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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 13 January

Solar and Stellar Astrophysics

HOPS-288: A Laboratory for Complex Organics in Proto-multiple Systems

Shih-Ying Hsu, Nadia M. Murillo, Chin-Fei Lee et al. (+21 more)

Complex organic molecules (COMs) in young stellar objects (YSOs) have attracted significant attention in recent years due to their potential connection to pre-biotic chemistry and their utility as tracers of warm or shocked gas components. Proto-binary and multiple systems with close separations are particularly valuable targets for investigating chemical inheritance and reaction, as their members are expected to form from similar material in their parental cloud. We present ALMA observations of the hierarchical proto-triple system HOPS-288, focusing on the physical structure, kinematics, and COM compositions. The system is treated as a proto-binary system consisting of HOPS-288-A and HOPS-288-B due to the limited spatial resolutions, with a separation of 200~au. Three COM-rich features are revealed: two hot corinos associated with the two members, rich in a variety of COMs, and an intervening component between the two members traced by CH$_3$OH and tentatively by CH$_3$CHO. The hot corino in HOPS-288-A exhibits rotational features and might trace a disk. The hot corino in HOPS-288-B is also possibly exhibiting rotational motion. The intervening component could possibly trace a shocked region in the circumbinary disk or a bridge between the two members. The column densities of COMs, including $^{13}$CH$_3$OH, CH$_2$DOH, CH$_3$CHO, HCOOCH$_3$, C$_2$H$_5$OH, $^{13}$CH$_3$CN, and NH$_2$CHO, are broadly similar between the two sources, possibly suggesting the complex organic similarities among proto-binary/multiple systems. Given the complexity of the studied physical structures, further detailed investigations will be essential to confirm this result.
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All authors Shih-Ying Hsu, Nadia M. Murillo, Chin-Fei Lee, Doug Johnstone, Tien-Hao Hsieh, Naomi Hirano, Leonardo Bronfman, Yo-Ling Chuang, David J. Eden, Shanghuo Li, Sheng-Jun Lin, Mark G. Rawlings, Ken'ichi Tatematsu, Sheng-Yuan Liu, Huei-Ru Vivien Chen, Kee-Tae Kim, Yi-Jehng Kuan, Woojin Kwon, Chang Won Lee, Jeong-Eun Lee, Tie Liu, Qiuyi Luo, Patricio Sanhueza, Hsien Shang

Cosmology and Nongalactic Astrophysics

Bound Dark Energy: Particle Physics model in alignment with recent DESI cosmological measurements

Axel de la Macorra and Jose Agustin Lozano Torres

We present observational constraints on the Bound Dark Energy Cold Dark Matter (BDE-CDM) model using DESI DR2 baryon acoustic oscillation measurements combined with Planck CMB data and Type Ia supernovae compilations (PantheonPlus, Union3, DESY5). In BDE-CDM, dark energy originates from the lightest meson field within a supersymmetric SU(3) dark gauge group with $N_f = 6$ flavors, governed by an inverse power-law potential $V(\phi) = \Lambda_{c}^{4+2/3} \phi^{-2/3}$. Unlike $\Lambda$CDM and $w_0w_a$CDM, the dark energy sector contains no free parameters – the condensation scale $\Lambda_c$ and transition epoch $a_c$ are determined by gauge coupling unification constraints. The equation of state evolves from relativistic behavior ($w = 1/3$) before condensation through a kinetic-dominated stiff phase ($w \simeq 1$), approaching $w_0 = -0.9298 \pm 0.0003$ at present, with $w > -1$ maintained throughout cosmic history, avoiding phantom-regime instabilities. We obtain $\Lambda_{c} = 43.93 \pm 0.13$~eV and $a_c = (2.489 \pm 0.007) \times 10^{-6}$, consistent with theoretical predictions. The $w_0$-$w_a$ confidence contours are approximately 10,000 times smaller than those of $w_0w_a$CDM while achieving comparable fits, and remain stable across different supernova datasets. Statistical analysis yields $\Delta\mathrm{DIC} = -6.77$ and $\Delta\mathrm{AIC} = -8.97$ relative to $\Lambda$CDM for BAO+DESY5, constituting strong evidence favoring BDE-CDM model. The model predicts distinctive signatures including 25% enhancement in the matter power spectrum at $k \approx 4.3\,h\,\mathrm{Mpc}^{-1}$. These results establish BDE-CDM as a theoretically motivated framework that successfully addresses the DESI-observed preference for dynamical dark energy while connecting particle physics with cosmological observations.
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Astrophysics of Galaxies

Resolved ISM properties and scaling relations in the barred galaxy NGC 3627: constraints from NIKA2 observations

S. Katsioli, E. M. Xilouris, F. Galliano et al. (+64 more)

We investigate the interplay between star formation, interstellar medium (ISM) components, and dust properties in NGC 3627 using new NIKA2 1.15 and 2 mm observations from the IMEGIN Large Program. Our goal is to analyze dust and radio emission, decompose contributions in the millimeter-centimeter regime, and explore ISM properties within the galaxy. We perform spectral energy distribution fitting, at both global and spatial scales, using the THEMIS dust model within the HerBIE code, applied to data from 3.4 $\mu$m to 6 cm. We decompose emission into dust, free-free, and synchrotron components, and examine correlations with gas surface density and star formation activity. Additionally, we analyze the small dust grain fraction and its variation across the galaxy. We find $\sim$10% radio emission at 2 mm, peaking at 18% in the southern bar-end, which hosts the highest star formation activity. However, an isolated star-forming region beyond this bar-end is the most efficient, as indicated by its elevated dust production efficiency and effective yield, predicted by our simplistic dust evolution model. The 160 $\mu$m emission shows the strongest correlation with molecular gas, while 1.15 mm better traces the dust mass surface density. Small grains, which make up $\sim$13% of dust mass (2 $\times$ 10$^{7}$ M$_{\odot}$), are depleted in intense radiation fields, with a notable deficit in the southern tidal tail. ISM properties and chemical evolution indicate that dynamical processes, such as bar-driven gas flows and tidal interactions, are crucial in shaping the galactic structure, influencing star formation efficiency, and dust distribution.
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All authors S. Katsioli, E. M. Xilouris, F. Galliano, R. Adam, P. Ade, H. Ajeddig, S. Amarantidis, P. André, H. Aussel, M. Baes, A. Beelen, A. Benoît, S. Berta, A. Bongiovanni, J. Bounmy, O. Bourrion, M. Calvo, A. Catalano, D. Chérouvrier, I. De Looze, M. De Petris, F.-X. Désert, S. Doyle, E. F. C. Driessen, G. Ejlali, A. Ferragamo, A. Gomez, J. Goupy, C. Hanser, A. Hughes, A. P. Jones, F. Kéruzoré, C. Kramer, B. Ladjelate, G. Lagache, S. Leclercq, J.-F. Lestrade, J. F. Macías-Pérez, S. C. Madden, A. Maury, F. Mayet, A. Monfardini, A. Moyer-Anin, M. Muñoz-Echeverría, I. Myserlis, A. Nersesian, A. Paliwal, L. Pantoni, D. Paradis, L. Perotto, G. Pisano, N. Ponthieu, V. Revéret, A. J. Rigby, A. Ritacco, H. Roussel, F. Ruppin, M. Sánchez-Portal, S. Savorgnano, K. Schuster, A. Sievers, M. W. L. Smith, F. Tabatabaei, J. Tedros, C. Tucker, N. Ysard, R. Zylka

