Astrophysics of Galaxies
Diverse ionized gas conditions in a dynamically hot, interacting galaxy at $z = 9.31$ revealed by JWST/NIRSpec IFU
Ryota Ikeda, Takahiro Morishita, Massimo Stiavelli et al. (+1 more)
We present a spatially and spectrally resolved study of an interacting
galaxy, Gz9p3 at $z=9.31$, using the James Webb Space
Telescope NIRSpec/G395H IFU observation with high-spectral resolution ($R\approx 2700$) mode. Gz9p3 consists of two sub-regions (`core' and `tail'), which show stark contrast in their physical properties. The HII regions in the core are characterized by high electron density ($n_{e}\gtrsim2900$ cm$^{-3}$), low gas-phase
metallicity ($0.25$ dex below the mass-
metallicity relation), and yet relatively low specific
star formation rate (sSFR) among the system. On the other hand, the tail exhibits low electron density ($n_{e}<70$ cm$^{-3}$), relatively high gas-phase
metallicity that is consistent with the mass-
metallicity relation, and high sSFR. The integrated spectrum thus shows the properties inbetween these two regions. No evidence of ordered rotation in ionized gas is found, suggesting that Gz9p3 is a dynamically hot system. Finally, we find ionized gas
outflows characterized by the secondary [OIII]5007 line component throughout most of the system. The
outflow velocity is below the escape velocity, making Gz9p3 one of the first
galactic systems experiencing a
galactic fountain. Overall, our findings indicate that this system is in a phase in which the pristine gas is falling efficiently into the core, diluting the gas
metallicity, and enhancing
star formation and
outflows after the
galaxy interaction.
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All authors Ryota Ikeda, Takahiro Morishita, Massimo Stiavelli, Antonello Calabrò
Astrophysics of Galaxies
Interacting stellar winds feeding Sgr A*: from the system of mass-losing stars to the binary IRS 16SW
Diego Calderón, Jorge Cuadra, Christopher M. P. Russell et al. (+3 more)
The discovery of cold structures around Sgr A* has challenged our understanding of the gas dynamics and thermodynamic state of the
plasma in its vicinity. This work aims to constrain the conditions for the formation of such structures, namely the cold disc-like structure and the recently discovered G-1-2-3 complex. We conduct hydrodynamic simulations of the observed Wolf-Rayet
stars feeding Sgr A*. Our simulations show that the
plasma chemical composition is crucial for determining the medium properties. We demonstrate that the formation of a cold disc is possible for chemical compositions that are consistent with observational constraints. However, it is not possible to reproduce all the properties of the observed disc which might suggest the interaction with another structure. Additionally, we present our first results on the hydrodynamic modelling of IRS 16SW as a colliding-wind binary. This is the first step to develop a realistic model on the formation of the G-1-2-3 complex.
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All authors Diego Calderón, Jorge Cuadra, Christopher M. P. Russell, Andreas Burkert, Stephan Rosswog, Mayura Balakrishnan
High Energy Astrophysical Phenomena
The Gamma-ray Burst Jet Energy Distribution Suggests A Quasi-universal, Weakly Magnetized Jet Evolving Over Cosmic Time
Nicole M. Lloyd-Ronning, Fabio De Colle, Gal Birenbaum et al. (+2 more)
We present distributions of gamma-ray burst observed and inferred properties for those GRBs with
redshifts. We show that the isotropic energy distribution, which spans over four orders of magnitude, can be reproduced reasonably well under a simplistic assumption that every observed GRB originates from a quasi-universal jet with roughly the same decreasing power-law profile of energy as a function of angle, with a power-law index of $ 3 \lesssim \zeta \lesssim 4$. The spread in the observed distribution can be explained by the variation in observer viewing angle alone. Furthermore, this power-law jet structure provides an even better fit to both the isotropic energy and luminosity distributions if the isotropic energy normalization evolves as a function of
redshift in a manner that has been suggested by a range of previously published studies. The relatively steep power-law index of this jet is consistent with the structure predicted by simulations of weakly magnetized jets in collapsars, whereas simulations of hydrodynamic jets predict a structure shallower than what we find here. The predicted afterglow light curves within this model framework show steepening behavior at times commensurate with observed jet break times.
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All authors Nicole M. Lloyd-Ronning, Fabio De Colle, Gal Birenbaum, Omer Bromberg, Jarrett Johnson
Earth and Planetary Astrophysics
GEMS JWST: Hold on to your HATS(-6 b), a sub-solar metallicity giant planet with water, methane and ammonia in its atmosphere
Giannina Guzmán Caloca, Caleb I. Cañas, Nicole L. Wallack et al. (+16 more)
HATS-6 b is one of several recently discovered
Giant Exoplanets orbiting M-
dwarf Stars (GEMS) and is part of a JWST survey that aims to compare bulk and atmospheric properties of these rare
planets against their FGK
star counterparts. HATS-6 b is a warm ($\mathrm{T_{eq}}\sim700$ K), Saturn-mass ($M_p\sim0.3~\mathrm{M_J}$), Jupiter-radius ($R_p\sim1~\mathrm{R_J}$)
planet that transits its
star every $\sim$ 3 days. In this study, we present the transmission spectrum of HATS-6 b obtained with two transits using the PRISM mode of JWST Near Infrared Spectrograph (NIRSpec), spanning a wavelength range of $0.6-5.3$ um. Analyzing these JWST observations using an iterative approach between forward modeling and free chemistry
retrievals, we derive a low
metallicity ($\log\mathrm{[M/H]}=-1.99^{+0.2}_{-0.2}$) sub-
solar C/O ($\log\mathrm{[C/O]=-0.46^{+0.2}_{-0.2}}$) atmosphere, and find strong evidence for H$_2$O, CH$_4$, and NH$_3$ at volume mixing ratios (in $\log[X]$) of $-4.88_{-0.24}^{+0.25}$, $-5.38_{-0.19}^{+0.18}$, and $-6.03_{-0.19}^{+0.18}$, respectively. We consistently retrieve a significantly lower $\mathrm{T_{eq}}$ than predicted from the orbital configuration of HATS-6 b, which was impervious to any data reduction and
retrieval choices, suggesting a non-zero bond albedo. Our planetary interior models retrieve bulk
metallicities three orders of magnitude larger than our retrieved atmospheric
metallicity, also suggesting that the atmosphere is not well-mixed. We find an excess feature around 3 um, and expand on possible explanations for this, such as the presence of HCN or hydrocarbons like C$_2$H$_4$. Yet, due to the degeneracies present for hydrocarbon features in this wavelength region, we do not draw any conclusions about the excess feature and instead encourage further observations and follow-up of this intriguing target.
