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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 15 April

High Energy Astrophysical Phenomena

Prospects for GRB Afterglow Discovery with the Eric and Wendy Schmidt Observatory System

James Freeburn, Dougal Dobie, Akash Anumarlapudi et al. (+9 more)

Two time domain surveys, recently funded as part of the Eric and Wendy Schmidt Observatory System; the Argus Array, in the optical, and the Deep Synoptic Array (DSA), in the radio, will transform gamma-ray burst (GRB) science via the serendipitous discovery of hundreds of GRB afterglows per year. In this work, we simulate DSA and Argus observations of GRB afterglows. We find that, of the long-duration GRBs (LGRBs) detected by the Fermi Gamma-ray Burst Monitor, (26$\pm$3)% will yield afterglow detections with Argus and (44$\pm$3)% with DSA, corresponding to rates of 51$\pm$5 and 86$\pm$8 per year respectively. We also compute rates for both upcoming and proposed GRB monitors; the forthcoming StarBurst Multi-messenger Pioneer, with 84$\pm$6 detections per year in Argus and 158$\pm$11 detections per year in DSA, and the Moon Burst Energetics All-sky Monitor (MoonBEAM) concept, with 90$\pm$9 per year in Argus and 160$\pm$14 per year in DSA. The observatory system will also detect 118$\pm$10 optical and 199$\pm$17 radio afterglows per year, independent of GRB triggers, exceeding the current annual rate with global follow-up. Afterglow counterparts to short-duration GRBs, originating from neutron star mergers, will be detected at 5-10% of the LGRB afterglow rate, which is promising for multi-messenger detections of gravitational wave sources and constraining the neutron star merger rate. The Argus Array, with its second-minute cadence, will detect afterglows before they peak $\sim$18% of the time, which will dramatically increase the sample of observed reverse shock and prompt optical emission.
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All authors James Freeburn, Dougal Dobie, Akash Anumarlapudi, Igor Andreoni, Brendan O'Connor, Eric Burns, Jonathan Carney, Hank Corbett, Michael W. Coughlin, Adam Goldstein, Anna Tartaglia, V. Ashley Villar

Solar and Stellar Astrophysics

Fundamental effective temperature measurements for eclipsing binary stars – VIII. NIRPS spectroscopy of CD-27 2812

N. J. Adshead, P. F. L. Maxted and A. Hahlin

There are very few M-dwarfs with accurate independent measurements of their mass, radius and effective temperature (T$_{\rm eff}$) that can be used to test stellar models for these low-mass stars. We aim to use high-resolution, near-infrared spectroscopy to measure the mass of M-dwarfs in eclipsing binary systems with solar-type stars and to measure the flux ratio between the two stars at near-infrared wavelengths. This information can then be combined with the analysis of the light curve, photometry, and the parallax to measure the mass, radius and T$_{\rm eff}$ for both stars. We have used the TESS light curve and spectra observed with the HARPS and NIRPS spectrographs to measure the following model-independent radii and masses for CD-27 2812, an F9 V star in an eclipsing binary with a much fainter M-dwarf companion on a short near-circular orbit (P=7.8 d) : $R_1 = 1.721 \pm 0.004 R_{\odot}$, $R_2 = 0.531 \pm 0.002 R_{\odot}$, $M_1 = 1.3597 \pm 0.0024 M_{\odot}$, and $M_2 = 0.5624 \pm 0.0006 M_{\odot}$ We show how the NIRPS spectra can be used to measure the flux ratio in the J and H bands. This information, combined with published photometry and the Gaia DR3 parallax, leads to the following effective temperature measurements: $T_{\rm eff,1} = 6197 \pm 55$ K, $T_{\rm eff,2} = 3770 \pm 28$ K. This study demonstrates that it is now feasible to use eclipsing binaries to accurately measure T$_{\rm eff}$ for M-dwarf stars for which we also have independent mass and radius measurements.
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High Energy Astrophysical Phenomena

Fast Neutrino-Flavor Conversion with Attenuation and Global Lepton Gradient

Masamichi Zaizen and Hiroki Nagakura

Fast neutrino-flavor conversion (FFC) can nontrivially alter neutrino radiation field in core-collapase supernovae (CCSN) and binary neutron-star merger (BNSM) remnants. However, its interplay with global geometry remains poorly understood because microscopic flavor conversion scales are much shorter than global transport scales. We perform global quantum kinetic neutrino transport simulations in spherical geometry with neutrino and matter backgrounds, using an attenuated oscillation Hamiltonian. We find that steep radial lepton gradients can suppress FFC, whereas the suppression is highly sensitive to the adopted attenuation parameter. This behavior is explained by an adiabatic condition: flavor coherence can grow sufficiently only while the flavor wave remains on the unstable branch in the local dispersion relation during propagation. Background variation shifts the unstable branch, while attenuation lengthens the growth timescale, making the flavor coherence following more difficult. We provide an approximate formula for the adiabaticity that can be used directly in CCSN and BNSM models developed by classical neutrino transport simulations. Our results show that attenuation artificially leads to an overestimation of the impact of background variation and should therefore be applied with caution in global simulations of neutrino flavor conversion.
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Solar and Stellar Astrophysics

Irregularly Sampled Time Series Interpolation for Binary Evolution Simulations Using Dynamic Time Warping

Ugur Demir, Philipp M. Srivastava, Aggelos Katsaggelos et al. (+9 more)

