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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 8 May

Solar and Stellar Astrophysics

Investigating Pre-flare Signatures in Spectroscopic Observations of an X9-class Solar Flare

Louis Seyfritz, Maria Kazachenko and Ryan French

On October 3rd, 2024, the Sun emitted an X9.0-class flare from active region NOAA 13842. The event was recorded by multiple space-based instruments, beginning hours before the eruption, granting a unique opportunity to provide insight into the flare's pre-flare phase. In this study, we employ analysis of Interface Region Imaging Spectrograph (IRIS) spectroscopic data to investigate pre-flaring phenomena associated with this flare. We present time-series and wavelet analysis of non-thermal velocity, Doppler velocity, and line intensity quantities of the IRIS Si IV 1403 angstrom line. We find two ranges of periodic oscillations during the pre-flare phase: ~7-10 min and ~18-21 min oscillations, with local enhancements occurring near the polarity inversion line. We also find a steady rise in Si IV line parameters beginning 3 hours before the flare in the same region, transitioning into strong non-thermal velocities and blueshifts ~15 minutes before onset. These findings are consistent with a slow destabilization of the coronal magnetic field, possibly driven by the gradual activation of a flux rope, followed by a rapid shift to intense reconnection activity leading to flare onset.
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Earth and Planetary Astrophysics

HAT-P-70b through the Eyes of MAROON-X: Constraining Elemental Abundances of Metals and Insights on Atmosphere Dynamics

Shi Lin Sun, Stefan Pelletier, Björn Benneke et al. (+6 more)

Ultra-hot Jupiters (UHJs) are exceptional laboratories for studying planetary atmospheres under extreme irradiation conditions. With close-in tidally locked orbits, these planets can have daysides hot enough for metals to be significantly ionized while still maintaining nightsides cold enough for refractory species to potentially condense. We present an analysis of the ultra-hot Jupiter HAT-P-70b taken with the MAROON-X high-resolution spectrograph. Using cross-correlations, we detect 14 neutral and singly ionized species, including Fe I, Fe II, Ti I, Ca I, Ca II, Cr I, Na I, V I, Mn I, Ni I, Mg I, Ba II, O I, and Sr I, with tentative evidence for H I, Co I, and K I. The absorption signals exhibit blueshifts on the order of a few $\mathrm{km\,s^{-1}}$, consistent with day-to-night winds. We further constrain relative abundances with atmospheric retrievals and demonstrate that some inferred elemental abundance ratios depend strongly on modeling assumptions. In particular, we show that a well-mixed retrieval approach neglecting ionization can strongly bias highly ionizable elements such as Ca and Ti. Accounting for the effects of equilibrium chemistry and thermal ionization generally results in inferred elemental abundance ratios that are closer to expectations for a solar-like composition, although not in all cases. Interestingly, we find a distinct nickel enrichment on HAT-P-70b, adding to the growing number of UHJ studies where the Ni abundance is seemingly enhanced. Our results underline the importance of considering physical and chemical atmospheric processes such as ionization when interpreting high-resolution transmission spectra of UHJs.
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All authors Shi Lin Sun, Stefan Pelletier, Björn Benneke, Bibiana Prinoth, Vivien Parmentier, Jacob L. Bean, Joost P. Wardenier, Yayaati Chachan, Valentina Vaulato

Earth and Planetary Astrophysics

A New Global Chemical Equilibrium Code: Refractory Element Signatures in Super-Earths and Sub-Neptunes

Simon Grimm, Marie-Luise Steinmeyer, Aaron Werlen et al. (+3 more)

The atmospheres of super-Earths and sub-Neptunes can be strongly modified by chemical exchange with their molten interiors during long-lived magma ocean phases. Interpreting atmospheric observations requires fast models that self-consistently couple atmospheric chemistry to the composition of the planetary interior. We present an updated implementation of the global chemical equilibrium (GCE) framework from (Schlichting & Young 2022), which computes the equilibrium composition of a coupled metal-silicate-gas system. The numerical solver has been improved using a gradient-based optimizer, reducing the computational cost of solving the chemical network by more than two orders of magnitude and enabling large parameter studies. We apply the framework to a large synthetic population of planets and explore the imprint of bulk refractory composition of Mg, Si, and Fe on atmospheric properties. We consider planets with different masses, thermal states, and volatile inventories. We find that the atmospheric mass fraction and atmospheric metal mass fraction are primarily controlled by the temperature at the atmosphere-magma ocean interface and the planetary water budget, while the accreted hydrogen mass fraction plays a minor role because most hydrogen dissolves into the interior. For planets that accreted water, the refractory ratios Mg/Si and Fe/Si strongly influence carbon partitioning between the gas, silicate, and metal phases, producing large variations in atmospheric atmospheric metal mass fraction and C/O ratios. These results demonstrate that atmospheric compositions of sub-Neptunes depend sensitively on both the volatile inventory and the bulk composition of rocky material, providing new constraints for interpreting atmospheric observations. The new GCE code is open-source.
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All authors Simon Grimm, Marie-Luise Steinmeyer, Aaron Werlen, Caroline Dorn, Hilke Schlichting, Ed Young

High Energy Astrophysical Phenomena

Detection of persistent helium absorption in the 91bg-like type Ia Supernova 2022an

Ping Chen, Avishay Gal-Yam, Subo Dong et al. (+14 more)

We present optical and near-infrared observations of the fast-declining Type Ia supernova (SN Ia) 2022an. The photometric and spectroscopic properties identify it as a standard 91bg-like event; however, our data reveal a relatively narrow absorption feature with a full width at half maximum (FWHM) of 75 angstroms near $1.037\,\mu$m in the rest frame of the observed spectra that persists from around 30 days to nearly 90 days after maximum light. We attribute this feature to He I $1.083\,\mu$m line with a blueshifted velocity of $1.3\times10^{4}$ km s$^{-1}$ and a FWHM of $2.1\times10^{3}$ km s$^{-1}$, supported by the detection of multiple optical He I transitions in earlier epochs at a higher velocity around $1.5\times10^{4}$ km s$^{-1}$. The high velocity of the helium could not be explained by helium external to the progenitor at the explosion, such as the stripped surface helium from a companion star. The properties of the helium absorption in SN 2022an spectra instead point to unburnt material in the outer ejecta, thus providing the most compelling evidence to date for helium-bearing ejecta in a 91bg-like SN Ia. Such helium has been predicted for sub-Chandrasekhar-mass double-detonation explosions involving a surface helium shell. No theoretical calculations of modern helium-shell double detonation have been performed at epochs similar to those observed for SN 2022an to study the effect of helium on their spectra, revealing a gap between observations and theoretical calculations in understanding the manifestation of helium in SNe Ia. Nevertheless, the discovery of persistent helium absorption in SN 2022an demonstrates the diagnostic power of NIR spectroscopy for understanding thermonuclear supernova explosions by probing the abundance and structure of their ejecta.
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All authors Ping Chen, Avishay Gal-Yam, Subo Dong, Renyue Cen, Boaz Katz, Kate Maguire, Steve Schulze, Jesper Sollerman, Joseph P Anderson, Ting-Wan Chen, L. Galbany, Mariusz Gromadzki, Chang Liu, Adam A.Miller, Tomás E. Müller-Bravo, Tanja Petrushevska, Giuliano Pignata

