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Papers

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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 27 January

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

A Remedy of the Trans-Planckian Censorship Problem with Smooth Slow-roll to Power-law Inflation Transitions in Scalar Field Theory

S.D. Odintsov and V.K. Oikonomou

It is known that if the standard slow-roll inflation is followed by a power-law inflationary regime, then the trans-Planckian modes may be safely be contained in the Hubble horizon and never exit it during inflation. In this work we investigate how to realize a smooth transition between a slow-roll and a power-law inflationary regime in the context of single scalar field inflation. As we show it is possible to realize such a smooth transition by generalizing the kinetic energy of single scalar field in the form $\dot{\phi}^2=\beta(\phi)V(\phi)$, where $\beta(\phi)$ is some appropriate function of the scalar field. Using two distinct approaches we show that it is possible to realize a smooth transition from a slow-roll to a power-law inflationary regime, and the two approaches produce identical results regarding the slow-roll regime. Also we show that the slow-roll regime is quite short, about $N\sim 30$ $e$-foldings, with the flatness and horizon problems being solved with the synergistic effect of the two inflationary patches. The slow-roll era is found to be compatible with the Atacama Cosmology Telescope data.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

General Scalar Field Inflation ACT Attractors: Utilizing the $n_s(r)$ relation

V.K. Oikonomou

The ACT data have severely constrained the single scalar field models. Known models of inflation, like the Starobinsky model, the Higgs model and the $a$-attractors are at least $2\sigma$ off the ACT data. In this work we aim to provide a top-to-bottom approach in single scalar field inflationary cosmology compatible with the ACT data. Specifically, inspired by the fact that the Starobinsky model, the Higgs model and the $a$-attractors, all being plateau potentials, result to the same attractor relation between the spectral index of scalar perturbations and the tensor-to-scalar ratio, which is of the form $n_s(r)=1-\alpha r^{1/2}$, in this work we seek for attractors of the form $n_s(r)=f(r)$ that may lead to ACT-compatible inflation. Specifically, we fix the function $f(r)$ to have a specific desirable form and then solve the differential equation $n_s(r)=f(r)$ to find the potential which results to the relation $n_s(r)=f(r)$. We discovered analytically three classes of potentials which are variants of the general form $n_s(r)=\gamma \pm \beta r \pm r^{1/2}$ and all these models are found to be compatible with the ACT data.
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Astrophysics of Galaxies

GLIMPSE-DDT spectroscopic properties of faint-end galaxies at $z\sim6$: Towards first metal enrichment, dust production, and ionizing photon production

Yoshihisa Asada, Seiji Fujimoto, John Chisholm et al. (+16 more)

Ultra-faint galaxies at high-$z$ are fundamental elements of the early galaxy assembly, and spectroscopic characterization of this population is essential to understand the earliest galaxy evolution. Leveraging the ultra-deep JWST/NIRCam and NIRSpec observations of a gravitational lensing field of Abell S1063, taken as part of the GLIMPSE survey, we present spectroscopic properties of 16 galaxies fainter than $M_{\rm UV}=-17$ mag, including the metallicity, dust attenuation, and the ionizing photon production efficiency. The emission lines are generally quite strong, roughly half of which cannot be replicated with standard stellar populations and require an extreme ionizing source. We also identify relatively strong [OIII] emission lines from all sample galaxies, which indicates that the low-mass end of the mass-metallicity relation is extended down to $M_\star\sim10^6\ M_\odot$ at $z\sim6$. The strong [OIII] line detection from the lowest-mass galaxy among the sample ($M_\star\sim10^{5.6}\ M_\odot$) stands in contrast to recent reports of extremely metal-poor galaxy candidates at similar mass and redshift, suggesting that there could be two distinct pathways of the earliest metal enrichment as simulations have predicted. Interestingly, we detect both dust attenuation and galactic outflow in one of the sample galaxies with $M_\star=10^{6.6}\ M_\odot$ at $z=5.5$. All the dust, metal, and outflow contents in this galaxy can be consistently explained by supernovae (SNe), indicative of the key roles of SNe in the earliest galaxy assembly such as dust production, metal enrichment, stellar feedback, and baryon cycle.
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All authors Yoshihisa Asada, Seiji Fujimoto, John Chisholm, Rohan P. Naidu, Hakim Atek, Gabriel Brammer, Lukas J. Furtak, Vasily Kokorev, Richard Pan, Arghyadeep Basu, Volker Bromm, Miroslava Dessauges-Zavadsky, Tiger Yu-Yang Hsiao, Michelle Jecmen, Damien Korber, Boyuan Liu, Jed McKinney, Kristen B. W. McQuinn, Daniel Schaerer

Instrumentation and Methods for Astrophysics

The Sound of Noise: Leveraging the Inductive Bias of Pre-trained Audio Transformers for Glitch Identification in LIGO

Suyash Deshmukh, Chayan Chatterjee, Abigail Petulante et al. (+2 more)

Transient noise artifacts, or glitches, fundamentally limit the sensitivity of gravitational-wave (GW) interferometers and can mimic true astrophysical signals, particularly the short-duration intermediate-mass black hole (IMBH) mergers. Current glitch classification methods, such as Gravity Spy, rely on supervised models trained from scratch using labeled datasets. These approaches suffer from a significant “label bottleneck," requiring massive, expertly annotated datasets to achieve high accuracy and often struggling to generalize to new glitch morphologies or exotic GW signals encountered in observing runs. In this work, we present a novel cross-domain framework that treats GW strain data through the lens of audio processing. We utilize the Audio Spectrogram Transformer (AST), a model pre-trained on large-scale audio datasets, and adapt it to the GW domain. Instead of learning time-frequency features from scratch, our method exploits the strong inductive bias inherent in pre-trained audio models, transferring learned representations of natural sound to the characterization of detector noise and GW signals, including IMBHs. We validate this approach by analyzing strain data from the third (O3) and fourth (O4) observing runs of the LIGO detectors. We used t-Distributed Stochastic Neighbor Embedding (t-SNE), an unsupervised clustering technique, to visualize the AST-derived embeddings of signals and glitches, revealing well-separated groups that align closely with independently validated Gravity Spy glitch classes. Our results indicate that the inductive bias from audio pre-training allows superior feature extraction compared to traditional supervised techniques, offering a robust, data-efficient pathway for discovering new, anomalous transients, and classifying complex noise artifacts in the era of next-generation detectors.
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All authors Suyash Deshmukh, Chayan Chatterjee, Abigail Petulante, Tabata Aira Ferreira, Karan Jani

