Earth and Planetary Astrophysics
How does ice shell geometry shape ocean dynamics on icy moons?
Yixiao Zhang, Wanying Kang and John Marshall
A poleward-thinning ice shell can drive circulation in the subsurface oceans of icy moons by imposing a meridional temperature gradient–colder at the equator than the pole–through the freezing point suppression due to pressure. This temperature gradient sets a buoyancy gradient, whose sign depends on the thermal expansion coefficient determined by ocean salinity. Together with vertical mixing, this buoyancy forcing shapes key oceanic features, including zonal currents in thermal wind balance, baroclinic instability of those currents, meridional heat transport by eddies, and vertical stratification. We use high-resolution numerical simulations to explore how variations in ice shell thickness affect these processes. Our simulations span a wide range of topographic slopes, pole-to-equator temperature differences, and vertical mixing strengths, for both fresh and salty oceans. We find that baroclinic eddies dominate large-scale circulation and meridional heat transport, consistent with studies assuming a flat ice-ocean interface. However, sloped topography introduces new effects: when lighter water overlies denser water along the slope, circulation weakens as a stratified layer thickens beneath the poles. Conversely, when denser water lies beneath the poles, circulation strengthens as topography increases the available potential energy. We develop a scaling framework that predicts heat transport and stratification across all simulations. Applying this framework to Enceladus, Europa, and Titan, we infer ocean heat fluxes, stratification, and
tidal energy dissipation and showing large-scale circulation constrains
tidal heating and links future observations of ice thickness and rotation to subsurface ocean dynamics.
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Instrumentation and Methods for Astrophysics
HS-ANET: Star Spectral Type Enhanced Astrometric Calibration for Hyper Spectral Space Imaging
Kevin Phan, William Mitchell, David Chaparro et al. (+2 more)
Traditional lost-in-space
algorithms, such as those implemented in astrometry.net, solve for spacecraft orientation by matching observed
star fields to celestial catalogs using
geometric asterisms alone. In this work, we propose a novel extension to astrometry.net that incorporates
stellar spectral type, which is derived from hyperspectral imagery, into the matching process. By adding this spectral dimension to each
star detection, we constrain the search space and improve match specificity, enabling successful astrometric solutions with significantly fewer
stars. Our modified pipeline demonstrates improved fit rates and reduced failure cases in cluttered or ambiguous
star fields, which is especially critical for autonomous space situational awareness and traffic management. Our results suggest that modest spectral resolution, when incorporated into existing
geometric frameworks, can dramatically improve robustness and efficiency in onboard
star identification systems.
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All authors Kevin Phan, William Mitchell, David Chaparro, Enrique De Alba, J. Zachary Gazak
Instrumentation and Methods for Astrophysics
A Natural Language Interface for Efficient Data Retrieval in SDSS
Prathamesh Tamhane
Modern astronomical surveys such as the Sloan Digital Sky Survey (SDSS) provide extensive astronomical databases enabling researchers to access vast amount of diverse data. However, retrieving data from archives requires knowledge of query
languages and familiarity with their schema, which presents a barrier for non-experts. This work investigates the use of Microsoft Phi-2, a compact yet powerful
transformer-based
language model, fine-tuned on natural
language–SQL pairs constructed from SDSS query examples. We develop an interface that translates user queries in natural
language into SQL commands compatible with SDSS SkyServer. Preliminary evaluation shows that the fine-tuned model produces syntactically valid and largely semantically correct queries across a variety of astronomy-related requests. Our results show that even small-scale models, when carefully fine-tuned, can provide effective domain-specific natural
language interfaces for large scientific databases.
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Astrophysics of Galaxies
Lyman-$\alpha$ radiation pressure regulates star formation efficiency
D. Manzoni and A. Ferrara
Order-unity
star formation efficiencies (SFE) in early
galaxies may explain the overabundance of bright
galaxies observed by JWST at high
redshift. Here we show that Lyman-$\alpha$ (Ly$\alpha$) radiation pressure limits the gas mass converted into
stars, particularly in
primordial environments. We develop a shell model including Ly$\alpha$ feedback, and validate it with one-dimensional hydrodynamical simulations. To account for Ly$\alpha$ resonant scattering, we adopt the most recent force multiplier fits, including the effect of Ly$\alpha$
photon destruction by
dust grains. We find that, independently of their gas surface density $\Sigma_g$, clouds are disrupted on a timescale shorter than a free-fall time, and even before
supernova explosions if $\Sigma_g \gtrsim 10^3\,M_{\odot}\ \rm pc^{-2}$. At $\log(Z/Z_{\odot}) = -2$, relevant for high-
redshift galaxies, the SFE is $0.01 \lesssim \hat{\epsilon}_{*} \lesssim 0.66$ for $10^3 \lesssim\Sigma_g [M_{\odot}\ \rm pc^{-2}] \lesssim 10^5$. The SFE is even lower for decreasing
metallicity. Near-unity SFEs are possible only for extreme surface densities, $\Sigma_{g} \gtrsim 10^5\;M_{\odot}\ \rm pc^{-2}$, and near-
solar metallicities. We conclude that Ly$\alpha$ radiation pressure severely limits a possible extremely efficient, feedback-free phase of
star formation in dense, metal-poor clouds.
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Earth and Planetary Astrophysics
Potential Thermal Profiles of The Third Interstellar Object 3I/ATLAS
Atsuhiro Yaginuma, Aster G. Taylor and Darryl Z. Seligman
We investigate the thermal
evolution of 3I/ATLAS, the third macroscopic interstellar object discovered on 2025 July 1. By comparing modeled thermal profiles with observations of volatile activity, it is possible to constrain bulk physical properties of a cometary
nucleus. 3I/ATLAS is actively producing a variety of cometary volatiles. In this paper, we calculate one-dimensional thermal profiles of the third interstellar object 3I/ATLAS throughout its trajectory in an attempt to gain insight into its bulk properties based on measurements of its volatiles. Assuming a variety of typical comet and asteroid bulk geophysical properties such as heat capacities, densities, and conductivities, we calculate the radial thermal profile as a function of depth throughout the
hyperbolic trajectory. The methods and code to generate the thermal profile are flexible for any
hyperbolic or bound orbit. The thermal profiles are benchmarked to the nominal sublimation temperatures of H$_2$O, CO$_2$ and CO, but are still applicable to any volatile. Comparison between the modeled surface temperatures and the observed onset of H$_2$O activity near 3 au indicates that surface temperatures exceeding $\sim$150 K can only be achieved if the albedo is below 0.2. We therefore set the upper limit on the albedo of 3I/ATLAS to be 0.2.
