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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 29 July

Instrumentation and Methods for Astrophysics

Tiny Observatory for Telescope Optimization (TOTO): testing algorithms for autonomous on-orbit alignment for space-based telescope systems

Solvay A. Blomquist, Sanchit Sabhlok, Hyukmo Kang et al. (+11 more)

The Tiny Observatory for Telescope Optimization (TOTO) is an optical testbed designed to evaluate the efficacy of autonomously driven alignment algorithms for space-based telescope systems. For space-based missions, active control of the telescope alignment on-orbit offers potential to relax passive alignment requirements and reduce on-ground verification activities. TOTO is used to evaluate and verify simulation work of two primary alignment algorithms, Stochastic Parallel Gradient Descent (SPGD) and focus-diverse phase retrieval (FDPR). Previous simulation work has confirmed that by using SPGD for coarse alignment followed by focus-diverse phase retrieval for fine alignment, we can reach diffraction-limited performance on-orbit. This paper presents the results of the autonomous alignment algorithm of a Cassegrain telescope using TOTO. We report the current status of TOTO as well as preliminary results from SPGD and phase retrieval on the testbed using monochromatic light source to simulate an on-axis point source.
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All authors Solvay A. Blomquist, Sanchit Sabhlok, Hyukmo Kang, Maggie Y. Kautz, Simran Agarwal, Heejoo Choi, Alexandra Kupersmith, Adam Schilperoort, Kelsey L. Miller, Kyle J. Van Gorkom, Corey Fucetola, Patrick Ingraham, Ewan S. Douglas, Daewook Kim

High Energy Astrophysical Phenomena

Radio Follow-Up of Einstein Probe Fast X-Ray Transients

Carmen Choza, Joe S. Bright, Francesco Carotenuto et al. (+3 more)

Fast X-ray transients (FXTs) are brief, luminous bursts of soft X-ray emission whose physical origins remain uncertain. The Einstein Probe (EP) mission has recently enabled prompt discovery of these events, providing opportunities for rapid multi-wavelength follow-up. We present a coordinated radio observing campaign targeting 20 FXTs detected by the EP in 2024. The core consists of 59 epochs with the Allen Telescope Array (ATA), sampling post-burst timescales from $\sim$1 to $\sim$65 days and reaching typical $3\sigma$ sensitivities of 0.6–1.5\,mJy across 1–8\,GHz. Two FXTs—EP240315a and EP241021a—have radio counterparts. For EP241021a, AMI-LA monitoring at 15.5\,GHz reveals a light curve peaking at $\sim$30 days with $F_{\nu}\approx1.0$\,mJy; equipartition analysis implies a Newtonian equipartition energy of $\sim3\times10^{49}$\,erg and a mildly relativistic on-axis solution with $\Gamma_{\rm on}\approx1.3$. Multi-frequency modelling of EP240315a, combining new VLA measurements with published MeerKAT, ATCA, and eMERLIN data, indicates highly relativistic early emission ($\Gamma\gtrsim3$) that decelerates with time, consistent with jetted outflow. The detections and ATA non-detections span luminosities overlapping the brightest GRB and relativistic tidal disruption event (TDE) afterglows, suggesting FXTs comprise a heterogeneous population including both relativistic and non-relativistic explosions. Under a GRB-like redshift prior, our $3\sigma$ ATA limits correspond to observer-frame specific-luminosity thresholds of $\sim10^{32}$–$10^{33}\,\mathrm{erg\ s^{-1}\ Hz^{-1}}$; for nearby events ($z\lesssim0.2$), $L_{\nu}\lesssim10^{30\text{--}31}\,\mathrm{erg\ s^{-1}\ Hz^{-1}}$. Planned ATA upgrades and next-generation arrays (SKA, DSA, ngVLA) will enable sensitive, population-level radio studies of the FXT radio sky.
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All authors Carmen Choza, Joe S. Bright, Francesco Carotenuto, Alex Pollak, Rob Fender, Andrew Siemion

Instrumentation and Methods for Astrophysics

PhoPS: An automated photometric pipeline for survey-era astronomy

Orhan Erece and Yucel Kilic

Modern astronomical surveys produce large volumes of imaging data together with highly accurate astrometric and photometric reference catalogues, creating a need for automated, robust, and instrument-independent reduction pipelines. We present PhoPS (Photometry and Astrometry of Point Sources), an open-source Python pipeline for fully automated astrometric calibration and photometric reduction of stellar and moving Solar System targets. PhoPS dynamically generates local Gaia DR3 astrometric index files propagated to the observation epoch, eliminating the need for pre-installed index collections while improving astrometric accuracy. Photometric calibration uses a field-dependent zero-point model based on Random Sample Consensus (RANSAC) linear regression to account for spatial systematics such as vignetting and detector non-uniformities. Astrometric performance was evaluated using 141672 matched measurements from 840 images obtained with the 1 m TUG100 telescope. Epoch propagation reduced the clipped N-weighted total RMS residual from 0.284 arcsec to 0.241 arcsec, a 15.0% improvement. The photometric uncertainty model was validated using 203 reference stars and 92980 measurements. Normalized residuals are centered near zero, but their widths are magnitude dependent, with sigma values of 2.069 for bright stars (10 <= G < 13), 1.129 for intermediate-brightness stars (13 <= G < 16), and 0.698 for faint stars (16 <= G < 18), indicating underestimated uncertainties for the brightest stars and conservative uncertainties for the faintest stars. PhoPS provides a lightweight, cross-platform solution for automated astronomical image reduction and is well suited to asteroid light-curve analysis, stellar variability studies, and the diagnosis of observational systematics.
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Cosmology and Nongalactic Astrophysics

Lyman-$\alpha$ forest holography: 3D predictions from 1D measurements

J. Chaves-Montero, A. Font-Ribera, J. Aguilar et al. (+68 more)

Cosmological analyses of Lyman-$\alpha$ forest clustering rely on either one-dimensional correlations along individual sightlines or three-dimensional correlations between different sightlines. Because these observables probe the matter distribution on very different scales, they have traditionally been analyzed independently. In this work, we bridge this gap using ForestFlow, an emulator trained on a suite of cosmological hydrodynamical simulations that provides a unified description of Lyman-$\alpha$ forest clustering from linear to nonlinear scales. This framework enables us to determine the range of three-dimensional clustering models compatible with the DESI one-dimensional flux power spectrum ($P_{\rm 1D}$). The resulting predictions successfully reproduce the large-scale clustering measured by the DESI BAO analysis and provide physically motivated priors on nonlinear clustering that are used in a companion paper presenting the full-shape analysis of the DESI DR2 Lyman-$\alpha$ forest. We validate our methodology using the large-volume, high-resolution hydrodynamical simulation ACCEL-2, demonstrating excellent agreement across the full range of scales considered. Finally, we combine constraints from the $P_{\rm 1D}$ and BAO analyses on the parameter combinations $b_\delta \sigma_8$ and $b_\eta f \sigma_8$, finding that the two probes provide comparable constraining power while exhibiting complementary parameter degeneracies. Our results establish a direct connection between one- and three-dimensional Lyman-$\alpha$ forest measurements through ForestFlow, an approach we term Lyman-$\alpha$ holography by analogy with the reconstruction of higher-dimensional structure from lower-dimensional information.
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All authors J. Chaves-Montero, A. Font-Ribera, J. Aguilar, S. Ahlen, E. Armengaud, A. Aviles, F. Beutler, D. Bianchi, S. Blasby, D. Brooks, K. Carrion, Z. Chen, T. Claybaugh, A. Cuceu, A. de la Macorra, A. Dey, P. Doel, W. Elbers, S. Ferraro, L. Flores, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, D. Gonzalez, A. X. Gonzalez-Morales, R. Gsponer, G. Gutierrez, C. Hahn, M. Herbold, H. K. Herrera-Alcantar, K. Honscheid, M. Ishak, S. Juneau, N. V. Kamble, D. Kirkby, A. Kremin, A. Lambert, M. Landriau, L. Le Guillou, K. Lodha, Z. Lukić, M. Manera, P. Martini, A. Meisner, R. Miquel, P. Mukherjee, A. Muñoz-Gutiérrez, S. Nadathur, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, H. Pulido-Hernández, I. Pérez-Ràfols, C. Ravoux, J. Rohlf, A. J. Rosado-Marín, G. Rossi, R. Ruggeri, M. F. Ruiz-Herrera Bernal, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, F. Sinigaglia, G. Tarlé, W. Turner, B. A. Weaver, H. Zhang