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All authors Giannina Guzmán Caloca, Caleb I. Cañas, Nicole L. Wallack, Erin M. May, Shang-Min Tsai, Simon Müller, Ravit Helled, Shubham Kanodia, Jacob Lustig-Yaeger, Knicole D. Colón, Ian Czekala, Megan Delamer, Peter Gao, Te Han, Jessica Libby-Roberts, Suvrath Mahadevan, Anjali A. A. Piette, Gu{\dh}mundur Stefánsson, Kevin B. Stevenson
Astrophysics of Galaxies
A comprehensive cluster census of Orion. An application of the Significance Mode Analysis (SigMA) algorithm
Alena Rottensteiner, Sebastian Ratzenböck, João Alves et al. (+2 more)
Precise astrometric surveys and modern clustering
algorithms are working in step to transform our view of
star-forming regions. By revealing a much richer substructure than previously accessible, they pave the way for reconstructing
star formation histories by accurately resolving and age-dating individual sub-populations. The Orion
star-forming complex is the best-studied
stellar nursery in the
solar neighborhood and the nearest one currently forming massive
stars. Even so, a comprehensive characterization of its substructure, including a homogeneous age mapping and extinction analysis, is still incomplete. Here, we present the most complete census of
stellar populations across the Orion complex from the newest version of the SigMA
algorithm and outline our additions and improvements to the
algorithm that have extended its usage to distant (>300 pc) regions. We separate the Orion complex into 47 co-spatial and co-moving
stellar groups comprising 11,996 reliable members, with ages ranging from 1.5 to 25 Myr. To evaluate the statistical robustness of each group, we derive cluster persistence values and individual membership probabilities for each source from 10 independent clustering repetitions. Our group memberships agree well with the literature, but SigMA consistently finds a factor of ~2-3 more members. In particular, it resolves more very young populations, such as NGC 2024, RV Orionis, B30, NGC 1977, NGC 2068, and NGC 2071, than previous
algorithms. In addition to recovering 28 known clusters and three groups previously classified as substructures, we present 16 new co-eval substructure candidates of the Orion
star-forming complex. This work builds up a new high-resolution time-resolved picture of Orion. This spatio-temporal map allows us to relate its
stellar content to the surrounding ISM and paves the way for a detailed analysis of its
star formation history in the future.
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All authors Alena Rottensteiner, Sebastian Ratzenböck, João Alves, Stefan Meingast, Sebastian Hutschenreuter
Earth and Planetary Astrophysics
Causes of Hot Jupiter Inflation from Causal Discovery
Zehao Jin, Mohamad Ali-Dib, Yujia Zheng et al. (+3 more)
Hot Jupiters often have radii larger than predicted by standard cooling–contraction models, but it remains unclear which process supplies or preserves the extra internal heat. We analyze 328 short-period
giant planets with measured $M_p$, $R_p$, $P_{\rm orb}$, and host-
star $T_{\rm eff}$ using causal discovery, a statistical framework that asks which observed properties remain directly connected to
planet radius after the others are accounted for. As a check, the same pipeline recovers the expected mass–radius connection for a super-Earth control sample. For hot Jupiters, the preferred graph links $R_p$ directly to $P_{\rm orb}$ and $T_{\rm eff}$, but not to $M_p$. Since incident flux increases with $T_{\rm eff}$ and decreases with $P_{\rm orb}$ at fixed
stellar properties, this paired dependence is naturally interpreted as a population-level signature of irradiation-regulated inflation. Comparing the graph with analytic radius-excess scalings suggests a comparatively important role for Gold–Soter thermal tides, with kinetic/mechanical heating and ohmic dissipation potentially contributing alongside them. Purely period-controlled gravitational tides are disfavored as the sole explanation because they lack a leading dependence on
stellar temperature. Distinguishing thermal tides, kinetic/mechanical heating, ohmic dissipation, and mixed scenarios will require radius-excess measurements that control for incident flux, age, composition,
stellar properties, and selection effects. More broadly, this work shows how causal discovery can turn population-level
exoplanet data into physically interpretable tests of hot-Jupiter inflation. Causal discovery complements parametric
Bayesian population models by testing which observables retain direct conditional dependence on $R_p$ without imposing a specific radius relation, although the modest sample size limits the scope of the inferred graph.
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All authors Zehao Jin, Mohamad Ali-Dib, Yujia Zheng, Mario Pasquato, Benjamin L. Davis, Andrea V. Maccio
Cosmology and Nongalactic Astrophysics
Merging Galaxy Clusters and the Search for New Physics of Dark Matter: A Review
Rogério Monteiro-Oliveira
Merging
galaxy clusters represent one of the most powerful macroscopic laboratories in the Universe for searching for new physics within the dark sector. High-velocity
cosmic collisions inherently separate the dark matter and
stellar components from the highly collisional, X-ray-emitting intracluster gas. These massive systems provide an ideal environment to probe the fundamental nature of dark matter, specifically testing whether it behaves as a strictly collisionless particle or exhibits non-zero self-interactions. While pioneering systems like the Bullet Cluster historically demonstrated the macroscopic decoupling of dark and ordinary matter, the field has evolved into a sophisticated discipline driven by multi-disciplinary methodologies. This review synthesizes recent theoretical and empirical advances in interpreting post-collision dynamics. It examines how the synergy of combined approaches—integrating multi-wavelength observations from gravitational
lensing and X-ray mapping with high-fidelity N-body hydrodynamical simulations—allows the translation of macroscopic spatial observables into stringent constraints on microscopic particle properties. Through this synthesis, the work evaluates how leveraging heterogeneous merger ensembles can reliably advance the ongoing search for physics beyond the standard cosmological model.
