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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 28 May

High Energy Astrophysical Phenomena

From reflection to scattering: Polarimetric signatures of funnel-type outflows. Modeling obscured ultraluminous X-ray sources

Varpu Ahlberg, Alexandra Veledina, Eugene Churazov et al. (+1 more)

Super-Eddington accretion onto compact objects is expected to produce optically thick outflows with a funnel-shaped cavity that may collimate the emission. At inclinations higher than the grazing angle of the funnel, the central source is obscured. Accordingly, the observed emission is dominated by scattered and reflected radiation, which can therefore be strongly polarized. The detection of strong X-ray polarization in the Galactic X-ray binary Cygnus X-3 provides the first direct probe of this geometry. In this work, we present a systematic study of the inclination-dependent radiative signatures of such systems using a combination of semi-analytical methods and Monte Carlo simulations. Our treatment explicitly accounts for multiple scatterings and demonstrates that both the polarization degree and the degree of collimation are highly sensitive to the albedo of the funnel surface. We find that a low albedo (significant absorption) is essential for producing high polarization, yet it simultaneously suppresses the collimation of the emission. Conversely, a high-albedo medium (nearly pure scattering) can modestly collimate radiation, but at the cost of substantially reducing the polarization degree. We discuss our results in the context of Imaging X-ray Polarimetry Explorer observations of Cygnus X-3 and propose a physical scenario for its spectral state transitions, considering a combination of reflection from the funnel surface and scattering by a diffuse medium above the funnel. Our model provides a general framework for interpreting X-ray polarimetric signatures of obscured accretors.
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All authors Varpu Ahlberg, Alexandra Veledina, Eugene Churazov, Ildar Khabibullin

Earth and Planetary Astrophysics

Optical transmission spectrum of HAT-P-47b: evidence for aerosols and tentative TiO absorption

Wan-Hao Wang, Guo Chen, Fei Yan et al. (+5 more)

Transmission spectroscopy enables the characterization of exoplanet atmospheres by probing absorption features in their terminator regions. In the optical, it is particularly sensitive to metal oxides and atomic species that can strongly influence atmospheric energy balance and thermal structure. We aim to investigate the atmospheric properties of the hot Jupiter HAT-P-47b through optical transmission spectroscopy. Thirteen TESS transits were analyzed to refine the planetary ephemeris and system parameters. Two ground-based transits were observed with LBT/MODS and GTC/OSIRIS+. Chromatic transit light curves were modeled to derive instrument-specific transmission spectra and multiple Bayesian spectral retrievals were performed to characterize the atmospheric properties. The MODS transmission spectrum provides moderate Bayesian evidence ($\Delta\ln\mathcal{Z}=2.68$) for TiO absorption, whereas the OSIRIS+ spectrum does not yield statistically significant evidence for any specific opacity source. Both datasets exhibit a wavelength-dependent slope indicative of enhanced aerosol scattering. The MODS and OSIRIS+ joint free-chemistry retrieval, dominated by the higher signal-to-noise MODS data, yields moderate evidence ($\Delta\ln\mathcal{Z}=3.44$) for TiO with a log mass fraction of $-6.86^{+0.64}_{-0.63}$ dex. The same model indicates an aerosol contribution to the optical scattering opacity approximately $5000\times$ larger than pure H$_2$ Rayleigh scattering. HAT-P-47b appears to host a cloudy atmosphere with evidence for aerosols and tentative evidence for TiO absorption. Future high-precision observations will be essential to confirm the presence of TiO and further characterize its atmospheric structure.
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All authors Wan-Hao Wang, Guo Chen, Fei Yan, Chengzi Jiang, Luigi Mancini, Enric Pallé, Felipe Murgas, Hannu Parviainen

Earth and Planetary Astrophysics

DELOS: Contrastive Deep Learning for Low-SNR Blind Transit Searches in Kepler Photometry

Qingtian Liu, Jian Ge, XingChen Yan et al. (+4 more)

We present DEtection in phase-folded Light curves with cOntrastive Scoring (DELOS), a deep-learning framework that uses contrastive scoring to perform blind searches for shallow transits in Kepler photometry. DELOS combines GPU-accelerated phase folding, optimized phase binning, and a custom one-dimensional convolutional encoder to assign a transit-likeness score to each folded light curve, thereby producing a score periodogram over trial periods without relying on pre-detected threshold-crossing events. Focusing on intermediate-to-long-period signals with orbital periods of 100-150 days, DELOS was trained on 20 million synthetic light curves generated with realistic transit models and Kepler-like noise properties, achieving a validation accuracy of 99.3% on the synthetic validation set. In controlled injection-recovery experiments, DELOS improves the combined precision-recall performance by 15.5% relative to Box-fitting Least Squares (BLS) and 11.25% relative to Transit Least Squares (TLS) in the low Signal-to-Noise Ratios (low-SNR) regime. It also accelerates the search by factors of approximately 3-5 and 74-80 compared with BLS and TLS, respectively. Applied to a selected Kepler validation sample, DELOS recovered all known shallow intermediate-to-long-period transit signals in the tested period range. These results demonstrate that DELOS provides an efficient and sensitive framework for low-SNR transit searches and represents a practical step toward future searches for longer-period terrestrial planets in Kepler, K2, TESS, PLATO, and Earth 2.0 data. Accordingly, this work is intended as a methodological development and validation study, with the detailed astrophysical validation of newly identified candidates deferred to future work.
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All authors Qingtian Liu, Jian Ge, XingChen Yan, Kevin Willis, Xinyu Yao, QuanQuan Hu, Jiapeng Zhu

High Energy Astrophysical Phenomena

A Note on QPE Timing: False Alarms in O-C

Cong Zhou, Zirui Zhang, Zhen Pan et al. (+1 more)

O-C timing analysis is a useful diagnostic tool for quasi-periodic eruptions (QPEs), but their interpretation depends sensitively on the integer cycle number assigned to each eruption. In this note, we show that even a small mismatch in the cycle number, $N_{\rm cyc}$, can produce large false signals in O-C diagrams, and a universal feature of these false signals is a large in-phase sinusoidal modulation between even and odd eruptions. Therefore, uncertainties in $N_{\rm cyc}$ must be inferred or marginalized over before physical interpretations are attached to O-C. We then apply both O-C and EMRI+disk to GSN 069 and eRO-QPE2. For GSN 069, the timing data favor an anti-phase modulation in even and odd eruptions, consistent with apsidal precession in a low-eccetricity EMRI crossing an equatorial disk. For eRO-QPE2, the data are well described by a near-circular EMRI and a precessing disk.
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All authors Cong Zhou, Zirui Zhang, Zhen Pan, Wen Zhao

High Energy Astrophysical Phenomena

The Impact of the New $^{59}$Fe Decay Rates on $^{60}$Fe and $^{26}$Al Nucleosynthesis in Massive Stars

