Cosmology and Nongalactic Astrophysics
From quantum fluctuations to galaxy power spectrum multipoles
Nhat-Minh Nguyen
These notes trace large-scale structure from primordial
curvature perturbations generated by inflationary
quantum fluctuations to
galaxy power-spectrum multipoles. Three core lectures develop the linear matter power spectrum, spherical and anisotropic collapse,
galaxy bias,
redshift-space distortions, the Kaiser model, and multipole
estimators with Gaussian covariance. The extension develops nonlinear bias and the one-loop effective field theory model used in full-shape analyses. Derivations are explicit; appendices collect longer calculations and solutions. The core lectures assume undergraduate-level cosmology; the extension assumes familiarity with perturbation theory.
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Astrophysics of Galaxies
The Ashes of Supermassive Stars: Globular Cluster-like Aluminum Enhancement in Little Red Dots
V. Kokorev, J. Chisholm, R. P. Naidu et al. (+16 more)
The relative abundances of elements in
galaxies serve as fossil records of the physical conditions and processes by which they were forged. While the Big Bang produced only the lightest elements, subsequent stellar nucleosynthesis imprinted characteristic abundance patterns onto the surrounding gas, set initially by the temperatures reached inside
stars and subsequently shaped by how the processed material was mixed and released. Globular clusters - dense, ancient groups of
stars - provide a striking unique example. Some contain
stars depleted in magnesium and enriched in aluminum, showing that they formed from gas exposed to exceptionally hot hydrogen burning. The
stars responsible remain unknown. Little Red Dots may provide this missing engine. These compact, luminous objects formed at
cosmic epochs similar to those associated with globular-cluster formation and are enshrouded by dense gas whose chemical composition can be measured with the James Webb Space
Telescope. Here, using deep spectroscopy from the SPURS program, we show that this abundance pattern characterizes the LRD central engine: magnesium-depleted and aluminum-enhanced gas with a
metallicity only 1% that of the Sun. This pattern is not produced by ordinary massive
stars at these
redshifts and cannot be mimicked by ionization, gas geometry or dust. Instead, it is reproduced by hot hydrogen burning in fully convective supermassive
stars, with the measured abundances implying masses of at least 10,000 solar masses - approximately 100 times larger than any
star observed in the present-day Universe. Little Red Dots may therefore reveal supermassive
stars during their brief lives or in the immediate aftermath of their direct collapse, simultaneously identifying the long-sought source of globular cluster abundance anomalies and a formation pathway for massive black hole seeds.
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All authors V. Kokorev, J. Chisholm, R. P. Naidu, M. Gieles, S. Finkelstein, D. Berg, H. Akins, A. Taylor, S. Fujimoto, L. J. Furtak, J. Greene, A. de Graaff, K. Hawkins, T. Hsiao, D. Nandal, J. Matthee, S. Monty, P. Rinaldi, M. Boylan-Kolchin
Astrophysics of Galaxies
RIGEL: Ultra-faint dwarf galaxy diversity shaped by inhomogeneous cosmic reionization
Yunwei Deng, Hui Li, Ewald Puchwein et al. (+7 more)
Ultra-faint dwarf
galaxies (UFDs) are among the smallest and oldest
galaxies in the Universe and are widely regarded as relics of
cosmic reionization. To investigate how reionization quenches
star formation and shapes the diversity of UFDs, we present a suite of eight cosmological zoom-in simulations of isolated UFDs with present-day
halo masses of $\sim10^9\,{\rm M}_\odot$. The simulations are performed with the radiation-magnetohydrodynamic
galaxy formation framework Realistic ISM modeling in
Galaxy Evolution and Lifecycles (RIGEL), coupled to realistic large-scale radiation fields extracted from the THESAN reionization simulation. Despite residing in similar $z=0$
halos, the simulated
galaxies span nearly two orders of magnitude in stellar mass and broadly reproduce the observed luminosities, sizes,
metallicities, and stellar kinematics of Local Group UFDs. We find that reionization quenches
star formation through a two-stage process. The arrival of the ionization front rapidly photoionizes the diffuse circumgalactic and intergalactic gas, suppressing further gas
accretion onto the
galaxy.
Star formation nevertheless continues for several hundred Myr using the surviving self-shielded gas reservoir and ceases only after this gas is consumed or dispersed. Within 500 Myr after reionization, less than 40% of the initial gas mass remains in the
halo, with photoevaporation constituting the dominant gas-loss channel. We further show that the
halo mass at the time of reionization is a key parameter governing the subsequent
evolution of UFDs.
Galaxies residing in more massive
halos at reionization retain gas for longer periods and undergo more extended chemical enrichment. Consequently, the
halo mass at reionization strongly correlates with the final stellar mass, stellar age spread, and chemical
evolution of the
galaxy.
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All authors Yunwei Deng, Hui Li, Ewald Puchwein, Boyuan Liu, Aaron Smith, Rahul Kannan, Federico Marinacci, Greg L. Bryan, Kung-Yi Su, Mark Vogelsberger
Astrophysics of Galaxies
SHELLQs. Black Hole Mass and Eddington Ratio Distributions of Intermediate-Luminosity Quasars at 6<z<7
Masafusa Onoue, John D. Silverman, Yoshiki Matsuoka et al. (+31 more)
We present near-infrared spectroscopy of 21
quasars at 6.07 < z < 6.90 obtained with JWST/NIRSpec and Subaru/MOIRCS. These targets have absolute ultraviolet magnitudes of -25 < M_1450 < -22 and are drawn from a sample of z>6
quasars identified in the Subaru High-z Exploration of Low-Luminosity
Quasars (SHELLQs) project. These
quasars occupy the intermediate-luminosity regime between luminous
quasars and the faint high-
redshift AGNs uncovered by JWST. We detect broad Balmer emission lines and MgII 2798 with underlying continua from the NIRSpec and MOIRCS targets, respectively. The virial black hole masses of this sample span a wide range of 7.2 < log M_BH/M_sun < 9.4, with Eddington ratios of -1.3 < log L_bol/L_Edd < 0.4. Combining these measurements with our previous mass estimates for other SHELLQs
quasars, we construct a sample of 27
quasars with M_BH estimates at 6 < z < 7 and derive the distributions of M_BH and L_bol/L_Edd. When compared with luminosity-matched
quasars at z ~ 1.3, we find median offsets of delta log M_BH/M_sun = -0.4 and Delta log L_bol/L_Edd = 0.2 in the high-
redshift sample. In addition, 11% of the high-
redshift quasars are accreting near or above the Eddington limit. As a systematic check, adopting the Eddington-ratio-dependent calibration of single-epoch M_BH estimates increases the inferred super-Eddington fraction to 22%. These results indicate that a representative population of distant supermassive black holes undergo a rapid
accretion phase, although not as extreme as that seen in the most luminous
quasar population, consistent with the anti-hierarchical growth scenario of supermassive black holes.
