Cosmology and Nongalactic Astrophysics
The Power of DESI for Photometric Redshift Calibration: A Case Study with KiDS-1000
Diana Blanco, Alexie Leauthaud, Johannes Ulf Lange et al. (+64 more)
Accurate
redshift estimates are a critical requirement for weak
lensing surveys and one of the main uncertainties in constraints on dark energy and large-scale
cosmic structure. In this paper, we study the potential to calibrate photometric
redshift (photo-z) distributions for gravitational
lensing using the Dark Energy Spectroscopic Instrument (DESI). Since beginning its science operations in 2021, DESI has collected more than 50 million
redshifts, adding about one million monthly. In addition to its large-scale structure samples, DESI has also acquired over 256k high-quality spectroscopic
redshifts (spec-zs) in the COSMOS and XMM and VVDS fields. This is already a factor of 3 larger than previous spec-z calibration compilations in these two regions. Here, we explore calibrating photo-zs for the subset of KiDS-1000
galaxies that fall into joint self-organizing map (SOM)
cells overlapping the DESI COSMOS footprint using the DESI COSMOS observations. Estimating the
redshift distribution in KiDS-1000 with the new DESI data, we find broad consistency with previously published results while also detecting differences in the mean
redshift in some tomographic bins with an average shifts of Delta Mean(z) = -0.028 in the mean and Delta Median(z) = +0.011 in the median across tomographic bins. However, we also find that incompleteness per SOM
cell, i.e., groups of
galaxies with similar colors and magnitudes, can modify n(z) distributions. Finally, we comment on the fact that larger photometric catalogs, aligned with the DESI COSMOS and DESI XMM and VVDS footprints, would be needed to fully exploit the DESI
dataset and would extend the coverage to nearly eight times the area of existing 9-band photometry.
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All authors Diana Blanco, Alexie Leauthaud, Johannes Ulf Lange, Angus H. Wright, Hendrik Hildebrandt, Sven Heydenreich, Darshika Ravulapalli, Joshua Ratajczak, Kyle S. Dawson, Jamie McCullough, Biprateep Dey, Jessica N. Aguilar, Steven Ahlen, Abhijeet Anand, Davide Bianchi, Chris Blake, David Brooks, Francisco J. Castander, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, John Della Costa, Arjun Dey, Ann Elliott, Ni Putu Audita Placida Emas, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Cristhian Garcia-Quintero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Dragan Huterer, Mustapha Ishak, Jorge Jimenez, Shahab Joudaki, Dick Joyce, Stephanie Juneau, David Kirkby, Anthony Kremin, Alex Krolewski, Claire Lamman, Martin Landriau, Laurent Le Guillou, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Seshadri Nadathur, Jeffrey A. Newman, Will Percival, Anna Porredon, Francisco Prada, Ignasi Pérez-Ràfols, Amy Robertson, Graziano Rossi, Eusebio Sanchez, Christoph Saulder, Agne Semenaite, David Schlegel, Hee-Jong Seo, Joseph H. Silber, David Sprayberry, Gregory Tarlé, Benjamin A. Weaver, Rongpu Zhou, Hu Zou
Cosmology and Nongalactic Astrophysics
Clustering redshift distribution calibration of weak lensing surveys using the DESI-DR1 spectroscopic dataset
R. Ruggeri, C. Blake, J. Aguilar et al. (+63 more)
We estimate the source
redshift distribution of current weak
lensing surveys by applying the clustering-based
redshift calibration technique, using the
galaxy redshift sample provided by the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1). We cross-correlate the Bright
Galaxy Survey (BGS), Luminous Red
Galaxies (LRGs) and Emission Line
Galaxies (ELGs) from DESI, within the
redshift range $0.1 < z < 1.6$, with overlapping tomographic source samples from the Dark Energy Survey (DES), Kilo-Degree Survey (KiDS), and Hyper Suprime-Cam (HSC) survey. Using realistic mock catalogues, we test the stability of the clustering
redshift signal to fitting scale, reference-sample choice, and the
evolution of source
galaxy bias. We calibrate a source
galaxy bias correction from simulations with conservative (factor-of-two inflated) priors to account for modelling uncertainties, and we explicitly model and marginalise over magnification contributions, which become non-negligible at $z \gtrsim 1$ due to the depth of the DESI ELG sample. We then compare the resulting bias-weighted
redshift distributions to \rossi{previously calibrated
redshift distributions from the literature, based on self-organising map (SOM) techniques}, finding agreement within uncertainties for all surveys and tomographic bins. Our results demonstrate that clustering
redshifts enabled by DESI's unprecedented spectroscopic sample provides a robust, complementary, and independent constraint capable of reducing one of the dominant systematic uncertainties in weak
lensing cosmology.
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All authors R. Ruggeri, C. Blake, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, A. Cuceu, K. S. Dawson, A. de la Macorra, B. Dey, P. Doel, A. Elliott, N. Emas, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, C. Garcia-Quintero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, B. Hadzhiyska, H. K. Herrera-Alcantar, S. Heydenreich, K. Honscheid, C. Howlett, D. Huterer, M. Ishak, S. Joudaki, R. Joyce, D. Kirkby, A. Krolewski, O. Lahav, C. Lamman, M. Landriau, J. U. Lange, A. Leauthaud, M. E. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, J. A. Newman, W. J. Percival, C. Poppett, A. Porredon, F. Prada, I. Pérez-Ràfols, A. Robertson, G. Rossi, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, A. Semenaite, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, P. Zarrouk, R. Zhou, H. Zou
Cosmology and Nongalactic Astrophysics
Cosmological Constraints from Full-Scale Clustering and Galaxy-Galaxy Lensing with DESI DR1
Johannes U. Lange, Alexandra Wells, Andrew Hearin et al. (+76 more)
We present constraints on
cosmic structure growth from the analysis of
galaxy clustering and
galaxy–
galaxy lensing with
galaxies from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. Our analysis includes four samples drawn from the Bright
Galaxy Survey (BGS) and the Luminous Red
Galaxy (LRG) target classes. Projected
galaxy clustering measurements from DESI are supplemented with
lensing data from the Dark Energy Survey (DES), the Kilo-Degree Survey (KiDS), and the Hyper Suprime-Cam (HSC) survey around the same targets. Our method relies on a simulation-based modeling framework using the AbacusSummit simulations and a complex
halo occupation distribution model that incorporates assembly bias. We analyze scales down to $0.4 \, h^{-1} \, \mathrm{Mpc}$ for clustering and $2.5 \, h^{-1} \, \mathrm{Mpc}$ for
lensing, leading to stringent constraints on $S_8 = \sigma_8 \sqrt{\Omega_\mathrm{m} / 0.3}$ and $\Omega_\mathrm{m}$ when fixing other cosmological parameters to those preferred by the CMB. We find $S_8 = 0.797_{-0.024}^{+0.023}$ and $\Omega_\mathrm{m} = 0.292 \pm 0.011$ when using
lensing measurements from DES and KiDS. Similarly, for HSC, we find $S_8 = 0.791_{-0.021}^{+0.020}$ and $\Omega_\mathrm{m} = 0.300 \pm 0.009$ when assuming the best-fit photometric
redshift offset suggested by the HSC collaboration. Overall, our results are in good agreement with other results in the literature while continuing to highlight the constraining power of non-linear scales.