Cosmology and Nongalactic Astrophysics

CoLoRe-2LPT: Lyman-$\alpha$ mock catalogues for the validation of DESI cosmological analyses

M. F. Ruiz-Herrera Bernal, S. Avila, A. Font-Ribera et al. (+90 more)

The Lyman-$\alpha$ (Ly$\alpha$) forest has become a crucial probe for studying the large-scale structure of the universe at high redshift ($z > 2$), providing powerful constraints on Baryon Acoustic Oscillations (BAO) and the full-shape (FS) clustering of matter. As a key ingredient for upcoming BAO and FS analyses, we present a new generation of fast cosmological Ly$\alpha$ mocks based on second-order Lagrangian perturbation theory (2LPT). These new mocks significantly improve upon previous log-normal approaches, both at accurately capturing small scale clustering and at recovering the non-linear broadening of the BAO peak. They are able to reproduce Ly$\alpha$ statistics within $10\%$ of the latest DESI measurement; including the Ly$\alpha$ bias and the redshift-space distortion $\beta$ parameter, mean transmitted flux, and 1D power spectrum. The corresponding quasar (QSO) clustering is also improved with respect to previous approaches, calibrated against high-resolution Abacus simulations, recovering the observational QSO linear bias to less than $5\%$ and improving redshift-space distortions via 2LPT velocities and the addition of Fingers-of-God effects. Furthermore, these mocks incorporate high column density systems and metal lines, allowing us to explore the effects and systematics induced by these astrophysical contaminants. This new set of mocks has been key for enhancing the modeling and validation of the DESI DR2 Ly$\alpha$ full shape cosmological analysis. This work provides a physically motivated and computationally efficient tool for simulating current and next-generation Ly$\alpha$ surveys and validating FS and BAO analysis.
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All authors M. F. Ruiz-Herrera Bernal, S. Avila, A. Font-Ribera, H. K. Herrera-Alcantar, D. Alonso, A. Cuceu, L. Casas, F. Sinigaglia, J. Aguilar, S. Ahlen, O. Alves, U. Andrade, E. Armengaud, A. Bault, F. Beutler, D. Bianchi, M. Bonici, A. Brodzeller, D. Brooks, A. Carnero Rosell, J. Chaves-Montero, Z. Chen, Y. Cho, T. Claybaugh, K. S. Dawson, A. de la Macorra, A. Dey, W. Elbers, S. Ferraro, J. E. Forero-Romero, G. Gambardella, S. Gontcho A Gontcho, D. Gonzalez, A. X. Gonzalez-Morales, C. Gordon, R. Gsponer, G. Gutierrez, J. Guy, C. Hahn, M. Herbold, K. Honscheid, M. Ishak, S. Jos, S. Juneau, N. V. Kamble, T. Karim, D. Kirkby, A. Kremin, M. Landriau, A. Leauthaud, Q. Li, W. Liu, K. Lodha, O. Manasoiu, M. Manera, P. Martini, A. Meisner, R. Miquel, J. Morawetz, P. Mukherjee, A. Muñoz-Gutiérrez, S. Nadathur, G. Niz, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, J. Pan, M. Pellejero Ibanez, W. J. Percival, C. Poppett, F. Prada, H. Pulido-Hernández, A. Pérez-Fernández, I. Pérez-Ràfols, C. Ravoux, J. Rohlf, G. Rossi, R. Ruggeri, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, H. Seo, J. Silber, T. Simon, M. Siudek, G. Tarlé, W. Turner, R. Vaisakh, M. Vargas-Magaña, B. A. Weaver, H. Yang, H. Zhang

Cosmology and Nongalactic Astrophysics

Validation of the DESI DR2 Ly$\alpha$ forest full-shape analysis

M. Herbold, A. Cuceu, P. Martini et al. (+100 more)

We present the validation of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) Lyman-$\alpha$ (Ly$\alpha$) forest full-shape analysis. This analysis combines three-dimensional Ly$\alpha$ forest auto-correlations and cross-correlations with quasars to extract information from both the baryon acoustic oscillation (BAO) feature and the broadband clustering signal, with primary emphasis on the Alcock-Paczynski (AP) measurement. Compared to the DESI DR1 analysis, the DR2 validation uses substantially larger and more realistic mock datasets, including CoLoRe 2LPT and AbacusSummit Ly$\alpha$ forest simulations. The modeling framework is also improved through analytic marginalization over small scales ($<10$ $h^{-1}$Mpc) and the impact of ultraviolet background fluctuations. The validation program was completed prior to unblinding and defines quantitative requirements for the cosmological parameters of interest, which are evaluated using hundreds of mock realizations. We further test the analysis through independent fits to the auto- and cross-correlations, multiple catalog splits, and a broad suite of analysis and modeling variations applied to both mocks and blinded observational data. We find that the BAO and AP parameters satisfy all validation requirements and remain stable across all tests. In contrast, mock studies reveal a significant bias in the inferred growth-rate parameter $f\sigma_8$, leading us to exclude this measurement from the final analysis. The consistency across mocks, data splits, and robustness tests demonstrates that the DR2 Ly$\alpha$ full-shape analysis provides a reliable and substantially improved broadband AP measurement over previous Ly$\alpha$ forest studies.
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All authors M. Herbold, A. Cuceu, P. Martini, H. K. Herrera-Alcantar, J. Guy, C. Gordon, O. Manasoiu, J. Aguilar, S. Ahlen, O. Alves, U. Andrade, E. Armengaud, S. Avila, A. Aviles, A. Bault, F. Beutler, D. Bianchi, M. Bonici, A. Brodzeller, D. Brooks, A. Carnero Rosell, E. Chaussidon, J. Chaves-Montero, Z. Chen, T. Claybaugh, K. S. Dawson, A. de la Macorra, A. Dey, W. Elbers, V. A. Fawcett, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, G. Gambardella, S. Gontcho A Gontcho, D. Gonzalez, A. X. Gonzalez-Morales, R. Gsponer, G. Gutierrez, B. Hadzhiyska, C. Hahn, K. Honscheid, D. Huterer, M. Ishak, S. Jos, S. Juneau, N. V. Kamble, N. G. Karaçayl{\i}, T. Karim, R. Kehoe, D. Kirkby, F.-S. Kitaura, A. Kremin, O. Lahav, M. Landriau, J. Lasker, L. Le Guillou, A. Leauthaud, M. E. Levi, Q. Li, W. Liu, K. Lodha, M. Manera, A. Meisner, R. Miquel, J. Morawetz, J. Moustakas, P. Mukherjee, A. Muñoz-Gutiérrez, S. Nadathur, G. Niz, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, J. Pan, M. P. Ibanez, W. J. Percival, F. Prada, H. Pulido-Hernández, A. Pérez-Fernández, I. Pérez-Ràfols, C. Ravoux, J. Rohlf, G. Rossi, R. Ruggeri, M. F. Ruiz-Herrera Bernal, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, H. Seo, J. Silber, T. Simon, F. Sinigaglia, M. Siudek, G. Tarlé, W. Turner, R. Vaisakh, M. Vargas-Magaña, B. A. Weaver, M. Wolfson, H. Yang, H. Zhang

