heavier targets such as W, which is specific to our model parameters. Because xenon probes the extreme high-speed tail, the signal exhibits a large annual modulation and a strong dependence on the assumed
halo distribution. We also examine how the infall of the Large Magellanic Cloud enhances the high-speed tail of the Milky Way's local dark matter distribution, extending the kinematic reach to larger hyperfine splittings.
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Astrophysics of Galaxies
Dynamical friction vs. subhalo heating in Cold Dark Matter haloes
Jorge Peñarrubia, Pierfrancesco Di Cintio, Eduardo Vitral et al. (+1 more)
The orbital
evolution of massive stellar systems embedded in dark matter
haloes is governed by competing processes. Dynamical friction removes orbital energy, whereas fluctuations in the gravitational field generated by dark matter subhaloes inject energy through
stochastic heating. We investigate the balance between these two mechanisms using analytical arguments and numerical experiments. We show that, for a given host
halo and subhalo population, there exists a critical mass $M_{\rm crit}$ at which heating and friction balance. Clusters with masses $M_{\rm cl}>M_{\rm crit}$ lose orbital energy and sink towards the centre of the
halo, whereas those with $M_{\rm cl}<M_{\rm crit}$ gain energy and expand outwards. At $M_{\rm cl}\simeq M_{\rm crit}$, the two processes balance, leading to a cluster population that, on average, neither sinks nor expands within the host
halo. In CDM
haloes, the critical mass is primarily controlled by the upper end of the subhalo mass function. Since massive subhaloes are intrinsically rare, the balance between heating and friction shows substantial
halo-to-
halo scatter. For dark matter
haloes in the mass range associated with dwarf spheroidal
galaxies (dSphs), we find $M_{\rm crit}\gtrsim 10^5M_\odot$, comparable to the masses of globular clusters in the Fornax dSph.
Stochastic heating by dark substructure may therefore significantly delay the orbital decay of globular clusters and help alleviate the Fornax timing problem.
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All authors Jorge Peñarrubia, Pierfrancesco Di Cintio, Eduardo Vitral, Matthew G. Walker
Astrophysics of Galaxies
Testing KMTNet–PRIME Optical–Near-Infrared Source-Color Constraints in KMT-2024-BLG-0211 and KMT-2024-BLG-1522
Kansuke Nunota, Jennifer C. Yee, Takahiro Sumi et al. (+37 more)
We present analyses of two 2024 microlensing events, KMT-2024-BLG-0211 and KMT-2024-BLG-1522, jointly observed by KMTNet in the optical and
PRIME in the near-infrared. For KMT-2024-BLG-0211, the KMTNet–
PRIME $I-H$ color provides a useful constraint on the angular source radius for a short-timescale finite-source event with a giant source. The event is consistent with a low-mass stellar lens, although the weak parallax constraint leaves the lens mass and distance uncertain. For KMT-2024-BLG-1522, we compare the results obtained from $V-I$, $I-H$, $V-H$, and $J-H$ color constraints. The microlensing parameters are nearly identical among the four analyses, yielding a robust binary-lens solution with nearly equal masses. However, the inferred source properties and lens physical parameters depend on the adopted source color because the different color estimates imply different angular source radii. Comparing the $(V-I)_{\rm KMT}$ versus $(I-H)_{\rm KMT,PRIME}$ plane shows that the inferred source colors lie off empirical color–color relations but within the scatter of observed
stars. The prevalence of such deviations should be tested with a larger sample of KMTNet–
PRIME events and this specific case can be further tested with future adaptive-optics follow-up, which can directly measure the lens–source relative proper motion and lens flux.