Astrophysics of Galaxies

Potamides: Mapping Dark Matter Halo Shapes from Stellar Stream Tracks in the Local Universe

Sirui Wu, Nathaniel Starkman, Sarah Pearson et al. (+3 more)

Stellar streams trace the gravitational potential of their host galaxies and offer a direct probe of dark matter halo geometry. Cosmological simulations predict that halo shapes depend on both baryonic physics and the nature of dark matter, yet observational constraints on halo flattening and orientation remain limited, especially for individual galaxies. We present Potamides, which utilizes the curvature of extragalactic stellar streams to derive constraints on halo shapes. We apply Potamides to 15 stellar streams from the Stellar Stream Legacy Survey to infer the projected axis ratios and orientation of their host halos. We find that some streams in our sample exclude large regions of halo flattenings and halo orientations. Systems with edge-on wrapping loops or sharp turning points yield the strongest constraints, whereas great circle-like streams remain largely uninformative. All streams in our sample support a spherical halo for a given flattening direction. These results demonstrate that stream morphology can provide halo shape constraints for individual external galaxies. With upcoming surveys (such as Euclid, Rubin, Roman, and ARRAKIHS) expected to discover large numbers of stellar streams, this curvature-based technique will enable rapid statistical tests of dark matter and baryonic physics through the shapes and alignments of halos and disks across cosmic time.
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All authors Sirui Wu, Nathaniel Starkman, Sarah Pearson, Jacob Nibauer, Juan Miro-Carretero, David Martinez-Delgado

High Energy Astrophysical Phenomena

Young Massive Star Clusters as TeV Emitters: Constraints from H.E.S.S. and LHAASO

Rowan Batzofin, Pierre Cristofari and Kathrin Egberts

Young massive star clusters (YMSCs) have been proposed as excellent candidates for the main sources of Galactic cosmic rays (CRs) up to the PeV range. The detection and study of gamma rays in the very-high-energy (E>100GeV) range has brought arguments in favour of this hypothesis. Current instruments have detected only a few YMSCs. Future observatories are expected to increase this number, providing a larger sample improving our ability to constrain the role of YMSCs in the origin of CRs. We study the population of TeV YMSCs detected and their properties, confronting simulations of the YMSC population to the observed sample, to address the fundamental questions concerning the spectrum of accelerated particles, the efficiency of CR production, and the fraction of the wind luminosity converted into turbulent magnetic fields. Using Monte Carlo methods, we simulate the Galactic population of YMSCs in the gamma-ray domain and confront our simulations to the catalogue of sources of the systematic survey of the Galactic plane performed by H.E.S.S. (HGPS) and the First LHAASO Catalogue of Gamma-Ray Sources. We systematically explore the parameter space of our model, including the slope of accelerated particles $\alpha$, the CR efficiency $\eta_{\rm CR}$, the fraction of the wind luminosity converted into turbulent magnetic field $\eta_{\rm b}$, and the diffusion regime. We found 5 possible sets of parameters for which >75% of realisations agree with the combined data from the HGPS and LHAASO 1st catalogue. Certain regions of the parameter space are strongly disfavoured, such as Bohm diffusion. Our model successfully reproduces the YMSC population observed in both catalogues. With future systematic surveys, e.g. the Cherenkov Telescope Array Observatory (CTAO), this approach will help break degeneracies and improve our understanding of particle acceleration at YMSC shocks in the Galaxy.
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Cosmology and Nongalactic Astrophysics · Cross-listed from stat.ML

TopoFisher: Learning Topological Summary Statistics by Maximizing Fisher Information

Matteo Biagetti, Mathieu Carrière, Francesco Conti et al. (+3 more)

Persistence diagrams provide stable, interpretable summaries of geometric and topological structure and are useful for simulation-based inference when low-order statistics miss key information. Yet persistence-based pipelines require hand-chosen filtrations, vectorizations, and compressors, typically without an objective tied to parameter uncertainty. We introduce TopoFisher, a differentiable persistent-homology pipeline that learns topological summaries by maximizing local Gaussian Fisher information. Using simulations near a fiducial parameter, TopoFisher optimizes trainable filtrations, diagram vectorizations, and compressors without posterior samples or supervised regression targets, while retaining stable topological inductive bias. We also give sufficient regularity conditions for the log-determinant Fisher loss to be locally Lipschitz in trainable parameters. Controlled experiments on noisy spirals and Gaussian random fields, where total Fisher information is known, show that TopoFisher recovers much of the available information and outperforms fixed topological vectorizations. Our main results are on weak gravitational lensing, a high-dimensional non-Gaussian cosmological field-inference problem. Learned topological summaries reach higher Fisher information than state-of-the-art cosmological summaries and approach an unconstrained Information Maximising Neural Network baseline with up to $\sim80\times$ fewer parameters. The learned filtrations also generalize better: under simulator shift from lognormal to LPT-based maps it retains most Fisher information, while the neural baseline drops, and in neural posterior estimation they give tighter constraints than the neural baseline, and of state-of-the-art cosmological summaries. These results support Fisher-based topological optimization as a robust, parameter-efficient front end for simulation-based inference.
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All authors Matteo Biagetti, Mathieu Carrière, Francesco Conti, Enrico Maria Ferrari, Sven Heydenreich, Karthik Viswanathan

Astrophysics of Galaxies

The diverse morphologies and evolution of low-luminosity edge-brightened radio galaxies