Cosmology and Nongalactic Astrophysics

DESI DR2 Results IV: Alcock-Paczyński Measurements from the Lyman Alpha Forest and Cosmological Constraints

DESI Collaboration: A. G. Adame, J. Aguilar, S. Ahlen et al. (+151 more)

We present Alcock-Paczyński (AP) measurements from the full shape of Lyman-$\alpha$ (Ly$\alpha$) forest correlation functions measured from the second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI). Our measurements include information from the Ly$\alpha$ forest auto-correlation and its cross-correlation with quasars. We constrain the AP effect with $1\%$ precision at an effective redshift $z_\mathrm{eff}=2.33$, which is twice as tight as the Baryon Acoustic Oscillation (BAO) constraint from the same data. When using the joint Ly$\alpha$ AP and BAO results, we measure the ratios $D_\text{H}(z_\mathrm{eff})/r_\text{d}=8.600 \pm 0.066$ and $D_\text{M}(z_\mathrm{eff})/r_\text{d}=39.32 \pm 0.33$, where $D_\text{M}$ is the transverse comoving distance, $D_\text{H}$ is the Hubble distance, and $r_\text{d}$ is the sound horizon at the drag epoch. Assuming $\Lambda$CDM, Ly$\alpha$ forest measurements combined with a nucleosynthesis prior produce a constraint on the Hubble constant $H_0=66.5\pm1.3\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$. The Ly$\alpha$ AP result corresponds to a matter fraction constraint $\Omega_\text{m}=0.325\pm0.018$ in $\Lambda$CDM, which is $1.4\sigma$ higher than DESI BAO. This impacts the DESI results relative to the Cosmic Microwave Background (CMB), slightly reducing their discrepancy from $2.4\sigma$ to $2.2\sigma$. We present updated constraints on extended models using the joint DESI DR2 BAO and Ly$\alpha$ forest full shape data, together with external data sets. When considering a time-evolving dark energy equation of state parametrized by $w_0$ and $w_a$, we find it is preferred over $\Lambda$CDM at $2.7\sigma$ for the combination of DESI and CMB data, and at $3.2\sigma$ when also including supernovae. With the new Ly$\alpha$ AP measurement, DESI provides its most precise anchor for the expansion history at $z > 1$ in the matter-dominated Universe.
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All authors DESI Collaboration: A. G. Adame, J. Aguilar, S. Ahlen, O. Alves, A. Anand, U. Andrade, E. Armengaud, S. Avila, A. Aviles, P. Bansal, A. Bault, J. R. Bermejo-Climent, F. Beutler, D. Bianchi, C. Blake, S. Blasby, M. Bonici, S. Brieden, A. Brodzeller, D. Brooks, A. Carnero Rosell, K. Carrion, L. Casas, F. J. Castander, E. Chaussidon, J. Chaves-Montero, D. Chebat, X. Chen, Z. Chen, Y. Cho, T. Claybaugh, A. Cuceu, T. M. Davis, K. S. Dawson, R. de Belsunce, A. de la Macorra, J. Della Costa, A. Dey, M. Doshi, H. Ebina, D. J. Eisenstein, W. Elbers, G. Farren, V. A. Fawcett, E. Fernández-García, S. Ferraro, A. Font-Ribera, D. Forero-Sánchez, J. E. Forero-Romero, C. S. Frenk, G. Gambardella, C. Garcia-Quintero, L. H. Garrison, H. Gil-Marín, S. Gontcho A Gontcho, A. X. Gonzalez-Morales, C. Gordon, D. Green, R. Gsponer, G. Gutierrez, J. Guy, B. Hadzhiyska, C. Hahn, S. He, M. Herbold, H. K. Herrera-Alcantar, M.-F. Ho, K. Honscheid, J. Hou, D. Huterer, V. Iršič, M. Ishak, J.-Q. Jiang, S. Jos, S. Juneau, N. V. Kamble, N. G. Karaçayl{\i}, T. Karim, D. Kirkby, A. Kremin, A. Krolewski, O. Lahav, C. Lamman, M. Landriau, J. Lasker, J.M. Le Goff, L. Le Guillou, A. Leauthaud, Q. Li, W. Liu, K. Lodha, Y. Luo, O. Manasoiu, M. Manera, P. Martini, M. Maus, A. Meisner, R. Miquel, J. Morawetz, J. Moustakas, E. Mueller, P. Mukherjee, A. Muñoz-Gutiérrez, A. D. Myers, S. Nadathur, J. Najita, G. Niz, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, J. Pan, M. P. Ibanez, W. J. Percival, A. Porredon, F. Prada, H. Pulido-Hernández, A. Pérez-Fernández, I. Pérez-Ràfols, A. Raichoor, M. Rashkovetskyi, J. Ratajczak, C. Ravoux, A. Robertson, A. Rocher, J. Rohlf, A. J. Ross, G. Rossi, R. Ruggeri, M. F. Ruiz-Herrera Bernal, L. Samushia, E. Sanchez, C. Saulder, D. Schlegel, H. Seo, A. Shafieloo, R. Sharples, J. Silber, T. Simon, F. Sinigaglia, M. Siudek, T. Tan, G. Tarlé, W. Turner, R. Vaisakh, M. Vargas-Magaña, B. A. Weaver, M. Wolfson, H. Yang, J. Yu, C. Yèche, H. Zhang, Y. Zhang, R. Zhao, R. Zhou

High Energy Astrophysical Phenomena

Binary neutron star populations across cosmic time: the impact of binary stellar evolution uncertainties

Mathieu Venet and Irina Dvorkin

We investigate the impact of uncertainties in binary stellar evolution on the formation efficiency and cosmological merger rate of BNS systems. In particular, we aim to determine whether robust signatures of binary evolution can be identified across a broad range of metallicities. We perform a systematic exploration of 72 binary evolution models using the population synthesis code COSMIC. We vary four key parameters controlling the onset and efficiency of common-envelope evolution, the natal kick prescription, and the treatment of kicks during the common envelope phase. For each model, we compute the BNS formation efficiency and cosmological merger rate using several prescriptions for the cosmic metallicity-redshift relation. We identify characteristic features in the metallicity dependence of the BNS formation efficiency that arise from specific evolutionary processes. These include the onset of first-giant-branch skipping at low metallicity and a non-monotonic evolution between $Z=10^{-3}$ and $7.5\times 10^{-3}$. All models also predict a bimodal distribution of BNS progenitor masses associated with two distinct formation channels. The common envelope ejection efficiency and natal kick prescription remain the dominant sources of uncertainty, producing variations of several orders of magnitude in both the BNS formation efficiency and the cosmological merger rate. Finally, we show that different combinations of binary-evolution parameters can produce similar merger-rate histories, highlighting significant degeneracies among population-synthesis models. Current gravitational-wave observations can rule out only the least efficient formation scenarios. Breaking these degeneracies will require larger samples of BNS mergers expected from future third-generation gravitational-wave observatories, and improved observational constraints on the evolution of metallicity across cosmic time.
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Astrophysics of Galaxies

Cosmic Pairs: A DESI Census of Dual and Offset AGN as Precursors to Massive Black Hole Binaries

Ekaterine Dadiani, Antonella Palmese, Yihao Zhou et al. (+52 more)