Solar and Stellar Astrophysics

Revisiting Stellar equatorial rotational velocities with Gaia DR3 line broadening – the dependence on temperature, mass and age

Amitay Sussholz, Tsevi Mazeh and Simchon Faigler

We used more than $10^5$ Gaia DR3 line broadening vbroad measurements to examine stellar rotation as a function of stellar temperature, mass and age. The large sample clearly displays the Kraft break at $\sim 6{,}500$\,K, or mass of $\sim1.3\,M_{\odot}$-while vbroad are small, on the order of $10$-$20$ km/s, for stars cooler than the Kraft break, they sharply rise above the break, reaching up $\sim100$ km/s with temperature of $7{,}000$ K. To follow the stellar rotation as a function of age, we consider vbroad as a function of scaled age-stellar age divided by the relevant Terminal Age Main Sequence (MS), for four narrow mass bins. We find that stellar rotation deceleration is slow during the MS phase and fast afterwards for stars hotter than the break, whereas deceleration rate is relatively high and does not vary much for the cool stars. Our findings are consistent with the theory that stellar rotation slowing is due to magnetic breaking, emanating from magnetic fields that are anchored to the stellar convective envelopes. Therefore, deceleration is high in cool stars, but in hot stars only after they leave the MS and develop convective outer layers
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Earth and Planetary Astrophysics

Exomoons and Exorings with the Habitable Worlds Observatory II: Finding Endor with Lunar Eclipses

Mary Anne Limbach, Beck Dacus, Brooke Kotten et al. (+6 more)

Giant planets in the habitable zone may host exomoons with conditions conducive to life. In this paper we describe a method by which the Habitable Worlds Observatory (HWO) could detect such moons: broadband reflected-light lunar eclipses (e.g., the moon passing into the shadow of the planet). We find that an Earth-like moon orbiting a Jovian-size planet at 1au can outshine its host planet near 1 micron, producing frequent (days time-scale) lunar eclipses with depths of order 50%. We determine that single eclipse events out to $\sim$12pc may be detectable for Earth-like moons around giant planets, down to $0.9R_\oplus$. Detection of smaller moons, $\sim$0.5$R_\oplus$ (corresponding to about the size of Mars or Ganymede), may be possible, but would generally require multiple events for most systems. These several-hour events provide a clear pathway to detecting habitable moons with HWO, given sufficient stare-time on each system to detect lunar eclipses. The occurrence rate of habitable exomoons remains unconstrained, however, making the ultimate yield uncertain. HWO will be capable of placing the first meaningful constraints on the frequency of habitable exomoons around giant planets; if it is non-negligible, HWO could also search for life on these worlds, possibly with lunar eclipse spectroscopy.
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All authors Mary Anne Limbach, Beck Dacus, Brooke Kotten, Elizabeth Lane, Jacob Lustig-Yaeger, Ryan MacDonald, Tyler D. Robinson, Jean-Baptiste Ruffio, Andrew Vanderburg

Instrumentation and Methods for Astrophysics

POEMMA-Balloon with Radio: A multi-messenger, multi-detector balloon payload

J.Adams, J.Alfaro, D.Allard et al. (+123 more)

A review of the current status of the field of Ultra-High-Energy Cosmic Ray (UHECR) including a summary of remaining open questions was presented in the white paper "Ultra-High Energy Cosmic Rays: at the Intersection of the Cosmic and Energy Frontiers" (Astropart. Phys. 147 (2023) 102794; arXiv:2205.05845). The authors concluded that two types of next-generation detectors are needed to answer these questions: high-accuracy instruments and detectors that maximize exposure at the highest energies. The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA), a proposed dual-satellite observatory, exemplifies the latter class and is designed to increase statistics of the highest-energy cosmic rays and to detect very-high-energy neutrinos following multi-messenger alerts. POEMMA-Balloon with Radio (PBR) implements a compact, balloon-borne version of the POEMMA concept, adapted for a Super-Pressure Balloon flight from Wanaka, New Zealand, with an expected campaign exceeding 20 days. PBR couples a wide field-of-view Schmidt telescope and a hybrid optical focal surface with a dedicated radio instrument to deliver simultaneous, complementary measurements of extensive air showers. The mission will validate the fluorescence detection strategy from space and raise technology readiness for a POEMMA-like space mission by observing UHECR-induced fluorescence light from suborbital altitudes, obtaining the first simultaneous optical Cherenkov and radio observations of high-altitude horizontal air showers above the cosmic-ray knee (E>3PeV), enabling energy-spectrum and composition studies at the PeV scale, and performing follow-ups of multi-messenger alerts to search for very-high-energy neutrinos via upward-going air showers. This paper summarizes the PBR payload and its expected performance.
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All authors J.Adams, J.Alfaro, D.Allard, P.Alldredge, R.Aloisio, R.Ammendola, A.Anastasio, L.Anchordoqui, D.Badoni, J.Baláž, B.Baret, L.Bar-On, M.Battisti, R.Bellotti, M.Bertaina, M.Betts, S.Blin, M.Boezio, P.Bořil, J.Brague, I.Buckland, J.Burton Heibges, F.S.Cafagna, P.Cao, J.Caraca, R.Caruso, M.Casolino, K.Černý, N.Cordrey, A.Creusot, A.Cummings, P.Degarate, C.De Santis, A.DiGiovanni, B.J.DiLella A.DiSalvo, J.Eser, S.Ferrarese, G.Filippatos, W.Finch, J.Ford, C.Fornaro, A.Fox-Smith, A.Froid, P.Gálvez Molina, S.Garbolino, D.Garg, B.Gockel, C.Guepin, A.Haungs, T.Heibges, J.Hicks, J.Hinkel, J.Krizmanic, L.Kupari, E.H.Lenzing, F.Liberatori, S.Mackovjak, D.Mandát, M.Manfrin, A.Marcelli, L.Marcelli, G.Masciantonio, V.Masone, E.Mayotte, E.Mentzell, A.Meli, M.Mese, S.Meyer, M.Mignone, M.Miller, M.Mongelli, J.Moses, E.Msihid, R.Munini, M.Murdock, A.Novikov, S.O'Brien, A.V.Olinto, Y.Onel, G.Osteria, B.Panico, E.Parizot, G.Passeggio, T.Paul, M.Pech, K.Penalo Castillo, F.Perfetto, C.Petta, P.Picozza, L.Piotrowski, Z.Plebaniak, H.Qureshi, E.Reali, M.H.Reno, M.Ricci, E.Ricci, A.Rivetti, A.Roy, F.Sarazin, V.Scherini, P.Schovánek, F.G.Schroeder, V.Scotti, C.Shay, A.Sotgiu, R.Sparvoli, B.Stillwell, I.Strhárský, J.Szabelski, Y.Takizawa, R.Torres, R.Triggiani, C.Trimarelli, C.Tussey, J.Tutt, M.Unger, T.Venters, M.Venugopal, P.von Ballmoos, L.Wanner, D.Washington, R.Webb, A.Weindl, L.Wiencke, S.Wissel, A.Yuan