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High Energy Astrophysical Phenomena
General relativistic hydrodynamics of stellar tidal disruptions in Kerr spacetime: methods, validation, and first applications
Diego Calderón and Stephan Rosswog
The disruption of a
star by the
tidal field of a super-massive black hole may provide insights into dormant and otherwise hard-to-study
galactic nuclei. State-of-the-art numerical tools have not converged on the importance of the strong relativistic effects in the disruption of
stars by potentially spinning black holes. We present a specialised numerical tool to perform global hydrodynamic simulations of
stellar tidal disruptions in curved spacetimes. We quantify the role of impact strength and black hole
spin onto the
stellar structures and mass fallback rates. We adapted the code SPHINCS_BSSN to perform General Relativistic Smoothed-Particle Hydrodynamics (GRSPH) simulations of
stellar tidal disruptions in Kerr metric. We coupled the code with a Newtonian self-
gravity module, and we added the option to use an
entropy evolution formulation to handle numerically challenging situations. Besides describing the implementation and code validation, we present a set of 18 simulations of
parabolic tidal disruptions of
stellar polytropes to investigate the effect of impact strength and black hole
spin. We demonstrate that SPHINCS is capable of performing GRSPH simulations, reproducing
benchmark tests to machine precision. Our
stellar tidal disruption simulations show that the fallback rates agree with state-of-the-art modelling. Deep events result into structures where self-
gravity plays no role, the mass fallback rates peak at lower values, and rise-to-peak timescales decrease with impact strength. In these cases the black hole
spin affects noticeable these quantities increasing (decrease) both fallback rate peak and rise-to-peak timescale for prograde (retrograde)
spin. Last, fallback rates tend to decay with the characteristic $t^{-5/3}$ on long timescales. The results show that SPHINCS can simulate high-resolution
stellar tidal disruptions in Kerr metric at a reasonable computational time.
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High Energy Astrophysical Phenomena
Resolving Nearby Supermassive Black Holes with the Black Hole Explorer
Yuto Akiyama, Kazunori Akiyama, Dominic W. Pesce et al. (+12 more)
Recent Event Horizon
Telescope results have demonstrated unique and transformative science in gravitational physics and black hole astrophysics enabled by event-horizon-scale imaging of supermassive black holes (SMBHs). Nevertheless, the angular resolution of current ground-based very long baseline interferometry (VLBI) arrays limits such studies to only two sources, precluding systematic investigations of horizon-scale emission across a nearby SMBH population. The proposed Black Hole Explorer (BHEX), a millimeter/submillimeter space VLBI mission, would overcome this limitation by delivering substantially higher angular resolution. Here, we present a series of simulated observations to assess a population of nearby horizon-scale targets accessible with BHEX. Based on a recently developed SMBH number density model, we find that BHEX could infer black hole masses for ~70-90 sources from size measurements, constrain
magnetic field structures through linear polarization imaging for ~20-30 sources, and resolve black hole shadows for ~20-25 sources. Targeted observations of ~50 nearby SMBHs are expected to yield measurements for ~30 source sizes and ~10 shadows and linear-polarization patterns. These projections are supported by detailed imaging simulations of general relativistic magnetohydrodynamic (GRMHD) models for eleven nearby SMBHs. Together, our results highlight BHEX as a powerful facility for revealing the demographics of SMBH properties across diverse
accretion states,
radio loudness, host
galaxy environments, and viewing geometries.
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All authors Yuto Akiyama, Kazunori Akiyama, Dominic W. Pesce, Daniel C. M. Palumbo, Angelo Ricarte, Paul Tiede, Marvin N. Martinez, Hikaru Yoshida, Avery E. Broderick, Aya E. Higuchi, Sara Issaoun, Neil M Nagar, Kotaro Niinuma, Venkatessh Ramakrishnan, Xinyue Alice Zhang
High Energy Astrophysical Phenomena
Probing the $\gamma$-ray emission region and the connection to jet ejections in NRAO 150 with VLBI
L. C. Debbrecht, G. F. Paraschos, E. Ros et al. (+7 more)
Relativistic jets launched by active
galactic nuclei are fundamental for understanding the physics of accreting supermassive black holes and their immediate environments, yet the origin of these jets remains an open question. NRAO 150 is a blazar with a complex relativistic jet morphology that evolves on short timescales due to strong projection effects, enabling detailed kinematic analysis. In this study, we utilise data by the Very Long Baseline Array and the European VLBI Network from 2010 until 2019 at 43 GHz, to understand the formation and launching processes of the jet in NRAO 150. We study the $\gamma$-ray and
radio light-curves, together with total intensity and linear polarisation information to probe the connection between flaring events, $\gamma$-ray emission, and the ejection of new jet features. Furthermore, we investigate the
magnetic field configuration in the innermost jet region, as captured in polarised light, to gain insights about its configuration before, during, and after a $\gamma$-ray
flare. Our results indicate a close temporal link between the $\gamma$-ray flaring activity and the ejection of new VLBI jet components, suggesting that the high-energy emission is produced downstream of the VLBI core. The combined kinematic and polarimetric evidence further points to a toroidal
magnetic field in the inner jet, highlighting the key role of
magnetic fields in governing both jet dynamics and high-energy emission in NRAO 150.
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All authors L. C. Debbrecht, G. F. Paraschos, E. Ros, I. Agudo, T. P. Krichbaum, H. Müller, S. G. Jorstad, A. P. Marscher, M. A. Gurwell, J. A. Zensus
High Energy Astrophysical Phenomena
A JWST/MIRI Study of Dust in a Sample of Normal Type IIP Core Collapse Supernovae
Bhagya M. Subrayan, David J. Sand, Olivia Culbert et al. (+24 more)
Core collapse
supernovae (CCSNe) are invoked as major
dust producers in the early Universe, yet the amount of
dust they form, the timescale over which it grows, and the physical conditions that regulate the yield remain uncertain. We present a detailed JWST/MIRI mid-infrared (MIR) imaging census of 11 nearby Type IIP CCSNe spanning $\sim$1-7 yr after explosion, investigating
dust emission across the different phases of their
evolution. The spectral energy distributions show a coherent
evolution from hot ($\sim$1500 K), 5-8 $\mu$m emission at $\sim$400 d to prominent 10 and 18 $\mu$m emission features at later epochs ($\sim$600-2500 d). The cool
dust temperatures range from $\sim120$ to $250$ K and
dust masses from $\sim10^{-4}$ to $10^{-2} M_{\odot}$. The current sample shows no statistically significant correlation between measured
dust mass and peak luminosity, plateau duration, or explosion energy. SNe with early high ionization features, indicative of confined CSM, are often among the
dust-rich objects in the sample. The measured 1-7 yr
dust yields are insufficient to account for
dust in typical $z > 6$
galaxies, but support a role for CCSNe as producers of seed
dust for subsequent grain growth.