Binary stellar evolution simulations are computationally expensive. Stellar population synthesis relies on these detailed evolution models at a fundamental level. Producing thousands of such models requires hundreds of CPU hours, but stellar track interpolation provides one approach to significantly reduce this computational cost. Although single-star track interpolation is straightforward, stellar interactions in binary systems introduce significant complexity to binary evolution, making traditional single-track interpolation methods inapplicable. Binary tracks present fundamentally different challenges compared to single stars, which possess relatively straightforward evolutionary phases identifiable through distinct physical properties. Binary systems are complicated by mutual interactions that can dramatically alter evolutionary trajectories and introduce discontinuities difficult to capture through standard interpolation. In this work, we introduce a novel approach for track alignment and iterative track averaging based on Dynamic Time Warping to address misalignments between neighboring tracks. Our method computes a single shared warping path across all physical parameters simultaneously, placing them on a consistent temporal grid that preserves the causal relationships between parameters. We demonstrate that this joint-alignment strategy maintains key physical relationships such as the Stefan-Boltzmann law in the interpolated tracks. Our comprehensive evaluation across multiple binary configurations demonstrates that proper temporal alignment is crucial for track interpolation methods. The proposed method consistently outperforms existing approaches and enables the efficient generation of more accurate binary population samples for astrophysical studies.
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All authors Ugur Demir, Philipp M. Srivastava, Aggelos Katsaggelos, Vicky Kalogera, Santiago L. Tapia, Manuel Ballester, Shamal Lalvani, Patrick Koller, Jeff J. Andrews, Seth Gossage, Max M. Briel, Elizabeth Teng

Solar and Stellar Astrophysics

SJET: An Interactive Solar Jet Extraction Tool

Song Tan, Alexander Warmuth, Frédéric Schuller et al. (+4 more)

Solar jets are dynamic collimated plasma flows in the solar atmosphere that play crucial roles in coronal heating and solar wind acceleration. Their complex and diverse morphologies pose significant challenges for developing universal algorithms for automatic identification and extraction, particularly for on-disk jets affected by projection effects and background contamination. We present SJET, an interactive tool for solar jet feature extraction using multiple algorithms developed in Python that integrates five thresholding algorithms with morphological operations. SJET implements a novel method for identifying start and end points based on circular regions that objectively determines jet propagation direction by exploiting morphological asymmetry, combined with modeling the axis using quadratic Bézier curves for accurate extraction of geometric parameters including length, width, curvature, and deflection angles. Validation analyses using Solar Orbiter/EUI high-resolution image and SDO/AIA observations demonstrate SJET's effectiveness across different observational conditions, with good agreement compared to traditional analysis methods, though the tool's accuracy remains dependent on user-defined threshold parameters and region of interest selection. SJET provides a solution to method inconsistency in solar jet research through standardized processing workflows, establishing a technical foundation for large-sample statistical studies.
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All authors Song Tan, Alexander Warmuth, Frédéric Schuller, Yuandeng Shen, Yue Fang, Jake A. J. Mitchell, Zedong Liu

Solar and Stellar Astrophysics

Understanding mechanisms underlying solar cycle predictability with a general framework

Binghang Li, Jie Jiang and Yukun Luo

The large-scale magnetic field observed at the solar surface is produced by the interior dynamo process. Whether this surface field also provides the dominant seed for the subsequent dynamo cycle, however, remains controversial, with important consequences for the predictive skill of solar dynamo models.We investigate the physical conditions under which this predictive skill of the surface field arises in dynamo models within a general framework.By applying Stokes' theorem to the magnetic induction equation, we establish a direct physical link between the surface magnetic field and the subsequent dynamo process. The dominance of the surface induction integral in the net toroidal flux generation rate provides a quantitative criterion for assessing dynamo predictability, which we apply to five representative dynamo models.This general framework shows that the surface magnetic field acquires predictive power when the surface poloidal field is efficiently coupled back into the dynamo loop through flux-transport processes (e.g., meridional circulation), a condition that can be satisfied in both Babcock-Leighton (BL)-type and $\alpha-\Omega$ mean-field dynamo models. The framework further identifies a new condition under which the surface magnetic field acquires predictive power: namely, that it represents the radial component of the interior poloidal field, as in the original BL-type dynamo scenario. In addition, the non-zero net toroidal flux across different dynamo models supports its use as a proxy linking the interior toroidal field to surface flux emergence.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Investigating the effect of sensitivity of KAGRA on sky localization of gravitational-wave sources from compact binary coalescences

Alvin K. Y. Li, Peony K. K. Lai, Elwin K. Y. Li et al. (+1 more)

The addition of KAGRA to the global gravitational-wave detector network introduces new baselines and complementary antenna response patterns that can enhance sky localization for compact binary coalescences. We investigate KAGRA's role in the LIGO-Virgo-KAGRA network using a systematic injection study of binary neutron star signals. Sky maps are constructed with a radiometric, coherence-based framework, allowing isolation of geometric and timing contributions from individual detectors. Localization performance is quantified using the fraction of events localized within $100~\mathrm{deg}^2$, cumulative area distributions, and the median $90%$ credible region. We also assess KAGRA's impact on detection rates by varying its sensitivity over a wide range. Even at its current sensitivity of $\sim10~\mathrm{Mpc}$, KAGRA provides measurable improvements by breaking degeneracies through additional baselines and directional constraints. As sensitivity increases, improvements in signal-to-noise ratio and timing precision lead to substantial reductions in localization area. We identify a binary neutron star range of $\sim30~\mathrm{Mpc}$ as a practical benchmark for reliable localization suitable for electromagnetic follow-up, noting this as a conservative estimate. In addition, KAGRA increases the number of detectable events by enabling lower signal-to-noise detections. These results demonstrate that even a modest-sensitivity detector can significantly enhance network performance through geometric complementarity, highlighting the importance of a geographically distributed network for multimessenger gravitational-wave astronomy.
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All authors Alvin K. Y. Li, Peony K. K. Lai, Elwin K. Y. Li, Otto A. Hannuksela

Instrumentation and Methods for Astrophysics

Simulation of non X-ray background for the DIffuse X-ray Explorer (DIXE) mission

Ruixuan Tian, Junjie Mao, Jiejia Liu et al. (+2 more)

