Astrophysics of Galaxies
COUGS-DESI: A Catalog of Unusual Galaxies with Polar Structures in the DESI Legacy Imaging Surveys
Seneca K. H. Bahr, Aleksandr V. Mosenkov, Jacob A. Guerrette et al. (+10 more)
Polar-structure
galaxies (PSGs) host photometrically and kinematically decoupled components oriented at large angles to one another. These systems, which include polar rings, polar disks, polar
halos, polar bulges, polar
dust lanes, and polar
tidal structures, provide valuable insights into
galaxy formation and
evolution, although their rarity has limited statistical studies. We aim to construct the largest and most homogeneous catalog of PSGs to date in order to enable robust statistical studies of their properties and occurrence rates in the local Universe. Using DESI Legacy Imaging Surveys (DR10) data, we identified PSG candidates in the Siena
Galaxy Atlas (SGA) through visual inspection, convolutional neural network classification, and cross-matching with previously reported systems. Each
galaxy was assigned a PSG subtype and host morphology. We analyzed general properties of PSGs and compared them with those for all
galaxies in the SGA. Simple image simulations were used to evaluate projection effects. The resulting Catalog of Unusual
Galaxies with polar Structures in the DESI Legacy Imaging Surveys (COUGS-DESI) contains 2,989 PSG candidates, including 342 previously known objects. Projection effects from random
galaxy overlaps are negligible. The sample spans a wide range of polar morphologies, with 1,113 polar rings, 75 polar bulges, 216 polar
halos, 185 polar
dust lanes, and 1,315 polar
tidal structures. PSGs constitute 2.2% of local non-
dwarf galaxies, with polar rings representing 0.7%. Approximately 1% of S0
galaxies in the SGA host polar rings, whereas spirals constitute the most common morphological type among the PSG hosts in our catalog. COUGS–DESI increases the number of known PSG candidates by an order of magnitude and provides a foundation for detailed studies of the formation and
evolution of polar structures.
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All authors Seneca K. H. Bahr, Aleksandr V. Mosenkov, Jacob A. Guerrette, Isaac H. Jensen, Jonah X. George, Thea E. Spigarelli, Ryan P. Smith, Brandon T. Burton, Kevan W. Beckstead, Jonah D. Seguine, Harrison K. Casper, Nefi Pineda, Michael Holland
Instrumentation and Methods for Astrophysics · Cross-listed from cs.AI
Orchestral AI: A Framework for Agent Orchestration
Alexander Roman and Jacob Roman
The rapid proliferation of LLM
agent frameworks has forced developers to choose between vendor lock-in through provider-specific SDKs and complex multi-package ecosystems that obscure control flow and hinder reproducibility. Integrating tool calling across multiple LLM providers remains a core engineering challenge due to fragmented APIs, incompatible message formats, and inconsistent streaming and tool-calling behavior, making it difficult to build portable, reliable
agent systems. We introduce Orchestral, a lightweight Python framework that provides a unified, type-safe interface for building LLM
agents across major providers while preserving the simplicity required for scientific computing and production deployment. Orchestral defines a single universal representation for messages, tools, and LLM usage that operates seamlessly across providers, eliminating manual format translation and reducing framework-induced complexity. Automatic tool schema generation from Python type hints removes the need for handwritten descriptors while maintaining type safety across provider boundaries. A synchronous execution model with streaming support enables deterministic behavior, straightforward debugging, and real-time interaction without introducing server dependencies. The framework's modular architecture cleanly separates provider integration, tool execution, conversation orchestration, and user-facing interfaces, enabling extensibility without architectural
entanglement. Orchestral supports advanced
agent capabilities found in larger frameworks, including rich tool calling, context compaction, workspace sandboxing, user approval workflows, sub-
agents,
memory management, and MCP integration.
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Instrumentation and Methods for Astrophysics
Optomechanical platform for high-frequency gravitational wave and vector dark matter detection
David Rousso, Moritz Bjoern Kristiansson Kunze and Christoph Reinhardt
We present a proposal for a nanomechanical membrane resonator integrated into a moderate-finesse ($\mathcal{F}\sim 10$) optical cavity as a versatile platform for detecting high-frequency gravitational waves and vector dark matter. Gravitational-wave sensitivity arises from cavity-length modulation, which resonantly drives membrane motion via the radiation-pressure force. This force also enables in situ tuning of the membrane's resonance frequency by nearly a factor of two, allowing a frequency coverage from 0.5 to 40 kHz using six membranes. The detector achieves a peak strain sensitivity of $2\times 10^{-23}/\sqrt{\text{Hz}}$ at 40 kHz. Using a silicon membrane positioned near a gallium-arsenide input mirror additionally provides sensitivity to vector dark matter via differential acceleration from their differing atomic-to-mass number ratios. The projected reach surpasses the existing limits in the range of $2\times 10^{-12}$ to $2\times 10^{-10}$ $\text{eV}/c^2$ for a one-year measurement. Consequently, the proposed detector offers a unified approach to searching for physics beyond the Standard Model, probing both high-frequency gravitational waves and vector dark matter.
