Instrumentation and Methods for Astrophysics
Nautilus Space Observatory: Unveiling the Diversity and Origin of Sub-Neptunes with the Nautilus Space Observatory
Luis Welbanks, Kylie E. Hall, Julien de Wit et al. (+10 more)
Sub-Neptunes are the most common class of
planets in the
Galaxy, yet they have no
Solar System analog and remain poorly understood as a population. JWST observations have revealed atmospheres spanning a wide range of
metallicities, compositions, and cloud properties, driving active debates over whether warm sub-Neptunes harbor
liquid water oceans beneath H2-rich envelopes, maintain stratified H2/H2O interiors, or have well-mixed, metal-rich envelopes. Open questions also remain over what physical processes drive transitions between hazy and clear atmospheres. These are intrinsically population-level questions that single-target observations, however deep, cannot resolve. Here we argue that a sub-Neptune population survey with the Nautilus Space Observatory, a proposed constellation of large-diameter space
telescopes, would deliver the first statistical map of sub-Neptune atmospheric diversity, test competing classification schemes, identify habitable candidates, and serve as a pathfinder population for the eventual habitable-worlds search. These goals are achievable across the proposed mission classes for the constellation, and this architecture is uniquely well-matched to this science case since population-level questions demand sample size and a uniform observing strategy.
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All authors Luis Welbanks, Kylie E. Hall, Julien de Wit, Ana Glidden, Noah Tuchow, Ilaria Pascucci, Dániel Apai, Robin Wordsworth, Benjamin V. Rackham, Chia-Lung Lin, Raymond Pierrehumbert, Mercedes López-Morales, A. D. Feinstein
Instrumentation and Methods for Astrophysics
The Simons Observatory: Overview of the Cryogenic Half-wave Plate Polarization Modulators
Junna Sugiyama, Kyohei Yamada, Bryce Bixler et al. (+5 more)
The Simons Observatory (SO) is a ground-based
Cosmic Microwave Background (CMB) experiment that is located in the Atacama plateau. The Small Aperture
Telescopes (SATs) of SO are optimized for polarimetry on the degree scale. Atmospheric $1/f$ contamination of the CMB signal poses a significant challenge for observations at this angular scale. In order to control the $1/f$ noise, the SATs utilize a Cryogenic Half-Wave Plate (CHWP) in their optics. The CHWP modulates the polarization signal to a higher frequency to separate it from the unpolarized atmospheric noise. Precision measurements of the CHWP rotation angle are required to successfully recover the target polarized signals. We present a method to reconstruct the CHWP rotation angle that achieves a noise level of 0.16 $\mu\mathrm{rad\sqrt{s}}$, meeting our requirement.
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All authors Junna Sugiyama, Kyohei Yamada, Bryce Bixler, Daichi Sasaki, Yuki Sakurai, Kam Arnold, Nicholas Galitzki, Akito Kusaka
Solar and Stellar Astrophysics
Stellar masses and ages in Gaia Data Release 4 from the Final Luminosity Age Mass Estimator algorithm
Orlagh L. Creevey, Laia Casamiquela, Yveline Lebreton et al. (+23 more)
The masses and ages of
stars are key quantities for understanding exoplanetary,
stellar, and
galactic evolution. In the context of
Gaia, these parameters provide insights into the
stellar populations, helping to trace the formation and history of the
Galaxy. As part of the
Gaia Data Processing and Analysis Consortium (DPAC), the Final Luminosity Age Mass
Estimator (FLAME) pipeline processes
Gaia data to derive
stellar parameters comprising luminosities, radii, masses and ages. This paper discusses the methods and data used in FLAME for
Gaia Data releases and the expected performances of FLAME for the 4th
Gaia Data Release. FLAME comprises two main components: the first one, which is analytical, is used to estimate luminosity, radius, and radial velocity correction due to gravitational
redshift by exploiting the atmospheric, astrometric, and photometric parameters produced within
Gaia. The second is a model inference based on two main approaches: a classical minimization approach, and a
Bayesian framework. It aims to derive mass, age, and evolutionary stage. The two step implementation offers flexibility in handling photometric properties that are prone to systematic errors. Tests with simulated data, the Sun, and well characterised samples of
stars show that the methods in FLAME perform as expected, producing results in statistical agreement with the literature. We provide new
stellar fundamental parameters for some high velocity
stars,
stars with very low mass companions, and a selection of
stars in the Plato Field of View. In
Gaia Data Release 4 approximately 500 million sources will have results from the pipeline. [abridged]
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All authors Orlagh L. Creevey, Laia Casamiquela, Yveline Lebreton, Christophe Ordenovic, Frederic Thevenin, Morgan Fouesneau, Rene Andrae, Coryn A. L. Bailer-Jones, Frederic Pailler, Bernard Pichon, Carine Babusiaux, Angelique Barbier, Nicolas Baudeau, Nathalie Brouillet, Santi Cassisi, Bengt Edvardsson, Oleg Kochukhov, Georges Kordopatis, Alessandro C. Lanzafame, Andreas Korn, Szabolz Meszaros, Camila Navarrete, Clement Robin, Rosanna Sordo, Caroline Soubiran, Daniel R. Reese
High Energy Astrophysical Phenomena
Constraining leptonic and hadronic gamma-ray emission from HESS J1825-137 and its environment
Rubens Costa Jr. and R. C. Anjos
We present a broadband spectral analysis of the $\gamma$-ray emission from the
pulsar wind nebula HESS~J1825$-$137, combining observations from
Fermi Large Area
Telescope (
Fermi-LAT), High Energy Stereoscopic System (H.E.S.S.), High-Altitude Water Cherenkov Observatory (HAWC), and Very Energetic Radiation Imaging
Telescope Array System (VERITAS) across the $\sim 0.1$~GeV–$160$~TeV energy range. The spectral energy distribution is modelled under purely leptonic, purely hadronic, and lepto-hadronic scenarios using the Naima radiative modeling framework with Markov Chain Monte Carlo parameter estimation. Model comparison via the
Bayesian Information Criterion reveals that the baseline GeV–TeV data favour a purely leptonic interpretation, while the inclusion of simulated Cherenkov
Telescope Array Observatory (CTAO) observations or Large High Altitude Air Shower Observatory (LHAASO) ultra-high-energy (UHE; $E_{\gamma} \ge 100\,\mathrm{TeV}$) measurements shifts the preference toward models incorporating a hadronic component ($\Delta\mathrm{BIC} = -28.87$ and $-7.89$, respectively). The inferred electron energy budget for the baseline GeV–TeV
dataset, $W_e = 4.25 \times 10^{48}$~erg, is consistent with previous estimates reported in the literature. The
proton energy budget, $W_p \approx 2.5 \times 10^{48}$~erg, is energetically compatible with $pp$ interactions in the dense molecular environment adjacent to the nebula. These results demonstrate that precise spectral measurements above $\sim 10$~TeV, where Klein–Nishina suppression of inverse Compton emission creates a window for hadronic processes, are essential to establish the dominant emission mechanism in this source.