B. Barkus, J. H. Croston, B. Mingo et al. (+3 more)

Fanaroff-Riley class I (FRI) radio galaxies show centre-brightened emission from disrupted lower power jets, while traditionally more luminous class II (FRIIs), are edge-brightened, with relativistic jets terminating in hotspots. Population studies of radio-loud AGN (RLAGN) with low frequency, deep, wide-field surveys have revealed FRII-like radio structures at lower luminosities. We present the first high-resolution morphological investigation of a representative LOFAR-selected sample of low-luminosity FRIIs, to determine whether this new population is physically distinct from traditional high-luminosity FRIIs. Using new $1.5$-GHz Jansky Very Large Array (VLA) observations for a sample of 19 low-luminosity FRIIs, from the LOFAR Two Metre Sky Survey Data Release 1 (LoTSS DR1), with luminosities up to three orders of magnitude lower than the typical FR break ($L_{150} = 10^{26}$ W Hz$^{-1}$). We examine the compact features and perform spectral index analysis to identify hotspots, cores and signatures of restarting or remnant activity. We find a higher prevalence of cores and a comparable number of hotspots in the low-luminosity FRII sample compared to a randomly-selected sample of luminous ($L_{150}>10^{26}$ W Hz$^{-1}$) FRIIs selected from the same parent LOFAR sample. Approximately 32 per cent of low-luminosity FRIIs show restarting or remnant behaviour, while $\sim 32$ per cent are active FRIIs with compact hotspots. Our results show that FRII source dynamics occur at low radio luminosities, but reinforce earlier conclusions that the population of low-luminosity edge-brightened RLAGN is highly diverse. Binary morphological classifications should be used cautiously as a first step towards more nuanced investigations of the complexity of jet life cycles and evolution.
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All authors B. Barkus, J. H. Croston, B. Mingo, M. J. Hardcastle, G. Gürkan, V. H. Mahatma

High Energy Astrophysical Phenomena

Advance warning of $\gamma$-ray blazar flares from Fermi-LAT light curves: a strictly causal machine-learning backtest

Zahir Shah and Sikandar Akbar

Long-term Fermi-LAT monitoring makes it possible to ask whether a blazar light curve shows signs of an upcoming flare before the flare becomes obvious in the $\gamma$-ray emission. We present a strictly causal machine-learning framework for forecasting $\gamma$-ray blazar flares from 3-d binned LAT light curves. Flare intervals are identified with Bayesian Blocks, and each light curve is sampled with 365-d trailing windows from which 42 variability features are measured. We train separate WATCH and TRIGGER models: WATCH predicts whether flare activity will appear within the next 90 d, while TRIGGER predicts whether a new flare onset will occur within the next 45 d. To avoid temporal leakage, all scaling, calibration, threshold selection, and validation use only the pre-cutoff data before MJD 60000. We apply the method to the FSRQ 4FGL\,J1048.4$+$7143, using 13 bright blazars as auxiliary training sources. Among logistic regression, polynomial logistic regression, and random forest classifiers, polynomial logistic regression gives the strongest held-out WATCH performance, with ROC AUC $=0.891$, average precision $=0.396$, and a block-permutation probability $p_{\rm perm}=0.006$. At the selected WATCH threshold, it recovers 18 of the 21 positive windows in the held-out WATCH set, corresponding to a recall of 0.86. The same model also gives the best held-out TRIGGER ranking, with TRIGGER AUC $=0.770$ and TRIGGER AP $=0.123$, although no reliable pre-onset TRIGGER alert is obtained. The WATCH state appears before both held-out flare episodes, with final alerts 4.5 and 2.5 d before onset. The corresponding broader WATCH-active periods begin 88.5 and 72.5 d before flare onset. These results suggest that long-term {\fermi} light curves contain useful predictive information about the build-up to blazar flares.
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Earth and Planetary Astrophysics

Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory

Damien Hutsemékers, Jean Manfroid, Cyrielle Opitom et al. (+8 more)

We present high-resolution UVES+VLT observations of neutral nickel and iron atoms in the coma of the interstellar comet 3I/ATLAS taken after perihelion. Metal emission was strong shortly after perihelion and persisted at large heliocentric distances. At $r_h \sim 2$ au the total metal production rate was found to be at least an order of magnitude larger than that of typical solar-system comets. Post-perihelion production rates exhibit pronounced asymmetry compared to the pre-perihelion behavior: production rates are higher after perihelion and decline more gradually with $r_h$, the difference being stronger for FeI. The NiI/FeI abundance ratio, initially anomalously large before perihelion, evolved toward values comparable to solar-system comets near 2 au, and shows a weaker $r_h$ dependence after perihelion. To interpret these results, we revisited and extended the carbonyl hypothesis in which FeI and NiI are produced by the rapid photodissociation of Fe(CO)$_5$ and Ni(CO)$_4$ vaporized from the nucleus. Fits that include direct sublimation of carbonyls reproduce the observed rates and the high NiI/FeI line ratio, which is determined by the higher volatility of Ni(CO)$_4$. Desorption of carbonyls from sublimating CO$_2$ and H$_2$O ices is found to be negligible. The temperature profiles needed to reproduce the observations were found to be shallower than the equilibrium $T \propto r_h^{-1/2}$ relation, suggesting that the sublimation could occur below the surface of the nucleus. Fits using temperature profiles from thermal models require sublimation from depths of several cm, especially post-perihelion. An additional transient heat source ($T \simeq$ 100-140~K), possibly linked to the amorphous-crystalline ice transition, is proposed to explain the early NiI excess before perihelion.
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All authors Damien Hutsemékers, Jean Manfroid, Cyrielle Opitom, Emmanuël Jehin, Aravind Krishnakumar, Fernando Massa Fernandes, Michele Bannister, Dennis Bodewits, Rosemary Dorsey, Fiorangela La Forgia, Brian Murphy

High Energy Astrophysical Phenomena

KM3-230213A and potential astrophysical sources

Per Arne Sevle Myhr

The recent detection of the ultra-high energy neutrino KM3-230213A by KM3NeT/ARCA marks the first observation of an astrophysical neutrino with energy above 100 PeV, opening a new window to the ultra-high energy Universe. In this contribution, the current global ultra-high energy neutrino landscape in light of this event is reviewed, including tension of this observation with existing limits set by the IceCube and the Pierre Auger Observatories. Different scenarios are discussed to explain its origin. Recent efforts to constrain features of potential source populations using the inferred diffuse ultra-high energy neutrino flux are also presented.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Probing the Inert Doublet Dark Matter with Stellar-Mass Black Hole Mini-Spikes