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All authors Johannes U. Lange, Alexandra Wells, Andrew Hearin, Gillian Beltz-Mohrmann, Alexie Leauthaud, Sven Heydenreich, Chris Blake, Jessica Nicole Aguilar, Steven Ahlen, Abhijeet Anand, Davide Bianchi, David Brooks, Francisco Javier Castander, Todd Claybaugh, Shaun Cole, Andrei Cuceu, Kyle Dawson, Axel de la Macorra, Biprateep Dey, Peter Doel, Ann Elliott, Ni Putu Audita Placida Emas, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Cristhian Garcia-Quintero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Julien Guy, Klaus Honscheid, Dragan Huterer, Mustapha Ishak, Shahab Joudaki, Dick Joyce, Robert Kehoe, David Kirkby, Theodore Kisner, Anthony Kremin, Alex Krolewski, Ofer Lahav, Claire Lamman, Martin Landriau, Laurent Le Guillou, Michael Levi, Marc Manera, Paul Martini, Aaron Meisner, Ramon Miquel, John Moustakas, Eva-Maria Mueller, Seshadri Nadathur, Jeffrey A. Newman, Gustavo Niz, Nathalie Palanque-Delabrouille, Will Percival, Claire Poppett, Anna Porredon, Francisco Prada, Ignasi Pérez-Ràfols, Amy Robertson, Graziano Rossi, Rossana Ruggeri, Eusebio Sanchez, Christoph Saulder, David Schlegel, Michael Schubnell, Agne Semenaite, Hee-Jong Seo, Joseph Harry Silber, David Sprayberry, Zechang Sun, Gregory Tarlé, Mariana Vargas Magana, Benjamin Alan Weaver, Risa Wechsler, Pauline Zarrouk, Rongpu Zhou, Hu Zou
Cosmology and Nongalactic Astrophysics
Joint cosmological fits to DESI-DR1 full-shape clustering and weak gravitational lensing in configuration space
A. Semenaite, C. Blake, A. Porredon et al. (+69 more)
We present a joint $3\times2$-pt cosmological analysis of auto- and cross-correlations between the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1) Bright
Galaxy Survey (BGS) and Luminous Red
Galaxy (LRG) samples and overlapping shear measurements from the KiDS-1000, DES-Y3 and HSC-Y3 weak
lensing surveys. We perform our analysis in configuration space and, in addition to the
cosmic shear correlation functions for each weak
lensing dataset, we fit the tangential shear of the weak
lensing source
galaxies around DESI lens
galaxies. Finally, we make use of the anisotropic BGS and LRG clustering information by fitting the full shape of the two-point correlation function multipoles measured over the full DESI-DR1 footprint, presenting the first full-shape analysis of DESI measurements in configuration space. We find that the addition of weak
lensing information serves to improve, with respect to the clustering-only case, the measurements of the power spectrum amplitude parameters $\ln(10^{10}A_{\rm{s}})$ and $\sigma_{12}$ by $15\%$ and $36\%$, respectively. It also improves measurements of the linear bias of the lens
galaxies by $15-20\%$, depending on the tracer. Our results show excellent consistency, regardless of the weak
lensing survey considered, and are furthermore consistent with a companion analysis that fits $3\times2$-pt correlations including DESI projected clustering measurements, as well as the results published by the weak
lensing collaborations themselves. Our measured values for weak
lensing amplitude are $S_{8}^{\mathrm{DESI\times HSC}}=0.787\pm0.020$, $S_{8}^{\mathrm{DESI\times DES}}=0.791\pm0.016$, $S_{8}^{\mathrm{DESI\times KiDS}}=0.771\pm0.017$, which are $1.9\sigma-2.9\sigma$ below the $S_8$ value preferred by Planck. Finally, our clustering-only results are in good agreement with the
Fourier space full-shape analysis of all DESI tracers.
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All authors A. Semenaite, C. Blake, A. Porredon, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, A. Cuceu, K. S. Dawson, A. de la Macorra, Biprateep Dey, P. Doel, A. Eggemeier, A. Elliott, N. Emas, S. Ferraro, A.Font-Ribera, J. E. Forero-Romero, C. Garcia-Quintero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, B. Hadzhiyska, H. K. Herrera-Alcantar, S. Heydenreich, K. Honscheid, C. Howlett, D. Huterer, M. Ishak, S. Joudaki, R. Joyce, E. Jullo, D. Kirkby, A. Kremin, A.Krolewski, O. Lahav, C. Lamman, M. Landriau, J. U. Lange, L. Le Guillou, A. Leauthaud, M. E. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, J. A. Newman, N. Palanque-Delabrouille, W. J. Percival, A. Pezzotta, C. Poppett, F. Prada, I. Pérez-Ràfols, A. Robertson G. Rossi, R. Ruggeri, A. G. Sánchez, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G.Tarlé, B. A. Weaver, P. Zarrouk, R. Zhou, H. Zou
Cosmology and Nongalactic Astrophysics
DESI-DR1 $3 \times 2$-pt analysis: consistent cosmology across weak lensing surveys
A. Porredon, C. Blake, J. U. Lange et al. (+70 more)
We present a joint cosmological analysis of projected
galaxy clustering observations from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1), and overlapping weak gravitational
lensing observations from three
datasets: the Kilo-Degree Survey (KiDS-1000), the Dark Energy Survey (DES-Y3), and the Hyper-Suprime-Cam Survey (HSC-Y3). This combination of large-scale structure probes allows us to measure a set of $3 \times 2$-pt correlation functions, breaking the degeneracies between parameters in cosmological fits to individual observables. We obtain mutually-consistent constraints on the parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3} = 0.786^{+0.022}_{-0.019}$ from the combination of DESI-DR1 and DES-Y3, $S_8 = 0.760^{+0.020}_{-0.018}$ from KiDS-1000, and $S_8 = 0.771^{+0.026}_{-0.027}$ from HSC-Y3. These parameter determinations are consistent with fits to the Planck
Cosmic Microwave Background
dataset, albeit with $1.5-2\sigma$ lower values in the $S_8-\Omega_{\rm m}$ plane. We perform our analysis with a unified pipeline tailored to the requirements of each
cosmic shear survey, which self-consistently determines cosmological and astrophysical parameters. We generate an analytical covariance
matrix for the correlation data including all cross-covariances between probes, and we design a new blinding procedure to safeguard our analysis against confirmation bias, whilst leaving goodness-of-fit statistics unchanged. Our study is part of a suite of papers that present joint cosmological analyses of DESI-DR1 and weak gravitational
lensing datasets.