Bingyang Tan, Wenyu Xin, Ruizheng Jiang et al. (+2 more)

The diffuse $\gamma$-ray emission from short-lived radioactive $^{26}$Al and $^{60}$Fe provides a direct probe of ongoing nucleosynthesis in the Galaxy. However, theoretical models have long struggled to reproduce the observed $^{60}$Fe/$^{26}$Al flux ratio, typically predicting values significantly higher than constraints derived from INTEGRAL/SPI observations. In this work, we investigate the impact of the recently measured, temperature-dependent stellar $\beta^-$ decay rate of $^{59}$Fe on the nucleosynthesis of these isotopes. We compute a grid of non-rotating massive star models ($14$-$80$ M$_\odot$) at solar metallicity using the MESA code, coupled with a rigorous numerical resolution analysis. We find that the updated rate significantly suppresses the net production of $^{60}$Fe by approximately 0.28 dex ($\sim 47\%$) compared to models using LMP theoretical rates, while leaving $^{26}$Al yields virtually unchanged. This reduction is primarily driven by the enhanced $\beta^-$ decay during convective carbon shell burning. Integrating these yields over a standard Salpeter Initial Mass Function, we predict a Galactic flux ratio of $\sim 0.18$, which is in excellent agreement with the observed value of $0.184 \pm 0.042$. Furthermore, this ratio exhibits a weak dependence on the IMF slope. Our results indicate that the updated nuclear physics input significantly alleviates the long-standing $^{60}$Fe overproduction problem, bringing theoretical predictions into much closer alignment with current Galactic observations.
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All authors Bingyang Tan, Wenyu Xin, Ruizheng Jiang, Gang Zhao, Koh Takahashi

High Energy Astrophysical Phenomena

Subluminous Type IIP SN 2024abfl as a Result of a Significantly Low-energy Fe-core Collapse

Rishabh Singh Teja, D. K. Sahu, G. C. Anupama et al. (+7 more)

We present extensive, well-sampled multiwavelength photometric and low-resolution optical spectroscopic observations of the low-luminosity Type IIP supernova SN 2024abfl. SN 2024abfl is found to be at the faintest end of Type IIP supernovae with unprecedented flat (0.1 mag/ 100 day) plateau evolution and a mid-plateau absolute magnitude of Mv~-13.8 mag, placing it among one of the faintest Type IIP supernovae discovered to date. SN 2024abfl is adjacent to SN 2018zd in the same host NGC~2146. Using various SN distance measurement probes, we provide independent estimates of the debated distance to the host NGC 2146 (7-9 Mpc). Spectral evolution of SN 2024abfl is found to be similar to other SNe spectra of this subclass but with very narrow line profiles, indicating moderately low expansion velocities of the ejecta. Detailed 1-D hydrodynamical modeling suggests a compact progenitor with an upper limit of 10 Msun, fairly consistent with the directly detected progenitor estimates. It exploded with very low-energy 0.05 foe or less with a very low nickel mass of 0.003 Msun, consistent with the observed parameters. These parameters provide important constraints on the nature of low-energy core-collapse explosions. We discuss possible progenitor scenarios and compare SN 2024abfl with other low-luminosity Type IIP supernovae.
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All authors Rishabh Singh Teja, D. K. Sahu, G. C. Anupama, Avinash Singh, Amrit Dutta, Gitika Rameshan, Hrishav Das, Koji S Kawabata, Mridweeka Singh, Varun Bhalerao

Astrophysics of Galaxies

ODIN: Rest-frame Optical Morphologies and Star Formation Activity of Ly{\alpha} Emitters at z=2.4, 3.1, and 4.5

Sang Hyeok Im, Ho Seong Hwang, Jeong Hwan Lee et al. (+19 more)

We analyze the rest-frame optical (~8000 Å) morphologies and star formation activity of Ly{\alpha} emitters (LAEs) at redshifts $2.4$, $3.1$, and $4.5$, identified in the ODIN survey. To compare their physical properties with those of other galaxies, we construct a comparison sample of typical star-forming galaxies (SFGs) at similar redshifts from the COSMOS2025 catalog. Using the JWST/NIRCam images from the COSMOS-Web survey, we measure the rest-frame optical sizes and Sérsic indices. We first examine their size-mass relations and find that LAEs at all three redshifts have smaller sizes than typical SFGs, with the size difference decreasing at higher redshifts. We also find that LAEs tend to have larger Sérsic indices at $z=2.4$ and $3.1$ than typical SFGs, but the difference becomes weaker at $z=4.5$. These trends are qualitatively reproduced in the Horizon Run 5 cosmological hydrodynamical simulation. We then investigate star formation activity and find that LAEs exhibit higher star formation rates than typical SFGs at all redshifts considered. Finally, we examine the connection between Ly{\alpha} emission and galaxy structure, finding that the rest-frame equivalent width (REW) of the Ly{\alpha} emission line has negative and positive correlations with size and Sérsic index, respectively. In addition, we find a strong positive correlation between the Ly{\alpha} REW and the ratio of the instantaneous star formation rate to that averaged over the last $100\;\mathrm{Myr}$ (i.e., $\mathrm{SFR_{inst}}/\mathrm{SFR_{100 Myr}}$). These results suggest the compact and starbursting nature of LAEs, and provide important constraints on the physical mechanism for the Ly{\alpha} photon escape from galaxies.
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All authors Sang Hyeok Im, Ho Seong Hwang, Jeong Hwan Lee, Robin Ciardullo, Eric Gawiser, Caryl Gronwall, Lucia Guaita, Woong-Seob Jeong, Ankit Kumar, Kyoung-Soo Lee, Changbom Park, Vandana Ramakrishnan, Akriti Singh, Hyunmi Song, Sungryong Hong, Juhan Kim, Jaehyun Lee, Christophe Pichon, Caitlin M. Casey, Maximilien Franco, Santosh Harish, Jeyhan S. Kartaltepe

Astrophysics of Galaxies

Modeling Solitonic Cores, Stabilization of Bar, and Suppression of Bar Dissolution in DDO 168 via GPP Formalism: A Detailed Analysis of Bose–Einstein Condensate/Fuzzy Dark Matter Halo Structure and Bar Dynamics in the Dwarf Galaxy DDO 168

Saroj Khanal, Sanjay Kumar Sah, Kiran Khanal et al. (+1 more)