Solar and Stellar Astrophysics

Stellar and orbital characterization of three low mass M dwarf binary stars with dynamical spectroscopy from the Habitable Zone Planet Finder

Suhani Surana, Chad F. Bender, Caleb I. Cañas et al. (+13 more)

Theoretical models of low-mass stars continue to be discrepant with observations when used to examine the mass-radius relationship and other physical parameters of individual stars. High-resolution spectroscopy that leads to dynamical measurements of binary stars can directly improve these models. We have been using the Habitable-zone Planet Finder spectrograph to monitor binary stars with M dwarf components. Here, we measure the orbital and stellar parameters for three such systems: LSPM J0515+5911, NLTT 43564, and NLTT 45468. Each system has dozens of spectra obtained over a baseline of several years. None of the systems appear to be eclipsing, so our ability to turn them into true benchmark binaries with purely dynamical measurements is limited. We use literature photometry to estimate each system's spectral energy distribution and utilize models in combination with detection limits of our spectroscopic measurements to probe characteristics of the companions. LSPM J0515+5911 is a double-lined spectroscopic binary with period of $126.948 \pm 0.029$ days and derived minimum masses, $M_1\sin^3i =0.058 \pm 0.002$ $M_\odot$ and $M_2\sin^3i = 0.046 \pm 0.001$ $M_\odot$ for the primary and secondary components, respectively. We solved NLTT 43564 with period of $1877 \pm 24$ days and NLTT 45468 with period of $9.686 \pm 0.001$ days as single lined systems, and modeled the primary masses to be $M_1 = 0.32\pm{0.02}$ $M_\odot$ and $M_1 = 0.35^{+0.02}_{-0.07}$ $M_\odot$, respectively.
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All authors Suhani Surana, Chad F. Bender, Caleb I. Cañas, Daniel M. Krolikowski, William D. Cochran, Mark Everett, Arvind F. Gupta, Shubham Kanodia, Suvrath Mahadevan, Andrew Monson, Joe P. Ninan, Leonardo A. Paredes, Paul Robertson, Arpita Roy, Christian Schwab, Gudmundur Stefansson

Astrophysics of Galaxies

A GLIMPSE into the UV Continuum Slopes of the Faintest Galaxies in the Epoch of Reionization

Michelle C. Jecmen, John Chisholm, Hakim Atek et al. (+23 more)

As observations have yet to constrain the ionizing properties of the faintest (M$_{\rm UV}$ > -16) galaxies, their contribution to cosmic reionization remains unclear. The rest-frame ultraviolet (UV) continuum slope ($\beta$) is a powerful diagnostic of stellar populations and one of the few feasible indicators of the escape fraction of ionizing photons (f$_{\rm esc}$) for such faint galaxies at high-redshift. Leveraging ultra-deep JWST/NIRCam GLIMPSE imaging of strong lensing field Abell S1063, we estimate UV continuum slopes of 555 galaxies at z $>$ 6 with absolute magnitudes down to M$_{\rm UV}$ $\simeq -$12.5. We find a modest evolution of $\beta$ with redshift and a flattening in the $\beta$-M$_{\rm UV}$ relation such that galaxies fainter than M$_{\rm UV}$ $\sim -$16.5 no longer exhibit the bluest UV slopes. The 138 ultra-faint galaxies with M$_{\rm UV}$ $> -$16 are a diverse population encompassing dusty (30%), old (15%), and low-mass (50%) galaxies. We apply the empirical $\beta$-f$_{\rm esc}$ relation from local Lyman continuum leakers, finding the mean f$_{\rm esc}$ peaks at $\sim 20\%$ at M$_{\rm UV}=-$16.5 and declines towards fainter galaxies, while remaining consistent with f$_{\rm esc}$ = 14% within uncertainties, in agreement with recent radiative transfer simulations. Incorporating GLIMPSE constraints on the UV luminosity function, ionizing photon production efficiency, and escape fractions produces a reionization history consistent with independent observational constraints. Our results indicate galaxies with M$_{\rm UV}$ between $-18$ and $-14$ supplied $\sim 60\%$ of the ionizing photons to cosmic reionization, while the lower f$_{\rm esc}$ of fainter galaxies produces a natural cutoff in the ionizing photon production rate density.
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All authors Michelle C. Jecmen, John Chisholm, Hakim Atek, Vasily Kokorev, Ryan Endsley, Iryna Chemerynska, Lukas J. Furtak, Richard Pan, Seiji Fujimoto, Rohan P. Naidu, Julian B. Muñoz, Angela Adamo, Yoshihisa Asada, Arghyadeep Basu, Danielle A. Berg, Jeremy Blaizot, Miroslava Dessauges-Zavadsky, Emma Giovinazzo, Tiger Yu-Yang Hsiao, Harley Katz, Damien Korber, Jed McKinney, Kristen. B. W. McQuinn, Pascal A. Oesch, A. Saldana-Lopez, Daniel Schaerer

Astrophysics of Galaxies

GLIMPSE-D: Metallicity Decline in Faint Galaxies: Implications for [O III]+Hb Luminosity Function and Reionisation Budget

Damien Korber, Daniel Schaerer, Rui Marques-Chaves et al. (+13 more)

We report the measurement of the R3=[O III]5008/Hb ratios for 54 galaxies in the GLIMPSE-D survey. Thanks to gravitational lensing, our sample includes galaxies with -20 < Muv < -14 at z=6-9. We derive oxygen abundances using calibrated relationships. We observe a significant decline in R3 values below Muv > -18, which we interpret as evidence of decreasing metallicities in fainter regimes. We explore four prescription models of the evolution of R3 with UV emission based on the new measurements and results from previous surveys. Applying these models to the GLIMPSE [O III]+Hb luminosity functions, we measure and extrapolate the ionising photon production rate $\dot{N}_{ion}$ of galaxies down to very faint limits SFR(Ha) > 5e-3 Msun/yr. Our results support the dominant contribution of star-forming galaxies to reionisation, and are consistent with the recent discovery of ultra-faint metal-poor galaxies. Our measurements of the relative contribution of each luminosity bin show that galaxies with L(Ha)~1e41 to 1e42 erg/s dominate at 8<z<9, but the relative contributions become more uniform at $7<z<8$. Extreme models either under- or over-estimate the ionising photon budget, while intermediate models align with recent observational constraints.
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All authors Damien Korber, Daniel Schaerer, Rui Marques-Chaves, Angela Adamo, Arghyadeep Basu, John Chisholm, Miroslava Dessauges-Zavadsky, B.W. Kristen. McQuinn, Alberto Saldana-Lopez, Hakim Atek, Ryan Endsley, Seiji Fujimoto, J. Lukas Furtak, Vasily Kokorev, P. Rohan Naidu, Richard Pan