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Earth and Planetary Astrophysics
NEOForCE: Near-Earth Objects' Forecast of Collisional Events
Dmitrii E. Vavilov and Daniel Hestroffer
Robust impact monitoring of near-Earth objects is an essential task of planetary defense. Current systems such as NASA's Sentry-II, the University of Pisa's CLOMON2, and ESA's Aegis have been highly successful, but independent approaches are essential to ensure reliability and to cross-validate predictions of possible impacts. We present NEOForCE (Near-Earth Objects' Forecast of Collisional Events), a new independent monitoring system for asteroid impact prediction. By relying on orbital solutions from DynAstVO at Paris Observatory and using an original methodology for uncertainty propagation, NEOForCE provides an alternative line of verification for impact assessments and strengthens the overall robustness of planetary defense. As other monitoring systems, NEOForCE samples several thousand virtual asteroids from the uncertainty region and integrates their orbits up to 100 years into the future. Instead of searching for close approaches of the virtual asteroids with the Earth, our system looks for times when the Earth comes close to the realistic uncertainty regions around them, which are mostly stretched along their osculating orbits. We also estimate the maximal impact probability, and only if this value is large enough do we continue to the next step. In this second step, we compute how the original asteroid orbit should be modified so that the new trajectory leads to an Earth impact, which allows us to confirm the possible collision and estimate the impact probability. We tested NEOForCE against NASA's Sentry-II system on five representative asteroids: 2000 SG344, 2005 QK76, 2008 JL3, 2023 DO and 2008 EX5. NEOForCE successfully recovered mostly all possible collisions reported by Sentry-II with impact probabilities above e-7, demonstrating the robustness of our approach. In addition, NEOForCE identified several potential impacts at the e-7 - e-6 level that Sentry-II did not report.
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Astrophysics of Galaxies
TRIShUL: Technique for Reconstructing magnetic Interstellar Structure Using starLight polarization
Namita Uppal, Konstantinos Tassis, Vasiliki Pavlidou et al. (+2 more)
We present a novel technique to decompose line-of-sight (LOS)
stellar polarization as a function of distance, aimed at reconstructing three dimensional (3D) plane-of-sky (POS)
magnetic structures in the interstellar medium (ISM). The method assumes that the observed polarization arises from discrete, thin
dust layers located at varying distances along the LOS. Using a simple frequentist framework, it identifies structural changes in the distance-sorted cumulative Mahalanobis distance of Stokes parameters (q and u) to detect the locations of
dust layers and estimate their associated physical properties (parallax and Stokes parameters) necessary to construct 3D maps. We
benchmark the method using mock
datasets representative of high-
Galactic-latitude regions, incorporating realistic
Gaia parallax uncertainties and polarization expected from the upcoming Pasiphae survey. Tests show that the method reliably recovers
dust cloud distances and polarization properties when the polarization exceeds 0.1%, and the effective background-
star fraction is greater than 10% in samples of about 345
stars. The dependence on background fraction decreases as the intrinsic polarization amplitude of the
dust field increases. We apply our method to existing polarization data from two illustrative sightlines, one at intermediate-high
Galactic latitude and one near the
Galactic plane, with known tomographic solutions, finding excellent agreement with the literature and demonstrating its accuracy across both regions. Comparing with the BISP-1 approach, both methods effectively recover
dust cloud properties, but our approach is prior-free and computationally more efficient in determining the optimal number of clouds along the LOS. These advantages make it flexible and broadly applicable for multi-layer
dust cloud reconstruction for the upcoming era of large-scale
stellar polarization surveys.
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All authors Namita Uppal, Konstantinos Tassis, Vasiliki Pavlidou, Vincent Pelgrims, Myrto Falalaki
Astrophysics of Galaxies
The universality of the relation between magnetic fields and star formation in galaxies
Davide Belfiori, Sergio Martin-Alvarez, Enrique Lopez-Rodriguez et al. (+1 more)
The interstellar medium (ISM) is permeated by
magnetic fields that affect gas dynamics and
star formation. These fields correlate with
supernova (SN)-driven
turbulence, but whether the scaling is universal across
galaxy properties, ISM phases, and energy budgets remains unclear. We quantify the dependence of
magnetic fields on
star formation activity including both regular and starburst
galaxies. We analyse 19 spiral disks from the cosmological RTnsCRiMHD Azahar suite, deriving line-of-sight integrated maps to measure median
magnetic-field strength ($B$), specific energies (thermal, turbulent,
magnetic, and
cosmic-ray), and
star formation rate (SFR),
star formation surface density ($\Sigma_{\mathrm{SFR}}$) and specific SFR (sSFR). We find an almost universal
magnetic-field-SFR scaling with slope $\alpha \approx 0.2$-$0.3$ across
galaxy mass and ISM phases. The $B$-$\Sigma_{\mathrm{SFR}}$ slope ($\alpha \approx 1/3$) supports an SN-driven,
turbulence-regulated origin. Neutral gas is generally
turbulence-dominated and in near equipartition with
magnetic energy for systems with sSFR $\gtrsim 0.1$ Gyr$^{-1}$ and SFR $\gtrsim 1$ $M_\odot$ yr$^{-1}$. The simulated trends match observations with similar slopes ($\alpha \approx 0.25$-$0.35$), indicating that SN-driven
turbulence is the main amplification mechanism behind the near-universal $B$-SFR relation.
