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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 10 July

Instrumentation and Methods for Astrophysics

Neural Posterior Estimation for Inferring Weak Lensing Shear

Tim White, Dingrui Tao, Camille Avestruz et al. (+2 more)

The prevailing approach to inferring weak gravitational lensing shear from images involves detecting galaxies, estimating their ellipticities, and calibrating these estimates to correct for image noise, selection bias, and model misspecification. Characterizing the statistical model and assumptions underlying this pipeline is challenging, which makes it difficult to propagate uncertainty through its various stages. As an alternative, we propose to infer shear using neural posterior estimation (NPE), a type of simulation-based inference. We train a deep neural network to map a simulated multiband image to a variational distribution over the underlying shear field, thereby folding galaxy detection, deblending, measurement, and calibration into a single implicit inference step. Once trained, the network accounts for all features present in the simulated images, including potential sources of bias. In experiments on simulated constant-shear images with increasingly complex observational effects, NPE produces accurate and well-calibrated posterior approximations for both shear components in the presence of blended galaxies, spatially varying point spread functions, stars, and detector artifacts. These results demonstrate that NPE can be a viable shear estimation method in settings where all anticipated features and artifacts can be simulated, a requirement that will become increasingly feasible as simulation fidelity improves in the coming decades.
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All authors Tim White, Dingrui Tao, Camille Avestruz, Jeffrey Regier, the LSST Dark Energy Science Collaboration

Astrophysics of Galaxies

Six-Class BPT Galaxy Classification for Survey-Scale AGN Candidate Prioritization: Deep Tabular Model and Informative Missingness Signals

Shanquan Gui

The Baldwin–Phillips–Terlevich (BPT) diagram is widely used to classify galaxies into star-forming systems, composite galaxies, and active galactic nuclei (AGNs), but its survey-scale application is limited by the requirement for high signal-to-noise emission-line measurements. We test whether machine-learning models can reproduce six-class BPT labels while using measured quantities, derived line ratios, and potentially informative missing-data patterns as inputs. We analyze 1.47 million galaxies with a 27-dimensional feature set that combines raw survey measurements, derived quantities, and missingness indicators. Five deep tabular architectures are benchmarked against gradient-boosted trees and classical machine-learning baselines, and the resulting probabilities are evaluated through hard-classification metrics, precision–recall curves, top-$k$ retrieval, ablation tests, and feature-interpretation diagnostics. {CNN–Transformer gives the strongest overall classification performance (accuracy = 0.8266), while boosted trees remain highly competitive for this low-dimensional tabular problem. In the binary star-forming-versus-AGN comparison, CNN–Transformer achieves a Class~1 versus Class~4 ROC AUC of 0.9998. Missingness indicators provide substantial predictive information, especially the OH\_P50N\_missing feature. Feature interpretation further shows that $\log([\mathrm{Ne\,III}]/[\mathrm{O\,II}])$, combined with stellar mass or specific star-formation rate, separates star-forming galaxies from AGN hosts. The models are most useful as AGN candidate-ranking tools that complement, rather than replace, traditional BPT diagnostics. High-ranked samples can reach high purity, while broader candidate lists recover most AGNs, but transferability to other surveys requires further validation.
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Instrumentation and Methods for Astrophysics

Efficient Optimal Image Reconstruction for the Nancy Grace Roman Space Telescope and Beyond: II. Implementation of Effortless

Kaili Cao

Weak gravitational lensing is a promising but technically demanding cosmological probe. For space missions like the forthcoming Nancy Grace Roman Space Telescope, a major challenge is that native images are undersampled and need to be reconstructed to enable accurate measurements. Effortless (EFFicient Optimal image ReconsTruction using LESS memory; previously known as Fast Imcom) is a new algorithm designed for that purpose. My companion paper has exhibited promising first results to demonstrate that Effortless can make point spread functions (PSFs) uniform and regular across reconstructed images more efficiently than its predecessor Imcom and has the potential to outperform Imcom in terms of control over systematic errors. In this paper, I present the mathematical formalism, software implementation, and practical issues in detail. Foremost, while the Nyquist–Shannon sampling theorem remains true, the conditions of the theorem are subtly (and importantly) different from the problem in survey data processing, and finite sampling effects can be substantially reduced via a simple post-measurement calibration. Imperfections caused by numerical artifacts, finiteness of input pixel windows, and unavailability of some input pixels are understood and under control. The Effortless application programming interface is general and can support use cases beyond weak lensing cosmology and beyond the Roman Space Telescope.
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Astrophysics of Galaxies

How Should We Understand the Core Mass Function? A memo of the CMF2IMF conference at ESO Garching

Fengwei Xu, Roberto Galvan-Madrid, Kaho Morii et al. (+4 more)

The origin of the stellar initial mass function (IMF) remains one of the central questions in astronomy. Nearly three decades ago, the resemblance between the core mass function (CMF) and the IMF inspired the community to suggest that the stellar mass spectrum might be imprinted early in molecular-cloud cores and then mapped to the IMF through a simple efficiency factor. It has become gradually clear, however, that this apparent mapping involves multiple non-linear physical processes. Motivated by the spirit of the CMF2IMF conference at ESO Garching, this memo first reviews the historical quest to understand the origin of the IMF, and then sets the stage for building a shared understanding of current CMF measurements. We therefore compile several observational core catalogues at various environments and evolutionary stages into a common framework, implemented in the public Python package CMF4All. We show that the inferred high-mass CMF slope depends strongly on the adopted minimum fitting mass. A significantly steeper slope is observed in the early-stage sample, indicating a potentially evolving mass function at the highest masses. We conclude by outlining future directions to spare more efforts for both the observational, numerical simulation, and theoretical sides.
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All authors Fengwei Xu, Roberto Galvan-Madrid, Kaho Morii, Thomas Nony, Aina Palau, Alessio Traficante, Alice Nucara

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

GRACE: An Open-Source Framework for GPU-Accelerated Numerical Relativity

Carlo Musolino, Christian Ecker, Konrad Topolski et al. (+6 more)