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All authors Masafusa Onoue, John D. Silverman, Yoshiki Matsuoka, Xuheng Ding, Camryn L. Phillips, Michael A. Strauss, Junya Arita, Takuma Izumi, Mahoshi Sawamura, Nobunari Kashikawa, Irham Andika, Kentaro Aoki, Shunsuke Baba, Anna-Christina Eilers, Seiji Fujimoto, Tomotsugu Goto, Masatoshi Imanishi, Kohei Inayoshi, Kazushi Iwasawa, Knud Jahnke, Yuki Kaneko, Toshihiro Kawaguchi, Kotaro Kohno, Chien-Hsiu Lee, Alessandro Lupi, Tohru Nagao, Dragan Salak, Malte Schramm, Yoshiki Toba, Hideki Umehata, Marta Volonteri, Fabian Walter, Feige Wang, Jinyi Yang
Astrophysics of Galaxies
A Spectral Framework for Testing the Quasi-Star Hypothesis in Little Red Dots I: Weighing LRDs by Their Super-Eddington Luminosity Ratios—No Signs of Overmassive Black Holes
Olivia Curtis, Nikko J. Cleri, Jakob M. Helton et al. (+2 more)
We present a spectral test of the quasi-
star hypothesis for Little Red Dots (LRDs) whereby a black hole grows inside a stellar-like envelope. We use Prospector to fit host
galaxies and TLUSTY photospheres to 5 LRDs that show strong molecular or atomic absorption. We approximate each object's electron-scattered Eddington luminosity ratio, $\phi \equiv \kappa_{\rm es}\sigma T_{\rm eff}^{4}/(gc)$, and we use MESA-QUEST to simulate their envelopes. All 5 are super-Eddington at $\phi = {87}$–$299$, with the caveat that the largest sources sit at the edge of our atmosphere grid and beyond our simulations. We derive envelope masses between $700$–${15{,}000}\,M_\odot$, where quasi-
star theory requires the black hole to be less than a third of that. GN-28074 falls 5 decades below its published virial mass estimate, alleviating the overmassive black hole problem. Their black holes double every $\sim0.05$–${0.2}$~Myr and can produce intermediate-mass black holes in $\lesssim30$~Myr. Our 3 water-absorbing objects have cold components that are $2$–$3$~dex denser than their hot components, which we interpret as the water forming in cold dense clouds. We then extend our measurements to 82 archival LRDs, finding that the population has super-Eddington photospheres and wind speeds that increase with $\phi$, which implies that LRDs evolve from massive sources with slow winds to having more eruptive winds as they mature and shed their outer envelopes. We thus constrain the Eddington ratios and masses of LRDs and show self-consistently that quasi-
stars may be the central engines powering LRDs.
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All authors Olivia Curtis, Nikko J. Cleri, Jakob M. Helton, Joel Leja, Jason T. Wright
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Reconstructing sign-switching dark energy histories: Scalar-field regularity, conditional potential comparison, and representative dynamics
Shahnawaz A. Adil, Özgür Akarsu, Mariam Bouhmadi-López et al. (+3 more)
Phenomenologically similar sign-switching dark-energy histories need not have comparable scalar-field realizations. We reconstruct minimally coupled scalars with fixed kinetic sign for three prescribed histories: the error-function model (ECDM), the compact smooth-step model (SSCDM), and the ladder-like model (L$\Lambda$CDM). Continuous negative-to-positive density crossings select the phantom branch. ECDM yields a smooth on-shell potential at every finite
redshift; its equation-of-state pole at the density zero is only a ratio singularity. Exact SSCDM has a regular trajectory but a $C^1$, non-$C^2$ endpoint potential, $V-V_e\propto|\phi-\phi_e|^{4/3}$. Its non-Lipschitz force permits delayed departures from frozen plateaus, so the reconstructed potential and plateau data do not uniquely generate the prescribed history. The exact Ladder requires distributional kinetic stress and has no ordinary classical realization in the adopted one-field action. In conditional synthetic comparisons, the sigmoid–Gaussian family ranks highest for ECDM and the generalized
axion-like family for SSCDM, although the fitted
axion exponents $n<1/2$ imply a divergent endpoint force. Representative regular forward solutions exhibit negative-to-positive scalar-density crossings, with the potential zero preceding the density zero. In a closure test, unretuned
evolution of the top-ranked ECDM template tracks the target approximately, $\max|\Delta\widetilde\Omega_\phi|\simeq0.16$. Closure fails structurally for compact SSCDM: no potential with a locally Lipschitz force can reproduce its exact finite-duration frozen plateaus from exactly frozen initial data. Field-map existence, invertibility, and endpoint regularity must be assessed before interpreting a phenomenological history as scalar dynamics. The phantom action is used only as a homogeneous effective proxy.
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All authors Shahnawaz A. Adil, Özgür Akarsu, Mariam Bouhmadi-López, Beñat Ibarra-Uriondo, Nihan Kat{\i}rc{\i}, J. Alberto Vázquez
Astrophysics of Galaxies
Virgo Filaments VII: MeerKAT HI-imaging of the VirgoIII filament
M. Ramatsoku, G. Nagaraj, P. Jablonka et al. (+11 more)
We present MeerKAT HI observations of
galaxies in the nearby Virgo III filament. At a median distance of $\sim30$ Mpc, the filament extends over $\approx16$ Mpc across $\sim56$ deg$^2$. Our survey comprises 15 targeted MeerKAT pointings centred on HI deficient
galaxies. Multi-resolution HI imaging at 8-90 arcsec with an rms of $\sim0.3$ mJy beam$^{-1}$ reaches column densities of $\sim4\times10^{20}$ to $\sim4\times10^{18}$ atoms cm$^{-2}$. This probes HI in
galaxy discs at $\sim1.2$ kpc resolution and their outskirts at $\sim13.5$ kpc. We detect HI emission from 80 sources within the 500-3000 km/s range; most are optically detected
galaxies, while 10 per cent lack confirmed counterparts. We also identify three HI clouds without optical counterparts near an interacting system, possibly displaced during the interaction.