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Instrumentation and Methods for Astrophysics
The Lazuli Space Observatory: Architecture & Capabilities
Arpita Roy, Stuart Feldman, Pete Klupar et al. (+51 more)
The Lazuli Space Observatory is a 3-meter aperture astronomical facility designed for rapid-response observations and precision astrophysics across visible to near-infrared wavelengths (400-1700 nm bandpass). An off-axis, freeform
telescope delivers diffraction-limited image quality (Strehl $>$0.8 at 633 nm) to three instruments across a wide, flat focal plane. The three instruments provide complementary capabilities: a Wide-field Context Camera (WCC) delivers multi-band imaging over a 35' $\times$ 12' footprint with high-cadence photometry; an Integral Field Spectrograph (IFS) provides continuous 400-1700 nm spectroscopy at R $\sim$ 100-500 for stable spectrophotometry; and an ExtraSolar Coronagraph (ESC) enables high-contrast imaging expected to reach raw contrasts of $10^{-8}$ and post-processed contrasts approaching $10^{-9}$. Operating from a 3:1 lunar-resonant orbit, Lazuli will respond to targets of opportunity in under four hours–a programmatic requirement designed to enable routine temporal responsiveness that is unprecedented for a space
telescope of this size. Lazuli's technical capabilities are shaped around three broad science areas: (1) time-domain and multi-messenger astronomy, (2)
stars and
planets, and (3) cosmology. These capabilities enable a potent mix of science spanning gravitational wave counterpart characterization, fast-evolving transients, Type Ia
supernova cosmology, high-contrast
exoplanet imaging, and spectroscopy of
exoplanet atmospheres. While these areas guide the observatory design, Lazuli is conceived as a general-purpose facility capable of supporting a wide range of astrophysical investigations, with open time for the global community. We describe the observatory architecture and capabilities in the preliminary design phase, with science operations anticipated following a rapid development cycle from concept to launch. [Abstract abridged]
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All authors Arpita Roy, Stuart Feldman, Pete Klupar, John DiPalma, Saul Perlmutter, Ewan S. Douglas, Greg Aldering, Gabor Furesz, Patrick Ingraham, Gudmundur Stefansson, Douglas Kelly, Fan Yang Yang, Thomas Wevers, Nicole Arulanantham, James Lasker, Mickael Rigault, Everett Schlawin, Sander R. Zandbergen, S. Pete Worden, Ramya Anche, Heejoo Choi, Ian J. M. Crossfield, Kevin Derby, Jerry Edelstein, Mike Eiklenborg, Suvi Gezari, Paul Giuliano, Justin Hom, Taylor J. Hoyt, Hyukmo Kang, Daewook Kim, Keerthi Kunnumkai, Leander Lacroix, Jared R. Males, Thomas J. Maccarone, Kian Milani, Timothy N. Miller, Kelsey Lynn Miller, Pierre Nicolas, Antonella Palmese, Jason Pero, Laurent Pueyo, Stephanie Rinaldi, David J. Sand, Christian Schneider, Sanchit Sabhlok, Arfon Smith, Irina I. Stefan, Saraswathi Kalyani Subramanian, Kyle Van Gorkom, Andre F. Wong, Jaegun Yoo, Md Abdullah Al Zaman, the Lazuli Science Team
Instrumentation and Methods for Astrophysics
Using 23 Years of ACS/SBC Data to Understand Backgrounds: Significant Reductions in Expected Background Levels
Christopher. J. R. Clark, Roberto J. Avila, Alyssa M. Guzman et al. (+1 more)
We have used 23 years of Hubble Space
Telescope ACS/SBC data to study what background levels are encountered in practice and how much they vary. The backgrounds vary considerably, with F115LP, F122M, F125LP, PR110L, and PR130L all showing over an order of magnitude of variation in background between observations, apparently due to changes in airglow. The F150LP and F165LP filters, which are dominated by dark rate, not airglow, exhibit a far smaller variation in backgrounds. For the filters where the background is generally dominated by airglow, the backgrounds measured from the data are significantly lower than what the ETC predicts (as of ETC v33.2). The ETC predictions for `average' airglow are greater than the median of our measured background values by factors of 2.51, 2.64, 105, and 3.64, for F115LP, F122M, F125LP, and F140LP, respectively. A preliminary analysis suggests this could be due to certain OI airglow lines usually being fainter than expected by the ETC. With reduced reduced background levels, the shorter-wavelength SBC filters can conduct background-limited observations much more rapidly than had previously been expected. As of ETC v34.1, a new option will be included for SBC calculations, allowing users to employ empirical background percentiles to estimate required exposure times.
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All authors Christopher. J. R. Clark, Roberto J. Avila, Alyssa M. Guzman, Norman A. Grogin
Earth and Planetary Astrophysics
Dearth of Photosynthetically Active Radiation Suggests No Complex Life on Late M-Star Exoplanets
Joseph J. Soliz and William F. Welsh
The rise of oxygen in the Earth's atmosphere during the Great Oxidation Event (GOE) occurred about 2.3 billion years ago. There is considerably greater uncertainty for the origin of oxygenic photosynthesis, but it likely occurred significantly earlier, perhaps by 700 million years. Assuming this time lag is proportional to the rate of oxygen generation, we can estimate how long it would take for a GOE-like event to occur on a hypothetical Earth-analog
planet orbiting the
star TRAPPIST-1 (a late M
star with Teff 2560 K). Although in the habitable zone, an Earth-analog
planet located in TRAPPIST-1e's orbit would receive only 0.9% of the Photosynthetically Active Radiation (PAR) that the Earth gets from the Sun. This is because most of the
star's light is emitted at wavelengths longer than the 400-700 nm PAR range. Thus it would take 63 Gyrs for a GOE to occur. But the linear assumption is problematic; as light levels increase, photosynthesis saturates then declines, an effect known as photoinhibition. Photoinhibition varies from species to species and depends on a host of environmental factors. There is also sensitivity to the upper wavelength limit of the PAR: extending just 50 nm increases the number of
photons by a factor of 2.5. Including these and other factors greatly reduces the timescale to roughly 1-5 Gyrs for a GOE. However, non-oxygenic photosynthetic bacteria can thrive in low-light environments and can use near-IR light out to 1100 nm, providing 22 times as many
photons. With this huge light advantage, and because they evolved earlier, anoxygenic photosynthesizers would likely dominate the ecosystem. On a late M-
star Earth-analog
planet, oxygen may never reach significant levels in the atmosphere and a GOE may never occur, let alone a Cambrian Explosion. Thus complex animal life is unlikely.
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Earth and Planetary Astrophysics
Tracing Pebble Drift History in Two Protoplanetary Disks with CO Enhancement
Tayt Armitage, Joe Williams, Ke Zhang et al. (+15 more)
Pebble drift is an important mechanism for supplying the materials needed to build
planets in the inner region of protoplanetary disks. Thus, constraining pebble drift's timescales and mass flux is essential to understanding
planet formation history. Current pebble drift models suggest pebble fluxes can be constrained from the enhancement of gaseous volatile abundances when icy pebbles sublimate after drifting across key snowlines. In this work, we present ALMA observations of spatially resolved $^{13}$C$^{18}$O J=2-1 line emission inside the midplane CO snowline of the HD 163296 and MWC 480 protoplanetary disks. We use radiative transfer and thermochemical models to constrain the spatial distribution of CO gas column density. We find that both disks display centrally peaked CO abundance enhancement of up to ten times of ISM abundance levels. For HD 163296 and MWC 480, the inferred enhancements require 250-350 and 480-660 Earth Masses of pebbles to have drifted across their CO snowlines, respectively. These ranges fall within cumulative pebble mass flux ranges to grow gas
giants in the interior to the CO snowline. The centrally peaked CO enhancement is unexpected in current pebble drift models, which predict CO enhancement peaks at the CO snowline or is uniform inside the snowline. We propose two hypotheses to explain the centrally-peaked CO enhancement, including a large CO desorption distance and CO trapped in water ice. By testing both hypotheses with the 1D gas and
dust evolution code chemcomp, we find that volatile trapping (about 30%) best reproduces the centrally peaked CO enhancement observed.