We present GRACE, a new GPU-accelerated numerical-relativity framework designed to run efficiently on heterogeneous high-performance computing platforms. Developed from scratch and built exclusively on open-source libraries, GRACE employs Kokkos for performance portability across CPU and GPU architectures and p4est for adaptive mesh refinement. The code evolves the equations of ideal GRMHD – with divergence-free magnetic fields maintained by constrained transport – self-consistently coupled to the Einstein equations in the Z4c formulation, on fixed or adaptively refined grids. We validate the implementation against a suite of standard tests, ranging from magnetized shock tubes and the magnetic rotor in flat spacetime, through (magnetized) Bondi accretion onto a Schwarzschild black hole and the ringdown of a perturbed spinning puncture, to neutron-star oscillation spectra in fixed and dynamical spacetimes and the merger of binary black holes. As more demanding applications, we evolve two binary neutron-star mergers – an equal-mass, unmagnetized system with an ideal-gas equation of state and an unequal-mass, magnetized system with a finite-temperature tabulated equation of state – finding the inspiral dynamics to agree well with the FIL code. We also report single-device throughput together with strong- and weak-scaling results on multiple GPU and CPU architectures. GRACE is publicly released together with GRACEpy, a basic post-processing and data-analysis environment.
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All authors Carlo Musolino, Christian Ecker, Konrad Topolski, Marie Cassing, Keneth Miler, Harry Ho-Yin Ng, Khalil Pierre, Elias R. Most, Luciano Rezzolla

Astrophysics of Galaxies

The black hole occupation fraction as a fossil record of seeding, dynamics, and galaxy assembly

Emma Jane Weller, Priyamvada Natarajan and Colin J. Burke

The black hole occupation fraction (BHOF) is a powerful but intrinsically layered diagnostic of massive black hole (BH) seeding and subsequent galaxy assembly. We measure the total, central, and wandering BHOF in the ASTRID cosmological hydrodynamical simulation from $z=5$ to $z=0$ in galaxies with stellar masses ranging from $10^7$-$10^{12} \, \mathrm{M}_\odot$. For the full population, the total BHOF remains close to unity across most stellar masses and redshifts, reflecting efficient seeding in eligible halos. At low stellar masses, the central BHOF declines toward the present day, while the wandering BHOF rises, indicating that mergers deposit BHs at off-center locations in galaxies. Compared to these full-population BHOFs, the heavy-seed BHOFs are substantially smaller at the low-mass end. The active BHOFs are smaller at all stellar masses, especially at late times, demonstrating that active galactic nuclei (AGN)-selected samples trace duty cycles rather than intrinsic BH occupation. At $z=0$, primary (central) galaxies have higher BHOFs than satellites, and star-forming low-mass galaxies preferentially host wandering rather than central BHs. Our results show that the BHOF, when decomposed by BH location, seeding history, accretion state, and larger-scale galactic environment, encodes a rich fossil record of BH origins and dynamics.
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Solar and Stellar Astrophysics

Benchmark Brown Dwarf Systems I: Chemical Abundance Analysis of FGK Stars with Wide-Separation Brown Dwarf Companions Using PEPSI

Caprice L. Phillips, Megan Bedell, Catherine Manea et al. (+11 more)

We present results from a spectroscopic survey of 32 FGK stars hosting brown dwarfs, using high-resolution optical spectra (R = 130,000 and 50,000) obtained with the PEPSI spectrograph on the Large Binocular Telescope. The primary goal of this survey is to determine precise stellar parameters and abundances for 11 elements (C, O, Mg, Si, Ca, Al, Ti, Fe, Y, S, and N) in these systems. We employ spectral synthesis within the BACCHUS framework to derive precise stellar properties and elemental abundance ratios. For our average S/N $>$ 200 data, we achieve a typical error of 42 K in T$_\mathrm{eff}$ and $\sim$0.03 dex for [Fe/H]. We observe a significant dispersion from a solar C/O ratio among the sample of brown dwarf host stars that host primarily wide-orbit brown dwarfs. Using established theoretical chemical frameworks, we discuss the implications of the observed Mg/Si and Ca/Al ratios for cloud properties in the brown dwarf companions. Finally, we evaluate the applicability of the [Y/Mg] stellar clock for our sample and discuss the broader implications of our results. This work provides a timely and uniform abundance analysis of host stars, supporting extended wavelength brown dwarf observations in the era of JWST.
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All authors Caprice L. Phillips, Megan Bedell, Catherine Manea, Alison Duck, Anusha Pai Asnodkar, Emily J. Griffith, Austin Rothermich, Emily Calamari, Jaqueline K. Faherty, Channon Visscher, Eileen C. Gonzales, Ilya Ilyin, Klaus Strassmeier, Ji Wang

High Energy Astrophysical Phenomena

Low-hard to high-soft spectral state transitions in the faintest early-X-ray-detected optical tidal disruption event TDE 2025aarm

Pietro Baldini, Arne Rau, Andrea Merloni et al. (+11 more)

We report the X-ray and optical spectroscopic properties of TDE 2025aarm, the second closest tidal disruption event (TDE) discovered to date. The proximity of this source, combined with a deep and intense X-ray monitoring campaign spanning six months, allowed us to probe the source down to an unprecedented 0.2-10 keV luminosity of $\sim7\times10^{39}$ erg s$^{-1}$ close to the optical peak. This renders TDE 2025aarm the faintest early-X-ray-detected TDE to date. After the first X-ray detection, the source brightened by nearly two orders of magnitude, reaching a peak luminosity of $\sim5\times10^{41}$ erg s$^{-1}$ about four months after the optical peak. Through time-resolved X-ray spectral analysis, we find that TDE 2025aarm evolved from an initially hard, power-law-dominated X-ray state into a softer, disk-dominated state as the luminosity increased, before hardening again at later times. Such low-hard-to-high-soft state transitions are commonly observed in black hole X-ray binaries (XRBs) but have not previously been reported in thermal TDEs. We show that the spectral evolution can be described by variations in the relative contributions of an accretion disk and a Comptonizing component, qualitatively resembling the disk–corona evolution observed in XRBs. We also present the results of our optical spectroscopic follow-up campaign with HET/LRS2, confirming the TDE classification and revealing NIII Bowen fluorescence features. The extremely faint early-time X-ray emission of TDE 2025aarm further supports the idea that the historical dichotomy between X-ray-bright and X-ray-undetected TDEs is largely driven by selection effects related to the depth, cadence, and duration of X-ray follow-up observations. TDE 2025aarm therefore provides new insight into both the accretion physics of TDEs and the possible universality of accretion across several orders of magnitude in black hole mass.
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All authors Pietro Baldini, Arne Rau, Andrea Merloni, Jean Somalwar, Seán J. Brennan, Elias Kyritsis, Hannah C. I. Wichern, Peter Boorman, Panos Charalampopoulos, Lixin Dai, Gaurava K. Jaisawal, Chichuan Jin, Tianying Lian, Kirpal Nandra

