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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 18 September

Solar and Stellar Astrophysics

A Quantitative Method to Investigate the Spectral Class Time Evolution of Novae

Maria Kopsacheili, Martín Guerrero and Diego Alejandro Vasquez Torres

Novae are spectroscopically classified as Fe II or He/N according to the dominance of Fe II, or He and N emission lines in their pre-nebular spectra, while spectra exhibiting both are classified as hybrid. Evidence suggests that these spectral classes represent spectral evolution. We investigate this scenario using a large spectroscopic dataset and introduce a quantitative coefficient, $\kappa$, to characterise the relative strength of Fe II and He/N emission. The coefficient is defined as the ratio of the flux of the Fe II ($\lambda5169$) line to the mean flux of five He and N emission lines, with $\kappa>1$ indicating Fe II-dominated spectra and $\kappa<1$ indicating He/N-dominated spectra. We apply this method to 26 novae using spectra from the Astronomical Ring for Amateur Spectroscopy (ARAS) Database and compare the evolution of $\kappa$ with optical light curves. Fifteen of the 24 classical novae and one of the two recurrent novae exhibit at least one transition between Fe II- and He/N-dominated phases, while temporal trends suggest this fraction could approach 90% with complete spectroscopic coverage. The $\kappa$ coefficient closely tracks the optical light curves and repeatedly crosses unity in novae exhibiting jitters, revealing non-monotonic spectral evolution linked to brightness fluctuations. These results support the interpretation of Fe II, He/N, and hybrid spectra as evolutionary stages rather than distinct nova types and establish $\kappa$ as a quantitative tool for tracing nova spectral evolution while reducing biases from incomplete spectroscopic coverage.
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Astrophysics of Galaxies

Dual Signatures of Bursty Star Formation in High-Redshift UV Luminosity Functions

Guochao Sun, Claude-André Faucher-Giguère, Steven R. Furlanetto et al. (+1 more)

The UV luminosity function (UVLF) encodes key information about galaxy formation. The slowly evolving bright-end UVLFs at $z\gtrsim10$ have made UV variability from bursty star formation a promising explanation, but the impact of such variability need not be restricted to the bright end. Motivated by ultra-deep measurements of the $z\simeq7$ UVLF, we investigate whether UV variability can provide a unified interpretation of the low-mass star formation efficiency (SFE) at $z\simeq7$ and the abundance of UV-bright galaxies at $z\gtrsim12$. Using abundance matching, we show that a steep faint-end UVLF at $z\simeq7$ admits a range of interpretations. For modest, mass-independent UV variability, the inferred median SFE starts flattening below $M_{\rm h} \sim10^{10.5} M_{\odot}$. If UV variability instead grows with decreasing halo mass—a possibility motivated by simulations and observations—the inferred median SFE is steeper and lower by a factor of about three at $\sim10^9 M_{\odot}$, consistent with stronger feedback suppression in low-mass halos. Calibrated to the common target $z\simeq7$ UVLF, these two scenarios diverge strongly when extrapolated to $12\lesssim z\lesssim17$ under redshift-independent UV variability and SFE prescriptions. Strongly mass-dependent $M_\mathrm{UV}$ scatter links the steep $z\simeq7$ faint-end slope and high $z\gtrsim12$ bright-end abundance as dual signatures of burstiness in similarly low-mass halos. Stronger variability makes bright galaxies contribute a larger fraction of the UV luminosity density, whereas weaker variability favors faint sources, despite their similar predicted reionization histories. At fixed $M_\mathrm{UV}$, UV variability broadens the halo mass distribution and lowers the clustering bias, which provides a useful diagnostic of burstiness for JWST and Roman.
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All authors Guochao Sun, Claude-André Faucher-Giguère, Steven R. Furlanetto, Adam Lidz

Instrumentation and Methods for Astrophysics

Probing Millisecond Optical Timescales with Continuous-Readout Mode Observations from ZTF

Shar Daniels, Federica Bianco, Igor Andreoni et al. (+6 more)