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Instrumentation and Methods for Astrophysics
Leveraging Multimodality for Real-Time Classification of Transients and Variables found by the Zwicky Transient Facility
Ved G. Shah, Nabeel Rehemtulla, Adam A. Miller et al. (+13 more)
Modern time-domain surveys such as the Zwicky Transient Facility (ZTF) generate hundreds of thousands of alerts each night, making real-time decisions for follow-up observations a central challenge in time-domain astronomy. Robust early classification is crucial for making informed decisions, but is hindered by sparse light curves and degeneracies between classes. In this work, we leverage multimodality to substantially improve real-time classification and demonstrate the practicality of our approach by deploying our model on the ZTF alert stream. Building on the Online Ranked Astrophysical CLass
Estimator (ORACLE), we introduce the ORACLE-2 models, which combine light curves, metadata, and images for real-time hierarchical classification. Using both real and simulated
datasets, we show that incorporating additional modalities consistently improves classification performance. On observations from ZTF's Bright Transient Survey, our best-performing model, ORACLE-2 Omni, achieves a macro F1 score of 0.73 – an improvement of up to 11% over models using light curves and metadata alone, and up to 40% over light-curve-only models, with the strongest gains realized at early times. To demonstrate applicability to the Legacy Survey of Space and Time, which will increase alert volume by more than an order of magnitude, we train a light curve + metadata variant on the simulated ELAsTiCC
dataset. This model achieves a macro F1 score of 0.88, an improvement of up to 13% over the light-curve-only variant, matching the performance of other state-of-the-art models. Finally, we quantify the trade-offs between performance and throughput, identifying regimes where
multimodal approaches offer the greatest benefit. These results show that combining multiple modalities improves early-time classification, enabling more effective triage of high-volume alert streams for current and future time-domain surveys.
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All authors Ved G. Shah, Nabeel Rehemtulla, Adam A. Miller, Sushant Sharma Chaudhary, Michael W. Coughlin, Antoine Le Calloch, Matthew J. Graham, Joahan Castaneda Jaimes, Theophile Jegou du Laz, Ashish A. Mahabal, Frank J. Masci, Josiah Purdum, Reed Riddle, Jesper Sollerman, Anastasia Wei, Mansi M. Kasliwal
High Energy Astrophysical Phenomena
Dense, multi-phase accretion disk atmosphere in the low-luminosity state of black hole transientV4641 Sgr
Zuobin Zhang, Rob Fender, James H. Matthews et al. (+11 more)
We present soft X-ray spectroscopy of the black-hole X-ray binary V4641~Sgr with the XMM-Newton Reflection Grating Spectrometer (RGS). The RGS spectrum shows narrow emission features from N\,vi–vii and O\,vii–viii superimposed on a partially covered disk blackbody continuum. A blind Gaussian search confirms the presence of significant lines at the expected rest wavelengths. He-like triplet ratios (high $G$, low $R$) and full photoionization modelling both indicate a dense, photoionized
plasma. Small redshifted velocities of $\sim 540$–$720\ \mathrm{km\ s^{-1}}$ are suggested, which are consistent with quasi-static or slowly flowing gas away from the observer after accounting for systematics. Photoionization modelling requires two xstar components with an intermediate ionization parameter ($\log\xi \simeq 3.1$) and a low ionization parameter ($\log\xi \simeq 0.36$), respectively. The simultaneous EPIC-pn spectrum suggests highly ionized Fe emission structures, hinting at an additional, more highly ionized component. These results imply the existence of a radially extended, multiphase, and dense disk atmosphere in the source. We compare the source with other X-ray binaries showing similar emission lines. V4641~Sgr shares a similarly high inclination with other sources; however, the presence of low ionization emission lines distinguishes it from the rest.
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All authors Zuobin Zhang, Rob Fender, James H. Matthews, Jiachen Jiang, Honghui Liu, Alessandra Ambrifi, Teo Muñoz-Darias, Maxime Parra, Megumi Shidatsu, Menglei Zhou, Yuexin Zhang, Abdurakhmon Nosirov, Cosimo Bambi, Justine Crook-Mansour
Instrumentation and Methods for Astrophysics
The Rubin Observatory Target-of-Opportunity System in the First Year of Operations
Sean Patrick MacBride, R. Lynne Jones, Peter Yoachim et al. (+41 more)
The NSF/DOE Vera C. Rubin Observatory is a discovery machine, with unprecedented survey speed, which can be used to identify exotic astrophysical transients. In its
prime mission, the ten year Legacy Survey of Space and Time will use 3% of its total time for Target of Opportunity observations, which includes response to gravitational wave events, high energy
neutrinos, potentially-hazardous asteroids, and other astrophysical phenomena. Target of Opportunity observations exist outside of the usual LSST operational mode, requiring special
attention to maximize performance. We review the Rubin Target of Opportunity system during its first year of Rubin Observatory operations, the Targets of Opportunity pursued since LSST first light, and the overall efficiency of the system.