DIffuse X-ray Explorer (DIXE) is a proposed high-resolution spectroscopic survey mission onboard the China Space Station. Equipped with microcalorimeters based on the Transition-edge sensor technology, it aims to survey the hot gas in the Milky Way. The performance of DIXE depends on the understanding of non X-ray background (NXB), which can strongly affect observations of diffuse X-ray emission. In this work, we simulated the NXB of DIXE in a low-earth orbit (LEO) using Geant4. A detailed mass model of the payload was constructed, and the major sources of NXB were identified, including cosmic rays, albedo neutrons and albedo photons. These components were implemented in Geant4 with realistic angular and spectral distributions. We simulated the relevant physical processes of space radiation interacting with the instrument and calculated the resulting NXB. We also evaluated the delayed background from trapped protons in the South Atlantic Anomaly (SAA). Our simulations show that, at the geomagnetic equator and under solar minimum conditions, the NXB is on average $4.46 \times 10^{-2} ~\mathrm{counts~s^{-1}~cm^{-2}~keV^{-1}}$ in 0.1–10 keV energy band, with dominant contributions from the induced particles generated by primary cosmic protons. The NXB increases toward higher geomagnetic latitudes, reaching a maximum of $1.55 \times 10^{-1} ~\mathrm{counts~s^{-1}~cm^{-2}~keV^{-1}}$. The delayed background induced by the SAA decays rapidly after exiting the anomaly and becomes negligible within approximately 5 minutes. The simulated NXB is consistent with that of similar X-ray observatories in LEOs.
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All authors Ruixuan Tian, Junjie Mao, Jiejia Liu, Hai Jin, Wei Cui

High Energy Astrophysical Phenomena

Relaxation of magnetically-confined mountains on accreting neutron stars through cross-field mass transport

Ryan Brunet, Andrew Melatos and Pedro Rossetto

Hydromagnetic instabilities modify the structure of a magnetically confined mountain on an accreting neutron star, once the accreted mass exceeds a critical value. Ideal magnetohydrodynamics and flux freezing break down, and mass diffuses across magnetic field lines locally, wherever instabilities are excited. Here a self-consistent, iterative, numerical scheme is used to evolve an axisymmetric magnetic mountain through a quasistatic sequence of Grad-Shafranov equilibria as a function of the accreted mass, $M_{\rm a}$, modified by instability-driven cross-field mass transport obeying the semi-analytic, Kulsrud-Sunyaev recipe. The results are compared to an artificially stabilised mountain, in which flux freezing does not break down, and there is no cross-field mass transport. It is shown that cross-field mass transport prevents instabilities from demolishing the mountain. Instead, the mass-flux distribution adjusts locally to nullify the instabilities and preserve a nonzero mass quadrupole moment indefinitely in the absence of ohmic dissipation.
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Cosmology and Nongalactic Astrophysics

Reconstructing inflationary features on large scales using genetic algorithm

Alipriyo Hoory, Dhiraj Kumar Hazra and L. Sriramkumar

[Abridged] A variety of model-dependent as well as model-independent approaches suggest that certain localized features in the primordial scalar power spectrum can lead to a significantly better fit to the observed anisotropies in the cosmic microwave background (CMB). In this work, we focus on three types of such features and examine whether these features can be generated in inflationary scenarios driven by a single, canonical scalar field. We consider a slowly rolling baseline model that is described by a specific time-dependence of the first slow roll parameter and we generate the desired features in the power spectrum through suitable modifications to the functional form of the slow roll parameter. To systematically reconstruct the desired features in the scalar power spectrum (or, equivalently, the modifications in the behavior of the first slow roll parameter) that are consistent with the data, we implement a machine learning pipeline based on the genetic algorithm (GA). Assuming the standard values for the background $\Lambda$CDM model (arrived at for a nearly scale-invariant primordial scalar power spectrum), we apply our method to the Planck 2018 CMB data, and show that the reconstructed features improve the fit to the observed angular power spectra by $\Delta \chi^2 \lesssim -10$. Moreover, we find that GA points to other sets of background parameters and primordial features, which lead to a similar level of improvement in the fit to the data. Such alternative sets of background parameters and scalar power spectra offer possible pathways to alleviate existing cosmological tensions. Our approach provides effective single-field inflationary dynamics to generate features that are supported by the data.
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Cosmology and Nongalactic Astrophysics

Double the axions, half the tension: multi-field early dark energy eases the Hubble tension

Marco Bella, Vivian Poulin, Sunny Vagnozzi et al. (+1 more)

We show that the strong constraints placed by Planck NPIPE Cosmic Microwave Background (CMB) data on axion-like early dark energy (EDE) are significantly alleviated in models with multiple fields. We find a $1.5\sigma$ residual tension with the Local Distance Network value of $H_0$ in a 2-field model, with no improvement beyond two fields, and a best-fit value of $H_0$ $\sim 1.4\sigma$ larger than in the 1-field case. The second field improves the fit to high-$\ell$ CMB data, where 1-field EDE is most strongly disfavored, and suggests modifications to the pre-recombination history over a wider redshift range.
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All authors Marco Bella, Vivian Poulin, Sunny Vagnozzi, Lloyd Knox

Solar and Stellar Astrophysics

CHARA Interferometry and TESS Asteroseismology of the Core-Helium Burning Red Giant $\kappa$ Cyg

Arnab Chowhan, Timothy R. Bedding, Daniel Huber et al. (+5 more)