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All authors A. Porredon, C. Blake, J. U. Lange, N. Emas, J. Aguilar, S. Ahlen, A. Bera, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, J. Coloma Nadal, A. Cuceu, K. S. Dawson, A. de la Macorra, Biprateep Dey, P. Doel, A. Elliott, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, C. Garcia-Quintero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, B. Hadzhiyska, H. K. Herrera-Alcantar, S. Heydenreich, K. Honscheid, C. Howlett, D. Huterer, M. Ishak, S. Joudaki, R. Joyce, D. Kirkby, A. Kremin, A. Krolewski, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, A. Leauthaud, M. E. Levi, M. Manera, A. Meisner, R. Miquel, S. Nadathur, J. A. Newman, G. Niz, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, A. Robertson, G. Rossi, R. Ruggeri, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, A. Semenaite, H. Seo, J. Silber, A. Souki, D. Sprayberry, G. Tarlé, M. Vargas-Magaña, B. A. Weaver, C. Zhou, R. Zhou, H. Zou
High Energy Astrophysical Phenomena
2D or not 2D? Exploring 3D relativistic magnetic reconnection dynamics with highly accurate numerical simulations
Vittoria Berta, Matteo Bugli, Andrea Mignone et al. (+3 more)
Fast reconnection in magnetically dominated
plasmas is widely invoked in models of dissipation in
pulsar winds, gamma-ray
flares in the Crab nebula, and to explain the
radio nanoshots of
pulsars. When current sheets evolve reaching a critical inverse aspect ratio, scaling as $S^{-1/3}$ with the
plasma Lundquist number, the so-called ideal tearing instability sets in, with modes growing, independently of $S$, extremely rapidly on timescales of only a few light-crossing times of the sheet length. We present the first set of fully 3D simulations of current-sheet disruption triggered by the ideal tearing instability within the resistive relativistic MHD approximation, as appropriate in situations where the Alfvén velocity approaches the speed of light. We compare 3D setups with different initial conditions with their 2D counterparts, and we assess the impact of dimensionality and of the
magnetic field
topology on the onset,
evolution, and efficiency of reconnection. In force-free configurations, 3D runs develop ideal tearing, secondary instabilities, and a thick, turbulent current layer, sustaining dissipation of
magnetic energy longer than in 2D. In pressure-balanced current sheets with a null guide field, 2D reference runs show the familiar reconnection dynamics, whereas in 3D tearing dynamics is quenched after the linear phase, as pressure-driven modes growing on forming plasmoids outcompete plasmoid coalescence and suppress fast dissipation of
magnetic energy. Taken together, these results suggest that the
evolution and efficiency of reconnection depend sensitively on the local
plasma conditions and current-sheet configuration, and can be properly captured only in fully 3D simulations.
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All authors Vittoria Berta, Matteo Bugli, Andrea Mignone, Giancarlo Mattia, Luca Del Zanna, Stefano Truzzi
Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG
Introduction to Symbolic Regression in the Physical Sciences
Deaglan J. Bartlett, Harry Desmond, Pedro G. Ferreira et al. (+1 more)
Symbolic regression (SR) has emerged as a powerful method for uncovering interpretable mathematical relationships from data, offering a novel route to both scientific discovery and efficient empirical modelling. This article introduces the Special Issue on Symbolic Regression for the Physical Sciences, motivated by the Royal Society discussion meeting held in April 2025. The contributions collected here span applications from automated equation discovery and emergent-phenomena modelling to the construction of compact emulators for computationally expensive simulations. The introductory review outlines the conceptual foundations of SR, contrasts it with conventional regression approaches, and surveys its main use cases in the physical sciences, including the derivation of effective theories, empirical functional forms and surrogate models. We summarise methodological considerations such as search-space design, operator selection, complexity control, feature selection, and integration with modern AI approaches. We also highlight ongoing challenges, including scalability, robustness to noise, overfitting and computational complexity. Finally we emphasise emerging directions, particularly the incorporation of
symmetry constraints, asymptotic behaviour and other theoretical information. Taken together, the papers in this Special Issue illustrate the accelerating progress of SR and its growing relevance across the physical sciences.
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All authors Deaglan J. Bartlett, Harry Desmond, Pedro G. Ferreira, Gabriel Kronberger
Astrophysics of Galaxies
The Era of Binary Supermassive Black Holes: Coordination of Nanohertz-Frequency Gravitational-Wave Follow-up
Sarah Burke-Spolaor, Tamara Bogdanović, Daniel J. D'Orazio et al. (+9 more)
Here we summarize discussions and conclusions from the conference “The Era of Binary Supermassive Black Holes: Coordination of Nanohertz-Frequency Gravitational-Wave Follow-up,” held at the Aspen Center for Physics from February 2-7, 2025. The meeting facilitated a crucial knowledge exchange between electromagnetic and gravitational-wave theorists, observers, and cyber-infrastructure experts. The central goal was to guide the development of multi-messenger follow-up strategies for binary supermassive black hole detections by
pulsar timing arrays. To build a common basis of understanding for the broader scientific community, this summary outlines the main considerations and recommendations from the meeting, summarizes the knowledge gaps identified, and ends with a potential roadmap to catalyze discussion about the search for electromagnetic counterparts to massive black hole binaries detected by
pulsar timing arrays.
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All authors Sarah Burke-Spolaor, Tamara Bogdanović, Daniel J. D'Orazio, Michael Eracleous, Suvi Gezari, Matthew J. Graham, Kayhan Gültekin, Jeffrey Hazboun, Chiara M. F. Mingarelli, Gautham Narayan, Polina Petrov, Nicolo Veronesi
Instrumentation and Methods for Astrophysics
Binarity Beyond Gaia: The case for a dedicated spectroscopic survey of binary stars
Borja Anguiano
Stellar multiplicity is a fundamental ingredient of
stellar astrophysics, yet binary statistics across the
Galaxy remain poorly constrained. The
Gaia mission has revolutionised binary
star astrophysics by delivering high-precision astrometry, photometry and global radial velocities, and by providing hundreds of thousands of non-single-
star solutions in DR3. However, the RVS magnitude limit, mission time span and scanning law impose strong selection effects in period, mass ratio, inclination and semi-amplitude, leaving large regions of the binary parameter space either sparsely sampled or effectively inaccessible. In this white paper we outline the case for a dedicated, wide-field, multi-epoch spectroscopic survey explicitly optimised for binary science: deeper than the
Gaia RVS limit, with flexible cadence from hours to years, and with moderate to high spectral resolution. Using a simplified forward model of
Gaia DR5-like performance, we highlight the populations for which robust orbital solutions will be rare (ultra short period, very long period, low-amplitude and compact-object binaries), and show how a “Binarity Beyond
Gaia” survey would fill these gaps. Such a programme would deliver a bias correctable census of
stellar multiplicity across the Milky Way and provide the spectroscopic backbone needed to exploit binary samples from Rubin/LSST, Roman and LISA.