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All authors Kansuke Nunota, Jennifer C. Yee, Takahiro Sumi, Ryusei Hamada, Ian A. Bond, Andrew Gould, Weicheng Zang, David P. Bennett, Aparna Bhattacharya, Kotaro Daimon, Yuki Hirao, Stela Ishitani Silva, Shuma Makida, Shota Miyazaki, Tutumi Nagai, Seiya Nakayama, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Nicholas J. Rattenbury, Yuki K. Satoh, Daisuke Suzuki, Takuto Tamaoki, Motohide Tamura, Sean K. Terry, Chihiro Ueda, Aikaterini Vandorou, Hibiki Yama, Michael D. Albrow, Sun-Ju Chung, Cheongho Han, Kyu-Ha Hwang, Youn Kil Jung, Yoon-Hyun Ryu, In-Gu Shin, Yossi Shvartzvald, Hongjing Yang, Dong-Jin Kim, Chung-Uk Lee, Byeong-Gon Park
Astrophysics of Galaxies
Broadband reverberation mapping of quasars at cosmic noon
Juan V. Hernández Santisteban
Broadband reverberation mapping provides a powerful tool to investigate the structure of the
accretion flow around supermassive black holes. The ultraviolet region of the
quasar spectrum is of particular interest, as it enables the disentanglement of the relative contributions from the
accretion disc and the broad-line region to the observed variability of
quasars in the local Universe. Observations of
quasars at
cosmic noon ($z\sim 1-2$) offer the opportunity to probe the UV emission across a diverse population, spanning a broad range of black hole masses and luminosities. Here we re-analysed the 36 multi-year
quasar lightcurves from the Dark Energy Survey (DES) between $z\sim0.7-2$ to retrieve interband delays and analyse their spectral energy distribution. Using PyROA, we were able to fit all multiple years of observations and the four optical bands simultaneously, significantly improving the lag detection as this method is able to interpolate over the seasonal gaps. We find robust detections of interband delays in 31/36
quasars, suggesting high-Eddington ratios for a large fraction of objects. Their spectral energy distribution is consistent with a geometrically thin disk $f_\nu\propto\lambda^{-1/3}$, with an ensemble slope of $-0.28\pm0.02$. The full sample of
quasars do not show excess around the Balmer jump region, suggesting the impact of the broad-line region to the reverberation signals in high-Eddington sources could be small as documented in some AGN in the local Universe. The prospect of LSST to observe thousands of
quasars in this
redshift range should motivate the detailed study of the UV-rest frame of high-Eddington
quasars to account for the BLR contribution and properly infer disc sizes.
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Astrophysics of Galaxies
Population search for dark matter spikes in megamaser rotation curves
Gonzalo Herrera
A black hole growing adiabatically inside a dark matter
halo is expected to develop a dense spike, with a power-law slope between 1.5 and 2.5, depending on
redshift and baryonic activity. Direct dynamical tests of this prediction are almost non-existent. Here we show that water megamaser disks offer one; their masers orbit within a parsec of the black hole and are mapped individually with very long baseline interferometry, so the enclosed mass at each radius can be read off the rotation curve. We develop a search method and apply it to eleven megamaser disks with public kinematics. Compared with a black hole alone, a spike is preferred in NGC 1194 and NGC 4258 and moderately improves the fit in several others. Allowing the disks to warp removes this preference in all but NGC 4258 and NGC 6264. No combination of disks, warped or not, allows a spike heavier than about ten per cent of the black hole mass, a sensitivity validated with mock injection tests. Mapping the warps with maser accelerations and detecting fainter inner masers, where a spike and a tilt differ most, can break the remaining degeneracy. Megamaser disks open a window onto dark matter around supermassive black holes, and, importantly, one that enables population statistics.
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Earth and Planetary Astrophysics
High-CO2 Climates and Observables in the Outer Habitable Zone
Daria Pidhorodetska, Edward W. Schwieterman, Thomas J. Fauchez et al. (+1 more)
The habitable zone (HZ) is a fundamental concept used to guide our search for temperate
exoplanets with stable surface
liquid water that would sustain remotely detectable biosignatures. So far, most advanced 3D
climate studies and prospective spectral simulations of HZ
planets have focused on inner HZ
planets that receive stellar radiation similar to Earth and would consequently maintain relatively low (e.g., hundreds of parts per million) atmospheric CO2. Here, we present a systematic investigation of outer HZ (OHZ)
planets, which require high CO2 for habitability, using the 3D Generic Planetary
Climate Model (PCM). Our 3D
climate results are compared with previous 1D predictions that show strong agreement between models. Simulated spectra of the modeled
planets indicate that high overlying CO2 levels affect remote signatures of habitability. We also determine substantial spectral differences that would distinguish habitable versus nonhabitable high-CO2 worlds with future direct-imaging observations for solar analogs and with transmission and emission spectroscopy for M dwarfs. Our results demonstrate that 3D models that include CO2 condensation are necessary to understand the potential planetary habitability and spectral impacts of clouds on terrestrial worlds in the OHZ.