The subminute-timescale phase space is an underexplored regime of the optical sky. Sub-second optical observations are difficult to accomplish with traditional CCD exposure-readout cycles, and alternative technologies like EMCCDs and CMOS have historically limited surveys to targeted observation. Continuous-readout mode enables millisecond-timescale observations on traditional cameras by leaving the shutter open during readout, enabling high-cadence observations on all-sky surveys. We present the first results from continuous-readout mode data from the Zwicky Transient Facility. We developed a deep-learning-based data analysis pipeline and report results on 141 square degrees, or 1128 star-hours, of data, sampled at 300x/second. Our Convolutional Neural Network can retrieve optical transients of duration 9.7-29.2 milliseconds with a precision of 66% and recall of 78% for brightness changes of 10% and greater, and our subsequent light curve-based analysis has an efficiency of >94.6%. We retrieve a total of ~300,000 candidates on sources of magnitude G_{RP} < 12, of which 100 are above SNR=1.55 and were visually inspected. After accounting for noise and filtering contaminants both known and unique to this mode of observation, these 100 candidates were eliminated as being astrophysical in nature, leading to upper limits on the observed rate of ~10-ms transient events associated with point sources as well as specifically with white dwarfs and quasars. This first survey-scale characterization of the bright millisecond optical transient and variable sky establishes the rarity of short-timescale variability in the optical regime.
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All authors Shar Daniels, Federica Bianco, Igor Andreoni, Ashish Mahabal, Rich Dekany, Gregory Dobler, Matthew Graham, Roger Smith, Rujula Yete

Astrophysics of Galaxies

Star Formation and Nebular Attenuation from Pa$\alpha$, Br$\alpha$, and Br$\beta$ in Massive Dust-obscured Galaxies at Cosmic Noon using JWST

Virginia Vanicek, Jed McKinney, Alexandra Pope et al. (+14 more)

Near-infrared hydrogen recombination lines can provide robust star-formation rates if the effects of dust attenuation continue to diminish towards longer wavelengths. To quantify near-infrared attenuation and ultimately measure accurate star-formation rates (SFRs) at the height of cosmic star-formation, we present Pa$\alpha$, Br$\alpha$, and Br$\beta$ detections in $27$ luminous infrared galaxies at $z\sim 1-2$, including pure star-forming galaxies as well as dust-obscure Active Galactic Nuclei (AGN). Using combined spectra from the JWST MIRI (Mid-Infrared Instrument) LRS (Low Resolution Spectrometer) and the Spitzer Space Telescope IRS we quantify the star formation rates of our sample using a sub-sample of 13 galaxies detected in Pa$\alpha$ emission ($1.87\, \mu$m), 14 galaxies detected in Br$\alpha$ ($4.05\, \mu$m), and 12 galaxies detected in Br$\beta$ ($2.63\, \mu$m). By combining multiple near-infrared recombination lines in individual galaxies we calculate nebular attenuation, finding $A_\lambda\sim3$ mag at $\sim2\,\mu$m and $A_\lambda\sim1$ mag at $\sim4\,\mu$m. Nebular lines trace the SFR on $\sim 10$ Myr timescales, which we compare to the total infrared luminosity ($L_{\rm IR}$) which probes the star formation over the last $\sim 100$ Myr. SFRs measured from $L_{\rm IR}$ using common conversions are systematically higher than the SFRs derived from attenuation-corrected nebular line measurements by a factor of $\sim2.5$. This could be indicative of a declining or static star formation history with a past burst or systematic effects on $\rm SFR_{{\rm IR}}$ such as dust heating from evolved stellar populations, and/or an active galactic nucleus.
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All authors Virginia Vanicek, Jed McKinney, Alexandra Pope, Anna Sajina, Stacey Alberts, Meredith Stone, Lee Armus, Sinclaire M. Manning, Olivia Cooper, Tanio DÍaz-Santos, Miriam Eleazer, Caitlin Casey, Thomas S.-Y. Lai, Steven Finkelstein, Leonid Sajkov, Allison Kirkpatrick, Anthony Taylor

Astrophysics of Galaxies

Linking X-ray emission to galaxy populations in GAMA groups

Selene Levis, Hernán Muriel, Valeria Coenda et al. (+3 more)

