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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 13 November

Astrophysics of Galaxies

Back to basics: Little Red Dots as galaxies and dust-obscured AGNs in a synthetic NIRCam sky simulated with L-GalaxiesBH

Diego Herrero-Carrión, Daniele Spinoso, David Izquierdo-Villalba et al. (+3 more)

The enigmatic Little Red Dots (LRDs) discovered by the James Webb Space Telescope (JWST) exhibit properties challenging their interpretation as common galaxies or Active Galactic Nuclei (AGN). Understanding their nature is key to placing them within our picture of early galaxy and massive black hole (MBH) evolution. To this aim, we build a realistic comparison between LRD observations with photometric properties of galaxies and AGN simulated by the L-GalaxiesBH model in a NIRCam mock sky. We model stellar continua and emission lines, the MBH emission from accretion disk, infrared radiation from dusty torus, and lines from narrow and broad line regions, accounting for dust attenuation and obscuration. Using realistic photometric cuts, we select a population of LRDs including both AGN and galaxies. The LRD fraction peaks at 40% ($\sim10^{-4}\rm Mpc^{-3}$) at $z\sim4$. Our LRDs are central galaxies spanning $M_*=10^8-10^{10.5}\rm M_\odot$. A population of galaxies with $M_*<10^9\rm M_\odot$ appear as LRDs due to older stellar populations. At higher masses, LRDs dominate the halo and stellar mass functions ($M_{\rm vir} > 10^{11.5}\rm M_\odot$, $M_* > 10^{9.5}\rm M_\odot$), and the interplay between AGN and galaxy emission drives the LRD selection. AGN dominate rest-frame UV-optical emission, while dust obscuration is secondary. LRDs host lighter MBHs ($\sim 10^{6.5}\rm M_\odot$) than non-LRDs ($\sim 10^{7.5}\rm M_\odot$), with fainter emission unable to balance their hosts Balmer breaks. We find no evidence for dominant heavy-seed origin of MBHs. LRD Galaxies (97% hosting MBHs) and LRD AGNs are disk-dominated, with LRD AGNs showing larger bulges formed mainly via disk instabilities.
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All authors Diego Herrero-Carrión, Daniele Spinoso, David Izquierdo-Villalba, Tong Su, Silvia Bonoli, Pablo Renard

Astrophysics of Galaxies

Reaching for the Edge II: Stellar Halos out to Large Radii as a Tracer of Dark Matter Halo Mass

Katya Leidig, Benedikt Diemer, Song Huang et al. (+3 more)

The diffuse outskirts of brightest cluster galaxies (BCGs) encode valuable information about the assembly history and mass of their host dark matter halos. However, the low surface brightness of these stellar halos has historically made them difficult to observe. Recent deep imaging, particularly with Hyper Suprime-Cam (HSC), has shown that the stellar mass within relatively large projected annuli, such as within $50$ and $100$ kpc, is a promising proxy for halo mass. However, the optimal radial definition of this "outskirt mass" remains uncertain. We construct an HSC-like mock observing pipeline to measure the stellar mass density profiles of BCGs in the IllustrisTNG simulations. Our mock observations closely reproduce HSC profiles across six orders of magnitude in surface density. We then systematically measure stellar masses within different annuli and how tightly they are connected to halo mass. We find that stellar masses measured within simple apertures exhibit considerably more scatter in the stellar mass-halo mass relation than those measured within projected ellipsoidal annuli. We identify an optimal range of definitions, with inner radii between $\sim 70$-$200$ kpc and outer radii between $\sim 125$-$500$ kpc. We also introduce two halo-mass-dependent Sérsic models for the average stellar halo profiles. We present a Sérsic-based fitting function that describes the profiles as a function of the halo mass, $M_{\rm vir}$, with a median error of $54\%$. Adding the central stellar mass of the BCG as a second parameter slightly improves the accuracy to a median error of $39\%$. Together, these results provide fitting functions for BCG stellar halos that can be applied to future wide-field surveys to infer halo masses from deep imaging data.
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All authors Katya Leidig, Benedikt Diemer, Song Huang, Shuo Xu, Conghao Zhou, Alexie Leauthaud

Instrumentation and Methods for Astrophysics

Practical Author Name Disambiguation under Metadata Constraints: A Contrastive Learning Approach for Astronomy Literature

Vicente Amado Olivo, Wolfgang Kerzendorf, Bangjing Lu et al. (+3 more)

The ability to distinctly and properly collate an individual researcher's publications is crucial for ensuring appropriate recognition, guiding the allocation of research funding and informing hiring decisions. However, accurately grouping and linking a researcher's entire body of work with their individual identity is challenging because of widespread name ambiguity across the growing literature. Algorithmic author name disambiguation provides a scalable approach to disambiguating author identities, yet existing methods have limitations. Many modern author name disambiguation methods rely on comprehensive metadata features such as venue or affiliation. Despite advancements in digitally indexing publications, metadata is often unavailable or inconsistent in large digital libraries(e.g. NASA/ADS). We introduce the Neural Author Name Disambiguator, a method that disambiguates author identities in large digital libraries despite limited metadata availability. We formulate the disambiguation task as a similarity learning problem by employing a Siamese neural network to disambiguate author names across publications relying solely on widely available publication metadata-author names, titles and abstracts. We construct the Large-Scale Physics ORCiD Linked dataset to evaluate the Neural Author Name Disambiguator by cross-matching NASA/ADS publications ORCiD. By leveraging foundation models to embed metadata into features, our model achieves up to 94% accuracy in pairwise disambiguation and over 95% F1 in clustering publications into their researcher identities. We release the testing dataset as a benchmark for physics and astronomy, providing realistic evaluation conditions for future disambiguation methods. The Neural Author Name Disambiguator algorithm demonstrates effective disambiguation with minimal metadata, offering a scalable solution for name ambiguity in large digital libraries.
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All authors Vicente Amado Olivo, Wolfgang Kerzendorf, Bangjing Lu, Joshua V. Shields, Andreas Flörs, Nutan Chen