Instrumentation and Methods for Astrophysics

Robust Photometry for Roman High-Latitude Imaging Survey Cosmology Using Roman and Rubin Imaging

Chun-Hao To, Tae-Hyeon Shin, Chihway Chang et al. (+18 more)

Accurate and precise photometry is essential for Roman cosmology because it affects photometric-redshift performance, galaxy and cluster selection, tomographic binning, and redshift-distribution characterization. Achieving robust photometry is challenging because Roman's depth leads to substantial source blending, particularly in joint Roman–Rubin analyses, where the two surveys have different spatial resolutions. In this work, we develop and validate slimfarmer, a model-fitting photometry pipeline designed for Roman High-Latitude Imaging Survey (HLIS) cosmological analyses. Building on The Farmer, slimfarmer introduces treatments of the correlated noise present in Roman images and of astronomical shot noise, together with model-fitting configurations tuned for Roman imaging. We validate the pipeline using Roman coadded simulated images and perform forced photometry on matched Rubin image simulations. We find that slimfarmer recovers galaxy colors with the mode of the color residuals within 20 millimag for Roman-based colors and within 70 millimag for Rubin-based colors. Properly accounting for correlated noise is essential for uncertainty quantification, as photometric uncertainties are otherwise underestimated by up to a factor of ~3. We also find that applying multi-object fitting consistently to both Roman and Rubin imaging substantially mitigates blending-induced color systematics. In crowded regions, single-object fitting produces environment-dependent color biases of up to ~0.5 mag, leading to environment-dependent degradation of photometric-redshift performance. Together, these results establish slimfarmer as a prototype photometric pipeline for Roman HLIS cosmology applications and identify the correlated-noise corrections, astronomical shot-noise treatment, and joint Roman–Rubin multi-object fitting required for robust photometric-redshift characterization.
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All authors Chun-Hao To, Tae-Hyeon Shin, Chihway Chang, Christopher Hirata, Brett H. Andrews, Ami Choi, Boyan Yin, Rachel Mandelbaum, Federico Berlfein, Kaili Cao, James Chiang, Nihar Dalal, Yuedong Fang, Axel Guinot, Michael Gabe, Andrew Hearin, Katherine Laliotis, Emily Macbeth, Sidney Mau, Edward F. Schlafly, M. A. Troxel

Astrophysics of Galaxies

Do we understand the star formation history of the universe?

Sahil Hegde, Steven R. Furlanetto and Smadar Naoz

The evolving relationship between a galaxy's mass and star formation rate – the so-called `star-forming main sequence' (MS) – provides a critical benchmark for understanding star formation across time. Despite its fundamental importance, the observed main sequence remains subject to substantial systematic uncertainties in normalization, shape, and redshift evolution, and a longstanding discrepancy persists between the main sequence and its integral, the stellar mass function. We revisit the star-forming MS in the era of the James Webb Space Telescope by asking what star formation rates are required by the stellar mass function to create a self-consistent picture of galaxies across time. We fit compiled ground- and space-based measurements of star-forming and quiescent mass functions from $z=0.1-9$. By tracing galaxy growth histories through these mass functions, we present a statistically-robust inference of the main sequence over $10^8 M_\odot \leq m_\star \leq 10^{11} M_\odot$, from the local universe to the first 500 Myr of cosmic history. Our procedure implies a main sequence that agrees with independent spectroscopic measurements of star formation rates from $z\sim 2-7$, is consistent with SED fitting-based analyses of photometric samples at $z\lesssim 3$, and aligns with theoretical models of galaxy evolution. However, we find that our MS differs from commonly-used `concordance' relations and thus caution against applications of these compilations without appropriately characterizing the underlying uncertainties. Finally, we explore the implications of our inferred main sequence for the galaxy-halo connection and star formation rate density, highlighting the need for further theoretical work to comprehensively understand the star formation history of the universe.
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Cosmology and Nongalactic Astrophysics

The Rise and Fall of Acoustic Oscillations at Cosmic Dawn

Hector Afonso G. Cruz, Gabriele Montefalcone, Julian B. Muñoz et al. (+2 more)

Cosmic dawn 21-cm observations will extend standard-ruler cosmology into the first billion years, unlocking epochs inaccessible by the cosmic microwave background and large-scale structure. Realizing this promise requires an accurate model of the acoustic structure imprinted onto early star formation. At such early times, two counterbalancing phenomena – matter overdensities and streaming velocities between cold dark matter and baryons – modulate the spatial statistics of star formation. While overdensities dictate where early galaxy-bearing haloes form, regions of high velocity suppress star formation. Their combined influence on the intergalactic medium yields 21-cm fluctuations with both baryon (BAO) and velocity-induced (VAO) acoustic oscillations. Here we present the first prescription to decompose the 21-cm power spectrum into its constituent acoustic features. We find a percent-level offset between the BAO and VAO shapes which, if ignored in standard-ruler analyses, would bias inferred values of $H(z)$ by $\sim 2\%$; we provide a correction. Moreover, as the relative prominence of BAOs and VAOs ebbs and flows non-monotonically across cosmic dawn, we demonstrate how their evolution is sensitive to the physics of early galaxy evolution and the first stars. Finally, we forecast how sensitive SKA will be to the BAO-VAO combined standard ruler. Our results establish joint BAO-VAO modeling as an essential ingredient of 21-cm acoustic inference, enabling robust constraints on both cosmic expansion and the first stars.
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All authors Hector Afonso G. Cruz, Gabriele Montefalcone, Julian B. Muñoz, Ely D. Kovetz, Alessandra Venditti