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All authors Tayt Armitage, Joe Williams, Ke Zhang, Sebastiaan Krijt, Leon Trapman, Richard A. Booth, Richard Teague, Charles J. Law, Chunhua Qi, David J. Wilner, Karin I. Öberg, Edwin A. Bergin, Sean M. Andrews, Romane Le Gal, Feng Long, Jane Huang, Jaehan Bae, Felipe Alarcón
Astrophysics of Galaxies
Composite Bulges – V. Detecting signatures of gas inflows in IFU data: The MUSE view of ionised gas kinematics in nearby galaxies
Tutku Kolcu, Witold Maciejewski, Peter Erwin et al. (+7 more)
Using VLT/MUSE data, we study the ionised-gas kinematics in a mass- and volume-limited ($M_* \geq 10^{10} M_\odot$, $D \leq 20$\,Mpc) sample of 21 nearby
galaxies to identify signatures of extended shocks within their inner kiloparsec, which appear as coherent velocity jumps in kinematic maps. By removing angular momentum, shocks in gas cause inflows, which can trigger
nuclear star formation and fuel AGN activity. To identify the signatures of extended shocks, we examine residual velocity fields after subtracting a modelled rotating disc, and we study velocity difference between various gas tracers. Combining our kinematic analysis with BPT ionisation diagnostic maps and
dust morphology, we find that 12 of 21
galaxies ($\sim$57%) show extended shock signatures with velocity jumps consistent with models of bar-driven shocks. This is likely a lower limit, as three additional
galaxies ($\sim$14%) exhibit shocks along bars, potentially reaching the
nucleus but obscured by AGN
outflows. We trace shock signatures inwards close to the resolution limit, which suggests that shocks may be the prevailing mechanism of inflow in the central kpc of
galaxies. The only two unbarred
galaxies in our sample are also the only systems with unperturbed kinematics and no shocks, strongly linking the perturbed gas dynamics in centres of
galaxies to the presence of bars. All
galaxies with inner bars show LINER- or Seyfert-like
nuclear emission, whereas
galaxies without inner bars exhibit all emission types, indicating that regardless of gas supply, inner bars suppress
star formation in
galactic nuclei.
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All authors Tutku Kolcu, Witold Maciejewski, Peter Erwin, Dimitri A. Gadotti, Francesca Fragkoudi, Paula R. T. Coelho, Victor P. Debattista, Adriana de Lorenzo-Cáceres, Camila de Sá-Freitas, Patricia Sánchez-Blázquez
Earth and Planetary Astrophysics
Catching 3I/ATLAS Using a Solar Oberth
Adam Hibberd, T. Marshall Eubanks and Andreas Hein
The third interstellar object to be discovered, 3I/ATLAS, has a unique and continually unfolding story to tell about its nature and origin as it is monitored by
telescopes on Earth, orbiting Earth and around the
Solar System. Previous research into missions using chemical propulsion have only really addressed the direct case, where the opportunity to launch already expired before 3I/ATLAS's discovery. In contrast, investigations herein exploit 'Optimum Interplanetary Trajectory Software' to simulate an alternative indirect option for chemical propulsion, namely the
Solar Oberth Manoeuvre (SOM). For a SOM, a low perihelion burn provides maximum benefit from the Oberth Effect, and accelerates the spacecraft rapidly towards the receding 3I/ATLAS. Though in principle feasible, results indicate this option presents significant challenges. For possible launch years between 2031 and 2037 inclusive, a 2035 launch permits the most efficient transfer to 3I/ATLAS. The reference mission requires a SOM at 3.2
Solar Radii from the Sun's centre, with an intercept after 35-50 years. It is found the SOM can leverage spacecraft masses up to $\sim{500}$ kg. Two or three solid propellant boosters could deliver the required SOM $\Delta$V, and furthermore a refuelled Starship Block 3 in LEO has sufficient performance for such a mission. As inevitable with a SOM, some of the payload mass would be needed for a heat shield to protect against the high
solar flux at low perihelion.
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Instrumentation and Methods for Astrophysics
Scalable Gaussian Processes for Integrated and Overlapping Measurements Via Augmented State Space Models
Ryan A. Rubenzahl, Soichiro Hattori, Simo Särkkä et al. (+4 more)
Astronomical measurements are often integrated over finite exposures, which can obscure latent variability on comparable timescales. Correctly accounting for exposure integration with Gaussian Processes (GPs) in such scenarios is essential but computationally challenging: once exposure times vary or overlap across measurements, the covariance
matrix forfeits any quasiseparability, forcing O($N^2$)
memory and O($N^3$) runtime costs. Linear Gaussian state space models (SSMs) are equivalent to GPs and have well-known O($N$) solutions via the Kalman filter and RTS smoother. In this work, we extend the GP-SSM equivalence to handle integrated measurements while maintaining scalability by augmenting the SSM with an integral state that resets at exposure start times and is observed at exposure end times. This construction yields exactly the same posterior as a fully integrated GP but in O($N$) time on a CPU, and is parallelizable down to O($N/T + \log T$) on a GPU with $T$ parallel workers. We present smolgp (State space Model for O(Linear/log) GPs), an open-source Python/JAX package offering drop-in compatibiltiy with tinygp while supporting both standard and exposure-aware GP modeling. As SSMs provide a framework for representing general GP kernels via their series expansion, smolgp also brings scalable performance to many commonly used covariance kernels in astronomy that lack quasiseparability, such as the quasiperiodic kernel. The substantial performance boosts at large $N$ will enable massive multi-instrument cross-comparisons where exposure overlap is ubiquitous, and unlocks the potential for analyses with more complex models and/or higher dimensional
datasets.
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All authors Ryan A. Rubenzahl, Soichiro Hattori, Simo Särkkä, Will M. Farr, Jacob K. Luhn, Megan Bedell, Daniel Foreman-Mackey
Astrophysics of Galaxies
The origin of strong $\alpha$-element bimodalities in FIRE simulations of Milky Way-mass galaxies
Megan Barry, Andrew Wetzel, Sarah Loebman et al. (+2 more)
One of the Milky Way's characteristic features is a strongly bimodal distribution of $\alpha$-process elements, such as Mg, at fixed [Fe/H] in
stellar abundances. We examine patterns in [Mg/Fe] versus [Fe/H] in FIRE-2 simulations of Milky Way-mass
galaxies. Out of 16
galaxies, 4 are capable of producing a strongly bimodal distribution. In all four
galaxies, the high-$\alpha$ population corresponds to an older, radially-compact, thick disk, and the low-$\alpha$ population corresponds to a younger, radially-extended, thin disk, similar to the MW.The transition from high- to low-$\alpha$ took $0.3-1.2\Gyr$ and began $5.5-6.5\Gyr$ ago. [Mg/Fe] decreased at relatively fixed [Fe/H], both in the
galaxy overall and at fixed radii: Fe enrichment nearly balanced gas
accretion (and therefore dilution), but Mg enrichment was weaker. Importantly, this transition occurred during a period of relatively low gas fraction ($5-15\%$), immediately after a rapid decline in
star formation (halving within a few hundred Myr), which caused an increase in Fe-producing white-
dwarf supernovae relative to Mg-producing core-collapse
supernovae. Only one case coincided with a major merger coalescence. We find similar trends in measuring
stars by their current radius and by their birth radius, therefore, radial redistribution did not play a dominant role in the formation of a bimodality or its spatial dependence today. Overall, in FIRE-2, strong $\alpha$-element bimodalities are relatively uncommon ($\sim25\%$), often not associated with a major merger, and arise primarily from a rapid decline in
star formation during relatively low gas fraction.