Galaxies in the filament lie below the field HI gas-fraction scaling relations at fixed stellar mass. Crucially, $\sim40$ per cent of
galaxies not selected for HI deficiency fall more than $1\sigma$ below these relations, with an even greater fraction lying under the mean relation itself, indicating that the low HI gas fractions are widespread in the filament rather than confined to the pre-selected deficient population. Quantifying HI morphologies using an asymmetry parameter, we find a wide range of disturbances without a clear trend with projected distance to the filament spine or local density, suggesting a combination of local interactions and the filament itself. This paper presents the survey description, catalogue, and HI atlas enabling investigations of gas removal mechanisms in Virgo III
galaxies.
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All authors M. Ramatsoku, G. Nagaraj, P. Jablonka, R. A. Finn, B. Vulcani, G. Rudnick, F. Combes, G. De Lucia, G. Castignani, D. Zaritsky, Y. Bahè, R. A. Koopmann, D. Zakharova, K. Conger
High Energy Astrophysical Phenomena
Decoding the Imprints of Energy-Momentum Squared Gravity in Neutron Stars with Machine Learning Analysis
Sayantan Ghosh, Premachand Mahapatra and Dipti Deb
Neutron stars (NSs) provide a unique laboratory for testing
gravity in the strong-field regime and for searching for deviations from General Relativity (GR). In this work, we investigate the effects of Energy-Momentum Squared
Gravity (EMSG) on NS structure and examine whether its signatures can be identified from observable stellar properties using supervised machine learning (ML). We solve the modified Tolman-Oppenheimer-Volkoff equations for approximately $10^{4}$ nuclear equations of state (EOSs) for EMSG coupling parameters $\alpha=\{-5.01,-2.50,0,+2.50,+5.01\}\times10^{-38}\,\mathrm{erg}^{-1}\mathrm{cm}^{3}$, and calculate the gravitational mass $M$, radius $R$, dimensionless tidal deformability $\Lambda$, and fundamental $f$-mode oscillation frequency for each stellar configuration. Imposing observational constraints on $M$, $R$, and $\Lambda$, we split our
datasets into train and test sets, and we employ Random Forest (RF), K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Logistic Regression (LR), and Gaussian Naive Bayes (GNB) to classify the representative sectors $\alpha=\{-5.01,0,+5.01\}\times10^{-38}\,\mathrm{erg}^{-1}\mathrm{cm}^{3}$ using $(M, R,\Lambda,f)$. The RF classifier performs best, achieving an accuracy of approximately $99.85\%$ with precision, recall, and F1-scores exceeding $99.8\%$, while KNN also achieves accuracy above $99\%$. The nearly diagonal confusion
matrices demonstrate that the observationally viable NS configurations associated with different EMSG sectors remain highly separable in the multidimensional observable space. Our results show that NS observables retain robust signatures of EMSG even after observational filtering, establishing ML-assisted NS observations as a promising complementary approach for probing modified
gravity with current and future multi-messenger observations.
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Cosmology and Nongalactic Astrophysics
Sizing the Universe with DESI Galaxy Sizes: Plain Fundamentals of Fundamental-Plane Lensing
Kun Xu, Jiaqi Wang, Ravi K. Sheth et al. (+44 more)
Weak gravitational
lensing provides a powerful way to map
cosmic structure, but most current measurements rely on
galaxy shape distortions from deep imaging surveys and are affected by systematics such as intrinsic
alignments, photometric-
redshift uncertainties and shape-measurement biases. Here we present a spectroscopic
galaxy-
galaxy lensing magnification measurement using Fundamental-Plane (FP) size residuals, $\delta_r\equiv\Delta\log_{10}R_\mathrm{e}$, from 3.26 million DESI luminous red
galaxy (LRG) sources behind DESI Bright
Galaxy Survey lenses. The FP-like relation predicts the intrinsic sizes of LRGs from
lensing-invariant quantities, including velocity dispersion $\sigma_0$ and surface brightness $I_\mathrm{e}$, with a scatter of about 0.06-0.07 dex.
Lensing magnifies LRG sizes, giving the direct convergence response $\delta_r(\kappa)=\kappa/\ln 10$, but we show that the full
lensing response is modified by magnification bias, because fitting $R_\mathrm{e}$ with $I_\mathrm{e}$ inevitably induces a magnitude dependence in $\bar{\delta}_r(m)$. After calibrating this response, we recover surface-density profiles with uncertainties comparable to those from individual Stage-III shear surveys using 5-20 million higher-
redshift sources. The corresponding excess surface-density profiles agree with shear-based measurements. We further show that the
estimator is robust to size-measurement uncertainties, with a convergence multiplicative bias only $\simeq -0.2$ times the size bias. FP
lensing therefore provides a clean, spectroscopic and complementary probe of
cosmic structure.
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All authors Kun Xu, Jiaqi Wang, Ravi K. Sheth, J. Aguilar, S. Ahlen, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, T. Claybaugh, A. de la Macorra, P. Doel, J. E. Forero-Romero, E. Gaztañaga, G. Gutierrez, K. Honscheid, C. Howlett, M. Ishak, J. Jimenez, S. Juneau, R. Kehoe, D. Kirkby, O. Lahav, M. Landriau, L. Le Guillou, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, J. A. Newman, W. J. Percival, F. Prada, I. Pérez-Ràfols, C. Ravoux, G. Rossi, R. Ruggeri, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, H. Seo, J. Silber, M. Siudek, G. Tarlé, B. A. Weaver, H. Zou
Cosmology and Nongalactic Astrophysics
Differential Polarization Calibration: A Consistency Test for Cosmic Birefringence
Anto I. Lonappan, Brian Keating and Kam Arnold
The
cosmic microwave background birefringence angle $\beta$ is exactly degenerate with a common instrumental polarization-angle offset. The Minami–Komatsu(MK) likelihood separates these quantities using Galactic foreground polarization, so its inferred detector angles merit a diagnostic that does not reuse the foreground-$EB$ model. We develop a birefringence-blind differential
estimator from antisymmetric and symmetric cross-spectra and apply it for the first time as an explicit consistency test of a foreground-assisted birefringence analysis. For a map pair, the common rotation cancels identically and the
estimator measures $\Delta\alpha_{ij}=\alpha_i-\alpha_j$; combining all pairs in a gauge-fixed network reconstructs the observable detector-dependent calibration pattern. Applied to eight Planck NPIPE detector-set maps, the differential reconstruction agrees with the MK pattern, giving $\chi^2=8.18$ for seven degrees of freedom (PTE=0.32), with all shared-data residuals below $1.8\sigma$. Because both reconstructions use the same maps, this is an independent
estimator and modeling route rather than an independent-data confirmation. The agreement therefore strengthens confidence in the calibration foundation of the MK-inferred $\beta$ without providing an independent absolute measurement of it. A conditional common-mode reconstruction gives $\beta=0.37\pm0.12^\circ$. The differential test uses existing data and can serve as a validation layer for future $EB$-based birefringence analyses.