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All authors Davide Belfiori, Sergio Martin-Alvarez, Enrique Lopez-Rodriguez, Rosita Paladino
Solar and Stellar Astrophysics · Cross-listed from physics.ed-ph
Ensuring Outcome-Based Curriculum Coherence through Systematic CLO-PLO Alignment and Feedback Loops
Moncef Derouich
This study proposes a quantitative framework to enhance curriculum coherence through the systematic
alignment of Course Learning Outcomes (CLOs) and Program Learning Outcomes (PLOs), contributing to continuous improvement in outcome-based education. Grounded in accreditation standards such as ABET and NCAAA, the model introduces mathematical tools that map exercises, assessment questions, teaching units (TUs), and student assessment components (SACs) to CLOs and PLOs. This dual-layer approach-combining micro-level analysis of assessment elements with macro-level curriculum evaluation-enables detailed tracking of learning outcomes and helps identify misalignments between instructional delivery, assessment strategies, and program objectives. The framework incorporates
alignment matrices, weighted relationships, and practical indicators to quantify coherence and evaluate course or program performance. Application of this model reveals gaps in outcome coverage and underscores the importance of realignment, especially when specific PLOs are underrepresented or CLOs are not adequately supported by assessments. The proposed model is practical, adaptable, and scalable, making it suitable for academic programs. Its systematic structure supports institutions in implementing evidence-based curriculum improvements and provides a reliable mechanism for aligning teaching practices with desired learning outcomes. Ultimately, this framework offers a valuable tool for closing the feedback loop between instructional design, assessment execution, and learning outcomes, thus promoting greater transparency, accountability, and educational effectiveness. Institutions that adopt this model can expect to strengthen their quality assurance processes and help ensure that students graduate with the competencies required by academic standards and professional expectations.
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Earth and Planetary Astrophysics
Atmospheric collapse and re-inflation through impacts for terrestrial planets around M dwarfs
Prune C. August, Robin Wordsworth, Mikayla Huffman et al. (+2 more)
Detection of an atmosphere around a terrestrial
exoplanet will be a major milestone in the field, but our observational capacities are biased towards to tidally locked, close-in
planets orbiting M-
dwarf stars. The atmospheres of these
planets are vulnerable to atmospheric erosion and collapse due to condensation of volatiles on the nightside. However, these collapsed volatiles accumulated as nightside ice constitute a stable reservoir that could be re-vaporised by meteorite impacts and re-establish the atmospheres. Through a simple energy balance model applied to atmospheric
evolution simulations with
stochastic impacts, we assess the viability and importance of this mechanism for CO$_2$ atmospheres. We find that moderate-sized impactors ($5-10 \rm{km}$ diameter) occurring at a frequency of $1-100 \rm{Gyr}^{-1}$ can regenerate observable transient atmospheres on previously airless
planets. We focus on specific targets from the JWST DDT Rocky Worlds programme, and compute the fraction of their
evolution spent with a transient CO$_2$ atmosphere generated through this mechanism. We find this fraction can reach $70\%$ for GJ 3929 b, $50\%$ for LTT 1445 Ac, $80\%$ for LTT 1445 Ab, at high impact rates and strong CO$_2$ outgassing over the
planet's lifetime. We also show that atmospheric collapse can shield volatiles from escape, particularly in the early, high-XUV phase of M-
dwarf evolution. Overall, our work suggests that terrestrial
planet atmospheres may not evolve monotonically but instead may be shaped by episodic external forcings.
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All authors Prune C. August, Robin Wordsworth, Mikayla Huffman, David Brain, Lars A. Buchhave
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Beyond general relativity: gravitational waves in non-minimally coupled theories
Stephon Alexander, Tatsuya Daniel and Tucker Manton
Non-minimal couplings between matter and
curvature tensors arise in many different contexts. Such couplings modify solutions of general relativity (GR) and therefore can be probed in various astrophysical systems. A particularly interesting scenario arises if dark matter experiences non-minimal couplings, as dark matter densities are expected to spike in the vicinity of binary black hole mergers. This gives a novel setting for simultaneously studying dark matter and (beyond) GR physics via observations of gravitational waves (GWs). In this work, we explore effects of various non-minimal couplings on GWs by working with a model-independent parameterization for left- and right-handed GW strains. We extend the parameterization proposed in \cite{Jenks:2023pmk,Daniel:2024lev} to include early-universe effects, and we write down the generic solution assuming slowly-varying matter fields. We then systematically apply our results to three models: Kalb-Ramond dark matter with dimension-four operators,
axion-dilaton-Chern-Simons-Gauss-Bonnet dimension-five operators, and dimension-six couplings to a (dark) vector field.
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Cosmology and Nongalactic Astrophysics
Mitigating gain calibration errors from EoR observations with SKA1-Low AA*
Eeshan Beohar, Abhirup Datta, Anshuman Tripathi et al. (+2 more)
The observations of the redshifted 21-cm signal from neutral hydrogen are a promising probe for understanding the
Cosmic Dawn and the Epoch of Reionisation (EoR). One of the primary obstacles to the statistical detection of the Cosmological signal is the presence of residual foreground arising from gain calibration errors. Previous studies have shown that gain calibration errors as small as 0.01$\%$ can lead to a biased interpretation of the observed signal power spectrum estimation, by nearly an order of magnitude. A recent study further highlights that to accurately retrieve astrophysical parameters, the threshold gain calibration error should be below 0.01$\%$. This work investigates the impact of residual extragalactic foregrounds arising from gain calibration errors on the efficacy of foreground mitigation strategies. We use an end-to-end pipeline $\textsc{21cmE2E}$ to simulate a realistic sky model and
telescope configuration within the 138-146 MHz frequency range and perform a detailed power spectrum analysis across several threshold levels of the gain calibration error. We introduce a hybrid mitigation technique that combines the foreground removal techniques, Gaussian process regression and principal component analysis, with foreground avoidance. Our results indicate that recovery of the \HI\ signal within 2$\sigma$ is possible for calibration gain error of $\leq 1\%$ with minimal loss of power spectrum sensitivity over the scale range $0.05 \leq k \leq 0.5$ Mpc$^{-1}$. We find that gain calibration errors beyond this threshold lead to signal suppression on large scales due to the loss of spectral smoothness of the residual foreground. In effect, this work offers a comparative assessment of three foreground mitigation strategies, removal, avoidance, and a hybrid approach, in the context of future SKA1-Low AA* observations.
