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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 21 July

Cosmology and Nongalactic Astrophysics

Accelerating expansion and isotropic sky-hemisphere consistency in Pantheon+ supernovae: a revised analysis in the dark energy debate

Saibal Ray, Maxim Khlopov, Aritra Sanyal et al. (+2 more)

We perform four independent decompositions of the deceleration parameter $q_0$ using 1564 Type Ia supernovae (SNe Ia) from the Pantheon+ catalogue: by redshift bin, sky hemisphere, host galaxy mass, and supernova colour, correcting a coordinate error identified by Sah, Rameez & Sarkar (SRS26) in the sky-hemisphere direction used in our original analysis. Without any progenitor-age correction, the full sample yields $q_m=-0.490$, consistent with the $\Lambda$CDM expectation of $-0.55$. Applying the Son et al. (S25) progenitor-age correction shifts this to $q_m=-0.267$, remaining in the accelerating regime. The sky hemisphere test, using the corrected CMB dipole direction (RA$=167.80^\circ$, Dec$=-7.10^\circ$), shows consistent results between the CMB dipole ($q_m=-0.527$) and anti-dipole ($q_m=-0.464$) hemispheres, supporting isotropy but not the strong deceleration values reported previously. Our revised results are consistent with \lcdm{} and do not support either the original claim of near-zero baseline acceleration or the S25/SRS26 claim of a decelerating universe.
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All authors Saibal Ray, Maxim Khlopov, Aritra Sanyal, Rikpratik Sengupta, Maxim Krasnov

Earth and Planetary Astrophysics

Dynamically Selected Mass-Radius Relationship for Low Mass Exoplanets

Brad Hansen and Austin Mao

We study the mass-radius relationship of planets in multiplanet systems as a function of their dynamical architecture. We isolate those planets whose proximity to resonance indicates that they have not undergone significant dynamical instability since formation, and therefore have not experienced a late giant impact with another planet. We compare the properties of these planets to those whose orbital architectures suggest a high probability of having experienced a giant impact. We find that planets that are likely to have experienced an impact are, on average, more massive than those that did not – consistent with prior claims. However, we find that the Hydrogen envelope mass fractions of these planets are no smaller than those of planets that did not experience collisions. Taken together, these findings suggest that dynamical evolution and planetary collisions are an integral part of the evolution of compact planetary systems, but that they must occur early enough that collisional remnants are still able to recapture gaseous envelopes from the dissipating protoplanetary disk.
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Cosmology and Nongalactic Astrophysics

Probing the matter-dominated expansion with multi-redshift Lyman-$\alpha$ BAO from DESI DR2

Hiram K. Herrera-Alcantar, Julien Guy, Alma X. Gonzalez-Morales et al. (+60 more)

We present a multi-redshift Baryon Acoustic Oscillations (BAO) analysis of the DESI Data Release 2 (DR2) Lyman-$\alpha$ (Ly$\alpha$) forest, splitting the forest auto-correlation and its cross-correlation with quasars into three redshift bins. We obtain BAO measurements at effective redshifts $z_{\rm eff} = 2.13$, $2.40$, and $2.81$ with $\sim2.0$–$2.5\%$ precision per bin in the radial and transverse directions, corresponding to $\sim1.1$–$1.2\%$ precision for the isotropic BAO measurement. Using the same data products and modeling framework as the DESI DR2 Ly$\alpha$ BAO analysis, we validate the pipeline on $400$ synthetic datasets and find unbiased BAO recovery with well-calibrated uncertainties. The measurements show an increase in the isotropic dilation parameter $D_V/r_d$ from $30.26\pm0.39$ to $32.22\pm0.47$ and in the Alcock-Paczyński parameter $D_M/D_H$ from $3.96\pm0.15$ to $5.63^{+0.22}_{-0.24}$. The Hubble distance $D_H/r_d$ decreases from $9.40\pm0.20$ to $7.22\pm0.17$, providing a direct measurement of the expansion history consistent with $\Lambda$CDM and the expected matter-dominated scaling, with $H(z)\propto(1+z)^n$ giving $n=1.34\pm0.16$. The redshift split also provides a self-consistent measurement of clustering evolution: the Ly$\alpha$ forest bias evolves as $(1+z)^\gamma$ with $\gamma_\alpha=3.05\pm0.16$, the RSD parameter has a redshift evolution described by $\gamma_\beta=-0.97\pm0.26$, and the quasar bias evolves with $\gamma_Q=1.56\pm0.23$, consistent with independent quasar clustering measurements. Combining these three-bin BAO measurements with DESI DR2 galaxy and quasar BAO measurements yields cosmological constraints consistent with the single-bin Ly$\alpha$ BAO analysis in flat $\Lambda$CDM and $w_0w_a$CDM and improves curvature constraints by $\sim12\%$ in $\Lambda$CDM$+\Omega_\mathrm{K}$.
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All authors Hiram K. Herrera-Alcantar, Julien Guy, Alma X. Gonzalez-Morales, Eric Armengaud, Edwin L. Pérez-Ochoa, Cristhian Garcia-Quintero, J. Aguilar, S. Ahlen, F. Beutler, D. Bianchi, A. Brodzeller, D. Brooks, E. Chaussidon, T. Claybaugh, A. Cuceu, K. S. Dawson, A. de la Macorra, Arjun Dey, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, G. Gutierrez, C. Hahn, K. Honscheid, D. Huterer, M. Ishak, T. Karim, R. Kehoe, D. Kirkby, A. Kremin, O. Lahav, A. Lambert, M. Landriau, L. Le Guillou, M. Manera, P. Martini, A. Meisner, R. Miquel, J. Moustakas, A. Muñoz-Gutiérrez, S. Nadathur, G. Niz, E. Paillas, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, C. Ravoux, G. Rossi, R. Ruggeri, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, H. Seo, J. Silber, G. Tarlé, B. A. Weaver, C. Yèche, R. Zhou

Instrumentation and Methods for Astrophysics

RNDR noise modeling in first-generation Single electron Sensitive Readout (SiSeRO) devices

Tonya L. Peshel, Abigail Y. Pan, Tanmoy Chattopadhyay et al. (+18 more)

