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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 16 April

Astrophysics of Galaxies

Do galaxy mergers increase star formation and turbulence at cosmic noon?

I. Kanowski, J. T. Mendel, E. Wisnioski et al. (+3 more)

Mergers and interactions can significantly affect the morphological and dynamical properties of galaxies, however the impact of mergers on turbulence at $z > 1$ has not been observationally constrained. In this work we use the interaction strength parameter $Q_P$ to identify likely interacting and isolated galaxies at cosmic noon ($z \sim 1-2$) within the KMOS\textsuperscript{3D} integral field spectroscopy survey, utilising redshifts from the 3D-HST, CANDELS and UVCANDELS surveys. For $186$ galaxies, we measure deconvolved H$\alpha$ kinematics, including velocity dispersion, using a spatially non-parametric approach to account for observational effects in the dynamically diverse range of galaxies. We compare offsets in H$\alpha$ flux, star formation rate (SFR), dust attenuations, and velocity dispersion of likely interacting galaxies to isolated control galaxies matched in mass and lookback time. We find increased H$\alpha$ fluxes and SFRs in the likely interacting sample at the level of $\sim 0.1$ dex, a similar enhancement to studies of local pairs. In contrast, we find no significant increase in the level of velocity dispersion in interacting galaxies compared to their controls. The lack of increase in dispersion may reflect a combination of physical and observational factors, including limits to increasing turbulent motions in an already turbulent medium and spectral resolution limits.
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All authors I. Kanowski, J. T. Mendel, E. Wisnioski, N. M. Förster Schreiber, A. Marchal, T. Tsukui

High Energy Astrophysical Phenomena

A simple relation: Neutron star magnetic field strength and spectral shape at low mass accretion rates

Nicolas Zalot, Ekaterina Sokolova-Lapa, Aafia Zainab et al. (+8 more)

The X-ray spectra of neutron stars with moderate magnetic fields ($B\sim 10^{12}$ G) in high-mass X-ray binaries (HMXBs) at low X-ray luminosities ($L_\mathrm{X}\lesssim 10^{35}$ erg/s) are characterized by a double humped shape. This shape has been explained either as the radiation from a two-temperature magnetized atmosphere, where thermal radiation dominates at soft X-rays below about 10 keV, and cyclotron radiation with an imprinted cyclotron line dominates at high energies, or by the complex redistribution of primary X-rays in a structured atmosphere. The theoretical explanations of the double humped structure predict the spectra to depend on the magnetic field. We aim to connect the model predictions with observations. We analyzed archival NuSTAR observations of four HMXBs consisting of a neutron star and a Be star (BeXRBs), with known magnetic fields at luminosities low enough to show the characteristic double-hump spectrum. We modeled these spectra empirically and derived a relation between the energy of the intersection of the two humps and the magnetic field strength. In a second step, we tested whether this correlation is supported by fitting synthetic spectra simulated with the physically self-consistent polcap model. We find a linear correlation between the magnetic field strength and the intersection energy for the real BeXRB NuSTAR spectra and polcap-based simulated NuSTAR spectra alike. The effect of the magnetic field on spectral formation results in an observable correlation between the field strength and spectral shape. This derived positive correlation between intersection energy and magnetic field strength also allowed us to roughly estimate the magnetic field strength. Additional observations of XRBs and dedicated modeling efforts will be necessary to determine whether this approach is valid beyond the B-field range that was tested in this work.
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All authors Nicolas Zalot, Ekaterina Sokolova-Lapa, Aafia Zainab, Philipp Thalhammer, Jakob Stierhof, Katrin Berger, Katja Pottschmidt, Ralf Ballhausen, Christian Malacaria, Esin Gulbahar, Jörn Wilms

Astrophysics of Galaxies

Enhanced activity in close dual-AGN systems in the local Universe

Lorenzo Battistini, Alessandra De Rosa, Paola Severgnini et al. (+16 more)

We present the study of an X-ray selected sample of active galactic nuclei (AGN) in pairs at projected spatial separations 1 <$ r_p$/kpc < 100 at z < 0.1, using XMM-Newton and Chandra data. The pair sample is derived from an initial pool of approximately 2,000 X-ray-selected AGN, and is composed of both AGN-AGN pairs (so called dual AGN) and AGN-galaxy pairs. From this selection, we find that approximately 10% of AGN reside in pairs, and about 4% are paired with another AGN. We performed a detailed X-ray and SDSS optical spectral analysis for AGN in duals and X-ray analysis for AGN in AGN-galaxy pairs, to characterise their absorption properties and investigate the possible triggering mechanisms. We then investigated how obscuration, luminosity, and Eddington ratio depend on projected separation $r_p$. Amongst all AGN in pairs, we found that ~55% are obscured (with hydrogen column density $N_H$ > $10^{22}$ cm$^{-2}$), amongst which ~6% are Compton-thick ($N_H$ > $10^{24}$ cm$^{-2}$). The fraction of absorbed AGN is significantly higher in late-stage mergers ($r_p$ < 30 kpc) compared to early-stage mergers ($r_p$ > 60 kpc). Amongst the AGN in pairs, we also observed an average excess of AGN pairs with respect to a control sample of inactive galaxies in pairs, and that such excess significantly increases with decreasing $r_p$ only for obscured AGN. Finally, in dual-AGN systems, both the bolometric luminosity and the Eddington ratio of the less massive black hole in the pair increase as the separation decreases. These findings suggest that mergers may have an important role in triggering AGN accretion and activity.
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All authors Lorenzo Battistini, Alessandra De Rosa, Paola Severgnini, Cristian Vignali, Jasbir Singh, Pedro R. Capelo, Elena Bertola, Stefano Bianchi, Quirino D'Amato, Matteo Guainazzi, Fabio La Franca, Isabella Lamperti, Filippo Mannucci, Manali Parvatikar, Enrico Piconcelli, Federica Ricci, Fabio Rigamonti, Martina Scialpi, Maria Vittoria Zanchettin

Astrophysics of Galaxies

ALMA-IMF XXII. Role of core subfragmentation in the IMF origin: Hierarchical fragmentation cascade and CMF in W43-MM1