Rameswar Sahu

The nature of dark matter remains a central unresolved problem in contemporary physics, motivating the exploration of well-defined extensions of the Standard Model. Among these, the Inert Doublet Model provides a minimal and theoretically consistent framework accommodating a viable weakly interacting massive particle dark matter candidate. In this work, we investigate the IDM parameter space through an analysis of FermiLAT observations of dark matter mini-spikes surrounding stellar-mass black holes. Owing to the strong gravitational compression of dark matter in the vicinity of these systems, the resulting annihilation signal can be significantly enhanced, rendering such environments exceptionally sensitive probes of dark matter interactions. We find that substantial regions of the IDM parameter space, particularly in the high-mass regime, are subject to stringent constraints extending into the multi-TeV range. These results underscore the increasingly important role of indirect detection in probing particle dark matter scenarios beyond the reach of current collider and direct detection experiments.
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Astrophysics of Galaxies

Dynamical evolution of Milky Way globular clusters on the cosmological timescale II. Terzan 2, 4, and 5 mass loss and collision tracking

M. Ishchenko, P. Berczik and D. Kuvatova

We investigate the long-term dynamical evolution of Ter2, Ter4, and Ter5, focusing on their mutual interactions, mass-loss behaviour, and survivability in the dense Galactic centre environment. We performed a suite of high-resolution direct N-body simulations over 8 Gyr, modelling three individual clusters that we also modelled as combined systems. We compared reference runs of isolated clusters with simulations of the full three-cluster system to quantify possible differences in mass loss, potential energy, and orbital behaviour. Our simulations reveal multiple close encounters between the Terzan clusters. The most significant encounters occur between Ter2-Ter4 and Ter4-Ter5, with their tidal radii exceeding the minimum separation. A notable case is the pair Ter2-Ter4, which approaches within 10 pc at a relative velocity of ~320 km/s. We found that the mass-loss rate is higher for the low-mass Ter2 and Ter4 systems in the combined three-cluster simulations than in our similar isolated runs, highlighting the importance of mutual cluster interactions. The common run clearly demonstrates that mutual gravitational interactions between clusters drive significant triaxial deformations, especially for Ter2 and Ter5, which evolve from nearly spherical to distinctly prolate shapes. In contrast, the isolated runs show clusters that remained almost perfectly spherical, confirming that the observed shape changes are correlated with the mutual interactions. The survivability and dynamical evolution of Galactic centre globular clusters cannot be fully understood without accounting for collective interactions among all systems within a few kiloparsecs. Our results emphasise the necessity of complex multi-cluster modelling in realistic Galactic potentials to capture the long-term fate of surviving and dissolved clusters
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High Energy Astrophysical Phenomena

Diffuse gamma-ray emissions around the stellar cluster Berkeley 59

Ziwei Ou, Xiaolong Yang and Songpeng Pei

We report a detailed analysis on the young stellar cluster Berkeley 59 using Fermi-LAT. Using up-to-date source catalog and background models, we found significant extended GeV emission around Berkeley 59, which can be modeled by a radial disk of 1.02 degree radius with a significance of the extension of 10.6 sigma. We investigated the molecular, neutral and ionized gas content and the hadronic origin. The gamma-ray spectrum of Berkeley 59 has a photon index of 2.88. The derived gas mass from H2 and HII around Berkeley 59 is about 289 solar mass. We derived the relationship between cosmic ray acceleration efficiency and diffusion coefficient. Our results suggest that the extended gamma-ray emission originates from cosmic rays accelerated by cluster winds interacting with surrounding gas.
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Earth and Planetary Astrophysics

Mass Production of 2023 KMTNet Microlensing Planets. III: Three Planets from the Subprime Field

Hongyu Li, Zhixing Li, Weicheng Zang et al. (+56 more)

To complete the analysis of the 2023 KMTNet subprime-field microlensing planetary events identified by its AlertFinder system, we present the analysis of six events, KMT-2023-BLG-(1810, 0084, 1118, 0584, 1697, 2218). We find that the first three events are securely confirmed as planetary, with inferred mass ratios of $\log q \sim -1.9$, $-2.0$, and $-2.6$, respectively. The remaining three events exhibit the well-known degeneracy between binary-lens/single-source (2L1S) and single-lens/binary-source (1L2S) models, and two of these also admit viable stellar binary solutions. A Bayesian analysis indicates that the companions in the confirmed planetary events are likely either super-Jupiters orbiting beyond the snow line of M- or K-dwarf hosts or, for two degenerate solutions of KMT-2023-BLG-1118, Saturn-mass planets orbiting late-type M dwarfs. To date, the 2023 KMTNet sample contains 25 unambiguous planetary events, and its mass-ratio distribution is consistent with that of the KMTNet planetary sample from 2016–2019.
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All authors Hongyu Li, Zhixing Li, Weicheng Zang, Yoon-Hyun Ryu, Andrzej Udalski, Takahiro Sumi, Hongjing Yang, Jiyuan Zhang, Shude Mao, Michael Albrow, Sun-Ju Chung, Andrew Gould, Cheongho Han, Kyu-Ha Hwang, Youn Kil Jung, In-Gu Shin, Yossi Shvartzvald, Jennifer Yee, Sang-Mok Cha, Dong-Jin Kim, Seung-Lee Kim, Chung-Uk Lee, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard Pogge, Przemek Mróz, Michał Szymański, Jan Skowron, Radoslaw Poleski, Igor Soszyński, Pawel Pietrukowicz, Szymon Kozłowski, Krzysztof Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz, Fumio Abe, David Bennett, Aparna Bhattacharya, Ian Bond, Ryusei Hamada, Yuki Hirao, Stela Silva, Shota Miyazaki, Yasushi Muraki, Kansuke Nunota, Greg Olmschenk, Clément Ranc, Nicholas Rattenbury, Yuki Satoh, Daisuke Suzuki, Takuto Tamaoki, Sean Terry, Paul Tristram, Aikaterini Vandorou, Hibiki Yama

High Energy Astrophysical Phenomena

Resonant Inverse Compton Scattering and Hard X-ray Emission in Magnetar Magnetospheres