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All authors Sean Patrick MacBride, R. Lynne Jones, Peter Yoachim, Tiago Ribeiro, Leanne P. Guy, Shreya Anand, Erin Leigh Howard, Ian S. Sullivan, Daniel L. Wang, Eric C. Bellm, Robert Armstrong, W. M. Wood-Vasey, Alex Drlica-Wagner, Kenneth Herner, Gautham Narayan, Tatiana Acero-Cuellar, Federica Bettina Bianco, Igor Andreoni, Bruno O. Sánchez, John Banovetz, Anastasia Alexov, Erik Dennihy, Robert D. Blum, Yousuke Utsumi, Marcelle Soares-Santos, Robert H. Lupton, Keith Bechtol, Željko Ivezić, Kris Mortensen, Paulina Venegas, Yijung Kang, Alysha B. Shugart, Narayan Khadka, Kshitija Kelkar, Danica Žilková, Kevin Fanning, Christopher W. Walter, Chris Weaver, Fabian Araneda-Baltierra, Andreja Gomboc, J. Anthony Tyson, Colin Orion Chandler, Pedro H. Bernardinelli, Devanshi Singh
Astrophysics of Galaxies
Precision near-IR spectroscopy for understanding AGN physics and shed light on the H0 tension – SHARP Science Book
M. Signorini, V. N. Bennert, E. Dalla Bontà et al. (+3 more)
The persistent tension between early- and late-Universe measurements of the Hubble constant (H0) remains on of the most significant challenges in modern cosmology. The Spectroastrometry and Reverberation Mapping (SARM) method offers a promising, calibration-independent approach to address this issue by combining time-delay measurements of the Broad-Line Region (BLR) with interferometric angular size determinations. Current implementations of SARM, however, are limited by the difficulty of performing near-infrared reverberation mapping (RM) on the same emission lines observed by
GRAVITY, restricting applications to only a few bright AGN. We propose using the capabilities of SHARP, the next-generation near-infrared spectrograph for the Extremely Large
Telescope (ELT), to overcome these limitations. SHARP's sensitivity and multi-object spectroscopy will enable (1) efficient long-term monitoring of existing
GRAVITY targets with minimal time investment, and (2) systematic RM campaigns for the fainter AGN that will be observed by
GRAVITY+. These advances will give us precise infrared lags for tens of AGN, enabling
geometric distance measurements and a robust, calibration-free determination of H0. Beyond cosmology, SHARP will allow detailed studies of BLR structure and kinematics in the infrared, advancing our understanding of AGN physics and with repercussion on the measurements of Supermassive Black Holes (SMBH) masses.
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All authors M. Signorini, V. N. Bennert, E. Dalla Bontà, F. Ricci, T. Treu, L. Villafaña
Astrophysics of Galaxies
The evolution of high-z proto-star clusters into local globular clusters
A. Della Croce, E. Vesperini, R. Pascale et al. (+4 more)
The James Webb Space
Telescope (JWST) detected numerous massive and relatively compact
stellar clumps around proto-
galaxies at high
redshift (z>0.5). Their properties suggest that these systems may represent proto-globular clusters (GCs), but their possible connection to local old GCs is poorly understood. In this Letter, we explore the dynamical
evolution of proto-
star clusters, building the missing evolutionary link between high-z systems observed by JWST and local GCs. Our simulations include the effects of
stellar interactions,
stellar evolution, and the strong time-dependent cosmological
tidal field in which these proto-
star clusters evolve. We also explore the role of multiple
stellar populations and
stellar-mass black holes (BHs), two fundamental ingredients in
stellar cluster dynamics. We show that systems hosting multiple populations (as routinely observed in local GCs) are more likely to endure the early strong
tidal field than single-population clusters. In addition, after 12 Gyr, such systems have properties consistent with those of
Galactic GCs. Our work confirms that the high-z clumps observed by JWST can be the progenitors of the local GCs. Finally, we show that a population of
stellar-mass BHs within a proto-
star cluster favors its disruption, but that surviving systems can retain a sizable population of BHs.
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All authors A. Della Croce, E. Vesperini, R. Pascale, A. Askar, F. Calura, E. Dalessandro, M. Giersz
Earth and Planetary Astrophysics
Prospects for Panspermia via Interstellar Objects like 3I/ATLAS
Shokhruz Kakharov and Abraham Loeb
We study the feasibility of natural and directed panspermia via interstellar objects (ISOs) like 3I/ATLAS. The paper is organized around two questions. First, could natural panspermia occur if microbes or biomolecules survived inside shielded ice and were later exposed during perihelion and outbound activity? Second, could directed panspermia occur if a technological civilization planted life-bearing material inside or onto an icy ISO so that it later transported life through the Milky Way? We combine data on 3I/ATLAS with order-of-magnitude thermal, biological, and mission constraints. SPHEREx provides the volatile and organic context through CO$_2$, H$_2$O, CO,
dust, and a broad C–H feature, while JWST/MIRI provides the first direct CH$_4$ detection in an interstellar object and confirms an unusual volatile inventory, including enhanced CO$_2$:H$_2$O and CH$_4$:H$_2$O ratios. We distinguish dormant interstellar cruise from active perihelion. Natural panspermia is plausible as microbes can survive or repair damage in ice films, veins, or frozen
matrices at very low metabolic rates. Methane production is more nuanced. Frozen survival metabolism would require $\sim10^{14}$–$10^{15}$ kg of biomass to match the JWST CH$_4$ rates, but active methanogenic archaea in warm,
liquid, substrate-rich settings can produce methane many orders of magnitude faster, reducing the required biomass in optimistic laboratory-rate comparisons. Directed panspermia faces a different challenge: a direct 60 km s$^{-1}$ impact releases $1.8\times10^9$ J kg$^{-1}$, hundreds of times the specific energy of TNT, and would destroy a biological capsule. 3I/ATLAS-like objects are therefore best treated as test cases for panspermia diagnostics rather than as evidence for life. Natural panspermia requires preservation plus a credible
liquid-water or near-surface activation pathway.