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Cosmology and Nongalactic Astrophysics
Baryonification IV: Constraining baryonic feedback with X-ray gas fractions
Jozef Bucko, Andrina Nicola, Aurel Schneider et al. (+8 more)
Baryonic feedback redistributes gas around dark matter
halos, suppressing the matter power spectrum at scales now probed by weak
lensing surveys. X-ray observations directly trace this hot gas, and are one of the main probes of its distribution and properties. We present a forward-modelling framework, built on the baryonification model, linking the three-dimensional gas density and temperature profiles of groups and clusters to observed X-ray surface brightness and luminosity profiles on one side, and to matter power spectrum suppression on the other. We validate the model against independent three-dimensional density reconstructions from the literature, and examine our temperature and
metallicity treatment in the group-scale regime. Applying this framework to the SZ-selected CHEX-MATE and X-ray-selected eFEDs samples, we measure gas fractions across the group-to-cluster mass range while accounting for X-ray selection effects, with the first published gas fractions based on CHEX-MATE data. Combining both samples, we derive a joint constraint on the hot gas fraction retained by groups and clusters as a function of mass and on the baryonic suppression of the matter power spectrum. We find $f_{\rm gas} = 0.029 \pm 0.006$ at $M_{500c} = 3\times 10^{13}M_\odot$, $f_{\rm gas} = 0.078 \pm 0.004$ at $M_{500c} = 3\times 10^{14}M_\odot$, and suppression of 6% at $k=1\,h/\rm Mpc$ and 23% at $k=5\,h/\rm Mpc$. Our findings are consistent with recent kinematic Sunyaev-Zel'dovich results, hinting at strong feedback. We also show that the $L_X$-$M$ relation is degenerate with feedback strength, and that different feedback scenarios produce distinct X-ray profile shapes that map onto the same $L_X$-$M$ point. This work is a first step toward extending the framework to forward-model diffuse X-ray emission at the map level for simulation-based inference in upcoming wide-area X-ray surveys such as eROSITA.
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All authors Jozef Bucko, Andrina Nicola, Aurel Schneider, Michael Kovač, Sambit K. Giri, Robert Reischke, Esra Bulbul, Nicolas Clerc, Ang Liu, Iacopo Bartalucci, Alexandre Refregier
Cosmology and Nongalactic Astrophysics
Mitigating baryonic effects in weak lensing with higher-order statistics
Andreas Tersenov, Sacha Guerrini, Jean-Luc Starck et al. (+1 more)
Weak gravitational
lensing is a premier cosmological probe, but its small-scale statistical power is compromised by baryonic feedback. Higher-order statistics capture non-Gaussian information that the power spectrum misses, yet their sensitivity to feedback remains a concern for Stage IV surveys. We quantify how unmodeled feedback biases the cosmological parameters inferred from the angular power spectrum (PS), starlet peak counts, and the starlet $\ell_1$-norm, and we determine the scale cuts needed to remove that bias. We also test the Bernardeau-Nishimichi-Taruya (BNT) transform as a strategy for more precise scale cuts. Our analysis is based on the cosmoGRID V1 suite, which imprints feedback on dark matter convergence maps with a baryon correction model, and on simulation-based inference with neural posterior estimation, carried out across footprints ranging from Stage III-like to the full sky. We find that biases grow with survey area, exceeding $2\sigma$ for all three statistics at Stage IV-like footprints, and removing them costs a substantial fraction of the signal. Restricted to these “baryon-safe” scales, the starlet $\ell_1$-norm still reaches a figure of merit almost twice that of the PS. The BNT transform localizes the baryonic sensitivity to the lowest transformed
redshift bin and improves the PS figure of merit by a factor of $\sim$1.4, while its linear mixing of shape noise inflates the contours of the map-based higher-order statistics. Higher-order statistics therefore deliver a substantial gain over the power spectrum with no baryonic modeling at all, and an even larger one as modeling improves.
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All authors Andreas Tersenov, Sacha Guerrini, Jean-Luc Starck, Martin Kilbinger
Astrophysics of Galaxies
The fading hierarchy of Galactic open clusters
Guimei Liu, João Alves, Yu Zhang et al. (+7 more)
Galactic open clusters provide a record of both hierarchical
star formation and the subsequent dynamical
evolution of the Milky Way disk. We use the two-point correlation function to characterize the spatial and kinematic clustering of open clusters in the solar neighborhood, considering their three-dimensional (3D) distributions and their projections onto the Galactic plane, as well as subsamples divided by age, mass, and survey volume. We quantify the clustering through fractal dimensions and characteristic correlation scales. We find that the youngest clusters have fractal dimensions comparable to those measured in the interstellar medium, suggesting that they retain part of the hierarchical structure of their natal molecular clouds. The clustering strength then decreases systematically with age and becomes weak on a characteristic timescale of order 100 Myr. This
evolution is scale dependent: the excess correlation at tens of parsecs fades more rapidly than the weaker correlation at hundreds of parsecs. By contrast, we find only a weak dependence of the clustering properties on cluster mass and volume. Using the same cluster sample, we derive an empirical mapping between projected and 3D fractal dimensions, providing an observational calibration for comparing the Milky Way with studies of external
galaxies, where only projected measurements are available. The open-cluster population exhibits characteristic spatial and kinematic clustering scales of approximately 370 pc and 11 km/s, respectively. These results support a picture in which young open clusters inherit a spatial hierarchy from
star formation and progressively lose their spatial correlations through subsequent
evolution.
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All authors Guimei Liu, João Alves, Yu Zhang, Emily L. Hunt, Ruqiu Lin, Josefa E. Großschedl, Efrem Maconi, Nora Wagner, Lilly Kormann, Cameren Swiggum
Cosmology and Nongalactic Astrophysics
A Two-Dimensional Test of Cosmological Parity Violation with the 3-Point Correlation Function
William Ortolá Leonard and Zachary Slepian
Searches for parity violation (PV) in the Universe's large-scale structure have recently been carried out using parity-odd modes of the
galaxy 4-Point Correlation Function (4PCF). Here, we introduce a new
estimator for a 3-Point Correlation Function (3PCF) that is sensitive to PV. The construction exploits the handedness of triangles formed on 2D spherical shells, where mirror-image configurations cannot be related by proper rotations within the surface. By dotting the oriented area vector with an externally-defined normal vector to the shell, we obtain sensitivity to PV. We present a discrete
estimator for this statistic and also show how to correct for the survey geometry. This parity-odd 3PCF provides a complementary test of PV in
galaxy surveys and a potential cross-check of PV 4PCF measurements.