Flagship observatories require single-photon detectors with ultra-fast readout, sub-electron noise performance, and scalable large-format architectures. The X-ray Astronomy and Observational Cosmology group at Stanford, in collaboration with the MIT Kavli Institute and MIT Lincoln Laboratory, is developing readout technologies for next-generation detectors. Prototypes employing Single-electron Sensitive Readout (SiSeRO) amplifiers demonstrate excellent read noise and spectral performance using repetitive non-destructive readout (RNDR), achieving 0.5 e$^-$ noise in under 57 cycles. We have modeled noise for longer RNDR cycles, exploring probabilistic mechanisms such as thermal leakage and impact ionization. Here we present our model results, including statistical limits on dark current-like signals. Maturation of SiSeRO technology will improve detector performance at soft X-ray energies, addressing technology gaps for future X-ray and UV/visible/near-IR observatories.
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All authors Tonya L. Peshel, Abigail Y. Pan, Tanmoy Chattopadhyay, Steven W. Allen, Marshall W. Bautz, Michael Cooper, Kevan Donlon, Catherine E. Grant, Sven Herrmann, Jill Juneau, Beverly J. LaMarr, Christopher Leitz, Adam B. Mantz, Eric D. Miller, R. Glenn Morris, Declan O'Neill, Peter Orel, Artem Poliszczuk, Gregory Y. Prigozhin, Haley R. Stueber, Keith Warner

Astrophysics of Galaxies

AGN Feedback Models and AGN Demographics II: Comparing Predictions of Radiative and Total Feedback to Observations

Arjun Suresh and Michael R. Blanton

We evaluate the radiative-mode active galactic nucleus (AGN) feedback models of EAGLE, SIMBA, and TNG100 by comparing their predictions for the AGN-host galaxy relationship to new observational constraints. Owing to incomplete knowledge of the underlying physics, these models differ substantially, and it remains unclear whether any of them accurately reflect reality. In a previous study, based on the demographics of narrow line AGN, we constrained $F_{\mathrm{AGN}}$, the intrinsic fraction of galaxies hosting a radiative AGN with Eddington ratio $\lambda > 10^{-3}$, as a function of host stellar mass ($M_*$) and specific star formation rate (sSFR). Observationally, $F_{\mathrm{AGN}}$ declines strongly with $M_*$ for quiescent galaxies, while remaining approximately constant for star-forming systems. In this study, we find that none of the simulations reproduce these trends even qualitatively, indicating a mismatch between the simulated and observed radiative AGN populations. Additionally, since EAGLE does not explicitly distinguish between radio and radiative modes, we compare its predictions for $F_{\mathrm{AGN}}(M_*, \mathrm{sSFR})$ to our novel measurements of the combined radiative and radio mode AGN fractions. For EAGLE's constant coupling efficiency $\epsilon_{\mathrm{f}} = 0.15$, and for the adopted standard bolometric and jet-power conversion factors in the observations, the total AGN feedback energy in EAGLE is broadly consistent with observations, though with Eddington ratios a factor of 10 greater than is observed. More detailed comparisons of EAGLE's assumptions with observations are therefore required before drawing firm conclusions.
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High Energy Astrophysical Phenomena

Shock cooling emission from late-time mass loss in low-mass He star binaries

Samantha C. Wu and Anthony L. Piro

A subset of hydrogen-poor supernovae (SNe) exhibit signatures of interaction with nearby dense circumstellar material (CSM). These SNe may originate from interacting binary systems, in which the SN progenitor experiences intense mass loss when it overflows its Roche lobe close to core collapse. In this work, we explore the appearance of SNe from low-mass stripped star progenitors in binary systems, for a range of initial orbital periods and masses. We model the CSM based on the stripped stars' mass loss history in binary stellar evolution simulations, then numerically explode the progenitors to calculate the SN light curves. Shock cooling emission (SCE) from the CSM dominates the early light curves, followed by SCE from the extended helium envelopes of the stripped stars, which form helium recombination plateaus. The appearance and properties of our model light curves are reflected in a subset of Type Ib/n SNe from the literature. Some of our models tend to evolve rapidly and are quite hot during SCE, so they may naturally explain some fraction of fast blue optical transients (FBOTs). Since the mass loss history of our binary progenitor models can produce dense CSM out to ~10^18 cm, interaction of this CSM with the SN shock could generate bright late-time radio emission in the years after the optical SN. Searching for late time rising radio emission from FBOTs could be used to test which events are explained by the scenario we explore here.
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Solar and Stellar Astrophysics

A Deep Learning Framework for Predicting Solar EUV Irradiance During Significant Flares

Sathvik Soman, Jason T. L. Wang, Haimin Wang et al. (+1 more)

We present FlareEUV, a multimodal deep learning framework for predicting daily extreme ultraviolet (EUV) irradiance at 6.5 nm over three consecutive days during significant solar flares, using multi-instrument observations from NASA's Solar Dynamics Observatory (SDO). We consider 33 significant flares in the period between 2011 and 2014 in Solar Cycle 24. The SDO observations include 13 co-aligned full-disk images, comprising eight AIA EUV/UV and five HMI magnetic/continuum products. FlareEUV learns the relationship between magnetic structure and coronal emission from the raw imaging data using a lightweight attention-based architecture. Our experimental results demonstrate the good performance of FlareEUV in short-term EUV irradiance forecasting during the significant flares and its superiority over baseline methods.
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All authors Sathvik Soman, Jason T. L. Wang, Haimin Wang, Haodi Jiang

Instrumentation and Methods for Astrophysics

Characterising the response of an International LOFAR Station

Letizia Vincetti, Sai C. Susarla, Owen A. Johnson et al. (+7 more)