F. Motte, N. Le Nestour, R. Veyry et al. (+29 more)

We aim to predict how the currently observed top-heavy CMF in the massive protocluster W43-MM1 evolves due to core subfragmentation. We used getsf to extract sources in 5 ALMA images of W43-MM1 at 3mm, with a spatial resolution ranging from 14kau to 270au. Then, we applied FAMILY, a graph-theory-based analysis tool, to create and characterize networks of nested sources in W43-MM1. We compared the hierarchical fragmentation cascade of W43-MM1 to those measured in NGC2264 and in synthetic images of a MHD protocluster. Assuming self-similarity, we measure a small fractality index of F3D = 1.19 +/-0.10 in W43-MM1, which means that, on average, a cloud structure will fragment into only 1.19 fragments each time the physical scale decreases by a factor of two. In line with values measured above the core scale in the NGC 2264 and synthetic protoclusters, the W43-MM1 fractality index increases by ~30% at larger scales. We also estimate an imbalanced mass partition between siblings, with 2/3 of the mass of siblings at a given scale belonging to the dominant sibling. The mass transfer efficiency, computed from one physical scale to another, is high and corresponds to a CFE from 2.4kau cores to 200au seeds of ~16%. Based on the measured fractality and efficiency values, the gravo-turbulent model predicts that its fragmentation below ~14kau is not driven by turbulence but by gravity. Using these parameters and the measured mass partition, we demonstrate that the seed mass function, from which the IMF emerges, has a high-mass end which remains top-heavy. Therefore, based on our current assumptions, core subfragmentation in W43-MM1, and perhaps more broadly in massive Galactic protoclusters, plays a minimal role in shaping the high-mass slope of the IMF.
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All authors F. Motte, N. Le Nestour, R. Veyry, N. Brouillet, T. Nony, B. Thomasson, F. Louvet, I. Joncour, E. Moraux, A. Men'shchikov, T. Yoo, A. Ginsburg, A. Gusdorf, A. M. Stutz, R. Galvan-Madrid, T. Csengeri, R. H. Alvarez-Gutierrez, M. Armante, Y. Bernard, M. Bonfand, S. Chevalier, N. Cunningham, P. Dell'Ova, M. Gonzalez, A. Koley, F. A. Olguin, D. Panda, Y. Pouteau, J. Salinas, P. Sanhueza, N. A. Sandoval-Garrido, M. Valeille-Manet

Cosmology and Nongalactic Astrophysics

Microscopic primordial black holes as macroscopic dark matter from large extra dimensions

Giuseppe Filiberto Vitale, Gaetano Lambiase, Tanmay Kumar Poddar et al. (+1 more)

We study the coupled cosmological evolution of primordial black holes (PBHs) and radiation in the Arkani-Hamed-Dimopoulos-Dvali (ADD) framework with $n$ large extra dimensions and a fundamental gravity scale $M_\star$ at the TeV scale. For PBHs with horizon radius smaller than the compactification scale, the higher-dimensional geometry implies a larger horizon size at fixed mass and therefore a suppressed Hawking temperature. As a result, radiation accretion can overcome evaporation in the early Universe and drive a “runaway” phase of rapid mass growth. By numerically solving the coupled mass and energy-density evolution equations, we show that for $n \geq 2$ initially microscopic PBHs with initial mass $M_i \gtrsim 10^{12}\,$g can grow by many orders of magnitude and potentially reach macroscopic, even solar-mass, scales by matter-radiation equality. We determine the critical initial abundance $\beta_{\rm crit}$ required for PBHs to account for the observed dark matter density and find that extra dimensions dramatically lower this threshold, allowing viable scenarios with $\beta_{\rm crit}\sim 10^{-44}$. This identifies a previously unexplored region of parameter space in which the dark matter abundance is achieved through dynamical mass growth rather than large initial collapse fractions.
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All authors Giuseppe Filiberto Vitale, Gaetano Lambiase, Tanmay Kumar Poddar, Luca Visinelli

Instrumentation and Methods for Astrophysics

Sky background accounting in spectral infrared observations of extended objects at the Caucasus Mountain Observatory of the SAI MSU

A.S. Gusev, A.M. Tatarnikov, S.G. Zheltoukhov et al. (+1 more)

The Caucasus Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University is the only one in Russia and one of the few in the world where is possible to obtain spectral data in the near-infrared (IR) range at $\lambda$=1-2.5 $\mu$m. However, there is a problem of processing the spectra of extended objects, the angular dimensions of which exceed the length of the slit (4.5 arcmin). Obtaining additional spectra of the sky in the immediate vicinity of such objects does not solve the problem, since bright atmospheric hydroxyl lines at $\lambda$~2 $\mu$m change their intensity significantly over a time shorter than the exposure time of a single frame. We have developed a technique that allows us to correctly account for and exclude the contribution of variable atmospheric lines in the spectra of extended objects. This technique has been successfully tested in spectroscopic studies of the star-forming region NGC 7538 (S158) in our Galaxy.
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All authors A.S. Gusev, A.M. Tatarnikov, S.G. Zheltoukhov, M.S. Kirsanova

Solar and Stellar Astrophysics

Numerical investigation of particle acceleration at interplanetary shocks: diffusive and superdiffusive scenarios

Giuseppe Prete, Gaetano Zimbardo and Silvia Perri

Energetic particles are ubiquitous in space and astrophysical plasmas, and interplanetary shocks are widely regarded as one of the main particle accelerators in the heliosphere. Indeed, in-situ measurements typically show that energetic particle fluxes peak at the shock, indicating a local acceleration process. Furthermore, the time profile of energetic particle fluxes is highly influenced by particle transport properties upstream and downstream of the shock. By advancing previous numerical test-particle models that simulate the transport of monoenergetic particles around an infinite planar shock, in this work we add the acceleration of such particles via energy gains at each shock crossing, in a first-order Fermi-type mechanism. Moreover, the acceleration of a 70 keV particle population, namely the seed population, is reproduced by integrating a Langevin-type equation upstream and downstream of an infinite planar shock. Particles can diffuse in the simulation box via random "kicks", which belong either to a Gaussian distribution (normal diffusion) or to a Levy distribution (superdiffusion). We perform several simulations by varying the parameters of the model. The particle energy spectra in both diffusive and superdiffusive simulations are in remarkable agreement with the theoretical predictions.The output energetic particle densities have been compared with those observed by the ACE spacecraft during an interplanetary shock crossing on December 14, 2006. We show not only that particle fluxes in different energy bins reproduce very well the observed ones upstream and downstream when superdiffusion is at work, but also that anomalous, superdiffusive transport speeds up the acceleration process and leads to values of particle energies consistent with observations.
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Cosmology and Nongalactic Astrophysics

Euclid. Populating a dark universe with galaxies using SciPIC

Euclid Collaboration: E. J. Gonzalez, J. Carretero, Z. Baghkhani et al. (+304 more)