Astrophysics of Galaxies

Polarization echoes from past nuclear activity in the quasi-periodic eruption source GSN 069

B. Agís-González, D. Hutsemékers, I. Liodakis et al. (+8 more)

Context. X-ray quasi-periodic eruptions (QPEs) are repeating, high-amplitude, soft X-ray bursts observed from the nuclei of a dozen nearby low-mass galaxies. Their origin remains a puzzle in the physics of accretion variability. Observational data indicate that X-ray and/or optical tidal disruption events (TDEs) may precede QPE detections. Although both kinds of outburst are driven by supermassive black holes, they are more frequently detected in faded active galactic nuclei (AGNs), when the TDE is not happening in a dormant galaxy. In the case of the QPE discovery source, GSN 069, it remains debated whether its past activity arose from a previous AGN phase or from an enhanced TDE rate. Aims. We investigated the origin of the past nuclear activity in GSN 069. Methods. Past AGN activity imprints detectable polarization in optical light, due to the expected delay between direct and scattered light. On 6 September 2019, we targeted GSN 069 with VLT/FORS2 in both imaging polarimetry and spectropolarimetry modes so that its optical polarization could be investigated while the first detected QPE phase was still active. Results. We measured a rising polarization, from ~0% to ~1.5%, as moving away from the nucleus of GSN 069. This rise is probed to be intrinsic to the central engine, confirming the already detected extended emission line region (EELR) by integral field unit data. Conclusions. The increasing radial polarization demonstrates a switched-off nucleus. The polarization angle traces an axis aligned with elongated [OIII], [NII], and H{\alpha} gas distributions, revealing an EELR that may be consistent with relic polarization cones, therefore suggesting the presence of a torus-like structure in the past. Thus, optical polarization echoes geometrically favor a faded AGN as the origin of the EELR rather than a past elevated TDE rate, although the latter cannot be excluded.
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All authors B. Agís-González, D. Hutsemékers, I. Liodakis, S. Cazzoli, D. Sluse, G. Miniutti, I. Márquez, J. Masegosa, F. Marin, J. A. Acosta-Pulido, C. Ramos Almeida

Astrophysics of Galaxies

One cloud is not enough: extreme conditions bias chemical abundances in high-redshift galaxies

Bianca Moreschini, Francesco Belfiore, Alessandro Marconi et al. (+18 more)

Since its launch, JWST has opened an unprecedented opportunity to characterise the ionised ISM of high-redshift galaxies using well-established rest-frame UV/optical diagnostics from the local Universe. At the same time, these observations challenge the validity of such classical methods when applied to the extreme environments typical at high redshift. We present an in-depth analysis of the ISM in three representative case studies at $z=2 - 6$ (MARTA 4327, the Sunburst Arc and RXCJ2248-ID) conducted within a multi-cloud photoionisation modelling framework (HOMERUN). We show that even a small fraction of unresolved high-density clumps can contribute more than half of the observed flux of auroral lines, while only negligibly to standard optical density tracers. As a result, $T_{\mathrm{e}}$-method metallicities can be underestimated by $\sim 0.15 - 0.3$ dex, as for MARTA 4327. By modelling rest-frame UV and optical data, we demonstrate that discrepancies between abundances obtained from diagnostics tracing different zones do not necessarily imply chemical inhomogeneities. In RXCJ2248-ID, the disagreement between UV and optical N/O may naturally arise from ionisation and density structure alone. In contrast, we find evidence for genuine chemical stratification in the Sunburst Arc, where a component enriched in nitrogen coexists with a chemically normal one. Finally, we argue that very-high-ionisation lines may be explained within a pure star-formation scenario invoking matter-bounded regions. However, in the case of RXCJ2248-ID, we cannot rule out a minor contribution from an AGN based solely on the observed fluxes. These results indicate that classical diagnostics can be significantly biased in high-redshift galaxies and that self-consistent, physically motivated tools are therefore essential to properly interpret the complex ISM conditions and chemical enrichment in the early Universe.
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All authors Bianca Moreschini, Francesco Belfiore, Alessandro Marconi, Elisa Cataldi, Mirko Curti, Amirnezam Amiri, Anna Feltre, Filippo Mannucci, Elena Bertola, Caterina Bracci, Matteo Ceci, Avinanda Chakraborty, Giovanni Cresci, Quirino D'Amato, Enrico di Teodoro, Michele Ginolfi, Isabella Lamperti, Cosimo Marconcini, Martina Scialpi, Lorenzo Ulivi, Maria Vittoria Zanchettin

Earth and Planetary Astrophysics

Can photoevaporation open gaps in protoplanetary discs?

Michael L. Weber, Barbara Ercolano and Giovanni Picogna

We investigate whether photoevaporation alone can open and sustain gaps in protoplanetary discs by coupling the evolving disc structure with the photoevaporative flow in two dimensional radiation hydrodynamical simulations. Our results show that once a density depression forms, the local mass-loss rate decreases sharply, suppressing further gap deepening. Viscous inflow and radial mass transport along the disc surface act to partially refill the depleted region, preventing complete clearing. The resulting configuration is a persistent, partially depleted zone whose evolution is largely insensitive to the initial disc morphology. This behaviour challenges the standard paradigm that photoevaporation efficiently carves clean inner cavities and directly produces transition discs. However, the pressure maximum at the outer edge of the depression may still trap dust grains, giving rise to transition disc like observational signatures. We also present a first-order prescription to approximate this behaviour in one dimensional disc evolution models, suitable for use in planet formation and population synthesis studies. Although the prescription improves upon static mass-loss treatments, it remains approximate, underscoring the need for further multidimensional simulations and parameter-space exploration to derive robust recipes for global disc and planet population models.
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Astrophysics of Galaxies