Cosmology and Nongalactic Astrophysics

Analytical approximations for curved primordial tensor spectra

Ezra Msolla and Ayngaran Thavanesan

We build upon previous analytical treatments of scalar perturbations in curved inflationary universes to obtain analytical templates for the primordial tensor power spectrum in models with non-zero primordial spatial curvature. These templates are derived without assuming a particular inflaton potential, within a background history consisting of an initial kinetically dominated phase followed by an ultra-slow-roll inflationary regime, thereby isolating the universal imprints of curvature on tensor modes. Our results predict characteristic large-scale features – including low-$\ell$ cut-offs and oscillatory patterns – that are consistent with numerical solutions and provide a clear physical interpretation of how curvature modifies the underlying dynamics. In particular, we show that curvature effects manifest mathematically as systematic shifts in the dynamically relevant wavevectors, mirroring the behaviour previously identified in the scalar power spectrum. These features translate into distinctive signatures in the large-angle $B$-mode polarisation spectrum, offering a potential discriminant for spatial curvature in forthcoming CMB observations.
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Astrophysics of Galaxies

Flexible Simulation Based Inference for Galaxy Photometric Fitting with Synthesizer

Thomas Harvey, Christopher C. Lovell, Sophie Newman et al. (+13 more)

We introduce Synference, a new, flexible Python framework for galaxy SED fitting using simulation-based inference (SBI). Synference leverages the Synthesizer package for flexible forward-modelling of galaxy SEDs and integrates the LtU-ILI package to ensure best practices in model training and validation. In this work we demonstrate Synference by training a neural posterior estimator on $10^6$ simulated galaxies, based on a flexible 8-parameter physical model, to infer galaxy properties from 14-band HST and JWST photometry. We validate this model, demonstrating excellent parameter recovery (e.g. R$^2>$0.99 for M$_\star$) and accurate posterior calibration against nested sampling results. We apply our trained model to 3,088 spectroscopically-confirmed galaxies in the JADES GOODS-South field. The amortized inference is exceptionally fast, having nearly fixed cost per posterior evaluation and processing the entire sample in $\sim$3 minutes on a single CPU (18 galaxies/CPU/sec), a $\sim$1700$\times$ speedup over traditional nested sampling or MCMC techniques. We demonstrate Synference's ability to simultaneously infer photometric redshifts and physical parameters, and highlight its utility for rapid Bayesian model comparison by demonstrating systematic stellar mass differences between two commonly used stellar population synthesis models. Synference is a powerful, scalable tool poised to maximise the scientific return of next-generation galaxy surveys.
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All authors Thomas Harvey, Christopher C. Lovell, Sophie Newman, Christopher J. Conselice, Duncan Austin, William J. Roper, Aswin P. Vijayan, Stephen M. Wilkins, Patricia Iglesias-Navarro, Vadim Rusakov, Qiong Li, Nathan Adams, Kai Magdwick, Caio M. Goolsby, Marc Huertas-Company, Matthew Ho

Cosmology and Nongalactic Astrophysics

Baryonic Feedback across Halo Mass: Impact on the Matter Power Spectrum

Kyle Miller, Surhud More and Bhuvnesh Jain

Upcoming weak-lensing surveys will probe the matter distribution at a few percent level on nonlinear scales ($k>1\,{\rm h\,Mpc}^{-1}$) where baryonic feedback from galaxy formation modifies the clustering of matter. Using the IllustrisTNG hydrodynamical simulations, we quantify the mass and radial dependence of baryonic suppression of the matter power spectrum by selectively replacing matter around the center of halos out to a specified radius in the collisionless run with that around their full-physics counterparts. We find that group-scale halos with $\log M_{\rm 200m}/h^{-1}M_\odot \in[13, 14]$ dominate the suppression, contributing a large fraction of the total reduction in power at $k\sim2-30\,h\,{\rm Mpc}^{-1}$, with smaller suppression on either sides of this mass bin. Correctly reproducing the full suppression of the power spectrum requires accounting for matter redistribution (while enforcing mass conservation) beyond the virial radius of each halo. We show that the same group-scale regime produces the most detectable deviations in the weak gravitational lensing of background galaxies measured around foreground galaxy groups binned by mass or richness. Such a lensing signal could be a powerful observational test of feedback models together with SZ measurements. Our results motivate emulators that jointly predict the matter power spectrum and halo-matter cross-power spectrum including baryonic effects, enabling unbiased cosmological inference from small scales.
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Cosmology and Nongalactic Astrophysics

A Bayesian Perspective on Evidence for Evolving Dark Energy

Dily Duan Yi Ong, David Yallup and Will Handley

The DESI Collaboration reports a significant preference for a dynamic dark energy model ($w_0w_a$CDM) over the cosmological constant ($\Lambda$CDM) when their data are combined with other frontier cosmological probes. We present a direct Bayesian model comparison using nested sampling to compute the Bayesian evidence, revealing a contrasting conclusion: for the key combination of the DESI DR2 BAO and the Planck CMB data, we find the Bayesian evidence modestly favours $\Lambda$CDM (log-Bayes factor $\ln B = -0.57{\scriptstyle\pm0.26}$), in contrast to the collaboration's 3.1$\sigma$ frequentist significance in favoring $w_0w_a$CDM. Extending this analysis to also combine with the DES-SN5YR supernova catalogue, our Bayesian analysis reaches a significance of $3.07{\scriptstyle\pm0.10}\,\sigma$ in favour of $w_0w_a$CDM. By performing a comprehensive tension analysis, employing five complementary metrics, we pinpoint the origin: a significant ($2.95{\scriptstyle\pm 0.04}\,\sigma$), low-dimensional tension between DESI DR2 and DES-SN5YR that is present only within the $\Lambda$CDM framework. The $w_0w_a$CDM model is preferred precisely because its additional parameters act to resolve this specific dataset conflict. Replacing DES-SN5YR with the recalibrated DES-Dovekie dataset, this tension is reduced and the three-probe Bayesian evidence for $w_0w_a$CDM vanishes ($\ln B = -0.30{\scriptstyle\pm0.19}$). The convergence of our findings with alternative statistical analyses suggests that the preference for dynamic dark energy is primarily driven by the resolution of inter-dataset tensions, warranting a cautious interpretation of its statistical significance.
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Cosmology and Nongalactic Astrophysics

The Atacama Cosmology Telescope: A demonstration of CMB lensing measurement from daytime data

Irene Abril-Cabezas, Frank J. Qu, Joshua Kim et al. (+30 more)