High-fidelity galaxy mocks are crucial for validating analysis pipelines and for cosmological inference. In this context, the Science Pipeline at PIC (SciPIC) is a pipeline specifically designed for the fast generation of synthetic galaxy catalogues from the halo properties identified in cosmological simulations. SciPIC delivers galaxy catalogues that aim to reproduce the observed luminosity function and clustering above a given flux detection limit over a wide redshift range. In this work, we introduce SciPICal, an automated pipeline that calibrates the parameters that set the main mock galaxy properties, namely number density, luminosities, colours, and positions. The pipeline is applied to the Euclid Flagship 2 Wide and Deep halo catalogues, specifically built to support the Euclid wide and deep surveys. Compared to the recently released Flagship 2 Wide mock, our calibrated version improves the clustering predictions by approximately 50% based on chi-squared values. Furthermore, we produce the Euclid Deep mock catalogue, which reaches up to $z = 10$ by populating a light-cone and a complementary snapshot at $z = 0$. We validate these catalogues using measurements from spectroscopic and photometric galaxy surveys, as well as with results from a hydrodynamical simulation. The obtained good agreement (within $15\%$ for most of the samples) in the clustering predictions across the different galaxy samples considered, validates our calibration strategy and demonstrates the strong predictive power of the generated mocks. This pipeline will allow us to improve the methodology applied in assigning the galaxy properties and ensures that the galaxy mocks remain up-to-date by incorporating constraints from upcoming observational data in the calibration procedure.
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All authors Euclid Collaboration: E. J. Gonzalez, J. Carretero, Z. Baghkhani, F. J. Castander, P. Fosalba, P. Tallada-Crespí, J. Stadel, D. Potter, I. Tutusaus, S. Ramakrishnan, M. L. van Heukelum, N. E. Chisari, F. Marulli, M. Bolzonella, L. Pozzetti, D. Navarro-Gironés, J. Chaves-Montero, G. Parimbelli, M. Manera, L. Blot, K. Hoffmann, M. Huertas-Company, P. Monaco, C. Scarlata, M.-A. Breton, S.-S. Li, R. Teyssier, M. Crocce, G. Congedo, A. Biviano, M. Hirschmann, A. Pezzotta, H. Hoekstra, W. J. Percival, P. A. Oesch, R. A. A. Bowler, V. Gonzalez-Perez, S. Avila, A. Kovács, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, H. Degaudenzi, S. de la Torre, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Escoffier, M. Farina, R. Farinelli, S. Farrens, F. Faustini, S. Ferriol, F. Finelli, S. Fotopoulou, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, R. J. Massey, N. Mauri, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, C. Moretti, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, V. Pettorino, S. Pires, G. Polenta, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, A. Secroun, S. Serrano, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, A. Spurio Mancini, L. Stanco, A. N. Taylor, I. Tereno, S. Toft, R. Toledo-Moreo, F. Torradeflot, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, V. Allevato, M. Ballardini, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, T. Castro, J. A. Escartin Vigo, J. García-Bellido, J. Macias-Perez, R. Maoli, J. Martín-Fleitas, R. B. Metcalf, A. Montoro, A. A. Nucita, M. Pöntinen, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, G. Angora, S. Anselmi, M. Archidiacono, F. Atrio-Barandela, L. Bazzanini, J. Bel, D. Bertacca, M. Bethermin, F. Beutler, A. Blanchard, M. Bonici, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, F. Caro, C. S. Carvalho, F. Cogato, A. R. Cooray, O. Cucciati, T. de Boer, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, M. Y. Elkhashab, A. Enia, Y. Fang, A. Finoguenov, A. Franco, K. Ganga, T. Gasparetto, R. Gavazzi, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, M. Guidi, C. M. Gutierrez, A. Hall, C. Hernández-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, K. Koyama, S. Kruk, M. C. Lam, M. Lattanzi, L. Legrand, M. Lembo, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, S. J. Liu, X. Lopez Lopez, A. Manjón-García, F. Mannucci, C. J. A. P. Martins, L. Maurin, M. Miluzio, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, S. Nesseris, F. Pace, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, C. Pattison, R. Paviot, A. Pisani, G. W. Pratt, S. Quai, M. Radovich, K. Rojas, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, E. Sarpa, A. Schneider, M. Schultheis, D. Sciotti, E. Sellentin, L. C. Smith, J. G. Sorce, I. Szapudi, K. Tanidis, F. Tarsitano, G. Testera, S. Tosi, A. Troja, C. Uhlemann, C. Valieri, A. Venhola, D. Vergani, G. Verza, P. Vielzeuf, S. Vinciguerra, M. von Wietersheim-Kramsta, N. A. Walton, A. H. Wright, H. W. Yeung

High Energy Astrophysical Phenomena

Deeper analysis of Fermi-LAT unassociated 4FGL J2112.5-3043 for possible identification

Federica Giacchino, Cristina Fernández-Suárez, Miguel Á Sánchez-Conde et al. (+3 more)

In the 4FGL-DR4 point-source catalog of the Large Area Telescope (LAT) onboard NASA's Fermi Gamma-ray Observatory (Fermi-LAT), around a third of the sources are still unidentified (unIDs). In this work, we perform a detailed study of one of them, namely 4FGL J2112.5-3043. Only gamma-ray emission has been detected from this unidentified source, with no counterpart observed at any other wavelength as of today. Together with its high detection significance, this makes 4FGL J2112.5-3043 a particularly compelling target for further investigation. The results of our spectral and spatial analyses show that the source photon spectrum is better described with a subexponential cutoff power-law spectral model, with no significant flux variability over time, and a morphology consistent with being a point-like source. We investigate and discuss the characterized emission within the context of both conventional and exotic astrophysics, namely a pulsar origin or potential dark matter (DM) annihilations in a nearby Galactic subhalo. Although our results are inconclusive and neither confirm a DM origin nor firmly establish an astrophysical nature, we find a spectral preference for the $b\bar{b}$ and $c\bar{c}$ DM annihilation channels over a pulsar origin, thus making this unID a particularly intriguing candidate for next multiwavelength observations.
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All authors Federica Giacchino, Cristina Fernández-Suárez, Miguel Á Sánchez-Conde, M.Ángeles Pérez-García, Stefano Ciprini, Dario Gasparrini

Instrumentation and Methods for Astrophysics

NOMAI : A real-time photometric classifier for superluminous supernovae identification. A science module for the Fink broker