Kun Hu, Nicholas Rackers and Alexander Y. Chen

Magnetars are a subclass of neutron stars with ultra-strong surface magnetic fields. Some magnetars exhibit persistent hard X-ray emission, characterized by power-law tails with photon indices around 1–1.5, extending from ${\sim}$10 keV to several hundred keV. The leading explanation for this hard X-ray component is resonant Compton scattering, in which the thermal seed photons are upscattered by relativistic electron-positron pairs flowing along magnetic field lines in the magnetosphere. In this work, we adopt the pair outflow framework of the magnetar magnetosphere and calculate the resonant Compton scattering opacity, as well as the spectrum and polarization of the upscattered emission. We find that resonant cooling can substantially modify the magnetospheric plasma density and impose strong optical depth constraints on the hard X-ray emission regions. Under the viewing geometry inferred from IXPE, an equatorial twist near the stellar surface provides a viable configuration for the NuSTAR hard X-ray spectrum of 4U 0142+61, while a polar-twist geometry is disfavored. Joint spectral, timing, and polarimetric modeling will be essential for distinguishing between the magnetospheric scattering geometries and understanding the physical properties of the pair plasma.
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High Energy Astrophysical Phenomena

Anisotropic Thermal Conduction as a Driver of Jet Collimation and Magnetic Field Amplification on Cold Fronts

Nana Matsuno, Takaaki Yokoyama and Mami Machida

Galaxy clusters contain a hot, diffuse, and weakly magnetized plasma known as the intracluster medium (ICM). In this environment, how thermal conduction influences plasma dynamics and the conditions under which it operates efficiently remain open questions in cluster physics. Systems in which active galactic nuclei (AGN) jets interact with cold fronts produced by cluster mergers provide a unique setting to examine the interplay between conduction, jet dynamics, and ordered magnetic fields. To interpret the detailed structures revealed by recent observations, it is therefore important, as a first theoretical step, to quantify how thermal conduction modifies AGN jet morphology and the surrounding magnetic-field configuration. We perform two-dimensional magnetohydrodynamic (MHD) simulations of an AGN jet in an ICM environment, incorporating anisotropic thermal conduction with varying efficiency. The simulations show that thermal conduction transports heat from the jet head backward along magnetic field lines into the inner cocoon. This process increases the inner cocoon pressure, enhancing jet collimation by a factor of $\sim 4$ compared to models without conduction. This stronger collimation stretches the magnetic fields along the cold-front surface, resulting in a maximum field strength up to a factor of $\sim 1.5$ larger. Jet collimation increases as the conduction efficiency increases, which is interpreted as a conductive collimation mechanism. These results suggest that anisotropic thermal conduction can operate effectively on jet scales in galaxy clusters, and that accounting for conduction may be important when interpreting jet morphology and magnetic field structure in merging cluster environments.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Formulation of testing gravitational redshift based on Laser Time link between China Space Station and a ground station

Rui Xu, Wenbin Shen, Hok Sum Fok et al. (+11 more)

This paper presents a high-precision gravitational redshift test using the China Space Station (CSS) Laser Time Transfer (CLT) system. We develop a comprehensive observation equation based on a c^{-3} order relativistic model for space-ground clock comparison. While the CSS optical clock system is currently in the orbital debugging phase, our simulation using actual CSS orbit data achieves a gravitational redshift verification precision of (1.8 \pm 47)*10^{-7} – approximately one order of magnitude improvement over previous experiments. Our work represents the first application of laser-based time transfer for gravitational redshift verification at such precision, and the first use of the CSS CLT link for testing this fundamental aspect of General Relativity. Unlike microwave-based methods, our laser approach avoids ionospheric effects and first-order Doppler shifts. Residual analysis identifies tropospheric delay variations and atmospheric turbulence as the primary remaining uncertainty contributors. The achieved precision enables gravitational potential difference measurements with 0.1 m^2/s^2 precision – offering new capabilities for both fundamental physics investigations and geodetic applications including intercontinental height transfer. This work establishes a new benchmark for high-precision tests of relativistic physics and demonstrates the transformative potential of space-based optical time transfer.
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All authors Rui Xu, Wenbin Shen, Hok Sum Fok, Pengfei Zhang, Lihong Li, Lei Wang, Kuangchao Wu, An Ning, Youchao Xie, Ziyu Shen, Lingxuan Wang, Yongqi Zhao, Kai Liu, Yuanjin Pan

Astrophysics of Galaxies

First Interstellar Detection of Methyl Carbamate: A New Observational Anchor for Glycine Chemistry

Chunguo Duan, Fengwei Xu, Jun Kang et al. (+5 more)

Glycine-the simplest amino acid-has remained undetected in the interstellar medium despite decades of sensitive searches, motivating alternative approaches to constrain its astrochemical origin. A promising strategy is to investigate the broader $\rm C_{2}H_{5}O_{2}N$ isomer family and identify detectable members that can serve as observational anchors for glycine-related chemistry. Herein, we report the first robust interstellar detection of methyl carbamate toward the hot molecular core G358.93-0.03 MM1 using ALMA 1 mm observations. Ten unblended rotational transitions are identified, yielding a column density of (4.21$\pm0.84)\times10^{15} \rm cm^{-2}$ and an excitation temperature of $204\pm10$ K. We also searched for other $\rm C_{2}H_{5}O_{2}N$ isomers with available rotational spectroscopic data, including glycine, but none were detected, allowing us to derive upper limits on their column densities. The resulting abundance pattern deviates significantly from the Minimum Energy Principle predictions, highlighting that the $\rm C_{2}H_{5}O_{2}N$ family is shaped primarily by kinetic chemical process rather than thermodynamic equilibrium. The observed methyl carbamate abundance is consistent with a grain-surface formation scenario involving radical-radical recombination ($\rm CH_{3}$O + $\rm NH_{2}$CO), further supported by its correlated abundances with its proposed precursors, methanol and formamide, across diverse astrophysical environments. This detection establishes methyl carbamate as a new observational anchor for glycine chemistry, providing critical constraints on the formation pathways of amino-acid-related molecules in star-forming regions.
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All authors Chunguo Duan, Fengwei Xu, Jun Kang, Qian Gou, Xuefang Xu, Laurent Pagani, Jiaxin Du, Xi Chen

Thursday 7 May

High Energy Astrophysical Phenomena

Nuclear Constraints on $^{12}$C$(\alpha,\gamma)^{16}$O and Their Impact on Black-Hole Mass Predictions