We present a cosmic microwave background (CMB) lensing power spectrum analysis using daytime data (11am-11pm UTC) gathered by the Atacama Cosmology Telescope (ACT) over the period 2017-2022 (ACT Data Release 6). This dataset is challenging to analyze because the Sun heats and deforms the telescope mirror, complicating the characterization of the telescope. We perform more than one hundred null and consistency checks to ensure the robustness of our measurement and its compatibility with nighttime observations. We detect the CMB lensing power spectrum at 18$\sigma$ significance, with an amplitude $A_\textrm{lens} = 1.071 \pm 0.060$ with respect to the prediction from the best-fit Planck-ACT CMB power spectrum $\Lambda$CDM cosmology. In combination with the Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation (BAO) data, this corresponds to a constraint on the amplitude of matter fluctuations $\sigma_8 = 0.842 \pm 0.026$. The analysis presented here is especially relevant for ground-based millimeter-wave CMB experiments at the Atacama site, paving the way for future analyses making use of both nighttime and daytime data to place tight constraints on cosmological parameters.
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All authors Irene Abril-Cabezas, Frank J. Qu, Joshua Kim, Mathew S. Madhavacheril, Karen Perez-Sarmiento, Zachary Atkins, Erminia Calabrese, Anthony Challinor, Mark J. Devlin, Adriaan J. Duivenvoorden, Jo Dunkley, Alexander van Engelen, Simone Ferraro, Emily Finson, Carlos Hervías-Caimapo, Matt Hilton, Arthur Kosowsky, Aleksandra Kusiak, Thibaut Louis, Niall MacCrann, Kavilan Moodley, Toshiya Namikawa, Sigurd Naess, Lyman A. Page, Adrien La Posta, Emmanuel Schaan, Neelima Sehgal, Blake D. Sherwin, Carlos E. Sierra, Cristóbal Sifón, Suzanne T. Staggs, Emilie Storer, Edward J. Wollack

Cosmology and Nongalactic Astrophysics

Dark Matter from Holography

Oem Trivedi and Robert J. Scherrer

Previous studies have examined the holographic principle as a means of producing dark energy. Here we propose instead the possibility of holographic dark matter. In this case, dark matter does not arise in the framework of particle physics but is derived from the infrared cutoff set by the horizon scale. Using the Ricci cutoff, and a universe containing only baryons and radiation, we can account for the dark matter and naturally explain the coincidence between baryonic and nonbaryonic contributions to the density. In the presence of a pre-existing vacuum energy density our model reverses the sign of this density, thus accounting for the fact that certain string theories generically predict a negative vacuum energy, but observations require a positive value.
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Cosmology and Nongalactic Astrophysics

New multiprobe analysis of modified gravity and evolving dark energy

Zhiyu Lu and Théo Simon

We study the $(w_0, \, w_a)$ parametrization of the dark energy (DE) equation of state, with and without the effective field theory of dark energy (EFTofDE) framework to describe the DE perturbations, parametrized here by the braiding parameter $\alpha_B$ and the running of the Planck mass $\alpha_M$. We combine the EFTofLSS full-shape analysis of the power spectrum and bispectrum of BOSS data with the tomographic angular power spectra $C_\ell^{gg}$, $C_\ell^{\kappa g}$, $C_\ell^{Tg}$ and $C_\ell^{T\kappa}$, where $g$, $\kappa$ and $T$ stand for the DESI luminous red galaxy map, Planck PR4 lensing map and Planck PR4 temperature map, respectively. To analyze these angular power spectra, we go beyond the Limber approximation, allowing us to include large-scale data in $C_\ell^{gg}$. The combination of all these probes with Planck PR4, DESI DR2 BAO and DES Y5 improves the constraint on the 2D posterior distribution of $\{w_0, \, w_a\}$ by $\sim 50 \%$ and increases the preference for evolving dark energy over $\Lambda$ from $3.8 \sigma$ to $4.6 \sigma$. When we remove BAO and supernovae data, we obtain a hint for evolving dark energy at $2.3 \sigma$. Regarding the EFTofDE parameters, we improve the constraints on $\alpha_B$ and $\alpha_M$ by $\sim 40 \%$ and $50 \%$ respectively, finding results compatible with general relativity at $\sim 2 \sigma$. We show that these constraints do not depend on the choice of the BAO and supernovae likelihoods.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Dark Matter and Baryon Asymmetry from Monopole-Axion Interactions

Raymond T. Co, Keisuke Harigaya, Isaac R. Wang et al. (+1 more)

We introduce a novel mechanism where the kinetic energy of a rotating axion can be dissipated by the interactions with dark magnetic monopoles. This mechanism leads to a framework where the QCD axion and dark monopoles account for the dark matter density, and the observed baryon asymmetry is generated through the rotating QCD axion via axiogenesis. The monopoles acquire masses from a nonzero axion field, and they can transition between different quantized dyonic levels in the presence of a rotating axion field. The axion kinetic energy is dissipated by the transition, and thus the axion abundance is depleted to the observed dark matter abundance. We predict that the axion decay constant should be below $10^9$ GeV to explain the observed dark matter and baryon densities.
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All authors Raymond T. Co, Keisuke Harigaya, Isaac R. Wang, Huangyu Xiao

Astrophysics of Galaxies

The Local Group L-band Survey: Probing Cold Atomic Gas in IC10 with Neutral Hydrogen Absorption

Ioana A. Stelea, Snezana Stanimirovic, Nickolas M. Pingel et al. (+20 more)

We present the first localized detections of the cold neutral medium (CNM) in IC10, offering a rare view of dense atomic gas in a low-metallicity (0.27 solar metallicity) dwarf galaxy. As a low-metallicity starburst, IC10's interstellar medium conditions could reflect small-scale physical conditions that mirror those of early galaxies, providing a unique window into the heating and cooling processes that shaped the interstellar medium in early-Universe environments. Leveraging the high angular (<5” ~ 15pc) and spectral (0.4 km/s) resolution of the Local Group L-band Survey, we searched for HI absorption against nine continuum radio sources and detected absorption along three sightlines corresponding to internal radio emission sources within IC10. Using Gaussian decomposition and radiative transfer, we characterize the CNM, deriving spin temperatures of ~30-55 K, column densities of (0.6-3.0)x 1$0^{21}$ cm$^{-2}$, cold HI fractions of ~ 21-37%, and line widths of ~ 5.6-13.6 km/s. For each individual detection of HI absorption, we find corresponding molecular emission from 12CO (J=1-0), HCO+ (J=1-0), and HCN (J=1-0) at similar velocities and with comparable linewidths, indicating a well-mixed cold atomic and molecular medium. In IC10, the CNM shows a clear kinematic connection to the high-density ISM, implying a stronger dynamical coupling with molecular gas than in the Milky Way, in line with expectations for low-metallicity environments. At the ~ 15 pc scales probed by slightly extended HII regions in IC10, unresolved CNM clouds likely contribute to line blending, so the observed broad HI linewidths may partly reflect spatial and kinematic averaging.
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All authors Ioana A. Stelea, Snezana Stanimirovic, Nickolas M. Pingel, Hongxing Chen, Eric W. Koch, Adam K. Leroy, Erik Rosolowsky, Chang-Goo Kim, Alberto D. Bolatto, Julianne J. Dalcanton, Michael P. Busch, Harrisen Corbould, J. R. Dawson, Cosima Eibensteiner, Amanda Kepley, Melanie Krips, Claire E. Murray, Julia Roman-Duval, Daniel R. Rybarczyk, Evan D. Skillman, Elizabeth Tarantino, Vicente Villanueva, Thomas G. Williams