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Solar and Stellar Astrophysics
Spectroscopic Monitoring of Metal Lines in Polluted White Dwarfs
Laura K. Rogers, Michael M. Shara, Amy Bonsor et al. (+12 more)
The disruption and
accretion of planetary material onto white
dwarfs is expected to be inherently dynamic and
stochastic, potentially driving variability in the
accretion rate and therefore the shape and depth of the photospheric metal absorption lines. This paper presents an 18-year optical spectroscopic monitoring campaign of five warm (11,000-23,000K) polluted white
dwarfs with sinking timescales of days-months, observed using Magellan/MIKE and SALT/HRS to directly test this prediction. At four of the five systems, no statistically significant variability is detected over baselines of 15-18 years corresponding to hundreds to thousands of
diffusion timescales, with inferred
accretion rates stable to within 15-30% (1$\sigma$) showing remarkably stable
accretion on decadal timescales. This implies that either the processes maintaining the
accretion of the disrupted planetary material are stable on the same timescales, or that currently uncharacterized photospheric processes act to smooth observable abundance variations on these timescales. The one exception, WD 0106$-$328, shows statistically significant variability in the 4481A Mg II doublet from the ground-based data. Yet no significant equivalent width or abundance changes are seen between two Hubble Space
Telescope ultraviolet spectra taken in 2016 and 2025, despite probing a larger set of transitions. This may imply that the ground-based observations witnessed a
stochastic excursion from a stable baseline
accretion rate, rather than a sustained change in the bulk
accretion rate.
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All authors Laura K. Rogers, Michael M. Shara, Amy Bonsor, Siyi Xu, Érika Le Bourdais, Patrick Dufour, John Debes, Omri Nolan, Ted von Hippel, Erik Dennihy, Simon Hodgkin, Andrew Swan, Mariona Badenas-Agusti, Mark C. Wyatt, Tim Cunningham
Astrophysics of Galaxies
How can we finally see the first light? Status and perspective in the search for Population III stars
Alessandra Venditti, Daniel Schaerer, Erik Zackrisson et al. (+26 more)
Finding the first (Population III or Pop III)
stars is one of the fundamental quests of astronomy, aiming to deliver the missing link in how
stars form at early
cosmic times. Yet their initial mass function, formation sites and feedback remain highly uncertain, as well as the timing and
topology of the transition to metal-enriched
star formation. The observability of their peculiar spectral features is also debated, due to their short lifetime and faintness. This review summarizes current theoretical expectations for Pop III
star formation, and the main observational strategies that have been adopted to constrain their properties across
cosmic time, including near-field cosmology studies, direct searches for extremely metal-poor
star-forming complexes and/or hard-ionizing spectral signatures at high and intermediate
redshifts, and prospects for identifying Pop III activity up to
Cosmic Dawn. The combination of JWST spectroscopy, time-domain searches,
lensing surveys,
stellar archaeology, absorption-line studies, as well as improved simulations, is yielding a growing number of observational candidates and narrowing the allowed parameter space for the first
stars, setting the stage for a “golden era” of Pop III searches.
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All authors Alessandra Venditti, Daniel Schaerer, Erik Zackrisson, Yoshihisa Asada, Harley Katz, Stefania Salvadori, Eros Vanzella, Julian B. Muñoz, Anatole Storck, Andrew J. Bunker, Alessandro Trinca, Dirk Scholte, Fabio Pacucci, Pablo G. Pérez-González, Seiji Fujimoto, Corinne Charbonnel, Roberto Maiolino, Andrea Ferrara, Mauro Giavalisco, Raffaella Schneider, Josephine Baggen, Hakim Atek, Volker Bromm, Karina Caputi, Laure Ciesla, Pratika Dayal, Chiaki Kobayashi, Marco Castellano, Paola Santini
Astrophysics of Galaxies
Far-infrared observations of dust in Ly$\alpha$ emitters at z=2-6
Rahul Rana, Julie L. Wardlow, Thomas M. Cornish et al. (+3 more)
The bright Ly$\alpha$ line is regularly used to identify high-
redshift star-forming
galaxies known as Ly$\alpha$ emitters (LAEs). However, Ly$\alpha$ is affected by resonant scattering and
dust absorption making interpretation of its brightness challenging without additional observations. We use SCUBA-2, PACS and SPIRE data to investigate the far-infrared emission, Ly$\alpha$ escape fraction ($f{esc}$(Ly$\alpha$)) and infrared excess (IRX=LIR/LUV) in $\sim$4000 LAEs at z=2.2-6 from SC4K. Five LAEs, all hosting AGN, are individually detected with fluxes $S_{850}$ = 3.7-5.5 mJy at 850$\mu\mathrm{m}$. Stacking is used to probe the average emission from all individually undetected LAEs, though the stacks are undetected at all wavelengths (e.g. $S_{850}$ < 0.09 mJy; 3$\sigma$). We group the sample into bins of
redshift,
stellar mass, Ly$\alpha$ luminosity and AGN status. Most subsets are undetected but LAEs containing AGN and that have high
stellar masses ($M_{\star} = 10^{10} - 10^{12}\, M_{\odot}$; including and excluding AGN) are detected at most wavelengths, suggesting that
stellar mass and AGN heating may be enhancing the
dust visibility. Individually detected LAEs and detected stacks have $f{esc}$(Ly$\alpha$)=1-7%, while all undetected stacks $\geq$ 10%. All LAEs together average over > 21% and display significant scatter, suggesting a clumpy ISM
dust distribution. Non-zero $f{esc}$(Ly$\alpha$) in massive and AGN-hosting LAEs suggests ionizing
photons may escape even from dusty
galaxies, challenging the idea that dusty
galaxies are poor leakers. Examination of the IRX-$\beta_{UV}$ relation shows LAEs have higher IRX than typical
star-forming
galaxies at similar
redshifts. However, our detections tend to favour more massive, AGN-hosting systems and deeper observations are therefore needed.