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Astrophysics of Galaxies
Dust evolution across cosmic times as seen through DUSTY-GAEA
Omima Osman, Gabriella De Lucia, Fabio Fontanot et al. (+2 more)
For many decades,
dust has been recognised as an important ingredient in
galaxy formation and
evolution. This paper presents a novel self-consistent implementation of
dust formation by
stars, destruction by
supernova shocks and hot gas, and growth within the dense interstellar medium (ISM) in the GAEA state-of-the-art
galaxy formation model. Our new model, DUSTY-GAEA, reproduces well the
dust buildup as a function of
stellar mass out to z $\sim$ 6, the scaling relations between the
dust-to-gas/
dust-to-metal ratios and
stellar mass/metallicty in the local Universe, and the
dust mass function in the local Universe and out to z $\sim$ 1. In the framework of our model,
dust growth dominates the
cosmic dust budget out to z $\sim$ 8, and we find that observational constraints beyond the local Universe can be reproduced only assuming such efficient
dust growth in the dense ISM. Yet, reproducing the estimated number densities of
dust-rich
galaxies at higher
redshifts remains challenging, as found also in independent theoretical work. We discuss our model predictions in comparison with both observational data and independent theoretical efforts, and highlight how further observational constraints at high
redshifts would help constrain
dust models.
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All authors Omima Osman, Gabriella De Lucia, Fabio Fontanot, Lizhi Xie, Michaela Hirschmann
Astrophysics of Galaxies
The Next Generation Fornax Survey (NGFS).VIII. A Support Vector Machine Approach for Disentangling Globular Clusters from other Sources
Yasna Ordenes-Briceño, Thomas H. Puzia, Paul Eigenthaler et al. (+8 more)
Wide-field, multi-band surveys now detect millions of unresolved sources in nearby
galaxy clusters, yet separating globular clusters (GCs) from foreground
stars and background
galaxies remains challenging. Scalable, automated classification is therefore essential to convert the forthcoming data from facilities such as the Vera C. Rubin/LSST, the Roman and Euclid into robust constraints on
galaxy assembly. We introduce a supervised classification method to separate GCs,
stars, and
galaxies based on their locations in color-color diagrams. The main objective is to recover a clean GC sample for future scientific analysis. The method exploits broad spectral energy distribution coverage, deep photometry, and is optimized for next-generation survey volumes. We use the central 3deg2 of the Next Generation Fornax Survey (NGFS), which images the Fornax cluster in u'g'i'JKs. We build a Support Vector Machine (SVM; svm.SVC, scikit-learn) using 15 features: all color combinations and basic morphological parameters. Spectroscopically confirmed sources define the training classes. Color pairs connecting near-UV/optical/near-IR. The full 15 feature model achieves 97.3% accuracy and a pruned 7 feature model built from the most informative, least correlated features achieves 96.6% accuracy. Misclassifications amount 8.4% and 10.4%, respectively. Omitting the u' or/and near-IR bands degrades performance. Emulating LSST filters with NGFS u'g'i' and DES r'z'Y shows that u' and Y bands are crucial, but models lacking NIR remain suboptimal. Combining broad SED coverage with simple morphological parameters enables precise, scalable separation of unresolved sources. Including NIR bands significantly improves GC classification, and joining LSST with forthcoming Euclid and Roman data will further enhance machine-learning frameworks.
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All authors Yasna Ordenes-Briceño, Thomas H. Puzia, Paul Eigenthaler, Matias Blaña, Juan P. Carvajal, Matthew A. Taylor, Bryan W. Miller, Rohan Rahatgaonkar, Evelyn J. Johnston, Prasanta K. Nayak, Gaspar Galaz
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Fifty shades of grayness: parametrizations of spectral distortions and applications in cosmology
Gabriela Barenboim, Julien Froustey, Cyril Pitrou et al. (+1 more)
Thermal distribution functions can only be of the
Fermi-Dirac or Bose-Einstein types, whereas distorted spectra encompass any possible deviations from these shapes. It is fruitful to devise parametrizations of these distortions with only a few parameters which depend on the physical system considered. A method proposed by Stebbins consists in describing a distorted spectrum as a sum of thermalized spectra with a distribution of temperatures, the moments of which are the parameters of interest. After revisiting and extending this approach by working at the level of the number density distribution instead of the standard spectrum, we build another method which consists in describing the distorted spectrum by a
polynomial modulating a reference thermalized spectrum. The distortion parameters are then the coefficients of a decomposition on a suitable orthonormal
polynomial basis. We advocate that the latter is computationally easier and allows to describe a wide range of distortions. With this formalism, we efficiently describe the standard distortions of the cosmological backgrounds of
neutrinos and
photons, and we obtain model-independent constraints on nonstandard distortions of these cosmological relics.
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All authors Gabriela Barenboim, Julien Froustey, Cyril Pitrou, Héctor Sanchis
Solar and Stellar Astrophysics
Observational constraints on the origin of the elements. X. Combining NLTE and machine learning for chemical diagnostics of 4 million stars in the 4MIDABLE-HR survey
Nicholas Storm, Maria Bergemann, Tomasz Różański et al. (+9 more)
We present the 4MOST-HR resolution Non-Local Thermal
Equilibrium (NLTE) Payne artificial neural network (ANN), trained on $404\,793$ new FGK spectra with 16 elements computed in NLTE. This network will be part of the
Stellar Abundances and atmospheric Parameters Pipeline (SAPP), which will analyse 4 million
stars during the five year long 4MOST consortium 4: 4MOST MIlky way Disc And BuLgE High-Resolution (4MIDABLE-HR) survey. A fitting
algorithm using this ANN is also presented that is able to fully-automatically and self-consistently derive both
stellar parameters and elemental abundances. The ANN is validated by fitting 121 observed spectra of low-mass FGKM type
stars, including main-sequence
dwarf, subgiant and
giant stars down to [Fe/H] $\approx -3.3$ degraded to 4MOST-HR resolution of $R\approx20\,000$, and comparing the derived abundances with the output of the classical radiative transfer code TSFitPy. We are able to recover all 18 elemental abundances with a bias~$<0.13$ and spread~$<0.16$\,dex, although the typical values are $<0.09$ dex for most elements. These abundances are compared to the OMEGA+
Galactic Chemical
Evolution model, showcasing for the first time, the expected performance and results obtained from high-resolution spectra of the quality expected to be obtained with 4MOST. The expected
Galactic trends are recovered, and we highlight the potential of using many chemical elements to constrain the formation history of the
Galaxy.