E. Russeil, R. Lunnan, J. Peloton et al. (+10 more)

Superluminous supernovae (SLSNe) are one of the most luminous stellar explosions known, yet they remain poorly understood. Because they are intrinsically rare, efficiently identifying them in the large alert streams produced by modern time-domain surveys is essential for enabling spectroscopic follow-up. We present NOMAI, a machine learning classifier designed to identify SLSN candidates directly from photometric alerts in the ZTF stream, using light curves accumulated over at least 30 days. It does not require any spectroscopic redshift and is running in real time within the Fink broker. ZTF light curves are transformed into a set of physically motivated features derived primarily from model-fitting procedures using SALT2 and Rainbow, a blackbody-based multi-band fitting framework. These features are used to train an XGBoost classifier on a curated dataset of labeled ZTF sources constructed using literature samples of SLSNe, along with TNS and internal ZTF labeled sources. The final training dataset contains 5280 unique sources, including 225 spectroscopically classified SLSNe. On the training sample, the classifier reaches 66% completeness and 58% purity. Deployed within the Fink broker, NOMAI has been running continuously since 18/12/2025 on the ZTF alert stream and publicly reports SLSN candidates every night by automatically posting them to dedicated communication channels. Based on this, we also report the first two-month as an evaluation period, where the classifier successfully recovered 22 of the 24 active SLSNe reported on the Transient Name Server. The achieved performances demonstrate that the classifier provides a valuable tool for experts to efficiently scan the alert stream and identify promising candidates. In the near future, NOMAI is intended to be adapted to operate on the Legacy Survey of Space and Time conducted by the Vera C. Rubin Observatory.
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All authors E. Russeil, R. Lunnan, J. Peloton, S. Schulze, P. J. Pessi, D. Perley, J. Sollerman, A. Gkini, Y. Hu, T.-W. Chen, E. C. Bellm, T. X. Chen, B. Rusholme

High Energy Astrophysical Phenomena

Influence of winds on shocked magnetized viscous accretion flows around rotating black holes

Camelia Jana and Santabrata Das

We study global transonic solution for a relativistic, magnetized, viscous advective accretion flow around a rotating black hole, incorporating the effects of mass and angular momentum loss through winds. Our model considers dominant toroidal magnetic fields with synchrotron radiation as the primary cooling mechanism. To self-consistently model mass loss, the mass accretion rate is prescribed to decrease inward as a power-law with disk radius. With this, we solve the governing equations that describe the accretion flows in presence of winds and obtain the flow structure in terms of the inflow parameters (energy $\mathcal{E}$, angular momentum $\lambda$, plasma-$\beta$, accretion rate $\dot{m}$, and viscosity $\alpha_{\rm B}$), the wind parameters ($p$, governing mass loss; and $l$, governing angular momentum transport by winds), and the black hole spin ($a_{\rm k}$). Our analysis reveals that winds substantially modify the accretion flow leading to a significant decrease in disk luminosity. We specifically identify global solutions that admit standing shocks and find that winds profoundly alter shock properties, such as the shock radius ($x_{\rm s}$), compression ratio ($R$), and shock strength ($S$). Furthermore, we determine the critical wind parameter $p^{\rm crit}$ beyond which steady shock solutions cease to exist. We demonstrate that increased viscosity and strong angular momentum extraction by winds lead to reduce $p^{\rm crit}$. These findings evidently highlight a complex interplay between viscosity and winds in governing the dynamics of shock formation in accretion disks.
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Astrophysics of Galaxies

FAST and Dark: A catalogue of Dark Galaxy Candidates within 50 Mpc

Marco Monaci, Duncan A. Forbes, Jonah S. Gannon et al. (+4 more)

Using the first data release of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) All-Sky HI survey (FASHI), we compile a catalogue of 70 dark galaxy candidates (DGCs) within 50 Mpc. We select DGCs without an identified optical counterpart at a limiting g-band magnitude of ~ 28 mag arcsec^-2 in the DESI Legacy Survey, using both automatic cross-checking with optical catalogues and visual inspection of the colour images. After validating our DGCs, excluding potential spurious detections, issues in the registered position of the HI sources, and possible Radio Frequency Interferences (RFIs), we analyse their distribution over the surveyed sky, HI mass, linewidths, and inferred distance. They appear evenly distributed across the surveyed area, with no apparent bias to isolation. We did not find any DGC within the Local Volume (11 Mpc) in the sky surveyed by this first release of FASHI. We compare the observed properties of DGCs with those of galaxies with optical counterparts, finding that DGCs tend to have higher linewidths for a given HI mass. We discuss our DGCs in light of theoretical works, and compare them with other observational samples from previous HI surveys. This work presents a catalogue of dark galaxy candidates, which can serve as a basis for follow-up studies.
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All authors Marco Monaci, Duncan A. Forbes, Jonah S. Gannon, Bärbel S. Koribalski, Kenji Bekki, Jean P. Brodie, Warrick J. Couch

High Energy Astrophysical Phenomena

Systematic assessment of disk truncation in the black hole X-ray binary Swift J1727.8-1613 using NICER

Ole König, James F. Steiner, Niek Bollemeijer et al. (+20 more)

The 2023/24 NICER monitoring campaign of the 7 Crab bright black hole X-ray binary Swift J1727.8-1613 covered the outburst in almost all accretion states. High-quality data are available in the high-Eddington-fraction hard-intermediate state, hard-to-soft transition, the soft state, and the poorly studied back-transition to the dim hard state, making it an ideal dataset to compare the accretion flow at vastly different accretion rates. We apply disk continuum fitting techniques to investigate the evolution of the inner disk radius throughout the outburst. Taking a temperature-dependent color-correction factor into account, we see evolution of the disk inner radius by a factor of a few comparing the hard states to the thermal/soft state. We tentatively detect an onset of disk truncation in the soft-to-hard transition, right after the source leaves the soft state. After accounting for model systematics, we find the disk to be more truncated in the high-luminosity bright hard state compared to the low-luminosity dim hard state.
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All authors Ole König, James F. Steiner, Niek Bollemeijer, Riley M. T. Connors, Thomas Dauser, Michal Dovčiak, Ningyue Fan, Javier A. García, David Horn, Adam Ingram, Matteo Lucchini, Guglielmo Mastroserio, Cal Miller, Edward Nathan, Michael A. Nowak, Katja Pottschmidt, Ron Remillard, Yujia Song, Jiří Svoboda, Michiel van der Klis, Santiago Ubach, Jörn Wilms, Yuexin Zhang