Phased-array radio interferometers with fixed antennas are a highly scalable design which can achieve a large gain. However they are complex systems and challenging to calibrate. Here we examine the response of an International LOFAR Station, the high-band antennas of the Irish LOFAR station. In modelling our measured responses, we account for projection effects, the frequency-dependence of the aperture efficiency and pulsar spectra, as well as sky and instrumental noise contributions. We perform long-track observations of 11 bright pulsars as they move across the sky, apply RFI mitigation and determine the signal-to-noise ratio response as a function of time, elevation and azimuth. We use the DreamBeam software to model the beam response of the station to compare with what is observed. The sensitivity map so obtained was validated using observations of PSR B0329+54 on the Swedish LOFAR station. As expected, the sensitivity is higher near the zenith. However, an asymmetry with respect to the zenith point is detected. Characterising the instrumental response in azimuth reveals a better performance as the targets rise, as compared to when they set. This trend is seen for all pulsars and is consistent with other International Stations. The magnitude of the effect can exceed 20%. We consider variations in the beam model and noise level, both frequency- and time- dependent, to try to account for this. A possible explanation for the hysteresis-like response in elevation could be an imbalanced signal weighting of the polarisation components. This work addresses the importance of accurate beam modelling and noise evaluation for the LOFAR 2.0 system upgrade as well as being relevant to the under-construction SKA-Low facility.
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All authors Letizia Vincetti, Sai C. Susarla, Owen A. Johnson, Evan F. Keane, David J. McKenna, Tobia D. Carozzi, Gavin Ramsay, Oisin Creaner, Peter T. Gallagher, Joe McCauley

Astrophysics of Galaxies

Systematic Effects in Gaia CRF Photometry Related to Scanning Geometry and BP/RP excess factor

Valeri V. Makarov

I report a previously undocumented, large-amplitude systematic dependence of the median Gaia $G$-band magnitude of CRF3 sources on ra\_dec\_corr, which reflects the preferred direction of scans, accompanied by a partially correlated trend in the BP/RP flux excess factor. Given the imminent release of Gaia DR4, the purpose of this note is alerting the community to this artifact.
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Earth and Planetary Astrophysics

Atmospheric retrieval evidence for water isotopologue HDO on exoplanet WASP-39b

Fabian Gruebel, Karan Molaverdikhani, Barbara Ercolano et al. (+5 more)

Hydrogen-isotopologues are commonly used to trace the chemical processing and origin of hydrogen-bearing species throughout the Universe, however, their abundance remains unconstrained for extrasolar planets. Here, we report atmospheric retrieval evidence for the deuterated water molecule HDO in an exoplanet atmosphere, retrieved from James Webb Space Telescope transmission spectra of the hot Jupiter WASP-39 b, resulting in a deuterium-to-hydrogen ratio in water of $4.0^{+1.3}_{-1.1} \times 10^{-3}$. The inferred value is substantially higher than those measured for the Solar System gas giants and overlaps numerically with values reported for some protostellar and inner Solar System environments. This enrichment may reflect either inherited water-rich material accreted beyond the snow line or isotopic processing in the observable atmosphere through transport, photochemistry, and subsequent escape.
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All authors Fabian Gruebel, Karan Molaverdikhani, Barbara Ercolano, Katy L. Chubb, Paola Caselli, Tommaso Grassi, Rosa Arenales-Lope, Dwaipayan Dubey

Astrophysics of Galaxies

Swing amplification in star-gas disks

Abhishek Hegade K. R. and Chris Hamilton

Recent JWST and ALMA observations have revealed stellar bars and spirals in gas-rich galactic disks at redshifts as high as $z \simeq 4$. The simplest theoretical paradigm we have for understanding such non-axisymmetric features is the linear theory of swing amplification (SA) in the 2D shearing sheet. However, while the SA mechanism in a gaseous shearing sheet was first studied in 1965, and that in a collisionless stellar sheet in 1966, the coupled star-gas linear SA equations have never been solved explicitly. Here we write down these equations and use them to study the evolution of non-axisymmetric swinging waves in stable disks. We find that waves are often amplified temporarily by factors of $10-100$ or more, and that the maximum non-axisymmetric amplification factor is tightly correlated with the system's distance from the axisymmetric stability boundary in the $(1/Q_\mathrm{s}, 1/Q_\mathrm{g})$ plane. The true star-gas behavior differs significantly from the `two-fluid' idealizations used in the past, because phase mixing of the collisionless stellar component acts as a sink of perturbation energy. Closely analogous results hold for finite-thickness disks except for the shifting of the stability boundary. We provide a python code that calculates the SA factors and maximally-amplified wavelength given the background disk parameters.
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Astrophysics of Galaxies

The Age-Thickness Relation as a Tracer of the Merger History of Disk Galaxies

Lekshmi Thulasidharan, Elena D'Onghia, Robert Benjamin et al. (+2 more)

In the hierarchical framework of galaxy formation, disk galaxies are shaped by a sequence of mergers and interactions, yet reconstructing this history from observations remains challenging. We show that the merger history of a galaxy leaves measurable imprints in the vertical structure of its stellar disk. Using Milky Way analogues from the TNG50 simulations, we demonstrate that the Age-thickness relation, quantified by the dispersion of vertical stellar positions ($\Delta_z$), encodes both the dynamical heating of pre-existing stars and the birth conditions of stars formed during perturbed phases. Major mergers produce pronounced, step-like features in the Age$-\Delta_z$ relation, reflecting strong disk heating and subsequent re-formation of a thin disk, while flyby interactions generate weaker, localized enhancements associated primarily with disturbed star formation. We show that this diagnostic is robust across different locations within the disk and largely insensitive to fractional distance uncertainties lower than 20%, though its temporal resolution is limited by uncertainties in stellar ages. Because the Age$-\Delta_z$ relation relies only on stellar positions and ages, it provides an observationally accessible alternative to traditional kinematic diagnostics. With current and upcoming surveys mapping the Milky Way with unprecedented precision, this framework offers a new avenue for reconstructing the merger history of our Galaxy and probing the dynamical evolution of disk galaxies across cosmic time.
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All authors Lekshmi Thulasidharan, Elena D'Onghia, Robert Benjamin, Ronald Drimmel, Eloisa Poggio