We present a detailed study of the secondary red clump star, $\kappa$ Cyg, by combining long-baseline visible interferometry using the PAVO beam combiner at the CHARA Array with high-precision asteroseismology from TESS. This dual approach allowed for a stringent test of stellar evolutionary models in the core helium-burning phase, which remains a regime of significant theoretical uncertainty. Using the PAVO interferometric data and fitting the limb-darkened intensity profile directly, we measured $R = 8.65\pm0.10 \rm R_\odot$. We fitted the spectral energy distribution (SED) using Phoenix model atmospheres and calculated $L = 44.46 \pm 1.09 \rm L_\odot$ and $T_{\rm eff} = 5066^{+47}_{-50} \mathrm{K}$. Using 16 sectors of TESS photometry, we detected clear solar-like oscillations in $\kappa$ Cyg. Through comparison of oscillation frequencies with MESA grids using either predictive mixing (PM) or exponential overshooting (OS), we found that models reproducing the oscillation frequencies systematically overestimate the stellar radius, with overshooting models performing only marginally better. The same models also under-predict the observed dipole-mode period spacing ($\Delta\Pi_1$). By inspecting the phase offset ($\epsilon_p$), we conclude that models misrepresent the interior structure of the star. Our results demonstrate that matching envelope-dominated asteroseismic observables alone is insufficient to ensure a correct core or even global structure, and highlight the need for improved treatments of convective boundary mixing in the models of core helium-burning (CHeB) stars.
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All authors Arnab Chowhan, Timothy R. Bedding, Daniel Huber, J. M. Joel Ong, Lea S. Schimak, Yaguang Li, Courtney L. Crawford, Timothy R. White

Astrophysics of Galaxies

A Unified HI Rotation Curve Corpus for Computational Astrophysics: 438 Galaxies from SPARC, THINGS, LITTLE THINGS, and WALLABY DR2

David C. Flynn

We present a unified corpus of 8,963 spatially resolved HI rotation curve measurements across 423 galaxies (438 total catalog entries including 15 metadata-only THINGS galaxies), drawn from four major surveys: SPARC (175), THINGS (34), LITTLE THINGS (26), and WALLABY DR2 (203). The corpus is distributed as a single structured JSON file with nested per-ring kinematic data, survey metadata, column definitions, and data-quality annotations, accompanied by a 438-row flat CSV for catalog-level filtering. All radii are in kiloparsecs, all velocities in km/s. Kinematic parameters have been verified against scanned primary tables. A two-tier quality system distinguishes hand-curated rotation curves with per-point uncertainties (Tier 1) from automated pipeline products (Tier 2). The corpus was designed for both traditional numerical analysis and Large Language Model retrieval-augmented generation (RAG) pipelines. Three worked examples demonstrate single-galaxy rotation curve plotting, multi-component baryonic analysis, and corpus-level parameter-space exploration, each requiring fewer than 15 lines of Python. The corpus is publicly available at Zenodo (DOI: 10.5281/zenodo.19563417) under CC BY 4.0.
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Instrumentation and Methods for Astrophysics

Site Quality Analysis for an Indian Submillimeter Telescope: A Reanalysis-Based Approach

Tanmay Singh, Mayuri Sathyanarayana Rao and Ritoban Basu Thakur

The Himalayan plateau region of Ladakh, India, is a potential host for a science-class submillimeter observatory, building on existing astronomical infrastructure near Hanle and Merak. Using the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5) data, we analyze precipitable water vapor (PWV) at monthly resolution over 184 months from January 2010 to April 2025, map PWV statistics across Ladakh, and identify candidate regions that reach PWV $\leq 1$ mm. For promising locations, we compute atmospheric transmittance and the corresponding atmospheric photon noise using the am (Atmospheric Model) radiative transfer code; we present transmittance and brightness temperature estimates over 10–1000 GHz and compare the inferred performance to sites hosting current or planned submillimeter facilities worldwide. We find Ladakh to be favorable for submillimeter observations, with multiple ERA5 grid cells reaching PWV $\leq 1$ mm. Within ERA5's spatial resolution, two regions emerge as particularly promising: Site A ($\approx 34.25^\circ$N, $78.75^\circ$E) and Site B ($\approx 32.50^\circ$N, $79.00^\circ$E), which satisfy PWV $\leq 1$ mm for about 23% and 19% of the study duration, respectively, compared to about 5% and 8% for the Hanle and Merak grid cells. These results motivate targeted in situ radiometer measurements for final site selection.
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Astrophysics of Galaxies

Substructures of the Milky Way's Retrograde Halo: Evidence for Multiple Accretion Events

Young Kwang Kim, Young Sun Lee and Timothy C. Beers

We investigate the progenitors of low-inclination retrograde substructures in the Milky Way (MW) halo, which are remnants of accreted dwarf galaxies on retrograde orbits. Our sample consists of halo stars with low orbital inclinations and eccentricities ($0 \le e \le 0.5$), constructed by combining spectroscopic data with $\it Gaia$ astrometry. We identify substructures using metallicity distribution functions (MDFs) in apogalactic distance-orbital phase space. In the low-eccentricity range ($0 \le e \le 0.3$), we find four substructures with MDF peaks at [Fe/H] $\approx -1.5$, $-1.9$, $-2.1$, and $-2.3$. In the intermediate-eccentricity range ($0.3 < e \le 0.5$), we identify five substructures that span [Fe/H] $\approx -1.5$ to $-2.3$. By combining chemical and dynamical information, we show that substructures with identical MDF peaks in the two eccentricity regions can either form coherent structures or remain dynamically distinct. This shows that MDF similarity alone is insufficient to uniquely identify progenitor systems and must be combined with dynamical information. We find that the retrograde halo was assembled through multiple accretion events rather than a single progenitor. The dominant contribution arises from a primary progenitor whose debris traces a coherent metallicity-energy sequence, consistent with hierarchical tidal stripping and core bifurcation. In addition, we identify independent progenitors that contribute to other substructures. In particular, the components with [Fe/H] $\approx -1.7$ are interpreted as a dual-origin population, likely associated with systems accreted at different epochs. These results highlight the complex, multi-progenitor origin of the retrograde stellar halo of the MW.
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Cosmology and Nongalactic Astrophysics

Into the Gompverse: A robust Gompertzian reionization model for CMB analyses

Paulo Montero-Camacho, Yin Li, Marco Barquero-Hernández et al. (+3 more)