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

A Fast Earth-scattering Formalism for Light Dark Matter with Dark Photon Mediators

Agustín Lantero-Barreda, Carlos Centeno-Lorca, Bradley J. Kavanagh et al. (+1 more)

While Dark Matter (DM) is typically assumed to interact only very weakly with the particles of the Standard Model, many direct detection experiments are currently exploring regions of parameter space where DM can have a large scattering cross section. In this scenario, DM may scatter in the atmosphere and Earth before reaching the detector, leading to a distortion of the DM flux and a daily modulation of the signal rate as the detector is shielded by more or less of the Earth at different times of day. This modulation is a distinctive signature of strongly-interacting DM and provides a powerful method of discriminating against time-independent backgrounds. However, the calculation of these Earth-scattering effects by Monte Carlo methods is computationally intensive, inhibiting a systematic exploration of the DM parameter space. Here, we present a semi-analytic formalism for calculating Earth-scattering effects, for models of MeV-mass DM which interacts via a dark photon mediator, and release the associated code Verne2. This formalism assumes that DM travels along straight-line trajectories until it scatters and is reflected back along its incoming path, along us to taking into account the affects of both attenuation and reflection in the Earth. We compare this formalism with the results of full Monte Carlo simulations for cross sections within reach of current and future DM-electron scattering searches. We find that Verne2 is accurate to better than 10-30%, making it suitable for performing signal modeling in the search for daily modulation, while reducing the computational cost by a factor of $\sim10^4$ compared to full Monte Carlo simulations.
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All authors Agustín Lantero-Barreda, Carlos Centeno-Lorca, Bradley J. Kavanagh, Núria Castello-Mor

Astrophysics of Galaxies

The relationship between warm and hot gas-phase metallicity in massive elliptical galaxies and the influence of AGN feedback

Valeria Olivares, Yuanyuan Su, Pasquale Temi et al. (+10 more)

Warm ionized gas is ubiquitous at the centers of X-ray bright elliptical galaxies. While it is believed to play a key role in the feeding and feedback processes of supermassive black holes, its origins remain under debate. Existing studies have primarily focused on the morphology and kinematics of warm ionized gas. This work aims to provide a new perspective on warm (10,000 K) ionized gas and its connection to X-ray-emitting hot gas (>10^6 K) by measuring and comparing their metallicities. We conducted a joint analysis of 13 massive elliptical galaxies using MUSE/VLT and Chandra observations. Emission-line ratios were measured for the warm ionized gas using MUSE observation, and used to infer the ionization mechanisms and derive metallicities of the warm ionized gas using HII, and LIN(E)R calibrations. We also computed the warm phase metallicity using X-ray/EUV, and pAGB stars models. For two sources at higher redshift, direct Te method was also used to measure warm gas metallicities. Our observations reveal that most sources exhibit composite ionization, with contributions from both star formation and LINER-like emission. A positive linear correlation was found between the gas-phase metallicities of the warm and hot phases, ranging from 0.3 to 1.5 Zsun, and suggest the intimate connection between the two gas phases, likely driven by gas cooling and/or mixing. In some sources the warm gas metallicity shows a central drop. A similar radial trend has been reported for the hot gas metallicity in some galaxy clusters. The ionization mechanisms of cooling flow elliptical galaxies are diverse, suggesting multiple channels for powering the warm ionized gas. The large variation in the warm gas metallicity further suggests that cold gas mass derived under the assumption of solar metallicity for the CO-to-H2 conversion factor needs to be revised by approximately an order of magnitude.
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All authors Valeria Olivares, Yuanyuan Su, Pasquale Temi, Ryan Eskenasy, Helen Russell, Massimo Gaspari, Philippe Salome, Francoise Combes, Ming Sun, Ezequiel Treister, Kevin Fogarty, Ana Jimenez-Gallardo, Patricio Lagos

Astrophysics of Galaxies

Co-evolution of baryons and dark matter halos of LYRA dwarf galaxies

Joaquin Sureda, Shaun T. Brown, Azadeh Fattahi et al. (+4 more)

We use the extremely high-resolution ($m_{\rm bary}=4\rm{M}_\odot$) LYRA cosmological galaxy formation simulations of six dwarf galaxies with $M_{\rm 200c}\sim10^9\rm{M}_\odot$ at $z=0$ to investigate their stellar assembly histories. Based on the age of stars in these galaxies at $z=0$, $40-100\%$ of their stellar mass was formed by the time of reionization, when star formation (SF) abruptly shuts down. Depending on their halo mass evolution, some of the dwarfs reignite SF post-reionization (rejuvenators), while others remain quenched for the rest of cosmic time (reionization relics). However, the stellar mass of relics can still grow by more than $50\%$ through mergers post-reionisation. We find clear correlations between metallicity distributions of the galaxies and the fraction of stars formed post-reionization ($f_{\rm post-reio}^\star$) such that relics have lower median $\rm [Fe/H]$ with a more prominent low metallicity tail. Moreover, the shape of the galaxies at $z=0$ correlates with their $f_{\rm post-reio}^\star$, with rejuvenators showing more spherical stellar distribution than relics. This difference arises only post-reionization when rejuvenators become rounder with more SF activity. Similarly, the shape of dark matter (DM) halos in the inner regions display more spherical distributions in rejuvenators than in relics. The shape evolution shows that DM haloes in all galaxy formation simulations become rounder in comparison to their collision-less, DM-only counterparts. However, DM haloes of rejuvenators evolve more significantly. We do not find any correlation between SF activity and formation of shallow DM density cores in these galaxies. These predictions can be tested using upcoming observational data. In particular, our results indicate that the scatter in the mass-metallicity relation in the low mass regime is correlated with SF histories and the shape of galaxies.
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All authors Joaquin Sureda, Shaun T. Brown, Azadeh Fattahi, Thales Gutcke, Sownak Bose, Jessica E. Doppel, Rüdiger Pakmor