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All authors Rahul Rana, Julie L. Wardlow, Thomas M. Cornish, Pascale H. Desmet, David Sobral, João Calhau
Instrumentation and Methods for Astrophysics
Rubin M1M3 Dynamic performance : stability and actuation during operations
HyeYun Park, Petr Kubánek, Kshitija Kelkar et al. (+20 more)
The Vera C. Rubin Observatory is preparing to commence the Legacy Survey of Space and Time with the fully integrated Simonyi Survey
Telescope. To verify that the primary/tertiary (M1M3) mirror system is ready to meet the demanding survey requirements, dynamic tests of the 8.4 m, 53 ton M1M3 system were conducted to assess safety, stability, and image quality under realistic operating conditions. The M1M3 is supported by 156 pneumatic force actuators and positioned, relative to its mirror
cell, by six hardpoint actuators that together must counteract gravitational and inertial loads during rapid
telescope motion. The Rubin Observatory
telescope mount is capable of moving at a rate that meets its nominal motion requirements, and can approach it maximum allowable values that are 50 percent higher. Even at just 20 % of its operational speed, it is an exceptionally fast motion for such a large structure. After slewing, the system must stabilize and dampen vibrations within 5 seconds to ensure image quality during observations. Achieving this rapid settling requires precise control of 156 force actuators, which must adjust dynamically with changes in
telescope elevation to compensate for
gravity effects. We present results for M1M3 from a comprehensive series of TMA dynamical tests spanning the operational envelope of slew velocities and accelerations. The analysis evaluates elevation axis balancing and lookup table updating as we install the M1M3 mirror; slew-and-settle behavior, force response and stability of the pneumatic actuator system across
telescope attitudes including responses to the earthquake. The results demonstrate the readiness of the M1M3 subsystem for routine survey operations and provide validation data for ongoing performance modeling.
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All authors HyeYun Park, Petr Kubánek, Kshitija Kelkar, Ignacio Sevilla-Noarbe, Andrea Jeremie, Brian Stalder, Bruno C. Quint, David Sanmartim, Dominique Boutigny, Douglas R. Neill, Erik Dennihy, Felipe Daruich, Freddy Muñoz Arancibia, Kevin Fanning, Kevin Reil, Laura Toribio San Cipriano, Malhar Sonaniskar, Marina S. Pavlovic, Noah Gonzalez, Paulina Venegas, Sandrine Thomas, Tiago Ribeiro, Yijung Kang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Cosmology with a Non-minimally Coupled Dark Matter Fluid II. Cosmological Perturbations
Samuele Silveravalle, Andrea Lapi, Francesco Benetti et al. (+1 more)
We extend our study of a cosmological scenario in which dark matter is non-minimally coupled to
gravity at the fluid level. In previous work, we showed that this interaction can drive an early phase of accelerated expansion, addressing the horizon and flatness problems, and can also lead to a cosmological bounce in the presence of negative spatial
curvature. Here we analyse the
evolution of linear perturbations in this framework. We derive the equations governing scalar, vector and tensor perturbations, and obtain analytic solutions in the relevant cosmological regimes. We find that perturbations generated during the accelerated expansion phase produce a strongly blue scalar power spectrum and are therefore incompatible with observations. By contrast, if
primordial fluctuations are generated during the contracting phase of a bouncing solution, the model yields an approximately scale-invariant scalar power spectrum while keeping the tensor-to-scalar ratio compatible with current bounds. Although our treatment relies on simplifying approximations that should be refined in future work, these results indicate that an observationally viable
primordial spectrum can be obtained only with a bouncing solution, and hence with a non-singular early-time
evolution.
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All authors Samuele Silveravalle, Andrea Lapi, Francesco Benetti, Stefano Liberati
High Energy Astrophysical Phenomena
Anomalous Air Showers and What They Reveal About Hadronic Interactions and Cosmic-ray Masses
Stijn Buitink, Vital De Henau, Sjoerd Bouma et al. (+28 more)
The identification of the sources and acceleration mechanisms of
cosmic rays require precise measurements of their mass composition. Currently, the most reliable method is to measure the atmospheric depth at which
cosmic ray air showers in our atmosphere reach their maximum (\Xmax). However, the hadronic interaction properties that govern the longitudinal development of air showers are not precisely known, which is a major source of systematic uncertainty on the mass composition. SKA-Low will observe
cosmic rays in the 10$^{16}$ - 10$^{18}$ eV energy range with unprecedented resolution and bandwidth. This allows for a much more detailed reconstruction of the longitudinal shower
evolution, which can be used to gain better understanding of the hadronic interactions, as well as the primary mass composition. After the first interaction of the
cosmic ray with an atom in an air molecule, the secondary particles still carry a significant fraction of the total energy. When one of these particle travels very far before interacting again, it produces a sub-shower that can be recognized as a secondary bump in the longitudinal profile. Simulations have demonstrated that SKA-Low can resolve such double bump profiles by virtue of its high
antenna density and broad bandwidth. In this chapter, we demonstrate how double-bump showers and other anomalous longitudinal developments can be used to constrain hadronic interaction properties, and to determine the mass composition of
cosmic rays in the
Galactic-to-extragalactic transition region.