We study how the presence of a detectable hot intragroup medium affects galaxy colour and star-formation properties, and how these trends depend on dynamical stage within the group. We analysed galaxies in GAMA groups with and without X-ray detection (XG and NXG) at 0.1 <= z <= 0.2, using samples with similar halo-mass distributions, compared with a field control sample. Galaxies were classified as red, green, or blue by UV-optical colour, and group galaxies further classified into dynamical classes based on projected phase-space position and host halo mass. We examined galaxy populations as a function of orbital class, star-formation activity, nuclear activity, and cluster-centric distance. The galaxy population is systematically more evolved in XG than NXG, with lower blue and star-forming fractions and higher red and passive fractions. The green fraction is stable across environments and orbital classes, though high-mass recent arrivals show a mild excess of green systems while retaining relatively high star-forming and low passive fractions, suggesting an intermediate quenching stage. The active galactic nucleus fraction shows no environmental dependence, while the post-starburst fraction increases strongly in XG, reaching nearly 20 percent, consistent with enhanced rapid quenching. Galaxy properties show stronger radial segregation in XG than NXG, with colour fractions differing from field values even at R/R200 ~ 3, consistent with preprocessing. Despite similar halo-mass distributions, the systematic differences between XG and NXG show that halo mass alone does not determine galaxy properties. A detectable hot intragroup medium is associated with enhanced environmental processing, stronger quenching, and more frequent rapid transitions, highlighting the role of the intragroup medium's thermodynamical state, beyond halo mass, in shaping galaxy evolution at group scales.
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All authors Selene Levis, Hernán Muriel, Valeria Coenda, Andrea Biviano, Héctor J. Martínez, Martín de los Rios

High Energy Astrophysical Phenomena

GRB 220706A: a gamma-ray burst with a month-long engine and a luminous supernova

Benjamin P. Gompertz, Nusrin Habeeb, Dheeraj R. Pasham et al. (+30 more)

While the progenitors of many long gamma-ray bursts (GRBs) are well established as the core collapse of very massive, envelope-stripped, rapidly-rotating stars, it has been suggested that bursts at the extremely long end of the duration distribution may be a separate population of `ultra-long' GRBs. With durations of thousands of seconds or more, these bursts are difficult to reconcile with the engine timescales expected from the compact Wolf-Rayet stars that are typically assumed to produce more `standard' long GRBs. Here, we present observations of GRB~220706A, where X-ray follow-up reveals flaring episodes that last until $\approx 51$ days after trigger. At the measured redshift of $z = 0.8577$, this corresponds to 27 days in the GRB rest frame, and represents the latest central engine activity ever observed in a GRB by a margin of $\approx 21$ rest-frame days. We also identify a likely supernova (SN) which, when accounting for the inferred optical extinction of $0.9 \leq A_V \leq 3.6$ mag (constrained by indirect arguments), has a peak absolute magnitude of $M_r \leq -20.25$, resembling the energetic SN\,2011kl found accompanying ultra-long GRB\,111209A, and consistent with super-luminous SNe. We discuss the implications GRB~220706A has for ultra-long GRB progenitor models and possible powering mechanisms for the extremely late central engine activity.
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All authors Benjamin P. Gompertz, Nusrin Habeeb, Dheeraj R. Pasham, Antonio de Ugarte Postigo, Daniele B. Malesani, Phil A. Evans, Kim L. Page, Ben Rayson, J. Feliciano Agui Fernandez, Michael Bremer, Andrew J. Levan, Genevieve Schroeder, Nial R. Tanvir, Christina C. Thone, Eric Burns, Valerio D'Elia, Massimiliano De Pasquale, Dimple, Dieter Hartmann, Pall Jakobsson, Sylvio Klose, Antonio Martin-Carrillo, Matt Nicholl, Ana M. Nicuesa Guelbenzu, David O'Neill, Giovanna Pugliese, Arne Rau, Andrea Rossi, Jesper Sollerman, Rhaana Starling, Darach Watson, Isabelle Worssam, Makenzie E. Wortley

Astrophysics of Galaxies

Multi-tracer constraints on quasar outflows. Acceleration from BLR to galactic scales