Cosmic reionization is driven by the formation of sources of ultraviolet photons, and hence it is an intrinsically asymmetric process, where its earlier stages occur at a slower pace relative to its later stages. Yet most modern cosmic microwave background (CMB) analyses rely on a hyperbolic tangent template, i.e. a symmetric sigmoid, that is not well suited for joint fitting of CMB and reionization observations. In this work, we introduce a physically motivated Gompertzian reionization model with three astrophysical (nuisance) parameters, designed to enable joint analyses of CMB and reionization data and to be applicable to a wide range of datasets and cosmological models. This robust Gompertzian model leverages the connection between cosmology and reionization, typically ignored in standard CMB analyses, to demote the optical depth ($\tau_{\rm reio}$) to derived parameter, reducing its uncertainty by approximately a factor of three compared to the conventional $\tanh$ prescription. The $\tau_{\rm reio}$ improvement enables tighter constraints on the sum of the neutrino masses, revealing potential tension with neutrino oscillation experiments even after accounting for the known relaxation of neutrino mass bounds in $w_0w_a$CDM models – a tension that is partially obscured by the conventional treatment of reionization. In addition, the inferred constraints on the astrophysical parameters governing reionization naturally synergize with current and upcoming 21 cm experiments, providing physically informed parameter ranges for future 21 cm studies.
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All authors Paulo Montero-Camacho, Yin Li, Marco Barquero-Hernández, Pablo Renard, Yang Wang, Xiao-Dong Li

Astrophysics of Galaxies

ALESS–JWST: Dust-driven Morphologies and Hidden Stellar Mass in $z\sim3$ Sub-millimeter Galaxies

J. Li, E. da Cunha, J. A. Hodge et al. (+17 more)

We present JWST/NIRCam and MIRI observations of twelve $z\sim3$ sub-millimeter galaxies (SMGs) from the ALESS survey, combined with high-resolution ($0.08''-0.16''$) ALMA 870$\mu$m imaging, enabling spatially resolved SED fitting on $\sim$kpc scales. We find a resolved star-forming main sequence linking surface densities of star formation rate and stellar mass, suggesting star formation remains tightly coupled to local mass distribution even in obscured systems. Our resolved SED analysis reveals a systematic stellar mass bias in integrated fits, even including rest-frame $\sim2\mu$m MIRI imaging. Rather than classical `outshining', this is mainly driven by spatially varying dust attenuation, indicating a `dust-obscuration bias' that causes obscured stellar mass to be missed. We show SMG morphologies are wavelength-dependent. At rest-frame optical wavelengths, central obscuration produces stellar-dust offsets and inflated sizes, while at longer wavelengths these effects diminish. The rest-frame $\sim1.5-3\mu$m MIRI imaging is less affected by dust than NIRCam and reveals compact stellar structures matching the 870$\mu$m dust continuum. We find centrally concentrated dust attenuation drives both offsets and size variations, demonstrating dust geometry is the main driver of structural diversity. Consequently, morphologies from rest-frame wavelengths $\lesssim1.6\mu$m can be biased without longer-wavelength constraints. The intrinsic stellar mass and dust continuum sizes are consistent ($R_\mathrm{e,870\mu m}/R_\mathrm{e,\ast}=1.0\pm0.4$), supporting a picture in which SMGs host compact, obscured star formation that builds dense stellar cores, consistent with evolution into massive quiescent galaxies. We suggest such obscured structures and associated biases may also be common among massive star-forming galaxies at $z\gtrsim1$, implying these effects are likely of broad relevance.
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All authors J. Li, E. da Cunha, J. A. Hodge, I. Smail, S. Kendrew, A. battisti, M. Cracraft, L. A. Boogaard, W. N. Brandt, C.-C. Chen, P. Cox, K. K. Knudsen, C.-L. Liao, G. Calistro Rivera, M. Rybak, A. M. Swinbank, P. van der Werf, F. Walter, A. Weiss, B. A. Westoby

Astrophysics of Galaxies

The DECam MAGIC Survey: Investigating the Jet Stellar Stream with Photometric Metallicities

H. Q. Do, A. Chiti, P. S. Ferguson et al. (+27 more)

Stellar streams are dynamically fragile structures formed by the tidal disruption of dwarf galaxies and stellar clusters. These objects are valuable tracers of the gravitational potential and accretion history of the Milky Way, and are key probes for the presence and interactions of starless dark matter subhalos. The Jet stream is a $\sim 30^\circ$-long stellar stream that is situated at 30.4 kpc and originates from a disrupted globular cluster. It consists of metal-poor stars that follow a retrograde orbit, reducing the impulse imparted from the Milky Way bar and making it especially sensitive to gravitational perturbations from dark matter subhalos. This paper investigates the known extent of the Jet stream by leveraging photometric metallicities derived from a narrowband filter centered on the Ca II H&K lines at $\sim$3950A on the Dark Energy Camera (DECam), as part of the Mapping the Ancient Galaxy in CaHK (MAGIC) survey. The wide field-of-view of DECam enables the efficient derivation of photometric metallicities for stars across the full extent of the stream, allowing for a metallicity-based selection to identify likely members. We demonstrate the efficacy of photometric metallicities in isolating stream members when used with Gaia DR3 proper motions, identifying a sample of 213 candidate Jet stream member stars. This then allows for the study of stream morphology, through which we identify a clear fanning of the stream toward the end farther from the Milky Way bar. We provide a list of candidate members, enabling spectroscopic follow-up of the Jet stream to facilitate further studies of its dynamics.
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All authors H. Q. Do, A. Chiti, P. S. Ferguson, A. P. Ji, G. Limberg, K. R. Atzberger, J. L. Carlin, W. Cerny, A. Drlica-Wagner, G. F. Lewis, T. S. Li, C. E. Martínez-Vázquez, S. L. Martell, G. E. Medina, N. E. D. Noël, A. B. Pace, V. M. Placco, A. H. Riley, D. J. Sand, G. S. Stringfellow, J. A. Carballo-Bello, L. R. Cullinane, D. Erkal, S. E. Koposov, B. Mutlu-Pakdil, M. Navabi, N. Shipp, A. K. Vivas, A. Zenteno, D. Zucker