We present a systematic census of dual and offset active galactic nuclei (AGN) using spectroscopic data from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI). After correcting for observational systematics, our final sample contains $>7,000$ dual AGN and 27,000 galaxy pairs containing one AGN over the redshift range $0 \lesssim z \lesssim 3.6$. This sample expands the known dual AGN sample by $\sim 1-2$ orders of magnitude at $0.2 \lesssim z \lesssim 0.4$, includes $\sim 50$ dwarf dual AGN candidates in a regime where only a handful were previously known, and triples the census at $z>2$. Dual AGN are preferentially found at small separations, consistent with merger-driven triggering of AGN activity. The two members of a pair differ in their star formation response: the more massive (primary) host changes little with separation, while the less massive (secondary) lies $\sim 0.3$ dex above matched inactive and one-AGN companions at the same projected separation in main-sequence offset. Using ASTRID simulations, we predict that the fraction of DESI dual AGN whose central black holes will merge by $z \sim 0$ increases with redshift, reaching $\sim 76\%$ by $z \sim 2$, while the fraction producing LISA-detectable mergers peaks at $\sim 37\%$ near $z \sim 0.9$. These results provide the largest uniformly selected spectroscopic sample of kpc-scale dual and offset AGN candidates from a single survey, connecting their host-galaxy and AGN demographics to the progenitor population of massive black hole mergers detectable by LISA.
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All authors Ekaterine Dadiani, Antonella Palmese, Yihao Zhou, Nianyi Chen, Tiziana Di Matteo, Alejandro Eróstegui, Mar Mezcua, Jessica Nicole Aguilar, Steven Ahlen, Stephen Bailey, Florian Beutler, Davide Bianchi, David Brooks, Todd Claybaugh, Axel de la Macorra, Arjun Dey, Biprateep Dey, Peter Doel, Victoria A. Fawcett, Benjamin Floyd, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Mustapha Ishak, Robert Kehoe, Anthony Kremin, Ofer Lahav, Andrew Lambert, Martin Landriau, Laurent Le Guillou, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Seshadri Nadathur, Enrique Paillas, Will J. Percival, Francisco Prada, Ignasi Pérez-Ràfols, Ragadeepika Pucha, Corentin Ravoux, Graziano Rossi, Rossana Ruggeri, Eusebio Sanchez, Christoph Saulder, David Schlegel, Michael Schubnell, Hee-Jong Seo, Joseph Harry Silber, Małgorzata Siudek, Gregory Tarlé, Benjamin Alan Weaver, DESI Collaboration

Astrophysics of Galaxies

Exploring the Limits of Spectral Line Stacking in Spectral Line Data and Application Toward the Detection of Bulk $^{13}$C Enrichment of Aromatics in TMC-1

Miya Duffy, Ryan A. Loomis, Martin S. Holdren et al. (+9 more)

The formation history of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium remains a topic of active debate, with proposed mechanisms ranging from high-temperature stellar ejecta processes to low-temperature chemistry within molecular clouds. Recently, the identification of small PAHs in the cold, dark cloud TMC-1 has provided some circumstantial evidence of the latter. If these are formed in situ, their isotopic ratios, particularly $^{12}$C/$^{13}$C, should reflect the local, bulk material of the molecular cloud; in contrast, PAHs formed in the circumstellar envelopes of evolved stars may show enhanced $^{13}$C abundances. The expected radio signals of these $^{13}$C substituted species will be faint, and thus we conducted a detailed proof-of-concept analysis examining whether spectral line stacking and matched filtering techniques can robustly retrieve signal from multiple singly substituted $^{13}$C isotopologues in aggregate. We find that while retrieved signal decreases in the limit of spectral line confusion, false-positive detections are exceedingly improbable at the adopted 5$\sigma$ matched filter response detection threshold. We then demonstrate the technique on actual observational data of isotopologues of HC$_9$N toward TMC-1. Finally, we show using synthetic data that if laboratory rotational spectra of all singly substituted $^{13}$C isotopologues of cyanonaphthalene and cyanopyrene isomers existed, current observations of TMC-1 would be sensitive enough to discriminate between a local, bulk $^{12}$C/$^{13}$C ratio and one with an enhanced $^{13}$C abundance suggestive of inheritance.
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All authors Miya Duffy, Ryan A. Loomis, Martin S. Holdren, Andrew Lipnicky, D. Archie Stewart, Gabi Wenzel, Ci Xue, Annapoorani Hariharan, Ilsa R. Cooke, Anthony J. Remijan, Michael C. McCarthy, Brett A. McGuire

Earth and Planetary Astrophysics

High-Resolution Dayside Spectroscopy of the Ultra-Hot Jupiter WASP-178b with GHOST/Gemini South

Caitlin E. Bell, Emily K. Deibert, Adam B. Langeveld et al. (+4 more)

We present high-resolution dayside spectroscopy of the ultra-hot Jupiter WASP-178b obtained with the Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South Observatory. The observations cover pre- and post-eclipse orbital phases, lasting approximately 9 hours in total, and represent the first published high-resolution optical dayside emission spectroscopy of WASP-178b's atmosphere, complementing previous near-infrared dayside spectroscopy. We verify the presence of a thermal inversion in the dayside atmosphere with a high-significance (8.3$\sigma$) detection of neutral iron emission via the Doppler cross-correlation technique, alongside hints of neutral Si and Ca emission. We also carry out model injection/recovery tests for other atmospheric species, which indicate that we do not expect to detect the majority of species searched for in this work, assuming our models are accurate representations of the planet's atmosphere. Finally, we place our results into context with previous work, showing how our tentative detection of neutral Si complements existing space-based observations and adds a new data point to previous detections of Si in ultra-hot Jupiter atmospheres. Our high-resolution observations provide important context about the dayside of WASP-178b, shedding light on 3D atmospheric processes and the extreme conditions present in ultra-hot Jupiter atmospheres.
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All authors Caitlin E. Bell, Emily K. Deibert, Adam B. Langeveld, Ernst de Mooij, Ray Jayawardhana, Laura Flagg, Jake D. Turner

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

Spectator Axions in String Inflation and Primordial Black Holes

Michele Cicoli, Dario L. Lorenzoni, Evan McDonough et al. (+1 more)

We study the impact of light spectator axions on the seeding of primordial black holes (PBHs) during inflation in string theory. Primordial black holes exhibit unique and novel phenomenology, and may constitute the observed dark matter. Cosmic inflation provides a mechanism for producing them, but such inflation models typically feature Planckian field excursions, necessitating an ultraviolet completion into quantum gravity. String theory provides a natural framework for doing so, and indeed Fibre Inflation has been shown to produce PBHs while satisfying constraints from cosmic microwave background data. In this work we study the dynamics of axions during Fibre Inflation, and find a diverse and rich set of possibilities, including turns in field space and enhancement of primordial perturbations. We find that across most of parameter space, notably an axion with a far sub-Planckian decay constant $f\ll M_{\rm Pl}$, there is a negligible impact on the power spectrum of curvature perturbations, indicating an overall robustness of the model. On the other hand, an axion with a larger but still sub-Planckian decay constant, $f\gtrsim {\cal O}(0.1) M_{\rm Pl}$, and an exponentially small prefactor of its non-perturbative potential, can enhance the growth of perturbations, making it easier to achieve the amplification needed to seed PBHs, effectively realizing axion-assisted PBHs in string theory.
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All authors Michele Cicoli, Dario L. Lorenzoni, Evan McDonough, Francisco G. Pedro