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All authors Megan Barry, Andrew Wetzel, Sarah Loebman, Jeremy Bailin, Hanna Parul
Astrophysics of Galaxies
Star Formation in Galaxy Collisions: Dependence on Impact Velocity and Gas Mass of Galaxies in GADGET-4 Simulations
Gustavo Neves Pereira and Paulo Laerte Natti
This work investigates variations in the
star formation rate during
galaxy collisions when the initial conditions of velocity and gas mass are altered. For this purpose, hydrodynamic simulations were performed using the GADGET-4 code, with initial conditions generated by the Galstep and SnapshotJoiner programs. Systems of two
galaxies on a head-on collision course were modeled with relative initial velocities ranging from 100 km/s to 1000 km/s, considering two scenarios: the first with identical
galaxies, and the second with
galaxies of different sizes. In simulations of systems with higher initial relative velocities, both found more intense peaks in the
star formation rate, triggered by the first contact of the collision, followed by a strong decline caused by gas dispersion. In contrast, for systems with lower initial velocities, mergers between
galaxies were observed, leading to multiple peaks in the
star formation rate. A greater initial distance between
galaxies has also been linked to whether or not the
galaxy system merges, since it implies longer timescales for gravitational action, which leads to higher relative velocities at the moment of collision. Furthermore, the
star formation rate in
galaxies was found to have a clear dependence on initial gas content. Furthermore, the initial gas content in
galaxies was found to have a clear dependence on
star formation rates. Overall, our results show that the relative impact velocity, the initial distance between the
galaxies, and the gas content are important parameters for analyzing the
star formation rate in colliding
galaxies.
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Solar and Stellar Astrophysics
Dynamically consistent analysis of Galactic WN4b stars
Roel R. Lefever, Andreas A.C. Sander, Matheus Bernini-Peron et al. (+6 more)
Many Wolf-Rayet (WR)
stars have optically thick winds that cloak the hydrostatic layers of the underlying
star. In these cases, traditional spectral analysis methods are plagued by degeneracies that make it difficult to constrain parameters such as the
stellar radius and the deeper density and velocity structure of the atmosphere. Focussing on the regime of nitrogen-rich WN4-
stars with strong emission lines, we employ hydrodynamically-consistent modelling using the PoWR-HD code branch to perform a next generation spectral analysis. The inherent coupling of the
stellar and wind parameters enables us to break parameter degeneracies, constrain the wind structure, and get a mass estimate. With this information, we can draw evolutionary implications and test current mass-loss descriptions for WR
stars. We selected a sample of six
Galactic WN4b
stars. Applying updated parallaxes from
Gaia DR3 and calculating PoWR-HD models that sufficiently resemble most of their spectral appearance, we obtain new values for the
stellar and wind parameters of the WN4b sample. We compare our results to previous studies employing grid models with a beta = 1 velocity structure and cross-check our derived parameters with
stellar structure predictions from GENEC and FRANEC
evolution tracks. For all six targets, we obtain a narrow range of
stellar temperatures T~140 kK, in contrast to previous grid-model analyses. We confirm the existence of WRs with luminosities as low as log L/Lsol = 5.0 and M~5 Msol. All derived velocity fields include a plateau feature at ~85% of the terminal velocity. Both the distance updates and the switch to dynamically-consistent atmospheres lead to substantial parameter adjustments compared to earlier grid-based studies. A comparison of the derived mass-loss rates favours a different description for the WN4b sample than for WN2
stars analysed with the same methodology.
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All authors Roel R. Lefever, Andreas A.C. Sander, Matheus Bernini-Peron, Gemma González-Torà, Wolf-Rainer Hamann, Joris Josiek, Varsha Ramachandran, Elisa C. Schösser, Helge Todt
Cosmology and Nongalactic Astrophysics
Gas rotation and turbulence in the galaxy cluster Abell 2029
T. Bartalesi, A. Simionescu, S. Ettori et al. (+4 more)
We constrain the rotation and turbulent support of the intracluster medium (ICM) in Abell 2029 (A2029), using dynamical
equilibrium models and a combination of state-of-the-art X-ray
datasets. We reduce and conduct the spectral analysis of the XRISM/Resolve data. The rotating, turbulent ICM in the model has a composite polytropic distribution in
equilibrium in a spherically-symmetric, cosmologically motivated dark
halo. The profile of rotation velocity and the distribution of turbulent velocity dispersion are described with flexible functional forms, consistent with the properties of synthetic clusters formed in cosmological simulations. Adopting realistic profiles for the
metallicity distribution of the ICM and for the point spread function of XRISM and XMM-Newton, we tune via a Markov chain Monte Carlo
algorithm the observables of the intrinsic quantities of the
plasma in our model to reproduce the radial profiles of the thermodynamic quantities as derived from the spectral analysis of the XMM-Newton and Planck maps and the measurements of the line-of-sight (LOS) non-thermal velocity dispersion and
redshift (probing the LOS velocity) in the XRISM pointings. Our model accurately reproduces the measurements of
redshift and LOS non-thermal velocity dispersion, as further demonstrated by simulating and analyzing synthetic counterparts of the XRISM spectra, in accordance with the posterior distribution of our model. We find
turbulence-to-total pressure ratio $\approx$ 2% across the (0 - 650) kpc radial range, and a rotation-to-dispersion velocity ratio peaking at 0.15 between 200 - 600 kpc. The hydrostatic-to-total mass ratio is $\approx$ 0.97 at r2500, the radius enclosing an overdensity of 2500 times the average value.