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All authors Nicholas Storm, Maria Bergemann, Tomasz Różański, Victor F. Ksoll, Thomas Bensby, Gregor Traven, Georges Kordopatis, Ross P. Church, Mingjie Jian, Weijia Sun, Guillaume Guiglion, Gražina Tautvaišienė
Astrophysics of Galaxies
Cored galaxies in cuspy dark matter halos
Fernando Valenciano, Jorge Martin Camalich, Arianna Di Cintio et al. (+4 more)
We investigate constraints on the inner
stellar density profile from photometric data of
dwarf spheroidal and ultra-faint
dwarf galaxies. Our aim is to clarify under what conditions cored
stellar profiles require dark matter
halos that are also cored, deviating from the cuspy profiles expected for cold dark matter
halos. We consider a variety of spherically symmetric
stellar profiles, which we classify as "strong" or "weak" cores and cusps according to the behavior of the slope ($b_0$) and logarithmic slope ($\gamma_0$) at their centers. We explore which profiles lead to unphysical negative distribution functions when embedded in a cuspy
halo, treating isotropic and anisotropic kinematics separately. We find that weakly-cored
stellar profiles in 3D (i.e., $b_0 \neq 0$, $\gamma_0=0$) can be consistent with cuspy dark matter profiles, but strong 3D cores ($b_0=\gamma_0=0$) are not. However, both weak and strong 3D cores yield nearly indistinguishable inner profiles in projection, which implies that ruling out a dark matter cusp from photometric data alone is highly challenging. As an example, we study the profiles of ultra-faint
dwarf galaxies and find that they are consistent with both weak and strong 3D cores. This is not just a result of the limited numbers of
stars in these systems, since we reach the same conclusion even for Fornax, one of the most luminous and best-studied
dwarf spheroidal companions of the Milky Way. We conclude that, based on current data and analysis techniques, cored surface density profiles in nearby
dwarf galaxies cannot be taken as strong evidence against the presence of cuspy dark matter
halos.
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All authors Fernando Valenciano, Jorge Martin Camalich, Arianna Di Cintio, Julio F. Navarro, Giuseppina Battaglia, Raphaël Errani, Justin I. Read
Cosmology and Nongalactic Astrophysics
The AIDA-TNG project. Abundance, radial distribution, and clustering properties of halos in alternative dark matter models
Massimiliano Romanello, Giulia Despali, Federico Marulli et al. (+3 more)
Warm and self-interactive dark matter cosmologies have been proposed as nonbaryonic solutions to the tensions between the $\Lambda$ cold dark matter model and observations at the kiloparsec scale. In this paper, we used the dark matter-only runs of the aida-tng project, a set of cosmological simulations of different sizes and resolutions, to analyze the macroscopic impact of alternative dark matter models on the abundance, radial distribution, and clustering properties of
halos. We adopted the
halo occupation distribution formalism to characterize the
evolution of its parameters $M_1$ and $\alpha$ with the mass and
redshift selection of our sample. By dividing the
halo population into centrals and satellites, we were able to study their spatial density profile. We found that a Navarro-Frenk-White model is not accurate enough to describe the radial distribution of subhalos and that a generalized Navarro-Frenk-White model is required instead. Warm dark matter models, in particular, present a cuspier distribution of satellites, whereas self-interacting dark matter exhibits a shallower density profile. Moreover, we found that the small-scale clustering of dark matter
halos provides a powerful tool for distinguishing among alternative dark matter scenarios, in preparation for a more detailed study that fully incorporates baryonic effects and for a comparison with observational data from
galaxy clustering.
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All authors Massimiliano Romanello, Giulia Despali, Federico Marulli, Carlo Giocoli, Lauro Moscardini, Mark Vogelsberger
Astrophysics of Galaxies
Shedding the envelope: JWST reveals a kiloparsec-scale [OIII]-weak Balmer shell around a z=7.64 quasar
Julien Wolf, Eduardo Bañados, Xiaohui Fan et al. (+25 more)
Luminous
quasars at the
redshift frontier z>7 serve as stringent probes of super-massive black hole formation and they are thought to undergo much of their growth obscured by dense gas and
dust in their host
galaxies. Fully characterizing the symbiotic
evolution of SMBHs and hosts requires rest-frame optical observations that span spatial scales from the broad-line region to the ISM and CGM. JWST now provides the necessary spatially resolved spectroscopy to do so. But the physical conditions that regulate the interplay between SMBHs and their hosts at the highest
redshifts, especially the nature of early feedback phases, remain unclear. We present JWST/NIRSpec IFU observations of J0313$-$1806 at z=7.64, the most distant luminous
quasar known. From the restframe optical spectrum of the unresolved
quasar, we derive a black hole mass of $M_\mathrm{BH}=(1.63 \pm 0.10)\times10^9 M_\odot$ based on H$\beta$ and an Eddington rate of $\lambda=L/L_\mathrm{Edd}=0.80\pm 0.05$, consistent with previous MgII-based estimates. J0313-1806 exhibits no detectable [O III] emission on
nuclear scales. Most remarkably, we detect an ionized gas shell extending out to $\sim 1.8$ kpc traced by H$\beta$ emission that also lacks any significant [O III], with a $3\sigma$ upper limit on the [O III]$ \lambda$5007 to H$\beta$ flux ratio of $\log_{10} \left( F(\mathrm{[OIII]})/F(\mathrm{H}\beta)\right)=-1.15$. Through photoionization modelling, we demonstrate that the extended emission is consistent with a thin, clumpy outflowing shell where [OIII] is collisionally de-excited by dense gas. We interpret this structure as a fossil remnant of a recent blowout phase, providing evidence for episodic feedback cycles in one of the earliest
quasars. These findings suggest that dense ISM phases may play a crucial role in shaping the spectral properties of
quasars accross
cosmic time.