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All authors Eeshan Beohar, Abhirup Datta, Anshuman Tripathi, Samit Kumar Pal, Rashmi Sagar
Astrophysics of Galaxies
A three-dimensional reconstruction of the interstellar magnetic field toward a star-forming region
Katia Ferrière, Ludovic Montier and Jean-Sébastien Carrière
Context. The polarized thermal emission from interstellar
dust offers a valuable tool for probing both the
dust and the
magnetic field in the interstellar medium (ISM). However, existing observations only yield the total amount of
dust emission along the line of sight (LoS), with no information on its LoS distribution. Aims. We present a new method designed to give access to the LoS distribution of the
dust emission, both in terms of intensity and polarization. Methods. We relied on three kinematic gas tracers (HI, 12CO, and 13CO emission lines) to identify the different clouds present along the LoS. We decomposed the measured intensity of the
dust emission, $I_d$, into separate contributions from these clouds. We performed a similar decomposition of the measured Stokes parameters for linear polarization, $Q_d$ and $U_d$, to derive the polarization parameters of the different clouds, and from this we inferred the clouds'
magnetic field orientations. Results. We applied our method to a $3~{\rm deg}^2$ region of the sky, centered on $(l,b) = (139{\deg}30',-3{\deg}16')$ and exhibiting signs of
star formation activity. We found this region to be dominated by an extended and bright cloud with nearly horizontal
magnetic field, as expected from the nearly vertical polarization angles measured by Planck. More importantly, we detected the presence of two smaller, depolarizing molecular clouds with very different
magnetic field orientations in the plane of the sky ($\simeq 65{\deg}$ and $\simeq 45{\deg}$ from the horizontal). This is a novel and viable result, which cannot be directly read off the Planck polarization maps. Conclusions. The application of our method to the G139 region convincingly demonstrates the need to complement 2D polarization maps with 3D kinematic information when looking for reliable estimates of
magnetic field orientations.
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Astrophysics of Galaxies
Chemical separation of stellar populations: analytic solutions for chemical evolution models with metallicity-dependent yields
Jason L. Sanders
Stellar abundances of elements with production channels that are
metallicity-dependent (most notably aluminium) have provided an empirical route for separating different
Galactic components. We present 'single-zone' analytic solutions for the chemical
evolution of
galaxies when the
stellar yields are
metallicity-dependent. Our solutions assume a constant
star formation efficiency, a constant mass-loading factor and that the yields are linearly dependent on the interstellar medium abundance (with the option of a saturation of the yields at high
metallicity). We demonstrate how the
metallicity dependence of the yields can be mathematically considered as a system-dependent delay time (approximately equal to the system's depletion time) that, when combined with system-independent delay times arising from
stellar evolutionary channels, produces the separation of different systems based on their
star formation efficiency and mass-loading factor. The utility of the models is highlighted through comparisons with data from the APOGEE spectroscopic survey. We provide a comprehensive discussion of the chemical
evolution models in the [Al/Fe]-[Mg/Fe] plane, a diagnostic plane for the separation of in-situ and accreted
Galactic components. Extensions of the models are presented, allowing for the modelling of more complex behaviours largely through the linear combination of the presented simpler solutions.
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High Energy Astrophysical Phenomena
25 Years of Groundbreaking Discoveries with Chandra
Patrick Slane, Ákos Bogdán and David Pooley
The Chandra X-ray Observatory is a mainstay of modern observational astrophysics. With the highest angular resolution of any X-ray facility, its imaging and spectral capabilities in the 0.5-10 keV band have led to both unique and complementary breakthroughs in nearly all areas of the field. Now more than a quarter century into its mission, Chandra continues to provide unique information on the contributions of compact objects to the
evolution of
galaxies, the nature of
supernova explosions, the impact of energetic jets from supermassive black holes on their host environments, and the fate of
exoplanet atmospheres in systems rich with
stellar flares. Here we provide a summary of Chandra results - one that is embarrassingly incomplete, but representative of both the exquisite past and promising future for Chandra's contributions to high energy astrophysics and all of mainstream astronomy.
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Astrophysics of Galaxies
Resolved HII regions in NGC 253: Ionized gas structure and suggestions of a universal density-surface brightness relation
Rebecca L. McClain, Adam K. Leroy, Enrico Congiu et al. (+23 more)
We use the full-disk VLT-MUSE mosaic of NGC 253 to identify 2492 HII regions and study their resolved structure. With an average physical resolution of 17 pc, this is one of the largest samples of highly resolved spectrally mapped extragalactic HII regions. Regions of all luminosities exhibit a characteristic emission profile described by a double Gaussian with a marginally resolved or unresolved core with radius <10 pc surrounded by a more extended
halo of emission with radius 20-30 pc. Approximately 80% of the emission of a region originates from the
halo component. As a result of this compact structure, the luminosity-radius relations for core and effective radii of HII regions depend sensitively on the adopted methodology. Only the isophotal radius yields a robust relationship in NGC 253, but this measurement has an ambiguous physical meaning. We invert the measured emission profiles to infer density profiles and find central densities of n_e = 10-100 cm-3. In the brightest regions, these agree well with densities inferred from the [SII]6716,30 doublet. The central density of HII regions correlates well with the surface brightness within the effective radius. We show that this same scaling relation applies to the recent MUSE+HST catalog for 19 nearby
galaxies. We also discuss potential limitations, including completeness, impacts of background subtraction and spatial resolution, and the generality of our results when applied to other
galaxies.