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All authors Daria Pidhorodetska, Edward W. Schwieterman, Thomas J. Fauchez, Martin Turbet
Earth and Planetary Astrophysics
A Bayesian Inference Framework for Binary Lens Events Fully Incorporating Higher-Order Effects
Kansuke Nunota and Kento Masuda
Higher-order effects, such as microlensing parallax and lens orbital motion, are essential for characterizing the physical properties of microlensing planetary systems including their masses and distances. In practice, higher-order effects are often included in light-curve modeling only when their signals are strong, because their inclusion in weakly constrained cases tends to drive the inferred parameters toward regions of parameter space that are disfavored by standard Galactic models. This binary choice over physically continuous effects introduces an event-dependent selection function that complicates population-level interpretation and prevents strong and weak detections from being combined within a single uniform framework. In this work, we investigate the origin of instabilities associated with higher-order effects, and show that such instabilities can arise from a mismatch between commonly adopted uninformative priors in the light-curve parameter space and the distributions predicted by Galactic models. Motivated by this, we develop a new
Bayesian framework that enables higher-order effects to be incorporated in a stable and uniform manner. As part of this framework, we introduce Galactic Prior Modeling Engine (gapmoe), a dedicated tool that enables efficient evaluation of the Galactic prior density and allows it to be incorporated directly into the light-curve inference. Using simulated events, we demonstrate that our framework robustly recovers the true physical parameters while fully accounting for microlensing parallax and lens orbital motion. This framework eliminates the need for ad-hoc model selection and provides a scalable and statistically consistent pathway for analyzing the large samples expected from next-generation surveys such as the Roman Space
Telescope.
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Astrophysics of Galaxies
A 210 Megaparsec Ionized Structure at $z=6.8$ Revealed by an Astrophysics Foundation Model
Minghao Yue, Yongda Zhu, Jiani Ding et al. (+2 more)
Reionization is the last major transition in the Universe that transforms the intergalactic medium (IGM) from neutral to highly ionized, yet its spatial structure remains poorly constrained. Using an astrophysics foundation model trained for James Webb Space
Telescope datasets, we identify a luminous
galaxy at
redshift $z=7.567$ showing significant Ly$\alpha$ transmission at $z=6.80\pm0.07$. This transmission, named “the First Ly$\alpha$ transmission in the Reionization Epoch at $z\sim7$" (FL$\alpha$RE-z7), indicates a cosmological-scale ionized structure extending over $210.5^{+55.7}_{-53.5}$ comoving Megaparsecs at
cosmic dawn. The hydrogen neutral fraction of the ionized structure is $x_{\rm HI}=(2.07^{+0.29}_{-0.30})\times10^{-6}$, about $10^5$ times lower than the
cosmic mean at similar
redshifts $(x_{\rm HI}\approx0.4)$. Cosmological simulations suggest a probability of $\approx10^{-5}$ for a random sightline to reproduce the transmission. We find no significant
galaxy overdensity associated with the transmission region, in tension with canonical inside-out reionization models. FL$\alpha$RE-z7 severely challenges existing reionization models in the standard $\Lambda$CDM Universe, indicating extreme spatial fluctuation in ionizing radiation or IGM temperature. Our result marks the first example of a foundation model discovering a previously unpredicted astrophysical phenomenon, demonstrating the power of deep learning methods for mining large astronomical
datasets and finding unexpected new astrophysics.
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All authors Minghao Yue, Yongda Zhu, Jiani Ding, Xiaohui Fan, Yufeng Luo
High Energy Astrophysical Phenomena
Combined constraints on the diffuse flux of cosmic neutrinos between 10^16 eV and 10^26 eV
S.V. Troitsky
Experimental constraints on the diffuse
neutrino flux above the PeV range have been obtained with Cherenkov
neutrino telescopes, air-shower arrays,
radio detectors in and above polar ice, and
radio observations of the Moon. Published results use different flavor, energy-bin, and statistical conventions, so their flux limits cannot be combined directly. We reconstruct energy-dependent exposures of the published searches and place them in a common convention for the total all-flavor $\nu+\bar\nu$ flux over $10^{16}$-$10^{26}$ eV. Published event counts and expected backgrounds are combined with a Poisson likelihood, and 90% C.L. quasi-differential limits are obtained for one-decade $E_\nu^{-1}$ test spectra using a one-sided profile-likelihood construction. Folding theoretical spectra of cosmogenic
neutrinos and selected new-physics scenarios with the combined energy-dependent exposure yields constraints on their flux normalizations. This homogeneous analysis provides a reproducible observational
benchmark across ten decades in
neutrino energy and a common reference for current and projected searches.