Astrophysics of Galaxies

Discovery of Optical Filaments in the North Polar Spur/eROSITA Bubble

Julian Shapiro

I report the discovery of optical filaments in H$\alpha$, [O III], and [S II], coincident with $144\,\mathrm{MHz}$ structure, associated with the North Polar Spur (NPS) region of the eROSITA bubbles. The optical emission is identified in the Northern Sky Narrowband Survey, and contains distinct structure and potentially elevated $\text{[S II]}/\mathrm{H}\alpha$ relative to typical high-$b$ outflows from the warm ionized medium (WIM). $\Delta$-variance and power spectrum analysis of the NPS H$\alpha$ shows a preference for filaments on the scale of lag $L\approx0.6^{\circ}$. The optical and $144\,\mathrm{MHz}$ emission peaks in intensity in an interior region of the NPS, aligned with surrounding Galactic magnetized structures, and also shows fainter signal at the eROSITA bubble edge. The required power to produce the background-subtracted $I_{\mathrm{H}\alpha}=1.85\pm1.04\,\mathrm{R}$ emission is $P_\mathrm{req}\approx5\mathrm{-}12\times10^{41}\,\mathrm{erg\,s}^{-1}$, comfortably exceeded by AGN jet models, plausible for AGN hot accretion flow and star formation ring models, and disfavoring star formation driven winds.
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Astrophysics of Galaxies

Mid-Infrared Colors Vary with Galactic Environment: Contrasting Star-Forming Disks, Young Centers, and Quiescent Star-Formation Deserts

Debosmita Pathak, Karin M. Sandstrom, Adam K. Leroy et al. (+27 more)

We present $50{-}100\,$pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the PHANGS-JWST survey. Mid-IR emission traces the dust column density, intensity ($U$) and hardness of the interstellar radiation field, and the physical state (charge, size) and abundance of polycyclic aromatic hydrocarbons (PAHs). Mid-IR colors that trace PAH band-ratios remain fairly constant in the diffuse ISM of star-forming disks. However, they show stark variations in extreme environments: highly star-forming central molecular zones (CMZs) and star-formation deserts/quiescent bulges. In CMZs, PAH-to-continuum ($3.3/21$, $7.7/21$, and $11.3/21\,\mu$m) and the $10/21\,\mu$m continuum colors are $0.2{-}0.4$ dex lower than in normal disks. We attribute this to higher $U$ based on the far-IR dust colors and the high $21\,\mu{\rm m}/\Sigma_{\rm Mol}$, which we suggest to be a good tracer of $U$ outside star-forming regions. Meanwhile, star-formation deserts show low $7.7\,\mu$m PAH emission, resulting in low $7.7/21\,\mu$m and $7.7/11.3\,\mu$m, while all other mid-IR colors remain typical. This suggests the presence of more neutral PAHs in star-formation deserts, where low $7.7\,\mu$m likely reflects ISM conditions similar to early-type and elliptical galaxies. All environments form part of a continuous trend in $7.7/11.3\,\mu$m vs.\ specific star-formation rate.
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All authors Debosmita Pathak, Karin M. Sandstrom, Adam K. Leroy, Ryan Chown, Daniel A. Dale, Hannah B. Koziol, Mansi Padave, Jessica Sutter, Thomas G. Williams, Dalya Baron, Alberto D. Bolatto, Mederic Boquien, Oleg V. Egorov, Eric Emsellem, Simon C. O. Glover, Ralf S. Klessen, Eva Schinnerer, Todd A. Thompson, Francesco Belfiore, Frank Bigiel, Enrico Congiu, Ivan Gerasimov, Jay Gonzalez Lobos, Annie Hughes, Laura A. Lopez, Justus Neumann, Elias K. Oakes, Hsi-An Pan, Erik Rosolowsky, Sumit K. Sarbadhicary

Astrophysics of Galaxies

Local morphology and asymmetry of galactic rotation curves in a kinetic gas transport framework: NGC 3198

Anton A. Lipovka and Anna A. Lipovka

We investigate whether the observed fine structure and asymmetry of non-averaged galactic rotation curves can be reconstructed directly from the observed HI distribution within the framework of a kinetic gas transport description. Using the observed HI density profiles separately for the approaching (north-eastern) side and the receding (south-western) side of the galaxy NGC~3198, we reconstruct the corresponding rotation curves based on the equation previously derived in \citet{Lipovka2022}. It is shown that the reconstructed curves reproduce not only the approximately flat large-scale behaviour of the observed rotation curves, but also their detailed local morphology and asymmetry separately for the north-eastern and south-western sides of the galactic disk. The obtained results indicate that the local structure of galactic rotation curves is closely connected with the local HI distribution and arises naturally as a consequence of kinetic gas transport processes in galactic disks.
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Astrophysics of Galaxies

Reading Between the Lines: Forward Modeling Dust, Continuum, and Spectral Cleaning for Multi-Line Intensity Mapping

Anirban Roy, Rachel S. Somerville and Anthony R. Pullen

Line intensity mapping (LIM) offers a tomographic view of galaxy evolution by measuring the aggregate emission from unresolved galaxies. In the optical and near-infrared, the line emission is accompanied by much brighter continuum emission that must be removed to recover line auto- and cross-power spectra. We develop a forward-modeling framework using a $\sim2$deg$^2$ lightcone drawn from a cosmological $N$-body simulation populated with galaxies using a physics-based semi-analytic model (SAM). We construct intensity maps for the stellar continuum and for the strongest optical lines, H$\alpha$, H$\beta$, [O III] $\lambda5007$, and [O II] $\lambda3727$, including nebular dust attenuation tied to galaxy properties. From these cubes, we measure cross-channel angular power spectra, $C_\ell(\lambda_i,\lambda_j)$, and the normalized correlation matrix $r_{ij}$. In line-only maps, the correlation matrices show same-redshift ridges between emission lines, demonstrating how multi-line intensity mapping (MLIM) can isolate large-scale structure and probe dust attenuation. We show that dust suppresses the line cross-power by an amount that depends on galaxy properties, wavelength, and line pair, so a single overall amplitude cannot capture its effect. In total maps, however, the continuum dominates the raw correlations and hides much of the line-ridge structure. We therefore apply principal component analysis (PCA)-based spectral cleaning and quantify the line-transfer function using the simulation truth. Removing 20 PCA modes gives the best trade-off between line recovery and continuum suppression in our mock maps. Our results demonstrate the promise and challenges of extracting dust-sensitive LIM observables from SPHEREx-like observations, and highlight the need to model continuum cleaning and its transfer function in quantitative inference pipelines.
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Solar and Stellar Astrophysics