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All authors Julien Wolf, Eduardo Bañados, Xiaohui Fan, Antoine Dumont, James E. Davies, David S. N. Rupke, Jinyi Yang, Weizhe Liu, Silvia Belladitta, Aaron Barth, Sarah Bosman, Tiago Costa, Frederick B. Davies, Roberto Decarli, Dominika Ďurovčíková, Anna-Christina Eilers, Hyunsung D. Jun, Yichen Liu, Federica Loiacono, Alessandro Lupi, Chiara Mazzucchelli, Maria Pudoka, Sofía Rojas-Ruiz, Jan-Torge Schindler, Wei Leong Tee, Benny Trakhtenbrot, Fabian Walter, Huanian Zhang
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Modeling the frequency-domain ringdown amplitude of comparable-mass mergers with greybody factors
Romeo Felice Rosato, Sophia Yi, Emanuele Berti et al. (+1 more)
It was recently shown that, in a binary coalescence, the greybody factor of the remnant black hole modulates the post-merger ringdown signal. In this work, we demonstrate that a simple four-parameter model based on the greybody factor accurately reproduces the frequency-domain amplitude of a large set of comparable-mass, aligned-
spin numerical relativity waveforms from the SXS catalog, achieving mismatches of order ${\cal O}(10^{-5})$ and improving existing models by roughly two orders of magnitude. We also identify the optimal initial frequency for applying the model in the frequency domain and provide analytical fits of the model parameters in terms of the progenitor masses and aligned
spins. Our results pave the way for new consistency tests of the ringdown phase, complementary to traditional black hole spectroscopy.
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All authors Romeo Felice Rosato, Sophia Yi, Emanuele Berti, Paolo Pani
Solar and Stellar Astrophysics
Bright Long Secondary Period Stars for Follow-up Observations
P. Iwanek, D. M. Skowron, G. Pojmański et al. (+1 more)
Long secondary period (LSP) variable
stars are a subclass of long-period variables (LPV) that exhibit additional long-term variability alongside pulsations. Despite being observed in over 30% of LPVs, the reason behind the LSP phenomenon is still debated. The most favoured explanation, supported by recent growing evidence, is binarity, where the pulsating
giant star has a substellar-mass companion. To further test this hypothesis, it is important to identify bright LSP variables, for which high-quality spectroscopic and interferometric observations can be obtained more easily. Motivated by the absence of a catalog of bright nearby LSPs, we searched the All Sky Automated Survey (ASAS) data in the $V$-band magnitude range 5.5-14 mag, and for declinations $< +28^\circ$. The resulting catalog contains 23 LSPs, 13 of which are new discoveries. We compare our catalog with the LSP lists available in the literature.
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All authors P. Iwanek, D. M. Skowron, G. Pojmański, I. Soszyński
High Energy Astrophysical Phenomena
Gravitational-wave Observations Suggest Most Black Hole Mergers Form in Triples
Jakob Stegmann, Fabio Antonini, Aleksandra Olejak et al. (+4 more)
The
spin-orbit tilt angles $\theta_{1(2)}$ of merging
stellar-mass black holes provide key insights into their astrophysical origin. Non-parametric population modelling of The LIGO, Virgo, and KAGRA Collaborations (2025a, arXiv:2508.18083) shows that the
spin-orbit tilt distribution of mergers in the latest Gravitational-Wave Transient Catalog 4.0 exhibits a global peak at near-perpendicular directions $\cos\theta_{1(2)}\approx0$. Here, we recover this feature using hierarchical
Bayesian inference with parametric models that are tailored to enhance the diagnostic power about astrophysical formation channels. We find that the
spin distribution of the low-mass bulk of the binary black hole merger population ($m_1\lesssim 44.3^{+8.7}_{-4.6}\,\rm M_\odot$) can be well-modelled by a dominant Gaussian component that peaks at $\cos\theta_{1(2)}\approx0$, possibly mixed with a subdominant isotropic component. Models that include a component with
spins preferentially aligned with the orbit are disfavoured by current data (with Bayes factors $|\Delta\ln\mathcal{B}|\approx1$ to $3$) and constrain its contribution to be likely small ($\xi\sim\mathcal{O}(1)\,\%$), although large contributions cannot yet ruled out with certainty. If these findings are reinforced by more detections, they would challenge any major contribution from the traditional isolated-binary formation scenario yielding closely aligned
spins. Instead, the dominant component with near-perpendicular
spins matches expectations from the
evolution of isolated massive
stellar triples in the
galactic field, where the Lidov-Kozai effect naturally produces a unique overabundance of mergers with $\cos\theta_{1(2)}\approx0$.
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All authors Jakob Stegmann, Fabio Antonini, Aleksandra Olejak, Sylvia Biscoveanu, Vivien Raymond, Stefano Rinaldi, Elizabeth Flanagan
Cosmology and Nongalactic Astrophysics
Dark Acoustic Oscillations as an Early-Universe Explanation of the DESI Anomaly
Mathias Garny, Florian Niedermann and Martin S. Sloth
DESI DR2 data have been widely interpreted as evidence for late-time evolving dark energy (DE) with an apparent phantom crossing. Here we investigate an alternative explanation, based on early-Universe physics. If dark acoustic oscillations (DAO) are close in scale to
baryon acoustic oscillations (BAO), they can bias the extraction of the BAO scale from the peak in the
galaxy correlation function. This leads to an apparent shift in the inferred distance if the superposition of BAO and DAO features is misinterpreted as being due to BAO only. Taking this shift into account, we find that a DAO with percent-level amplitude can reconcile DESI DR2 with Planck 2018 as well as Pantheon+
supernovae data, with fit improvement at a similar level compared to evolving DE. Notably, a DAO feature with the required properties has been predicted in a previously proposed scenario that resolves the Hubble tension via a pre-recombination decoupling of dark matter and dark radiation (DRMD). The presence of a DAO feature close to the BAO peak can be scrutinized with future full-shape
galaxy clustering data from DESI and Euclid.
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Cosmology and Nongalactic Astrophysics
The AIDA-TNG project: dark matter profiles and concentrations in alternative dark matter models
Giulia Despali, Carlo Giocoli, Lauro Moscardini et al. (+3 more)
In the standard Cold Dark Matter (CDM) scenario, the density profiles of dark matter
haloes are well described by analytical models linking their concentration to
halo mass. Alternative scenarios, such as warm dark matter (WDM) and self-interacting dark matter (SIDM), modify the inner structure of
haloes and predict different profile shapes and central slopes. We employ the AIDA-TNG simulations to investigate how alternative dark matter physics and baryonic processes jointly shape the internal structure of
haloes. Using dark-matter-only and full-physics runs, we measure the dark matter density profiles of
haloes spanning six orders of magnitude in mass, from 10^9.5 Msun to 10^14.5 Msub, and characterise them with multiple analytical models. We provide the distribution of the best-fitting parameters, as well as the concentration-mass relation in WDM and SIDM. The Einasto profile well reproduces the inner flattening produced in WDM models, both in the collisionless and in the full-physics runs. In SIDM dark-matter-only runs,
haloes are better described by explicitly cored profiles, with core sizes that depend on mass and on the self-interaction model. When
baryons are included, the differences between CDM and SIDM decrease, and such large dark-matter cores no longer form because adiabatic contraction in the
baryon-dominated region counteracts self-interactions. Nevertheless, the coupling between
baryons and self-interactions induces a broader range of inner slopes, including cases that are steeper than CDM at Milky Way masses. Alternative dark matter physics thus leaves clear signatures in the inner
halo structure, even if
baryons significantly reshape these differences. Our results are useful for future studies that need to predict the properties of
haloes in multiple dark matter models.