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All authors Bhagya M. Subrayan, David J. Sand, Olivia Culbert, Jennifer E. Andrews, Jeniveve Pearson, Griffin Hosseinzadeh, Saurabh W. Jha, Stefano Valenti, K. Azalee Bostroem, Conor L. Ransome, Aravind P. Ravi, Aysha Aamer, Moira Andrews, Emma R. Beasor, Collin Christy, Yize Dong, Noah Franz, Emily Hoang, Brian Hsu, Jacob Jencson, Lindsey A. Kwok, M. J. Lundquist, Darshana Mehta, Nicolas Meza Retamal, Manisha Shrestha, Nathan Smith, Sergiy Vasylyev
Astrophysics of Galaxies
A Critical Eddington Ratio for X-Shaped Radio Galaxies
David Garofalo
We derive a quantitative condition for the formation of X-shaped
radio galaxies by evaluating the competition between black hole
spin evolution and the radiative fading of relic
plasma within our previously proposed framework. The simultaneous visibility of two jet axes requires that the timescale for
spin evolution across zero, t_trans, be shorter than the fading timescale of relic
radio emission, t_fade. We estimate the transition timescale as t_trans about 5 million /lambda yr, where lambda is the Eddington ratio, and derive a visibility timescale t_fade about equal to 5-20 Myr based on the
evolution of the synchrotron break frequency for typical lobe
magnetic fields and
redshifts. This leads to a critical Eddington ratio lambda_crit in the range 0.3-1, above which systems can exhibit X-shaped morphologies. We show that this threshold naturally produces an environmental dependence, as radiatively efficient
accretion is more readily sustained in low-density environments, while feedback in rich clusters tends to drive systems toward radiatively inefficient states with a larger fraction of systems having lambda much less than lambda_crit, suppressing XRG formation. We further demonstrate that the observed low fraction of X-shaped
radio galaxies (about 1-5%) arises from the limited overlap window combined with
geometric and detectability effects. These results provide a quantitative and testable extension of our previous model, linking X-shaped morphology to
accretion rate and environmental conditions through a simple timescale criterion.
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Instrumentation and Methods for Astrophysics
TomoSphero: Fast Differentiable Projector for Planetary and Solar Tomography on Spherical Grids
Evan Widloski and Lara Waldrop
Computational
tomography is a tool for determining the internal structure of objects from a set of projections, typically taken along some regular path. In recent years, methods and GPU-accelerated libraries have emerged that allow for fast reconstruction from projections along more complicated paths. Most of these libraries rely on a Cartesian discretization of the object, which is not appropriate for all scenarios. We present TomoSphero, a differentiable tomographic projector over spherical grids which are often used in planetary and
solar tomography. TomoSphero is designed to be used as a building block in reconstruction
algorithms and includes common projection types such as cone-beam and parallel-beam, but is flexible enough to accommodate arbitrary projections. TomoSphero is implemented in PyTorch which allows for fast projection computation on GPUs, easy access to modern machine learning optimizers, and automatic differentiation for rapid prototyping of parametric models.
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High Energy Astrophysical Phenomena
The first comprehensive spectral and timing study of the ultra-compact X-ray binary 4U 1812-12 with NICER and NuSTAR
Swarnendu Jana, Aditya S. Mondal, Aru Beri et al. (+1 more)
The source 4U 1812-12 is a persistent, weakly variable low-mass X-ray binary containing a
neutron star. The source was observed by NICER between 2019 and 2021 and, more recently, by NuSTAR in 2025. During the NICER and NuSTAR observations, the source was detected in a hard spectral state with a bolometric luminosity of $\sim 1.90\times 10^{36}$ ergs s$^{-1}$. Its $3-70$ keV NuSTAR spectrum is characterized by a soft thermal emission from the disc, a hard Comptonized emission from the corona, and its reflection from the
accretion disc. The NuSTAR energy spectrum exhibits the clear presence of disc reflection features, fitted using a self-consistent relativistic reflection model relxill. Our reflection modeling indicates a moderately ionized
accretion disc (log\:$\xi\sim2.72$) extending close to the
neutron star surface ($R_{in}\lesssim 1.72\:R_{ISCO}$), and viewed through a small inclination angle ($i\sim 25$ degrees). Assuming that the
magnetic field ($B$) truncates the disc, we found $B\lesssim 2.54\times 10^{8}$ G, comparable to the typical values observed for NS LMXBs. The $1.0-9.5$ keV NICER spectra are also characterized by a soft thermal component and a dominant hard Comptonized component. During NICER observations, the disc temperature exhibits a small variation within $\sim 0.69-0.84$ keV. In contrast, the power law
photon index, $\Gamma$, exhibits a large variation of $\sim 0.8-1.5$, implying a substantial change in the Comptonized emission. Moreover, NICER timing analysis reveals broadband aperiodic variability with significant QPO-like features at $0.379\pm 0.008$ Hz and $0.724\pm 0.025$ Hz, having fractional rms amplitudes of $2.9\pm 0.6\%$ and $4.1\pm 0.5\%$, respectively.