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

Exploring non-equilibrium effects in sequential freeze-in

Shiuli Chatterjee and Andrzej Hryczuk

Freeze-in of multi-component dark sectors is governed not only by the interaction with the thermal plasma, but also by their internal dynamics. Full thermalisation within the dark sector is not guaranteed, raising the question of impact of departures from local thermal equilibrium onto the evolution and ultimately relic abundance and momentum distribution of dark matter. In this work we explore this question in a minimal two-scalar model, which can give rise to observable signatures in indirect detection and long-lived particle searches at forward physics experiments. Focusing on the phenomenologically viable regions, we analyse the impact of non-thermal evolution on the dark matter abundance, finding deviations of up to an order of magnitude between the full phase-space treatment and the traditional number-density approach. Our results highlight the importance of phase-space level computation for accurate freeze-in predictions and further motivate dedicated numerical tools for studying the evolution of multi-component dark sectors at the phase space level.
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Cosmology and Nongalactic Astrophysics

Fast modelling of ionization balance in the intergalactic medium: I- implications for the IGM metallicity

Bhaskar Arya, Kartick C. Sarkar and Shiv K. Sethi

Ionization balance in the intergalactic medium (IGM) is central to the interpretation of quasar absorption spectra, linking observed ionic columns to the underlying gas density, temperature, metallicity, and ionizing radiation field. Because ionization, recombination, and cooling timescales can be comparable to the timescales over which the ultraviolet background (UVB) and gas thermodynamic state evolve, ion populations may retain a strong memory of their past history. To this end, we present a fast, metals-inclusive, zero-dimensional framework for modeling the redshift evolution of the IGM. The model follows the coupled thermal and ionization evolution of a Lagrangian gas parcel in a redshift-dependent UVB, solving stiff, time-dependent rate equations for H, He, and 107 metal ions while self-consistently evolving the temperature through photoheating and standard cooling processes. We validate the framework against full three-dimensional hydrodynamical non-equilibrium calculations and find that it reproduces the thermal and ionization histories of the IGM with good accuracy over a wide redshift range, including the heating associated with $\rm He_{\,\rm II}$ reionization. As an application, we predict the cosmic $\rm C_{\,\rm IV}$ density parameter, $\Omega_{\rm CIV}$, and use it to infer the origin of metal ions in the IGM and the corresponding metallicities from observational measurements, obtaining values broadly consistent with literature constraints. The framework is well suited for rapid parameter studies of how reionization timing, UVB spectral hardness, self-shielding, and UVB inhomogeneity shape the thermal and ionization history of the IGM and the resulting metal-line observables.
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Astrophysics of Galaxies

A simple yet effective model of galaxy mergers

Cesare Chiosi, Mauro D'Onofrio and Emanuela Chiosi

In the context of the hierarchical formation of galaxies, we investigated the role played by mergers in shaping the scale relations of galaxies, that is the projections of their Fundamental Plane onto the \IeRe, \IeSig, \MRa\ and \Lsig\ planes. To this aim, we developed a simple model of multiple dry mergers among galaxies by suitably combing the formalism and properties of the so-called infall models of galaxy formation and evolution with the formalism of the scalar Virial Theorem. In this context, we mimicked the hierarchical formation of galaxies and generated simple models of galaxies undergoing a number mergers in the course of their evolution. The results are used to interpret the large scale simulations and the companion scale relations from observational and theoretical perspectives. The aim is to interpret the observational data of the MANGA and WINGS samples and the results of theoretical detailed numerical cosmo-hydro-dynamical simulations, such as Illustris-TNG100. In this context, we derived the above scale relations for our theoretical models and compared them with the observational counterparts from the MANGA and WINGS database, (and indirectly the large scale simulations of Illustris-TNG100). The multiple dry merging mechanism is able to explain all the main characteristics of the observed scale relations of galaxies, such as slopes, scatters, curvatures and zones of exclusion. The distribution of galaxies in these planes is continuously changing across time because of the merging activity and other physical processes, such as star formation, quenching, energy feedback, and so forth.} The precision of the present simple merger theory is comparable with that obtained by the modern cosmo-hydro-dynamical simulations, with the advantage of providing a rapid exploratory response on the consequences engendered by different physical effects.
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Cosmology and Nongalactic Astrophysics

Constraining Quintessential Inflation with ACT: A Gauss-Bonnet Gateway

Yogesh, Imtiyaz Ahmad Bhat, Mayukh R. Gangopadhyay et al. (+1 more)

Recent results from the Atacama Cosmology Telescope (ACT), indicating a higher and more tightly constrained scalar spectral index, $n_s = 0.9743 \pm 0.0034$, place several inflationary models under tension, with quintessential inflation pushed close to or beyond the $2\sigma$ boundary in the $r$–$n_s$ plane. In this work, we revisit quintessential inflation within the framework of Einstein–Gauss–Bonnet (EGB) gravity, where a scalar field non-minimally coupled to the Gauss–Bonnet invariant modifies the inflationary dynamics. We consider three representative coupling functions – exponential, hyperbolic secant, and hyperbolic tangent – and show that the exponential and sech-type couplings can shift the predicted values of $r$ and $n_s$ into the $1\sigma$ region allowed by ACT, thereby restoring consistency with observations. In contrast, the tanh-type coupling remains disfavored, underscoring the sensitivity of inflationary observables to the coupling structure. We further investigate the reheating phase using a model-independent parametrization and demonstrate that viable thermal histories can be realized even in the absence of a potential minimum, with reheating temperatures consistent with Big Bang nucleosynthesis bounds. Overall, our analysis shows that EGB corrections provide a viable and robust extension that reconciles quintessential inflation with current precision cosmological data, and we identify the corresponding allowed parameter space.
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All authors Yogesh, Imtiyaz Ahmad Bhat, Mayukh R. Gangopadhyay, M. Sami

Cosmology and Nongalactic Astrophysics

Closing the Observational Gap in Cosmic Dynamics: AI-Enabled Reconstruction of the Universe's Vorticity and Rotational Flow Morphology

Ziyong Wu, Xu Xiao, Fuyu Dong et al. (+7 more)