Tuesday 14 April

Astrophysics of Galaxies · Cross-listed from physics.flu-dyn

Effect of gap width on turbulent transition in Taylor-Couette flow

Chang-Quan Zhou, Hua-Shu Dou, Lin Niu et al. (+1 more)

Simulations of the transitional flow in Taylor-Couette configuration are carried out to study the effect of the gap width on turbulent transition. The research results show that, under the same radius and the rotating speed of the inner cylinder, as the gap width increases, the flow becomes more stable. It is discovered that the average velocity distribution in the gap approaches the free vortex flow as the width increase and the stability of the flow is enhanced. It is found that, as the gap width increases, the maximum of the energy gradient function (from the energy gradient theory) in the gap decreases, which delays the turbulent transition. As such, the larger the gap width, the later the transition occurs. As the gap width increases, the Reynolds number based on the gap width alone is not able to characterize the flow behavior in Taylor-Couette flows, and the effect of the radius ratio should be taken into account.
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All authors Chang-Quan Zhou, Hua-Shu Dou, Lin Niu, Wen-Qian Xu

Instrumentation and Methods for Astrophysics · Cross-listed from cs.DL

OverCite: Add citations in LaTeX without leaving the editor

Cheyanne Shariat

Adding citations while drafting in LaTeX often requires leaving the editor, searching for a paper in mind, copying its BibTeX entry into the project bibliography, renaming the cite key, and then returning to the sentence. OverCite is an open-source, lightweight tool that lets authors find, select, and insert citations without leaving the writing environment. In Overleaf, OverCite uses rough citation placeholders (e.g., $\texttt{\textbackslash citep\{Perlmutter1999\}}$) and local sentence context to query ADS/SciX-indexed literature, rank likely matches, and insert the selected reference, without leaving the editor. A companion VS Code extension provides the same functionality for local LaTeX projects. The ADS/SciX database includes astronomy, physics, computer science, mathematics, biology, and all indexed arXiv e-prints, making OverCite useful across a broad range of scientific disciplines.
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High Energy Astrophysical Phenomena

Consistent Treatment of Muons in Binary Neutron Star Mergers

Henrique Gieg, Ramon Jaeger, Maximiliano Ujevic et al. (+1 more)

We present a set of numerical-relativity binary neutron star merger simulations incorporating muons and muonic reactions for two baseline baryonic equations-of-state. In order to investigate the possible impact of muons and muonic weak reactions, we treat neutrinos with a gray (energy-independent) truncated moments scheme and an implicit-explicit time integrator. Newly computed neutrino rates are employed within the full kinematics approach for a set of relevant reactions, and pair-processes are modeled via opacities computed using reaction kernels, that allow a consistent treatment of neutrino interaction rates. We find that equilibration between matter and radiation is successfully captured by a novel two timescales approach. Of astrophysical interest is the general agreement between our muonic and non-muonic results regarding the remnant evolution, disk and outflow properties. Average electron fractions, asymptotic velocities and temperatures are different by less than $\sim 6\%$, while the main impact of muons is a reduction in ejecta masses by at most $\sim 17\%$. Therefore, based on our findings, accounting for the presence of muons and muonic reactions might result much less severe consequences regarding nucleosynthetic yields and electromagnetic counterparts than previously reported in the literature.
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All authors Henrique Gieg, Ramon Jaeger, Maximiliano Ujevic, Tim Dietrich

Astrophysics of Galaxies

CII fine-structure line observations of the Sagittarius C Region in the Galaxy's Central Molecular Zone

DEnise Riquelme-Vasquez, Rolf Guesten, Mark R. Morris et al. (+7 more)

Context. Sagittarius C (Sgr C) is a massive, relatively quiescent complex at the western edge of the Galaxy's Central Molecular Zone (CMZ). While the Sgr B2 region has been extensively studied, Sgr C has received comparatively less attention. Aims. We aim to characterize the kinematics and physical state of the gas in Sgr C using spatially and velocity-resolved [CII] 158 microns emission. This line traces the multi-phase interstellar medium, providing a crucial complement to molecular, infrared, and radio observations. Methods. We present a fully sampled 74x47 pc map of the [CII] line toward Sgr C, observed with SOFIA. The data feature a 0.55 pc spatial and 1 km/s spectral resolution. These observations are analyzed in conjunction with ancillary maps of the CO(2-1) transition and its isotopologues from the APEX telescope. Results. [CII] emission is widespread, showing a continuous structure extending from Sgr A to Sgr C with complex morphology. The bulk emission arises at negative radial velocities, consistent with Galactic rotation. The most prominent feature is the giant Sgr C HII region, where [CII] reveals an expanding, ring-like shell interpreted as a photo-dissociation region (PDR). Kinematic modelling yields an expansion velocity of 23 km/s and a dynamical age of about 0.13 Myr. Our analysis suggests that stellar winds from known massive stars are insufficient to power the observed expansion, pointing toward alternative drivers like a buried supernova. Finally, we find a striking spatial association between this shell and a non-thermal radio filament, indicating that the shell's expansion has triggered high-mass star formation at its edge.
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All authors DEnise Riquelme-Vasquez, Rolf Guesten, Mark R. Morris, Andrwe I. Harris, Miguel A. Requena-Torres, Esteban F.E. Morales, Juergen Stutzki, Robert Simon, Christophe Risacher, Ronan Higgins