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All authors Stijn Buitink, Vital De Henau, Sjoerd Bouma, Justin Bray, Arthur Corstanje, Edwin Dickinson, Brian Hare, Andreas Haungs, Haoning He, Jörg Hörandel, Tim Huege, Clancy James, Philipp Laub, Xingyu Li, Hermann-Josef Mathes, Katharine Mulrey, Anna Nelles, Subhadip Saha, Felix Schlüter, Olaf Scholten, Ralph Spencer, Christopher Sterpka, Karen Terveer, Satyendra Thoudam, Gia Trinh, Paulina Turekova, Darko Veberic, Keito Watanabe, Chao Zhang, Pengfei Zhang, Yi Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Modified Cosmology from Mass-to-Horizon Relation: Background Evolution
Pranav Prasanthan, Hussain Gohar and Vincenzo Salzano
We investigate the cosmological implications of the mass-to-horizon relation, which provides a unified framework for thermodynamically consistent generalized horizon-
entropy functionals. Using the Cai-Kim formulation of the first law of thermodynamics, we derive the corresponding modified Friedmann equations and examine the resulting background
evolution. We find that cosmological viability sharply restricts admissible deviations from the Bekenstein-Hawking area law: phenomenologically acceptable scenarios are confined to a narrow neighborhood of the standard
entropy, while more pronounced deviations generically spoil the standard radiation-matter-dark-energy sequence. Power-law
entanglement corrections can give rise to a moderate early-dark-energy component, but only within a tightly constrained region of parameter space, whereas
quantum-
gravity corrections are suppressed by the Planck scale and remain observationally irrelevant. Consequently, all viable models predict a $\Lambda$CDM-like cosmological background at the present epoch. These findings demonstrate that background cosmology alone imposes stringent constraints on thermodynamically consistent generalized
entropy constructions of this class.
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Astrophysics of Galaxies
SchwarMAX: a GPU-friendly Schwarzschild orbit-superposition modelling framework
HanYuan Zhang, David Chemaly, Eugene Vasiliev et al. (+3 more)
The Schwarzschild orbit-superposition method is a highly flexible dynamical modelling tool. It constrains the mass distribution of a
galaxy using line-of-sight velocity and photometric observations. However, constructing such a dynamical model of a
galaxy is computationally expensive. We present SchwarMAX, a new publicly available GPU implementation of the Schwarzschild orbit-superposition method. The GPU-native code is significantly faster than other implementations, with entire model construction taking around a second on GPU A100. Using SchwarMAX, we can explore the distributions of both baryonic and dark matter in a
galaxy across a high-dimensional parameter space. We demonstrate its performance using mock integrated-field spectroscopic unit data generated from an N-body simulated barred
galaxy. We explore the 12-dimensional space of disc, bar and
halo parameters using Markov Chain Monte Carlo. The density profiles and the bar pattern speed of the
galaxy are recovered with good accuracy. We show that the code can be applied to barred
galaxies across a wide range of inclination angles and can be easily extended to other
stellar systems, such as elliptical and
dwarf galaxies.
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All authors HanYuan Zhang, David Chemaly, Eugene Vasiliev, Vasily Belokurov, N. Wyn Evans, Juntai Shen
Cosmology and Nongalactic Astrophysics
The Quiescent Sloshing Core of Abell 496 with XRISM
Angie Veronica, Thomas H. Reiprich, Naomi Ota et al. (+9 more)
Gas motions provide insight into the dynamical history and physical processes within
galaxy clusters. We investigate the kinematics of the ICM in the core of A496, a nearby, X-ray bright, strong cool-core cluster, using high-resolution data from the Resolve micro-calorimeter on board XRISM. We compared our measurement with other Resolve cluster core measurements and further compared our results with simulations and multiwavelength observations. From an optical
redshift analysis, we found that the BCG is at rest with respect to the systemic velocity of the cluster. Despite multiple previously detected cold fronts and harboring a weak central
radio source, Resolve observation shows that the core of A496 is dynamically quiescent. The ICM is moving with respect to the BCG with a LOS bulk velocity of $v_{\rm bulk}=-69_{-20}^{+25}\,\mathrm{km\,s}^{-1}$. We measured a turbulent velocity of $\sigma_{\rm v}=78_{-16}^{+18}\,\mathrm{km\,s}^{-1}$, the lowest value reported by the instrument on a cluster core to date. This value is in good agreement with the velocity dispersion of the H$\alpha$ filament in the core, which may indicate condensation of ICM in the wake of the
radio bubble. Assuming isotropic
turbulence, the ICM turbulent velocity corresponds to a subsonic 3D Mach number of $0.15_{-0.03}^{+0.04}$ and a non-thermal pressure fraction of $1.2_{-0.5}^{+0.6}\,\%$. The mechanical AGN feedback from the recent activity of the central
radio source is estimated to contribute about 7-9% to the ICM heating. The 1D LOS bulk velocity from the SLOW constrained Universe simulation is consistent with the measured value, suggesting that AGN feedback has a negligible contribution. The A496 SLOW turbulent velocity, as in other reported Resolve–simulation comparisons, is higher, but remains within $1.5\sigma$ uncertainty. A496 may represent one of the most quiescent sloshing cores observed so far.
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All authors Angie Veronica, Thomas H. Reiprich, Naomi Ota, Jakob Dietl, Frederick Groth, Klaus Dolag, Efrain Gattuzz, Florian Pacaud, Elke Roediger, Jeremy S. Sanders, Benjamin Seidel, Yuanyuan Zhao
High Energy Astrophysical Phenomena
JWST Observations of Calcium-Strong Transients: I. Complex Nebular He Emission in SN 2024uj
Saarah Hall, Lindsey A. Kwok, Aravind P. Ravi et al. (+29 more)
We present the first JWST observations of a Calcium-Strong Transient (CaST), SN 2024uj, a rare class of
supernovae (SNe) with observable properties that are consistent with both thermonuclear explosions of white
dwarfs (WDs) and the core collapse of massive
stars. SN 2024uj is offset by $\sim6.6$ kpc from its host and exhibits a double-peaked light curve consistent with shock cooling of nearby circumstellar material. At early times, its optical spectra resemble those of normal SNe Ib, but strong [Ca II] $\lambda\lambda$7291, 7324 emission emerges between $+$2 and $+$17 days after maximum light. Radiative-transfer models of a massive stripped He
star cannot reproduce this early forbidden Ca emission, even with artificially enhanced surface Ca, whereas it arises naturally in thermonuclear scenarios. The $+$150 d JWST/NIRSpec spectrum reveals highly asymmetric, multicomponent He I at both 1.083 and 2.058 $\mu$m. The He extends to $\gtrsim+$5000 km/s, with a strong, narrow peak at $+$1500 km/s, indicating that He is distributed throughout the ejecta with a concentration offset from center. This He distribution overlaps central [Ca II] and [O I], implying a degree of mixing difficult to produce in a massive
star explosion. The He peak might further trace interaction with a shocked, ejected companion in a thermonuclear system. The NIRSpec spectrum also shows molecular CO emission and a rising continuum that, together with a 10 $\mu$m photometric detection, indicates
dust emission extending into the mid-infrared. Given the remote environment, early forbidden Ca, mixed He/Ca/O ejecta, and possible companion signature, we favor a thermonuclear origin for SN 2024uj involving at least one low-mass, partially He-rich WD.