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All authors T. Bartalesi, A. Simionescu, S. Ettori, C. Nipoti, V. Ghirardini, A. Sarkar, M. Sun
Astrophysics of Galaxies
Dynamical Origins of Azimuthal Metallicity Variations in the Galactic Disk: Insights from Kinematic Ridges with Gaia
Carlos Jurado, Keith Hawkins, Jason A. S. Hunt et al. (+4 more)
Kinematic and spectroscopic studies in the past few years have revealed coherent azimuthal
metallicity variations across the Milky Way's disk that may be the result of dynamical processes associated with non-axisymmetric features of the
Galaxy. At the same time,
stellar kinematics from
Gaia have uncovered ridge-like features in the velocity space, raising the question of whether these chemical and dynamical substructures share a common origin. Using a sample of disk
stars from
Gaia DR3, we find that azimuthal
metallicity variations are correlated with kinematic ridges in the V_phi-R plane, suggesting a shared origin. We utilize a suite of Milky Way test-particle simulations to assess the role of transient spiral arms, the bar, and interactions with a Sagittarius-like
dwarf galaxy in simultaneously shaping both chemical and kinematic substructures. Among the physical mechanisms explored, bar and spiral arm interactions are the ones that consistently reproduce both the chemo-kinematic features and
alignment observed in the
Gaia data. While our model of an interaction with a Sagittarius-like
dwarf galaxy can also induce kinematic and
metallicity substructure, the amplitude of the azimuthal
metallicity variations are too weak, suggesting this is likely not the dominant influence. Although additional contributing processes cannot be ruled out, the azimuthal
metallicity variations observed in
Gaia are best explained by a dynamical origin. Our results support the view that that azimuthal
metallicity variations in the
Galaxy are driven by similar dynamical mechanisms responsible for generating the kinematic ridges and co-moving groups.
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All authors Carlos Jurado, Keith Hawkins, Jason A. S. Hunt, Zoe Hackshaw, Carrie Filion, Neige Frankel, Christopher Carr
Solar and Stellar Astrophysics
The intermediate neutron capture process. VI. Proton ingestion and i-process in rotating magnetic asymptotic giant branch stars
A. Choplin, L. Siess, S. Goriely et al. (+2 more)
The intermediate
neutron-capture process (i-process) can occur during
proton ingestion events (PIEs), which may take place in the early evolutionary phases of asymptotic
giant branch (AGB)
stars. We investigate the impact of rotational and
magnetic mixing on i-process nucleosynthesis in low-
metallicity, low-mass AGB
stars. We computed AGB models with [Fe/H] = $-2.5$ and $-1.7$ and initial masses of 1 and 1.5 $M_{\odot}$ using the STAREVOL code, including a network of 1160
nuclei coupled to transport equations. Rotating models incorporate a calibrated Tayler-Spruit (TS) dynamo to account for core rotation rates inferred from asteroseismic observations of
solar-
metallicity sub-
giants and
giants. Initial rotation velocities of 0, 30, and 90 km s$^{-1}$ were considered, along with varying assumptions for
magnetic mixing. We find that rotation without
magnetic fields strongly suppresses the i-process due to the production of primary $^{14}$N, which is subsequently converted into $^{22}$Ne $-$ a potent
neutron poison during the PIE. Including
magnetic fields via the TS dynamo restores the models close to their non-rotating counterparts: strong core-envelope coupling suppresses shear mixing and prevents primary $^{14}$N synthesis, yielding i-process nucleosynthesis similar to non-rotating models. We also find that rotational mixing during the AGB phase is insufficient to affect the occurrence of PIEs.
Proton ingestion event-driven nucleosynthesis proceeds similarly in asteroseismic-calibrated
magnetic rotating AGB
stars and non-rotating
stars, producing identical abundance patterns.
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All authors A. Choplin, L. Siess, S. Goriely, P. Eggenberger, F. D. Moyano
High Energy Astrophysical Phenomena
Thick Disks, Thin Hopes: Suppressed Capture and Merger Rates in AGN
Yashvardhan Tomar, Philip F. Hopkins and Kyle Kremer
Multiple models have been suggested over the years to explain the structure and support of
accretion disks around supermassive black holes, from the standard thin thermal-pressure-dominated $\alpha$-disk model to more recent models that describe geometrically thicker radiation or
magnetic or
turbulence-dominated disks. In any case, objects embedded in the disk (e.g. compact objects,
stars, gas,
dust) can undergo gravitational and hydrodynamic interactions with each other leading to interesting processes such as binary interaction/capture, gravitational wave merger events, dynamical friction,
accretion, gap opening, etc. It has long been argued that disks of active
galactic nuclei (AGN) can enhance the rates for many of these events; however, almost all of that analysis has assumed specific thin-disk models (with aspect ratios $H/R \lesssim 0.01$). We show here that the rates for processes such as these that are mediated by gravitational cross-sections has a very strong inverse dependence on the thickness $H/R$ (scaling as steeply as $(H/R)^{-8}$), and $H/R$ can vary in the outer disk (where these processes are often invoked) by factors $\gtrsim 1000$ depending on the assumed source of pressure support in the disk. This predicts rates that can be lower by tens of orders-of-magnitude in some models, demonstrating that it is critical to account for disk parameters such as aspect ratio and different sources of disk pressure when computing any meaningful predictions for these rates. For instance, if
magnetic pressure is important in the outer disk, as suggested in recent work, capture rates would be suppressed by factors $\sim 10^{10}-10^{20}$ compared to previous studies where
magnetic pressure was ignored.
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Earth and Planetary Astrophysics
Models and Observational Predictions of Dust Traps in Protoplanetary Discs
Paola Pinilla
This manuscript investigates the impact of key
dust evolution parameters on
dust retention and trapping in protoplanetary discs. Using models with and without pressure bumps, combined with radiative transfer simulations, images of the
dust continuum emission at (sub-)millimeter wavelengths, their fluxes and observed disc sizes are presented. For discs without pressure bumps (smooth discs), significant
dust mass can only be retained over Myr timescales when
dust fragmentation velocities are low (1m/s) and with viscosity values of $\alpha=10^{-3}$. For such a combination of fragmentation velocity and viscosity, the synthetic images show a bright inner emission follow by a shallow emission with potential gaps if they are present in the gas profile as well. At higher fragmentation velocities (5-10m/s), most
dust is lost due to radial drift at million-year timescales unless pressure traps are present, in which case
dust masses can increase by orders of magnitude and structures are observed in synthetic images. The viscosity parameter strongly shapes observable features, with low $\alpha$ producing sharper, potentially asymmetric inner wall cavities in inclined discs due to optically thick emission. High $\alpha$ favors the appearance of shoulders around the predominant rings that
dust trapping produces. However, distinguishing between different fragmentation velocities observationally remains challenging. The inferred
dust disc sizes from synthetic observations do not always correspond directly to
dust model sizes or to the location of pressure bumps. Finally, we discuss implications for pebble fluxes and the delivery of volatiles to the inner disc. These results emphasize the strong degeneracies among
dust evolution parameters and highlight the need for multi-wavelength, high-resolution observations to disentangle the processes shaping the formation of
planets in protoplanetary discs.
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Astrophysics of Galaxies
CHANG-ES XXXVII. Effects of spectral aging on radio scale heights
D. C. Smolinski, V. Heesen, M. Brüggen et al. (+7 more)
Context.