The cosmic vorticity field, an essential tracer of nonlinear structure formation, has remained observationally inaccessible because transverse galaxy motions are difficult to measure and analytic models struggle to capture shell-crossing. Here we report an empirical reconstruction of this field by applying an artificial intelligence framework trained on simulations of the concordance LambdaCDM model to Sloan Digital Sky Survey galaxies. The recovered three-dimensional velocity and vorticity fields reveal coherent vortical structures, including spiral flows in clusters, filaments, and voids, and the cosmic web inferred from vorticity closely matches that derived from density segmentation. The power spectra of the reconstructed velocity and vorticity fields agree statistically with LambdaCDM predictions, and the inferred velocity field effectively removes redshift-space distortions, yielding an almost isotropic clustering signal. These converging lines of evidence, obtained from an independent perspective, reinforce the concordance cosmological model. By closing a long-standing observational gap, our results highlight the potential of AI-driven reconstruction to access otherwise unobservable quantities and to address fundamental questions in cosmology and galaxy formation.
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All authors Ziyong Wu, Xu Xiao, Fuyu Dong, Juhan Kim, Yan-Chuan Cai, Yang Wang, Xi Kang, Le Zhang, Xin Wang, Xiao-Dong Li

Solar and Stellar Astrophysics

Revisiting Ca II Activity Indices in FGK Stars: Systematic Biases in Infrared Triplet Measurements

Xiaozhen Yang, Xiaoting Fu, Mingjie Jian et al. (+10 more)

Synthetic-template subtraction is widely used to measure chromospheric activity in large spectroscopic surveys. However, many solar-like FGK stars show systematically negative Ca II infrared triplet (IRT) activity indices. We investigate this effect using solar-like stars from LAMOST DR9, MaStar, and XSL DR3, measuring activity indices (R^+) for both the Ca II H&K and IRT lines within a uniform framework. We find that observational effects contribute to the scatter but do not explain the systematic negative bias in R^+_IRT. This bias mainly arises because radiative-equilibrium photospheric models lack the chromospheric layers, which exhibit a temperature rise and provide additional Ca II IRT opacity. This additional opacity makes the observed IRT cores deeper than those in the synthetic photospheric profiles. NLTE effects may contribute but are unlikely to dominate. The different behavior of the H&K and IRT diagnostics can be related to their different source-function behavior: the stronger chromospheric source-function enhancement of H&K makes their cores more likely to appear in emission. Increasing the adopted microturbulent velocity partially mitigates the negative offset, serving as an empirical compensation for missing atmospheric physics. In addition, R^+ values derived from different synthesis configurations show systematic offsets but generally preserve strong linear correlations, indicating that they can be cross-calibrated. These results clarify the origin of negative Ca II IRT residual indices and help interpret template-dependent systematics in chromospheric activity measurements.
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All authors Xiaozhen Yang, Xiaoting Fu, Mingjie Jian, Jingkun Zhao, Hailong Yuan, Zhongrui Bai, Mengxin Wang, Yiqiao Dong, Mingkuan Yang, Ziyue Jiang, Qian Liu, Ganyu Li, Haotong Zhang

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

Inflaton Regeneration via Scalar Couplings: Generic Models and the Higgs Portal

Kunio Kaneta, Tomo Takahashi and Natsumi Watanabe

The standard cosmological paradigm assumes that the inflaton field becomes dynamically negligible during the post-reheating evolution of the Universe. We demonstrate that this assumption fails for a broad class of inflationary models where the potential behaves as a monomial form $V(\phi) \propto \phi^k$ (with $k \ge 4$) around the minimum. In such scenarios, the effective inflaton mass depends on the field amplitude and vanishes asymptotically as the Universe expands. This vanishing-mass mechanism renders the inflaton kinematically accessible to the thermal plasma long after reheating, facilitating the regeneration of inflaton quanta through 1-to-2 decays and 2-to-2 scatterings of bath particles. This mechanism is quite generic and the coupling responsible for reheating can be constrained if the inflaton is overproduced, while the inflaton quanta can constitute dark matter in specific scenarios. Furthermore, if reheating occurs via the Standard Model Higgs portal, the process can be further constrained by big bang nucleosynthesis, cosmic microwave background, and colliders such as the LHC. This mechanism provides a new framework for probing post-inflationary reheating.
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Solar and Stellar Astrophysics

Upper bound of ejecta mass in a nova outburst

Izumi Hachisu and Mariko Kato

We present the maximum ejecta mass $(M_{\rm ej})_{\rm max}$ and the maximum ratio of ejecta mass and accreted mass $(M_{\rm ej}/M_{\rm acc})_{\rm max}$ of a nova for various white dwarf (WD) masses ($M_{\rm WD}=0.6$ - 1.38 $M_\odot$) and mass accretion rates ($\dot{M}_{\rm acc}=1\times 10^{-11}$ - $3\times 10^{-7} ~M_\odot$ yr$^{-1}$) based on the energy balance with nuclear burning. These maximum values serve as an upper bound of mass ejection for individual novae. Recently, B. E. Schaefer concluded that the WD masses in the recurrent novae U Sco and T CrB decreased at nova explosions, because the ejected mass is much larger than the accreted mass, i.e., $M_{\rm ej}/M_{\rm acc}= 26$ and $540$, respectively. These values are derived from the orbital period change at the nova explosions. Recurrent novae have been considered to be a progenitor system of Type Ia supernovae (SNe Ia) because their WD masses are now close to, and will possibly grow up to, 1.38 $M_\odot$ at which WDs explode as SNe Ia. From the different view point of energy generation at the thermonuclear runaway, we have obtained the much smaller value of the maximum ratio of $M_{\rm ej}/M_{\rm acc}\lesssim 2.6$ for a $1.37 ~M_\odot$ WD. This conclusion simply means that the nuclear (hydrogen) burning cannot release energy enough to expel such a large ejecta mass as B. E. Schaefer's claims. We also conclude that $(M_{\rm ej}/M_{\rm acc})_{\rm max}$ hardly increases even if we include the effect of frictional mass ejection process in the common envelope phase of a nova.
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Astrophysics of Galaxies

Disk-like galaxies at 4 < z < 7.7 : JWST/NIRCam morphologies revealed by denoising VAE-GCNN classification

S.S. Mirzoyan, A. Avagyan and V.G. Gurzadyan

Understanding the prevalence of disk-like galaxies at very high redshifts is crucial for constraining the early formation of angular momentum-supported structures. The advent of JWST now permits rest-frame UV and optical morphological studies deep into cosmic epochs where disks have traditionally been considered uncommon. We apply an identical denoising VAE-GCNN classification pipeline to multi-filter JWST/NIRCam cutouts in order to obtain homogeneous, morphology-based disk fractions across the sample. Our approach comprises two steps: (i) a U-Net Variational Autoencoder (VAE) is trained to remove astrophysical and instrumental contaminants while preserving intrinsic morphology, and (ii) a rotation - and reflection - equivariant GCNN classifier is applied to the denoised cutouts to distinguish disk-like galaxies from non-disks. We determine the fraction of disk-like galaxies as 0.34 for a sample of JWST 100 galaxies over the redshift range 4 < z < 7.7, also in dependence on the galaxy mass range. Our GCNN-based morphological analysis indicates that disk-like systems constitute a significant fraction of the considered high-redshift population and underscore the importance of such studies for the models of disk formation in the first billion years.
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Astrophysics of Galaxies