Spinning compact object and chaos in galactic centres

Ushasee Paria, Uditi Nag, Yeasin Ali et al. (+1 more)

Galactic centres are extremely complex environments, consisting primarily of a supermassive black hole (SMBH) surrounded by asymmetric mass distributions such as nuclear star clusters (NSC) and molecular gas, which form disks or halos. Together these components exert a gravitational field which, combined with relativistic corrections from the spin of the SMBH, generates strongly nonlinear dynamics and chaotic orbits. We model this region using a multipolar expansion potential, in which the central compact object is represented by the Artemova-Björnsson-Novikov pseudo-Newtonian potential, which mimics the spin dependence of a Kerr-like BH. The surrounding halo is modelled as an axisymmetric, shell-like mass distribution expanded to dipole order to induce asymmetry. Previous works have mostly quantified the chaos caused by the BH spin and dipole moment using Poincaré sections, SALI and other chaos indicators. In this study, we incorporate stability analysis and Newton-Raphson basins of convergence to provide a global view of the dynamics of the system. Stability analysis around fixed points gives deeper insight into the local behaviour, while basins of convergence show sensitivity to initial conditions and reveal fractal boundaries. Our results show that the BH spin substantially reshapes the equilibrium landscape. Depending on its magnitude, it can either intensify the chaos induced by the halo asymmetry or simplify the phase space. These results improve our understanding of how relativistic spin effects and multipole moments collectively affect particle motion in galactic centres.
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All authors Ushasee Paria, Uditi Nag, Yeasin Ali, Suparna Roychowdhury

Cosmology and Nongalactic Astrophysics

A possible pathway to UHZ1-type systems at z~10 by heterogeneous mass primordial black holes as dark matter

Alexander Kashlinsky, Fernando Atrio-Barandela and Diego Martín-González

Recent space-based observations discovered several unusual objects, exhibiting similar properties, at redshifts $z\gtrsim 10$. Among them is the UHZ1 system at $z=10.1$, containing $\sim 10^8M_\odot$ in stars, with a similarly massive central black hole of $\sim 10^{7-8}M_\odot$. Here we propose a possible mechanism for forming such systems which hinges on the presence of primordial black holes (PBHs) covering a range of masses while contributing a significant fraction of the dark matter (DM). We evaluate the accurate expression for the small-scale power responsible for the collapse of the first halos in the presence of the PBH population. The extra power in the matter density field, produced by the granulation term, will cause an earlier collapse of DM halos, populated by PBHs of different masses. In these collapsed and virialized systems the PBHs will undergo 2-body relaxation, driving the more massive PBHs to the halo center under dynamical friction. We quantify this evolution for a distribution of PBH orbital parameters and halo properties. The analysis shows that PBHs can have appropriate mass functions capable of producing systems with parameters similar to what is observed for UHZ1. We suggest that the proposed mechanism could account for a subset of other systems newly discovered with the JWST at high redshifts, including the Little Red Dots.
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Cosmology and Nongalactic Astrophysics

A comparative test of different pressure profile models in clusters of galaxies using recent ACT data

Denis Tramonte

Context. The electron pressure profile is a convenient tool to characterize the thermodynamical state of a galaxy cluster, with several studies adopting a "universal" functional form. Aims. This study aims at using Sunyaev-Zel'dovich (SZ) data to test four different functional forms for the cluster pressure profile: generalized Navarro-Frenk-White (gNFW), $\beta$-model, polytropic, and exponential. The goal is to assess to what level they are universal over a population-level cluster sample. Methods. A set of 3496 ACT-DR4 galaxy clusters, spanning the mass range $[10^{14},10^{15.1}]\,\text{M}_{\odot}$ and the redshift range $[0,2]$, is stacked on the ACT-DR6 Compton parameter $y$ map over $\sim13,000\,\text{deg}^2$. An angular Compton profile is then extracted and modeled using the theoretical pressure recipes, whose free parameters are constrained against the measurement via a multi-stage MCMC approach. The analysis is repeated over cluster subsamples spanning smaller mass and redshift ranges. Results. All functional forms are effective in reproducing the measured $y$ profiles within their error bars, without a clearly favored model. While best-fit estimates are in broad agreement with previous findings, hints of residual subsample dependency are detected favoring higher amplitudes and steeper profiles in high-mass, low-redshift clusters. Conclusions. Population-level cluster studies based on SZ data alone are likely unable to accurately constrain different pressure profile models. Residual trends at population level and scatter at individual cluster level undermine the universal pressure model assumption whenever high precision is required. Finally, functional forms different from the gNFW prove equally effective while being more physically motivated.
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High Energy Astrophysical Phenomena

Expanding the High-z Supernova Frontier: "Wide-Area" JWST Discoveries from the First Two Years of COSMOS-Web

Ori D. Fox, Armin Rest, Justin D. R. Pierel et al. (+48 more)

Transient astronomy in the early Universe (z > 2) remains largely unexplored, lying beyond the rest-frame optical spectroscopic reach of most current observatories. Yet this regime promises transformative insights, with high-redshift transients providing direct access to the early Universe and enabling studies of how stellar populations and cosmology evolve over cosmic time. JWST is uniquely equipped to probe these redshifts efficiently in the rest-frame optical and near-IR. We present results from an initial pathfinder search, covering an area of ~133 arcmin^2 (~0.037 deg^2) independently imaged by the PRIMER and COSMOS-Web (hereafter COSMOS) extragalactic surveys. Although neither program was designed for time-domain astronomy, combining their data results in difference images separated by roughly one year, leading to the discovery of 68 supernovae (SNe) with host photometric redshifts reaching z < 5. For most SNe, only a single epoch is available, but the combination of host redshift, classification, color, and magnitude enables us to prioritize candidates for detailed photometric and spectroscopic follow-up. Among the most notable sources are a relatively bright, blue CCSN at z > 3 (SN 2023aeab) and a young, normal SN Ia at z > 2 (SN 2023aeax). The sample distribution highlights the increasing likelihood that a wide-area JWST program can uncover younger, bluer, and potentially more extreme explosions. While this pathfinder effort is limited in cadence and number of filters, it demonstrates the strong potential of a dedicated, well-planned time-domain survey with JWST to obtain the sample sizes and rate measurements needed to chart SN populations deep into the early Universe.
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All authors Ori D. Fox, Armin Rest, Justin D. R. Pierel, David A. Coulter, Caitlin M. Casey, Jeyhan S. Kartaltepe, Hollis B. Akins, Maximilien Franco, Mike Engesser, Conor Larison, Takashi J. Moriya, Robert M. Quimby, Marko Shuntov, Matthew R. Siebert, Christa DeCoursey, Rodrigo Angulo, James M. DerKacy, Nicole E. Drakos, Eiichi Egami, Steven L. Finkelstein, Carter Flayhart, Seiji Fujimoto, Estefania Padilla Gonzalez, Massimo Griggio, Santosh Harish, Olivier Ilbert, Kohei Inayoshi, Anton M. Koekemoer, Vasily Kokorev, Clotilde Laigle, Erini Lambrides, Rebecca L. Larson, Xiaolong Li, Daizhong Liu, Georgios E. Magdis, Jacqueline E. McCleary, Henry J. McCracken, Nicolas McMahon, Jed McKinney, Thomas Moore, Louise Paquereau, Jason Rhodes, Brant E. Robertson, David B. Sanders, Sogol Sanjaripour, Koji Shukawa, Louis-Gregory Strolger, Sune Toft, Qinan Wang, Robert E. Williams, Yossef Zenati