Earth and Planetary Astrophysics

The CO snow line favours strong clumping by the streaming instability in protoplanetary discs with porous grains

Jean-François Gonzalez and Stéphane Michoulier

Context: The radial drift and fragmentation of small dust grains in protoplanetary discs impedes their growth past centimetre sizes. Several mechanisms have been proposed to overcome these planet formation barriers, such as dust porosity or the streaming instability (SI), which is today regarded as the most promising mechanism to form planetesimals. Aims: Here, we examine whether the conditions for the SI to lead to strong clumping, the first step in planetesimal formation, are realised in protoplanetary discs containing porous grains. Methods: We used results from previous simulations of the evolution of porous grains subjected to growth, fragmentation, compaction and bouncing in protoplanetary discs. In the ensuing disc structures, we determined the regions where the dust-to-gas ratio exceeds the critical value for strong clumping found in simulations of the SI including external turbulence. Results: We find that the conditions for strong clumping are met within the first hundred thousand years in large regions of protoplanetary discs containing porous grains, provided that the CO snow line is taken into account. If the CO snow line is neglected, the conditions are met only very close to the inner disc edge early on, or over large areas well after 200,000 yr.
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Solar and Stellar Astrophysics

The Role of Long Period Variable Stars in Observational Astrophysics

Dorota M. Skowron and Igor Soszyński

Long-period variables (LPVs) are evolved red giant and supergiant stars whose pulsations provide unique insights into late stages of stellar evolution and serve as essential tools in modern astrophysics. Their period-luminosity and period-age relations make them valuable distance and age indicators, while their light curve morphology, amplitudes, and multiperiodicity reveal the underlying physics of stellar interiors and mass-loss. In this review, we provide an overview of the current status of LPV studies, focusing on their observational properties and applications, including: - Modern classification of LPVs into Miras, semiregular variables (SRVs), and OGLE small-amplitude red giants (OSARGs), which occupy multiple period-luminosity sequences associated with different pulsation modes, chemical compositions, and evolutionary stages - Mira variables as reliable distance indicators across diverse stellar environments and their increasing role as standard candles - The increasing role of SRVs and OSARGs - Long secondary period (LSP) variables as potential tracers of exoplanets Together with advances in theoretical modeling, these developments establish LPVs as valuable tracers of Galactic structure, stellar populations, and the extragalactic distance scale.
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Cosmology and Nongalactic Astrophysics

An X-ray-Emitting Proto-Cluster at $z\approx5.7$ Reveals Rapid Structure Growth

Akos Bogdan, Gerrit Schellenberger, Qiong Li et al. (+1 more)

Galaxy clusters are the most massive gravitationally bound structures in the universe and serve as tracers of the assembly of large-scale structure. Studying their progenitors, proto-clusters, sheds light on the earliest stages of cluster formation. Yet, detecting proto-clusters is demanding: their member galaxies are loosely bound and the emerging hot intracluster medium (ICM) may only be in the initial stages of virialization. Recent JWST observations located several proto-cluster candidates by identifying overdensities of $z\gtrsim5$ galaxies. However, none of these candidates was detected by X-ray observations, which offer a powerful way to unveil the hot ICM. Here, we report the combined Chandra and JWST detection of a proto-cluster, JADES-ID1, at $z\approx5.68$, merely one billion years after the Big Bang. We measure a bolometric X-ray luminosity of $L_{\rm bol} = (1.5^{+0.5}_{-0.6}) \times10^{44} \ \rm{erg \ s^{-1}}$ and infer a total gravitating mass of $M_{500}= (1.8^{+0.6}_{-0.7}) \times 10^{13} \ \rm{M_{\odot}}$, making this system a progenitor of today's most massive galaxy clusters. The detection of extended, shock-heated gas indicates that substantial ICM heating can occur in massive halos as early as $z\approx5.7$. In addition, given the limited survey volume, the discovery of such a massive cluster is statistically unlikely, implying that the formation of the large-scale structure must have occurred more rapidly in some regions of the early universe than standard cosmological models predict.
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All authors Akos Bogdan, Gerrit Schellenberger, Qiong Li, Christopher J. Conselice

Solar and Stellar Astrophysics

A constrained linear model for continuum normalization of stellar spectra

Andrew R. Casey, Adam Wheeler, Megan Bedell et al. (+3 more)

Inferring stellar parameters and chemical abundances by forward modeling stellar spectra usually requires a spectral synthesis code, or an emulator constructed from a curated training set. In these situations continuum normalization is often implemented as a pre-processing step that is independent of stellar parameters. This leads to results that are biased, or inconsistent across signal-to-noise ratios. A more justified approach is to forward model spectra with all nuisances simultaneously, but in practice this can be an expensive or non-convex optimization procedure. Here we describe a constrained linear model that can fit stellar absorption, telluric transmission, the joint continuum-instrument response. Stellar absorption and telluric transmission are each modeled by factorizing a grid of rectified theoretical spectra into two non-negative matrices with a chosen number of basis components. This model characterizes all possible spectra in many fewer parameters than comparable data-driven models. The non-negativity constraint ensures basis vectors are strictly additive, which limits rectified flux to less than or equal to unity, such that we can distinguish normalized spectra from the joint instrument-continuum response. The model requires no initial guess, and the linearity ensures that inference is convex, stable, and fast. This model allows us to reliably fit nuisances (e.g., tellurics, continuum), and is readily extensible to radial velocity and rotational broadening, without any prior knowledge about the fundamental stellar properties. We demonstrate our method by fitting ESO/HARPS high-resolution echelle spectra of BAFGKM-type stars. With repeat observations of $\alpha$-Centauri A we present results that are best in class: consistent across time to 0.2% at S/N ~ 100, and to better than 0.5% at S/N ~ 30.
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All authors Andrew R. Casey, Adam Wheeler, Megan Bedell, David W. Hogg, Andrew Sayjdari, Lily Zhao