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All authors Giulia Despali, Carlo Giocoli, Lauro Moscardini, Annalisa Pillepich, Mark Vogelsberger, Massimo Meneghetti
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Kination and the Inert Doublet Model
Geneviève Bélanger, Nicolás Bernal, Andreas Goudelis et al. (+1 more)
The inert doublet model is a two-
Higgs-doublet extension of the standard model that provides a minimal and versatile framework for frozen-out dark matter. Assuming standard cosmology, if the dark matter mass ranges between approximately 120 GeV and 500 GeV then it turns out to be underabundant, as gauge interactions render its annihilation too efficient. In this work, we show that this mass window becomes allowed in cosmological scenarios where dark matter freeze-out occurs during a period with a stiff equation of state, $w > 1/3$, such as kination. This predictive setup satisfies all current experimental constraints while remaining within the reach of upcoming detection efforts.
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All authors Geneviève Bélanger, Nicolás Bernal, Andreas Goudelis, Alexander Pukhov
Earth and Planetary Astrophysics
A second planetesimal collision in the Fomalhaut system
Paul Kalas, Jason J. Wang, Maxwell A. Millar-Blanchaer et al. (+7 more)
The nearby
star Fomalhaut is orbited by a compact source, Fomalhaut b, which has previously been interpreted as either a
dust-enshrouded
exoplanet or a
dust cloud generated by the collision of two planetesimals. Such collisions are rarely observed but their debris can appear in direct imaging. We report Hubble Space
Telescope observations that show the appearance in 2023 of a second point source around Fomalhaut, resembling the appearance of Fomalhaut b twenty years earlier. We interpret this additional source as a
dust cloud produced by a recent impact between two planetesimals. The positions and motion of two impact-generated
dust clouds over twenty years provide constraints on the collisional dynamics in the debris belt.
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All authors Paul Kalas, Jason J. Wang, Maxwell A. Millar-Blanchaer, Bin B. Ren, Mark C. Wyatt, Grant M. Kennedy, Maximilian Sommer, Thomas M. Esposito, Robert J. De Rosa, Michael Fitzgerald
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Particle Production by Time-Varying Dark Energy and the End of Cosmic Expansion
Nicolas Patino and Paul J. Steinhardt
We consider various possible consequences of time-varying dark energy due to a quintessence scalar field whose energy density is partially converted to particles as the field evolves down its potential. This particle production acts as a source of thermal friction on the field that can make it difficult to distinguish whether dark energy is due to a radiating field rolling down a steep potential, a purely self-interacting field moving down a flatter potential, or a cosmological constant. By reducing the acceleration of the scalar field, thermal friction increases the amount of accelerated expansion and can cause a sizable bump in the quintessence equation of state. We take special interest in the case where a steep potential rapidly changes from positive to negative as the field evolves, resulting in the end of
cosmic expansion and the beginning of contraction. Even in this case, we find that thermal friction lengthens the period of accelerated expansion and consequently delays the end of
cosmic expansion, making it challenging to detect the impending transition to contraction using conventional cosmological tests. However, particle production can also provide alternative avenues for detection by generating a background of thermal dark radiation, partly comprised of
neutrinos or other particles, whose energy density exceeds the remnant
photon energy density.
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Instrumentation and Methods for Astrophysics
Hunting exomoons with a kilometric baseline interferometer
Thomas O. Winterhalder, Antoine Mérand, Sylvestre Lacour et al. (+3 more)
Despite numerous search campaigns based on a diverse set of observational techniques, exomoons - prospective satellites of extrasolar
planets - remain an elusive and hard-to-pin-down class of objects. Yet, the case for intensifying this search is compelling: as in the
Solar System, moons can act as proxies for studying
planet formation and
evolution, provide direct clues as to the migration history of the planetary hosts and, in favourable cases, offer potentially habitable environments. Here, we present an investigation into how the search for exomoons would benefit from a new interferometric facility operating in the optical wavelength domain and leveraging baselines substantially longer than the ones the VLTI is currently equipped with. We find that an interferometer providing an astrometric precision of 1$\,\mu$as would be able to robustly detect Earth-mass and sub-Earth-mass exomoons on dynamically stable orbits around Jupiter-like
planets at distances between 50 and 200 pc.
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All authors Thomas O. Winterhalder, Antoine Mérand, Sylvestre Lacour, Jens Kammerer, Guillaume Bourdarot, Frank Eisenhauer
Cosmology and Nongalactic Astrophysics
The AIDA-TNG project: 3D halo shapes
C. Giocoli, G. Despali, L. Moscardini et al. (+4 more)
Context. The shapes of dark matter
halos can be used to constrain the fundamental properties of dark matter. In standard Cold Dark Matter (CDM) cosmologies,
halos are typically triaxial, with a preference for prolate configurations, particularly at low masses and high
redshift. Aims. We focus on the characterization of total matter 3D shape in alternative dark matter models, such as Self-Interacting Dark Matter (SIDM) and Warm Dark Matter (WDM). These scenarios predict different structural properties due to collisional effects or the suppression of small-scale power. Methods. We measure the different
halo component shapes - dark matter,
stars and gas - at various radii from the center in the AIDA-TNG (Alternative Interacting Dark Matter and Astrophysics - TNG), which is a suite of high-resolution cosmological simulations built upon the IllustrisTNG framework. The intent is to systematically study how different dark matter models - specifically, SIDM and WDM - affect
galaxy formation and the structure of dark matter
halos, when realistic baryonic physics is also included. Results. SIDM models tend to produce rounder and more isotropic
halos, especially in the inner regions, as a result of momentum exchange between dark matter particles. WDM
halos are also slightly more spherical than their CDM counterparts, and are typically less concentrated. In all cases, the inclusion of self-consistent baryonic physics makes the central regions of all
halos rounder, while still revealing clear distinctions among the various dark matter models. Conclusions. The general framework presented in this work, based on the 3D
halo shape, can be useful to interpret multi-wavelength data analyses of
galaxies and clusters.