Instrumentation and Methods for Astrophysics

Laboratory characterization of iLocater

Marcelo Tala Pinto, Marshall C. Johnson, Julia Brady et al. (+18 more)

iLocater is a diffraction-limited, fiber-fed spectrograph designed for the Large Binocular Telescope (LBT), which targets high-precision radial velocity measurements in the near-infrared. Prior to deployment, comprehensive laboratory characterization was essential to validate instrument performance and inform alignment strategies. This paper presents results from four key areas of lab characterization: (1) adjustment and optimization of detector orientation to optimize spectrum alignment with the detector pixel grid across the focal plane; (2) the design and installation of a LED illumination source to enable high-fidelity flat-fields; (3) a model-based focusing methodology using OpticStudio image simulations to optimize the optical alignment of the spectrograph; and (4) assessment of instrument mechanical and optical stability under laboratory conditions. Together, these efforts established baseline performance metrics and demonstrated instrument readiness for delivery and on-sky commissioning.
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All authors Marcelo Tala Pinto, Marshall C. Johnson, Julia Brady, Xavier Lesley-Saldaña, Jonathan Crass, Allie Renshaw, Michael Engelman, Brian Sands, Daniel Pappalardo, Christian Schwab, Julian Stürmer, Dane Zielinski-Nicolson, Stanimir Letchev, Matheus J. Castro, Thomas Legero, Ondrej Kitzler, Jacob Pember, Richard Pogge, Justin R. Crepp, Andrew Bechter, Eric Bechter

Earth and Planetary Astrophysics

A Systematic Trend in the Observed vs. Predicted Radii of Transiting Brown Dwarfs

Thomas G. Beatty

Transiting brown dwarfs provide a direct empirical test of substellar evolutionary models, and with more than 50 now known we can carry out this test at the population level. We compared the observed masses and radii of 31 field-age, weakly irradiated transiting brown dwarfs to the Sonora Diamondback, Sonora Bobcat, and ATMO 2020 grids, and a subset of 23 of them to the irradiated models of Mukherjee et al. (2026). In every comparison we find a radius-dependent trend, with fits of $R_{\rm pred}$ versus $R_{\rm obs}$ yielding slopes of $0.3{-}0.4$, shallower than the one-to-one relation at $3.7{-}8\sigma$. The mean inflation is $5{-}14\%$ depending on the grid, reaching $\sim20\%$ among the largest objects. We also measure an intrinsic dispersion of $8{-}12\%$, two to three times the measurement uncertainty. While the mean inflation offset varies by a factor of three among grids, this dispersion does not, indicating that it is a property of the population and not the models. We find no correlation with mass, equilibrium temperature, orbital separation, tidal heating rate, or age, and only a marginal ($1.7\sigma$) trend with host-star metallicity. Most notable is the absence of any trend with irradiation, which argues against hot Jupiter-like stellar heating as the primary cause. We instead suggest that brown dwarfs span a wider range of atmospheric boundary conditions than current grids represent. The brown dwarf radius inflation is comparable to that in fully convective M dwarfs, and it is likely the transiting counterpart to the luminosity discrepancies seen in dynamical-mass benchmarks. If the trend extends below the deuterium-burning limit, it would bias directly imaged planet mass estimates, overestimating luminosity-age masses by several to ten percent and requiring spectroscopic-gravity masses to be revised upward by $\sim20{-}45\%$.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics

New techniques for high-resolution imaging and high-precision wavefront sensing via masked-aperture interferometry

Nithyanandan Thyagarajan, Bojan Nikolic, Chris Carilli et al. (+2 more)

Achieving high-angular-resolution imaging on subarcsecond scales is fundamentally limited by wavefront aberrations imparted by the propagation medium and by optical elements along the light path. Accurate recovery of source structure at these fine angular scales therefore relies on precise, real-time sensing and correction of wavefront aberrations. Drawing inspiration from radio interferometry, we have developed different approaches using masked apertures that directly measure both the amplitude and phase of the distortions to the electromagnetic wavefront while simultaneously reconstructing the underlying source structure. First is radio interferometry style self-calibration which can recover the complex electric field aberrations across the aperture with subarcsecond phase accuracy, equivalent to nanometer-level precision in optical pathlength, and simultaneously reconstruct the source structure with milliarcsecond (sub-micron) accuracy. Second is closure invariant-based source reconstruction which allows to bypass self-calibration and errors therein entirely while achieving comparable fidelity in the recovered source structure. These methods have been validated on the ALBA synchrotron beamline. Together, these methods provide a reliable framework for nanometre-scale high-precision wavefront sensing and subarcsecond-scale high angular resolution imaging, enabling new possibilities for masked-aperture interferometry. Potential applications span laboratory and synchrotron facilities to astronomy, including beam diagnostics in the Large Hadron Collider and masked-aperture interferometry on space telescopes such as the James Webb Space Telescope.
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All authors Nithyanandan Thyagarajan, Bojan Nikolic, Chris Carilli, Laura Torino, Ubaldo Iriso

Solar and Stellar Astrophysics · Cross-listed from hep-ex

First Experimental Bounds on Transverse Plasmon Solar Axions with ANAIS-112

S. J. Hollick, M. Giannotti, J. Ruz et al. (+16 more)

Solar axion-like particles (ALPs) can be resonantly produced through the conversion of transverse plasmons in the magnetic field of the solar interior, introducing a production mechanism complementary to the conventional Primakoff process. In this Letter, we report the first experimental search for solar ALPs produced through this mechanism. Using an exposure of 625.75 kg$\times$yr from ANAIS-112, we search for the annual modulation of the flux induced by the variation of the Earth–Sun distance, assuming detection through inverse Primakoff conversion in the detector. Modulation amplitudes fitted in 1 keV bins between 1–20 keV are consistent with the absence of modulation, yielding the first constraints on the axion–photon coupling that include the resonant transverse-plasmon flux, $g_{a\gamma} < 1.32\times 10^{-9} \mathrm{GeV}^{-1}$ (90% C.L.) at $m_a \simeq 150$ eV. This previously unexplored production channel extends the sensitivity of ANAIS-112 in the mass range 35–280 eV, where, for the expected solar magnetic-field models, the transverse-plasmon flux exceeds the Primakoff flux by up to two orders of magnitude.
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All authors S. J. Hollick, M. Giannotti, J. Ruz, J. K. Vogel, R. M. Alkaddah, J. Amaré, J. Apilluelo, S. Bharat, S. Cebrián, D. Cintas, I. Coarasa, E. García, M. Martínez, Y. Ortigoza, A. Ortiz de Solórzano, T. Pardo, J. Puimedón, M. L. Sarsa, C. Seoane

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Inflation in unimodular loop quantum cosmology

Steffen Gielen and Rita B. Neves

We study inflation in the setting of unimodular loop quantum cosmology, where time evolution is defined in unimodular time rather than with respect to a free, massless scalar field as is standard in loop quantum cosmology. The unimodular setting leads to a natural Schrödinger time evolution in a time coordinate with clear geometric meaning, defined independently of any particular matter content; an inflaton can be included but is not needed as a clock. We review the unimodular version of loop quantum cosmology and comment on possible connections to full (unimodular) loop quantum gravity. Then, focusing on semiclassical effective equations, we derive analytical solutions in simple cases such as a constant potential, emphasising the use of a unimodular time coordinate. We also discuss numerical solutions for phenomenologically interesting cases such as a quadratic potential and Starobinsky inflation, comparing different possible choices of initial conditions. In particular, we show that choosing an $\alpha$-attractor potential allows for models of a bounce either dominated by kinetic or potential energy, which are compatible with observations while potentially including observable imprints of the quantum-gravity regime.
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Cosmology and Nongalactic Astrophysics