The cusp-core problem remains a challenge to the $\Lambda$CDM model, since dwarf galaxies often exhibit flat central density cores rather than the steep cusps ($\rho \propto r^{-1}$) predicted by collisionless $N$-body simulations. We model the dark-matter-dominated dwarf irregular galaxy DDO 168 within the Bose–Einstein condensate (BEC) or fuzzy dark matter (FDM) framework, in which ultralight bosons form a solitonic core governed by the Gross–Pitaevskii–Poisson (GPP) equations, with the soliton mass–radius relation enforced. We numerically validate the ground-state solution of the GPP system as a consistency check and fit the inner rotation curve of DDO 168 using SPARC data. Within this framework, the data are consistent with an axion mass \[ m = (1.3^{+0.3}_{-0.2}) \times 10^{-23}\,\mathrm{eV}, \] and yield a solitonic core with characteristic radius \[ R_c = 2.40^{+0.24}_{-0.22}\,\mathrm{kpc}, \] enclosing a mass \[ M(<2.47\,\mathrm{kpc}) \simeq (1.5 \pm 0.2)\times10^{9}\,M_\odot. \] The observed flat inner rotation curve is reproduced and the presence of a weak H\,I bar is compatible with multigigayear survival timescales, consistent with reduced Chandrasekhar dynamical friction in a shallow central potential. These results demonstrate that the BEC/FDM framework provides an internally consistent description of DDO 168, simultaneously reproducing the observed rotation curve, alleviating the cusp-core tension, and allowing long-lived weak bars under conservative dynamical assumptions.
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All authors Saroj Khanal, Sanjay Kumar Sah, Kiran Khanal, Sapana Khanal

Instrumentation and Methods for Astrophysics

Development and demonstration of a Modular Astrobiological Experiments (MAEx) payload for autonomous biological monitoring in Low Earth Orbit (LEO)

Yamini Jangir, Samrat Ghosh, Vinay Nayaka et al. (+11 more)

The spaceflight environment presents unique physicochemical conditions, including microgravity, ionizing radiation, altered fluid transport, and confined engineered habitats, which influence biological systems and biomolecular assembly processes. These conditions also provide opportunities for orbital biomanufacturing and autonomous biofabrication that are difficult to reproduce under terrestrial gravity, motivating the development of compact autonomous experimental platforms for spaceflight research. Here, we present the Modular Astrobiology Experiment (MAEx) platform, a compact 3U spaceflight-compatible payload designed for autonomous multimodal biological characterization under space-relevant conditions. MAEx was engineered to operate within the constraints of orbital deployment, including limited volume, low power consumption, thermal regulation, and autonomous data acquisition. To demonstrate platform versatility, representative biological systems, including the electroactive bacterium Shewanella oneidensis MR-1, the radiation-resistant fungus Ustilago maydis FB1, and the human eye lens protein {\gamma}D-crystallin, spanning cellular and molecular scales were incorporated. MAEx platform integrates imaging, absorption and fluorescence spectroscopy, and electrochemical sensing within a modular architecture, enabling simultaneous monitoring of microbial growth, extracellular electron transfer (EET), and protein aggregation dynamics.
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All authors Yamini Jangir, Samrat Ghosh, Vinay Nayaka, Mubashir Ali, Dharshan Hegde, Kunal Mooley, Arunima Saha, Hariharan VC, Sujata Malik, Amey Bagare, Saurav Mishra, Mukuljeet Singh Mehrolia, Saravanan Matheswaran, Ashwani Kumar Thakur

Solar and Stellar Astrophysics

Modeling the Effect of the Heliospheric Magnetic Field on Cosmic Ray Muon Shadows

MINOS+ Collaboration: P. Adamson, I. Anghel, A. Aurisano et al. (+73 more)

Shadows cast in the cosmic ray (CR) muon sky by the Sun were located using muon data from the MINOS far detector in Northern Minnesota. The shadows were observed independently across three time periods; near solar minimum, near solar maximum, and over the entire 13 year span of the data. A distribution of muon positions for each shadow was then sampled to simulate CR motions near the Sun using the Parker spiral model of the Heliospheric Magnetic Field (HMF) and a dipole model of the Geomagnetic Field (GMF). The resulting particle distributions were then compared to their position with respect to the Sun. Results show that the Parker spiral model is most consistent with the solar minimum shadow and least consistent with the solar maximum shadow, as expected. The simple Parker spiral is more consistent with the data for a harder CR spectrum than is actually present, indicating the need for a more detailed HMF model. Plausible modifications to the Parker spiral model which would affect the overall shift of the Sun's CR shadow are discussed.
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All authors MINOS+ Collaboration: P. Adamson, I. Anghel, A. Aurisano, G. Barr, A. Blake, S. V. Cao, T. J. Carroll, C. M. Castromonte, R. Chen, S. Childress, J. A. B. Coelho, S. De Rijck, J. J. Evans, G. J. Feldman, W. Flanagan, S. Fogarty, M. Gabrielyan, H. R. Gallagher, S. Germani, R. A. Gomes, M. C. Goodman, P. Gouffon, N. Graf, N. Grossman, K. Grzelak, A. Habig, S. R. Hahn, J. Hartnell, R. Hatcher, A. Holin, J. Huang, L. W. Koerner, M. Kordosky, A. Kreymer, J. Krueger, K. Lang, P. Lucas, W. A. Mann, M. L. Marshak, N. Mayer, R. Mehdiyev, J. Meier, W. H. Miller, G. Mills, D. Naples, J. K. Nelson, R. Nichol, J. OConnor, R. B. Pahlka, Ž. Pavlović, G. Pawloski, A. Perch, M. M. Pfützner, D. D. Phan, R. K. Plunkett, N. Poonthottathil, X. Qiu, A. Radovic, P. Sail, M. C. Sanchez, A. Schreckenberger, R. Sharma, N. Skuza, A. Sousa, N. Tagg, J. Thomas, M. A. Thomson, A. Timmons, J. Todd, S. C. Tognini, R. Toner, D. Torretta, P. Vahle, A. Weber, L. H. Whitehead, S. G. Wojcicki

High Energy Astrophysical Phenomena

Recoil-regulated extreme mass-ratio inspirals in AGN disks

LingQin Xue, Zoltán Haiman, Hiromichi Tagawa et al. (+1 more)

Extreme mass-ratio inspirals (EMRIs) are among the primary targets of future space-based gravitational-wave observatories, such as LISA, TianQin, and Taiji. Active galactic nucleus (AGN) disks provide a gas-rich environment in which stellar-mass black holes can migrate toward central supermassive black holes and form EMRIs. Previous studies of this “wet” channel have largely neglected stellar interactions within the disk. Here we show that binary formation, hierarchical mergers, and recoil kicks fundamentally regulate wet EMRI formation in AGN disks. Using semi-analytical AGN disk models combined with Monte Carlo simulations across supermassive black hole masses of $10^5$–$10^7M_\odot$ and Eddington ratios of $10^{-3}$-1, we find that recoil kicks from mergers and binary–single interactions repeatedly lift stellar-mass black holes out of the disk plane, temporarily interrupting migration and strongly suppressing EMRI formation in much of parameter space. Detectable EMRIs are therefore preferentially produced in young AGNs, typically within $\sim$ 10-20Myr of disk formation, and often involve merger-grown secondary black holes. We predict LISA detection rates of $\sim$ 1-30yr$^{-1}$, with the observable population dominated by low-mass AGNs and sensitive to the poorly constrained demographics of faint active nuclei. Our results identify stellar interactions as a key ingredient in the evolution of compact objects in AGN disks and show that future EMRI observations can probe both AGN disk physics and the low-mass AGN population.
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All authors LingQin Xue, Zoltán Haiman, Hiromichi Tagawa, Imre Bartos