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Cosmology and Nongalactic Astrophysics
TILING I: Field-level Bayesian reconstruction of cosmological initial conditions during the epoch of reionization
Nikolaos Triantafyllou, Andrei Mesinger, Steven Murray et al. (+1 more)
Reconstructing the initial conditions (ICs) of the matter field for an observed volume gives a complete picture of that region's temporal
evolution. IC reconstruction is common at low
redshifts but largely unexplored during the epoch of reionization (EoR; $z\gtrsim 5$), partly due to difficulties modeling inhomogeneous
cosmic radiation fields. Yet the EoR spans half the observable Universe, offering unmatched potential for astrophysics and cosmology. Here we quantify how well upcoming
galaxy and 21cm observations can constrain ICs during the EoR. We develop $\tt TILING$ ($\bf T$omographic $\bf I$nference of $\bf L$inear $\bf I$Cs via $\bf N$etwork $\bf G$rafting): a hybrid machine learning pipeline that first produces a point estimate of the ICs, which then improves a score-based
diffusion network for generating posterior samples. We train $\tt TILING$ on mock
galaxy maps at varying UV magnitude limits, plus corresponding 21cm maps at varying noise levels and foreground "wedge" contamination. For fiducial survey choices, we achieve accurate IC reconstruction (posterior mean cross-correlation coefficients >0.8 and power spectrum errors under a few percent) down to $\text{k}\lesssim 0.2 \text{cMpc}^{-1}$. While 21cm interferometry aids recovery of IC power spectra, most constraining power, especially for IC
Fourier phases, comes from
galaxy maps, underscoring the need for complementary observations when interpreting the 21cm signal. We show how $\tt TILING$ can recover 21cm power spectrum modes excised by foreground contamination. Our framework can also: (i) guide follow-up observations of sub-volumes of interest; (ii) reconstruct
galaxy evolution and reionization morphology for specific volumes; and (iii) isolate the contribution to reionization from the vast majority of
galaxies unobservable by optical/IR
telescopes like $\it JWST$. Our code is publicly available.
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All authors Nikolaos Triantafyllou, Andrei Mesinger, Steven Murray, Samuel Gagnon-Hartman
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
NRHJSur3dq8: a spectral numerical-relativity surrogate family for non-eccentric aligned-spin binary-black-hole waveforms
Vaishak Prasad
We present NRHJSur3dq8, a family of numerical-relativity (NR) surrogates for non-eccentric aligned-
spin binary-black-hole waveforms inspired by an action-angle parameterization. The model provides both the dynamics: the
Hamiltonian values, azimuthal action $J_\phi(\Phi)$, the orbital clock $\tau(\Phi)$ as functions of its phasing, and the radiative pieces: the waveforms, their near-analytic derivatives, and modeling errors associated with each. The surrogated variables are conditioned into pieces that vary slowly on the radiation-reaction timescale, represented on shared $hp$-adaptive Chebyshev elements, and regressed across the intrinsic parameters with a Gaussian-process model. A time-parameterized merger-ringdown set of elements is attached where the adiabatic description breaks down. Leave-one-out validation of the central NRHJSur3dq8_AA flavor against NR reaches a $(2,2)$ unweighted mismatch of $1.3^{+32}_{-1.2}\times10^{-6}$ and an all-mode mismatch of $2.3^{+59}_{-2.2}\times10^{-6}$ over the full inspiral-merger-ringdown span. Sky-averaged and SNR-weighted over $32$ orientations per simulation, the released model's full-IMR in-sample mismatch against the NR simulations used for training is $8.9\times10^{-7}$ to $2.8\times10^{-5}$ across total masses $40$-$120\,M_\odot$. Waveforms are hybridized using post-Newtonian waveforms. Beyond accuracy, NRHJSur3dq8 provides two capabilities uncommon in NR surrogates: nearly analytic derivatives of the strain with respect to the physical parameters, and a calibrated Gaussian-process predictive uncertainty of the model. A full non-hybridized inspiral-merger-ringdown waveform evaluates in $12$ ms on a single CPU call. Batched evaluation amortizes this to $0.39$ ms per waveform at a batch of $4096$, measured at a starting frequency of $20$ Hz.
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High Energy Astrophysical Phenomena
Hierarchical Inference of the Supermassive Black Hole Binary Merger Rates from Joint Searches using Pulsar Timing Arrays
Sharon Mary Tomson, Rutger van Haasteren and Boris Goncharov
Gravitational-wave searches do more than identify individual sources - they provide a way to infer the underlying astrophysical populations that produce them. Currently,
Pulsar Timing Arrays (PTAs) constrain the supermassive black-hole binary (SMBHB) merger-rate density through both the
stochastic gravitational-wave background (SGWB) and searches for individual SMBHB signals. The latter implies converting source upper limits into rate upper limits using detection efficiencies estimated empirically. We instead develop a hierarchical
Bayesian framework that places the SMBHB merger-rate density model directly inside the PTA likelihood. The unknown catalog of individual SMBHB merger signals is modeled as a Poisson point process on source-parameter space, so that the number of merger signals is inferred from the data rather than imposed by a detection threshold. We describe two computational routes: a catalog-marginal likelihood based on analyses with fixed numbers of candidate sources, and an explicit transdimensional sampling approach that jointly samples population hyperparameters, latent merger signals, and noise. We validate the method with a toy merger-only population model and then apply it to an astrophysical SMBHB merger-rate density model that jointly predicts the SGWB amplitude and the expected merger-catalog size. In simulations, an individual merger signal adds complementary information to the SGWB and can tighten constraints on the merger-rate population.