Gravitational Waves as a Source of Large-Scale White Noise: New Constraints

Gabriela Barenboim and Albert Stebbins

A stochastic gravitational wave (GW) background sources a shear in the flow of cosmic fluid which, through non-linear mode coupling, generates large-scale white noise (LSWN) in the kurvature density field. Building on the LSWN framework of our previous work, we derive the amplitude of this GW-induced LSWN and translate the observational non-detection of LSWN into bounds on the production redshift and density of gravity waves. In particular, a minimal constraint on gravity waves with $z=0$ density parameter $\Omega_\mathrm{GW0}^*$ in frequency band $f_*$ generated at redshift $z_*$ must satisfy ${z_*}^2\,\Omega_\mathrm{GW0}^*<5\times10^7\,(f_*/\mathrm{nHz})^{3/2}$. This, for example, precludes the gravity waves recently detected by pulsar timing arrays \cite{NANOGrav:2023hvm} from being present before $z_*\sim10^8$, long after the quark hadron phase transition. While orders of magnitude stronger than other constraints on gravity waves, this is a minimal LSWN constraint as realistic modeling of early universe gravity wave production, including the granularity of the gravity-wave sources and the LSWN produced by the associated acoustic waves would probably tighten this constraint by orders of magnitude.
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High Energy Astrophysical Phenomena

Exploring cosmic magnetism with gamma-ray burst afterglow emission

Paolo Da Vela, Davide Miceli, Lara Nava et al. (+1 more)

The nature and origin of magnetic fields on cosmological scales are still unclear. Magnetic fields detected in galaxies and galaxy clusters are typically interpreted as the result of the amplification of weak seed fields, but their nature remains largely unknown with two scenarios considered: the cosmological and the astrophysical origin. Signatures of magnetization in cosmic voids from observations of very high energy (VHE, E > 100 GeV) photons from extragalactic sources can provide crucial results. Indeed, if a non-negligible intergalactic magnetic field (IGMF) is present in the voids, a time-delayed emission known as pair-echo is expected. The timing and intensity of this signal encode information on the IGMF strength B and properties. Given the recent detection of gamma-ray burst (GRB) afterglows at TeV energies, for this study we performed a detectability study of pair-echo signatures from GRBs. We simulated afterglow emission for different values of the jet kinetic energy (E$_{k,iso}$ = 10$^{49}$ - 10$^{55}$ erg), redshift (z = 0.03 - 1), and lightcurve break times, and estimated the expected pair-echo radiation for IGMF strengths in the range B = 10$^{-19}$ - 10$^{-16}$ G. We investigated the capability of CTAO to detect the resulting emission at tens of GeV. We find that a subsample of GRBs in the z - E$_{k,iso}$ parameter space can produce a detectable pair-echo component for CTAO for all the tested IGMF strengths. A steepening of the GRB afterglow light curve, caused e.g. by an early (0.1 - 1 days) jet break, is a key factor to increase the chances of detection. CTAO observations starting from 10 - 12 h after the GRB trigger and extending up to a few days can provide valuable information on the IGMF.
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All authors Paolo Da Vela, Davide Miceli, Lara Nava, Giancarlo Ghirlanda

High Energy Astrophysical Phenomena

Relativistic effects of PSR~J1856–0039 double neutron star system in a 2.36-hour compact orbit

Z. L. Yang, J. L. Han, W. Q. Su et al. (+11 more)

Compact double neutron star (DNS) systems are unique laboratories for testing gravitational theories and studying DNS mergers. Here we report the properties of a new DNS system, PSR J1856–0039, discovered in the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is mildly recycled with a period of 23.4~ms in a compact eccentric orbit ($e=0.106$) with an orbital period of 2.36 hours. By following up FAST observations, we measured the relativistic effects, including the orbital period derivative $\dot{P}_{\rm orb}=-1.284\pm0.019\times10^{-12}$ s s$^{-1}$, periastron advance $\dot\omega=17.5859\pm0.0007$ deg yr$^{-1}$, and Einstein delay $\gamma=0.445\pm0.011$ ms. This DNS system has a low orbital inclination of $i=133^\circ.2\pm1^\circ.1$ and the lowest total mass of any known DNS, $M_{\rm tot}=2.48841\pm0.00015 M\odot$, with a determined pulsar mass of $1.304\pm0.022 M_\odot$ and a companion mass of $1.185\pm0.022 M_\odot$, one of the lowest neutron-star masses. The observed orbital decay due to gravitational-wave emission $\dot{P}^{\rm GW}_{\rm orb,obs}$ and the orbital decay predicted by general relativity $\dot{P}^{\rm GW}_{\rm orb,pred}$ are consistent at a level of $\dot{P}^{\rm GW}_{\rm orb,obs}/\dot{P}^{\rm GW}_{\rm orb,pred}=$1.009(14) (68% confidence). This DNS will merge after 82 Myr and may form a stable neutron star or collapse into a black hole after spin-down. Long-term monitoring could potentially probe the Lense-Thirring precession.
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All authors Z. L. Yang, J. L. Han, W. Q. Su, P. F. Wang, C. Wang, T. Wang, D. J. Zhou, Yi Yan, J. Xu, W. C. Jing, N. N. Cai, R. X. Xu, H. G. Wang, X. P. You

Instrumentation and Methods for Astrophysics

Commissioning and on-sky performance verification of iLocater

Marshall C. Johnson, Marcelo Tala Pinto, Jonathan Crass et al. (+59 more)

iLocater is a high-resolution near-infrared extreme precision radial velocity (EPRV) spectrograph that was deployed to the Large Binocular Telescope (LBT) in June 2026. iLocater operates over $\lambda=966-1312$ nm with a median resolving power of $R=205,000$ as measured in the laboratory. We present the commissioning and initial on-sky verification program using solar and night-time observations at the LBT. First light was achieved on 27 June 2026, and nearly 150 on-sky spectra have now been recorded. Observations include single stars ranging in spectral type from B5 to M6. iLocater uses the LBT AO system, and we have demonstrated its ability to obtain spatially resolved spectra of close ($\theta < 1''$) binary stars.
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All authors Marshall C. Johnson, Marcelo Tala Pinto, Jonathan Crass, Brian Sands, Jackson Datkuliak, Sai Vidyud Senthil Nathan, Justin R. Crepp, Michael Engelman, Daniel Pappalardo, Julia Brady, Mark Derwent, Xavier Lesley-Saldaña, Andrew Bechter, Eric Bechter, Christian Schwab, David Aikens, Chad Bender, Chris Brandon, Cynthia Brooks, Matheus J. Castro, Jeffrey Chilcote, Al Conrad, Gregory Delo, Erin Duell, Matthew Engstrom, Steve Ertel, Louis Fantano, John Keith Feggans, Hali Flores, B. Scott Gaudi, David King, Ondrej Kitzler, Kaitlin M. Kratter, Jeffrey Kruk, Thomas Legero, Stanimir Letchev, Jerry Mason, Joaquin Mason, Matthew Misch, Jacob Pember, Richard Pogge, Andreas Quirrenbach, Joshua Schlieder, Augustyn Waczynski, Joseph Shields, Daewook Kim, Mark Smithwright, Allie Renshaw, Austin Richie, Alexa Rizika, Nandini Sadagopan, Jonathan Shover, James Smous, Jayde Spiegel, Julian Stürmer, Sahil Sura, Robert Switzer, Joe Thomes, Ji Wang, Lauren Weiss, Daniel Wilson, Dane Zielinski-Nicolson