A Probabilistic Framework for Population Studies of the Solar Neighborhood: Application to SDSS-V and Gaia

Ilija Medan, Keivan G. Stassun, Zachary Way et al. (+8 more)

Studies of the Solar Neighborhood require spectroscopic follow-up of stars identified in astrometric surveys to fully characterize their physical properties. The SDSS-V Solar Neighborhood Census (SNC) is a dedicated program to observe stars within 100~pc. However, due to competing observing programs and fiber assignment constraints, the resulting sample carries severe and complex selection effects. A framework is presented for characterizing the selection function of the SDSS-V SNC relative to the Gaia Catalog of Nearby Stars (GCNS), along with a forward modeling method to infer the properties of stellar subpopulations across the GCNS-defined 100 pc sample. The selection function is based on a method that models the selection probability as a function of sky position, Gaia G magnitude, and BP-RP. The resulting detection probabilities faithfully reproduce the known survey planning logic. This work further introduces the concept of a "subpopulation probability" – a grid of posterior estimates across the Hertzsprung-Russell (HR) diagram representing the likelihood that a GCNS member belongs to a given SDSS-V defined subpopulation. The framework is validated with a mock dataset and its scientific utility is demonstrated through two applications using data from the Data Release 19: mapping H$\alpha$ emission across the HR diagram and measuring the variation of stellar density with mass and metallicity. These results illustrate how statistically robust population studies can be conducted with an incomplete spectroscopic survey when the selection function is well characterized. The code is made publicly available with this work, which will serve as an important tool for future studies.
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All authors Ilija Medan, Keivan G. Stassun, Zachary Way, Guy S. Stringfellow, Alexandre Roman-Lopes, Jiadong Li, Madeline Lucey, Andrew R. Casey, Bárbara Rojas-Ayala, Ricardo López-Valdivia, José G. Fernández-Trincado

Cosmology and Nongalactic Astrophysics

The silent dark sector: a field-theory approach to unified dark fluids with vanishing speed of sound

Javier de Cruz Pérez, Darío Jaramillo-Garrido, Antonio L. Maroto et al. (+1 more)

We introduce a novel class of field-theory models that provide a unified description of the dark sector as a single perfect fluid with vanishing sound speed. These models also admit the interpretation of cold dark matter interacting with vacuum energy while avoiding any phantom behavior and including standard $\Lambda$CDM as a particular case. Built upon a single scalar field invariant under transverse diffeomorphisms, the framework naturally implements the constraints imposed in the so called mimetic models. We analyze a particular simple example exhibiting an effectively evolving dark energy and find that it can reproduce the DESI best-fit CPL evolution with the same number of free parameters.
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All authors Javier de Cruz Pérez, Darío Jaramillo-Garrido, Antonio L. Maroto, Prado Martín-Moruno

Astrophysics of Galaxies

Rapid growth in a dual AGN during a gas-rich merger at z~4.5

Hyewon Suh, Roberto Decarli, Emanuele Paolo Farina et al. (+15 more)

The late stages of galaxy mergers - when two supermassive black holes (SMBHs) reach kiloparsec-scale separations - represent a critical phase for understanding SMBH growth, galaxy co-evolution, and the progenitors of low-frequency gravitational waves. Yet confirmed close-separation (<3 kpc) dual active galactic nuclei (AGNs) remain confined to the local Universe, despite predictions that such systems should be common in the merger-rich early Universe. Here we report the discovery of LID-1166, a dual AGN with a projected separation of ~1.5 kpc at z~4.5, representing the first such system known beyond the local Universe. Spatially resolved JWST/NIRSpec integral-field spectroscopy reveals two spatially and kinematically distinct narrow-line emission components with a line-of-sight velocity offset of ~ -164 km/s. Both components additionally exhibit broad Ha emission, including a compact off-nuclei broad Ha component associated with the companion source, confirming two actively accreting SMBHs. Independent ALMA [CII] 158 um observations reveal corresponding spatially and kinematically distinct cold gas components associated with the same nuclei, demonstrating that the system is a gas-rich merger. While undergoing super-Eddington accretion during a late-stage merger, the SMBHs already lie on the local black hole-host mass relation for massive elliptical galaxies within the uncertainties, suggesting that rapid, obscured growth may help establish this relation early in cosmic history. LID-1166 reveals a previously hidden phase of SMBH growth and points to a missing population of heavily obscured, merger-driven dual AGNs at high redshift.
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All authors Hyewon Suh, Roberto Decarli, Emanuele Paolo Farina, Julia Scharwächter, Mar Mezcua, Giorgio Lanzuisi, Federica Loiacono, Brian C. Lemaux, Sukyoung K. Yi, Stefano Marchesi, Marta Volonteri, Günther Hasinger, Francesca Civano, Anniek Gloudemans, Ena Choi, Yeonwoo Nam, Adi Foord, Silvia Onorato

Instrumentation and Methods for Astrophysics

A Scalable Fast Multipole Method Poisson Solver for the RAMSES code: II. Adaptive Mesh Refinement and Adaptive Time Stepping

Jun-Young Lee and Romain Teyssier

We present an extended implementation of a scalable, O(N) Poisson solver based on the fast multipole method (FMM), fully compatible with adaptive mesh refinement (AMR) and adaptive time stepping (ATS) within the RAMSES framework. Building on the unigrid algorithm in Lee & Teyssier (2026), we introduce several novel elements, including the use of multiple FMM trees, one for each AMR level, a merged FMM tree for all active levels to optimize neighbor searches, and the introduction of the concept of "nearest-field" to enforce force symmetry across refinement levels. Across a broad set of test problems, we find excellent, percent-level agreement with our reference traditional multigrid (MG) solver. We show, however, that FMM exhibits better momentum conservation properties across coarse-fine AMR interfaces. Finally, despite the overhead introduced by the spatio-temporal adaptivity, FMM shows better scalability than MG across various AMR configurations, with the largest gains obtained for the largest configurations.
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High Energy Astrophysical Phenomena