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

Searching for heavy charged relics in the Earth

Reza Ebadi, Peter W. Graham, Surjeet Rajendran et al. (+2 more)

We propose a method for detecting an ambient density of heavy, electrically-charged particles. Such particles would impact the Earth, lose energy in terrestrial matter, and become trapped. We study the accumulation of these rare particles in multiple target materials that provide large exposure, such as water and geological rocks. We discuss strategies for concentrating the particles by centrifugation or gravitational settling, along with particle identification using mass spectrometry. This method enables the discovery of charged relics with masses $1-10^{12}\,{\rm TeV}$ comprising a tiny fraction of the local dark matter density, reaching down to $f_X\sim 10^{-20}$ at the lowest masses. A pathfinder experiment using only a liter of water and one centrifuge (or $\sim \text{m}^3$ and no centrifuge) operating for a month can already reach $f_X\sim 10^{-10}$ and probe new parameter space.
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All authors Reza Ebadi, Peter W. Graham, Surjeet Rajendran, Erwin H. Tanin, Samuel S. Y. Wong

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Compact stars in a large-tension braneworld: mildly negative Weyl coupling consistent with NICER and gravitational-wave data

Samuel Isidoro dos Santos Júnior, Rafael Camargo Rodrigues de Lima and Pedro Henrique Ribeiro da Silva Moraes

We use Bayesian inference on multi-messenger observations to constrain the parameter space of compact stars in a phenomenological braneworld model inspired by the effective Sahni–Shtanov scenario. Stellar structure is described by modified Tolman–Oppenheimer–Volkoff equations including local quadratic brane corrections and a phenomenological closure for the nonlocal Weyl sector, parametrized by the brane tension $\lambda$, the Weyl coupling $\alpha_{\mathcal{U}}$, and the Weyl equation-of-state parameter $w_{\mathcal{U}}$. Using the SLy equation of state, we perform an affine-invariant ensemble Markov Chain Monte Carlo analysis combining mass–radius posteriors from GW170817 (LIGO/Virgo) and NICER observations of PSR~J0740$+$6620 and PSR~J1231$-$1411. The posterior yields $\log_{10}(\lambda/\mathrm{km}^{-2})=3.98^{+1.52}{-1.44}$ (68%), indicating a large-brane-tension regime where local high-energy corrections are subdominant. The Weyl coupling is constrained to $\alpha{\mathcal{U}}=-0.15^{+0.30}{-0.08}$ (68%), while $w{\mathcal{U}}$ remains weakly constrained, with a 95% credible interval of $[-1.25,,1.02]$. The inferred stellar properties are $M_{\max}=2.30^{+0.14}{-0.08},M\odot$ and $R_{1.4}=13.31^{+0.54}_{-0.57},\mathrm{km}$ (68%), exceeding the corresponding General Relativity predictions for the SLy equation of state. The 95% posterior interval extends into the GW190814 secondary-mass range, although the median and best-fit values remain below it. These results show that a large-tension braneworld with a mildly negative Weyl coupling is consistent with current NICER and gravitational-wave constraints without requiring large deviations from General Relativity.
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High Energy Astrophysical Phenomena

Identifying and characterizing extragalactic circum-CBC exoplanets with future gravitational-wave detectors

Avinash Tiwari, Aditya Vijaykumar, Shasvath J. Kapadia et al. (+1 more)

Exoplanets are high-value targets for a variety of ground and space-based telescopes. All known exoplanets are Galactic, and a fraction of them orbit compact objects. In this work, we investigate the possibility of detecting extragalactic exoplanets orbiting stellar-mass compact binary coalescences (CBCs), such as binary neutron stars, neutron star-black holes, and binary black holes, using future gravitational wave (GW) detectors, including A+ (LIGO in O5), Einstein Telescope, and DECIGO. We use the technique of reconstructing an external potential's profile by extracting information about the centre-of-mass (CoM) kinematics of a CBC encoded in the GWs it emits. In this work, the external potential is provided by the circum-CBC exoplanet, and the resulting signature on the GW waveform comes from the “wobble” of the CBC's CoM around the CBC-exoplanet barycentre. As a proof of principle, we consider a few example CBCs detectable with future detectors and a range of circum-CBC exoplanet parameters in circular and eccentric orbits. We find that for a significant fraction of the range of parameters considered, we can identify the presence of a circum-CBC exoplanet by extracting its mass (up to an unknown orbital inclination angle) within a factor $\mathcal{O}(1)$ of its true value, at $68\%$ confidence.
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All authors Avinash Tiwari, Aditya Vijaykumar, Shasvath J. Kapadia, Sourav Chatterjee

Earth and Planetary Astrophysics

HD 148797: A bright F-type star with two moderate-period low-density sub-Jovian planets. Compact multi-planet architectures are common in the Neptunian savanna

J.M. Almenara, A. Castro-González, R. Mardling et al. (+26 more)

We report the confirmation and characterisation of two moderate-period sub-Jovian planets transiting the bright F-type star HD 148797 (G=9.4 mag, Teff=6441 +/- 51 K). Using photometric time series from TESS and CHEOPS, we determine orbital periods of 42.1 d for HD 148797 b and 68.2 d for HD 148797 c, putting the period ratio very close to the golden mean at 1.619 and therefore near several strong harmonics, and measure planetary radii of 8.25 +/- 0.37 RE and 8.37 +/- 0.38 RE, respectively. We detect significant anti-correlated transit-timing variations for both planets, which contain enough harmonic information to yield photodynamical masses of 39.3 +13 -8.5 ME for HD 148797 b and 39.6 +/- 9.3 ME for HD 148797 c. The corresponding bulk densities, 0.39 +/- 0.12 and 0.377 +/- 0.084 g/cm3, place both planets among the low-density sub-Jovians of the Neptunian savanna. The architecture of HD 148797 is not unusual within this regime: we find that detected multi-system fractions in the savanna remain at ~70-90%, and that most savanna multi-planet systems contain at least one adjacent planet pair with Pout/Pin < 3. This pattern suggests that savanna sub-Jovians are commonly found in dynamically cold systems, consistent with smoother migration pathways such as disk-driven migration rather than disruptive high-eccentricity tidal migration. As a bright, co-evolved system hosting two warm savanna sub-Jovians with similar radii and masses, HD 148797 is also a promising target for comparative atmospheric characterisation.
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All authors J.M. Almenara, A. Castro-González, R. Mardling, T. Guillot, X. Bonfils, L. Thomas, L. Gauvrit, L. Abe, A. Agabi, J. Aubert, F. Bouchy, C. Cadieux, A. Deline, R.F. Díaz, D. Ehrenreich, T. Forveille, A. Heitzmann, P. Hirling, R.M. Hoogenboom, A. Leleu, M. Lendl, D. Mékarnia, S. Pelletier, A. Psaridi, E. Rea, X. Song, O. Suárez, A.H.M.J. Triaud, S. Udry