High Energy Astrophysical Phenomena

UHECRs Propagation and their Multimessengers: Upper limits and the Impact of the Extragalactic Magnetic Field

Rodrigo Sasse, Rubens Costa Jr, Adriel G.B Mocellin et al. (+2 more)

The detection of high-energy astrophysical multimessengers establishes a connection between ultra-high-energy cosmic rays (UHECRs) and powerful cosmic accelerators. Interactions of UHECRs with radiation fields and interstellar matter generate very-high-energy (VHE) gamma rays and neutrinos, making them key components in the multimessenger framework. This study examines the cosmogenic gamma-ray and neutrino fluxes resulting from UHECR propagation in starburst galaxies with supernova remnants, with a particular focus on NGC 1068, a well-established high-energy neutrino source. Using extragalactic simulations, we calculate the upper limit on cosmic-ray luminosity, applying upper limits on gamma-ray fluxes derived from observations by H.E.S.S. and MAGIC observatories. Our analysis incorporates the effects of both extragalactic and galactic magnetic fields on particle propagation, constraining the maximum extragalactic magnetic field (EGMF) intensity to $10^{-14}~\mathrm{G}$ to ensure that at least 90% of injected UHECRs successfully reach Earth. The results provide upper limits on gamma-ray and neutrino fluxes, estimates of UHECR luminosity for individual sources, and predictions for the detection capabilities of the Cherenkov Telescope Array Observatory regarding gamma-ray emission from NGC 1068. Combining gamma-ray, neutrino, and UHECR observations reinforces the importance of multimessenger approaches in understanding the nature of high-energy astrophysical sources and their role in cosmic-ray acceleration.
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All authors Rodrigo Sasse, Rubens Costa Jr, Adriel G.B Mocellin, Carlos H. Coimbra Araújo, Rita de Cássia dos Anjos

Astrophysics of Galaxies

Carbox: an end-to-end differentiable astrochemical simulation framework

Gijs Vermariën, Tommaso Grassi, Marie Van de Sande et al. (+6 more)

Since the first observations of interstellar molecules, astrochemical simulations have been employed to model and understand its formation and destruction path- ways. With the advent of high-resolution telescopes such as JWST and ALMA, the number of detected molecules has increased significantly, thereby creating a need for increasingly complex chemical reaction networks. To model such complex systems, we have developed Carbox, a new astrochemical simulation code that leverages the modern high-performance transformation framework Jax. With Jax enabling computational efficiency and differentiability, Carbox can easily utilize GPU acceleration, be used to study sensitivity and uncertainty, and interface with advances in Scientific Machine Learning. All of these features are crucial for modeling the molecules observed by current and next-generation telescopes.
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All authors Gijs Vermariën, Tommaso Grassi, Marie Van de Sande, Serena Viti, Stefano Bovino, Alessandro Lupi, Alexander Ruf, Lorenzo Branca, Catherine Walsh

High Energy Astrophysical Phenomena

Constraining the nature of the most extreme Galactic particle accelerator. H.E.S.S. observations of the microquasar V4641 Sgr

A. Acharyya, F. Aharonian, H. Ashkar et al. (+131 more)

Microquasars have emerged as promising candidates to explain the cosmic-ray flux at petaelectronvolt energies. LHAASO observations revealed V4641~Sgr as the most extreme example so far. Using $\approx$100~h of H.E.S.S. data, we performed a spectro-morphological study of the gamma-ray emission around V4641~Sgr. We employed HI and dedicated CO observations of the region to infer the target material for cosmic-ray interactions. We detected multi-TeV emission around V4641~Sgr with a high significance. The emission region is elongated. We found a power-law spectrum with an index $\approx$1.8, and together with results from other gamma-ray instruments, this reveals a spectral energy distribution that peaks at energies of $\approx$100~TeV for the first time. We found indications (3$\sigma$) of a two-component morphology, with indistinguishable spectral properties. The position of V4641~Sgr is inconsistent with the best-fit position of the single-component model and with the dip between the two components. We found no significant evidence of an energy-dependent morphology. No dense gas was found at any distance towards V4641~Sgr. The peak of the SED at $\approx$100~TeV identifies V4641~Sgr as a candidate cosmic-ray accelerator beyond the so-called knee. The absence of dense target gas places stringent energetic constraints on hadronic interpretations, however. The H.E.S.S. measurement requires an unusually hard ($\approx 1.5$) spectral index for the protons. A leptonic scenario faces fewer obstacles if the particle transport is fast enough to avoid losses and to reproduce the observed energy-independent morphology. The absence of bright \xray emission across the gamma-ray emission region requires a magnetic field strength $\lesssim3$~$\mu$G, however. Our findings favour a leptonic origin of the gamma-ray emission. This conclusion does not exclude hadron acceleration in the V4641~Sgr system.
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All authors A. Acharyya, F. Aharonian, H. Ashkar, M. Backes, R. Batzofin, D. Berge, K. Bernlöhr, M. Böttcher, C. Boisson, J. Bolmont, F. Brun, B. Bruno, C. Burger-Scheidlin, T. Bylund, S. Casanova, J. Celic, M. Cerruti, A. Chen, M. Chernyakova, J. O. Chibueze, O. Chibueze, B. Cornejo, G. Cotter, J. de Assis Scarpin, M. de Bony de Lavergne, M. de Naurois, E. de Oña Wilhelmi, A. G. Delgado Giler, J. Devin, A. Djannati-Ataï, A. Dmytriiev, K. Egberts, K. Egg, J.-P. Ernenwein, C. Escañuela Nieves, P. Fauverge, K. Feijen, M. D. Filipovic, G. Fontaine, S. Funk, S. Gabici, Y.A. Gallant, J.F. Glicenstein, J. Glombitza, P. Goswami, M.-H. Grondin, L. Heckmann, B. Heß, J.A. Hinton, W. Hofmann, T. L. Holch, M. Holler, M. Jamrozy, F. Jankowsky, A. Jardin-Blicq, I. Jaroschewski, D. Jimeno, I. Jung-Richardt, K. Katarzyński, D. Kerszberg, B. Khélifi, N. Komin, K. Kosack, D. Kostunin, R.G. Lang, S. Lazarević, A. Lemière, M. Lemoine-Goumard, J.-P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, V. Marandon, M. G. F. Mayer, A. Mehta, A.M.W. Mitchell, R. Moderski, L. Mohrmann, A. Montanari, E. Moulin, J. Niemiec, L. Olivera-Nieto, M.O. Moghadam, S. Panny, R.D. Parsons, U. Pensec, P. Pichard, T. Preis, G. Pühlhofer, M. Punch, A. Quirrenbach, A. Reimer, O. Reimer, I. Reis, Q. Remy, H. X. Ren, B. Reville, F. Rieger, G. Roellinghoff, G. Rowell, B. Rudak, K. Sabri, S. Safi-Harb, V. Sahakian, A. Santangelo, M. Sasaki, F. Schüssler, J.N.S. Shapopi, W. Si Said, H. Sol, Ł. Stawarz, S. Steinmassl, T. Tanaka, A.M. Taylor, G. L. Taylor, R. Terrier, Y. Tian, A. Timmermans, M. Tsirou, N. Tsuji, T. Unbehaun, C. van Eldik, M. Vecchi, C. Venter, J. Vink, V. Voitsekhovskyi, S.J. Wagner, A. Wierzcholska, M. Zacharias, A.A. Zdziarski, A. Zech, W. Zhong, S. Takekawa