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All authors Saarah Hall, Lindsey A. Kwok, Aravind P. Ravi, Adam A. Miller, Luc Dessart, W. V. Jacobson-Galán, Huei Sears, Moira Andrews, K. Azalee Bostroem, Thomas G. Brink, Joseph Farah, Alexei V. Filippenko, Ryan J. Foley, Griffin Hosseinzadeh, D. Andrew Howell, Saurabh W. Jha, Conor Larison, Chang Liu, Colin W. Macrie, Kate Maguire, Curtis McCully, Nicolas E. Meza-Retamal, Maryam Modjaz, Megan Newsome, Estefania Padilla Gonzalez, David J. Sand, Steve Schulze, Giacomo Terreran, C.-G. Touchard-Paxton, Stefano Valenti, Yi Yang, WeiKang Zheng
Astrophysics of Galaxies
AGN radiative feedback as the main regulator of [O III] outflow activity and obscuration in X-ray AGN
Carolina Andonie, Andrea Merloni, Catarina Aydar et al. (+12 more)
Large-scale ionised
outflows and
nuclear obscuration are fundamental manifestations of AGN activity, yet direct observational evidence linking these phenomena remains scarce. We use the eROSITA Final Equatorial Depth Survey, among the largest uniform optical spectroscopic
datasets of X-ray AGN, to investigate how AGN
accretion rate affects ionised
outflow kinematics and X-ray obscuration. Our sample comprises 2.840 AGN at z<0.82 with high-quality SDSS spectra. Through optical spectral fitting, we measure Eddington ratios ($\lambda_{Edd}$) and [O III] emission-line kinematics, tracing ionised
outflows. In addition, we use archival eROSITA X-ray spectroscopy with X-ray stacking analyses to constrain the obscuration of the sample, $N_H$. We find that (1) 35% of the entire sample hosts a [O III]
outflows ($W_{80}>600$ km/s), with the
outflow incidence increasing with the AGN luminosity from 15% at $L_{AGN}<10^{44}$ erg/s up to 60% at $L_{AGN}>10^{46}$ erg/s; (2) the
outflow incidence increases with Eddington ratio from 29% at $\log \lambda_{Edd}<-2.3$ to 50% at $\log \lambda_{Edd}>-1.7$; and (3) the AGN obscuration decreases with Eddington ratio, as sources with $\log\lambda_{Edd}>-1.7$ are 5 times less obscured than lower Eddington ratios AGN. In addition, we find that 1% of the sample populates the "forbidden region" of the $N_H-\lambda_{Edd}$ plane, where the
outflow incidence peaks at 52%, consistent with a short-lived feedback phase. Notably, when matching the Eddington ratios samples in AGN luminosity, these trends vanish, implying that radiation pressure drives changes in
outflow activity and obscuration, while the black hole mass does not play a significant role. Our results are in agreement with AGN radiative feedback scenarios, where the Eddington ratio regulates the AGN environment by driving powerful,
galaxy-wide
outflows and shaping the amount of circumnuclear material.
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All authors Carolina Andonie, Andrea Merloni, Catarina Aydar, Benny Trakhtenbrot, Johannes Buchner, Brivael Laloux, Mara Salvato, Peter Boorman, David M. Alexander, Marcella Brusa, Pietro Baldini, Tiago Costa, Victoria A. Fawcett, Zsofi Igo, Kirpal Nandra
Astrophysics of Galaxies
The Stellar "Snake"-V: the census within 3 kpc in the Solar Neighborhood
Xiang-Ming Yang, Ju-Yong Zhang and Hai-Jun Tian
We present a
Gaia DR3 source-level catalogue of
Stellar Snake complexes within 3 kpc of the Sun. We define a
Stellar Snake as a mutually coherent association of
stellar overdensities, characterised by consistent positions, kinematics, orbital invariants, and ages, rather than a single gravitationally bound object. Moving beyond catalogue searches seeded by known open clusters, our framework operates directly on
Gaia sources to recover extended, low-density substructures and interconnecting
stellar bridges. The multi-stage pipeline extracts statistically significant, non-overlapping base nodes, infers homogeneous parameters using a PointNet point-cloud regressor, and links these nodes into large-scale macro-structures in a nine-coordinate feature space spanning positions, velocities, age log t, and derived dynamical quantities (E, L_Z). After FoF-
topology checking and boundary resolution, the final catalogue contains 1,180
Stellar Snake candidates with 4,196 base nodes and 692,408 unique member-
star entries. Derived parameters are compared with external open-cluster catalogues and spectroscopic
benchmarks. We introduce a graph-relation Snake Reliability Index (SRI) with Gold/Silver/Bronze grades to quantify structural coherence. A spatial-kinematic partition diagnostic identifies candidate subdivisions and provides core scores. At the population level, the catalogue shows an age–
metallicity pattern in the jointly inferred parameters, a declining upper envelope of observed member-
star entries toward older inferred ages, and a projected association between young Snake nodes, nearby spiral-arm loci, and the Radcliffe Wave. This homogeneous inventory provides an observational foundation for probing the formation, coherence, and dynamical
evolution of hierarchical
stellar complexes in the Milky Way.