Astrophysics of Galaxies

Spatial decomposition of Little Red Dots with JWST/NIRSpec IFU into broad-line red cores and narrow-line blue host galaxies

Yuzo Ishikawa, Anna-Christina Eilers, Rohan P. Naidu et al. (+11 more)

Little Red Dots (LRDs) are a population of compact red sources discovered by the James Webb Space Telescope (JWST). Imaging and spectroscopy have shown that LRDs exhibit a complex spectrum with a “V-shaped" continuum, broad Balmer emission lines, and in some cases Balmer absorption. While the physical origin of these components remains debated, recent studies propose that they arise from a compact central engine likely hosting a rapidly growing black hole embedded within a more extended host galaxy. We test this central engine + host galaxy model using JWST/NIRSpec integral field unit (IFU) spectroscopy to spectrally decompose the observed continuum, narrow and broad emission lines, and absorption. We spatially map each component for five broad Ha-selected LRDs at z~5 observed with both the prism and high-resolution G395H grating. We find that the blue continuum emission is co-spatial with the narrow emission line region, while the red continuum arises from a compact core co-spatial with the broad Balmer emission and absorption. Spatial maps of the [OIII] equivalent width reveal a pronounced decrease in the central core. Our work provides further evidence that the LRD emission is produced by at least two distinct physical components arising from a red central engine embedded within a blue host galaxy.
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All authors Yuzo Ishikawa, Anna-Christina Eilers, Rohan P. Naidu, Jorryt Matthee, Rongmon Bordoloi, John Chisholm, Jenny E. Greene, Yilun Ma, Pascal A. Oesch, Wendy Q. Sun, Alberto Torralba, John R. Weaver, Stijn Wuyts, Mengyuan Xiao

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Periodic line-of-sight velocity-driven modulations to gravitational waves emitted by compact binaries in Keplerian outer orbits

Avinash Tiwari, Shasvath J. Kapadia, Aditya Vijaykumar et al. (+1 more)

The centre of mass (CoM) of compact binary coalescences (CBCs) occurring in the vicinity of a supermassive black hole, through interaction with an arbitrary third body (e.g., of stellar mass), or in a dense stellar environment, will undergo a time-varying line-of-sight (LOS) velocity. This in turn leads to a time-varying Doppler shift and corresponding modulations in the shape of the gravitational waves (GWs). The phase and amplitude corrections arising from constant LOS acceleration and its higher-order time derivatives are already known. Specifically, these effects lead to corrections to the GW waveform at $-4n$ post-Newtonian (PN) order, where $n$ is the $n^{th}$ time derivative of the LOS velocity. In the context of a circular or eccentric outer orbit of the CoM of the CBC, these effects can be thought of as approximations to the LOS velocity in the limit: observation duration $\ll$ period of the outer orbit. However, this condition is not necessarily always satisfied. In this paper, we present phase and amplitude corrections to the GW waveforms arising from a periodic non-relativistic LOS velocity for circular and eccentric outer orbits of the CBC's CoM. Specifically, these lead to phase and amplitude modulations at 4 PN order, and reduce to the known corrections for constant kinematic parameters under appropriate limits mentioned above. We also perform a Fisher matrix analysis to forecast constraints on the environment that is sourcing the time-varying LOS velocity, for various future ground and space-based detectors. We further show that constraints acquired using GW waveforms derived in this work improve significantly in comparison to those acquired from approximate methods valid for constant kinematic parameters.
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All authors Avinash Tiwari, Shasvath J. Kapadia, Aditya Vijaykumar, Sourav Chatterjee

Earth and Planetary Astrophysics

Beyond the Cube: Overlapping Grid Methods for Debris Collision Risk Assessment

Yacob Medhin and Simone Servadio

The cube method reduces conjunction screening in orbital debris simulations to $\mathcal{O}(N)$ cost by evaluating only object pairs sharing the same grid cell at each snapshot, but systematically assigns zero collision probability to pairs separated by a cell boundary at that epoch, a failure known as boundary blindness. This paper introduces the Double Cube (DC) method, which recovers boundary-crossing conjunctions through a spatially shifted secondary grid using bin-index lookup alone, preserving $\mathcal{O}(N)$ complexity. In an isotropic convergence benchmark at $L = 50$ km, DC reduces the blindness rate from $\beta_{\mathrm{Cube}} = 7.09\%$ to $\beta_{\mathrm{DC}} = 0.55\%$, and a synchronized experiment separates the temporal component from the geometric one and leaves DC below $0.01\%$ against $0.80\%$ for the cube. Recovering these pairs changes which pairs are evaluated and leaves the probability formula untouched, so it does not improve calibration by itself, and both uncorrected methods remain substantially miscalibrated, with a reliability slope of $m = 1.1314$ for the cube and $m = 1.0996$ for DC. The formula applies the full cell volume to every evaluated pair irrespective of separation, which is the same bias characterized in the no-time-counter scheme of Direct Simulation Monte Carlo. Two corrections are derived from the geometry of the uniform cell alone: a power-law form referenced to the Robbins mean separation $\bar{d} = 0.6617L$ and a Gaussian form using both that mean and the analytically derived standard deviation $\sigma = 0.2494L$, with no quantity fitted to simulation output. The power-law correction moves the reliability slope to $0.9973$ at $k = 1$ and $0.9429$ at $k = 2$, and the Gaussian correction reaches $0.9806$ with an intercept of $0.975$, the only configuration within $3\%$ of unity on both. Both corrections have been implemented in MOCAT-MC.
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Cosmology and Nongalactic Astrophysics