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Solar and Stellar Astrophysics
Exploring pulsational instabilities in the O-type supergiant HD 152249
Subharthi Dasgupta, Abhay Pratap Yadav, Sugyan Parida et al. (+1 more)
Variability in O-type supergiants is a well known phenomena although their origin is not fully understood. In very massive, luminous
stars, strange mode pulsations have been suggested to play a role in the variability. Here, we present a preliminary theoretical study of O-type supergiant models corresponding to the observed parameters of the
star HD 152249, which shows line profile variability. Non-adiabatic linear stability analysis with respect to radial perturbations is carried out for the considered models of this
star. Instabilities with growth rates of the order of dynamical timescale are found, with characteristics suggestive of strange modes. Non-linear simulations for selected models indicate that the instabilities could lead to significant envelope inflation, finite amplitude pulsation and may contribute to enhanced mass loss.
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All authors Subharthi Dasgupta, Abhay Pratap Yadav, Sugyan Parida, Santosh Joshi
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Breaking binary formation mechanism degeneracies with gravitational wave clustering
Nicola Bellomo, Michele Bosi, Sarah Libanore et al. (+4 more)
Thanks to the almost 400 gravitational wave events detected, we are currently able to grasp the fundamental features of black hole mass,
spin, and distance distributions. However, such a fast increase in the precision of the measurements does not necessarily correspond to a better theoretical understanding of gravitational wave sources, especially in current scenarios where the number of free parameters is significantly larger than the number of inferred properties of the black hole population. In this work, we showcase how the landscape of theoretical models can be chipped away by complementary data-analysis strategies, in particular by studying the statistical properties of gravitational wave anisotropic distribution. Specifically, we show how gravitational wave clustering is sensitive to two unique features of each binary formation mechanism: the time-delay distribution and the properties of the binary hosts. First, we consider a model-agnostic scenario and show the impact that different time-delay distributions have on the gravitational wave bias. Then, we consider a realistic scenario where gravitational wave events are sourced either by isolated binary
evolution or dynamical processes in globular clusters, and study how the gravitational wave bias is unique sensitive to the specific properties of the environment. In both scenarios, we show how the cross-correlation between
galaxy and gravitational wave catalogs is able to distinguish between models with different time delays or with different binary sub-populations originated in specific formation channels.
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All authors Nicola Bellomo, Michele Bosi, Sarah Libanore, Michele Liguori, Michela Mapelli, Federico Semenzato, Stefano Torniamenti
Astrophysics of Galaxies
Small-Scale Clustering of Primordial Black Holes: The Little Red Dot Mass Function and the High-Redshift Galaxy Tension
Borui Zhang, Wei-Xiang Feng and Haipeng An
Supermassive black holes (SMBHs) in "little red dots" (LRDs) discovered by the James Webb Space
Telescope (JWST) may result from runaway mergers of primordial black holes (PBHs) in clusters—through long-short mode coupling on small scales in the early Universe. In this framework, we derive the SMBH mass function, together with the compactness and overmassive features of LRDs. We also estimate that the dense gas residing in PBH clusters is consistent with LRD observations. In addition, SMBHs formed from PBH clusters can help accelerate
galaxy formation at high
redshifts, thus alleviating tension with $\Lambda$CDM cosmology.
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Earth and Planetary Astrophysics
The Discovery of K2-232c: Divergent Formation Histories for Hot and Warm Jupiters Based on Outer Companion Eccentricity
Jessica A. Ranshaw, Xian-Yu Wang, Jennifer A. Burt et al. (+6 more)
Ever since their discovery, hot Jupiters have been one of the most studied types of
exoplanets to exist thanks to their significant size, their proximity to their host
star, and their significant departure from anything present in our solar system. Yet, the details of their formation and
evolution remain unclear, including their connection, if any, to the wider-orbiting warm Jupiter population. In this work, we present the discovery of K2-232c, an eccentric cold Jupiter ($P = 1950 ^{+140}_{-120}$ days, $e=0.352^{+0.095}_{-0.076}$, $M\sin{i} = 5.31^{+0.48}_{-0.45} {M_{\rm Jup}}$) companion in a known warm Jupiter ($P = 11.1684377 \pm 0.0000010$ days, $e=0.245^{+0.023}_{-0.024}$, $M = 0.427^{+0.039}_{-0.036} {M_{\rm Jup}}$) system. Placing this system in context with the literature, we find that cold Jupiter eccentricities are generally higher in hot Jupiter systems as compared to warm Jupiter systems, suggesting the formation of hot Jupiters is more dynamically violent than warm Jupiters. This adds further evidence to the claim that these two populations are independent from one another with cold Jupiters appearing to play a crucial role in shaping the formation of both.
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All authors Jessica A. Ranshaw, Xian-Yu Wang, Jennifer A. Burt, Juan I. Espinoza-Retamal, Brandon T. Radzom, R. Paul Butler, Bradford P. Holden, Steven S. Vogt, Songhu Wang
Earth and Planetary Astrophysics
The size and mass distribution of cold classical TNOs for $5<H<13$
Gary M. Bernstein, Wesley C. Fraser, Marielle R. Eduardo et al. (+7 more)
The cold classical trans-Neptunian objects (CCs) are the only observable in situ population of planetesimal remnants believed to have escaped collisional grinding. Recent JWST observations make it possible to fit the differential absolute magnitude distribution $dN/dH$ of the CCs from $5<H_r<13,$ and infer the differential mass distribution $dN/dM$ across $\ge5$ orders of magnitude in mass. We find $dN/dM$ well fit by a lognormal distribution, and equally well by a generalized $\Gamma$ distribution or a double power law. The maximum fraction of the total CC mass per log interval in $M$ is in bodies near 75~km diameter, or $\approx10^{-7.5}M_\oplus.$ Extrapolation of the fitted $dN/dH$ functions to $H_r>13$ is unwise, as the different analytic forms diverge. It remains unclear if $dN/dH$ turns over at faint $H.$ The uncertainty in the total mass of the CC belt is dominated by uncertainty in the relation between $M$ and $H$. A calibration using CC binaries suggests a total CC mass of 1.7–2.7$\times10^{-3}\,M_\oplus.$ A trend toward lower density and/or higher albedo for smaller bodies may be present in the data, and would lower the estimated total CC mass. Qualitative comparison of the derived mass distribution to the results of numerical simulations of the streaming instability (SI) suggest the simulations produce $dN/dM$ distributions that are more sharply peaked, and steeper at the bright end, than the CCs. Such differences could be ascribed to inhomogeneous formation conditions in the classical belt that are not yet included in modeling. The variety and uncertainty of $dN/dM$ derived from state-of-the-art SI simulations currently preclude any definitive test of the SI hypothesis.