Earth and Planetary Astrophysics

The steady-state population of Earth's co-orbitals of lunar provenance

Elisa Maria Alessi and Robert Jedicke

The population of natural objects in a 1:1 mean motion resonance with Earth are known as Earth's co-orbitals. Main belt objects can dynamically evolve into Earth co-orbitals but taxonomic studies of some of them have suggested that they are more likely to be lunar material. While it has long been known that lunar ejecta can achieve Earth co-orbital status, in this work we calculate their expected steady-state size-frequency distribution from the impact rate of asteroids and comets on the Moon's surface, the ejecta's size-frequency and speed distribution, and dynamical integration of the particles for millions of years, among other factors. We also classify known and synthetic co-orbitals by their regime (quasi-satellite, horseshoe, tadpole, or compound) and compute the probability of transitions between them. Our nominal solution predicts that there are $\gtrsim 70$ Earth co-orbitals in the steady-state population larger than $10$ m in diameter with a lunar provenance but there are orders-of-magnitude systematic uncertainty on the value. We used NEOMOD3 to calculate that about 1600 are expected in the co-orbital population with a main belt provenance and they have higher eccentricity and inclination than those from the Moon. New taxonomic classifications for more Earth co-orbitals will reduce the uncertainties on e.g. crater scaling relations that will, in turn, reduce the uncertainties in the calculation of the steady-state population of Earth's co-orbitals with a lunar origin. The mineralogy and abundance of Earth's co-orbitals is also of interest to commercial asteroid mining ventures because they are the lowest $\Delta v$ targets in the asteroid population.
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Astrophysics of Galaxies

The Great Escape of ionizing photons during Cosmic Morning

Kanak Saha, Roland Bacon, Anne Verhamme et al. (+8 more)

The end of the Cosmic Dark Age marked the onset of reionization, driven by extreme-UV photons from the first galaxies. Direct detection of such photons has remained challenging due to strong intergalactic attenuation. Here, we report the first direct detection of ionizing photons at rest-frame wavelengths $350\r{A}$, $392\r{A}$, and $485\r{A}$, using deep UV imaging from two independent space observatories: AstroSat and HST. These photons emerge from a stacked sample of spectroscopically confirmed Ly$\alpha$ emitters at $5.9<z<6.0$ in the Hubble Ultra Deep Field identified with VLT/MUSE and JWST/NIRSpec. These detections imply a higher transparency of the interstellar and intergalactic media to ionizing radiation than predicted by current models. The stacked spectrum, representative of faint galaxies with $M_{\mathrm{UV}}=-18.77\pm0.05$ ($\sim0.1L^{\ast}$), exhibits a hard slope ($-2.3\pm0.1$) and produces ionizing photons with $\text{log}_{10}\xi_{\text{ion}}^{true}$ = $25.86 \pm 0.02$ Hz erg$^{-1}$ and escape fraction $f_{esc}\simeq 0.8$. Individual measurements reveal very blue UV continua ($\beta \leq -3$) for three galaxies), young ages ($< 6$ Myr for four), and low metallicities ($Z \sim 0.02 - 0.05\ Z_{\odot}$ for two), indicating the possible presence of very hot, massive stars capable of producing enough ionizing photons to drive cosmic reionization, thereby providing new constraints on its sources. Furthermore, detection of photons with energies $>24.6\ $eV provide evidence that HeI reionization has begun by this epoch.
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All authors Kanak Saha, Roland Bacon, Anne Verhamme, Soumil Maulick, Akio Inoue, Souradeep Bhattacharya, Marc Rafelski, Edmund Christian Herenz, Rogier Windhorst, Michael Rutkowski, Shyam N. Tandon

Earth and Planetary Astrophysics

Rings Around Non-Spherical Worlds: Sub-mm Dust Retention Around Triaxial Small Bodies in the Solar System

Zs. Regaly, V. Frohlich, Cs. Kalup et al. (+1 more)

We investigated the millennial-scale evolution of narrow innermost rings composed of pebble-sized to sub-millimeter particles around the four known ring-bearing small bodies Chiron, Chariklo, Quaoar, and Haumea. Using a GPU-accelerated 8th-order Hermite integrator, we modeled the combined effects of solar radiation pressure (RP), shadowing of the rings by the host body, heliocentric motion, and the non-axisymmetric gravitational field of the rotating triaxial central body. The calculations compare spherical and triaxial-body models, as well as coplanar and inclined ring configurations. In spherical models, solar RP excites particle eccentricities, leading to accretion onto the central body above a critical RP parameter. This effect is strongest for the lower-mass systems, Chiron and Chariklo, where particles with relatively modest radiation forcing are rapidly removed. In contrast, when the triaxial shape of the host body is included, rapid apsidal precession suppresses RP-driven eccentricity growth and prevents material loss from the ring over the simulated interval. The triaxial models also suppress the previously identified Sun-facing reorientation of highly inclined rings and instead produce moderate vertical broadening. Strongly confined rings persist for RP parameters corresponding to particle sizes larger than about 7-40 micrometers, depending on composition. Their characteristic radial widths are about 10 km for Chiron and Chariklo and about 40-70 km for Quaoar and Haumea. The vertical thicknesses of the rings are estimated to be on the order of 1 km for Chiron and Chariklo, and only several hundred meters for Quaoar and Haumea. Our results suggest that narrow rings around triaxial small bodies in the Solar System can plausibly retain sub-millimeter particles over dynamically relevant timescales shorter than Poynting-Robertson drag.
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All authors Zs. Regaly, V. Frohlich, Cs. Kalup, Cs. Kiss

Astrophysics of Galaxies

Requiem for a belt: A spatial and kinematical reinterpretation of Gould's Belt in light of Gaia

Michelangelo Pantaleoni González, João Alves, Cameren Swiggum et al. (+1 more)

We reassess the long-standing idea of Gould's Belt using Gaia DR3 for a sample of young massive stars and nearby young clusters. The structure surrounding the Sun, often interpreted as an inclined, expanding, and rotating ring, emerges in our analysis as a transient alignment of a few cluster families rather than an individual, coherent dynamical feature. By combining the ALS III catalog of OB stars with a homogeneous sample of clusters younger than 70 Myr, and by tracing their motions in a realistic Galactic potential, we show that neither the spatial distribution nor the kinematics form a unified system. The inferred expansion, rotation, and bulk motion of the Belt can be reproduced by the superposition of the $\alpha$Per, Cr135, M6, and $\gamma$Vel cluster families and are further amplified by solar reflex motion and historical assumptions about the local standard of rest (LSR). The classic inclined geometry is largely explained by the oscillatory pattern of the Radcliffe Wave, which contributes a major arc of the supposed ring. Taken together, these results indicate that Gould's Belt is not a physical structure but a 3D asterism shaped by a complex local star formation history, observational biases, and projection effects.
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All authors Michelangelo Pantaleoni González, João Alves, Cameren Swiggum, Isak Niederbrunner