Cosmology and Nongalactic Astrophysics

A Designer's Guide to Lunar Far-Side Interferometer Array: Power Spectrum Measurement and Cosmological Constraints from the Dark Ages

Yuewei Wen, Bin Yue, Yidong Xu et al. (+4 more)

The 21-cm emission line from neutral hydrogen during the cosmic Dark Ages can be a powerful probe of cosmological models and early universe physics. This work provides a quantitative forecast for the design requirements of a lunar far-side interferometer array aimed at measuring the 21-cm power spectrum and constraining inflationary models through the running of the spectral index $\alpha_s$. During the Dark Ages, larger collapsed objects have not yet formed, allowing linear perturbation theory to remain valid down to much smaller scales than is possible in current large-scale structure or CMB surveys. We first validate this linearity assumption by quantifying the contribution of minihalos to the 21-cm signal. We then establish a generalized and flexible analytical framework for the baseline density distribution of interferometers that may consist of an arbitrary number of stations or sub-arrays. Incorporating a realistic noise model, we determine the configurations necessary to reach the detection threshold and demonstrate that distributing the total collecting area into multiple stations can improve the signal-to-noise ratio of the power spectrum at a tunable small scale of interest by up to two orders of magnitude. We then show that a lunar array requires at least $\sim30,000$ probed Fourier modes to achieve a constraint on inflation of $\sigma(\alpha_s) = 0.034$, a result competitive with the Planck 2018 results and capable of distinguishing between different inflationary scenarios. We quantitatively explain how thermal noise severely erodes modes at high redshifts and small scales – scales previously considered easily accessible to Dark Ages observations in the literature – and discuss the prospects for Dark Ages observations as a new and independent probe despite this limitation.
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All authors Yuewei Wen, Bin Yue, Yidong Xu, Furen Deng, Chen Zhang, Fengquan Wu, Xuelei Chen

Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

Statistical study of energy dissipation in magnetic structures during turbulent reconnection in the Earth's magnetotail

Rachel Wang, Hantao Ji, Adam Robbins et al. (+7 more)

Magnetic reconnection is a ubiquitous plasma phenomenon that plays a critical role in particle heating and energization. During reconnection, the topology of magnetic field rearranges, depositing energy into the surrounding plasma through bulk flow, thermal heating, or non-thermal particle acceleration. While the pathways of this transformation from magnetic energy into kinetic have been studied extensively in recent years through theoretical or case-by-case observations, comprehensive statistical studies remain limited. In this paper, we present a statistical investigation using data from the Magnetospheric Multiscale (MMS) mission, and detail the particle energization mechanisms in magnetic structures found near reconnecting regions in turbulent Earth's magnetotail. We find that electrons with motion perpendicular to the magnetic field dominate $\vec{j}\cdot\vec{E}$ dissipation. In contrast to the conventional picture of unidirectional energy transfer to particles by laminar two-dimensional (2D) reconnection, we find that energy exchange within magnetic structures during turbulent reconnection tends to be bidirectional with only a small positive bias from electromagnetic fields to particles. Specific electron energization mechanisms are quantified, including those due to parallel electric field, Fermi energization from curvature drift, betatron heating from magnetic field inhomogeneity, and polarization drift.
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All authors Rachel Wang, Hantao Ji, Adam Robbins, Kendra Bergstedt, Narges Ahmadi, Robert Ergun, Li-Jen Chen, Jongsoo Yoo, Peiyun Shi, Yuka Doke

Earth and Planetary Astrophysics

Constraints on the Atmospheric Composition of 2002 XV$_{93}$ from JWST Spectroscopy

Ian Wong, Silvia Protopapa and Emmanuel Lellouch

The recent detection of an atmosphere surrounding the trans-Neptunian object (TNO) 2002 XV$_{93}$ from stellar occultation measurements has challenged the longstanding view that only the largest TNOs can sustain an atmosphere. Atmospheric refraction modeling of the occultation light curves indicated a surface pressure of 100$-$200 nbar, despite 2002 XV$_{93}$'s relatively small size (~510 km in diameter) and weak surface gravity. Together with the detection of methane fluorescence on Makemake, this result suggests that tenuous atmospheres may be more common among TNOs than previously thought. We report JWST/NIRSpec observations acquired before and after the 2024 stellar occultation measurements, obtained with the PRISM and medium-resolution gratings at resolving powers of ~100 and ~1000, respectively. We detect no statistically significant emission features attributed to methane or carbon monoxide gas. By comparing the higher spectral resolution data with synthetic fluorescence models, we report upper limits for the methane and carbon monoxide surface partial pressures of $(3-10)\times10^{-6}$ and $(50-300)\times10^{-6}$ nbar, respectively, substantially below the atmospheric pressure inferred from the occultation measurements. Additionally, we report no evidence of an extended source of either methane gas or refractory material. Our results indicate that the atmospheric interpretation of the occultation measurements may require either a composition dominated by volatile species other than methane and carbon monoxide, with nitrogen and argon as possible candidates, or a methane-dominated atmosphere confined near the surface with a steeply decreasing vertical density profile.
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Wednesday 27 May

High Energy Astrophysical Phenomena

Assessing the Relative Importance of Neutrino Matter Interaction Channels in Post-Merger Remnant of Binary Neutron Stars

Samantha Rath, Francois Foucart, Lawrence E. Kidder et al. (+2 more)

Neutron star mergers are amongst the most promising sources for the joint detection of gravitational waves and electromagnetic signals. They are also potential sites for the production of r-process elements and probes of the equation of state of matter above nuclear saturation density. Neutrino-matter interactions during and after merger strongly influence the thermodynamic evolution and composition of the remnant and its outflows, thereby affecting kilonova emission and nucleosynthesis yields. However, existing merger simulations remain limited by significant approximations in the treatment of neutrino transport and interaction rates. In this work, we assess the thermodynamic conditions under which neutrinos decouple from matter and show the effect of charged-current absorption, quasi-elastic scattering on nucleons and nuclei, pair-production processes, and inelastic neutrino-electron scattering for electron neutrinos, electron antineutrinos, and heavy-lepton neutrinos in the different thermodynamical conditions sampled by a simulation using an energy-dependent Monte Carlo neutrino transport. We first estimate opacities in the post-merger remnant assuming neutrinos in equilibria with the fluid, and find results consistent with previous studies performed on simulations using a gray two-moment scheme. We note the very distinct regions in which nucleon-nucleon Bremmstrahlung and electron-positron annihilation are active (high and low density regions, respectively). We then evaluate opacities using the actual distribution function of neutrinos within a Monte Carlo simulation. We show greatly increased pair annihilation rates in cold, low-density regions, especially for heavy-lepton neutrinos. We also show that inelastic scattering on electrons, which has not been included in merger simulations so far, makes important contributions to the thermalization of heavy-lepton neutrinos.
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All authors Samantha Rath, Francois Foucart, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel

Earth and Planetary Astrophysics

Shock wave formation in the thermosphere by an earthgrazing fireball: Empirical evidence for volatile-enhanced hydrodynamic shielding

Elizabeth A. Silber, Denis Vida, Miro Ronac Giannone et al. (+7 more)

Hydrodynamic shielding is a theoretically well-established but observationally elusive and experimentally difficult-to-replicate phenomenon with implications that extend far beyond meteor physics. Rare earthgrazing meteoroids with infrasound signatures that penetrate to the ground can be used to probe hydrodynamic shielding that leads to strong shock formation at high altitude. Here, we report the first coordinated optical and multi-station infrasound observations of a centimeter-scale earthgrazing fireball that generated sustained cylindrical line shock at thermospheric altitudes near 92 km. The event was recorded by numerous optical stations and three infrasound arrays, allowing trajectory reconstruction, ablation behavior, acoustic source localization, and shock characteristics. Optical observations indicate early mechanical erosion and ablation/evaporation at exceptionally low dynamic pressure, consistent with a cometary or a porous, volatile-bearing CM chondritic object. Independent infrasound detections localize shock generation to multiple points along a 164 km trajectory segment near perigee. Weak-shock modeling yields a consistent blast radius of ~30 m, implying an acoustic-equivalent source size far exceeding the physical dimensions of the ~45 g nucleus. We demonstrate that classical gas dynamics and ablation-driven hydrodynamic shielding alone cannot account for these observations under ambient thermospheric conditions. We show that volatile release provides the additional flow-field density enhancement required to amplify hydrodynamic shielding, reduce the effective local Knudsen number, and sustain a shock envelope capable of radiating detectable infrasound. These results demonstrate that small, volatile-rich meteoroids can transiently establish continuum-like flow in rarefied environments.
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All authors Elizabeth A. Silber, Denis Vida, Miro Ronac Giannone, Jamie Shepherd, Sarah Albert, Daniel C. Bowman, Tammy Do, Margaret Campbell-Brown, Peter Jenniskens, Reynold E. Silber

Astrophysics of Galaxies

Compact near infrared sources in the center of the extraordinary galaxy IC 860

J. S. Gallagher, L. Schisgal, G. C. Privon et al. (+7 more)

Hubble Space Telescope (HST) images are used to study the structure of the central regions of the luminous infrared galaxy (LIRG) IC 860. IC 860 is of special interest as a system due to its extreme central concentration of molecular gas cloaking its compact obscured nucleus (CON). The CON provides most of the 1.5E11 Lsun luminosity in IC 860 from an undetermined combination of stellar and AGN power sources. We mapped and photometered the central molecular zone (CMZ) of IC 860 motivated by a previous NIR detection of a luminous compact nuclear source. Our objective was to study properties of the CMZ and its relationship to the CON, that we identified as an opaque central region in archival near infrared (NIR) images. Coordinates of the compact NIR source, IC860-a, came from HST image coordinates calibrated with Gaia positions. Photometry of the HST images yielded magnitudes, colors, and high V-band dust optical depths based on foreground screen dust models. Photometry corrected for dimming by dust yielded NIR luminosities of IC860-a and the CMZ. We found IC 860 has distinct compact central luminosity sources: Most of the NIR luminosity is from the CMZ while the LIRG-CON is an obscured region centered in the CMZ. IC860-a, in the northeast side of the CMZ, is offset by about 0.2 arcsec from the CON, has a luminosity of approximately 1E9 Lsun, and may be a massive young stellar complex or intruding nucleus. We concluded that the inner CMZ in IC 860 contains two luminous compact objects: The CON is identified for the first time as an obscured central source while the structure of the CMZ and CON is complicated by the presence of the IC860-a compact object, possibly a massive young stellar system or second nucleus. The presence of IC 860-a in combination with the CON is a further signature of the unusual evolution of the gas-rich IC 860 CMZ.
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All authors J. S. Gallagher, L. Schisgal, G. C. Privon, S. Aalto, S. König, R. Kotulla, J. Mangum, W. St. John, D. Rigopoulou, K. Alatalo

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

Dynamical Tsallis WIMP Freeze-Out and Residual Memory Channels in the Radiation Sector

Matias P. Gonzalez

In this work we generalize the thermal decoupling, or freeze-out, of weakly interacting massive particle dark matter within the Tsallis nonextensive formalism. The generalization is implemented through $q$-deformed distribution functions obtained from the maximum entropy principle with Curado-Tsallis constraints. The Tsallis parameter $q$, which measures deviations from extensivity with respect to the limit $q=1$, is promoted to a dynamical quantity depending on the dimensionless variable $x=m_\chi/T$, where $m_\chi$ is the dark matter mass. This dynamical evolution is characterized by a relaxation toward extensivity, while requiring that the nonextensive deformation is not completely erased before freeze-out. We solve the Boltzmann equation assuming a sectorial deformation, where only the dark matter equilibrium abundance is generalized and the radiation background remains extensive. The relic abundance is computed for different dark matter masses and initial values of the Tsallis parameter. From this evolution, we extract the residual value $q_\chi^{\rm fo}$ at freeze-out, which is then used as the initial input for a phenomenological memory channel. This channel propagates the residual nonextensivity into the radiation sector, specifically into the electron-positron plasma and neutrinos, while photons are kept extensive in order to avoid direct tensions with CMB physics. The resulting deformation modifies the neutrino energy density and the photon reheating contribution, producing a correction to $N_{\rm eff}$. We compare the predicted values with the compressed CMB+BAO constraint on $N_{\rm eff}$ and find that the residual-memory scenario can remain phenomenologically compatible with current bounds.
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High Energy Astrophysical Phenomena

The MeerKAT Thousand-Pulsar Polarization Array I: Properties of the Polarization and Rotation Measure Time Series Data

Michael Sarkis, Zi-Yan Yuwen, Yin-Zhe Ma et al. (+4 more)