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All authors Swarnendu Jana, Aditya S. Mondal, Aru Beri, Gulab C. Dewangan
Astrophysics of Galaxies
Identifying AGNs from X-ray detections$-$II: Metallicity calibrations for the $\rm N_2O_2$ and $\rm N_2S_2$ diagnostics
Mark Armah, O. L. Dors, Rogério Riffel et al. (+4 more)
Emission-line ratios from ions with nearly identical ionization potentials offer a robust solution to the degeneracies inherent to traditional active
galactic nuclei (AGNs)
metallicity diagnostics. We introduce new semi-empirical
metallicity calibrations for the $\rm N_2O_2$ and $\rm N_2S_2$ diagnostics, explicitly designed to isolate the chemical abundance from the incident radiation field. By coupling an extensive grid of CLOUDY photoionization simulations directly to the intrinsic 2$-$10 keV X-ray luminosity ($L_{\rm X}$) and benchmarking against Seyfert~2
nuclei from the Burst Alert
Telescope AGN Spectroscopic Survey (BASS), we establish robust relations valid across the
metallicity regime of $8.0 \lesssim 12+\log({\rm O/H}) \lesssim 9.1$ ($0.2 \lesssim Z/Z_{\odot} \lesssim 2.6$). The $\rm N_2O_2$ and $\rm N_2S_2$ indices trace co-spatial emitting volumes within the narrow-line regions (NLRs), enabling this framework to resolve the significant $L_{\rm X}$-driven systematic biases we previously identified in the standard $\rm N_2$ and $\rm N_2O_3$ indices. While the $\rm N_2O_2$ ratio proves to be virtually independent of nebular structural variations, the $\rm N_2S_2$ index exhibits a subtle, yet discernible, electron density ($N_{\rm e}$) susceptibility due to the low critical density ($N_{\rm c}$) of the [S II]$\lambda\lambda6716,6731$ doublet. Nevertheless, both diagnostics yield highly precise
metallicity constraints with tight root-mean-square residual dispersions of $\sim 0.081$ dex for $\rm N_2O_2$ and $\sim 0.121$ dex for $\rm N_2S_2$. We propose the $\rm N_2O_2$ and $\rm N_2S_2$ calibrations as highly optimized, unbiased
metallicity tracers for AGNs.
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All authors Mark Armah, O. L. Dors, Rogério Riffel, M. V. Cardaci, G. F. Hägele, Rogemar A. Riffel, J. M. Vílchez
Solar and Stellar Astrophysics
Eta Carinae's historical light curve: evidence for cyclic Roche lobe overflow from the primary star
Augusto Damineli, Leonardo A. Almeida, Francisco J. Jablonski et al. (+5 more)
The large amount of ground-based photometric measurements of $\eta$ Carinae obtained since 1940 have remained problematic for quantitative modeling due to the blending of flux from the
stellar core and the surrounding circumstellar nebula. In the era of the Hubble Space
Telescope, spatially resolved imaging & spectrophotometry have enabled disentanglement of these components, allowing recovery of the
stellar core $V$-band brightness from ground-based observations. We isolate the $V$-band fluxes of the
stellar core and nebula using 1999–2020 HST (ACS and STIS) observations, and use these to calibrate coeval ground-based photometry. The main finding is an orbital light curve with an amplitude $\Delta m \approx \pm 0.2\,$mag, many times higher than that modeled by ellipsoidal deformation of the primary. The observations suggest that Roche lobe overflow starts at $- 75$ days before periastron in coincidence with the start of rising in the orbital light curve, and remains for 150 days. An expanding (and afterwards dissipating) gas cloud reflecting the light from the primary would explain the observed large amplitude of the orbital light curve. A sharp periodic photometric peak occurs at $\sim -18$ days from the periastron. It is followed by a broad minimum around the superior conjunction of the secondary (T$_0+5.2$ days), which we interpret as a partial eclipse of the ejected material, in coincidence with the shallow minimum in X-rays, which also has been attributed to an eclipse.
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All authors Augusto Damineli, Leonardo A. Almeida, Francisco J. Jablonski, Eduardo Fernández-Lajús, Felipe Navarete, Eder Martioli, Gerd Weigelt, Rodrigo Capobiango
Earth and Planetary Astrophysics
Eclipse Timing of the Eccentric Planet HD 80606b with JWST: Constraints on a Second Planet and other Dynamical Effects
Charles Beichman, Billy Quarles, B.J. Fulton et al. (+6 more)
A variety of effects can perturb the orbital properties of single
planets in close orbits around their host
stars. HD80606 b is a highly eccentric ($\epsilon$=0.93)
exoplanet orbiting its host G5V
star, HD80606. HD80606 b became a compelling target for
exoplanet research after (Laughlin et al 2009) discovered that the 4.16 MJup
planet transits and is eclipsed by HD80606, thereby enabling photometric and spectroscopic observations to yield a wealth of information about the object. The exquisite precision of recent JWST eclipse timing offers an opportunity to investigate whether the orbit of HD80606 b is modified due to a variety of mechanisms, including General Relativity,
tidal torques, or the presence of a second perturbing
planet. We have used over 25 years of radial velocity data plus eclipse and transit observations to place limits on the precession of HD80606 b's orbit and to assess which of these effects, if any, are observable. The new models are consistent with constant values of period, eccentricity and the argument of periastron, $\omega$, with a limit on $\dot{\omega}$ at the level of the predicted GR drift. The PRV and timing data limit the mass and location of a second
planet external to HD80606b. Timing offsets between JWST eclipses relative to the Pearson et al (2022) predictions are attributed to the poor constraints on $\sqrt{\epsilon} (\cos\ \omega, \sin\ \omega)$ with only the single eclipse measurement available (Spitzer 2009) in that analysis and to an over-weighting of the eclipse timing in that earlier analysis.
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All authors Charles Beichman, Billy Quarles, B.J. Fulton, Nikole Lewis, Ryan Challener, Julien de Wit, Malena Rice, Julie Inglis, Tiffany Kataria
Astrophysics of Galaxies
JWST Whirlpool Galaxy Treasury: Mid-Infrared Emission in M51 and its Relation to Gas Column and Star Formation
Mansi Padave, Karin M. Sandstrom, Daniel A. Dale et al. (+25 more)
Using JWST/MIRI imaging of M51 in eight broadband filters, we investigate correlations of mid-infrared emission from polycyclic aromatic hydrocarbons (PAHs) and
dust continuum with molecular, atomic, and ionized gas traced by CO(1-0), HI, and Pa-alpha, respectively. In molecular gas-dominated regions, PAH-dominated filters (F560W, F770W, F1130W, F1280W) exhibit near-linear correlations with CO(1-0) at 40 pc scale, indicating that PAHs are well-mixed with gas and experience relatively constant radiation field intensities. The F1500W, F1800W, and F2100W
dust continuum-dominated filters show shallower slopes with CO(1-0), reflecting contributions from
star-forming regions with high radiation field intensities. This is reinforced by the near-linear scaling between F2100W and Pa-alpha. PAH-dominated bands do not show this linear trend with Pa-alpha, likely due to their destruction in ionized regions. F1000W behaves similarly to PAH bands in its correlations with CO(1-0) and Pa-alpha. Modeling mid-infrared emission with an empirical decomposition into gas- and
star-formation-associated components shows that PAH-dominated filters receive comparable contributions from both, while the relative contribution associated with the Pa-alpha template increases toward longer wavelengths, reaching $\sim$75% in F2100W. These results demonstrate that mid-infrared simultaneously traces the gas column and
star formation, but with a systematic wavelength-dependent shift in what drives the correlations: PAHs being more gas-tracing and
dust-continuum reflecting
star formation. Lastly, considering both HI and H$_2$ at 440 pc resolution, we find a tight, linear relation between $\Sigma_{HI+H_2}$ and PAH-dominated filters. Although most of our coverage is in H$_2$-dominated regions, we note similar observations with HI, suggesting that PAHs are also well-mixed with atomic gas.