Searching for signatures of fuzzy dark matter in cosmic filament profiles

Callum J. O'Kane, Alfonso Aragón-Salamanca, Ulrike Kuchner et al. (+1 more)

Current observations reveal persistent tensions with the standard cold dark matter paradigm, raising the question of whether these can be explained by baryonic physics alone or require alternative dark matter models. One such alternative is fuzzy (or wave) dark matter, consisting of ultralight particles with mass $m \sim 10^{-22}$ eV and de Broglie wavelengths on kpc to Mpc scales, which may give rise to large–scale interference patterns in non-linear structures around the cosmic web, such as filaments and clusters. In this work, we search for possible signatures of these interference fringes by investigating periodicities in the distribution of galaxies around cosmic web filaments. To demonstrate our methodology, we compare the filament profiles to a simple model that includes a periodic component of the form $A\cos(2\pi d/ \lambda)$, where $A$ is the maximum density contrast (amplitude) of the periodic component, with wavelength $\lambda=\lambda_0 \cos\theta$ for some face-on wavelength $\lambda_0$ inclined at an angle $\theta$ to the line of sight. Exploiting the large Sloan Digital Sky Survey (SDSS) Main Galaxy Sample, we analyse a sample of 4,394 filaments from the Tempel et al. filament catalogue, each containing at least 10 member galaxies. We find a vast portion of the parameter space is consistent with the observations at the $2\sigma$ level, including all models with $A = 0$ (no periodicity). We identify a region of the parameter space in tension with the observations, allowing us to exclude values of $A > 0.16 \lambda_0 + 0.18$ for $0.2\,\text{Mpc}\,\lesssim \lambda_0 \lesssim 2\,\text{Mpc}$ at the $3\sigma$ level, demonstrating the ability to test models of filament dark matter structure using this methodology.
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All authors Callum J. O'Kane, Alfonso Aragón-Salamanca, Ulrike Kuchner, Meghan E. Gray

Cosmology and Nongalactic Astrophysics

CHEFT: A Hybrid Effective Field Theory halo model

Marcos Pellejero Ibáñez, David Alonso, John A. Peacock et al. (+2 more)

We present a hybrid halo model, which improves the description of the 2-halo term by incorporating non-linear information from simulations. A linear computation of the halo-halo power spectrum is inaccurate at the transition between the 1-halo and 2-halo regimes, whereas nonlinear approaches such as Hybrid Effective Field Theory (HEFT) are not naturally compatible with the halo model decomposition. We address this limitation by constructing a collapsed HEFT (CHEFT) framework, in which the power-spectrum templates of the HEFT operator expansion are measured from simulations where 1-halo contributions are removed by collapsing particles to their halo centres. The halo-halo power spectrum is then expressed as a sum over bias operators, with mass-dependent bias parameters deduced from simulation using the probabilistic bias approach. This provides a predictive model in which there are no free bias parameters. We validate the model for a range of weighting schemes designed to mimic the halo-mass dependence of astrophysical observables, including the Sunyaev-Zeldovich effect, the Cosmic Infrared Background, and galaxy abundances described via a halo occupation distribution. For the matter field, the model recovers the power spectrum to percent-level accuracy across the transition regime. For weighted tracers, the baseline model achieves accuracies of $\sim 5-10\%$ in power, which improves to the $\sim 3-5\%$ level when including an effective higher-derivative, Laplacian-like contribution in the bias expansion. The CHEFT model thus retains the precision and flexibility of the EFT approach, while allowing the transparent incorporation of astrophysical effects that are directly associated with haloes.
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All authors Marcos Pellejero Ibáñez, David Alonso, John A. Peacock, Matteo Zennaro, Samuel Brieden

High Energy Astrophysical Phenomena

Hamiltonian variational reconstruction of the 3D magnetic geometry of relativistic jets: accuracy across GRMHD models and the fundamental sign degeneracy

Fabio Buffoli

Every resolved image of a relativistic jet encodes its magnetic field, yet no image records which way the field points along the axis. Synchrotron intensity and linear polarization are blind to this: both probe the field only through even combinations of its components. We introduce H-MOG, a variational method that reconstructs the 3D field on a lattice from two projected observables, the jet width W(z) and the linear polarization p(z), regularized by a Hamiltonian prior and optimized with automatic differentiation. We apply H-MOG to ten GRMHD simulations spanning MAD and SANE states and five black-hole spins (a* = -0.94, -0.5, 0, +0.5, +0.94), and test three routes to break the intrinsic sign degeneracy of the reconstruction: a Faraday rotation-measure term, full 3D sampling, and a Blandford-Znajek spin prior. The unsigned field orientation is recovered at <|cos|> ~ 0.95-0.98, far above the random expectation of 0.5. The sense of the poloidal field, however, is not recovered, and we prove it cannot be: W and p are invariant under B -> -B. All three routes to break this degeneracy fail for distinct physical reasons; the spin-sense relation in these turbulent jets is not monotonic, differing sharply between MAD and SANE. Recovering the sense requires a parity-odd observable: Faraday tomography or circular polarization.
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Instrumentation and Methods for Astrophysics

ESO User Support and Observation Preparation for VLTI Science Operations

M. Wittkowski, G. Beccari, A. Corporaal et al. (+15 more)

We present recent enhancements to VLTI observing capabilities from a user-oriented perspective, together with new developments in ESO's Observation Handling Tools and end-to-end operations model for VLTI. Key upgrades include GRAVITY+ Coudé guiding with laser guide stars at the UTs, improved limiting magnitudes for GRAVITY and MATISSE, and a new MATISSE narrow-field off-axis mode, all supported by a streamlined, uniform template structure. Phase 2 tools now enable finding-chart generation and the selection of Coudé guide stars and fringe-tracker targets, and will soon offer expanded preparation features and uv-coverage visualisation. We summarise usage statistics for snapshot, astrometric, imaging, and time-series observations, outline VLTI scheduling considerations, and present new video tutorials. Starting in 2026, an archive data stream of reduced GRAVITY dispersed visibilities has become available. Complementary community engagement in VLTI operations continues to grow. We close by identifying operational lessons for future interferometric facilities, including the importance of an end-to-end data-flow and user-support model, flexible scheduling, high-level observation-preparation tools, and coordinated community support to keep complex interferometric facilities usable by a broad community.
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All authors M. Wittkowski, G. Beccari, A. Corporaal, A. J. Frost, O. Hainaut, X. Haubois, J. Kammerer, A. Labdon, A. Mérand, J. Olofsson, A. Pala, C. Paladini, I. Percheron, M. Petr-Gotzens, J. Pritchard, M. Rejkuba, M. Vioque, J. Woillez