M. Brazzini, M. Bischetti, S. Hagen et al. (+14 more)

Black hole-driven outflows are a fundamental component of the Active Galactic Nuclei (AGN) paradigm, and may play a major role in regulating the evolution of both supermassive black holes and their host galaxies. Yet, their physical properties remain challenging to constrain, due to their multi-phase and multi-scale nature which demands a combined approach of different complementary observational tracers. In this work, we investigate AGN-driven ionized outflows from nuclear to galaxy scale within individual quasars, with the aim of establishing whether and how these phenomena are physically connected. We assemble a luminosity-matched sample of 148 quasars with bolometric luminosities higher than 10^47 erg/s, spanning the redshift range z~2-6.5. We perform a homogeneous analysis of CIV emission and broad absorption line (BAL) profiles to derive outflow properties on different spatial scales. We find statistically significant correlations between emission- and absorption-based outflow diagnostics, including the minimum and maximum BAL velocities, vmin,BAL and vmax,BAL, and the v98 of CIV emission lines. These correlations are tighter in high redshift quasars. We also find evidence for an evolution of outflow properties across cosmic time, with high-redshift quasars exhibiting systematically larger CIV line shifts and broader profiles, and faster BAL outflows. According to our outflow toy model, these correlations suggest a scenario in which a clumpy BAL wind is composed of expelled and accelerated broad-line region gas clouds.
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All authors M. Brazzini, M. Bischetti, S. Hagen, V. D'Odorico, N. Arav, G. Becker, G. Cupani, F. Fiore, M. Ghosh, E. Piconcelli, F. Salvestrini, M. Sharma, A. Travascio, A. Tortosa, G. Vietri, L. Zappacosta, C. Feruglio

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

Resonant Gravitational Production of Chiral Dark Photons

Leah Jenks, Marc Kamionkowski and Edward W. Kolb

Vector fields with a chiral, parity-odd coupling to a pseudoscalar field are known to undergo resonant amplification. In this work, we study this phenomenon in the context of cosmological gravitational particle production during early-universe inflation. We consider a massive vector (dark photon) field with a parity-odd coupling to the inflaton. There are two regimes of production, delineated by the relative size of the coupling and the dark photon mass, arising from a tachyonic instability, and a parametric resonance, respectively. As a result of the coupling, the transverse modes, subdominant in both the minimally and nonminimally coupled theories, can dominate the total late-time abundance. The viable parameter space for dark-photon dark matter is thus widened. Furthermore, in the tachyonic case, the production is dominated by a single helicity mode, leading to a population of chiral dark photons that can lead to potential parity-violating observational signatures. We further explore the dependence of the production on the reheating history, and find that information about reheating is encoded in the number density spectrum.
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High Energy Astrophysical Phenomena

Geometrically Thin Sub-Eddington AGN Accretion Disks show a suppressed Lyman Edge

Ish Kaul, Yan-Fei Jiang, Omer Blaes et al. (+1 more)

The observed ultraviolet continua of active galactic nuclei (AGN) generally lack a strong intrinsic HI Lyman edge predicted by classical optically thick accretion disk atmosphere models. We revisit this long-standing problem using our previous sub-Eddington ($L/L_{\rm Edd}\sim 0.03$) geometrically thin 3D accretion disk simulation evolved with gray angle-dependent radiation magnetohydrodynamics (MHD) around a $10^8M_{\odot}$ black hole. This disk is magnetic pressure dominated, and has surface densities more than two orders of magnitude below the corresponding radiation-pressure-supported $\alpha$-disk prediction. By restarting the simulation with multiple frequency groups, we compute the emergent continuum directly from the frequency-dependent radiation fluxes and find no sharp HI Lyman edge at 13.6 eV. This suppressed Lyman edge is mainly caused by the low densities in a magnetic pressure supported disk where the Lyman opacity jump is far weaker than in standard disk models. These results indicate that magnetic pressure support may provide a possible solution to reconciling optically thick AGN disks with the smooth observed continuum emission around the Lyman edge. However, in this simulation, a substantial fraction of the emission near 13.6 eV is expected to originate at smaller radii closer to the central black hole, which is outside our simulation domain. More detailed predictions of the spectrum will require an extension to the inner disk, non-LTE radiation transfer, higher frequency resolution and a survey across a broader range of accretion rates.
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All authors Ish Kaul, Yan-Fei Jiang, Omer Blaes, Lizhong Zhang

Astrophysics of Galaxies

The AGN Channel in 3D: Scattering Belts and the Importance of Eccentricity in the Black Hole Population