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All authors Mansi Padave, Karin M. Sandstrom, Daniel A. Dale, Adam K. Leroy, Eric W. Koch, Tony D. Weinbeck, Angela Adamo, Jessica Sutter, Lindsey Hands, Torsten Böker, Martha L. Boyer, Ryan Chown, Bruce T. Draine, Ilse de Looze, Brandt A. L. Gaches, Simon C. O. Glover, Dario Colombo, Robert C. Kennicutt Jr., Hannah Koziol, Ralf S. Klessen, Sean T. Linden, Desika Narayanan, Alex Pedrini, Julia Roman-Duval, Eva Schinnerer, J.D.T. Smith, Sophia K. Stuber, Fabian Walter
High Energy Astrophysical Phenomena
A Cross-Band (X-ray $\times$ Optical) Periodicity Search for Supermassive Black Hole Binaries: A Null Result and the First Completeness-Corrected Constraint
Karan Akbari
We present the first sample-level search for supermassive black hole binaries (SMBHBs) requiring coherent quasi-periodicity at a common period in the X-ray and optical bands, over 1194 Swift-BAT hard X-ray AGN (Stage 1) and 175 4XMM-DR14 AGN (Stage 2). No source is a co-periodic candidate. Each light curve is modelled as a damped random walk (DRW) and searched with a Lomb-Scargle periodogram and a look-elsewhere-corrected Monte-Carlo significance. Because DRW red noise is largely independent between corona and disc, we require both bands individually significant with periods coincident within 5%, and gate the survivors with the model-independent null-signal-template test of Robnik et al. (2024). Over $P=100$-$900$ d the completeness-corrected 95% upper limit on the co-periodic fraction is amplitude-dependent: $\lesssim 3\%$ for hard-X-ray fractional modulation $\gtrsim 0.3$, $\approx 15\%$ (precision-limited) at 0.2, and uninformative below $\sim 0.15$ (the $\epsilon=1$ floor is 0.25%). The sensitivity is set by the hard X-ray monitoring, not the optical photometry or the statistics, the opposite of the usual assumption. Daily MAXI and RXTE/ASM monitoring of the brightest AGN raises the X-ray completeness 5-8-fold, and the search remains null. Integrated over the BAT black-hole mass function, the expected all-amplitude co-periodic fraction is $\sim 3\times10^{-2}\, f_{\rm bin}\, \delta_{\rm mod}$ (modulo a factor $g<1$), with $f_{\rm bin}$ the sub-pc binary fraction, $\delta_{\rm mod}$ the modulating duty cycle, and $g$ the fraction reaching recoverable hard-X-ray amplitude, so a null is expected. We deliver a validated cross-band framework and the first completeness-corrected constraint on the co-periodic fraction, ready for the denser X-ray monitoring of Einstein Probe and eROSITA.
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High Energy Astrophysical Phenomena
Inclination Diffusion in Relativistic Loss Cones
Wenkang Xin
Relativistic capture and
tidal disruption around a spinning black hole depend on both the magnitude and direction of the
star's angular momentum, yet loss-cone models often assume fixed orbital inclinations by ignoring the associated
diffusion. We show that this is not justified: for isotropic two-body relaxation near a small loss threshold, angular-momentum magnitude $L$ and inclination $x = L_{z}/L$ diffuse on comparable timescales, $t_{E} \gg t_{L} \sim t_{x}$. For Kerr capture, retaining inclination
diffusion significantly amplifies the prograde–retrograde contrast while leaving the total inclination-integrated flux nearly unchanged. An almost correct integrated flux can hide a badly wrong angular distribution. The three-dimensional
diffusion problem nevertheless retains enough angular structure to permit analytic treatment. By representing pericenter removal as a continuous sink, we obtain a closed-form loss flux solution for a nearly linear Kerr
tidal-disruption boundary, finding close agreement with phase-resolved calculations. Inclination-dependent loss therefore requires inclination-resolved
diffusion even when integrated rates appear robust.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Nuclear Drip Line and the Composition of Supernova Matter
S. Maity and S. Mallik
The
nuclear drip line plays a crucial role in determining the composition of matter under extreme astrophysical conditions. In core-collapse
supernovae and
neutron-
star crusts, matter is driven far from saturation density and
nuclear stability;
nuclei coexist with a sea of free
neutrons, an effect that is present even at zero temperature in
neutron-
star crusts and becomes more pronounced in the hotter,
neutron-rich
supernova environment. This makes a careful treatment of drip-line physics essential for a realistic description of the equation of state and composition. In this work, the influence of the
nuclear drip line on the baryonic composition of
supernova matter is investigated within the framework of
nuclear statistical
equilibrium (NSE). The composition is evaluated in terms of free nucleons, light clusters, and heavy
nuclei at finite temperature and global sub-saturation densities. The results indicate that, at low
proton fractions and higher densities, the inclusion of
nuclei beyond the drip line enhances the formation of extremely
neutron-rich light clusters, leading to a significant reduction in the free-
neutron density and the charge fraction of heavy
nuclei. These findings demonstrate that drip-line physics has a significant impact on the composition of
supernova matter and should be carefully incorporated in
supernova modeling and nucleosynthesis studies.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Linear Dilaton in Cosmology and Particle Physics
Eugenio Megias and Mariano Quiros
A warped extra dimension in a five-dimensional (5D) anti-de Sitter (AdS) background was introduced in 1999 by Lisa Randall and Raman Sundrum to solve the gauge hierarchy problem in particle physics. As a bonus, a
holographic interpretation in terms of four-dimensional (4D) conformal field theories (CFTs) was found. Interestingly enough, another 5D background, linear dilaton (LD), was found to have a
holographic interpretation in terms of Little String Theory. In this review, we will show how a set of 5D backgrounds, parametrized in terms of a real parameter $\nu$, generalizes both theories and gives rise, in particular, to AdS for $\nu=0$ and to LD for $\nu=1$. Furthermore, working in the 5D theory, we will consider applications of the LD background to: (i) particle physics, so that the 5D Planck scale can be lowered to sub-Planckian values, and (ii) Brane World Cosmology (BWC), based on the appearance of an extra
vacuum characterized by a 5D black hole. In all cases, we find a gapped continuum for bulk propagating fields, which makes a connection with unparticles. In the case of BWC, we also point out the existence of a pressureless
holographic fluid that could play the role of dark matter (DM), with feeble (gravitational) interactions with the Standard Model (SM), decoupled from the thermal SM bath, and generated by a freeze-in mechanism after inflation. We also point out the additional possibility of identifying DM with a long-lived, feebly interacting massive graviton, as an isolated resonance generated by radiative corrections to the continuum graviton propagator self-energy.