Instrumentation and Methods for Astrophysics

The Calibration System of the iLocater Spectrograph

Sai Vidyud Senthil Nathan, Jonathan Crass, Julia E. Brady et al. (+21 more)

iLocater is a new near-infrared, extreme precision radial velocity (EPRV) instrument delivered to the Large Binocular Telescope in the summer of 2026. The instrument utilizes single-mode fibers (SMFs) for light transmission, including its calibration systems. We present an overview of the iLocater calibration system, detailing the specific sources and the hardware required to inject calibration light into the SMFs. Furthermore, we discuss the hardware that efficiently switches between these sources and distributes the light to all necessary instrument locations, entirely eliminating the need for free-space propagation.
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All authors Sai Vidyud Senthil Nathan, Jonathan Crass, Julia E. Brady, Mark Derwent, Marcelo Tala Pinto, Brian Sands, Jackson Datkuliak, Jonathan Shover, Christian Schwab, Julian Stürmer, Stanimir O. Letchev, Jacob Pember, Jayde Spiegel, Erin Duell, Daniel Pappalardo, Marshall C. Johnson, Michael Engelman, Matheus J. Castro, Justin R. Crepp, Ondrej Kitzler, Thomas Legero, Xavier Lesley-Saldaña, Richard Pogge, Dane Zielinski-Nicolson

Astrophysics of Galaxies

An Exploratory Analysis of New Large Gaia-informed Quasar Samples in SDSS-V

Shir Aviram, Benny Trakhtenbrot, Tom Dwelly et al. (+22 more)

Quasars are luminous objects that provide insights into the physics and evolution of supermassive black holes (SMBHs) and their accretion flows, galaxy evolution, and even cosmology. In this study, we present an exploratory study based on the ongoing fifth generation of the Sloan Digital Sky Survey (SDSS-V) and its unique dual-hemisphere, wide-field, and multi-object spectroscopic capabilities, with the aim of creating a comprehensive, all-sky quasar sample. The targets were selected through two novel methods, GUA and Skewt-QSO, that rely primarily on data from WISE and Gaia, aiming to address gaps in previous large quasar samples. Our sample includes over 250,000 spectroscopically confirmed quasars reaching z~5, with tens of thousands of newly identified quasars in the southern hemisphere. The selection methods are highly pure, with well over 80% of the spectra collected being genuine quasars; the main contaminants are M-type stars. The detailed spectral decomposition procedure we employed shows that the quasars in the sample span a wide range of luminosities (Lbol~$10^{44}-10^{48} erg s^{-1}$), SMBH masses (MBH~$10^6-10^{10}$ Msun), and accretion rates (L/LEdd~0.01-1). The distributions of these properties are consistent with those of previous quasar catalogs, which are based on past generations of SDSS, once we account for potential selection biases related to the various survey depths. Our findings confirm that novel selection methods based on optical+IR colors and/or astrometry can yield a large, high-purity quasar sample over wide sky areas, including in cases where more nuanced multi-band photometry and/or multi-wavelength data in the X-ray or radio is not available. This SDSS-V sample, which will continue to grow, establishes a robust reference for future southern (time-domain) surveys, while enhancing and complementing our understanding of quasar demographics and SMBH evolution.
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All authors Shir Aviram, Benny Trakhtenbrot, Tom Dwelly, Scott F. Anderson, Sean Morrison, Michael Eracleous, Yue Shen, Mara Salvato, Donald P. Schneider, Roberto J. Assef, Catarina Aydar, Franz E. Bauer, W.N. Brandt, Joel R. Brownstein, Johannes Buchner, Jeremy Darling, Jose G. Fernandez-Trincado, Patrick B. Hall, Dong-Woo Kim, Anton M. Koekemoer, Stephanie LaMassa, Andrea Merloni, Claudio Ricci, Qian Yang, Grisha Zeltyn

Solar and Stellar Astrophysics

PANTERA. I. Hunting for the Most Metal-Rich Stars in the Solar Neighborhood with High-Resolution Spectroscopy

Serat M. Saad, D. M. Rowan, K. Z. Stanek et al. (+4 more)

We present PANTERA (Project for Astrophysical Nucleosynthesis and Targeted Exploration of metal-Rich Abundances), a high-resolution spectroscopic survey of the most metal-rich stars in the solar neighborhood. In this first paper, we report iron abundances for 56 metal-rich stars, selected from Gaia DR3 XP spectrophotometric metallicities. These targets were observed with the PEPSI spectrograph on the Large Binocular Telescope (LBT), the Levy spectrograph on the Automated Planet Finder (APF) telescope, and the HIRES spectrograph on the Keck telescope. We measure [Fe/H] from an equivalent-width analysis of iron lines, with the effective temperature taken from photometry and the surface gravity from the Gaia parallax. We verify our measurement using Gaia benchmark stars, observing some sources with more than one spectrograph, using a second synthesis code, and an independent equivalent-width measurement. We find that the Gaia-XP metallicities over-predict [Fe/H] for part of our sample: they are consistent for the dwarfs, though a selection bias limits what the dwarf agreement can show, and reach $0.16\pm0.02$ dex for the cool giants. We attribute the over-prediction in part to the strong blue line blanketing of the cool metal-rich giants and to the survey labels on which the XP metallicities were trained. We also found 25 of the 56 stars to be ultra-metal-rich ([Fe/H] $> 0.4$), with the most iron-rich stars reaching [Fe/H]$=+0.58$. We discuss the implications of our result on studying metal-rich populations.
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All authors Serat M. Saad, D. M. Rowan, K. Z. Stanek, Ilya Ilyin, Benjamin J. Fulton, Howard Isaacson, Jessica Lu

High Energy Astrophysical Phenomena

Semi-analytic Inference of Satellite Densities in the Cold Dark Matter Model Part II. Implications for Dark Matter Indirect Detection Constraints

Kailash Raman, Dylan Folsom, Manoj Kaplinghat et al. (+2 more)

Dwarf galaxies provide excellent targets to search for signals of dark matter annihilation or decay. Using a calibrated semi-analytic model and the latest stellar kinematic data (presented in Part I), this paper updates the astrophysical J-factors for the Milky Way's dwarf spheroidal galaxies. We infer the probability distributions for the J-factors of 39 dwarfs by conditioning a population of subhalos, generated with the SatGen semi-analytic satellite model, on either a dwarf's kinematically determined dynamical mass or its stellar mass. We also compute the J-factors using the Jeans equation with updated stellar kinematics and priors that incorporate varying degrees of SatGen information. We use the computed J-factors to recast existing limits from Fermi-LAT data on the annihilation cross section. Our main result is that variations in the J-factors computed using the Jeans analysis introduce a factor of 2-4 uncertainty into the inferred limits on the cross section. We argue that a cosmologically informed prior is a motivated choice that excludes thermal relic annihilation cross sections to $b\bar{b}$ below about 70 GeV. For comparison, the more commonly used priors, which can lead to unphysical halo parameters, exclude masses below 130 GeV at 95% confidence level. We also show that the highest-J-factor dwarfs are spatially extended, approximately one degree on the sky, which challenges the validity of the point-source approximation adopted in many analyses of Fermi data. Finally, based on the semi-analytic model and the kinematic data, the highest J-factor halos have already been discovered, suggesting future ultra-faint discoveries are unlikely to substantially strengthen limits on annihilating dark matter.
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All authors Kailash Raman, Dylan Folsom, Manoj Kaplinghat, Mariangela Lisanti, Benjamin R. Safdi