Four, One, and None: Quantifying the Ultra-High-Energy Neutrino Anomaly Across ANITA-IV, KM3NeT, and IceCube

Dibya S. Chattopadhyay, Carlos A. Argüelles and Vedran Brdar

The four near-horizon neutrino-like events reported by ANITA-IV and the ultra-high-energy track-like event KM3-230213A observed by KM3NeT imply neutrino event rates that are in tension with the absence of corresponding events at IceCube. In this work, we perform a joint analysis of these events, taking into account the absence of any corresponding ones at IceCube. We construct semi-analytic, energy- and direction-dependent effective areas for the three detectors and account for the time-dependent ANITA-IV and KM3NeT exposures. For a diffuse all-sky power-law flux varying both the normalization and the spectral index, the measured event rates across the three detectors are not reproduced. The best-fit configuration, corresponding to a tension of $\sim7.5\sigma$, predicts approximately five IceCube events while strongly underpredicting the ANITA-IV and KM3NeT counts. In contrast to the diffuse scenario, the tension can be substantially alleviated if the events arise from short-duration transients that occur exactly along the observed directions during the ANITA-IV and KM3NeT detection windows. Such a realization, however, is highly fine-tuned. If rare transients are instead distributed randomly across the full sky over the $\sim15$-year IceCube observation period, additional sources inevitably contribute to the IceCube exposure. For benchmark populations with a probability of approximately $10^{-4}$ to produce four favorable transients at ANITA-IV, the best-fit configuration of sources, out of $10^5$ Monte Carlo realizations, remains in $5.9\sigma$ tension. We conclude that, within the Standard Model, directional and temporal variations alone can not reconcile the ANITA-IV and KM3NeT observations with the IceCube null result, under both a diffuse all-sky flux and a rare-transient source hypothesis.
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Astrophysics of Galaxies

Extreme Variability Reveals How the Eddington Ratio Regulates Coronal Power in Active Galactic Nuclei

Arghajit Jana, Claudio Ricci, Franz E. Bauer et al. (+13 more)

The bolometric luminosity ($L_{\rm bol}$) of active galactic nuclei (AGNs) is a key tracer of accretion physics, but its direct determination is often hindered by limited spectral coverage and contamination of the host galaxy. Bolometric corrections ($\kappa_{\lambda} = L_{\rm bol}/L_{\lambda}$) offer a practical means of estimating $L_{\rm bol}$, with the X-ray bolometric correction ($\kappa_{\rm 2-10}$) being crucial for exploring the coupling between the accretion disk and the X-ray corona. Here we present multi-epoch, multi-wavelength observations of five highly variable, changing-state AGNs that span more than three orders of magnitude in Eddington ratio ($-3.6\lesssim \log \lambda_{\rm Edd} \lesssim -0.5$). This unique data set reveals a remarkably tight relation between $\kappa_{\rm 2-10}$ and $\lambda_{\rm Edd}$, with an intrinsic scatter of only $\sim0.05$ dex. We find that while the sources show bolometric corrections following different tracks in luminosity space that depend on black hole mass, they all display the same $\kappa_{\rm 2-10}-\lambda_{\rm Edd}$ trend. This shows unambiguously that $\lambda_{\rm Edd}$ is the primary driver of X-ray bolometric corrections, and points to a tight underlying trend that can be used to obtain reliable estimates of bolometric output from X-ray luminosities. Our results highlight how time-domain, multi-wavelength observations of variable AGN offer unique insights into the accretion flow structure and its radiative output.
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All authors Arghajit Jana, Claudio Ricci, Franz E. Bauer, Kriti Kamal Gupta, Benny Trakhtenbrot, Alessia Tortosa, Ruancun Li, Luis C. Ho, Richard Mushotzky, Hsiang-Kuang Chang, Yaherlyn Diaz, Georgios Dimopoulos, Kristína Kallová, Michael J. Koss, Stéphane Paltani, Matthew J. Temple

Astrophysics of Galaxies

A pilot sample of Planck-selected strongly lensed sub-mm galaxies: NOEMA observations and physical characterisation

Leonardo Trobbiani, Matteo Bonato, Ivano Baronchelli et al. (+6 more)

The extreme brightness of high-$z$ strongly lensed galaxies detected by Planck surveys, thanks to their exceptionally large gravitational magnifications, offers a unique opportunity to investigate in extraordinary detail their structure and kinematics during their active star-formation phase. As a step in this direction, we present and analyse NOEMA imaging and spectroscopic data for four lensed high-z galaxy candidates. We performed continuum and line imaging of the sources at 2 and 3 mm bands down to $1''.2$ spatial resolution and 40 $\rm{km}\,{\rm s}^{-1}$ spectral resolution, reconstructed and fitted the line profiles, and produced moment maps of the line emission to investigate the spatial distribution and kinematics of the molecular gas. We also carried out the gravitational lens modelling for one of the sources. The continuum images showed multiple components for at least two of the sources, strongly supporting the strong lensing scenario. We detected with high S/N ratios two CO lines for all sources, at CO(3-2), CO(4-3) and CO(5-4) transitions; for one source, we also detected the [CI](1-0) line. We derived accurate spectroscopic redshifts $2.3 \lesssim z \lesssim 3.3$, with $1\sigma$ uncertainties $\delta z \approx 10^{-4}$ in redshift. All four sources lie well above the CO line luminosity-linewidth relation for unlensed galaxies, providing independent confirmation of their strongly lensed nature. Three sources exhibit broad (FWHM$\gtrsim 400\,{\rm km}\,{\rm s}^{-1}$), double-peaked line profiles and substantial velocity gradients, while the last one shows relatively narrow, single-peaked lines and no detectable velocity gradients, possibly indicating a nearly face-on geometry or intrinsically simple kinematics.
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All authors Leonardo Trobbiani, Matteo Bonato, Ivano Baronchelli, Gianfranco De Zotti, Mattia Negrello, Marika Giulietti, Stefano Berta, Cristian Vignali, Marcella Massardi