Solar and Stellar Astrophysics

VELOCE III. Reconstructing Radial Velocity Curves of Classical Cepheids

Giordano Viviani and Richard I. Anderson

We present a novel framework for accurately reconstructing radial velocity (RV) curves of classical Cepheids from sparsely sampled time-series data suitable for application in large spectroscopic surveys. The framework provides a prior for the principal components of RV curves established based on high-precision measurements from the VELOCE project; template RV curves of Cepheids can be readily extracted from our results. We demonstrate the ability of our framework to estimate unbiased pulsation average velocities, $v_\gamma$, to within $20-30$ m/s, and peak-to-peak amplitudes, $P2P$, to within $\sim 1.1\%$. Subsampling the initial data set, we show that $v_\gamma$ and $P2P$ can be determined to within $\sim 500$ m/s and $\sim 4\%$, respectively, from as few as three observations at random pulsation phases, with the phase of minimum radius fitted rather than assumed. We fitted existing time-series RV data of Cepheids in the LMC and SMC, obtaining typical residuals of $0.5-2.0$ km/s. The typical total uncertainty on $v_\gamma$ achieved for the SMC Cepheids is $\sim 0.84$ km/s, providing sensitivity to spectroscopic binaries (SB). We identified 8 SB1 systems; two and one of which are new detections in the LMC and SMC, respectively. This yields single-lined SB fractions of $\sim 25\%$ and $27\%$ in the two galaxies, similar to the Milky Way's SB fraction of $29\%$ established as part of VELOCE. Despite their relatively small number, LMC Cepheids reproduce the known line-of-sight component of the LMC's large-scale rotation (amplitude $>80$ km/s). The SMC's kinematics are more complex and not yet sufficiently sampled. Our framework is designed to yield accurate $v_\gamma$ and $P2P$ of Cepheids observed by large spectroscopic surveys, such as 4MOST, SDSS-V, and others, and will unlock new insights into the kinematics and multiplicity of evolved intermediate-mass stellar populations.
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High Energy Astrophysical Phenomena

Shapiro Delay Measurements from Fifteen Years of PSR J1231$-$1411 Radio Observations

H. Thankful Cromartie, Matthew Kerr, Scott M. Ransom et al. (+5 more)

We present 15 years of Nançay and Green Bank radio telescope timing observations for PSR J1231$-$1411. This millisecond pulsar is a primary science target for the Neutron Star Interior Composition Explorer telescope (NICER, which discovered its X-ray pulsations), has accumulated near-continuous $\gamma$-ray data since the Fermi-Large Area Telescope's launch, and has been studied extensively with the Green Bank and Nançay radio telescopes. We have undertaken a campaign with the Green Bank Telescope targeting specific orbital phases designed to improve our constraint on the pulsar's mass through the detection of a relativistic Shapiro delay. Both frequentist and Bayesian techniques – the latter incorporating priors from white dwarf binary evolution models – are applied to fifteen years of radio observations, yielding relatively weak constraints on the companion and pulsar masses of $0.23^{+0.09}_{-0.06}$ M$_{\odot}$ and $1.87^{+1.11}_{-0.67}$ M$_{\odot}$, respectively (68.3% CI from Bayesian fits); however, the orbital inclination is measured to better relative precision ($79.80^{+3.47}_{-4.70}$ degrees). Restricting the maximum allowed pulsar mass to 3 M$_{\odot}$ improves the constraint and lowers the measured mass to $1.71^{+0.70}_{-0.56}$ M$_{\odot}$. A fully-generalized Bayesian fit that simultaneously samples the noise and timing models yields a pulsar mass in close agreement with this value. While our radio-derived inclination result has informed recent NICER X-ray studies of PSR J1231$-$1411, the lessons learned from this troublesome pulsar will also bolster future high-precision mass measurement campaigns and resulting constraints on the neutron star interior equation of state.
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All authors H. Thankful Cromartie, Matthew Kerr, Scott M. Ransom, Paul S. Ray, Lucas Guillemot, Ismaël Cognard, Emmanuel Fonseca, Gilles Theureau

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

Long-lived resonances of massive scalar fields in the Reissner-Nordström black-hole spacetime: Analytic treatment in the large-mass regime

Shahar Hod

The physical and mathematical properties of the composed Reissner-Nordström-black-hole-massive-scalar-field system are studied analytically in the dimensionless large-mass $M\mu\gg1$ regime [here $\{M,\mu\}$ are respectively the mass of the central black hole and the proper mass of the scalar field]. It is proved that, for a given value ${\bar Q}\equiv Q/M$ of the dimensionless charge parameter of the central black hole, the system is characterized by the presence of quasi-resonances, linearized perturbation modes with arbitrarily long lifetimes. In particular, using analytical techniques, we determine the black-hole-field critical mass spectrum $\{M\mu_{\text{crit}}({\bar Q})\}$ which characterizes the long-lived resonances of the composed physical system.
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Cosmology and Nongalactic Astrophysics

Bayesian model comparison and validation with Gaussian Process Regression for interferometric 21-cm signal recovery