Impact of Baseline, Cadence, and Host Contamination on AGN Variability Metrics: A Systematic Study with ZTF

Diego Martínez Collipal and Swayamtrupta Panda

Variability in active galactic nuclei (AGN) probes the physics of accretion onto supermassive black holes. This variability is characterized using metrics derived from the flux distributions of temporally separated epochs. We studied the stability of two variability metrics, the Stetson index "J" and the smoothness "s", against baseline, cadence, and host galaxy contamination. We studied 23 nearby AGNs using Zwicky Transient Facility's Data Release 24. Both metrics are robust to baseline variations of $\sim 2$ years. However, s is sensitive to cadence, showing variations $\gtrsim 40\%$, while J shows minor variations $\lesssim10\%$. We studied the host galaxy impact using Mrk 493 as a representative case. We found that J remains unchanged after host subtraction, while s increases. We concluded that J is a robust tool for characterizing AGN variability, while s should be interpreted with caution.
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Earth and Planetary Astrophysics

Misaligned circumbinary discs around unequal-mass eccentric binaries: alignment, morphology, and binary accretion variability

Ruiqi Yang, Jeremy L. Smallwood, Hongping Deng et al. (+4 more)

Binary systems are ubiquitous in the Universe and often host circumbinary discs that are misaligned with the binary orbital plane. Such misalignments can affect disc evolution and binary accretion variability. We here present 3D hydrodynamical simulations of circumbinary discs with initial tilts $i_0$ from $0^\circ$ to $180^\circ$, around eccentric binaries with secondary-to-primary mass ratios of $0.11-0.67$. We find that both the initial tilt and mass ratio can affect the long-term accretion variability in our simulations. Discs evolving towards polar and coplanar retrograde generally favour accretion onto the primary star, while discs evolving towards coplanar prograde generally favour accretion onto the secondary. We find preferential accretion ratio $\eta=\langle\dot{M_2}\rangle/\langle\dot{M_\mathrm{b}}\rangle$ to be a non-monotonic function of the mass ratio. For discs close to coplanar prograde alignment, $\eta$ increases with decreasing mass ratio, whereas for discs with $30^\circ \le i_0 \le 135^\circ$, $\eta$ decreases for smaller mass ratios. Polar discs show the lowest mass loss rates, slightly lower than those of coplanar prograde discs, while retrograde discs lose mass faster than their prograde counterparts. Discs that undergo strong warping or breaking experience rapid mass loss. Our findings provide insights into observed circumbinary discs and have implications for circumbinary planet formation.
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All authors Ruiqi Yang, Jeremy L. Smallwood, Hongping Deng, Ya-Ping Li, Alessia Franchini, Ruobing Dong, Shang-Fei Liu

Astrophysics of Galaxies

Discovery of low-redshift analogues to "Little Red Dots" in DESI: A later evolutionary stage of compact LRDs?

Weiyu Ding, Xu Kong, Wei-Jian Guo et al. (+8 more)

The James Webb Space Telescope (JWST) has recently discovered a population of compact, red sources at z > 4 known as "Little Red Dots" (LRDs). They are characterized by their V-shaped continuum spectra and prominent broad Balmer emission lines. As their underlying physical nature remains debated and direct study at high-redshift is challenging; therefore, we seek to identify and characterize LRD analogues in the low-redshift universe to constrain their properties and potential evolutionary pathways. We identified five candidates at z = 0.2-0.4 from the Dark Energy Spectroscopic Instrument (DESI) that exhibit spectral energy distributions (SEDs) and broad Balmer emission lines closely resembling their high-redshift counterparts. However, we find significant differences: our low-redshift sample occupies a different region on the Baldwin, Phillips & Terlevich (BPT) diagram, and their stellar masses are significantly higher, suggesting a more substantial host galaxy contribution. These sources are not necessarily direct local analogues of high-redshift LRDs, but may represent later evolutionary stages of compact, rapidly accreting systems, or systems with related observational properties arising under different physical conditions. This sample provides a valuable laboratory for detailed follow-up studies to elucidate the nature of LRD-like phenomena.
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All authors Weiyu Ding, Xu Kong, Wei-Jian Guo, Hu Zou, Jialai Wang, Fujia Li, Hongxin Zhang, Jie Song, Jingyi Zhang, Niu Li, Wen-Xiong Li

Astrophysics of Galaxies

The GECKOS survey: Resolving the molecular and ionised gas in the galactic outflow of ESO~484-036

J. Hernández-Yévenes, D. B. Fisher, B. Mazzilli Ciraulo et al. (+20 more)

We present a spatially resolved, multiphase study of the outflow in the edge-on starburst galaxy ESO~484-036 from the GECKOS survey, combining VLT/MUSE H$\alpha$ and ALMA CO(1$-$0) observations to analyse the atomic ionised and cold molecular gas. Both show extraplanar emission consistent with a conical outflow. Ionised gas is enclosed by molecular gas, which is detected up to 2.5 kpc from the disc. Molecular gas dominates near the disc, except at the nuclear base, while ionised gas extends beyond 3 kpc. The deprojected outflow velocities are $\lesssim400\ \rm km\ s^{-1}$ in both phases and are consistent with ballistic motion, with some gas possibly falling back onto the disc. We find that the mass outflow rates are in the range of $\dot M_{\rm ion}\sim1-5\ \rm M_\odot\ \rm yr^{-1}$ and $\dot M_{\rm mol}\sim13-54\ \rm M_\odot\ \rm yr^{-1}$, giving mass loading factors of $\eta_{M\rm, ion}\sim 0.1-0.6$ and $\eta_{M\rm, mol}\sim 1.5-6.2$. These ranges reflect velocity and geometric uncertainties. Despite the short depletion time ($\tau_{\rm dep} = 16-48\rm\ Myr$), the outflow may regulate rather than permanently quench the gas reservoir. Energy loading ($\eta_E\leq0.16$) and momentum loading ($\eta_p\lesssim1$) support a purely starburst-driven outflow. Comparing ESO~484-036 with a literature sample, we find a systematic 1~dex shift in mass-loading relations when molecular gas is included. This produces a $\sim3.5$~dex discrepancy with cosmological simulations in $\eta_{M\rm, mol}/\eta_{M\rm, ion}$, implying that current models strongly underpredict cold gas production and the role of short-range recycling flows in starburst galaxies.
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All authors J. Hernández-Yévenes, D. B. Fisher, B. Mazzilli Ciraulo, R. L. Davies, M. Martig, A. Fraser-McKelvie, J. van de Sande, M. R. Hayden, R. Elliot, E. Emsellem, F. Combes, A. D. Bolatto, J. Bland-Hawthorn, L. Cortese, T. A. Davis, B. Catinella, L. M. Valenzuela, S. M. Croom, S. A. Fortuné, L. A. Silva-Lima, C. López-Cobá, A. Mailvaganam, G. van de Ven