Solar and Stellar Astrophysics

Large Magellanic Cloud Globular Clusters in the Near-infrared. I. RR Lyrae in Reticulum

Anupam Bhardwaj, Susmita Das, Prashant Nishad et al. (+10 more)

Reticulum is an old, metal-poor, and sparsely populated globular cluster in the outer regions of the Large Magellanic Cloud (LMC) and hosts a rich population of RR Lyrae stars. Being as close as possible to a single stellar population with negligible metallicity spread and low reddening, Reticulum is an ideal laboratory for testing stellar pulsation models and calibrating population II distance indicators. We present homogeneous multi-epoch near-infrared (NIR, JHKs) observations of RR Lyrae variables in Reticulum obtained with the Flamingos-2 imager on the 8.1-m Gemini South Telescope. Using NIR light-curve templates, we derive accurate intensity-averaged magnitudes and peak-to-peak amplitudes for 32 RR Lyrae stars, including 22 fundamental-mode (RRab), 4 first-overtone (RRc), and 6 mixed-mode (RRd) pulsators. The empirical JHKs period-luminosity (PL) relations of Reticulum RR Lyrae are very tight, exhibiting dispersions (~0.05 mag) comparable to those observed in Galactic globular clusters. The derived PL slopes are shallower than those reported for Galactic cluster variables. Adopting recent empirical and theoretical period-luminosity-metallicity (PLZ) calibrations based on Galactic globular clusters and pulsation models, we derive a true distance modulus of $\mu_0 = 18.472 \pm 0.035$ mag to Reticulum. This cluster distance is in excellent agreement with the precise geometric distance to the LMC and places Reticulum close to the LMC barycentric distance. The well-characterized RR Lyrae population and a precise distance make Reticulum a potential anchor for calibrating Population II distance ladder.
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All authors Anupam Bhardwaj, Susmita Das, Prashant Nishad, Marina Rejkuba, Giulia De Somma, Marcella Marconi, Chow-Choong Ngeow, Vincenzo Ripepi, Sarang Shah, Subhajit Kar, Shashi Kanbur, Matteo Monelli, Massimo Dall'Ora

Astrophysics of Galaxies

The GOLIATH Survey: OVI Absorption Reveals CGM Evolution through the Starburst-to-Quiescent Transition in Massive Galaxies

Derick Flores, Rongmon Bordoloi, Jason Tumlinson et al. (+12 more)

We present the GOLIATH survey (Galaxies, Outflows, and the Lifecycle of Immense, Active, Transforming Halos), a study of the multiphase circumgalactic medium (CGM) of massive ($\langle\log M_\star/M_\odot\rangle \approx 11$), blue ($u-r < 1.65$) starburst and post-starburst galaxies at $\langle z\rangle \approx$ 0.43. This work characterizes the warm-hot CGM through OVI absorption in the inner halo ($R/R_{\rm vir} \leq 0.6$) of these rare systems. Across the star-forming population, OVI column density rises by nearly 1~dex from $\log M_\star/M_{\odot} \sim 8$ to $\sim 11.5$ and increases with specific star-formation rate (sSFR). Two GOLIATH galaxies with the highest sSFR show the strongest CGM OVI absorption ($\log N_{\rm O\,VI}[\rm cm^{-2}] \gtrsim 15$). In the $\log M_\star/M_{\odot} = [11,12)$ inner-CGM region, massive star-forming galaxies exceed quiescent galaxies on average by a factor of $\sim 3$ in OVI column density and $\sim 1.5$~dex in CGM OVI mass ($\log(M_{\rm O\, VI}/M_\odot) \approx 7.3$ versus $\approx 5.8$), with covering fractions roughly three times higher (62.5% versus 24% at $\log N_{\rm O\,VI}[\rm cm^{-2}] \geq 14$). The OVI line widths and column densities are consistent with feedback-driven radiative cooling, in which outflow shocks heat the CGM and the gas cools back through the OVI window; the short cooling time, $t_{\rm cool} \sim 10$-$100$~Myr, requires continuous replenishment by active feedback to sustain this reservoir. The residual OVI in quiescent systems may arise from ambient gas at the high-temperature end of the cooling curve. OVI thus traces feedback on short timescales and probes the star-forming–quiescent transition at $\log M_\star/M_{\odot} \gtrsim 11$.
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All authors Derick Flores, Rongmon Bordoloi, Jason Tumlinson, J. Christopher Howk, Nicolas Lehner, Mary Rickel, Benjamin Oppenheimer, Joseph Burchett, Ahmed Shaban, John O'Meara, Andrew Fox, J. Xavier Prochaska, Simon Xinlin Wu, Jack Higginson, Robert A. Simcoe

Cosmology and Nongalactic Astrophysics

Cosmic CORALS: Timing the Universe with high-z star clusters

Elena Tomasetti, Martin Millon, Licia Verde et al. (+5 more)

In this work, we explore the potential of anchoring the age-redshift relation across cosmic time by probing the oldest star clusters at high redshift, now observed thanks to the James Webb Space Telescope in strongly lensed fields. As a case study, we consider one of the highest-redshift systems observed, the Cosmic Gems arc at $z=9.625$. We perform image deconvolution of multi-band JWST imaging, identifying a total of 20 point sources along the arc. We derive the stellar ages through a cosmology-independent spectral energy distribution (SED) fitting framework, ensuring that these measurements can be used as unbiased cosmological anchors. By combining these high-z systems with state-of-the-art local globular cluster ages, we perform a joint Bayesian fit to the age-redshift relation in a flat $\Lambda$CDM model, measuring $H_0=70^{+27}_{-16}\ \rm{km\ s^{-1}\ Mpc^{-1}}$ and $\Omega_m=0.33^{+0.37}_{-0.21}$. While these constraints are still loose, we show that the slope of the degeneracy, a power-law in the $\Omega_m - H_0$ plane, is highly dependent on the redshift of the sources, becoming shallower as redshift increases. Leveraging this geometric rotation, we present forecasts showing that a future sample of $\sim 300$ lensed proto-globular clusters well-distributed up to $z \approx 10$ could tighten the statistical precision to $4\%$ on $H_0$ and $11\%$ on $\Omega_m$, competitive with and independent of methods currently in use. The present work, therefore, represents a new avenue in cosmology and comes at a timely moment, when JWST observes high-redshift lensed star clusters routinely, Euclid and the Nancy Grace Roman Space Telescope uncover new strong lensing fields, and close to the start of operation of the ESO Extremely Large Telescope.
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All authors Elena Tomasetti, Martin Millon, Licia Verde, Frédéric Courbin, Raul Jimenez, Michele Moresco, Carmela Lardo, Andrea Cimatti