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Astrophysics of Galaxies
Search for Quasar Pairs with ${\it Gaia}$ Astrometric Data. III. Discovery of 9 dual and projected quasars
Qihang Chen, Zizhao He, Zhuojun Deng et al. (+3 more)
We report the low-resolution long-slit spectroscopic observations and confirmations of 11
quasar pair candidates, which are selected from the MGQPC catalog presented in the first paper of our series work (hereafter, Paper-I) and the early version of this catalog. The spectroscopic follow-up was carried out with 5 spectrographs equipped on 3
telescopes, and the major discoveries include 6 dual
quasars and 3 projected
quasars. One of the dual
quasars has a high
redshift of $\sim$ 3.1. The LQ hypothesis of 3 dual
quasars cannot be completely ruled out. We investigated the reason why previous spectroscopic surveys missed several new
quasars. We discussed a projected
quasar with a wide-separation
lensing configuration, as well as two
quasar-
star projections that mimic the configuration of lensed
quasars. The photometric
redshifts for the 11 observed candidates were extracted from the second paper of our series work (hereafter, Paper-II) to illustrate their positive role in mitigating contamination from projected
quasars and
quasar-
star projections. We also reviewed and discussed the confirmation strategies for dual and lensed
quasar candidates, and outlined future confirmation strategies for them in the context of the era dominated by large-scale spectroscopic and imaging surveys.
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All authors Qihang Chen, Zizhao He, Zhuojun Deng, Liang Jing, Xingyu Zhu, Jianghua Wu
Earth and Planetary Astrophysics
Planet formation in chemically diverse and evolving discs II. Chemical fingerprints in planetary atmospheres
E. Pacetti, D. Turrini, E. Schisano et al. (+13 more)
Giant planets form in protoplanetary discs, where the coupled dynamical and chemical
evolution of gas and solids determines the composition of the material they accrete. We investigate how
planet formation and migration shape the
primordial elemental makeup of
giant-
planet atmospheres. Our aim is to link atmospheric compositions to
planets' formation pathways and the time-dependent chemical properties of their natal discs. We couple 1D models of viscously evolving discs - incorporating radial
dust drift and volatile chemistry - with N-body simulations of planetesimals interacting with a growing and migrating
giant planet. Four chemical scenarios and three representative grain sizes (0.1, 20, and 100 micron) are explored. We track the
accretion of carbon, oxygen, nitrogen, and sulphur to derive atmospheric elemental ratios normalised to
stellar values (* denotes
stellar normalisation). We identify three atmospheric classes corresponding to distinct
accretion regimes: gas-dominated, characterised by N/O* > C/O* > C/N* and unconstrained or substellar S/N* (near-
stellar C/S*); planetesimal-dominated, showing N/O* < C/O* < C/N*, S/N* >= C/N*, and C/S* <= C/O*; and drift-enhanced, exhibiting N/O* < C/O* < C/N* and markedly superstellar volatile-to-refractory ratios. N/O*, C/N*, and S/N* vary systematically with migration extent, although degeneracies arise for
planets forming beyond the CO and N2 snowlines; C/O* remains largely insensitive.
Metallicity alone does not uniquely trace the solid-to-gas
accretion balance in drift-dominated regimes. Variations in the disc's chemical state and
dust size imprint distinctive volatile-ratio patterns across these classes, providing complementary constraints on disc properties. This multi-element framework establishes predictive trends to guide the interpretation of atmospheric spectra from facilities like JWST and Ariel.
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All authors E. Pacetti, D. Turrini, E. Schisano, S. Molinari, C. Walsh, C. P. Dullemond, S. Fonte, R. S. Klessen, U. Lebreuilly, P. Hennebelle, S. L. Ivanovski, R. Politi, D. Polychroni, P. Simonetti, L. Testi, V. Cottini
Astrophysics of Galaxies
The multiwavelength structure of post-starburst galaxies at 0.5 < z < 3 with JWST PRIMER: compact morphologies and residual disturbances
David T. Maltby, Omar Almaini, Vivienne Wild et al. (+9 more)
We investigate the multi-wavelength structure of recently quenched post-starburst (PSB)
galaxies at 0.5 < z < 3, using photometrically selected samples from the Ultra Deep Survey (UDS). Leveraging deep eight-band JWST/NIRCam imaging from the PRIMER programme, we analyze ~120 PSBs across the rest-frame optical-to-near-infrared, and compare with a reference sample of ~3000 passive and
star-forming
galaxies. Structural parameters (effective radius Re and Sersic index n) are derived independently in each waveband, and reveal that PSBs exhibit minimal structural variation with wavelength, indicating negligible
stellar population age gradients or internal
dust obscuration. We confirm that PSBs follow the established
redshift-mass trends: at z > 1, massive PSBs (M* > 10^10 Msun) are compact spheroids resembling massive passive
galaxies, albeit significantly more compact, whereas at 0.5 < z < 1, PSBs are typically low-mass (M* < 10^10 Msun) compact, disc-dominated systems akin to low-mass passive discs. Furthermore, for the first time, we systematically quantify disturbance indicators (residual flux fraction RFF, asymmetry, residual asymmetry) across a large PSB sample. At all masses, PSBs exhibit low RFF and asymmetry values comparable to passive systems and consistent with smooth, largely undisturbed morphologies. However, at z > 1, massive PSBs (M* > 10^10.25 Msun) show enhanced residual asymmetry relative to the passive population, indicating a previously unrecognized level of structural disturbance masked beneath a smooth
stellar distribution. These results suggest that, while structural transformation is largely complete by the PSB phase, residual disturbances persist at high
redshift, supporting a scenario in which rapid quenching proceeds via two distinct pathways: highly disruptive events (e.g. major mergers) at high z and high mass, and comparatively gentle processes at later times.
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All authors David T. Maltby, Omar Almaini, Vivienne Wild, Elizabeth Taylor, Kate Rowlands, Thomas de Lisle, Guillaume Hewitt, Maya Skarbinski, James S. Dunlop, Adam C. Carnall, Anton M. Koekemoer, Derek J. McLeod