Astrophysics of Galaxies

Measuring the Vertical Structure of Active Galactic Nuclei Disks with Transformer Models and the Vera C. Rubin Observatory

Amy Secunda, Sebastian Wagner-Carena, Helen Qu et al. (+1 more)

Reverberation mapping is one of the main techniques used to study active galactic nuclei (AGN) accretion disks. Traditional continuum reverberation mapping uses short lags between variability in different wavelength AGN light curves on the light crossing timescale of the disk to measure the radial structure of the disk. The harder-to-detect long negative lag measures lags on the longer inflow timescale, opening up a new window to mapping out the vertical structure of AGN disks. The Vera Rubin Observatory, with its 6 wavebands, long baseline, and high cadence, will revolutionize our ability to detect short and long lags. However, many challenges remain to detect these long lags, such as seasonal gaps in Rubin light curves, the weak signal strength of the long lag relative to the short lag, and the enormous influx of data for millions of AGN from Rubin. Machine learning techniques have the potential to solve many of these issues, but have yet to be applied to the long negative lag problem. We develop and train a transformer-based machine learning model to detect long and short lags in mock Rubin AGN light curves. Our model identifies whether a light curve in our test set has a long negative lag with 96% recall and 0.04% contamination, and is 98% accurate at predicting the true long lag. This accuracy is an enormous improvement over two baseline methods we test on the same mock light curves, the interpolated cross correlation function and javelin, which are only 54% and 21% accurate, respectively.
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All authors Amy Secunda, Sebastian Wagner-Carena, Helen Qu, Shirley Ho

Earth and Planetary Astrophysics

Origin of asteroid (469219) Kamo`oalewa: the main asteroid belt or the Giordano Bruno crater on the Moon?

M. Fenucci, B. Novaković, M. Granvik et al. (+1 more)

Asteroid Kamo`oalewa is the target of the Tianwen-2 sample-return mission by CNSA. Because of its orbit and its spectral properties, it was proposed that Kamo`oalewa originated from the Moon as impact ejecta, possibly from the Giordano Bruno crater. We aim at estimating the relative contribution of Kamo`oalewa-like objects originating from the general near-Earth asteroid (NEA) population which originated in the main asteroid belt, and compare it with the relative contribution of Giordano Bruno ejecta. We first estimate the average fraction of quasi-satellite orbits at any given time. By using recently developed NEA population models, we extract the expected number of Earth co-orbitals of the same size of Kamo`oalewa, and then get an estimate of the average number of Kamo`oalewa-like objects using the fraction computed before. Similarly, we obtain an estimate for the number of Kamo`oalewa-like objects that may originate as ejecta from the Giordano Bruno impact. We also performed survey simulations to estimate their efficiency in the detection of Kamo`oalewa-like objects. We found that the main belt accounts for 1.23 \pm 0.13 Kamo`oalewa-like objects on average. The expected number of Kamo`oalewa-like objects originated as Giordano Bruno ejecta is 0.042, which is more than order of magnitude smaller. We found a discovery efficiency of Earth quasi-satellites between 95% and 70% for absolute magnitude between 22 and 25 for the Pan-STARRS survey, and population models show that this is in agreement with the known population. The Vera Rubin Observatory should reach an efficiency of 92% down to absolute magnitude 25. These estimates show that population models of NEAs are capable to account for Kamo`oalewa-like objects, thus supporting the hypothesis that that Kamo'oalewa originated from the main belt. This will be further investigated by the in-situ exploration of the Tianwen-2 mission.
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All authors M. Fenucci, B. Novaković, M. Granvik, P. Zhang

Solar and Stellar Astrophysics

Numerical Insights into Disk Accretion, Eccentricity, and Kinematics in the Class 0 phase

Adnan Ali Ahmad, Benoît Commerçon, Elliot Lynch et al. (+4 more)

The formation and early evolution of protoplanetary disks are governed by a wide variety of physical processes during a gravitational collapse. Observations have begun probing disks in their earliest stages, and have favored the magnetically-regulated disk formation scenario. Disks are also expected to exhibit ellipsoidal morphologies in the early phases, an aspect that has been widely overlooked. We aim to describe the birth and evolution of the disk while accounting for the eccentric motions of fluid parcels. Using 3D radiative magnetohydrodynamic (MHD) simulations with ambipolar diffusion, we self-consistently model the collapse of isolated $1~\mathrm{M_\odot}$ and $3~\mathrm{M_\odot}$ cores to form a central protostar surrounded by a disk. We account for dust dynamics, and employ gas tracer particles to follow the thermodynamical history of fluid parcels. We find that magnetic fields and turbulence drive highly anisotropic accretion onto the disk via dense streamers. This streamer-fed accretion, occurring from the vertical and radial directions, drives vigorous internal turbulence that facilitates efficient angular momentum transport and rapid radial spreading. Crucially, the anisotropic inflow delivers material with an angular momentum deficit that continuously generates and sustains significant disk eccentricity ($e\sim 0.1$). Our results reveal ubiquitous eccentric kinematics in Class 0 disks, with direct implications for disk evolution, planetesimal formation, and the interpretation of cosmochemical signatures in Solar System meteorites.
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All authors Adnan Ali Ahmad, Benoît Commerçon, Elliot Lynch, Francesco Lovascio, Sebastien Charnoz, Raphael Marschall, Alessandro Morbidelli