Yuchen Liu, Eloy de Lera Acedo and Peter Sims

The 21-cm signal from neutral hydrogen traces the formation and evolution of early cosmic structures during the Cosmic Dawn and the subsequent Epoch of Reionization. However, the intrinsic faintness of the signal, as opposed to astrophysical foregrounds, poses a formidable challenge for its detection. Motivated by the recent success of machine learning based Gaussian Process Regression (GPR) methods in LOFAR and NenuFAR observations, we perform a Bayesian comparison among five GPR models to account for simulated 4-hour tracking observations with the SKA-Low telescope. The simulations incorporate the beam response of the telescope and include realistic radio sources and thermal noise from 122 to 134 MHz. A Bayesian model evaluation framework is applied to five GPR models to discern the most effective modelling strategy and determine the optimal model parameters. The GPR model with wedge parametrization ($\textit{Wedge}$) and its extension ($\alpha\textit{Noise}$) with noise scaling achieve the highest Bayesian evidence of the observed data and the least biased 21-cm power spectrum recovery. The $\textit{Wedge}$ and $\alpha\textit{Noise}$ models also forecast the best local power-spectrum recovery, demonstrating fractional differences of $0.10\%$ and $-0.24\%$ respectively, compared to the injected 21-cm power at $k = 0.32\ \mathrm{h\ cMpc}^{-1}$. We additionally perform Bayesian null tests to validate the five models, finding that the two optimal models also pass with the remaining three models yielding spurious detections in data containing no 21-cm signal.
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Solar and Stellar Astrophysics

Les Trente Glorieuses: 29 years of helioseismic observations with the Luminosity Oscillations Imager

Thierry Appourchaux

The Luminosity Oscillations Imager (LOI) of the Variability of Solar Irradiance and Gravity Oscillations (VIRGO) instrument aboard the SoHO mission has been operating for almost the past 30 years. I report on the effect of solar activity upon mode frequencies, linewidths, height and energy rate. I report on the variation as a function of frequency for frequency, $a_2$ coefficient and linewidth changes, as well as the average over the degree and the frequency of these changes. Using the 29-year time series, I report on the frequencies, linewidths and mode height fitted with progFIT. Using the collapsogram technique, I also report on the detection of modes below 1600 $\mu$Hz, making the lowest frequencies detected with an instrument observing the Sun in intensity. I also report on the detection of p mode in the high voltage and guiding pixel signals with a mode height about 5 to 10 times larger than what is observed in the Sun-as-a-star signal for $l=1$. The ratios of the observed mode visibilities for the different signals are provided following a calibration of the size of the guiding pixels. While the visibility ratios for the signals excluding the limb are in good agreement with theory, those covering the solar limb are in strong disagreement.
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Astrophysics of Galaxies

Revealing the Connection Between the Filamentary Hierarchy and Star Cluster Formation in a Simulated NGC 628 Galaxy

Tamara Koletic, Rachel Pillsworth and Ralph E. Pudritz

There is abundant observational evidence for the hierarchical, interconnected nature of filaments in the interstellar medium (ISM) extending from galactic down to sub-parsec scales. New JWST images of NGC 628 in particular, show clusters forming along the two spiral arms of this galaxy. In this paper we investigate filament and cluster properties in an NGC 628-like multi-scale high-resolution magnetohydrodynamic simulation. We use a filament finding tool to identify filaments and derive the probability density functions (PDFs) for the filament lengths and masses. Using a clustering algorithm we identify star clusters formed between 268 to 278 Myr and follow this population as the galaxy evolves for 60 Myr, calculating their mass PDFs, average radius growth rate, and average mass loss rate. We find a power-law index of alpha_m = -1.35 for the filament masses. Calculating the power-law index from our cluster mass PDF, we find a value of alpha_{c,m} = -1.35 when the clusters first form, exactly our filament mass power-law index. This shows that properties of young clusters arise from the gravitational fragmentation of their host filaments. We track the post-formation evolution of the clusters as they become unbound, increase in radius and decrease in mass yielding an ever steeper mass power-law index. After 60 Myr, the mass power-law index is alpha_{c,m} = -1.55, matching other simulations and observations.
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Solar and Stellar Astrophysics

Collisional and magnetic effects on the polarization of the solar oxygen infrared triplet

Moncef Derouich and Saleh Qutub

Context: The scattering polarization of the infrared (IR) triplet of neutral oxygen (O\,i) near 777\,nm provides a powerful diagnostic of solar atmospheric conditions. However, interpreting such polarization requires a rigorous treatment of isotropic depolarizing collisions between O\,i atoms and neutral hydrogen. Aims: We aim to investigate the combined effects of collisional and magnetic depolarization in shaping the alignment of O\,i levels (and thus the polarization of the O\,i IR triplet). Methods: We compute, for the first time, a comprehensive set of collisional depolarization and polarization transfer rates for the relevant O\,i energy levels. These rates are incorporated into a multi-level atomic model, and the statistical equilibrium equations (SEE) are solved to quantify the impact of collisions and magnetic fields on atomic alignment. Results: Our calculations indicate that elastic collisions with neutral hydrogen, together with the Hanle effect of turbulent magnetic fields stronger than about 20 G, efficiently suppress the bulk of the atomic alignment in deep photospheric conditions where hydrogen densities exceed $n_{\mathrm{H}} \sim 10^{16}$ cm$^{-3}$. In the chromosphere, however, the lower hydrogen density weakens collisional depolarization, allowing polarization to persist. Conclusions: Our results are consistent with a chromospheric origin for the linear polarization signals of the O I IR triplet. Future studies should combine accurate non-LTE radiative transfer with reliable collisional rates in order to achieve fully consistent modeling.
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High Energy Astrophysical Phenomena

Disk warping and black hole X-ray binaries I. Tentative unification of low-frequency quasi-periodic oscillations

Gregoire Marcel, Samuel Turner, Benjamin Ricketts et al. (+6 more)

X-ray binaries exhibit complex variability patterns studied in the power-spectrum. These include the broad-band noise (BBN) components and various types of narrow components called quasi-periodic oscillations (QPOs). There is currently no consensus about either what determines the presence/absence of the BBN or what generates the QPOs. Many believe the latter is due to frame-dragging effects caused by Lense-Thirring torques. We wish to investigate the potential impact of those frame-dragging effects on the accretion disk itself. In particular, we focus on its impact on the observed variability and the presence (and types) of QPOs associated. We make analytical estimates to assess the potential presence of a geometric warp in the inner accretion disk during state transitions. We show that the presence of a warp can modify the spectral-timing properties in a way that matches the observed transition between QPO types during outbursts. We also discuss the peculiar case of Cyg X-1, as well as how the hard-to-soft transition could be driven by the warp itself. The (expected) emergence of a warp provides a consistent explanation for the evolution of both the BBN and the QPO properties during state transitions. This offers a first path toward unifying the variability of black hole X-ray binary.
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All authors Gregoire Marcel, Samuel Turner, Benjamin Ricketts, Vanessa Lopez-Barquero, Douglas Buisson, Federico Vincentelli, Matthew Middleton, Christopher Reynolds, Mark Avara