Cosmic rays and
magnetic fields play an important role for the formation and
evolution of
galaxies.
Radio continuum observations allows us to study them in the
haloes of edge-on
galaxies. Aims. We explore the frequency dependence of the
radio scale height which depends on
cosmic ray transport and electron cooling. We test the influence of fundamental
galaxy properties, such as
star-formation rate (SFR), mass and size. Methods. We used
radio continuum data of 16 edge-on
galaxies from the Continuum
HAloes in Nearby
Galaxies – an EVLA Survey (CHANG-ES). We included maps from the LOw Frequency ARray at 144 MHz and from the Jansky Very Large Array at 3 GHz with 7" angular resolution. We extracted vertical intensity profiles within the effective
radio radius and fitted beam-convolved double-exponential models to separate thin and thick discs. For the thick
radio discs, we computed mean spectral indices and scale-height ratios between 144 MHz and 3 GHz. Results. We find a mean scale-height ratio of 1.26 \pm 0.16. This is much lower than what we would expect for either
cosmic ray
diffusion or advection if synchrotron and inverse Compton losses dominate for the electrons. There is a moderate positive correlation between the ratio and spectral index of the thick disc:
galaxies with high ratios have flat
radio spectra. The ratio does not depend on any other
galaxy parameter. The
radio spectrum of the thick disc, as indicated by the
radio spectral index, steepens with total mass (strong correlation) and flattens with SFR-to-mass surface density (moderate correlation). Conclusions.
Galaxies with
galactic winds have flat
radio continuum spectra and large scale heights at low frequencies. This shows effective transport of
cosmic rays in such systems.
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All authors D. C. Smolinski, V. Heesen, M. Brüggen, J.-T. Li, M. Weżgowiec, M. Stein, L.-Y. Lu, T. Wiegert, J. Irwin, R.-J. Dettmar
High Energy Astrophysical Phenomena
Resolving the Fe K$\alpha$ Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM
Stephen DiKerby, Shuo Zhang, Kumiko Nobukawa et al. (+3 more)
Fe K$\alpha$ line emission from
Galactic center molecular clouds can be produced either via fluorescence after illumination by an X-ray source or by
cosmic ray ionization. Unparalleled high-resolution X-ray spectroscopy obtained by XRISM-Resolve for the
galactic center molecular cloud G0.11-0.11 resolves its Fe K$\alpha$ line complex for the first time, and points to a new method for discrimination between the X-ray reflection and
cosmic ray ionization models. The Fe K$\alpha$ line complex is resolved into Fe K$\alpha_1$ at $E_{1} = 6.4040 \: \rm{keV}$ and Fe K$\alpha_2$ at $E_{2}= 6.3910 \:\rm{keV}$. Both lines have non-instrumental FWHM of $\approx 3 \:\rm{eV}$, close to the predicted
quantum mechanical width of the lines, suggesting scant other sources of line broadening other than instrumental and
quantum effects. We measure a radial velocity of $v_{\rm{LSR}} = 50 \pm 12_{fit} \pm 14_{scale} \:\rm{km/s}$ for G0.11-0.11, achieving the same precision reached by
radio observations of such clouds. The high-resolution spectrum tests for the presence of secondary Fe K$\alpha$ lines, expected as a signature of
cosmic ray
proton/ion ionization. The absence of the secondary lines argues against the
cosmic ray ionization model for G0.11-0.11. In the preferred X-ray reflection model, if the illuminating source is Sgr A$^{\star}$, the required luminosity for an X-ray outburst about 200 years ago is $L_8 \approx 10^{38} \:\rm{erg/s}$ in an $8\:\rm{keV}$-wide band at $8\:\rm{keV}$.
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All authors Stephen DiKerby, Shuo Zhang, Kumiko Nobukawa, Masayoshi Nobukawa, Yuma Aoki, Jack Uteg
Astrophysics of Galaxies
Cosmic Chance Superpositions: Largest Catalog of Quasar-Galaxy Pairs at a Projected Separation of $D \lesssim 20$ kpc
Labanya Kumar Guha, Raghunathan Srianand and Rajeshwari Dutta
We present the largest catalogue to date of
Galaxies On Top Of
Quasars (GOTOQs), systems where the sightline to a background
quasar passes directly through or very close to a foreground
galaxy. Using $\approx$1.1 million
quasar spectra from SDSS DR16 and the DESI Early Data Release, we identify 1345 unique GOTOQs over the
redshift range $0.0045 \leq z \leq 1.09$, more than quadrupling the number previously known. The catalogue combines both absorption agnostic and absorption selected searches, enabling a robust characterization of gas in
galaxies at projected separations $D \lesssim 20$ kpc. The GOTOQ emission line ratios indicate that their host
galaxies are predominantly normal,
star forming disks with typical
dust extinctions of $A_V \approx 0.5$ mag. We measure the MgII covering fraction at $D \lesssim 20$ kpc and find it to be remarkably high, $f_c = 98.2^{+1.3}_{-4.5}$ per cent, indicating that these systems trace gas rich, metal enriched regions at the disk-
halo interface. The median colour excess towards the
quasar line of sight, $E(B-V) = 0.087$, is significantly higher than that of typical MgII absorbers, underscoring the
dust rich nature of GOTOQ sightlines. From a high signal to noise composite spectrum, we report the first statistical detection of the diffuse interstellar band at $\lambda 4428$ ($W_r = 0.055 \pm 0.011$ angstrom) and at $\lambda 5780$ ($W_r = 0.051\pm 0.012$ angstrom), revealing the presence of complex organic molecules at the disk
halo interface. This catalogue provides a powerful reference sample for future multi wavelength studies of gas flows, cold gas, and
dust evolution in the inner circumgalactic medium.
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Earth and Planetary Astrophysics
Towards a global model for planet formation in layered MHD wind-driven discs: A population synthesis approach to investigate the impact of low viscosity and accretion layer thickness
Jesse Weder and Christoph Mordasini
Planet formation is inherently linked to protoplanetary disc
evolution, which recent developments suggest is driven by magnetised winds rather than turbulent viscosity. We study
planet formation in magnetohydrodynamic (MHD) wind-driven discs, assuming
accretion occurs in a laminar surface layer above a weakly turbulent midplane. Our goal is to assess the global consequences of recent hydrodynamical results, including inefficient midplane heating and the existence of two Type II migration regimes: slow viscosity-dominated and fast wind-driven migration. We perform single-embryo planetary population syntheses with varying initial disc conditions (i.e. disc mass, size and angular momentum transport), and embryo starting locations, testing different prescriptions for the
accretion layer thickness $\Sigma_\text{active}$. Thin ($\lesssim0.01\mathrm{g\,cm^{-2}}$) or fast ($\gtrsim12\%$ sonic velocity)
accretion layers result in slow, viscosity-dominated regime which strongly limits the extent of Type II migration. For thick ($\gtrsim1\mathrm{g\,cm^{-2}}$) or slow ($\lesssim3\%$ sonic velocity)
accretion layers, fast wind-driven Type II migration occurs frequently, leading to long-range inward migration that sets in once
planets reach masses sufficient to block the accreting layer. Disk-limited gas
accretion is also strongly affected by deep and early gap opening, limiting maximum
giant planet masses. These effects strongly influence the final mass-distance distribution. For thin layers,
giant planets form nearly in situ once they have entered Type II migration, which happens already at a few Earth masses, while thick layers lead to numerous migrated Hot Jupiters. Overall, we find that while the global properties of the emerging
planet population are strongly modified relative to classical viscous discs, key properties of the observed population can be reproduced within this new paradigm.