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All authors Gary M. Bernstein, Wesley C. Fraser, Marielle R. Eduardo, William M. Grundy, Bryan Hilbert, Matthew J. Holman, Anastasia N. Morgan, Kevin J. Napier, John A. Stansberry, David E. Trilling
Astrophysics of Galaxies
Active galactic nucleus activity in brightest cluster galaxies at intermediate redshifts in Sunyaev-Zel'dovich–selected clusters
N. Hatamkhani, R.E. Skelton, J. Delhaize et al. (+4 more)
Context. Brightest cluster
galaxies (BCGs) host powerful active galactic
nuclei (AGNs) and help regulate the heating–cooling balance of the intracluster medium. While
radio-mode feedback is well established locally, its prevalence at intermediate
redshifts remains poorly constrained. Aims. We investigate the incidence,
accretion state, and host-
galaxy properties of AGNs in BCGs in Sunyaev–Zel'dovich (SZ)-selected clusters at $0.3 < z < 0.8$, testing dependences on
cosmic epoch, cluster mass, and dynamical state. Methods. We analyse 171 BCGs from the Atacama Cosmology
Telescope SZ catalogue, combining Southern African Large
Telescope spectroscopy, WISE mid-infrared photometry, and Rapid ASKAP Continuum Survey
radio data with X-CIGALE modelling to derive stellar masses,
star formation rates, and Eddington-scaled
accretion rates. Results. Thirty-eight BCGs (22%) host
radio-loud AGNs. Only two ($\sim$5%) are high-excitation
radio galaxies; the remainder are low-excitation systems. Most AGNs have low Eddington ratios ($-3 \lesssim \log_{10}\lambda_{\mathrm{Edd}} \lesssim -1$), consistent with radiatively inefficient
accretion.
Accretion efficiency increases with
redshift, while correlations with cluster mass and dynamical state are weak.
Radio luminosity is independent of cluster mass. Compared to field
radio AGNs, BCG
radio-loud AGNs have similar
radio powers but are hosted by
galaxies $\sim0.8$ dex more massive. Conclusions. BCG
radio-loud AGNs at $0.3 < z < 0.8$ are predominantly low-excitation, radiatively inefficient systems, indicating that maintenance-mode
accretion was widespread in massive clusters ($M_{500c} \simeq 3.2 \times 10^{14},M_\odot$) by $z \sim 1$.
Accretion appears regulated primarily by fuel availability and
cosmic evolution rather than global cluster properties, while the cluster environment mainly sets the host-
galaxy mass scale.
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All authors N. Hatamkhani, R.E. Skelton, J. Delhaize, M. Hilton, S.I. Loubser, N. Gupta, K. M. Mogotsi
Earth and Planetary Astrophysics
The Luminosity Function of Ultra-Faint Trans-Neptunian Objects Detected by JWST
Marielle R. Eduardo, Anastasia N. Morgan, Wesley C. Fraser et al. (+8 more)
We present a definitive discovery of 27 trans-Neptunian objects (TNOs) using the Near-Infrared Camera (NIRCam) aboard the James Webb Space
Telescope (JWST). By employing a shift-and-stack technique and a machine learning network geared specifically to identifying false-positive detections in JWST images produced through the shift-and-stack process, we achieved a 40% detection threshold of $m_{F150W2}=28.8$ mag (corresponding to $m_r\sim29.8$ mag) across a sky area of $0.05 \ \text{deg}^2$. This marks the deepest Solar System survey to date, reaching magnitudes that allow us to explore never-before-seen regions of the TNO size distribution. Our faintest detection has $m_{F150W2}=29.3$ mag and diameter of $\sim10$ km (assuming 15% albedo). Within our sample, we find that both the Cold and Hot TNO subpopulations exhibit a power-law slope. The distribution of apparent magnitudes of our nominal sample (detections at all epochs) are well fit by a single power law $dN/dm \propto 10^{\alpha m}$ with $\alpha=0.29^{+0.08}_{-0.07}$. The dynamically hot and cold subsamples in our discovery set are consistent with the same power law, suggesting that the planetesimal formation process yields similar slopes despite the differing disk conditions at the presumed $\sim25$ and $\sim45$~au formation regions of the two populations.
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All authors Marielle R. Eduardo, Anastasia N. Morgan, Wesley C. Fraser, David E. Trilling, Gary M. Bernstein, John A. Stansberry, Bryan Hilbert, Matthew J. Holman, William M. Grundy, Thomas L. Storer, Kevin J. Napier
Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
On the modeling of oblique firehose instabilities in regularized Kappa plasmas using ALPS
D. L. Schröder, M. Lazar, H. Fichtner et al. (+2 more)
In-situ measurements in space
plasmas indicate that the velocity distributions of charged particles are not in thermal
equilibrium, deviating from a standard Maxwellian mainly due to anisotropies and suprathermal populations which enhance high-energy tails. Although the Standard ąppa}-Distribution (SKD) is well established in modeling these non-
equilibrium distributions, its application is often viewed controversially due to certain unphysical implications, in particular divergent velocity moments. To address these issues, the Regularized ąppa}-Distribution (RKD) was introduced. Such advanced, in general anisotropic RKDs are invoked here for the first time to investigate oblique firehose instabilities, including those induced by the temperature anisotropy of electrons and
protons, the dominant species in space
plasmas. In weakly collisional
plasmas, both of these instabilities are expected to play significant roles in the self-regulation of the macroscopic properties of space
plasmas (e.g. the expanding solar wind) reported by observations. Is not yet possible to resort to a general dispersion tensor related to RKD
plasmas (whose derivation is still a challenge), instead the Arbitrary Linear
Plasma Solver (ALPS) is exploited here. The unstable solutions obtained for the already established Maxwellian & SKDs successfully validate the capability of ALPS. For RKDs, the instabilities confirm the stimulating effect of suprathermal populations, with lower ąppa} values generally enhancing the firehose growth rates. For the oblique electron firehose instability, RKDs substantially modify the competition between periodic & aperiodic branches only at intermediate angles & can sustain significantly increased growth rates of especially aperiodic modes at highly oblique propagation beyond both the Maxwellian unstable regime & the one that is accessible with SKDs.
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All authors D. L. Schröder, M. Lazar, H. Fichtner, K.G. Klein, D. Verscharen
High Energy Astrophysical Phenomena
Wolf-Rayet stars and black holes: mass distributions and evolutionary connection
I.A. Shaposhnikov, K.A. Postnov and A.M. Cherepashchuk
The form and relationship between the mass distributions of Wolf-Rayet
stars and black holes are analyzed using a direct method for estimating the distribution function from a sample of mass values with individual distributions obtained from current observations. It is shown that, taking into account the mass loss of WR
stars by the end of this evolutionary stage, the mass distribution of black holes is close to that of the CO-cores of WR
stars before gravitational collapse, $M_\mathrm{BH}\simeq M_\mathrm{CO}$.