Akram Mukhamedzhanov

Gravitational-wave observations have renewed interest in the black-hole mass gap and in the maximum mass of first-generation black holes below its lower edge. The \(^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}\) reaction plays a central role in this problem because it determines the carbon-to-oxygen ratio after core-helium burning and thereby affects the later evolution of massive stars toward pulsational pair instability and pair-instability supernovae. Recent attempts to constrain \(S(300~{\rm keV})\) from gravitational-wave population inferences face important limitations, because the lower edge of the black-hole mass gap is not directly measured. It is inferred model dependently from assumptions about stellar evolution, metallicity, mass loss, rotation, binary evolution, hierarchical mergers, selection effects, priors, and the adopted population model. Therefore, values of \(S(300~{\rm keV})\) inferred from black-hole populations must remain consistent with independent nuclear-physics constraints. In this work we reanalyze the low-energy \(^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}\) \(S\) factor using updated information on the subthreshold \(1^{-}\) and \(2^{+}\) ANCs and on the ground-state ANC of \(^{16}{\rm O}\), together with direct capture data. These constraints favor a lower \(S(300~{\rm keV})\) than the older central evaluation and disfavor very large values required by some black-hole-population interpretations. Using the resulting ANC-constrained \(S(300~{\rm keV})\) range and the transformed relation between this quantity and the lower edge of the pair-instability mass gap, we estimate \[ \frac{M_{\rm BH}}{M_\odot}\simeq 61\text{--}75 . \] Thus, the present nuclear-physics constraints favor a relatively high lower edge of the first-generation black-hole mass gap.
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Solar and Stellar Astrophysics

Characterizing the Extended Molecular Hydrogen Winds in Protoplanetary Disks from the JWST Disk Infrared Spectroscopic Chemistry Survey

Mayank Narang, Klaus M. Pontoppidan, Colette Salyk et al. (+14 more)

We present a comprehensive analysis of extended H$_2$ emission from 34 protoplanetary disks observed with the JWST Disk Infrared Spectroscopic Chemistry Survey (JDISCS), supplemented by archival data. We investigated the morphology, kinematics, excitation conditions, and mass dynamics of H$_2$. Extended emission from pure rotational H$_2$ lines is found to be common, with 16 sources exhibiting clear signatures of disk winds. These include monopolar and bipolar structures in inclined disks and ring-like or bubble-like morphologies in face-on systems features indicative of wide-angle disk winds. Our analysis shows that the H$_2$ is consistent with slow {(4.2$^{+6.7}_{-3.0}$ km s$^{-1}$)} MHD driven winds. For ten disks, we model the wind morphology and find a median half-opening angle of $45\arcdeg^{+5}_{-4}$ and a characteristic power-law index of $\alpha \sim$ 1.6. Excitation analysis yields a median gas temperature of 624 $\pm$ 130 K and a column density of $\log(N_{\mathrm{tot}}\,[\mathrm{cm}^{-2}]) = 18.6 \pm 0.6$. The median wind mass-loss rate, ${\rm log_{10}}(\dot{\rm M}_{\rm wind}^{\rm tot}) = -9_{-0.4}^{+0.8}\,{\rm M_\odot\,yr^{-1}}$, implies that, if molecular winds are the dominant mechanism responsible for disk dispersal, a typical disk with a mass of $2-3\,M_{\rm Jup}$ would dissipate on a $\sim$2-3 Myr timescale, consistent with observed disk lifetimes. The $\dot{\rm M}_{\mathrm{\rm wind}}^{\rm tot}$ span a relatively narrow range ($\sim$2 dex) and do not correlate strongly with accretion rates onto the star, suggesting that the mass loss rate and the accretion rates are probing different timescales. Our findings demonstrate that spatially extended warm H$_2$ emission is a widespread and reliable tracer of molecular disk winds in protoplanetary systems.
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All authors Mayank Narang, Klaus M. Pontoppidan, Colette Salyk, Nicole Arulanantham, Geoffrey A. Blake, Andrea Banzatti, Joan Najita, Ilaria Pascucci, Jane Huang, Sebastiaan Krijt, Karin Oberg, Giovanni Rosotti, Till Kaeufer, Emma Dahl, L. Ilsedore Cleeves, Ke Zhang, Joel Green

Earth and Planetary Astrophysics

Exploring TRAPPIST-1 Climate States with an Energy Balance Model

Jacob Haqq-Misra

This paper presents a version of the HEXTOR energy balance model that has been configured for the study of habitable terrestrial planets orbiting low-mass stars. The model is validated for rapidly-rotating Earth-like planets using latitudinal coordinates, which shows expected patterns of bistability. A tidally-locked coordinate transformation is then applied to the model, which is calibrated to match mean values of the minimum, average, and maximum surface temperatures from a general circulation model ensemble of TRAPPIST-1 e. This calibrated energy balance model is used to characterize the possible climate states of such a synchronously rotating planet across a parameter space of instellation and carbon dioxide partial pressure. These calculations suggest a state of partial ice cover for TRAPPIST-1 e and complete ice cover for TRAPPIST-1 f. TRAPPIST-1 e becomes fully ice-free only above ~0.4 bar CO$_2$, while TRAPPIST-1 f remains ice-covered unless CO$_2$ partial pressure approaches ~1.2 bar. This approach demonstrates the capability of a simplified one-dimensional model to study the climates of terrestrial planets in synchronous rotation, which can help guide more complex models and observations toward the most promising targets of interest.
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Astrophysics of Galaxies

Scylla VI: Parsec-Scale Dust Extinction Maps in the SMC and LMC

Christina W. Lindberg, Claire E. Murray, Christopher J. R. Clark et al. (+14 more)

We present a novel methodology for mapping dust extinction in nearby galaxies at parsec-scale resolution. We apply it to HST 68 fields within the Small and Large Magellanic Clouds (23 fields in the SMC and 45 fields in the LMC) using multi-band HST photometry from the Scylla and METAL surveys. Our technique leverages kriging, a geostatistical interpolation method built on the principles of Gaussian Process regression, combined with Gaussian mixture modeling to statistically isolate background stellar sources and account for line-of-sight depth effects. 3D dust simulations demonstrate the method's capability to recover column densities to an accuracy of $A_V \approx 0.1$ mag in fields with at least 1000 sources. The resulting $4^{\prime\prime}$ resolution ($\sim1$-pc) dust maps reveal detailed structure and strong spatial correlation with ancillary ISM tracers, especially in star-forming regions like 30 Doradus. Global extinction of total column densities follows log-normal profiles in both galaxies, with the SMC exhibiting slightly higher mean extinction ($e^{\mu}=0.47$ mag) than the broader LMC ($e^{\mu}=0.43$ mag), likely due to significant line-of-sight depths. We find systematic offsets between dust mass surface densities ($\Sigma_{D}$) derived from extinction versus FIR emission in both galaxies, with $\Sigma_{D, FIR}/\Sigma_{D, A_V}$ ratios ranging from $0.6-1.8$. This work provides the highest-resolution dust extinction maps in SMC and LMC to date, which offer a vital independent benchmark for constraining dust emissivity, $\text{CO}$-dark gas fractions, and the multi-scale structure of the ISM in low-metallicity environments.
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All authors Christina W. Lindberg, Claire E. Murray, Christopher J. R. Clark, Caroline Bot, Clare Burhenne, Yumi Choi, Roger E. Cohen, Steven R. Goldman, Karl D. Gordon, Kristen B. W. McQuinn, Julia Roman-Duval, Karin M. Sandstrom, Edward F. Schlafly, Elizabeth Tarantino, Benjamin F. Williams, Petia Yanchulova Merica-Jones, Catherine Zucker