Astrophysics of Galaxies

MAJORS II: HCO+& HCN Abundances in W40

René Plume, David J. Eden, Malcolm J. Currie et al. (+34 more)

We present observations of HCN and HCO$^+$ J = $3 - 2$ in the central $424'' \times 424''$ region of the W40 massive star forming region. The observations were taken as part of a pilot project for the MAJORS large program at the JCMT telescope. By incorporating prior knowledge of N(H$_2$) and $T_K$, assuming a constant density, and using the RADEX radiative transfer code we found that the HCN and HCO$^+$ abundances range from $X$(HCN) = $0.4-7.0 \times 10^{-8}$ and $X$(HCO$^+$) = $0.4-7.3 \times 10^{-9}$. Additional modelling using the NAUTILUS chemical evolution code, that takes H$_2$ density variations into account, however, suggests the HCN and HCO$^+$ abundances may be fairly constant. Careful modelling of three different positions finds $X$(HCN) = $1.3-1.7 \times 10^{-8}$, $X$(HCO$^+$) = $1.3-3.1 \times 10^{-9}$. Cross-comparison of the two models also provides a crude estimate of the gas density producing the HCN and HCO$^+$ emission, with H$_2$ densities in the range $5 \times 10^4 - 5 \times 10^5$ cm$^{-3}$, suggesting that the HCN and HCO$^+$ emission does indeed arise from dense gas. High UV intensity (e.g. $G_o >$ a few thousand) has no effect on the abundances in regions where the visual extinction is large enough to effectively shield the gas from the UV field. In regions where $A_V < 6$, however, the abundance of both species is lowered due to destructive reactions with species that are directly affected by the radiation field.
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All authors René Plume, David J. Eden, Malcolm J. Currie, Lawrence K. Morgan, Xue-Jian Jiang, James DiFrancesco, Masatoshi Imanishi, Kee-Tae Kim, Tie Liu, Raffaele Rani, Alessio Traficante, Jane Cohen, Neal J. Evans II, Luis C. Ho, Eun Jung Chung, Sihan Jiao, Chang Won Lee, Dana Alina, Toby Moore, Jonathan M. C. Rawlings, Florian Kirchschlager, Sudeshna Patra, Andrew J. Rigby, Hsien Shang, Jihye Hwang, Patricio Sanhueza, Mark G. Rawlings, Kianoosh Tahani, Junfeng Wang, Kate Pattle, James S. Urquhart, Quang Nguyen-Luong, Sarah E. Ragan, Yang Su, Xindi Tang, Agata Karska, Michael G. Burton

Cosmology and Nongalactic Astrophysics · Cross-listed from stat.CO

SunBURST: Deterministic GPU-Accelerated Bayesian Evidence via Mode-Centric Laplace Integration

Ira Wolfson

Bayesian evidence evaluation becomes computationally prohibitive in high dimensions due to the curse of dimensionality and the sequential nature of sampling-based methods. We introduce SunBURST, a deterministic GPU-native algorithm for Bayesian evidence calculation that replaces global volume exploration with mode-centric geometric integration. The pipeline combines radial mode discovery, batched L-BFGS refinement, and Laplace-based analytic integration, treating modes independently and converting large batches of likelihood evaluations into massively parallel GPU workloads. For Gaussian and near-Gaussian posteriors, where the Laplace approximation is exact or highly accurate, SunBURST achieves numerical agreement at double-precision tolerance in dimensions up to 1024 in our benchmarks, with sub-linear wall-clock scaling across the tested range. In multimodal Gaussian mixtures, conservative configurations yield sub-percent accuracy while maintaining favorable scaling. SunBURST is not intended as a universal replacement for sampling-based inference. Its design targets regimes common in physical parameter estimation and inverse problems, where posterior mass is locally well approximated by Gaussian structure around a finite number of modes. In strongly non-Gaussian settings, the method can serve as a fast geometry-aware evidence estimator or as a preprocessing stage for hybrid workflows. These results show that high-precision Bayesian evidence evaluation can be made computationally tractable in very high dimensions through deterministic integration combined with massive parallelism.
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High Energy Astrophysical Phenomena

Fading Echoes of Interaction: Probing Centuries of Preexplosion Mass-Loss in Four Type IIn Supernovae

Elizabeth Hillenkamp, Raphael Baer-Way, Poonam Chandra et al. (+6 more)

Supernovae characterized by enduring narrow optical hydrogen emission lines (SNe IIn) are believed to result primarily from the core-collapse of massive stars undergoing sustained interaction with a dense circumstellar medium (CSM). While the properties of SN IIn progenitors have relatively few direct constraints, the ongoing ejecta-CSM interaction provides unique information about late-stage stellar mass-loss preceding core-collapse. We present late-time X-ray and radio observations of four $\geq$3000 day-old SNe IIn: SN 2013L, SN 2014ab, SN 2015da, and KISS15s. The radio and X-ray emission from KISS15s indicate a mass-loss rate of \eq{\dot M\sim4\times 10^{-3}~\rm{M_{\odot}\,yr^{-1}}} at $\sim$450 years pre-supernova – 2 orders of magnitude below earlier optical estimates (which probed the mass loss immediately preceding the supernova). We find hints of a spectral inversion in the radio SED of KISS15s; a possible signature of a secondary shock due to a binary system or the emergence of a pulsar wind. For SN 2013L, we obtain a mass-loss rate of \eq{\dot M\sim2 \times 10^{-3}~\rm{M_{\odot}\,yr^{-1}}} at $\sim$400 years pre-explosion based on the X-ray detection. For SN 2014ab and SN 2015da, we find a upper limits on the mass-loss rates of \eq{\dot M<2\times10^{-3}~M_{\sun}\,yr^{-1}} explosion at $\sim$300 and 250 years pre-explosion, respectively. All four objects display mass-loss rates lower than estimates from earlier optical analyses by at least 1-2 orders of magnitude, necessitating a rapidly evolving progenitor process over the last centuries pre-explosion. Our analysis reveals how X-ray and radio observations can elucidate progenitor evolution when these objects have faded at optical wavelengths.
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All authors Elizabeth Hillenkamp, Raphael Baer-Way, Poonam Chandra, Arkaprabha Sarangi, Roger Chevalier, Nayana A.J., Annika Deutsch, Keiichi Maeda, Nathan Smith

Earth and Planetary Astrophysics

A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2

Alexander Venner, Andrew Vanderburg, Chelsea X. Huang et al. (+7 more)