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Astrophysics of Galaxies
A posteriori correction of Gaia CRF proper motions using conditional probability and zero-parallax prior
Valeri V. Makarov
Precision of proper motions and positions given in the
Gaia Celestial Reference Frame (CRF) catalog can be statistically improved introducing conditional probability based on the prior knowledge of zero parallax for these extremely distant sources. The method developed in this study produces statistically conditioned proper-motion estimates under the assumed per-source Gaussian covariance model. It is demonstrated that thus corrected proper motion vectors of 1.2 million CRF objects in
Gaia DR3 show a tighter distribution around zero and a general reduction in the rate of outliers by approximately 15%. A general vector spherical harmonic fit to degree 4 is produced with the corrected data for a filtered subset of CRF
quasars with
redshifts between 1 and 1.5. This application, predicated on the unknown
stochastic component of the global parallax field, shows a 3-sigma change in the estimated magnitude of the Galactocentric acceleration of the
solar system barycenter, quantifying the sensitivity of this fundamental determination to the proposed conditioning of proper motions.
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Astrophysics of Galaxies
High Velocity Neutral Gas in the Fermi Bubbles: New Kinematic Limits and Spatial Structure
Felix J. Lockman, Enrico M. Di Teodoro, Savannah Cary et al. (+1 more)
We have detected hundreds of neutral clouds entrained in the Milky Way's
nuclear wind using HI data from new surveys made with the Green Bank
Telescope that cover about 500 sq-degrees around the
Galactic center (GC).
Galactic winds are common throughout the Universe, and these data at 9.1' angular resolution (22 pc at the GC) provide the most detailed analysis of the vertical profile of a neutral
nuclear wind in any
galaxy. A set of 228 of these
Fermi Bubble clouds with the largest values of |VLSR| has been analyzed to examine the distribution and kinematics of the outflowing gas. The clouds span -335 km/s $\leq$ VLSR $\leq$ +438 km/s, the largest positive LSR velocities ever reported for neutral HI associated with the Milky Way disk. The highest velocities are found furthest from the GC, suggesting that clouds are accelerated from a low velocity near the
nucleus to at least 500 km/s at a radial distance of $\lesssim 4$ kpc. Clouds appear disrupted as they are accelerated: their line brightness and NHI decreases steadily with distance from the GC, and the population becomes more uniform. There is an abrupt cutoff in the neutral clouds at a vertical distance of $\approx2$ kpc from the
Galactic plane. Kinematic models of an outflowing cloud population that fills the FB volume are used to identify structure in the gas. The kinematics of the highest velocity, highest latitude clouds imply a past azimuthal asymmetry in the
outflow.
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All authors Felix J. Lockman, Enrico M. Di Teodoro, Savannah Cary, Andrew J. Fox
Instrumentation and Methods for Astrophysics
Anti-windup PI controller for millimeter-wave adaptive optics: a Nobeyama 45 m radio telescope simulation
Ichiro Jikuya, Yoichi Tamura, Akio Taniguchi et al. (+8 more)
This work addresses the control problem for Millimeter-wave Adaptive Optics (MAO), which we define as compensating for the distance variation between the primary reflector (M1) and the receiver. We utilize a measurement system developed by Tamura et al. to track these variations. The challenge is formalized as an asymptotic constant disturbance suppression problem. We demonstrate that an anti-windup proportional-integral (AWPI) controller effectively solves this problem while respecting the physical movement constraints of the optical driving system. Simulation results, based on the Nobeyama 45-m
Telescope with a two-axis translating sub-reflector (M2), validate the performance of the proposed AWPI approach.
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All authors Ichiro Jikuya, Yoichi Tamura, Akio Taniguchi, Masaki Sakakibara, Akinobu Miyake, Masato Hagimoto, Kianhong Lee, Chihiro Imamura, Shion Takeno, Sachiko S. Okumura, Nozomi Okada
Instrumentation and Methods for Astrophysics · Cross-listed from physics.space-ph
In-situ measurements of space plasma: recent progress and future challenges
Daniel Verscharen
Space
plasmas like the
solar wind or the Earth's space environment offer unique opportunities to observe fundamental
plasma processes and their impact in situ. With modern space instrumentation, we measure the velocity distribution function of the
plasma particles as well as the electromagnetic fields at high resolution and with minimal perturbation of the observed
plasma systems.
Plasma measurements like this are often not possible in laboratory settings on Earth. This review article focuses on modern diagnostic methods for the in-situ detection of
plasma particles in space. It presents the detection principle of top-hat electrostatic analysers and highlights recent examples of scientific discoveries based on data from the heliospheric space missions Parker
Solar Probe and
Solar Orbiter. These examples demonstrate the capabilities of modern space
plasma instrumentation. The article then discusses future directions in space
plasma physics as well as the involved challenges in terms of the required
plasma diagnostics. These new developments include, for example, upcoming and proposed space missions such as the operational space-weather mission Vigil, the multi-spacecraft mission HelioSwarm, the Mars mission M-MATISSE, and the electron-astrophysics mission Debye.