High Energy Astrophysical Phenomena

X-ray spectroscopy mass constraints on V1674 Her: the fastest nova does not have a near-Chandrasekhar white dwarf

Tekeba Olbemo, Manel Errando and Andrea Gokus

V1674 Her (Nova Her 2021) is the fastest classical nova ever recorded, with an optical decline time of $t_2 \sim 1$ day, typically interpreted as evidence for a white dwarf mass close to the Chandrasekhar limit. We present a broadband X-ray study of V1674 Her combining contemporaneous XMM-Newton and NuSTAR observations in quiescence to directly constrain the white dwarf mass and magnetic field strength. The hard X-ray emission is modeled using a physically motivated post-shock accretion column model that accounts for the temperature gradient in the flow and reflection from the white dwarf surface. Under the assumption that the accretion disk is truncated at the co-rotation radius, we obtain a white dwarf mass of $M = 1.09^{+0.07}_{-0.06}\,M_\odot$. An independent constraint derived from timing analysis of the X-ray power spectrum yields a consistent value of $M = 1.12 \pm 0.06\,M_\odot$. These values are significantly lower than those inferred from empirical decline-time relations, suggesting that such relations may overestimate white dwarf masses in extreme fast novae. From the inferred accretion rate and magnetospheric radius, we estimate a surface magnetic field strength of $B = 21.3^{+6.6}_{-5.7}\,(\mathrm{stat})^{+12.9}_{-8.1}\,(\mathrm{sys})\,\mathrm{MG}$, placing V1674 Her at the high end of the magnetic field distribution for intermediate polars. Our results demonstrate that even the fastest novae do not necessarily host near-Chandrasekhar white dwarfs, highlighting the importance of direct X-ray constraints and suggesting that additional parameters beyond white dwarf mass play a key role in setting nova timescales.
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Earth and Planetary Astrophysics

You Only Stack Once (YOSO): A Motion-Filtered, Deep-Learning Framework for Detecting Faint Moving Sources

Nitya Pandey, César Fuentes, Pedro Bernardinelli et al. (+15 more)

We present You Only Stack Once (YOSO), an automated pipeline designed to detect faint, slow-moving Solar System objects in wide-field astronomical surveys. The pipeline integrates a novel Gaussian Motion Filter (GMoF) that operates at the pixel level to enhance signal-to-noise for objects exhibiting a range of apparent rates of motion. Unlike conventional shift-and-stack methods, which rely on discrete velocity trials, GMoF amplifies trails while suppressing random noise and static background features. Applied to a subset of DEEP observations from the Dark Energy Camera, YOSO recovered 45 out of 73 previously detected objects, as well as 11 new TNOs. It also discovered 216 objects in the near Solar System. Although alternative shift-and-stack methods are sensitive to objects about 0.88 magnitudes fainter, YOSO's false positive rate is extremely low, since it detects only sources that exhibit a trail and are consistent with a point source when shifted at the right rate. We show how this method can be deployed on large surveys like LSST, and adapted for other domains that require motion-based signal enhancement, including exoplanet imaging through Angular Differential Imaging (ADI), and near-Earth object (NEO) detection for missions like NEO Surveyor. YOSO thus provides a versatile, scalable approach for extracting faint, motion-dependent signals in the era of data-intensive astronomy.
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All authors Nitya Pandey, César Fuentes, Pedro Bernardinelli, Valeria Frías, Colin Orion Chandler, David E. Trilling, Matthew J. Holman, Steven Stetzler, Dallin Spencer, Hsing Wen Lin, Luis E. Salazar Manzano, Darin Ragozzine, Ryder Strauss, Mario Jurić, Andrew J. Connolly, Hayden Smotherman, Scott S. Sheppard, Kevin Napier

Earth and Planetary Astrophysics

Diverse dust vertical height and settling strength conditions in protoplanetary discs

Juanita Antilen, Paola Pinilla, Dafa Li et al. (+5 more)

The settling of dust particles plays a critical role in the growth and dynamics of dust grains. We performed a detailed modeling of the ALMA continuum substructures for six highly inclined protoplanetary discs using radiative transfer simulations, to constrain the vertical height of millimetre dust grains and the settling strength. Our modeling results are a very thin millimetre dust disc in T Cha ($\text{h}_{\text{dust}}<$ 0.1 au throughout the disc), a vertically extended dust disc in DoAr 25 ($\text{h}_{\text{dust}}$ of $\sim$ 4.7 au at 140 au) and tentatively a thin disc in MY Lup ($\text{h}_{\text{dust}}<$ 0.5 au at 70 au). From lower resolution observations we found a very thin disc for PDS 111 ($\text{h}_{\text{dust}}<$ 0.1 au throughout the disc) and a more vertically extended millimetre dust disc in V409 Tau ($\text{h}_{\text{dust}}$ of $\sim$ 1.3 au at 35 au). We could not measure the vertical height in the asymmetric disc of RY Lup. We also found that the input dust opacities are a source of degeneracy in our models. Our tentative results, assuming the Ricci dust opacities, point to a diverse settling strength in our sample and possible radial variations. We also compared the models that best fit the ALMA data with the SPHERE data to test if they can reproduce the vertical distribution of small dust grains. This comparison suggests that models that reproduce the dust density distribution in the midplane cannot reproduce the distribution of small dust grains in the upper layers, reinforcing the need for more complex models.
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All authors Juanita Antilen, Paola Pinilla, Dafa Li, Marion Villenave, Anibal Sierra, Yao Liu, Myriam Benisty, Christian Ginski

Astrophysics of Galaxies

$Ab$ $initio$ modeling of Galactic dust polarized CMB foreground

Alexei G. Kritsuk, Ka Wai Ho, Ka Ho Yuen et al. (+1 more)