Cosmology and Nongalactic Astrophysics

Note on pulsar timing array correlation functions induced by peculiar velocities

Neha Anil Kumar, Keisuke Inomata and Marc Kamionkowski

Several papers have recently calculated the contribution to pulsar timing array overlap reduction functions (ORFs) induced by our peculiar velocity with respect to the rest frame of the stochastic gravitational-wave background. Here we show that a harmonic-space calculation confirms the most recent result. We note that, with the harmonic-space calculation, the ORFs for spin-1 GWs and the correlations with astrometry measurements are also easily obtained.
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Instrumentation and Methods for Astrophysics

LUMOS : Linear programming Utility for Multi-messenger Optical Scheduling

Yogesh P. Wagh, Michael W. Coughlin, Leo P. Singer et al. (+1 more)

The detection of gravitational-wave events by LIGO-Virgo-KAGRA has opened new avenues for multi-messenger astrophysics; however, electromagnetic counterparts remain elusive due to large localization uncertainties. Wide-field optical surveys like the Zwicky Transient Facility (ZTF) play a crucial role in follow-up, but efficient scheduling is essential. In this work, we present LUMOS, a Mixed Integer Linear Programming (MILP) approach that selects fields via a maximum coverage problem and schedules observations to maximize cumulative probability while respecting observability constraints. Using 1199 GW events from O4, we compare the LUMOS scheduler with gwemopt, showing an 84.7 percent higher mean cumulative probability and better performance in nearly all cases. While designed for ZTF, LUMOS's framework parallels the M4OPT toolkit for space missions, highlighting the broader applicability of MILP-based scheduling to both ground- and space-based follow-up.
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All authors Yogesh P. Wagh, Michael W. Coughlin, Leo P. Singer, Varun Bhalerao

Astrophysics of Galaxies

The miniJPAS survey: Dissecting galaxy properties across environments with spatially resolved photometry

J.E. Rodríguez-Martín, R.M. González Delgado, L.A. Díaz-García et al. (+27 more)

The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is an ongoing survey mapping thousands of square degrees in the Northern Hemisphere using 56 narrow-band filters, delivering IFU-like photometric data well suited for studying galaxy properties and evolution. As a precursor, the miniJPAS survey observed a 1 deg$^2$ field with the same filter system, providing an ideal testbed for the study of spatially resolved galaxies. In this work, we investigate the resolved stellar population and emission-line properties of 51 miniJPAS galaxies, classified by spectral type (red or blue) and environment (group or field), and assess the role of environment in galaxy evolution. We use the Py2DJPAS pipeline to process the data, homogenise the images to a common PSF, define galactic regions, and extract photo-spectra. Radial profiles are analysed using elliptical annuli spaced by 0.7 R_EFF, combined with an inside-out segmentation to study star formation histories. Stellar population parameters are derived with the Bayesian SED-fitting code BaySeAGal, while artificial neural networks are used to estimate the equivalent widths of the H$\alpha$, H$\beta$, [NII], and [OIII] emission lines. We find clear trends in a mass density-colour diagram: denser, redder regions are older, more metal-rich, and have lower specific star formation rates, while bluer, less dense regions show stronger emission lines and higher sSFRs. Red and blue galaxies are well separated in these relations, whereas environmental classification shows no clear distinction. Radial profiles support an inside-out formation scenario, with significant differences between red and blue galaxies but no strong environmental dependence. We suggest that the weak environmental effects may be due to the relatively low stellar masses of the galaxy groups in our sample.
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All authors J.E. Rodríguez-Martín, R.M. González Delgado, L.A. Díaz-García, G. Martínez-Solaeche, R. García-Benito, A. de Amorim, J. Thainá-Batista, R. Cid Fernandes, I. Márquez, M. Maturi, A. Fernández-Soto, R. Abramo, J. Alcaniz, N. Benítez, S. Bonoli, S. Carneiro, A. J. Cenarro, D. Cristóbal-Hornillos, R. A. Dupke, A. Ederoclite, A. Hernán-Caballero, C. Hernández-Monteagudo, C. López-Sanjuan, A. Marín-Franch, C. Mendes de Oliveira, M. Moles, L. Sodré, K. Taylor, J. Varela, H. Vázquez Ramió

Astrophysics of Galaxies

Digging into the Interior of Hot Cores with ALMA (DIHCA). VI. The Formation of Low-mass Multiple Systems in High-mass Cluster-forming Regions

Qiuyi Luo, Patricio Sanhueza, Stella S. R. Offner et al. (+14 more)

Most stars form in multiple systems, with profound implications in numerous astronomical phenomena intrinsically linked to multiplicity. However, our knowledge about the process on how multiple stellar systems form is incomplete and biased toward nearby molecular clouds forming only low-mass stars, which are unrepresentative of the stellar population in the Galaxy. Most stars form within dense cores in clusters alongside high-mass stars (>8 M$_{\odot}$), as likely the Sun did. Here we report deep ALMA 1.33 mm dust continuum observations at ~160 au spatial resolution, revealing 72 low-mass multiple systems embedded in 23 high-mass cluster-forming regions, as part of the Digging into the Interior of Hot Cores with ALMA (DIHCA) survey. We find that the companion separation distribution presents a distinct peak at ~1200 au, in contrast to the one at ~4000 au observed in nearby low-mass regions. The shorter fragmentation scale can be explained by considering the higher pressure exerted by the surrounding medium, which is higher than the one in low-mass regions, due to the larger turbulence and densities involved. Because the peak of the companion separation distribution occurs at much larger scales than the expected disk sizes, we argue that the observed fragmentation is produced by turbulent core fragmentation. Contrary as predicted, the multiplicity fraction remains constant as the stellar density increases. We propose that in the extremely dense environments where high-mass stars form, dynamical interactions play an important role in disrupting weakly bound systems.
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All authors Qiuyi Luo, Patricio Sanhueza, Stella S. R. Offner, Fernando Olguin, Adam Ginsburg, Fumitaka Nakamura, Kaho Morii, Yu Cheng, Kei E. I. Tanaka, Junhao Liu, Tie Liu, Xing Lu, Qizhou Zhang, Kotomi Taniguchi, Piyali Saha, Shanghuo Li, Xiaofeng Mai

Solar and Stellar Astrophysics

IK Pegasi and the Double-merger Path to Type Ia Supernovae

Na'ama Hallakoun, Sahar Shahaf, Sagi Ben-Ami et al. (+3 more)