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

Observational constraints on nonlocal black holes via gravitational lensing

Rocco D'Agostino and Vittorio De Falco

In this paper, we study the gravitational lensing around the static and spherically symmetric DD black holes, which we recently derived as perturbations of the Schwarzschild geometry within the revised Deser-Woodard theory of nonlocal gravity. We first present general analytical expressions for the deflection angle in both weak- and strong-deflection limits, explicitly relating them to the nonlocal corrections to Schwarzschild spacetime. Subsequently, we analyze lensing observables, such as the post-Newtonian effects and the black hole shadow, to constrain the DD black hole parameter space using current observational bounds. Finally, we perform a joint statistical analysis based on the Fisher information matrix, combining these findings with our previously obtained constraints from quasinormal modes. Our results indicate consistency with general relativity at the $1.13\sigma$ level. This work provides a first assessment of the DD parameter space and offers new insights to probe deviations from Einstein's gravity in view of future larger datasets.
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Astrophysics of Galaxies

Sparks II: Panchromatic SED modeling and galaxy physical properties across the starburst to post-starburst sequence

Dalya Baron, David J. Setton, Yilun Ma et al. (+4 more)

The Sparks survey provides rest-frame near-infrared spectroscopy for 93 local massive galaxies spanning the rapid transition from starburst to post-starburst, including Balmer-strong galaxies as well as systems with active galactic nuclei (AGN). Interpreting these extreme systems requires reliable physical properties, yet these can vary substantially when derived from rest-frame optical spectroscopy versus multi-wavelength photometry, and across different fitting codes and assumptions. We assemble far-ultraviolet to far-infrared photometry for the Sparks sample and compare the resulting galaxy properties across data types and modeling approaches, identifying the final measurements adopted for the survey. With stellar masses recovered relatively robustly, we focus on the more model-dependent quantities of star formation rates (SFRs) and histories (SFHs), and AGN activity. Fits to optical stellar continuum alone, dominated by strong Balmer absorption, systematically favor rapidly declining SFHs and suppress ongoing star formation. Benchmarking against H$\alpha$-based SFRs in the star-forming Sparks galaxies shows that Prospector fits to the optical continuum spectroscopy underestimate the SFR by 0.76 dex (scatter 0.42 dex), whereas panchromatic SED-based SFRs perform better, with a -0.15 dex offset and 0.14 dex scatter. We therefore adopt the panchromatic SED-based SFRs for composite and AGN hosts, finding that many exhibit higher levels of star formation than previously inferred. Finally, we test the AGN torus model in Prospector, finding that it successfully distinguishes optically-classified AGN from star-forming galaxies, but yields torus luminosities an order of magnitude below expectations from AGN bolometric luminosities, possibly indicating intrinsically low covering factors in Sparks AGN shaped by black-hole feedback during coalescence.
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All authors Dalya Baron, David J. Setton, Yilun Ma, J. X. Prochaska, Ric Davies, Jenny E. Greene, Dieter Lutz

Astrophysics of Galaxies

Sparks: The Magellan/FIRE survey from starburst to post-starburst

Dalya Baron, David J. Setton, Yilun Ma et al. (+5 more)

Rapid transitions from starburst to quiescence constitute a key evolutionary pathway in galaxy formation. Post-starburst galaxies trace this brief phase, exhibiting optical spectra dominated by intermediate-age stellar populations with strong Balmer absorption features. Although rare locally, such systems are commonly revealed by JWST observations among massive galaxies at $z \gtrsim 3$. In the nearby Universe, their evolutionary stage remains uncertain: Balmer-strong galaxies hosting active galactic nuclei (AGN) show conflicting star formation rates (SFRs), with optical diagnostics implying quenching while far-infrared emission suggests ongoing obscured star formation. We present Sparks, an infrared survey designed to study the transition from starburst to post-starburst. Using the FIRE spectrograph on the Magellan Telescope, Sparks provides near-infrared spectra (0.82-2.51 $\mu$m) for 93 local massive galaxies spanning three orders of magnitude in SFR, from starbursts to quenched post-starbursts, including AGN hosts. Here, we describe the survey goals, sample selection, observations, and data reduction, and examine galaxy properties derived from stellar population synthesis fitting of photometric data covering far-ultraviolet to far-infrared. Our new panchromatic-based SFR and star formation history measurements divide the sample into three groups: galaxies undergoing their first major starburst in the past $\sim 1$ Gyr; galaxies undergoing their second major starburst, with optical continua dominated by intermediate-age stellar populations formed during the previous recent burst; and post-burst quenching systems. AGN appear predominantly in the second group, explaining why systems with strong Balmer absorption and AGN show elevated far-infrared emission, and implying a short delay between starburst and black hole accretion.
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All authors Dalya Baron, David J. Setton, Yilun Ma, J. X. Prochaska, Gabriela Canalizo, Ric Davies, Jenny E. Greene, Dieter Lutz

Instrumentation and Methods for Astrophysics

An Information-Theoretic Metric for Transient Classification and Novelty Detection

Yu-Qian Ouyang, Alex I. Malz, Ming Lian et al. (+3 more)

The development of the observing strategy for the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) requires a broad optimization across science cases inside and outside of time-domain astronomy. We introduce a novel metric for transient science with LSST based on information-theoretic cross-entropy. We demonstrate its utility for distinguishing populations of objects and discuss applications for observing strategy / detection pipeline optimization as well as novelty detection and follow-up resource allocation.
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All authors Yu-Qian Ouyang, Alex I. Malz, Ming Lian, Shar Daniels, Federica Bianco, Mathilda Nilsson