The transit method is currently one of our best means for the detection of potentially habitable "Earth-like" exoplanets. In principle, given sufficiently high photometric precision, cool Earth-sized exoplanets orbiting Sun-like stars could be discovered via single transit detections; however, this has not previously been achieved. In this work, we report a 10-hour long single transit event which occurred on the $V=10.1$ K-dwarf HD 137010 during K2 Campaign 15 in 2017. The transit is comparatively shallow ($225\pm10$ ppm), but is detected at high signal-to-noise thanks to the exceptionally high photometric precision achieved for the target. Our analysis of the K2 photometry, historical and new imaging observations, and archival radial velocities and astrometry strongly indicate that the event was astrophysical, occurred on-target, and can be best explained by a transiting planet candidate, which we designate HD 137010 b. The single observed transit implies a radius of $1.06^{+0.06}_{-0.05}$ $R_\oplus$, and assuming negligible orbital eccentricity we estimate an orbital period of $355^{+200}_{-59}$ days ($a=0.88^{+0.32}_{-0.10}$ AU), properties comparable to Earth. We project an incident flux of $0.29^{+0.11}_{-0.13}$ $I_\oplus$, which would place HD 137010 b near the outer edge of the habitable zone. This is the first planet candidate with Earth-like radius and orbital properties that transits a Sun-like star bright enough for substantial follow-up observations.
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All authors Alexander Venner, Andrew Vanderburg, Chelsea X. Huang, Shishir Dholakia, Hans Martin Schwengeler, Steve B. Howell, Robert A. Wittenmyer, Martti H. Kristiansen, Mark Omohundro, Ivan A. Terentev

Astrophysics of Galaxies

Discovery of Galactic center ejected star in DESI DR1

Manuel Cavieres, Sergey E. Koposov, Elena Maria Rossi et al. (+2 more)

Hypervelocity stars (HVSs) are stars ejected from the Galactic Centre (GC) through tidal interactions with the central supermassive black hole. Formed in the immediate vicinity of Sgr~A$^\ast$, these stars are accelerated to velocities high enough to escape the GC and be observable in the Galactic halo. Using spectroscopy from the Dark Energy Spectroscopic Instrument (DESI) and astrometry from Gaia, we conducted a six-dimensional search for HVSs and identified a compelling candidate, hereafter DESI-312, whose bound trajectory can be confidently traced back to the central 2 kpc of our galaxy. The star resides in the inner halo and exhibits supersolar metallicity ([Fe/H] $= 0.27\pm 0.09$), distinct from other known stellar populations with radial orbits. Its inferred GC ejection velocity of $698^{+35}_{-27}$ is consistent with a Hills mechanism ejection, supporting an origin in the innermost regions of the Milky Way. We considered alternative origins for the star, including disk ejections from young clusters and globular clusters, but these scenarios fail to explain both its orbit and metallicity. Unlike previously identified A- and B-type HVSs, DESI-312 is a $\sim 1\,M_{\odot}$ star on the main sequence or early subgiant branch, thus enabling a detailed chemical analysis of its atmosphere and offering a rare window - unobscured by dust and crowding - into the composition of the central regions of the Galaxy.
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All authors Manuel Cavieres, Sergey E. Koposov, Elena Maria Rossi, Zephyr Penoyre, Sill Verberne

Astrophysics of Galaxies

Prompt cusps in hierarchical dark matter halos: Implications for annihilation boost

Shin'ichiro Ando, Martín Moró González and Youyou Li

Recent simulations have identified long-lived “prompt cusps” – compact remnants of early density peaks with inner profiles $\rho\propto r^{-3/2}$. They can survive hierarchical assembly and potentially enhance signals of dark matter annihilation. In this work, we incorporate prompt cusps into the semi-analytic substructure framework SASHIMI, enabling a fully hierarchical, environment-dependent calculation of the annihilation luminosity that consistently tracks subhalos, sub-subhalos, and tidal stripping. We assign prompt cusps to first-generation microhalos and propagate their survival through the merger history, including an explicit treatment of cusps associated with stripped substructure. We find that the substructure hierarchy converges rapidly once a few levels are included, and that prompt cusps can raise the total annihilation boost of Milky-Way–size hosts at $z=0$ to $B\sim 50$ for fiducial cusp-occupation assumptions, compared to a subhalo-only baseline of $B_{\rm sh}\sim\mathrm{few}$. Across a wide range of host masses and redshifts, prompt cusps increase the normalization of $B(M_{\rm host},z)$ while largely preserving its mass and redshift trends. Compared to universal-average, peak-based estimates, our fiducial boosts are lower by about a factor of a few, primarily reflecting a correspondingly smaller inferred cusp abundance in host halos, highlighting the importance of unifying peak-based cusp formation with merger-tree evolution and environmental dependence.
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Cosmology and Nongalactic Astrophysics

Testing the Equivalence Principle in Galaxy Clusters

Enea Di Dio, Sveva Castello and Camille Bonvin

Clusters of galaxies have been used to measure a subtle effect predicted by Einstein: gravitational redshift. This signal encodes pristine information about our Universe, since it is sensitive to the depth of the clusters' gravitational potential wells. In this work, we show how gravitational redshift can be used to test a fundamental physical principle: the weak equivalence principle. This principle stipulates that all matter falls in the same way in a gravitational potential, regardless of its nature. By comparing the amplitude of the gravitational redshift signal with the velocity dispersion in galaxy clusters, we build a novel test of this principle targeted to the unknown dark matter. Our test is sensitive to any additional interaction that would alter the way dark matter falls in gravitational potentials, hence leading to a violation of the equivalence principle. We show that currently available data can constrain the presence of a fifth force in clusters at the level of 7-14%, while the newest surveys will reach a precision of a few percents. This demonstrates the crucial role played by galaxy clusters in testing fundamental properties of dark matter.
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Cosmology and Nongalactic Astrophysics

Banana Split: Improved Cosmological Constraints with Two Light-Curve-Shape and Color Populations Using Union3.1+UNITY1.8

David Rubin, Taylor Hoyt, Greg Aldering et al. (+1 more)