High Energy Astrophysical Phenomena

Ultrahigh-energy cosmogenic neutrino emissions in the high-redshift universe

Shigeru Yoshida and Maximilian Meier

The James Webb Space Telescope (JWST) revealed a large population of active galactic nuclei (AGN) with redshifts greater than five. We show that if they emit ultrahigh-energy protons with energies up to $\lesssim 10^{19}$ eV, the cosmogenic neutrino production in the high-redshift CMB field yields a neutrino flux with a bump at around 50 PeV. This flux is potentially consistent with the current neutrino intensity estimate by the IceCube Neutrino Observatory within the parameter space allowed from the AGN luminosity and number density estimates by JWST. Future neutrino observations that confirm the 50-PeV bump and constrain the small-scale anisotropy will infer ultra-high energy cosmic-ray emissions in the early universe.
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Cosmology and Nongalactic Astrophysics

Forecasting neutrino mass constraints from the Nancy Grace Roman Space Telescope

Francesco Spezzati, Yun Wang and Andrew Hearin

We present realistic forecasts for the constraining power of the Nancy Grace Roman Space Telescope on fundamental cosmological parameters, with particular emphasis on the absolute neutrino mass scale, using full-shape analyzes of the galaxy power spectrum. We analyze simulated lightcone mock catalogs of H$\alpha$ emission-line galaxies spanning the redshift range $0.5 < z < 2$ over $2400\ \mathrm{deg}^2$, designed to reproduce the expected properties of the Roman High Latitude Wide Area Spectroscopic Survey. We perform parameter inference on the galaxy power spectrum multipoles using two complementary theoretical frameworks: a model-dependent approach based on the Effective Field Theory of Large-Scale Structure (EFT of LSS) within $\Lambda$CDM, and a model-independent phenomenological approach that makes no assumptions about the background cosmological model. In the $\Lambda$CDM analysis, we find $m_\nu < 0.380(0.162)\ \mathrm{eV}$ at $95(68)\%$ C.L. using Big Bang Nucleosynthesis (BBN) prior and a broad prior on $n_s$, which tightens to $m_\nu < 0.276(0.121)\ \mathrm{eV}$ when Planck priors on $\omega_b$, $\omega_\mathrm{cdm}$, and $n_s$ are added. Our forecasts show that Roman can additionally constrain $H_0$, $\Omega_m$, and $\sigma_8$ with precisions of $1.3\%$, $4.3\%$, and $2.9\%$ in line with Stage IV galaxy survey measurements and forecasts. In the model-independent analysis, we demonstrate that the phenomenological model can robustly recover unbiased measurements of the angular diameter distance, the Hubble parameter, and the growth of structure across all redshift bins, in the same range of scales as the EFT model, and obtain $m_\nu < 0.63(0.36)\ \mathrm{eV}$ at $95(68)\%$ C.L. when Planck priors are included.
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Astrophysics of Galaxies

The Last Galactic Firework: Timing the last significant merger with stars, globular clusters and $\omega$Centauri

Chervin F. P. Laporte and Matthew D. A. Orkney

We present a robust method to empirically infer the timing of the last significant merger in the Milky Way which is tested against fully cosmological models of galaxy formation. We apply it to Milky Way subgiant stars with spectro-photometric ages, finding that the last significant merger (Gaia-Sausage-Enceladus, GSE), occurred $\sim11\,$Gyrs ago. This coincides with the birth of a coeval in-situ group of globular clusters (GCs), which constrains the merger-induced starburst (hereafter {\it Tainá) to have occurred at $11.2\pm 0.1\,\rm{Gyr}$, the most precise dating of this merger event. The GSE's most metal-rich GCs were also born around this time ($\tau=10.9\pm0.1\,\rm{Gyr}$) and likely formed during the merger interaction prior to disruption of the GSE. We argue that $\omega$ Centauri is the most likely candidate for the surviving remnant of the GSE, and show that its stellar populations have final ages and metallicities consistent with the GSE GCs together with observational evidence it may have been affected by bar resonances. Furthermore, we argue that the mean metallicity for which stellar orbits transition from halo-like to disc-like kinematics shows an upward inflexion point at $[\rm{Fe/H}]\sim-1.33$, and this sets an upper-limit for the age when the disc was forming. To corroborate this, we identify proto-MW GCs with highly disc-like orbits that formed before the last significant merger (with ages up to $\tau=13.0\pm0.5\,\rm{Gyr}$). This places the disc formation time as far back as as $z_{\rm disc\, form}\gtrsim4$.
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Wednesday 15 April

Instrumentation and Methods for Astrophysics · Cross-listed from cs.RO

On-Orbit Space AI: Federated, Multi-Agent, and Collaborative Algorithms for Satellite Constellations

Ziyang Wang

Satellite constellations are transforming space systems from isolated spacecraft into networked, software-defined platforms capable of on-orbit perception, decision making, and adaptation. Yet much of the existing AI studies remains centered on single-satellite inference, while constellation-scale autonomy introduces fundamentally new algorithmic requirements: learning and coordination under dynamic inter-satellite connectivity, strict SWaP-C limits, radiation-induced faults, non-IID data, concept drift, and safety-critical operational constraints. This survey consolidates the emerging field of on-orbit space AI through three complementary paradigms: (i) {federated learning} for cross-satellite training, personalization, and secure aggregation; (ii) {multi-agent algorithms} for cooperative planning, resource allocation, scheduling, formation control, and collision avoidance; and (iii) {collaborative sensing and distributed inference} for multi-satellite fusion, tracking, split/early-exit inference, and cross-layer co-design with constellation networking. We provide a system-level view and a taxonomy that unifies collaboration architectures, temporal mechanisms, and trust models. To support community development and keep this review actionable over time, we continuously curate relevant papers and resources at https://github.com/ziyangwang007/AI4Space.
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