We present the analysis of high-resolution synthetic dust polarization maps derived from large-scale simulations of magnetized multiphase interstellar turbulence carried out with the AthenaK code on the $Frontier$ exascale supercomputer at the Oak Ridge National Laboratory. Our turbulence model accurately captures spectral properties of the $E$- and $B$-modes measured by $Planck$ at 353 GHz. The simulations provide new insights into the physical origins of the observed $E/B$ asymmetry and positive $TE$ signal, facilitating the development of advanced models of Galactic foreground emission for current and future CMB experiments.
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All authors Alexei G. Kritsuk, Ka Wai Ho, Ka Ho Yuen, Raphael Flauger

Astrophysics of Galaxies

$V/\sigma$ Trends with Mass for Dwarf Galaxies from the Marvelous Massive Dwarfs Suite

Dilys Ruan, Alyson M. Brooks, Leonardo A. Barba et al. (+7 more)

Galaxy formation scenarios can be interpreted through galaxy morphology and the level of rotational versus pressure support, quantified through the ratio of a galaxy's rotation speed to its velocity dispersion: $V/\sigma$. Observational studies of dwarf galaxies find that $V/\sigma$ does not strongly depend on environment, and may weakly depend on galaxy mass, which could shift our understanding of how dwarf galaxies form. We utilize the Marvelous Massive Dwarfs suite to examine whether $V/\sigma$ depends on mass in simulations, and understand how this varies for different baryonic components of the galaxy: HI gas, young stars ($<$ 1 Gyr) and old stars ($>$ 1 Gyr). We use a simulation sample of 67 isolated dwarf galaxies with M$_\star=10^6-10^9$ M$_\odot$ and produce line-of-sight maps for rotation speed and dispersion for different viewing angles of each galaxy. We find that $V/\sigma$ increases with mass, and that HI gas and young stars are more rotation-supported ($V/\sigma\approx 1-13$) while old stars are more dispersion-supported ($V/\sigma\approx 0.2-5$). This result is consistent with the scenario where young stars are born from dynamically cold gas in the interstellar medium and undergo dynamical heating over time. We quantify the effects of spatial resolution in observational determinations of $V/\sigma$ and find that existing observations using old stars may underestimate the intrinsic $V/\sigma$. We find a correlation between $V/\sigma_\mathrm{HI,global}$ and HI line profile shape that is qualitatively similar to previous simulation results, but we find higher $V/\sigma_\mathrm{HI,global}$ compared to prior work which found values $\lesssim 2$ for most galaxies in this mass range. Our results motivate future work to examine $V/\sigma$ and dwarf galaxy formation with different kinematic tracers of the galaxy.
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All authors Dilys Ruan, Alyson M. Brooks, Leonardo A. Barba, Mithi A. C. de los Reyes, Akaxia Cruz, Robel Geda, Annika H. G. Peter, Benjamin W. Keller, Thomas Quinn, James W. Wadsley

Solar and Stellar Astrophysics

On the origin of the rotation of massive stars

André Oliva, Facundo D. Moyano, Luca Sciarini et al. (+3 more)

We explore the origin of the rotation rates of massive stars. Contrary to their low-mass siblings, most massive stars do not have detectable magnetic fields, so that star-disk interaction models used for the formation of rotating low-mass stars do not apply. We investigate whether the magnetic fields of protostellar jets present in the parent molecular cloud prevent the protostar from reaching the critical angular velocity. Starting from the gravitational collapse of a molecular cloud, we run two two-dimensional radiation-gravito-magnetohydroynamical simulations to study the formation of an accretion disk and the launching of magnetically-driven protostellar outflows (of particular interest is the formation of a magnetocentrifugal jet originating from the protostar and inner disk). We then study the angular momentum transfer from the disk and jet onto the protostar. Finally, we compute one-dimensional stellar evolution models of the pre-main sequence including our results from the disk-jet simulations and follow the angular momentum redistribution within the structure of the protostar. We find that the angular momentum transported outwards by the magnetically-driven protostellar outflows is sufficient for keeping the protostar below the critical speed at all times. Moreover, we are able to link the strength of the jet, and thus the rotation rate at the end of the accretion epoch, to the initial conditions for star formation. Our results show that the jet strength produces a variety of stellar rotation rates, suggesting that protostellar jets fix the rotation rate of massive stars.
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All authors André Oliva, Facundo D. Moyano, Luca Sciarini, Sylvia Ekström, Patrick Eggenberger, Georges Meynet

Astrophysics of Galaxies

Spectrally and spatially resolved (sub)millimeter HCN-to-HCO$^{+}$ flux ratios in nearby ultraluminous infrared galaxies

Masatoshi Imanishi, Yuri Nishimura, Shunsuke Baba et al. (+2 more)

We present the results of our investigations of spectrally and spatially resolved (sub)millimeter HCN-to-HCO$^{+}$ flux ratios at J=2-1, J=3-2, and/or J=4-3 in 18 nearby ($z <$ 0.15) ultraluminous infrared galaxies (ULIRGs), using ALMA $\lesssim$0.2" ($\lesssim$500 pc) resolution data. The geometry of elevated HCN-to-HCO$^{+}$ flux ratios (with $>$3$\sigma$ detections for both molecular lines) in position-position-velocity (PPV) space is visually classified into (i) spherical shell (spectrally and spatially distinct), (ii) spectrally distinct and spatially compact, and (iii) filled (spectrally filled and spatially compact). These can naturally be explained by the elevation of the flux ratio due to (i) a spatially resolved outflow, (ii) an AGN and/or a spatially unresolved outflow with blueshifted and redshifted emission components, and (iii) an AGN and/or a spatially confined outflow with not clearly separated blueshifted and redshifted velocity components, respectively. Signatures of elevated HCN-to-HCO$^{+}$ flux ratios originated from (a) spatially resolved outflow and (b) AGN and/or spatially unresolved outflow are seen in seven and nine ULIRGs, respectively. In the former spatially resolved outflow-origin case, modest-velocity components relative to the maximum outflow velocity tend to be probed by spaxels with elevated HCN-to-HCO$^{+}$ flux ratios. The spectrally and spatially resolved HCN-to-HCO$^{+}$ flux ratios can provide additional information on the physical origin of the elevated flux ratios in nearby ULIRG nuclei, compared to previously conducted spatially integrated and/or velocity-integrated analyses.
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All authors Masatoshi Imanishi, Yuri Nishimura, Shunsuke Baba, Kouichiro Nakanishi, Takuma Izumi