Astrophysics of Galaxies

The first dusty galaxies across $6 \lesssim z \lesssim 14$: Blue monsters, red monsters, and the bimodality of dust content in early galaxies

Sergio Martínez-González, Casiana Muñoz-Tuñón and Santiago Jiménez

JWST has revealed galaxies at $z>10$ with extremely blue UV-continuum slopes approaching $\beta_{\rm UV}\lesssim-2.4$, and low inferred dust contents. At similar redshifts, JWST and ALMA reveal dusty massive systems reaching $\beta_{\rm UV}\gtrsim-1$. We aim to explain blue monsters and red monsters at $z\gtrsim10$ as different outcomes of supernova dust retention in clustered star-forming systems and connect this bimodality to dusty massive galaxies at $z\simeq6$–7. We model dust removal in a cluster-dominated regime through cloud-scale mechanical blowout followed by breakout from stratified high-redshift disks. The shock-processed dust mass retained in the UV-attenuating layer is converted into a UV-continuum slope using absorption opacities derived from 3D hydrodynamical simulations of clustered supernovae in porous molecular clouds. In compact, gas-rich galaxies, efficient cloud blowout and disk breakout reduce the retained dust fraction to blue-monster levels, yielding $\beta_{\rm UV}\lesssim-2.4$. Larger stellar masses increase the retained dust column and produce red-monster-like systems with $\beta_{\rm UV}\gtrsim-1.5$, reaching $\beta_{\rm UV}\simeq-0.5$ when radiative losses weaken large-scale driving. The transition depends on whether clustered-supernova ejecta cross both the natal cloud and the galactic gas layer. Supernova dust production, shock processing, radiative losses, and mechanical venting can jointly explain UV-bright dust-poor galaxies and red dusty massive systems across $6\lesssim z\lesssim14$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Can the universe be matter-dominated after a supercooled first-order phase transition?

Henda Mansour, Yann Gouttenoire and Felix Kahlhoefer

We show that the answer is generally no, at least not immediately. Bubble collisions leave behind a highly inhomogeneous scalar field with persistent relativistic gradients, producing an equation of state between matter and radiation. Using lattice simulations in one, two and three spatial dimensions, we find that the equation of state is controlled by the wall Lorentz factor at collision $\gamma_\star$: walls with larger $\gamma_\star$ populate higher-momentum modes and drive the fluid closer to radiation. Matter domination begins only after these modes redshift, at $a/a_\star \simeq \gamma_\star$, or after the field thermalises through self-scattering and number-changing processes. This delay has direct implications for gravitational waves, primordial black holes and dark matter production.
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Instrumentation and Methods for Astrophysics

Strong Gravitational Lensing Posterior Sampling in Pixel-Space Using Diffusion Models and Recurrent Inference Machines

Guillaume Payeur, Laurence Perreault-Levasseur, Gabriel Missael Barco et al. (+1 more)

Modeling galaxy-galaxy strong gravitational lenses to infer the brightness of the source galaxy and the mass distribution of the foreground galaxy is computationally challenging, particularly for high-resolution, high signal-to-noise ratio observations. In this regime, high-dimensional representations of both the source and the foreground mass distribution are necessary to model the data down to the noise level. This inference problem has been challenging for both traditional and machine learning-based methods because of its high dimensionality and its non-linearity in the foreground mass distribution. We present a method to generate joint posterior samples of the source galaxy and foreground mass distribution as pixelated images conditioned on observations. The method combines diffusion-based generative modeling and recurrent inference machines. It can model realistic gravitational lensing simulations with background and foreground galaxies drawn from cosmological hydrodynamical simulations down to the noise level.
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All authors Guillaume Payeur, Laurence Perreault-Levasseur, Gabriel Missael Barco, Yashar Hezaveh

Astrophysics of Galaxies

Resolving Galactic and Cluster Dynamics Without Dark Matter: Tsallis Entropy as the Unique Foundation of Emergent Gravity

S. Shamari and A. Sheykhi

While modified entropy models-such as Barrow, Tsallis, Kaniadakis,Power-law, Logarithmic, and Rényi entropies-have been widely explored in cosmological contexts, their implications on galactic scales remain largely untested. These generalizations of the Bekenstein-Hawking entropy encode quantum gravitational, nonextensive, or fractal spacetime effects and can alter the gravitational entropy-area relation. In this paper, we demonstrate that the entropic force framework, when applied to galactic rotation curves and the baryonic mass of galaxy clusters, uniquely selects Tsallis entropy as the specific generalized entropy formulation. We then extend this Tsallis modified gravity to globular clusters to complete the structural hierarchy from galaxies to galaxy clusters to globular clusters and to investigate its behavior as a function of system scale. We will show that the nonextensive parameter exhibits no correlation with any of the macroscopic quantities characterizing gravitational systems, such as mass, radius, temperature, or density. Furthermore, it has previously been shown that entropy is not well-defined within the standard thermodynamic approach to gravity. The adoption of nonextensive statistics provides a foundation for entanglement, thereby enabling a consistent definition of entanglement entropy. We predict the existence of galaxy clusters with $\delta = 1$ (i.e., clusters whose dynamics require no dark matter) analogous to $\delta = 1$ systems already observed at galactic and globular cluster scales. This prediction provides a unique observational test to discriminate Tsallis gravity from $\Lambda$CDM and MOND. Therefore, for the entropic gravity paradigm to be consistent with observational data across all scales-from globular clusters to galaxies to galaxy clusters-it is inevitably required to be built upon Tsallis entropy.
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