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All authors Rebecca L. McClain, Adam K. Leroy, Enrico Congiu, Ashley. T. Barnes, Francesco Belfiore, Oleg Egorov, Eric Emsellem, Erik Rosolowsky, Amirnezam Amiri, Mederic Boquien, Jeremy Chastenet, Ryan Chown, Daniel A. Dale, Sanskriti Das, Simon C. O. Glover, Kathryn Grasha, Remy Indebetouw, Eric W. Koch, Smita Mathur, J. Eduardo Mendez-Delgado, Elias K. Oakes, Hsi-An Pan, Karin Sandstrom, Sumit K. Sarbadhicary, Bradley C. Whitmore, Thomas G. Williams
Solar and Stellar Astrophysics
New Pipeline for Efficient Analysis of Large Spectroscopic Samples of OB Stars
PA Crowther and JM Bestenlehner
We present a new spectroscopic pipeline designed to analyse large numbers of hot massive
stars homogeneously. The pipeline has been developed to utilise large grids of FASTWIND non-LTE, line blanketed models in which spherical geometry is adopted, and uniquely incorporates model errors. The pipeline has been applied to three contemporary
datasets involving Very Large
Telescope spectroscopy of OB
stars in the Magellanic Clouds, namely the VLT FLAMES Tarantula Survey (VFTS), XShooting-ULLYSES (XShootU) and Binaries at Low
Metallicity (BLOeM). We find satisfactory agreement with previous detailed temperatures and surface gravities, although strong nebular contamination, binarity and disk emission from OBe
stars are problematic for automatic pipelines, requiring visual inspection of fits. The tool has been incorporated into the pipeline for the VISTA/4MOST pipeline.
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Solar and Stellar Astrophysics
WOCS XCIII: NGC 7789: the Evolution of Li, Stellar Rotation, and Extended Main Sequence Turnoffs
Barbara J. Anthony-Twarog, Samantha W. Brunker, Constantine P. Deliyannis et al. (+4 more)
Precision UBVRI photometry of NGC 7789 is combined with
Gaia data to map reddening variations across the cluster face. HYDRA spectra,
Gaia astrometry, and isochrone fitting constrain the absolute reddening, apparent modulus, and age to E(B-V) = 0.30 +/- 0.02, (m-M)=12.51 +/- 0.06, and 1.46 +/- 0.02 Gyr for [Fe/H] between -0.2 and
solar; the spectroscopic [Fe/H] = -0.13 +/- 0.068 (MAD) from 156 single-
star members. Corrections for variable reddening reduce the scatter in the unevolved main sequence below the turnoff. A(Li) is derived for only single
star members from the G-
dwarf Li-Plateau to the tip of the red
giant branch.
Giants separate into two distinct groups, probable first-ascent
giants with detectable Li that declines with
evolution toward the red
giant tip and
stars within the clump and the asymptotic
giant branch which only exhibit upper limits. A(Li) structure from the turnoff to the unevolved main sequence, including the Li-Dip, and the presence of an extended color spread among the upper main sequence
stars are attributed to the V_ROT distribution, indicating the wall of the Li-Dip as the true hot boundary of the Kraft break. Differences in the color-magnitude diagram
topology of NGC 7789 and NGC 752 are explored and attributed to differences in the individual cluster V_ROT distributions. Prior indications that main sequence
stars more massive than the Li-Dip evolve redward across the Li-Wall, undergoing rotational spindown and Li depletion like
stars within the Li-Dip, are confirmed.
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All authors Barbara J. Anthony-Twarog, Samantha W. Brunker, Constantine P. Deliyannis, Evan Rich, Aaron Steinhauer, Qinghui Sun, Bruce A. Twarog
Astrophysics of Galaxies
Spiral Structure Diversity in Milky Way Analogs from TNG50: The Role of Gas and Disk Dynamics
Soumavo Ghosh and Elena D'Onghia
The generation of spiral arms and the mechanisms controlling their properties within a realistic cosmological framework - the complete understanding is still beyond our grasp. Using a statistically significant sample of Milky Way- and Andromeda-like (MW/M31) analogs from the high-resolution TNG50 cosmological simulation, we carry out the first systematic investigation of spiral-arm formation, their observable properties, and the underlying physical drivers. The selected analogs predominantly exhibit two-armed ($m = 2$) spirals in both
stars and gas, while the gaseous disks often display stronger, more tightly wound, and multi-armed patterns ($m>2$). Spiral features appear across
stellar populations of different ages, confirming their density-wave nature and producing coherent spirals in both
metallicity and mean
stellar age distributions-consistent with recent
Gaia observations of the Milky Way. Our analysis reveals a diverse dynamical scenario for spiral generation: gas content, disk coldness, and shear jointly regulate the growth and morphology of spiral perturbations. We find that the gas content and the dynamical coldness of the disk jointly regulate spiral growth:
galaxies with higher gas fractions and colder disks develop more prominent spirals. The measured relation between spiral pitch angle and disk shear shows significant scatter around the analytic prediction, likely due to the combined influence of bars, gas inflows, and feedback. These results demonstrate that spiral density waves can persist in fully cosmological disks, linking internal dynamical processes to
galaxy assembly and offering testable predictions for present and future surveys such as JWST and Roman.
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Instrumentation and Methods for Astrophysics
Braginskii Viscosity in Cosmological Simulations of Galaxy Clusters: Implementation, Validation, and First Application
Tirso Marin-Gilabert, Ulrich P. Steinwandel, Milena Valentini et al. (+2 more)
We present the implementation of an anisotropic viscosity solver within the magnetohydrodynamics (MHD) framework of the TreeSPH code OpenGadget3. The solver models anisotropic viscous transport along
magnetic field lines following the Braginskii formulation and includes physically motivated limiters based on the mirror and firehose instability thresholds, which constrain the viscous stress in weakly collisional
plasmas. To validate the implementation, we performed a suite of standard test problems – including two variants of the sound wave test, circularly and linearly polarized Alfven waves, fast magnetosonic wave, and the Kelvin-Helmholtz instability – both with and without the
plasma-instability limiters. The results show excellent agreement with the AREPO implementation of a similar anisotropic viscosity model, confirming the accuracy and robustness of our method. Our formulation integrates seamlessly within the individual adaptive timestepping framework of OpenGadget3, avoiding the need for subcycling. This provides efficient and stable time integration while maintaining physical consistency. Finally, we applied the new solver to a cosmological zoom-in simulation of a
galaxy cluster as a proof-of-concept application, demonstrating its capability to model anisotropic transport and
plasma microphysics in realistic large-scale environments. Our implementation offers a versatile and computationally efficient tool for studying anisotropic viscosity in magnetized astrophysical systems.