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Instrumentation and Methods for Astrophysics
ECLIPSE-X: Plate-Scale Calibration as the Binding Constraint on Relativistic Astrometry with Spacecraft Navigation
Pedro J. Llanos
Precision stellar astrometry near the Sun can constrain the parametrized post-Newtonian (PPN) parameter gamma through gravitational light deflection. This study develops ECLIPSE-X, a localized multi-frame estimation architecture in which one persistent relativistic parameter is estimated simultaneously with frame-dependent spacecraft line-of-sight and roll states, separated by their differing spatial signatures and by the persistence of gamma across frames. The aim is not a competitive determination of gamma, but an assessment of whether such a joint solution and its formal covariance stay statistically valid under realistic astrometric model error. A synthetic field of 250
stars spanning 1.22-8 apparent solar radii is observed over 40 frames at 5-s cadence; weighted least squares estimates gamma with three navigation states per frame, and Schur-complement marginalization gives the formal uncertainty in gamma after navigation coupling. The nominal solution recovers gamma = 1.0001198167 with sigma_gamma = 3.075104e-4, and a 1000-realization ensemble confirms calibration. Perturbations unknown to the
estimator identify plate-scale mismatch as the dominant failure mechanism: a 300-ppm scale error alone inflates the empirical-to-formal uncertainty ratio to 7126.6 with zero 1-sigma and 2-sigma coverage, against 2.18 for catalog-coordinate mismatch and 1.12 for a frame-coherent radial perturbation, while every realization converges numerically: convergence does not guarantee statistical validity. Augmenting the state with a plate-scale parameter restores consistency, at a fixed 21.2% cost in the precision of gamma set by the correlation between the two persistent parameters. A calibration sweep shows the unaugmented
estimator is covariance-consistent only below sigma_p = 2.7884e-8, so the augmented state is a requirement, not a refinement, for near-Sun relativistic astrometric
estimators.
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Cosmology and Nongalactic Astrophysics
Everything Everywhere All At Once: A Hierarchical Framework for Mapping Anisotropies in the Local Universe
Aryan Bansal, Edward N. Taylor, Michelle Cluver et al. (+1 more)
We present a
Bayesian hierarchical forward model for mapping the local luminosity-density field from heterogeneous
redshift surveys. By dividing the survey volume into angular
cells and
redshift shells, we model the observed
galaxy distribution directly in apparent-magnitude and
redshift space. This allows us to infer
cell-level luminosity functions and densities while preserving each survey's unique selection function. Simultaneously, the ensemble of
cells constrains the
cosmic-mean luminosity function, its
redshift evolution, and the hyperparameters describing
cell-to-
cell variation. We apply the framework to 2MRS, 6dFGS, and GAMA over $0.005<z<0.065$, combining wide sky coverage with deeper and fainter
galaxy samples. The model successfully recovers global $J$-band luminosity-function parameters and a mean luminosity density consistent with previous low-
redshift measurements. The inferred luminosity-density scatter decreases with volume, consistent with the
cosmic-variance amplitude expected in a $\Lambda$CDM universe. Within the volume we probe, we find no evidence for a large coherent underdensity. Instead, the local Universe is broadly consistent with smooth
evolution and
cosmic variance. The nearest shell at $z \simeq 0.01$ is the clearest exception, lying $\simeq 0.12$~dex ($\simeq 25\%$) below the smooth global model, a $-2.6\sigma$ underdensity with a one-sided significance of $\simeq 99.5\%$. This framework offers a scalable architecture for mapping
cosmic density fields with next-generation wide and deep surveys.
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All authors Aryan Bansal, Edward N. Taylor, Michelle Cluver, Matthew Colless