SNe Ia have been used to provide key constraints on the equation-of-state parameter of dark energy. They are generally standardized under the assumption that they belong to a single population, with luminosities standardized in a continuous (roughly linear) fashion using the observed light-curve timescale. We update the Union3+UNITY1.5 SN cosmology analysis in light of increasing evidence for at least two core populations of SNe Ia and apply this "UNITY1.8" model to the updated "Union3.1" compilation (Hoyt et al. 2026). In addition to finding evidence for two different light-curve-shape (x1) distributions, we also find that the color distributions are different, that the light-curve-shape/magnitude standardization relations are different, and that these populations have different distributions across host-galaxy stellar mass and redshift. Importantly, we find that the residual host-mass luminosity step found in prior SN Ia cosmology analyses is now consistent with zero for unreddened SNe. We report a significantly tightened constraint on the split in the red-color standardization between SNe in low- and high-mass galaxies. We find that the estimated uncertainties shrink on cosmological parameters when fitting the same SNe assuming two modes versus one mode. We confirm similar trends in simulated data when running both versions of UNITY on the same (two-mode) simulations. For a flat {\Lambda}CDM cosmology, we find Omega_m=0.334+0.025-0.024 from SNe alone; for a flat w_0-w_a cosmology, we find w_0 = -0.760+0.084-0.082 and w_a = -0.79+0.28-0.30 when including SNe, BAO, and CMB. In the 2D w0-wa plane, UNITY1.8 decreases the tension with flat {\Lambda}CDM by 0.1 sigma to ~ 3 sigma compared to single-mode UNITY.
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All authors David Rubin, Taylor Hoyt, Greg Aldering, Saul Perlmutter

Astrophysics of Galaxies

Dynamical Evidence for a Billion Solar Mass Black Hole in Galaxy NGC 4061 from ALMA $^{12}$CO(2-1) Kinematics

Dieu D. Nguyen, Long Q. T. Nguyen, Elena Gallo et al. (+6 more)

We present the first robust dynamical measurement of the supermassive black hole (SMBH) mass in the massive early-type galaxy NGC 4061 using high-spatial-resolution ALMA observations of the $^{12}$CO(2-1) emission. By combining archival Cycle 6 data with new Cycle 7 observations, we achieve a synthesized beam of $0''.16 \times 0''.13$, comparable to the expected sphere of influence of the central black hole. The molecular gas forms a regularly rotating circumnuclear disk aligned with the prominent dust lane seen in HST imaging. We model the full three-dimensional ALMA data cube using the KinMS forward-modeling framework, exploring both data-driven and analytic prescriptions for the gas surface brightness distribution. Our Bayesian analysis yields a best-fitting SMBH mass of $M_{\rm BH} = (1.17^{+0.08}_{-0.10}\,[{\rm stat.}] \pm 0.43\,[{\rm syst.}]) \times 10^{9}$ M$_\odot$ and an $I$-band stellar mass-to-light ratio of $M/L_{\rm F814W} = 3.46^{+0.07}_{-0.06}\,[{\rm stat.}] \pm 0.10\,[{\rm syst.}]$ M$_\odot$/L$_\odot$. The inferred black hole mass is fully consistent across different modeling assumptions and remains insensitive to plausible radial variations in the $M/L_{\rm F814W}$ profile. Our results resolve the long-standing discrepancy between previous indirect mass estimates based on conflicting stellar velocity dispersion measurements and demonstrate that the exceptionally large dispersion reported in the literature is likely spurious. This study highlights the power of high-resolution ALMA molecular gas kinematics for precision SMBH mass measurements at the high-mass end of the local black hole mass function.
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All authors Dieu D. Nguyen, Long Q. T. Nguyen, Elena Gallo, Hai N. Ngo, Que T. Le, Fabio Pacucci, Tinh Q. T. Le, Tuan N. Le, Tien H. T. Ho

Cosmology and Nongalactic Astrophysics

An essential building block for cosmological zoom-in perturbation theory

Obinna Umeh

The evolution of large-scale structure within the standard model of cosmology is well posed only up to the onset of shell crossing, where particle trajectories appear to intersect. Beyond this point, the evolution equations become non-predictive and perturbative approaches break down. We show that in General Relativity, a matter horizon forms before caustics develop for a well-defined initial over-density on an expanding FLRW spacetime. The matter horizon was first identified by Ellis and Stoeger in 2010 as a dynamical causal boundary that encloses a sub-region of spacetime where structure formation actually takes place. We construct a multi-scale hierarchical framework for the propagation of geodesic congruences that avoids the shell-crossing singularity by cutting the spacetime at the matter horizon and glueing to another spacetime with opposite orientation. We identify a relationship between the multi-scale hierarchical framework and the cosmological zoom-in N-body simulation approach, and relate the local sub-region that decouples from the Hubble flow to the region of interest in cosmological zoom-in N-body simulations. Most importantly, the multi-scale hierarchical framework provides a more robust way of implementing boundary conditions, which could benefit cosmological zoom-in N-body simulation approaches.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Equation of State of Highly Asymmetric Neutron-Star Matter from Liquid Drop Model and Meson Polytropes

Elissaios Andronopoulos and Konstantinos N. Gourgouliatos

We present a unified description of dense matter and neutron-star structure based on simple but physically motivated models. Starting from the thermodynamics of degenerate Fermi gases, we construct an equation of state for cold, catalyzed matter by combining relativistic fermion statistics with the liquid drop model of nuclear binding. The internal stratification of matter in the outer crust is described by $\beta$-equilibrium, neutron drip and a gradual transition to supranuclear matter. Short-range repulsive interactions inspired by Quantum Hadrodynamics are incorporated at high densities in order to ensure stability and causality. The resulting equation of state is used as input to the Tolman–Oppenheimer–Volkoff equations, yielding self-consistent neutron-star models. We compute macroscopic stellar properties including the mass-radius relation, compactness and surface redshift that can be compared with recent observational data. Despite the simplicity of the underlying microphysics, the model produces neutron-star masses and radii compatible with current observational constraints from X-ray timing and gravitational-wave measurements. This work demonstrates that physically transparent models can already capture the essential features of neutron-star structure and provide valuable insight into the connection between dense-matter physics and astrophysical observables while they can also be used as easy to handle models to test the impact of more complicated phenomena and variations in neutron stars.
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Solar and Stellar Astrophysics

Chemically peculiar stars investigated by the BRITE Mission

Teja Begari, Klaus Bernhard, Ernst Paunzen et al. (+1 more)

We present a comprehensive analysis of BRITE photometry for 85 chemically peculiar stars, aimed at refining or determining their rotational periods. Utilizing a uniform Lomb-Scargle-based pipeline, we derived significant periods for 47 targets. A comparison with existing literature periods reveals generally good agreement, although several stars exhibit discrepant or previously unrecognized behavior. Notably, six targets display clear multiperiodicity, which, when combined with archival TESS data, suggests that these six candidates are likely misclassified, for example, as a magnetic CP2 or a CP4 star and instead exhibit characteristics consistent with a Be/shell star. Furthermore, eleven stars show no detectable periodic variations within the precision limits of BRITE. Our analysis demonstrates the effectiveness of long-term nanosatellite photometry, particularly when complemented by TESS data, in verifying catalogue periods, identifying multiperiodic behavior, and detecting potential misclassifications among bright CP stars.
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All authors Teja Begari, Klaus Bernhard, Ernst Paunzen, Prapti Mondal