Recent Gaia astrometry has revealed thousands of main-sequence + white-dwarf binaries (MS+WD) at separations of ~0.1-10 au, including a subset hosting unusually massive (>~0.8 Msun) WDs. We argue that s-process enrichment in the non-degenerate companion provides a powerful diagnostic for identifying WDs that formed via mergers in hierarchical triple systems. For a massive WD, standard single-star evolution requires a massive (>~4 Msun) progenitor, yet such progenitors produce negligible s-process yields. We define IK Peg-type systems as those exhibiting this mass-yield tension: barium-enhanced companions orbiting WDs too massive to have descended from efficient s-process producers. The well-known system IK Peg exemplifies this class. Applying this framework to published spectroscopic data reveals several additional candidates, and we estimate that a few dozen such systems should exist in the current Gaia sample. If these systems trace inner-binary mergers in primordial triples, they represent observable intermediate stages toward eventual Type Ia supernovae via the double-merger pathway, as predicted by recent population-synthesis models.
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All authors Na'ama Hallakoun, Sahar Shahaf, Sagi Ben-Ami, Oren Ironi, Param Rekhi, Hans-Walter Rix

Instrumentation and Methods for Astrophysics

Planet-Host Stars Across the Galaxy in the 2040s

M. Tsantaki, K. Biazzo, F. Zahra Majidi et al. (+2 more)

By the 2040s, the exoplanet field will have moved from the discovery of a few thousand planets to hundreds of thousands, thanks to Gaia DR5, TESS, PLATO, Roman, and their successors. At that stage, the key bottleneck will no longer be planet detection, but our ability to understand how planetary systems form, evolve, and diversify across different stellar and Galactic environments. To address this, we need a large-scale, high-resolution spectroscopic survey of planet-host stars, spanning a broad range of Galactic environments (thin and thick disks, bulge, halo, clusters, associations), and including a well-defined control sample of non-hosts. Such a survey must deliver homogeneous stellar parameters, detailed abundance determinations, ages, and kinematics for tens of thousands of hosts, extending to the faint magnitudes probed by future missions but are beyond the reach of existing and currently planned spectroscopic facilities.
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All authors M. Tsantaki, K. Biazzo, F. Zahra Majidi, G. Tautvaisiene, I. Busa

Solar and Stellar Astrophysics

The drastic impact of Eddington-limit induced mass ejections on massive star populations

D. Pauli, N. Langer, A. Schootemeijer et al. (+6 more)

Massive stars are the key engines of the Universe. However, their evolution and thus their ionizing feedback are still not fully understood. One of the largest gaps in current stellar evolution calculations is the lack of a model for the mass ejections that occur when the stars reach the Eddington limit, such as during an Luminous Blue Variable (LBV) phase. We aim to remedy this situation by providing a physically motivated and empirically calibrated method applicable in any 1D stellar evolution code to approximate the effect of such mass loss on stellar evolution. We employ the 1D stellar evolution code MESA, in which we implement a new mass-loss prescription that is acting when stellar models inflate too much when reaching the Eddington limit. Synthetic massive-star stellar populations using calculated grids of single-star models with this mass loss prescription are compared with the observed populations in the Large and Small Magellanic Clouds. In combination with already computed grids of binary evolution models, we investigate the impact of binarity on our predictions. Our single-star models reproduce key features of the observed stellar populations, namely (i) the absence of stars located beyond the Humphreys-Davidson limit, (ii) an upper limit of RSG luminosities, (iii) the faintest observed single WR stars, (iv) the absolute number of O-stars, WRs, and RSGs, (v) WO stars in low metallicity environments, and (vi) the positions of LBV stars in the HRD. Our binary population explains at the same time the 70% binary fraction of O-stars and the 40% binary fraction of WR stars. However, our synthetic population also has caveats, such as an overproduction of bright H-free WN stars. Our results show that the effect of Eddington-limit induced mass ejections on the structure and evolution of massive stars can remove tension between predicted and observed massive star populations.
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All authors D. Pauli, N. Langer, A. Schootemeijer, P. Marchant, H. Jin, A. Ercolino, A. Picco, R. Willcox, H. Sana

Astrophysics of Galaxies

A precessing jet from an active galactic nucleus drives gas outflow from a disk galaxy

Justin A. Kader, Vivian U, Loreto Barcos-Muñoz et al. (+30 more)

To reproduce observed galaxy properties, cosmological simulations require that massive galaxies experience feedback from active galactic nuclei, which regulates star formation within those galaxies. However, the energetics and timescales of these feedback processes are poorly constrained. We combine optical, infrared, sub-millimeter and radio observations of the active galaxy VV 340a, hosting a low-power jet launched from a supermassive black hole at its center. We find that the jet undergoes precession, with a period of (8.2 $\pm~$5.5) $\times~$10$^5$ years, and drives an outflow of gas at a rate of 19.4 $\pm~$7.9 solar masses per year. The jet shocks the gas, producing highly ionized plasma extending several kiloparsecs from the nucleus. The outflow ejects sufficient gas from the galaxy to influence its star formation rate.
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All authors Justin A. Kader, Vivian U, Loreto Barcos-Muñoz, Marina Bianchin, Sean T. Linden, Yiqing Song, Gabriela Canalizo, Archana Aravindan, George C. Privon Tanio Díaz-Santos, Christopher Hayward, Matthew A. Malkan, Lee Armus, Rosalie C. McGurk, Jeffrey A. Rich, Anne M. Medling, Sabrina Stierwalt, Claire E. Max, Aaron S. Evans, Christopher J. Agostino, Vassilis Charmandaris, Tianmu Gao, Justin H. Howell, Hanae Inami, Thomas S.-Y. Lai, Kirsten L. Larson, Christopher D. Martin, Mateusz Matuszewski, Joseph M. Mazzarella, James D. Neill, Nikolaus Z. Prusinski, Raymond Remigio, David B. Sanders, Jason Surace

Cosmology and Nongalactic Astrophysics

Evidence of sloshing-driven mini-halo formation in the cool-core cluster RXCJ1558.3-1410

Vishal S. Kale, Sonali K. Kadam, Sameer Salunkhe et al. (+6 more)