The polarimetry of recent pulsar observations has provided a wealth of observational data with which to test physical theories of emission mechanisms, radiative transfer and even theories that extend beyond the Standard Model. In this work, we have outlined the data analysis of the polarisation time series data of a population of 513 pulsars from the Thousand Pulsar Array observing programme, laying the foundation for building the MeerKAT Thousand-Pulsar Polarization Array as a probe for ultralight Axion-Like Dark Matter (ALDM). From this large dataset we have focused on the temporal trends in the observed polarisation angle (PA) through a measure we call the PA offset, and characterised the trends due to the effects of Faraday Rotation within the interstellar medium and the Earth's ionosphere, as well as generic white and red noise models that are estimated within a Bayesian MCMC analysis. Then, motivated by potential extra contributions to the rotation of the PA that may not be Faraday-like, arising from the proposed ALDM field, we have investigated a derived time dependence for the rotation measure (RM) required to explain the observed PA offset. Comparison of these estimates to RM values that are measured in typical pulsar studies, through a technique known as RM Synthesis, provides a probe of any wavelength-independent contribution to the rotation of the PA. Although we find no evidence for oscillatory behaviour within our dataset's observation timespan, we do find cases of deviation from the usual RM values in several `pulsars of interest', as well as long-term linear trends in the time evolution of Faraday rotation that have been presented in the literature before.
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All authors Michael Sarkis, Zi-Yan Yuwen, Yin-Zhe Ma, Tao Liu, Jing Ren, Patrick Weltevrede, Xiao Xue

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Visible inelasticity as a probe of tau flavor content of astrophysical neutrinos

Alex Y. Wen, Carlos A. Argüelles and Sergio Palomares-Ruiz

Astrophysical neutrinos provide a unique probe of neutrino flavor changes over cosmological baselines. While the tau component of the neutrino flux is expected to arise almost entirely from mixing, current measurements rely primarily on rare double-cascade signatures. We investigate a complementary method to measure the tau fraction using the visible inelasticity of starting track events in neutrino telescopes. Muonic decays of tau leptons produce tracks with systematically larger visible inelasticity than those from muon neutrino interactions, potentially enabling statistical separation of the two flavors. Using realistic IceCube exposures and detector performance, we show that this observable already yields competitive sensitivity to the tau-to-muon flux ratio, $R_{\tau\mu}$, achievable with existing data. This approach may further enable flavor measurements of individual sources and the selection of tau-enhanced source catalogs. Starting-track inelasticity thus provides a powerful and immediately accessible probe of astrophysical neutrino flavor and of potential physics beyond standard neutrino mixing.
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Earth and Planetary Astrophysics

Next-generation Exo-REM atmospheric models: application to VHS 1256 b to emulate patchy clouds

Alice Radcliffe, Benjamin Charnay, Anne-Marie Lagrange et al. (+7 more)

Condensate clouds are a defining feature of brown dwarf and exoplanet atmospheres, producing a broad range of colours on the CMD and giving rise to spectral features such as the distinct $\sim 10 \mu$m spectral imprint. Cloud cover is likely to be heterogeneous in many objects, with observed rotational variability providing evidence for the presence of thick and thin cloud regions rotating in and out of view. Yet current 1D atmosphere models often fail to reproduce the spectra of highly cloudy substellar objects, especially those with complex cloud structures. We address these limitations by upgrading the Exo-REM atmosphere model, and by devising a more nuanced approach to describe heterogeneous cloud cover with pre-computed 1D grids. We present new Exo-REM grids, hereafter Exo-REM k26, featuring critical updates: (1) the incorporation of a cloud sedimentation parameter, $f_{sed}$, to govern cloud opacity, thereby enabling even the reddest of objects to be accessed on a CMD, revealing a trend of decreasing $f_{sed}$ along the L–T transition (2) the substantial update of molecular opacities and abundances used, including new experimentally validated alkali line lists, and (3) the implementation of strict convergence criteria that entirely avoid unstable model solutions. Correcting an erroneous $\text{CH}_3\text{D}$ abundance leads to spectral changes for low-$T_{eff}$ objects. Applying Exo-REM k26 to the cool GJ 504 b thus leads to a revision of its parameters ($T_{eff} = 473^{+14}_{-12}$ K, $\log g = 4.0 \pm 0.1$ dex). For the variable VHS 1256 b, a two-column framework that emulates cloud heterogeneities achieves an improved global fit over a single 1D model. A ~60-40% split of thick and thin clouds best describes its atmosphere, further confirming the presence of patchy clouds. This reproduces the strong $10 \mu$m silicate absorption in the JWST data of VHS 1256 b.
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All authors Alice Radcliffe, Benjamin Charnay, Anne-Marie Lagrange, Flavien Kiefer, Bruno Bézard, Simon Petrus, Paulina Palma-Bifani, Matthieu Ravet, Jérémy Leconte, Gabriel-Dominique Marleau

Astrophysics of Galaxies

Equilibrium Core and Vortex Solutions of Bose Einstein Condensate Dark Matter around a Black Hole

Ivan Alvarez-Rios and Francisco S. Guzman

We present the construction of stationary solutions of Bose-Einstein condensate dark matter (BECDM) around a point-like gravitational source representing a black hole. The problem is formulated for general axisymmetric configurations, and we focus on two cases: the ground-state core solution and the first nonzero winding number configuration corresponding to a line vortex solution. The stationary equations are solved using an imaginary-time approach, which enables the construction of families of solutions across a wide range of self-interaction and black hole masses. We analyze the impact of these parameters on the density distribution and on the stability properties of the solutions, assessing stability through the turning point criterion based on the enthalpy functional, which allows us to identify stable and unstable branches along each family of solutions. It has been shown in the past that spherical core solutions act as attractors in the collapse of BECDM around black holes in the non-interacting case ($g=0$), supporting their astrophysical relevance. In the present work, the existence of a maximum mass for configurations with attractive self-interaction ($g<0$) allows us to infer the parameter range in which such solutions may also arise in this regime. Building on this picture, we show that stable vortex solutions of BECDM can also exist in the presence of a black hole, whose stability properties suggest that these configurations may likewise be compatible with physically relevant formation scenarios.
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Solar and Stellar Astrophysics

Using GALEX UV Excess to Search for Metal-poor Halo Stars

Chase L. Smith, Maxwell Moe, Megan Frank et al. (+10 more)