Cosmology and Nongalactic Astrophysics

Turbulent Transport of Galactic Magnetic Fields into Cosmic Voids: Insights from IllustrisTNG

Yuri Yamashita, Hiroyuki Tashiro and Kiyotomo Ichiki

Astrophysical processes associated with galaxies may contribute to the magnetization of cosmic voids. We investigate the diffusion of galactic magnetic fields in an expanding universe in the presence of turbulent magnetic diffusivity. To estimate the turbulent magnetic diffusivity, we analyze the TNG50-1 data set of the IllustrisTNG simulation and derive its redshift dependence from the characteristic turbulent velocity and turbulent scale of the intergalactic medium. Using the resulting diffusivity, we find a present-day magnetic screening length of $\sim 7\,{\rm Mpc}$, roughly twenty times larger than previous estimates based on a constant turbulent diffusivity due to the larger turbulent scale obtained in our analysis. This scale corresponds to a significant fraction of the characteristic size of cosmic voids and suggests that galactic magnetic fields can play a more important role in void magnetization than previously estimated.
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High Energy Astrophysical Phenomena

Neutron contribution to the force on a proton vortex in superconducting neutron-star matter

Oleg A. Goglichidze and Mikhail E. Gusakov

We investigate the forces acting on a proton vortex in superconducting neutron-star matter composed of neutrons, protons, and electrons, accounting for Fermi-liquid interactions in the neutron-proton subsystem. While the force arising from electron scattering by the vortex magnetic field is well known, we demonstrate that normal neutrons also exert a force on proton vortices due to Fermi-liquid coupling with superconducting protons. Using a kinetic approach based on Landau Fermi-liquid theory, we show that neutron quasiparticles scatter off a proton vortex through the spatially varying condensate momentum, giving rise to a longitudinal force proportional to the relative neutron-vortex velocity. In contrast to the electron contribution, this force has no transverse component and vanishes in the absence of neutron-proton Fermi-liquid interaction. Within a simple model, we analyze the main properties of this force and provide physically motivated estimates of its magnitude.
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Astrophysics of Galaxies

Characterising the Kinematics and Evolution of Young Stellar Groups within 1 kpc of the Sun Using Gaia DR3

Long-Fei Ding, Yun-Qian Li, Bing-Qiu Chen et al. (+2 more)

Star-forming regions are key to understanding the formation and early evolution of stars. Young stellar objects (YSOs) form groups with distinct kinematic and spatial properties, inherited from the turbulent dynamics of their parent molecular clouds. The high-precision astrometry and photometry from Gaia Data Release 3 (DR3) enable detailed studies of these groups' three-dimensional motions and their evolutionary stability. This study aims to investigate the kinematic properties and evolutionary consistency of YSO associations in the solar neighbourhood. Here, we show that HDBSCAN clustering of Gaia DR3 data yields 145 YSO groups comprising 5713 stars within 1 kpc, with a derived Larson's relation of $\sigma_v = (1.10 \pm 0.13) \times r^{0.38 \pm 0.03}$, consistent across age bins up to 20 Myr. This slope aligns with the canonical value of 0.38 and typical ranges of 0.4–0.5. The stable Larson's relation across ages indicates that the inherited turbulent structure from parent clouds persists without significant disruption. These findings establish a benchmark for studying the kinematic legacy of star-forming regions.
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All authors Long-Fei Ding, Yun-Qian Li, Bing-Qiu Chen, Guang-Xing Li, Hai-Bo Yuan

Astrophysics of Galaxies

Project Hephaistos – IV. James Webb Space Telescope Observations of Two Dyson Sphere Candidates

Erik Zackrisson, Arjan Bik, Anita Ali Asgar et al. (+11 more)

We report on JWST/MIRI imaging and spectroscopy of two M-dwarf stars previously singled out by project Hephaistos as potential Dyson-sphere candidates (their candidates D and E) due to the presence of excess flux at mid-infrared wavelengths. We find that the infrared excess does not originate from Dysonian megastructures, or other radiation mechanisms close to these stars, but from background galaxies projected within $\sim 1$ arcsec of the M dwarfs, thereby confusing previous mid-infrared photometry obtained with the WISE telescope. The candidate D background galaxy lies at redshift $z\approx 0.9$, appears point-source dominated in imaging and has a mid-infrared spectrum consistent with being a Hot Dust Obscured Galaxy (Hot DOG). The candidate E background galaxy lies at $z\approx 0.4$, displays an extended morphology with bright knots and a spectrum consistent with a dusty starburst.
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All authors Erik Zackrisson, Arjan Bik, Anita Ali Asgar, Olivia Curtis, Jason T. Wright, Tongtian Ren, Roberto J. Assef, Andrew Blain, Alexis Brandeker, Michael A. Garrett, Uma Gorti, Andreas J. Korn, Priyatam K. Mahto, Armin Nabizadeh

Earth and Planetary Astrophysics

Companion architectures of sub-Saturns: Distinct migration pathways across the Neptunian landscape

Luis Thomas, Louise D. Nielsen, Alex J. Cridland et al. (+2 more)