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All authors C. Giocoli, G. Despali, L. Moscardini, M. Meneghetti, R. K. Sheth, A. Pillepich, M. Vogelsberger
Astrophysics of Galaxies
From "The Cliff" to "Virgil": Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec
Guillermo Barro, Pablo G. Perez-Gonzalez, Dale Kocevski et al. (+26 more)
One of JWST's most unexpected discoveries is the emergence of "Little Red Dots” (LRDs): compact sources at $z \gtrsim 3$ with blue rest-frame UV continua, red optical slopes, and broad Balmer emission lines that challenge standard models and suggest a population of early, unusual active
galactic nuclei (AGNs). Using a comprehensive photometric selection and public NIRSpec/PRISM spectroscopy across six JWST deep fields, we identify a large sample of 118 LRDs with high-S/N spectra, enabling a population-wide analysis of their UV-optical continuum and emission lines. We find clear correlations between rest-frame color ([0.3-0.9\,$\mu$m]) and slopes: bluer LRDs have blue UV slopes ($\beta_{\nu,\mathrm{UV}} \sim 0.3$) and red optical slopes, while redder LRDs exhibit redder UV slopes ($\beta_{\nu,\mathrm{UV}} \sim 1.1$). The continuum shape shows a similar trend: redder LRDs display prominent Balmer breaks and
curvature, while bluer LRDs follow power-law-like optical SEDs. From literature compilations, $\sim$60% of known broad-line AGNs satisfy our LRD criteria, and up to 90% of LRDs show broad Balmer lines. Emission-line diagnostics reveal a shift from high H$_{\alpha}$/H$_{\beta}$ and low [OIII]$\lambda5007$/H$_{\beta}$ in redder LRDs to the opposite in bluer ones, along with stronger narrow-line equivalent widths, suggesting a transition from AGN- to host-dominated emission. We fit the spectra with a two-component model combining a gas-enshrouded black hole (BH) and a
galaxy host. Redder LRDs require higher-luminosity, unreddened BHs and modestly reddened hosts; bluer LRDs require lower-luminosity, reddened BHs and
dust-free
galaxies. This framework reproduces the diversity in colors and spectral shape by varying BH luminosity, obscuration, and host-to-BH luminosity ratio.
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All authors Guillermo Barro, Pablo G. Perez-Gonzalez, Dale Kocevski, Jonathan R. Trump, Mark Dickinson, Pablo Arrabal Haro, Madisyn Brooks, Callum T. Donnan, James S. Dunlop, Steven L. Finkelstein, Maximilien Franco, Giovanni Gandolfi, Mauro Giavalisco, Norman A. Grogin, Michaela Hirschmann, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Rebecca L. Larson, Gene C. K. Leung, Ray A. Lucas, Elizabeth J. McGrath, Casey Papovich, Borja Perez-Diaz, Rachel S. Somerville, Elizabeth Taylor, Anthony J. Taylor, Roberta Tripodi, L. Y. Aaron Yung, Xin Wang
Earth and Planetary Astrophysics
Revealing Callisto's Near Subsurface Thermophysical Properties with ALMA Calibration Data
Cole Meyer, Maria Camarca, Katherine de Kleer et al. (+3 more)
Thermal images at different wavelengths probe varying subsurface depths of planetary bodies, and therefore can inform us about their compositions, thermophysical properties, and impact histories. We identified six archival observations of Callisto obtained by the Atacama Large Millimeter/submillimeter Array (ALMA) between 2012 July 17 and 2012 November 4 at wavelengths of 0.43-0.47 mm (701.9-641.5 GHz). These wavelengths are shorter than those of nearly all other Callisto ALMA data and are sensitive to subsurface emission at depths (the upper ~cm) between those sounded by millimeter and infrared observations. We estimate the disk-averaged brightness temperature as 133$\pm$15 K, and use a thermophysical mixture model to find that Callisto's thermal emission is best fit by a ~50-50% two-component thermal inertia mixture of $\Gamma_{\text{low}}$~15-40 and $\Gamma_{\text{high}}$~1200-2000 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$, consistent with recent ALMA observations of Callisto at longer wavelengths. Finally, we present several previously unpublished Galileo Photopolarimeter-Radiometer (PPR) observations of Callisto and derive thermal inertia and spectral emissivity maps using the same model. Altogether, these ALMA and PPR maps improve our understanding of the thermal properties and spatial distribution of Callisto's shallow subsurface regolith, and demonstrate the value of ALMA flux density calibrator data for extending frequency coverage of existing science data.
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All authors Cole Meyer, Maria Camarca, Katherine de Kleer, Alexander Thelen, Christopher Chyba, Bryan Butler
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmological Neutron Stars Produce Diffuse Axion X-Ray Signatures
Orion Ning, Kailash Raman and Benjamin R. Safdi
Axion-like particles can be abundantly produced through scattering processes in the cores of
neutron stars (NSs). If they are ultralight ($m_a \lesssim 10^{-4}$ eV), then they can efficiently convert to detectable
photons in the external NS magnetospheres, and if they are heavy ($m_a \gtrsim 1$ eV), then they can decay into
photons before reaching Earth. In this work, we search for the resulting X-ray signatures from both of these channels summing over the $\textit{cosmological}$ NS population. We compare the predicted
axion-induced X-ray signal to the
cosmic X-ray background today as measured by a number of instruments such as NuSTAR, HEAO, Swift, and INTEGRAL. We model the
axion-induced signal using NS cooling simulations and
magnetic field
evolution models. We find no evidence for
axions and derive strong constraints for both ultralight and heavy
axion scenarios, covering new parameter space for the
axion-
photon and
axion-nucleon couplings. Our results rule out the
axion-explanation of the Magnificent Seven X-ray excess from nearby isolated NSs.
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High Energy Astrophysical Phenomena
Self-confinement of relativistic pair beams in magnetized interstellar plasmas: the case of pulsar X-ray filaments
Luca Orusa and Lorenzo Sironi
The observation of filamentary X-ray structures near bow-shock
pulsar wind nebulae (PWNe) – such as the Guitar, Lighthouse, and PSR J2030$+$4415 nebulae – and of slow-
diffusion regions around
pulsars like Geminga, Monogem, and PSR J0622$+$3749, challenges the standard picture of
cosmic-ray transport in the interstellar medium, implying a
diffusion coefficient two orders of magnitude smaller than the
Galactic average. The suppressed
diffusion can be attributed to self-generated
magnetic turbulence, driven – via the non-resonant streaming instability – by electron-positron pairs escaping the PWNe. This instability requires a net current, yet the beam of escaping pairs is expected to be charge-neutral. We show that a charge-neutral pair beam propagating through an electron-
proton plasma can spontaneously generate a net current. Using fully kinetic two-dimensional particle-in-
cell simulations with realistic mass ratio, we find that beam electrons get focused into self-generated
magnetic filaments produced by the nonlinear
evolution of the Weibel instability, while beam positrons remain unconfined. We show that in three-dimensional simulations the resulting net (positron) current drives the non-resonant streaming instability, further amplifying the
magnetic field. This mechanism provides a pathway for the onset of charge asymmetries in initially charge-neutral pair beams and for the growth of
magnetic fluctuations that efficiently scatter the beam particles, with implications for the formation of X-ray filaments and, potentially, for particle self-confinement in TeV
halos around PWNe.
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