Metal-poor solar-type stars display a significant reduction in metal-line blanketing at short wavelengths, leading to an excess of near-ultraviolet (NUV) flux compared to their metal-rich counterparts. We utilize GALEX NUV and $\it{Gaia}$ DR3 photometry along with ground-based spectroscopy to establish a correlation between NUV excess and [Fe/H]. We construct a sample of 492 solar-type (F5-G9) halo stars with NUV excess and measured metallicitices. We perform our own observations with the KOSMOS spectrograph at Apache Point Observatory's 3.5m telescope to measure the abundances of 13 halo stars, 11 of which did not have previous metallicity measurements. Our targeted 13 halo stars span $-$2.92 $<$ [Fe/H] $<$ $-$1.97 and are all $\alpha$ enhanced with [$\alpha$/Fe] = 0.05-0.73. For our full sample of 492 objects, we find an anti-correlation between NUV excess and [Fe/H] that is statistically significant at the 8$\sigma$ level. GALEX NUV excess can be used to distinguish very metal-poor (VMP) stars ([Fe/H] $<$ $-$2) from their metal-rich counterparts. However, there is significant dispersion in the relation due to NUV chromospheric variability caused by rotational effects and magnetic cycle activity. The NUV chromospheric variability inhibits our ability to reliably distinguish extremely metal-poor (EMP) stars ([Fe/H] $<$ $-$3) from VMP stars based on photometry alone. UV spectra of EMP halo stars are needed to better calibrate their atmospheric properties and variability.
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All authors Chase L. Smith, Maxwell Moe, Megan Frank, Raven Cilley, Javier Fregoso, Alexander Gleason, Ella Morton, Grace Nelson, Mary Kate Petrykovets, Daniel Reshan, Kaitlyn Schultz, Daniel A. Dale, Nikhil Patten

Earth and Planetary Astrophysics

Ejected Surface Regolith as a Potential Source Material for Centaur Rings

Kaustub Parvir Anand, David A. Minton and Julie Brisset

Ring systems have been observed around Centaur Chariklo (10199) and other small bodies but their origin and dynamical histories are still debated. These small body ring systems challenge conventional models for the origin of planetary rings, especially when considering Centaurs' often erratic cometary activity, their non-spherical shapes, and their relatively short dynamical lifetimes (~$10^7$ years). A collisional origin for these rings is disfavored based on the low probability of collisions within their lifetimes, and so their mechanism of formation remains an open question. In this work, we use Swiftest, a N-body integrator with collisional fragmentation and higher-order gravitational harmonics, to test a hypothesis that rings could be formed from regolith ejected from a cometary outburst that is subsequently captured into a stable orbit. We show that ejected surface regolith is captured in orbit around ellipsoidal Centaurs like Chariklo and Chiron to form a proto-ring disk for at least 100 rotations. This captured disk may serve as a starting point that can evolve into observed ring systems. Inter-particle collisions and the ellipsoidal gravity field facilitate this capture. Among the tested scenarios, a landslide or avalanche-like ejection from the equatorial plane shows the highest rate of capture, ~30 - 90% depending on the initial ejection parameters. This implies that rings could be an indicator of past activity on a Centaur and may be a more common feature among Centaurs depending on their shape and frequency of outbursts.
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Solar and Stellar Astrophysics

Multi epoch spectroscopic variability of the B supergiant HD75149

J. Chamoun-Contreras, C. Arcos, N. Machuca et al. (+6 more)

Massive stars continuously enrich the surrounding interstellar medium by supplying it with stellar material driven by their powerful winds. B supergiant stars (BSGs) in particular are a type of massive star characterized by strong winds and notable photometric and spectroscopic variability. We aim to conduct a pilot study of the optical spectroscopic variability of the BSG HD75149 between 2004 and 2025. Its extended temporal baseline and pronounced variability amplitude make it particularly well suited for investigating the physical origin of the observed short-term variability within a consistent hydrodynamical and radiative-transfer framework. We analyzed 25 nightly averaged optical spectra obtained with different instruments and telescopes, some of them with observations over several consecutive days. We measured the radial velocities (RVs) and equivalent widths (EWs) of 17 spectral lines (H, HeI, SiIII, NII, MgII, CII). We modeled the Halpha emission, absorption, and P-Cygni profiles using the ISOSCELES grid and the delta-slow hydrodynamic regime. Halpha shows variability in intervals of a few days, including P-Cygni changes, while metal lines show small RV amplitudes, consistent with pulsating oscillations. The largest variation in the mass-loss rate corresponds to an increase of a factor of 1.8 within four days. In contrast, the terminal velocity remains barely affected during the same time interval. The pronounced variation observed in hydrogen lines, in contrast with the variability of other lines, suggests that it is due to mass-loss rate episodes driven by a slow wind occurring on a timescale comparable to photometric variations. We found no evidence of a close binary companion in the sample used, but we cannot completely exclude the possibility of a wide or low-inclination companion.
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All authors J. Chamoun-Contreras, C. Arcos, N. Machuca, C. E. Perez-Ramirez, L. S. Cidale, M. Curé, I. Araya, D. Turis-Gallo, M. Hadjara

Instrumentation and Methods for Astrophysics

Kolmogorov–Arnold Networks as Implicit Regularizers: Noise Robustness and Interpretability for Stellar Classification

Kristian Sestak

This paper tests whether Kolmogorov–Arnold Networks (KAN 2.0) are genuinely more noise-robust than Multi-Layer Perceptrons (MLP) and XGBoost for stellar classification (star/galaxy/quasar, 100,000 SDSS DR17 objects). A naive comparison suggests so: KAN retains +9 percentage points over MLP at SNR=5. But equalizing baseline accuracy via weight decay eliminates the gap – a properly regularized MLP matches KAN to within 1 p.p. at all SNR levels, both with and without spectroscopic redshift. The same holds on an independent DESI DR1 sample with different photometric bands. KAN's robustness thus traces to implicit regularization by C^2-smooth B-spline activations, not to architecture. Per-class analysis (20 trials) shows that stars degrade fastest (F1: 0.97 to 0.75 at SNR=5), while QSOs remain stable. KAN's native feature importance and SHAP on MLP produce different rankings (Spearman rho = -0.37), capturing complementary aspects of the classification. Colour-index features (u-g, g-r, r-i, i-z) widen KAN's relative advantage, and a hybrid pipeline routing uncertain MLP predictions to KAN improves low-SNR accuracy. KAN is best understood as a convenient auto-regularizer whose genuine advantage is built-in interpretability.
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High Energy Astrophysical Phenomena

Nebular Fingerprints of a Violent White Dwarf Merger: 3D NLTE Modelling of Type Ia Supernovae