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Cosmology and Nongalactic Astrophysics
Halo Mass of ULIRGs at Cosmic Noon
Jun Pan, Ming Li, Cheng Cheng et al. (+1 more)
We present a clustering analysis of $\sim 3000$ ultraluminous infrared
galaxies (ULIRGs) at $z\sim 2$, uniformly selected by $24\mu {\rm m}$ flux and IRAC colors in the COSMOS and BOOTES fields. We measure the angular correlation functions of ULIRGs in both fields and fit them with
galaxy clustering models. Linear theory modeling shows that these ULIRGs reside in dark matter
halos with characteristic masses of $\log M_{\rm h} /({h^{-1}\rm M_{\odot}}) = 12.64\pm 0.50$ in COSMOS and $12.72\pm 0.13$ in BOOTES. The
halo occupation distribution (HOD) modeling yields occupation-weighted effective
halo masses of $\log M_{\rm eff} /({h^{-1}\rm M_{\odot}}) =12.50^{+0.26}_{-0.28}$ for COSMOS and $12.89^{+0.11}_{-0.12}$ for BOOTES. These host
halos are expected to evolve into
halos with masses of $\sim 10^{13.6-13.9}\ {h^{-1}\rm M_{\odot}}$ at $z=0$. The HOD fits allow for a non-negligible satellite contribution to the clustering of
galaxies in the BOOTES field, but the satellite fraction derived in the COSMOS field appears nearly zero.
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All authors Jun Pan, Ming Li, Cheng Cheng, Jasheng Huang
Astrophysics of Galaxies
Two domains of extended Lyman-alpha emission around galaxies: from local radiation to environmental regulation
Daria Kozlova, Lutz Wisotzki, John Pharo et al. (+7 more)
We examine the relation between extended Ly$\alpha$
halos around high-
redshift galaxies and the main factors responsible for driving the emission in such
halos, in particular at distances around and beyond one virial radius $r_\mathrm{vir}$. To reach the required surface brightness sensitivity we take advantage of the MUSE eXtremely Deep Field (MXDF) survey, allowing us to probe levels as faint as $\sim 10^{-20}$ erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ in individual Ly$\alpha$
halos. Our sample consists of the 21 apparently core- and
halo-brightest (yet intrinsically low luminosity $\log_{10}$L$_{\mathrm{Ly}\alpha} < 42.3$ erg s$^{-1}$) Ly$\alpha$ emitters (LAEs) in the MXDF at $3<z<4$, with typical virial radii around 20 kpc. We measure their radial surface brightness profiles out to 50 kpc (more than $2r_{\mathrm{vir}}$) and investigate the correlations between surface brightness and internal (
star formation rates of the host
galaxies, SFR) or external influences (environmental density, $\delta+1$). We find a clear break in these correlations at radii around or just below $1r_{\mathrm{vir}}$. Below this break the emission correlates tightly with SFR (as expected) and not at all with $\delta+1$. Beyond $\sim 1r_\mathrm{vir}$(20 kpc) we observe the opposite trend with no dependence on SFR, but an emerging correlation with $\delta+1$. We compare our measurements with the expected integrated surface brightness from ultrafaint, individually undetected LAEs and find that the latter is insufficient to drive the observed correlation. We conclude that Ly$\alpha$ emission from the outer
halos is regulated by the surrounding environment, but originates mostly from diffuse gas rather than discrete sources.
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All authors Daria Kozlova, Lutz Wisotzki, John Pharo, Tanya Urrutia, Ramona Augustin, Yucheng Guo, Haruka Kusakabe, Joop Schaye, Daniil Smirnov, Ismael Pessa
High Energy Astrophysical Phenomena
Collisionless Shock Driven by a Supersonic Velocity Shear
Kazuki Kamiido and Yutaka Ohira
The long-term
evolution of a relativistic collisionless velocity shear in an unmagnetized electron-positron
plasma is investigated using a first-principle particle-in-
cell simulation. The Alves instability converts the shear kinetic energy into thermal and
magnetic field energy. The resulting pressures push the
plasma, leading to the formation of collisionless shocks. The generated collisionless shocks would accelerate high energy particles, which is a possible solution to the injection problem of shear acceleration. In addition, the collisionless shocks generate a
magnetic field
turbulence that is required for the shear acceleration to work.
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Instrumentation and Methods for Astrophysics
Galaxy Morphology Classification: Uncertainty Modeling and Out of Distribution Detection
Prem Prakash, Shantanu Desai and P.K. Srijith
We present a comprehensive framework for
galaxy morphology classification that combines enhanced “out-of-distribution (OOD)” detection with improved uncertainty quantification. Using “
Galaxy Zoo DECaLS”, we trained a ResNet-34 architecture under three configurations: standard cross-
entropy loss as a baseline, IsoMaxPlus loss function for OOD detection, and hybrid IsoMaxPlus+MonteCarlo Dropout for enhanced uncertainty quantification. IsoMaxPlus replaces the conventional SoftMax logits with distance-based class representations, preserving inter-class separability and enabling reliable OOD detection, without requiring additional architectural modifications or hyperparameter tuning. Coalescing IsoMaxPlus with MC Dropout provides a fast
Bayesian approximation by performing multiple
stochastic forward passes during inference. Our results show that IsoMaxPlus substantially improves OOD detection, increasing TNR@TPR95 by nearly $90\%$ relative to the cross-
entropy baseline, while maintaining a competitive accuracy of 97% across nine morphological classes. Additionally, with MC Dropout, the model yields more stable predictions and a reduction in calibration error, providing more reliable uncertainty estimates. The Expected Calibration Error (ECE) is reduced from $0.0095$ to $0.0026$ ($\approx73\%$) for IsoMaxPlus and $0.0033$ ($\approx65\%$) when combined with MC Dropout, compared to the baseline. Misclassified or underconfident predictions exhibit higher predictive
entropy and lower minimum distance scores, providing an interpretable metric for identifying unreliable predictions. These methods are well-suited for current and upcoming large-scale surveys, where reliable automated morphological classification and awareness of uncertainty are essential for identifying rare or previously unseen
galaxy morphologies.
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