Radio mini-halos are perplexing features, typically hosted by X-ray cool-core galaxy clusters. Understanding the connection between thermal X-ray and non-thermal radio emission is key to uncovering their origin. Here, we present a multiwavelength study of the cool-core cluster RXCJ1558.3-1410 using archival Chandra X-ray and wideband uGMRT radio data (Bands 3, 4 and 5). Our improved analysis confirms a previously known X-ray cavity at $\sim$36 kpc south-east of the cluster centre and we report a new cavity at $\sim$42 kpc to the north-west. These cavities suggest that the AGN provides mechanical power of $\sim$$6.0 \times 10^{44}$ erg s$^{-1}$, sufficient to offset radiative cooling in the ICM. We also detect a sharp surface brightness edge at $\sim$72 kpc south-east of the centre, characterised by a temperature jump and pressure continuity, consistent with a cold front, likely caused by gas sloshing from a minor merger. Our uGMRT images reveals an interesting diffuse emission surrounding the brightest cluster galaxy (BCG), with its edge spatially coinciding with the sloshing cold front and roughly with the cooling radius. Furthermore, a low star formation rate and uniform metal abundance up to the sloshing edge are consistent with the earlier findings of suppression of star formation and metallicity homogenisation by mixing core gas through sloshing. Finally, the spatial correlation between the mini-halo and the observed X-ray features indicates that ICM sloshing, rather than AGN feedback, plays a dominant role in powering the proposed radio mini-halo emission.
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All authors Vishal S. Kale, Sonali K. Kadam, Sameer Salunkhe, Satish S. Sonkamble, Nilkanth D. Vagshette, Surajit Paul, Ruta Kale, S. Ilani Loubser, M. K. Patil

Astrophysics of Galaxies

First direct electron temperature measurement in [O II] zone in I Zw 18

I. A. Zinchenko, J. M. Vílchez, C. Kehrig et al. (+2 more)

We present new precise measurements of electron temperatures and oxygen abundances in the southeast knot of I Zw 18, one of the most metal-poor blue compact dwarf galaxies known, using spectroscopic data from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1). For the first time in I Zw 18, we directly measure electron temperature in the low-ionization zone using the rarely detected [O II] $\lambda\lambda7320,7330$ doublet. We also detect the auroral lines [O III] $\lambda4363$ and [S III] $\lambda6312$, associated with high and intermediate ionization zones, respectively. We derive $T_{\mathrm{e}}([\mathrm{O}\,\mathrm{III}])=21\,200\pm860\ \mathrm{K}$, $T_{\mathrm{e}}([\mathrm{O}\,\mathrm{II}])=16\,170\pm950\ \mathrm{K}$, and $T_{\mathrm{e}}([\mathrm{S}\,\mathrm{III}])=17\,290\pm1750\ \mathrm{K}$, highlighting a significant temperature difference between ionization zones. Using these direct temperature measurements, we determine a total oxygen abundance of $12+\log(\mathrm{O}/\mathrm{H})=7.066\pm0.046$, $\log(\mathrm{N}/\mathrm{O})=-1.509\pm0.097$, and $\log(\mathrm{S}/\mathrm{O})=-1.558\pm0.041$. Our results extend the calibration of $t_2$–$t_3$ relations to the highest temperatures, providing important anchor points for the temperature structure of extremely metal-poor H II regions, including high-redshift galaxies where direct temperature measurements are especially challenging.
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All authors I. A. Zinchenko, J. M. Vílchez, C. Kehrig, P. Papaderos, J. E. Méndez-Delgado

High Energy Astrophysical Phenomena

Evolution and afterglow emission of gamma-ray burst jets from binary neutron star mergers

Emma Dreas, Om Sharan Salafia, Andrea Pavan et al. (+2 more)

Relativistic jets launched in binary neutron star (BNS) mergers are widely accepted as the engines powering most of the population of short gamma-ray bursts (GRBs). Understanding their structure and dynamics-particularly during and after breakout from the merger ejecta-is crucial for interpreting GRB afterglows, especially for off-axis observers. Traditional models often assume simple angular or radial jet profiles, potentially missing key features emerging for jets piercing through realistic environments. This work aims to investigate the formation and evolution of the jet structure as it propagates through a non-homogeneous, anisotropic BNS merger environment. We focus on how the interaction with the ambient medium shapes the jet's angular and velocity distributions and assess the impact of this realistic structure on the resulting afterglow light curves. We perform a series of 3D relativistic magnetohydrodynamic simulations of jets launched in post-merger environments, exploring different injection conditions. Simulations are evolved to late times, approaching the ballistic regime, where further dynamical evolution becomes negligible. From the resulting outflows, we extract energy and velocity profiles and compute multi-wavelength afterglow light curves using a semi-analytic model that includes radial stratification and the full 3D jet geometry. More energetic or earlier-launched jets drill more efficiently through the ejecta, but all develop asymmetries that leave clear imprints in the off-axis afterglow light curves. All models exhibit a complex multi-shock breakout structure responsible for an early, dimmer peak in the afterglow. Despite structural differences, all simulated jets are consistent with the observational data of the multi-messenger BNS merger event GW170817.
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All authors Emma Dreas, Om Sharan Salafia, Andrea Pavan, Riccardo Ciolfi, Annalisa Celotti

Astrophysics of Galaxies

Stellar masses of optically dark galaxies: uncertainty introduced by the attenuation law and star-formation histories

Yash Lapasia, Sandro Tacchella, Francesco D'Eugenio et al. (+11 more)

Recent studies using JWST have suggested that some high-redshift galaxies may be ultra-massive, thereby challenging standard models of early galaxy formation. We analyse the stellar masses using different modelling assumptions and in conjunction with new data of three galaxies (S1, S2 and S3), whose photometric and NIRCam/grism redshifts were consistent with $z>5$. These three “optically dark” galaxies were reported to host exceptionally high stellar masses ($M_{\star}\gtrsim10^{11}~M_{\odot}$) and star-formation rates ($\mathrm{SFR}\gtrsim600~M_{\odot}~\mathrm{yr}^{-1}$), implying extremely high star-formation efficiencies. Recent NIRSpec/IFU observations for S1 indicate a spectroscopic redshift of $z_{\rm spec}=3.2439\pm0.0002$, revising the previous redshift. Using the Bayesian spectral energy distribution (SED) modelling tool Prospector, we investigate the impact of key model assumptions on stellar mass estimates, such as the choice of star-formation history (SFH) priors (constant versus rising SFH base for the non-parametric SFH prior), the dust attenuation law, and the treatment of emission line fluxes. Our analysis yields revised stellar masses of $\log_{10}(M_{\star}/M_{\odot}) \approx 10.36, 10.95$ and $10.31$ for S1, S2, and S3, respectively. We find that adopting a rising SFH base prior results in lower inferred stellar masses compared to a constant SFH base prior. Additionally, we identify a significant degeneracy between the dust attenuation curve slope, the amount of dust attenuation, and stellar mass. Our results highlight various systematics in SED modelling due to SFH priors and dust attenuation that can influence stellar mass estimates. Nevertheless, even with these revised stellar mass estimates, two of the three galaxies remain among the most massive and actively star-forming systems at their respective redshifts, implying high star-formation efficiencies.
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All authors Yash Lapasia, Sandro Tacchella, Francesco D'Eugenio, Dávid Puskás, Andrew J. Bunker, A. Lola Danhaive, Benjamin D. Johnson, Roberto Maiolino, Brant Robertson, Charlotte Simmonds, Irene Shivaei, Christina C. Williams, Christopher Willmer, Mengyuan Xiao