J. M. Pollin, R. Pakmor, L. J. Shingles et al. (+6 more)

Binary systems composed of two carbon-oxygen white dwarfs (WDs) are a leading progenitor candidate for Type Ia supernovae. One widely discussed scenario is the dynamically driven double-degenerate double-detonation (D$^6$) of a sub-Chandrasekhar-mass WD binary, where detonations are triggered by dynamical interaction. However, some systems are expected to undergo violent mergers, in which the primary ignites through direct carbon ignition as the secondary strikes its surface. We present the first 3D nebular-phase radiative-transfer calculations of a violent merger, using a $1.1 M_\odot$ and $0.7 M_\odot$ sub-Chandrasekhar binary. Our simulations employ a full NLTE (non local thermodynamic equilibrium) treatment of excitation and ionisation, including non-thermal electron contributions. By comparing 1D and 3D realisations, we show that multidimensional modelling improves the ionisation state and reveals features absent from 1D calculations, most notably [O I] from unburned material associated with the secondary. The model reproduces much of the panchromatic spectrum of the normal SN 2021aefx, but underpredicts [Ni II] while producing strong high-ionisation stable-Ni features, illustrating that stable-Ni signatures depend not only on abundance, but also on ionisation state. Although the model does not reproduce the strong [Ar II] and [Ne II] emission observed in the 03fg-like SN 2022pul, our calculations suggest that this event may require a similar merger configuration, involving full disruption of the secondary or a more massive companion with more extensive burning. Finally, viewing-angle variation is substantial, with signatures distinct from D$^6$-like scenarios, suggesting that JWST nebular samples, combined with multidimensional modelling, can discriminate between channels.
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All authors J. M. Pollin, R. Pakmor, L. J. Shingles, F. P. Callan, S. A. Sim, L. A. Kwok, C. E. Collins, F. K. Roepke, A. L. McGarrity

High Energy Astrophysical Phenomena

JWST's Dusty Blue BOAT – GRB 221009A

Nguyen M. Khang, Gavin P. Lamb, Helena-M.S. Grabham et al. (+6 more)

GRB 221009A, the Brightest Of All Time (BOAT), presents a challenge for afterglow modelling due to its low Galactic latitude and consequent high line-of-sight extinction. This has led to a wide range of conflicting values for the optical spectral index and dust extinction in the literature. We present a re-analysis of the afterglow spectra, using VLT X-Shooter data at 0.5, 4, and 10.5 days, and JWST NIRSpec$/$MIRI data at 13.3 days post-burst. We fit the data with single and smoothly broken power-law models and perform a joint fit with a double smoothly broken power-law (DSBPL) across all epochs. Our analysis reveals a strong degeneracy between the assumed extinction and the inferred intrinsic spectral index, particularly in the optical, explaining the diversity of previous results. The joint DSBPL fit yields a total line-of-sight extinction of $A_{V} = 4.40 \pm 0.01$ and a blue continuum, with an intrinsic spectral index of $\beta = 0.447 \pm 0.001$. Although marginally preferred by the spectral fits, a wind medium can be rejected by the temporal evolution of the afterglow light curve. The fit spectral index and temporal decline are only consistent with a uniform density medium if an early jet break at $\sim 0.5-1.0$ days is invoked. Our results imply a hard electron distribution index of $p = 1.89 < 2$, challenging standard particle acceleration models and suggesting a narrow, energetic jet core dominates the early optical-to-X-ray emission.
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All authors Nguyen M. Khang, Gavin P. Lamb, Helena-M.S. Grabham, Conor M. B. Omand, Hamid Hamidani, Andrew J. Levan, Nial R. Tanvir, Valerio D'Elia, Luca Izzo

Instrumentation and Methods for Astrophysics

Three-dimensional Conditional Diffusion Models for Cosmological 21 cm Lightcone Emulation

Bin Xia and John H. Wise

We investigate conditional diffusion modeling for three-dimensional 21 cm lightcone emulation, focusing on cubes with a sky-plane size of $64\times64$ and a line-of-sight depth up to 1024 cells. Relative to earlier 2D studies, the 3D setting is substantially harder because memory limits enforce very small micro-batches while the underlying voxel distribution is highly skewed and long tailed. We perform controlled comparisons across preprocessing choices, dynamic-range compression settings, architecture depth, and training duration using $25{,}600$ training lightcones and validation ensembles at fixed parameter points. For validation, each reference parameter point contains 800 21cmFAST realizations with independent initial conditions, and we use 800 samples per model and per reference set for the reported ensemble comparisons. We evaluate generated lightcones with complementary diagnostics in both image and summary-statistic spaces: brightness-temperature slices, the global signal, the power spectrum, and reduced scattering coefficients. Across the tested configurations, preprocessing is the dominant factor governing stable training and the resulting physical fidelity. Among the configurations explored here, Yeo-Johnson preprocessing combined with moderate amplitude compression gives the most consistently favorable trade-off, with the strongest quantitative support coming from rankings based on the standard-deviation-normalized mean absolute error ($\mathrm{MAE}_{\rm std}$) of the global signal and qualitatively compatible behavior in the complementary diagnostics. At the same time, visually plausible 3D samples still retain measurable biases in two-point and higher-order statistics. We therefore view the present work as a simulation-level baseline for three-dimensional 21 cm emulation and for future studies that incorporate more realistic observational effects.
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Astrophysics of Galaxies

A Deep Study of the Spiral Galaxy W2246f

Evelyn J. Johnston, Sorya Lambert, Aparna Nair et al. (+10 more)

In this era of large surveys and statistical studies of galaxies, the beauty in the details of individual galaxies is often lost. We present a deep study of the spiral galaxy W2246f with MUSE, exploring the spatially-resolved stellar and ionized gas properties to understand how it formed and evolved over time. The unusually deep observations of this galaxy give us a rare opportunity to study this phenomenon with better spatial resolution than can normally be achieved with the current IFU surveys of galaxies at a similar redshift ($z\sim0.09$). We analyse the stellar and gas kinematics, as well as the spatially resolved stellar populations and gas properties, including gas metallicity and the dominant ionization sources. The derived properties include the stellar mass, radial profiles of luminosity- and mass-weighted mean ages and metallicities, and ionized gas characteristics such as E(B-V), H$\alpha$ extinction, dust-corrected H$\alpha$ flux, oxygen abundance using the O3N2 calibrator, and H$\alpha$-based star formation rate. Analysis of the stellar populations revealed a negative metallicity gradient, and the mass-weighted ages showed uniformly flat ages across the disc while the luminosity-weighted ages show a negative gradient. We find that the gas metallicity and star formation rate density also drop in the central region of the galaxy where the older luminosity-weighted stellar populations are found. Analysis of the WHAN and WHaD diagrams reveal that in fact the central region is retired while the rest of the disc is star forming. We conclude that W2246f is a nice example of a cLIER galaxy, where the central kpc is dominated by old, metal-poor stars with little star formation. The central LIER emission is primarily powered by hot evolved stars, while the rest of the disc displays ongoing star formation. These findings are consistent with a scenario of inside-out quenching.
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All authors Evelyn J. Johnston, Sorya Lambert, Aparna Nair, Alejandra Z. Lugo-Aranda, Manuel Aravena, Roberto J. Assef, Tanio Diaz Santos, Román Fernández Aranda, Hyunsung D. Jun, Guodong Li, Mai Liao, Devika Shobhana, Chao-Wei Tsai