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All authors Tirso Marin-Gilabert, Ulrich P. Steinwandel, Milena Valentini, John A. ZuHone, Klaus Dolag
Astrophysics of Galaxies
Figuring Out Gas & Galaxies In Enzo (FOGGIE) XI: Circumgalactic O VI Emission Traces Clumpy Inflowing Recycled Gas
Cassandra Lochhaas, Molly S. Peeples, Brian W. O'Shea et al. (+11 more)
The circumgalactic medium (CGM) is host to gas flows into and out of
galaxies and regulates
galaxy growth, but the multiphase, diffuse gas in this region is challenging to observe. We investigate the properties of gas giving rise to O VI emission from the CGM that upcoming missions, such as the Aspera SmallSat, will be able to map in local
galaxies. We use the FOGGIE simulations to predict the O VI emission from edge-on
galaxies across the
redshift range $z=1\rightarrow0$. O VI emission is brightest surrounding small, clumpy structures near the
galaxy where the gas density is high. Most of the O VI surface brightness originates from collisionally ionized, $T\sim10^{5.5}$ K, inflowing gas and is not preferentially aligned with the major or minor axis of the
galaxy disk. Simulated
galaxies with higher
halo masses, higher median CGM gas density, and higher
star formation rates produce brighter and more widespread O VI emission in their CGM. We show that while O VI emission primarily originates in inflowing gas, turning off
outflows in a simulation without
star formation feedback eliminates most of the O VI emission. Enrichment from feedback is necessary to mix with the inflowing gas and allow it to glow in O VI. Collectively, our findings point towards a picture where O VI emission traces warm, ionized envelopes of cooler clouds that are accreting onto the
galaxy in a metal-enriched
galactic fountain. Finally, we show that the detection limit of Aspera is sufficient to detect O VI emission tens of kpc from the
galaxy center for $\sim L^\star$
galaxies.
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All authors Cassandra Lochhaas, Molly S. Peeples, Brian W. O'Shea, Jason Tumlinson, Lauren Corlies, Vida Saeedzadeh, Nicolas Lehner, Anna C. Wright, Jessica K. Werk, Cameron W. Trapp, Ramona Augustin, Ayan Acharyya, Britton D. Smith, Carlos J. Vargas
High Energy Astrophysical Phenomena
Demystifying flux eruptions: Magnetic flux transport in magnetically arrested disks
Jonatan Jacquemin-Ide, Mitchell C. Begelman, Beverly Lowell et al. (+3 more)
Magnetically arrested disks (MADs) are a compelling model for explaining variability in low-luminosity active
galactic nuclei (AGN), including horizon-scale outbursts like those observed in Sagittarius A*. MADs experience powerful flux eruptions-episodic ejections of
magnetic flux from the black hole horizon-that may drive the observed luminosity variations. In this work, we develop and validate a new formalism describing large-scale
magnetic field transport in general relativistic magnetohydrodynamic simulations of MADs with geometrical thicknesses of $h/R=0.1$ and $h/R=0.3$. We introduce a net flux transport velocity, $v_\Phi$, which accounts for both advective and diffusive processes. We show that MADs maintain a statistical quasi-steady state where advection and
diffusion nearly balance. Flux eruptions appear as small deviations from this
equilibrium, with $v_\Phi/V_k\ll1$, where $V_k$ is the local Keplerian velocity. Using this framework, we analytically derive a recurrence timescale for flux eruptions, $t_{\rm rec}\sim1500\, r_g/c$. This timescale closely matches simulation results. The smallness of $v_\Phi$ explains the long recurrence times of flux eruptions compared to other system timescales. We also take a closer look at the
diffusion of the
magnetic field by performing the first measurement of turbulent resistivity in MADs. We then estimate the turbulent
magnetic Prandtl number, defined as the ratio of turbulent viscosity to turbulent resistivity. We find $\mathcal{P}_m\sim3$, consistent with shearing-box simulations of magneto rotational instability-driven
turbulence. While flux eruptions excite large-scale non-axisymmetric modes and locally enhance turbulent resistivity,
magnetic field
diffusion is dominated by smaller-scale turbulent motions. These results provide new insight into the nature of AGN variability and the fundamental physics of
magnetic field transport.
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All authors Jonatan Jacquemin-Ide, Mitchell C. Begelman, Beverly Lowell, Matthew Liska, Jason Dexter, Alexander Tchekhovskoy
Astrophysics of Galaxies
Exploring the quasar disc-wind-jet connection with LoTSS and SDSS
Charlotte L. Jackson, James H. Matthews, Imogen H. Whittam et al. (+4 more)
We investigate the relationship between disc winds,
radio jets,
accretion rates and black hole masses of a sample of $\sim$100k
quasars at z $\approx$ 2. Combining spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS) with
radio fluxes from the 2nd data release of the Low Frequency ARray (LOFAR) Two-Meter Sky Survey (LoTSS), we statistically characterise a
radio loud and
radio quiet population using a two-component Gaussian Mixture model, and perform population matching in black hole mass and Eddington fraction. We determine how the fraction of
radio loud sources changes across this parameter space, finding that jets are most efficiently produced in
quasars with either a very massive central black hole ($M_{\textrm{BH}} > 10^9 \textrm{M}_{\odot}$) or one that is rapidly accreting ($\lambda_{\textrm{Edd}}>0.3$). We also show that there are differences in the blueshift of the CIV $\lambda$1549Å line and the equivalent width of the HeII $\lambda$1640Å line in
radio loud and
radio quiet
quasars that persist even after accounting for differences in the mass and
accretion rate of the central black hole. Generally, we find an anti-correlation between the inferred presence of disc winds and jets, which we suggest is mediated by differences in the
quasars' spectral energy distributions. The latter result is shown through the close coupling between tracers of wind kinematics and the ionising flux – which holds for both
radio loud and
radio quiet sources, despite differences between their emission line properties – and is hinted at by a different Baldwin effect in the two populations.