Cosmology and Nongalactic Astrophysics

One-Loop Tensor Power Spectrum from a Non-Canonical Spectator Field during Inflation

Zhe Li, Chen Yuan and Qing-Guo Huang

We compute the full one-loop corrections to the primordial tensor power spectrum in an inflationary scenario with a {non-canonical spectator field}, using the in-in formalism. We derive semi-analytic results for the scalar-sourced one-loop tensor spectrum and the effective tensor-to-scalar ratio, $r_{\mathrm{eff}}$. We consider two representative coupling functions: a localized Gaussian dip (Model G), which leads to moderate loop corrections, and a rapidly oscillatory coupling (Model O), which can yield much larger loop contributions. For Model G, we find a $\mathcal{O}(1)$ correction to $r_{\mathrm{eff}}$ while Model O can significantly enhance $r_{\mathrm{eff}}$ by several orders of magnitude (relative to the tree-level value). We further calculate the energy density of primordial gravitational waves. Assuming that primordial black holes with mass $10^{-12}M_{\odot}$ generated in this scenario, constitute all of the dark matter, we find that the results are several orders of magnitude lower than the sensitivities of Taiji/TianQin/LISA.
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Instrumentation and Methods for Astrophysics

Blind Deconvolution in Astronomy: How Does a Standalone U-Net Perform?

Jean-Eric Campagne

Aims: This study investigates whether a U-Net architecture can perform standalone end-to-end blind deconvolution of astronomical images without any prior knowledge of the Point Spread Function (PSF) or noise characteristics. Our goal is to evaluate its performance against the number of training images, classical Tikhonov deconvolution and to assess its generalization capability under varying seeing conditions and noise levels. Methods: Realistic astronomical observations are simulated using the GalSim toolkit, incorporating random transformations, PSF convolution (accounting for both optical and atmospheric effects), and Gaussian white noise. A U-Net model is trained using a Mean Square Error (MSE) loss function on datasets of varying sizes, up to 40,000 images of size 48x48 from the COSMOS Real Galaxy Dataset. Performance is evaluated using PSNR, SSIM, and cosine similarity metrics, with the latter employed in a two-model framework to assess solution stability. Results: The U-Net model demonstrates effectiveness in blind deconvolution, with performance improving consistently as the training dataset size increases, saturating beyond 5,000 images. Cosine similarity analysis reveals convergence between independently trained models, indicating stable solutions. Remarkably, the U-Net outperforms the oracle-like Tikhonov method in challenging conditions (low PSNR/medium SSIM). The model also generalizes well to unseen seeing and noise conditions, although optimal performance is achieved when training parameters include validation conditions. Experiments on synthetic $C^\alpha$ images further support the hypothesis that the U-Net learns a geometry-adaptive harmonic basis, akin to sparse representations observed in denoising tasks. These results align with recent mathematical insights into its adaptive learning capabilities.
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Astrophysics of Galaxies

MUSE-ALMA Haloes XIII. Molecular gas in $z \sim 0.5$ HI-selected galaxies

Victoria Bollo, Celine Peroux, Martin Zwaan et al. (+11 more)

We present new results from the MUSE-ALMA Haloes survey, covering 79 galaxies associated with strong HI absorption at redshift about 0.5. Our ALMA Cycle 10 observations add 39 systems to the initial 21, bringing the total to 60 galaxies. CO emission is detected in 9 new galaxies, and in 12 of 60 total, doubling the number of CO-emitting HI-selected galaxies and probing 1.2 dex deeper in molecular gas mass than previous studies. These galaxies span a wide range of stellar masses and metallicities. By comparing CO(2-1) and CO(3-2) properties with star formation rates and gas-phase metallicities from VLT/MUSE and HST, we find a dual behaviour in star formation efficiency: low-mass systems follow main-sequence scaling relations, while high-mass systems show suppressed star formation. This diversity indicates that HI absorbers trace both evolved and younger galaxies, providing a key step toward completing the baryon census at redshift about 0.5.
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All authors Victoria Bollo, Celine Peroux, Martin Zwaan, Jianhang Chen, Varsha Kulkarni, Capucine Barfety, Simon Weng, Natascha Forster Schreiber, Linda Tacconi, Benedetta Casavecchia, Tamsyn O'Beirne, Laurent Chemin, Ramona Augustin, Mitchell Halley

Earth and Planetary Astrophysics

Rare Near-Opposition Alignment of 3I/ATLAS on 22 January, 2026

Mauro Barbieri and Abraham Loeb

We point out that on 22 January 2026, the interstellar object 3I/ATLAS will align to within an exceptionally small angle, alpha= 0.69 degrees, with the Earth-Sun axis. This rare alignment provides unique circumstances for measuring the opposition surge and polarimetric properties of interstellar cometary dust. We characterize the alignment geometry, outline key scientific opportunities, and define the observational requirements for data collection. Observations before and after the alignment time offer an unprecedented opportunity which may not repeat for decades, for characterizing the albedo, structure, and composition of interstellar matter.
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Cosmology and Nongalactic Astrophysics

Primordial Gravitational Waves from Scalar Backreaction in Axion-SU(2) Inflation

Mattia Cielo, Ema Dimastrogiovanni, Matteo Fasiello et al. (+1 more)

In this work, we perform the first numerical study of strong scalar backreaction in spectator chromo-natural inflation (SCNI) in the case where the spectator sector decays during inflation. The tachyonic instability in scalar fluctuations, activated as the system crosses the $m_Q = \sqrt{2}$ threshold, amplifies perturbations and may significantly alter the background dynamics. The strong scalar backreaction regime introduces an effective quartic term in the potential for the gauge field background that rapidly drives it to zero, accelerating the axion-gauge system decay. We describe the dynamics of such decay and derive the gravitational wave spectrum for a set of benchmark parameters. Interestingly, the signal may peak at interferometer scales and lie within LISA's projected sensitivity.
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All authors Mattia Cielo, Ema Dimastrogiovanni, Matteo Fasiello, Alexandros Papageorgiou