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High Energy Astrophysical Phenomena
The Maximum Gravity Model for partial Tidal Disruption Events: Mass Loss, Peak Fallback Rate and Dependence on Stellar Properties
Ananya Bandopadhyay, Eric R. Coughlin and C. J. Nixon
A
star entering the
tidal sphere of a supermassive black hole (SMBH) can be partially stripped of mass, resulting in a partial
tidal disruption event (TDE). Here we develop an analytical model for properties of these events, including the peak fallback rate, $\dot{M}_{\rm peak}$, the time at which the peak occurs, $t_{\rm peak}$, and the amount of mass removed from the
star, $\Delta M$, for any
star and any pericenter distance associated with the
stellar orbit about the black hole. We compare the model predictions to 1276 hydrodynamical simulations of partial TDEs of main-sequence
stars by a $10^6 M_\odot$ SMBH. The model yields $t_{\rm peak}$ predictions that are in good agreement (to within tens of percent) with the numerical simulations for any
stellar mass and age. The agreement for $\dot{M}_{\rm peak}$ is weaker due to the influence of self-
gravity on the debris stream dynamics, which remains dynamically important for partial TDEs; the agreement for $\dot{M}_{\rm peak}$ is, however, to within a factor of $\sim 2-3$ in the majority of cases considered, with larger differences for low-mass
stars ($M_\star \lesssim 0.5 M_\odot$) on grazing orbits with small mass loss. We show that partial TDE lightcurves for disruptions caused by $\sim 10^6M_\odot$ SMBHs can span $\sim 20-100$ day peak timescales, whereas grazing encounters of high-mass
stars with high-mass SMBHs can yield longer peak timescales ($t\gtrsim 1000$ days), associated with some observed transients. Our model provides a significant step toward an analytical prescription for TDE lightcurves and luminosity functions.
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Astrophysics of Galaxies
Hunting for the First Explosions at the High-Redshift Frontier
Junehyoung Jeon, Volker Bromm, Alessandra Venditti et al. (+2 more)
The James Webb Space
Telescope (JWST) has spectroscopically confirmed
galaxies up to $z\sim14$, 300 Myr after the Big Bang, and several candidates have been discovered at $z\sim15-25$, with one candidate as high as $z\sim30$, only 100 Myr after the Big Bang. Such objects are unexpected, since theoretical studies have not predicted the existence of detectable
galaxies at $z\sim30$. While any $z\sim30$ candidates may be contaminants at lower
redshifts, we explore whether such extreme
redshift sources could be consistent with hyper-energetic transient events linked to the formation of the first, metal-free,
stars. Specifically, we consider pair-instability
supernovae (PISNe), a predicted class of extreme thermonuclear explosions that leave no remnant behind. Using cosmological simulations, we investigate an overdense
cosmic region, where
star formation and subsequent PISNe occur at $z\sim30-40$, even within standard cosmology. Assessing the likelihood of such a region, the corresponding number of PISNe at $z\gtrsim20$, and their observed flux, we find that JWST has a non-negligible chance to detect a PISN event at extremely high
redshifts. If a transient event were confirmed at $z\sim30$, this would provide a direct glimpse into the epoch of first
star formation, dramatically extending the empirical reach of astronomy.
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All authors Junehyoung Jeon, Volker Bromm, Alessandra Venditti, Steven L. Finkelstein, Tiger Yu-Yang Hsiao
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Resonances in binary extreme mass ratio inspirals
João S. Santos, Vitor Cardoso, Alexandru Lupsasca et al. (+2 more)
Stellar-mass binaries evolving in the vicinity of supermassive black holes (SMBHs) may be common in the universe, either in active
galactic nuclei or in other astrophysical environments. Here, we study in detail the resonant excitation of SMBH modes driven by a nearby
stellar-mass binary. The resulting resonant energy fluxes vary with the orbital location and frequency of the binary, exhibiting a rich and complex structure. In particular, we find that the total energy flux radiated to infinity is maximized at a gravitational-wave frequency that is close to, but not exactly equal to, the real part of the corresponding quasinormal-mode frequency. Moreover, as the binary is moved farther away from the SMBH, this offset from the mode frequency becomes increasingly pronounced. In addition, for suitable orientations, the binary can effectively “feed” the light ring of the SMBH, selectively exciting particular oscillation modes. For rotating (Kerr) black holes, the mode spectrum is significantly more intricate; however, individual modes are also less strongly damped, leading to an enhanced – but more difficult to interpret – resonant response.
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All authors João S. Santos, Vitor Cardoso, Alexandru Lupsasca, José Natário, Maarten van de Meent
High Energy Astrophysical Phenomena
Exceptionality of exceptional gravitational-wave events
Rodrigo Tenorio and Davide Gerosa
In gravitational-wave astronomy, as in other scientific disciplines, “exceptional” sources attract considerable interest because they challenge our current understanding of the underlying (astro)physical processes. Crucially, “exceptionality” is defined only relative to the rest of the detected population. For instance, among all gravitational-wave events detected so far, GW231123 is the binary black hole with the largest total mass, while GW241110 is the binary black hole with the most strongly misaligned
spin relative to the orbital angular momentum. Mandel [Astrophys. J. Lett. 996, L4 (2026)] argued that apparent “exceptionality” may reflect measurement error rather than an extreme true value, and suggested that the total mass of GW231123 may be significantly overestimated. Here we present a quantitative analysis that supports this conceptual point. We find that claims of “exceptionality” obtained under population-agnostic priors should be critically questioned whenever measurement uncertainties are comparable to the width of the underlying population. Specifically, we find that the total mass of GW231123 is unlikely to be meaningfully affected by this effect while the
spin of GW241110 is far less likely to be antialigned than initially claimed: about 70% of realizations that appear to yield an “exceptionally antialigned”
spin are in fact consistent with either nonspinning or aligned configurations.