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All authors Charlotte L. Jackson, James H. Matthews, Imogen H. Whittam, Matt J. Jarvis, Matthew J. Temple, Amy L. Rankine, Paul C. Hewett
Astrophysics of Galaxies
Model-Independent Inference of Galaxy Star Formation Histories in the Local Volume
Robin Eappen and Pavel Kroupa
Understanding the diversity of
star formation histories (SFHs) of
galaxies is key to reconstructing their evolutionary paths. Traditional models often assume parametric forms such as delayed-tau or exponentially declining models, which may not reflect the actual variety of formation processes. We aim to assess what types of SFHs are consistent with the observed present-day
star formation rates (${\text{SFR}}_0$) and time-averaged
star formation rates ($\langle \text{SFR} \rangle$) of
galaxies in the Local Volume, without assuming any fixed functional form. We construct a non-parametric framework by generating large ensembles of randomized SFHs for each
galaxy in the sample. For each SFH, we compute its predicted
stellar mass and present-day SFR and retain only those consistent with the observed values within a 20% tolerance. We then infer the statistical distribution of power-law slopes $\eta$ (fitted as ${\text{SFR}}(t) \propto (t-t_{\text{start}})^\eta$) and 50%
stellar mass formation times $t_{50}$. Both $\eta$ and $t_{50}$ correlate strongly with the SFR ratio (Spearman $\rho > 0.75$, $p \ll 10^{-16}$), indicating that the shape and timing of
star formation are primarily governed by this ratio. The $t_{50}$ distribution shows sharp spikes near 7.74 and 7.86 Gyr, which we attribute to grid discretization combined with filtering, rather than a physical bimodality. Our results confirm that strongly declining SFH templates are disfavored in the Local Volume: most systems are consistent with flat long-term SFHs, with only mild decline or occasional rising. Importantly, this is demonstrated through a fully model-independent, data-driven approach, with per-
galaxy uncertainties quantified using the standard error of $\eta$ and $t_{50}$ from the ensemble of accepted SFHs.
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Astrophysics of Galaxies
Extended Components of Little Red Dots in the Rest-Frame Optical
Yiyang Zhang, Xuheng Ding, Lilan Yang et al. (+26 more)
Recent JWST observations have revealed a population of red, compact, high-
redshift objects called Little Red Dots (LRDs), whose host components have remained largely unconstrained, possibly due to their extreme compactness. Current morphological studies suggest the presence of extended emission in LRDs at rest-frame ultraviolet wavelengths. However, in the rest-frame optical regime, investigations have been limited by small sample sizes and insufficient imaging depth, hindering reliable separation between point-like and potential extended components. Here we perform the image stacking analysis of 217 LRDs in four NIRCam bands, a large and homogeneous sample observed with the COSMOS-Web survey. Our results reveal the detection of faint extended emission in the F444W band, with a typical size of ~200 parsecs and magnitude of ~27.7 AB at z~6.5. We perform four-band photometric spectral energy distribution fitting based on
galaxy templates and derive an average
stellar mass of log(M*/M_sun) = 9.02 +0.20/-0.18. Given this
stellar mass, the host
galaxy is compact, that is, ~2.5 times smaller than
star-forming
galaxies of similar mass at comparable
redshifts. This work provides direct observational evidence for the existence of LRD host
galaxies at rest-frame optical wavelengths and offers new insights into the
stellar buildup of these systems within the first billion years after the Big Bang.
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All authors Yiyang Zhang, Xuheng Ding, Lilan Yang, Erini Lambrides, Hollis Akins, Andrew J. Battisti, Caitlin M. Casey, Chang-hao Chen, Isa Cox, Andreas Faisst, Maximilien Franco, Aryana Haghjoo, Luis C. Ho, Kohei Inayoshi, Shuowen Jin, Mitchell Karmen, Anton M. Koekemoer, Jeyhan S. Kartaltepe, Kai Liao, Ghassem Gozaliasl, Masafusa Onoue, Vasily Kokorev, Namrata Roy, R. Michael Rich, John D. Silverman, Takumi S. Tanaka, Bei You, Hassen M. Yesuf, Jorge A. Zavala
Cosmology and Nongalactic Astrophysics
Updated dark pixel fraction constraints on reionization's end from the Lyman-series forests of XQR-30
Frederick B. Davies, Sarah E. I. Bosman, Valentina D'Odorico et al. (+16 more)
The fraction of "dark pixels" in the Ly$\alpha$ and other Lyman-series forests at $z\sim 5-6$ provides a powerful constraint on the end of the reionization process. Any spectral region showing transmission must be highly ionized, while dark regions could be ionized or neutral, thus the dark pixel fraction provides a (nearly) model independent upper limit to the volume-filling fraction of the neutral intergalactic medium, modulo choices in binning scale and dark pixel definition. Here we provide updated measurements of the 3.3 comoving Mpc dark pixel fraction at $z=4.85-6.25$ in the Ly$\alpha$, Ly$\beta$, and Ly$\gamma$ forests of 34 deep $5.8\lesssim z\lesssim 6.6$
quasar spectra from the (enlarged) XQR-30 sample. Using the negative pixel method to measure the dark pixel fraction, we derive fiducial $1\sigma$ upper limits on the volume-average neutral hydrogen fraction of $\langle x_{\rm{HI}}\rangle \leq \{0.030 + 0.048, 0.095 + 0.037, 0.191 + 0.056, 0.199 + 0.087\}$ at $\bar{z} = \{5.481, 5.654, 5.831, 6.043\}$ from the optimally sensitive combination of the Ly$\beta$ and Ly$\gamma$ forests. We further demonstrate an alternative method that treats the forest flux as a mixture of dark and transparent regions, where the latter are modeled using a physically-motivated parametric form for the intrinsic opacity distribution. The resulting model-dependent upper limits on $\langle x_{\rm{HI}}\rangle$ are similar to those derived from our fiducial model-independent analysis. We confirm that the bulk of reionization must be finished at $z>6$, while leaving room for an extended "soft landing" to the reionization history down to $z\sim 5.4$ suggested by Ly$\alpha$ forest opacity fluctuations.