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

Seesaw Cosmology

Nicolás Bernal, Chee Sheng Fong and Óscar Zapata

We study perturbative reheating in which the inflaton transfers its energy to the Standard Model through right-handed neutrinos (RHNs) responsible for light-neutrino masses via the type-I seesaw mechanism. We refer to the resulting nonstandard thermal history as $seesaw$ $cosmology$. When produced relativistically and sufficiently long lived, the RHNs generate a characteristic sequence of inflaton, relativistic-RHN, nonrelativistic-RHN, and Standard Model radiation domination. We solve the Boltzmann system while retaining the production-time dependence of the nonthermal RHN distribution and its relativistic-to-nonrelativistic transition. The Standard Model temperature rapidly approaches a plateau during inflaton domination and subsequently scales as $a^{-1/4}$ and $a^{-3/8}$ during relativistic- and nonrelativistic-RHN domination, respectively. We investigate the implications of seesaw cosmology for dark-matter production. Direct production through inflaton decays can be enhanced relative to conventional reheating by a factor of order $m_\phi/(2m_N)$, while ultraviolet freeze-in exhibits the critical temperature powers $p = 12$ and $20$, leading to potentially large contributions before the final radiation-dominated era. Seesaw cosmology therefore connects neutrino-mass generation, the pre-BBN thermal history and phenomena such as dark-matter production and baryogenesis.
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Solar and Stellar Astrophysics

The T-GEX project. I. Stealth UV-bright Sun-like stars in the Galaxy as candidate contributors to the UV upturn

M. L. L. Dantas, D. Beltrán, R. E. Giribaldi et al. (+3 more)

We constructed the Tiny Gaia-ESO + GALEX (T-GEX) catalogue by combining Gaia-ESO spectroscopy, Gaia DR3 astrometry, GALEX UV photometry, and 2MASS and AllWISE infrared measurements for 37 stars. Astrometric and spectroscopic quality cuts minimise obvious multiplicity and spectral peculiarity, although unresolved companions cannot be excluded. We classified the stars relative to the empirical FGK UV-normal locus, applied a 3-component Gaussian mixture model in the FUV-NUV versus NUV-$G$ plane, measured H$\alpha$ $\lambda 6563$ diagnostics for 24 stars, and performed an IMF-based empirical scaling calculation for three UV-upturn galaxies. Approximately 2/3 of the sample are UV-abnormal. The GMM identifies a cool, strongly UV-excess group (G1), a hotter UV-normal group (G2), and an intermediate UV-excess group (G3). G1 occupies a narrow, predominantly sub-solar [Fe/H] range and is $\alpha$-enhanced, with the highest median [Mg/Fe]. G3 has the highest median [Fe/H], while G2 spans the broadest metallicity range and has the youngest median age. G1 and G3 extend to old ages, although their youngest estimates are affected by isochrone degeneracy. Enhanced H$\alpha$ core emission occurs only among hotter G2 stars in the available subsample, but only one G1 star has H$\alpha$ coverage. The extragalactic contribution is strongly template-dependent: the median G1 template accounts for at most $\sim20\%$ of the observed UV output, whereas the bluest template could match most or all of the NUV and FUV emission if shared by $\sim10$–$15\%$ of surviving FGK stars.
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All authors M. L. L. Dantas, D. Beltrán, R. E. Giribaldi, R. Smiljanic, P. R. T. Coelho, P. B. Tissera

Instrumentation and Methods for Astrophysics

Emulating Cosmic Structure Formation with a Lagrangian Neural Cellular Automaton

Cooper Jacobus, Beatriz Tucci and Oliver Philcox

Field-level inference of cosmological initial conditions from galaxy surveys requires a forward model that is simultaneously accurate in the non-linear regime, computationally efficient, and fully differentiable. Traditional N-body simulations are accurate but computationally prohibitive for iterative inference, while approximate solvers like Lagrangian Perturbation Theory (LPT) fail to capture the knotty halo-forming dynamics of the cosmic web at late times. We introduce the Lagrangian Neural Cellular Automaton (LNCA), a hybrid deep learning framework that can be applied to emulate structure formation as a local, iterative dynamical process on a comoving lattice. Unlike convolutional emulators which map fixed grids in a single pass, the LNCA operates in the Lagrangian frame, iteratively advecting the computational graph itself to follow the flow of mass. By training the network to learn only the residual displacement corrections to the Zeldovich approximation, we achieve high-fidelity emulation of the non-linear physics while guaranteeing accuracy at large scales. We further constrain our model to produce complete trajectories, not just final states, by adopting an equivariant cellular automaton architecture, which recurrently iterates on its internal states to yield a dynamic history. The resulting update rule acts on a single fixed neighborhood, is translationally and rotationally equivariant, and is integrated over discrete substeps to yield trajectories, making it a differentiable forward model for reconstructing the initial conditions of the universe from lightcone data. We train our model to emulate the real-space matter distributions of a diverse set of N-body simulations from the Quijote suite, for a range of redshifts and cosmologies, given only the initial conditions.
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Astrophysics of Galaxies

The influence of feedback on the baryonic content of haloes in the COLIBRE simulations

Jonathan J. Davies, Joop Schaye, Filip Huško et al. (+7 more)

We present predictions for the relation between the halo gas mass fraction and halo mass, $f_{\rm gas}^{200}-M_{200}$, from the COLIBRE cosmological simulations of galaxy formation, and explore how the gas content of haloes is influenced by feedback from supernovae and active galactic nuclei (AGN) over time. The $f_{\rm gas}^{200}-M_{200}$ relation in COLIBRE is non-monotonic, with a peak at $M_{200}\sim 10^{11.5-12}$~M$_\odot$. Below this mass, feedback from supernovae efficiently expels gas from the haloes of dwarf galaxies, and above it, AGN feedback efficiently depletes the haloes of galaxy groups. The fiducial COLIBRE model yields gas fractions for galaxy groups and clusters that agree with constraints from Chandra and XMM-Newton X-ray data, but which are high relative to gas fractions inferred from eROSITA stacks and measurements of the kinetic Sunyaev-Zel-dovich (kSZ) effect. COLIBRE's hybrid AGN feedback model, which combines thermal and jet-driven feedback, produces lower gas fractions in better agreement with eROSITA and kSZ measurements. COLIBRE produces lower gas fractions for groups and clusters than EAGLE and other contemporary simulations, and better agreement with observational constraints. We investigate the origin of this improvement relative to EAGLE, and how the resolution of the simulation affects the impact of feedback. Our results demonstrate that halo gas fractions are a sensitive probe of feedback physics, and that they can differ significantly between simulations that otherwise produce very similar galaxy populations.
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All authors Jonathan J. Davies, Joop Schaye, Filip Huško, Ruby J. Wright, Evgenii Chaikin, Matthieu Schaller, Robert J. McGibbon, Alejandro Benítez-Llambay, Sylvia Ploeckinger, Alexander J. Richings

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

Wading the String Bog: CMB Birefringence in the Swampland

Guido D'Amico, Nemanja Kaloper and Alexander Westphal

We point out that observations of cosmic birefringence may provide direct experimental tests of Swampland conjectures. Ultralight scalar field birefringence mechanisms are constrained by Weak Gravity Conjecture, limiting their parameter space. Conversely, confirming that CMB birefringence is caused by ultralight scalars could spell problems for the Swampland framework. Resolving these difficulties without a revision of Swampland ideology points toward thin axionic domain walls, which can explain birefringence without propagating ultralight degrees of freedom. Importantly these conflicting scenarios for cosmic birefringence could be experimentally distinguished by a search for, or exclusion of, birefringence anisotropies, that could be measured by POLARBEAR, Simons Observatory and LiteBIRD. We also note that cosmic birefringence observables emerge via a Sakharov-like asymmetry, where linear polarization is first generated cosmologically and subsequently twisted by a parity-violating dynamics after last scattering.
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