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Cosmology and Nongalactic Astrophysics
A possible challenge for Cold and Warm Dark Matter
S. Vegetti, S. D. M. White, J. P. McKean et al. (+5 more)
Measuring the density profile and mass concentration of dark-matter
haloes is a key test of the standard cold dark matter paradigm. Such objects are dark and thus challenging to characterise, but they can be studied via gravitational
lensing. Recently, a million-
solar-mass object was discovered superposed on an extended and extremely thin gravitational arc. Here we report on extensive tests of various assumptions for the mass density profile and
redshift of this object. We find models that best describe the data have two components: an unresolved point-mass of radius $\leq10$ pc centred on an extended mass distribution with an almost constant surface density out to a truncation radius of 139 pc. These properties do not resemble any known astronomical object. However, if the object is dark matter-dominated, its structure is incompatible with cold dark matter models, but may be compatible with a self-interacting dark matter
halo where the central region has collapsed to form a black hole. This detection could thus carry substantial implications for our current understanding of dark matter.
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All authors S. Vegetti, S. D. M. White, J. P. McKean, D. M. Powell, C. Spingola, D. Massari, G. Despali, C. D. Fassnacht
Astrophysics of Galaxies
Electron temperature relations and the direct N, O, Ne, S and Ar abundances of 49959 star-forming galaxies in DESI Data Release 2
D. Scholte, F. Cullen, J. Moustakas et al. (+42 more)
We present the largest direct-method abundance catalogue of
galaxies to date, containing measurements of 49959
star-forming
galaxies at z < 0.96 from DESI Data Release 2. By directly measuring electron temperatures across multiple ionisation zones, we provide constraints on a number of electron temperature relations. Using the temperature measurements, we derive reliable abundances for N, O, Ne, S and Ar and measure the
evolution of abundances and abundance ratios of as a function of
metallicity and other
galaxy properties. Our measurements include direct oxygen abundances for 49507
galaxies, leading to the discovery of the two most metal-poor
galaxies in the nearby Universe, with oxygen abundances of 12+log(O/H) = $\rm 12+\log(O/H) = 6.77_{-0.03}^{+0.03}~\rm dex $ (1.2% $\rm Z_{\odot}$) and $\rm 12+\log(O/H) = 6.81_{-0.04}^{+0.04}~\rm dex$ (1.3% $\rm Z_{\odot}$). We identify a rare outlier population of 24
galaxies with high N/O ratios at low
metallicity, reminiscent of
galaxy abundances observed in the early Universe. We find the Ne/O ratio is constant at low
metallicity but increases gradually at $\rm 12+log(O/H) > 8.105\pm0.004$ dex. We show that the S/O and Ar/O abundance ratios are strongly correlated, consistent with the expected additional Type Ia enrichment channel for S and Ar. In this work we present an initial survey of the key properties of the sample, with this
dataset serving as a foundation for extensive future work on
galaxy abundances at low
redshift.
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All authors D. Scholte, F. Cullen, J. Moustakas, H. Zou, A. Saintonge, K. Z. Arellano-Cordova, T. M. Stanton, B. Andrews, J. Sui, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, F. J. Castander, T. Cheng, T. Claybaugh, A. de la Macorra, B. Dey, P. Doel, K. Douglass, S. Ferraro, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, R. Joyce, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, P. Martini, A. Meisner, R. Miquel, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, Z. Shao, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver
Instrumentation and Methods for Astrophysics
Exposure-averaged Gaussian Processes for Combining Overlapping Datasets
Jacob K. Luhn, Ryan A. Rubenzahl, Samuel Halverson et al. (+1 more)
Physically motivated Gaussian process (GP) kernels for
stellar variability, like the commonly used damped, driven simple harmonic oscillators that model
stellar granulation and p-mode oscillations, quantify the instantaneous covariance between any two points. For kernels whose timescales are significantly longer than the typical exposure times, such GP kernels are sufficient. For time series where the exposure time is comparable to the kernel timescale, the observed signal represents an exposure-averaged version of the true underlying signal. This distinction is important in the context of recent data streams from Extreme Precision Radial Velocity (EPRV) spectrographs like fast readout
stellar data of asteroseismology targets and
solar data to monitor the Sun's variability during daytime observations. Current
solar EPRV facilities have significantly different exposure times per-site, owing to the different design choices made. Consequently, each instrument traces different binned versions of the same "latent" signal. Here we present a GP framework that accounts for exposure times by computing integrated forms of the instantaneous kernels typically used. These functions allow one to predict the true latent oscillation signals and the exposure-binned version expected by each instrument. We extend the framework to work for instruments with significant time overlap (i.e., similar longitude) by including relative instrumental drift components that can be predicted and separated from the
stellar variability components. We use Sun-as-a-
star EPRV
datasets as our primary example, but present these approaches in a generalized way for application to any
dataset where exposure times are a relevant factor or combining instruments with significant overlap.
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All authors Jacob K. Luhn, Ryan A. Rubenzahl, Samuel Halverson, Lily L. Zhao
High Energy Astrophysical Phenomena
Neutrino flavor instabilities in neutron star mergers with moment transport: Slow, fast, and collisional modes
Julien Froustey, Francois Foucart, Christian Hall et al. (+5 more)
Determining where, when, and how
neutrino flavor oscillations must be included in large-scale simulations of hot and dense astrophysical environments is an enduring challenge that must be tackled to obtain accurate predictions. Using an angular moment-based linear stability analysis framework, we examine the different kinds of
flavor instabilities that can take place in the context of the post-processing of a
neutron star merger simulation, with a particular focus on the collisional
flavor instability and a careful assessment of several commonly used approximations. First, neglecting anisotropies of the
neutrino field, we investigate the extent to which commonly used monoenergetic growth rates reproduce the results obtained from a full multi-energy treatment. Contrary to the large discrepancies found in core-collapse
supernova environments, we propose a simple combination of energy-averaged estimates that reproduces the multi-energy growth rates in our representative simulation snapshot. We then quantify the impact of additional physical effects, including
nuclear many-body corrections, scattering opacities, and the inclusion of the
vacuum term in the
neutrino Hamiltonian. Finally, we include the
neutrino distribution anisotropies, which allows us to explore, for the first time in a multi-energy setting, the interplay between collisional, fast, and slow modes in a moment-based
neutron star merger simulation. We find that, despite a dominance of the fast instability in most of the simulation volume, certain regions exhibit only a collisional instability, while others, especially at large distances, exhibit a slow instability that is largely underestimated if anisotropic effects are neglected.
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All authors Julien Froustey, Francois Foucart, Christian Hall, James P. Kneller, Debraj Kundu, Zidu Lin, Gail C. McLaughlin, Sherwood Richers