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Generating optimal Gravitational-Wave template banks with metric-preserving autoencoders

Giovanni Cabass, Digvijay Wadekar, Matias Zaldarriaga et al. (+1 more)

Matched filtering for signal detection in noisy data requires template banks that capture variation in signal waveforms while minimizing computational cost. Dimensionality reduction of signal waveforms can be important for building efficient template banks. In various domains of physics, dimensionality reduction is very commonly performed using linear methods such as singular value decomposition (SVD). This can, however, introduce redundancies if the signals span curved, nonlinear manifolds in parameter space. Alternatively, autoencoders are a type of neural networks that can be used for non-linear dimensionality reduction. We use a variation of the autoencoder which preserves the metric in its latent space ($g_{ij}^{\text{latent}} \approx g_{ij}^{\text{physical}}$); this enables template banks to be constructed by simply placing a uniform grid in the autoencoder's low-dimensional latent space. We apply our method for creating geometric template banks for gravitational wave searches and show that our banks require fewer dimensions compared to using the SVD basis. Our method can also be useful for other applications requiring dimensionality reduction, such as gravitational waveform modeling, fast parameter estimation and model-independent tests of general relativity. Finally, we discuss extensions to other domains including cosmological parameter estimation, and we show tests of our method in extreme cases of periodic signal manifolds.
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All authors Giovanni Cabass, Digvijay Wadekar, Matias Zaldarriaga, Zihan Zhou

Astrophysics of Galaxies

Correlations of ALMA CO(2-1) with JWST mid-infrared fluxes down to scale of $\lesssim$100 parsec in nearby star-forming galaxies from PHANGS

Tao Jing and Cheng Li

We investigate the correlations of CO (2-1) emission (${I_{\rm CO}}$) with PAH (${I_{\rm F770W, PAH}}$ and ${I_{\rm F1130W}}$) and dust (${I_{\rm F2100W}}$) emission down to scales of $\lesssim$ 100 pc, by applying ${\tt raddest}$, a novel regression technique recently developed by T. Jing & C. Li (2025) that effectively handles uncertainties and outliers in datasets, to 19 nearby star-forming galaxies in the PHANGS sample. We find that for the majority of the data points in all galaxies, the scaling of ${I_{\rm CO}}$ with ${I_{\rm F770W, PAH}}$, ${I_{\rm F1130W}}$, and ${I_{\rm F2100W}}$ can be well described by log-log linear relations, though with substantial dependence on ionization conditions (i.e., HII-like, composite-like, and AGN-like). Under given ionization conditions, significant galaxy-to-galaxy variations are identified, and are primarily attributed to variations of intercept $b$, which exhibits clear bimodality. This bimodality is related to the normalized overall host galaxy star formation rate, such as specific star formation and star formation efficiency. The differences in slope $k$ and intrinsic scatter $\sigma$ across different MIR bands (${I_{\rm F770W, PAH}}$, ${I_{\rm F1130W}}$, and ${I_{\rm F2100W}}$) are minor compared to their galaxy-to-galaxy variations. All parameters ($k$, $b$, and $\sigma$) depend on the spatial scale of measurement, suggesting that the coupling among CO, PAH, and dust is regulated by different mechanisms at varying scales. We identify deviations from the log-log linear relation in the brightest regions, primarily characterized by a flattening of the slope. No significant (3$\sigma$) correlations are found between global properties and the best-fit parameters. We discuss the comparison to previous studies and plausible physics behind the statistical results obtained in this work.
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Instrumentation and Methods for Astrophysics

A scalable and accurate framework for self-calibrating null depth retrieval using neural posterior estimation

Baoyi Zeng, Marc-Antoine Martinod and Denis Defrère

Accurate null depth retrieval is critical in nulling interferometry. However, achieving accurate null depth calibration is challenging due to various noise sources, instrumental imperfections, and the complexity of real observational environments. These challenges necessitate advanced calibration techniques that can efficiently handle such uncertainties while maintaining a high accuracy. This paper aims to incorporate machine-learning techniques with a Bayesian inference to improve the accuracy and efficiency of null depth retrieval in nulling interferometry. Specifically, it explores the use of neural posterior estimation (NPE) to develop models that overcome the computational limitations of conventional methods, such as numerical self-calibration (NSC), providing a more robust solution for accurate null depth calibration. An NPE-based model was developed, with a simulator that incorporates real data to better represent specific conditions. The model was tested on both synthetic and observational data from the LBTI nuller for evaluation. The NPE model successfully demonstrated improved efficiency, achieving results comparable to current methods in use. It achieved a null depth retrieval accuracy down to a few $10^{-4}$ on real observational data, matching the performance of conventional approaches while offering significant computational advantages, reducing the data retrieval time to one-quarter of the time required by self-calibration methods. The NPE model presents a practical and scalable solution for null depth calibration in nulling interferometry, offering substantial improvements in efficiency over existing methods with a better precision and application to other interferometric techniques.
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Astrophysics of Galaxies

How much can we learn from resolved stellar kinematics of galactic haloes using action-based dynamical models?

Paula Gherghinescu, Eugene Vasiliev, Payel Das et al. (+1 more)

Dynamical models are used to study dark matter (DM) in galaxies, how galaxies assemble through mergers, and to test galaxy formation models. Despite its widespread use, there has been no systematic study quantifying how much information can be obtained from just two on-sky positions and line-of-sight velocities, which are typically available for nearby external galaxies. In this work, we introduce axisymmetric, action-based dynamical models that use the positions and velocities of stellar halo stars to jointly constrain the total mass distribution of galaxies and the underlying DM component, as well as the stellar halo phase-space distribution. We rigorously test the method using both idealised equilibrium galaxy mocks and cosmological hydrodynamical simulations from the Auriga suite, systematically assessing how its performance degrades as the available phase-space information is progressively reduced. We further examine the impact of galaxy inclination, modelling assumptions, and methodological systematics on the recovered mass profiles. A crucial development in this work is the improved marginalisation of the model likelihood over missing phase-space dimensions. Our models successfully recover the total and DM mass distributions, as well as the kinematic properties of the stellar tracers, within the derived confidence intervals. However, we find that with limited (3D or 4D) phase-space information, the flattening of the DM halo cannot be constrained with any degree of certainty. Nevertheless, the recovered mass profile is insensitive to the flattening. This finding is independently validated by Schwarzschild modelling tests.
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All authors Paula Gherghinescu, Eugene Vasiliev, Payel Das, Justin Read