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High Energy Astrophysical Phenomena
Detection of episodic Ultra-fast Outflows in the Low-luminosity quasar Mrk 205 using XMM-Newton data
César Ivan Victoria-Ceballos, Anna Lia Longinotti, Yair Krongold et al. (+3 more)
Ultra-fast outflows (UFOs) from Active Galactic
Nuclei (AGN) are winds which reach velocities up to 0.3c, and show mass outflow rates of 0.01-1 $M_{\odot} yr^{-1}$ and kinetic energies of $10^{42-45}$ erg/s. Their extreme properties allow UFOs to carry substantial kinetic power, sufficient to drive AGN feedback by injecting energy and momentum into the interstellar medium, regulating the host
galaxy evolution and the supermassive black hole growth. In this work, we present a detailed analysis of XMM-Newton X-ray spectra of the low-luminosity
quasar Mrk205. We find evidence of multi-component ultra-fast outflows, traced by two components detected in the high-resolution data, showing velocities in the range of $\sim$0.07c to $\sim$0.1c. In addition, we marginally detected an ultra-fast outflow feature in the Fe K band. According to our analysis, Mrk 205 shows episodes of wind launches, rather than persistent winds. We further discuss whether the energy carried by the UFOs in Mrk 205 is capable of producing significant feedback on its host
galaxy.
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All authors César Ivan Victoria-Ceballos, Anna Lia Longinotti, Yair Krongold, Giorgio Lanzuisi, Miriam Gudiño, Armando Lara-DI
Solar and Stellar Astrophysics
Open Clusters as Laboratories for Cool Star Evolution: Highlights from the Cool Stars 23 Splinter Session
Deepak Chahal, Beatrice Caccherano, Edward Gillen et al. (+16 more)
Open clusters remain among the most powerful laboratories for calibrating how fundamental stellar properties such as rotation,
magnetic activity, surface chemistry, and internal structure evolve over the pre-main-sequence to main-sequence and post-main-sequence stellar lifetime. Because cluster members share a common age, galactic environment, and initial composition, they provide empirical anchors upon which age-dating techniques such as gyrochronology, activity-age relations, and chemical clocks are built. This paper summarizes the Cool
Stars 23 splinter session - Open Clusters as Laboratories for Cool
Star Evolution, held on 15 June 2026 in Tokyo, Japan. The session comprised one invited review, ten contributed talks, and ten poster pop-up presentations, organized around three themes: the
evolution of rotation,
magnetic activity, and chemical abundances (Li-depletion, [C/N], [Y/Mg], and
neutron-capture elements). We close with a summary of the open questions identified in the panel discussion and the observational and theoretical work that new surveys (e.g. Gaia DR4, 4MOST, WEAVE) and missions (e.g. PLATO, Roman) will enable over the coming years. Together, these efforts will help assess the current state of the field and shape its future directions.
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All authors Deepak Chahal, Beatrice Caccherano, Edward Gillen, Dario J. Fritzewski, Robin D. Jeffries, Kevin R. Covey, Andrew Boyle, Lyra Cao, Federica Chiti, Alexander Hughes, Leslie Moranta, Natalie R. Myers, Emily K. Pass, Phil Van-Lane, Fábio C. Wanderley, Mackenna L. Wood, Stephanie T. Douglas, David Montes, Loredana Prisinzano
Astrophysics of Galaxies
Closed-Form of the Local Galactic Potential and Stellar Distribution Function from Gaia DR3
Indranil Das, Adam Kamoski, Dora Demiri et al. (+3 more)
The local dark matter density determines the strength of the signal expected in direct-detection experiments, yet published estimates from stellar motions disagree by more than their errors, and the most recent machine-learning analysis of Gaia data finds a local density consistent with zero. According to Jeans'
theorem, a distribution function built from integrals of motion satisfies the collisionless Boltzmann equation (CBE) trivially for any choice of potential, so a search that simultaneously fits the distribution function and the potential to the CBE identifies neither. Our pipeline instead estimates the distribution function in isolation, linearizing the equation in terms of accelerations and allowing for direct measurement of the local force field, and then fits closed forms to that field via symbolic regression. Throughout, we find that the usable information lies not in the CBE residual but in the stellar number counts, the observable most distorted by survey selection. Along the vertical profile, our recovered potential agrees with the classical self-gravitating isothermal disc.
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All authors Indranil Das, Adam Kamoski, Dora Demiri, Brianna Isola, Hanieh Karimi, Dmitrii S. Zagorulia
Earth and Planetary Astrophysics
Combined JWST and HST Deep Imaging to Characterize the Smallest Known Trans-Neptunian Objects
Anastasia N. Morgan, Marielle R. Eduardo, David E. Trilling et al. (+9 more)
We present optical-near-infrared (NIR) color measurements for small ($\leq 40$ km) Trans-Neptunian Objects (TNOs) using coordinated and nearly simultaneous observations from the James Webb Space
Telescope (JWST) and the Hubble Space
Telescope (HST). JWST/NIRCam data provided detections and NIR photometry for faint TNOs, while HST/ACS and WFC3 imaging enabled recovery in the optical, together yielding optical-NIR colors spanning 0.35-3.2 $\mu$m. Thirteen JWST-detected TNOs were recovered in the HST observations, and trailed PSF photometry was used to derive mean magnitudes, colors, and rotational lightcurves. The color distribution of our small cold classical TNO discoveries is narrow and consistent with the occupation of a single reflectance (color) sequence previously identified for larger cold classical TNOs. We find no evidence for a change in this sequence at smaller sizes. In contrast, the dynamically excited TNOs we discovered exhibit a broader range of colors consistent with multiple compositional classes seen at larger sizes. Lightcurve amplitudes were generally low for both dynamical groups in our sample. 2015 GK56, a previously known TNO in our field, displays a large-amplitude, structured lightcurve consistent with a contact binary. Our results indicate that the characteristic color distribution of TNOs extends to smaller sizes than previously studied, suggesting a primordial origin rather than size-dependent collisional processing.
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All authors Anastasia N. Morgan, Marielle R. Eduardo, David E. Trilling, Wesley C. Fraser, John A. Stansberry, Gary M. Bernstein, Bryan Hilbert, Matthew J. Holman, William M. Grundy, Kevin J. Napier, Stephen C. Tegler, Cesar Fuentes