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All authors Frederick B. Davies, Sarah E. I. Bosman, Valentina D'Odorico, Sofia Campo, Andrei Mesinger, Yuxiang Qin, George D. Becker, Eduardo Bañados, Huanqing Chen, Stefano Cristiani, Xiaohui Fan, Simona Gallerani, Martin G. Haehnelt, Laura C. Keating, Samuel Lai, Emma Ryan-Weber, Feige Wang, Jinyi Yang, Yongda Zhu
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
$\lambda\phi^4$ as an Effective Theory in de Sitter
Sebastian Cespedes, Zhehan Qin and Dong-Gang Wang
Effective field theories (EFTs) provide a powerful framework to parametrise unknown aspects of possible ultraviolet (UV) physics. For scalar fields in de Sitter space, however, new emergent phenomena can arise when the cut-off scale of the theory lies below the horizon scale $H$, as seen in the
stochastic formalism of inflation. In this work, we study EFTs that, at leading order, reproduce the standard quartic theory in de Sitter, but with a variable cut-off identified with the mass of an integrated-out hidden sector. We perform the complete analytic computation for the tree- and loop-level matching between the effective $\lambda\phi^4$ theory and two possible UV realisations. We find that when the cut-off is much larger than the horizon, the theory admits a
unitary description, up to exponentially suppressed corrections. In contrast, when the cut-off is lowered below $H$, the system evolves into a mixed state and diffusive effects emerge. Nevertheless, at leading order, the EFT remains local and reproduces the same effective quartic coefficient as in the
unitary regime. Furthermore, for the EFT matching at the loop-level, the effective quartic coupling changes sign and becomes negative as the cut-off decreases, in agreement with the result obtained from the
stochastic formalism. In general, for cosmological EFTs, our findings highlight the role of non-
unitary effects and illustrate their regimes of validity, within and beyond perturbation theory.
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Instrumentation and Methods for Astrophysics
The Ray Tracing Sampler: Bayesian Sampling of Neural Networks for Everyone
Peter Behroozi
We derive a family of Markov Chain Monte Carlo (MCMC) sampling methods based on following ray paths in a medium where the refractive index $n(x)$ is a function of the desired likelihood $\mathcal{L}(x)$, extending past work on isokinetic sampling. The simplest ray tracing method propagates rays at constant speed through parameter space, leading to orders of magnitude higher resilience to heating for
stochastic gradients as compared to both
Hamiltonian Monte Carlo (HMC) and
Stochastic Gradient HMC, as well as the ability to cross any likelihood barrier, including holes in parameter space. Using the simplest ray tracing method, we sample the posterior distributions of neural network outputs for a variety of different architectures, including a preliminary exploration of the 1.5 billion-parameter GPT-2 (Generative Pre-trained
Transformer 2) architecture, all on a single consumer-level GPU. We also show that prior samplers including traditional HMC, the original microcanonical HMC, Metropolis, Gibbs, and even Monte Carlo integration are special cases within a generalized ray tracing framework, which can sample according to an arbitrary weighting function. Public code and documentation for C, JAX, and PyTorch are available at https://bitbucket.org/pbehroozi/ray-tracing-sampler/src
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Cosmology and Nongalactic Astrophysics
The kSZ optical depth degeneracy and future constraints on local primordial non-Gaussianity
Avery J. Tishue, Charuhas Shiveshwarkar and Gilbert Holder
Recent reconstructions of the large-scale cosmological velocity field with kinetic Sunyaev Zeldovich (kSZ)
tomography have returned an amplitude that is low with respect to the
halo model prediction, captured by the kSZ velocity reconstruction bias $b_v <1$. This suggests that common choices for modeling the
galaxy-electron cross correlation have systematically overestimated the true power, at least over scales and
redshifts used in the velocity reconstruction measurements. In this paper, we study the implications of this overestimation for constraints on local-type
primordial non-Gaussianity in current and near-future cosmological surveys. For concreteness, we focus on kSZ velocity reconstruction from a Vera Rubin Observatory-like survey in tandem with contemporary
cosmic microwave background measurements. Assuming standard choices for the fiducial model of the small-scale
galaxy-electron cross correlation, we find that upcoming kSZ
tomography measurements can significantly improve constraints on local
primordial non-Gaussianity via measurement of scale-dependent
galaxy bias, in broad concordance with previous studies of the application of kSZ
tomography to
primordial non-Gaussianity. However, when we instead modify the assumed
galaxy-electron cross-spectrum to be consistent with recent measurements of the velocity reconstruction bias, this picture can change appreciably. Specifically, we find that if the inferred suppression of
galaxy-electron power persists at higher
redshifts $z\gtrsim 1$, kSZ-driven improvement in local
primordial non-Gaussianity constraints may be less significant than previously estimated. We explore how these conclusions depend on various modeling and experimental assumptions and discuss implications for the emerging program of kSZ velocity reconstruction.
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Solar and Stellar Astrophysics
Tidally driven inertial waves enhance eccentricity damping and spin evolution in planets and stars
Janosz W. Dewberry
Tidal interactions influence the orbital motions of binary
star systems and extrasolar
planets alike. Tides also affect
stellar and planetary rotation rates. We demonstrate that in addition to altering
spin synchronization and pseudosynchronization, tidally driven inertial waves in the convective envelopes of low-mass
stars and gas
giant planets can enhance
tidal eccentricity damping. Analytically, we find that eccentricity damping by inertial waves can be orders of magnitude faster than
equilibrium tides, independent of any eddy viscosity prescription. We use simplified numerical experiments to demonstrate this enhancement, and to explore the effects of different mixing length treatments of convective
turbulence, as well as a
spin-down torque from
magnetic braking. These calculations demonstrate that tidally driven inertial waves can produce an extended cool core of nearly circular binaries, helping to reconcile a longstanding discrepancy between observed and predicted main-sequence binary circularization. Our calculations additionally suggest that tidally driven inertial waves may leave identifiable signatures in the ratios of orbital to rotation periods for
stellar binaries, including synchronous and sub-synchronous rotation periods reminiscent of populations identified in Kepler, TESS, and
Gaia data.
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