Earth and Planetary Astrophysics

Polarimetry and albedo of the Near-Earth Asteroid 2025 FA22

J.-P. Rivet, S. Bagnulo, P. Bendjoya et al. (+17 more)

We report spectropolarimetric and broadband polarimetric observations of the near-Earth asteroid 2025 FA22 during its close approach of 18 September 2025 (about two Moon distances). With a diameter estimated between 130 and 290 m, 2025 FA22 is among the largest NEAs observable at such proximity, prompting an International AsteroidWarning Network (IAWN) rapid-response campaign. Although early orbital solutions indicated a possible impact in 2089, further follow-up astrometric observations ruled out collision hazard. The favourable geometry of this close encounter enabled a dense coverage of the positive part of the phase-polarisation curve, from the high polarisation domain (high phase angles), nearly to the inversion angle where the linear polarisation fraction vanishes. The spectropolarimetric observations provided the wavelength dependence of the polarisation fraction. Using empirical relationships, an estimate of the geometric albedo could be drawn from the slope of the phase-polarisation curve at inversion angle : $\rho_v = 0.17\pm0.04$ in the V band. This value, together with the spectropolarimetric trend, provides constraints on the taxonomic class, with the results being most consistent with an M-type classification. These results demonstrate the interest of polarimetry and spectropolarimetry for rapid characterisation of newly discovered NEAs in planetary defence campaigns.
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All authors J.-P. Rivet, S. Bagnulo, P. Bendjoya, G. Borisov, A. Cellino, M. Devogèle, Z. Gray, S. Ieva, L. Kolokolova, Y. G. Kwon, A. Berdyugin, S. V. Berdyugina, L. Boulanger, E. Dotto, P. Fatka, E. Frank, M. Lazzarin, V. Piirola, P. Pravec, the NEOPOPs team

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

Effect of noise characterization on the detection of mHz stochastic gravitational waves

Nikolaos Karnesis, Quentin Baghi, Jean-Baptiste Bayle et al. (+1 more)

Pulsar timing arrays' hint for a stochastic gravitational-wave background (SGWB) leverages the expectations of a future detection in the millihertz band, particularly with the LISA space mission. However, finding an SGWB with a single orbiting detector is challenging: It calls for cautious modelling of instrumental noise, which is also mainly stochastic. It was shown that agnostic noise reconstruction methods provide robustness in the detection process. We build on previous work to include more realistic instrumental simulations and additional degrees of freedom in the noise inference model and analyze the impact of LISA's sensitivity to SGWBs. Particularly, we model the two main types of noise sources with separate transfer functions and power spectral density spline fitting. We assess the detectability bounds and their dependence on the flexibility of the noise model and on the prior probability, allowing us to refine previously reported results.
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All authors Nikolaos Karnesis, Quentin Baghi, Jean-Baptiste Bayle, Nikiforos Galanis

Astrophysics of Galaxies

Exploring the effects of diffuse ionised gas in two local analogues of high-redshift star-forming galaxies

P. Lagos, A. Nigoche-Netro, T. C. Scott et al. (+2 more)

Aims. We investigate the impact of diffuse ionised gas (DIG) on the determination of emission line ratios and gas-phase metallicities in two local analogues of high-redshift star-forming galaxies: UM 462 and IIZw 40. Understanding how DIG affects these quantities is essential for interpreting unresolved observations of distant galaxies, where integrated spectra are often used to trace their chemical evolution. Methods. Using archival Very Large Telescope, Multi-Unit Spectroscopic Explorer (MUSE) data, we spatially resolved the warm ionised medium of both galaxies. We derived oxygen abundances through the direct method and several HII-based strong-line calibrators, and we used the H$\alpha$ surface brightness ($\Sigma$(H$\alpha$)) to distinguish regions dominated by HII or DIG emission. Results. Oxygen abundances derived from the N2 and O3N2 indices show an inverse correlation with $\Sigma$(H$\alpha$), ionisation parameter, and EW(H$\alpha$), with DIG-dominated regions exhibiting higher 12+log(O/H) than the galaxy mean by $\sim$0.2 dex in UM 462 and $\sim$0.1 dex in IIZw 40. The metallicity differences between HII-dominated and DIG-dominated $\Sigma$(H$\alpha$) bins reach $\sim$0.4 dex and $\sim$0.3 dex in UM 462 and IIZw 40, respectively. The observed trends with $\Sigma$(H$\alpha$), metallicity, EW(H$\alpha$), and ionisation parameter indicate smoothly varying ionisation conditions rather than true abundance variations. These effects reflect different ionisation sources and levels, and can produce spurious metallicity gradients in galaxies with extended DIG structures, potentially mimicking signatures of metal-poor gas infall. In our sample, DIG ionisation is most likely dominated by photon leakage from H II regions, with additional contributions from feedback-driven shocks.
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All authors P. Lagos, A. Nigoche-Netro, T. C. Scott, C. Sengupta, R. Demarco

Instrumentation and Methods for Astrophysics

Accelerating radio astronomy imaging with RICK: a step towards SKA-Mid and SKA-Low

Giovanni Lacopo, Emanuele De Rubeis, Claudio Gheller et al. (+2 more)

The data volumes generated by modern radio interferometers, such as the SKA precursors, present significant computational challenges for imaging pipelines. Addressing the need for high-performance, portable, and scalable software, we present RICK 2.0 (Radio Imaging Code Kernels). This work introduces a novel implementation that leverages the HeFFTe library for distributed Fast Fourier Transforms, ensuring portability across diverse HPC architectures, including multi-core CPUs and accelerators. We validate RICK's correctness and performance against real observational data from both MeerKAT and LOFAR. Our results demonstrate that the HeFFTe-based implementation offers substantial performance advantages, particularly when running on GPUs, and scales effectively with large pixel resolutions and a high number of frequency planes. This new architecture overcomes the critical scaling limitations identified in previous work (Paper II, Paper III), where communication overheads consumed up to 96% of the runtime due to the necessity of communicating the entire grid. This new RICK version drastically reduces this communication impact, representing a scalable and efficient imaging solution ready for the SKA era.
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All authors Giovanni Lacopo, Emanuele De Rubeis, Claudio Gheller, Giuliano Taffoni, Luca Tornatore