Close-in sub-Saturns (4.0 - 8.5 R$_\oplus$) are depleted in the Neptunian desert, accumulate in a narrow overdensity near P = 3.2 - 5.7 d (the Neptunian ridge), and thin out into the more moderately populated savanna at longer periods. We test whether sub-Saturns have systematically different companion architectures, as predicted if desert and ridge planets arrived through high-eccentricity migration while savanna planets migrated quiescently. We compile 86 systems with both transit and RV data, construct completeness maps and combine them into detection probability surfaces for companions. The combined completeness maps are used to calculate companion occurrence rates across different companion types with a joint Poisson occurrence model. Companion architectures differ significantly across the landscape. $91.1_{-4.3}^{+3.2}\%$ of savanna sub-Saturns have nearby companions (P < 200 d) compared to only $36_{-14}^{+16}\%$ of desert and ridge sub-Saturns. This contrast is driven almost entirely by small ($M_\mathrm{c} < 20\,\mathrm{M}_\oplus$) companions, which accompany $88.2_{-5.5}^{+4.2}\%$ of savanna but only $29_{-14}^{+17}\%$ of desert and ridge sub-Saturns, while medium-mass and giant companions within 200\,d are rare ($\lesssim 13\%$) everywhere. Savanna sub-Saturns moreover typically reside in compact multi-planet systems. These contrasts are robust to crosscuts in sub-Saturn radius, bulk density, eccentricity, and host-star properties. Desert and ridge sub-Saturns reside in dynamically emptied systems whose nearby companion rates match those of hot Jupiters, while savanna sub-Saturns inhabit compact multi-planet systems resembling those of warm Jupiters. This parallel supports two migration channels operating within a single population: HEM delivering planets to the desert and ridge, and quiescent disk migration or in-situ formation populating the savanna.
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All authors Luis Thomas, Louise D. Nielsen, Alex J. Cridland, Martin Schlecker, Sydney Vach

Cosmology and Nongalactic Astrophysics

Dynamics of Biased Domain Walls: The Rocket Effect

R. B. Vilhena, P.P. Avelino and C. dos Santos

We investigate the dynamics of domain walls in scalar field theories with degenerate vacua (i.e., vacua of equal energy density) in which the scalar field mass depends on the vacuum state. Using analytical arguments and numerical simulations, we show that this vacuum dependence of the scalar field mass renders the emission of scalar radiation from domain walls anisotropic, preferentially toward regions with smaller scalar field mass. We further show that the resulting recoil (rocket) effect biases the evolution of cosmological domain wall networks in favor of the lower-mass vacuum, thereby promoting network decay. We also demonstrate that the biased evolution of domain walls in theories with degenerate vacua, previously attributed to asymmetries of the potential barrier near the local maximum, is instead primarily controlled by the vacuum dependence of the scalar field mass. More generally, in theories with non-degenerate vacua, this recoil mechanism constitutes an additional source of dynamical bias that can either hasten or delay network decay relative to the standard expectation based solely on differences in vacuum energy density.
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Solar and Stellar Astrophysics

JWST Edge-on Disk Ice (JEDIce): Vibrationally hot, rotationally cold H$_2$ in the outer disk of Oph 163131 non-thermally excited by UV and cosmic rays

Korash Assani, Zhi-Yun Li, Jennifer B. Bergner et al. (+19 more)

Constraining ionization and excitation processes in protoplanetary disks is essential for understanding the chemical structure and evolution of disk material, shaping planet formation pathways. We present JWST/NIRSpec IFU observations of the edge-on disk Oph 163131, which reveal a unusual ro-vibrational H$_2$ spectrum dominated by the 1–0 O(2) line (2.627 $\mu$m), with suppressed higher-$J$ emission despite excitation to $v=2$ and $3$. This vibrationally hot, rotationally cold H$_2$ emission is spatially extended, broadly following the molecular disk traced by CO($J{=}2$–1), with emission increasing above and below a thin midplane dark lane and extending radially beyond $\sim$200 au, where near-IR scattered-light emission is no longer dominant. We interpret the observed H$_2$ emission as arising from non-thermal excitation in cold, dense outer-disk gas, where collisions depopulate higher-$J$ rotational levels within each vibrational manifold prior to emission, producing the characteristic “$v$-hot, $J$-cold" spectrum. We consider both ultraviolet irradiation and cosmic-ray excitation as contributors to the H$_2$ emission and find that their combined action, together with collisional de-excitation of high-$J$ level populations, broadly reproduces the observed line ratios and morphology. Within this framework, we infer a rather high effective cosmic-ray ionization rate of $\sim(1$-$10)\times10^{-15}$ s$^{-1}$ in the presence of a moderate UV field ($\chi_{UV}=100-1000$, in Draine units). These results for disks, together with the recent findings by Bialy et al. 2025 for the lower-density starless core B68, highlight the potential of ro-vibrational H$_2$ emission as a novel probe of cosmic-ray ionization.
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All authors Korash Assani, Zhi-Yun Li, Jennifer B. Bergner, David A. Neufeld, Daniel Harsono, Maria N. Drozdovskaya, Marco Padovani, Emmanuel Dartois, Jennifer A. Noble, Nicole Arulanantham, Alice S. Booth, Yao-Lun Yang, Mayank Narang, Will E. Thompson, Elizabeth Yunerman, Karin I. Öberg, Julia C. Santos, Charles Mentzer, Jon P. Ramsey, Lukas Welzel, Klaus M. Pontoppidan, Melissa McClure

Instrumentation and Methods for Astrophysics

Exploration of small footprint stick-slip piezoelectric actuators for use in the FLEX fibre positioner system for the Wide-field Spectroscopic Telescope (WST)

Joseph W. Barrow, Suryansh Saxena, Jon S. Lawrence et al. (+2 more)

This work presents a novel stick-slip piezoelectric actuator for the FLEX fibre positioner, addressing the challenge of reducing footprint while maintaining precision in next-generation multi-object spectroscopic instruments such as the Wide-field Spectroscopic Telescope (WST). The actuator combines compact geometry (3.2 mm diameter, sub 70 mm length) with high-resolution incremental motion, low power consumption, and high reliability. Three actuators can be integrated into a sub 7 mm diameter circle, enabling a simplified, single-plane assembly. This design offers a promising solution for miniaturized, accurate fibre positioning in wide-field spectroscopic applications.
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All authors Joseph W. Barrow, Suryansh Saxena, Jon S. Lawrence, Aaron Omadutt, Roelof S. de Jong