Connar Rowan and Martin E. Pessah

Active galactic nuclei (AGN) are a promising origin for observed gravitational wave mergers. Current population synthesis models are limited to 1D N-body or Monte Carlo methods which rely on statistical approaches to resolving dynamical scatterings. We present three-dimensional hybrid $N$-body simulations of a population of black holes (BHs) surrounding an AGN using a new code in development, AGNBI, where close interactions are directly simulated for both single and binary objects. Our results show binary formations occur throughout the AGN disk, particularly where the migration time is long. While BHs efficiently migrate and pair up in migration traps, they are frequently disrupted by ionisation or exchanges from binary-single and binary-binary interactions. We report a broadened radial distribution of formations and mergers about the trap radius when accounting for binary-single and binary-binary interactions, which we describe as a "scattering belt”. We assess the influence of the pre-existing BH population. When we model a non-zero eccentricity distribution in the BH population, the binary formations and mergers are suppressed by an order of magnitude compared to a non-eccentric population as fewer BHs embed in the AGN disk. We report an approximate merger rate of $\mathcal{R}_\mathrm{GW}\approx2\text{--}12\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$ with maximum BH masses of $10^2\text{--}10^3\,M_\odot$ through hierarchical mergers, where lower initial velocity dispersions produce larger BHs. The mass and mass ratio distributions are comparatively flat, suggesting AGN may be more relevant for high-mass or unequal-mass gravitational wave sources.
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Solar and Stellar Astrophysics

Multi-Epoch Stability in the Rotational Modulation of the Planetary-Mass Companion Ross 458C

Elena Manjavacas, Jared Bull, Paulo Miles-Paez et al. (+7 more)

Spectroscopic variability is detected in brown dwarfs across all spectral types, suggesting atmospheric patchiness in brown dwarf atmospheres. We present JWST/NIRSpec time series observations of the T8.0 planetary-mass companion Ross 458C. We compared our derived spectral variability and light curve to those obtained using HST/WFC3 observations more than 7.5 yr before and published by Manjavacas et al. (2019). We found that the light curve of Ross 458C is remarkably similar in the two epochs in terms of shape and variability amplitude potentially created by stable weather patterns. We measured a rotational period of 11.57+\-0.09 hr, demonstrating that the previously reported HST/WFC3 period of 6.75+\-1.58 hr is most likely a second-order harmonic produced by an unresolved double-peaked rotational modulation, likely due to the higher uncertainties of the HST/WFC3 light curve and the short time baseline of those observations. We measured the variability amplitude in the white light curve created using only the wavelength range covered by HST/WFC3 (1.10-1.63 micron), obtaining a value of 1.47+\-0.18%, which is consistent with that measured in the HST/WFC3 light curve.
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All authors Elena Manjavacas, Jared Bull, Paulo Miles-Paez, Natalia Oliveros-Gomez, Theodora Karalidi, Ben W. P. Lew, Zhoujian Zhang, Yifan Zhou, Daniel Apai, Xianyu Tan

Astrophysics of Galaxies

Discovery, Characterization, and Potential Origins of a Stream in the Stellar Halo of Nearby LMC-Mass Galaxy NGC 55

Benjamin N. Velguth, Burçin Mutlu-Pakdil, Erik Tollerud et al. (+32 more)

We present a previously undetected stellar stream in the halo of the LMC-mass dwarf galaxy NGC 55 (2 Mpc), as part of an ongoing effort to characterize the stellar halos of LMC/SMC-mass dwarfs in the DEEP component of the DECam Local Volume Exploration (DELVE) survey. This structure is aligned with an outflow traced by H$\alpha$ emission, a spur and cloud of neutral hydrogen, and the ultra-diffuse and possibly disrupting satellite galaxy NGC 55-dw1. We investigate possible ex-situ progenitor scenarios for this stream through the local luminosity-metallicity relation and a set of toy dynamical models that include gaseous, stellar, and dark matter components. If the stream is a product of a previous merger, the progenitor galaxy had an absolute magnitude $M_V \leq -7.2$ and a stellar mass $M_* \geq 10^5 M_{\odot}$ based on extrapolations of the detected stellar populations. If it is disrupted material from the ultra-diffuse satellite, their shared progenitor had an absolute magnitude $M_V \leq -8.3$ and a stellar mass $M_* \geq 10^{5.2} M_{\odot}$. We compare our stream and progenitor scenarios to those for NGC 300, a galaxy with a stellar mass similar to that of NGC~55 and known to host multiple structures in its halo. Our results demonstrate that even relatively isolated LMC-mass galaxies can have complex accretion histories, providing new tests of hierarchical galaxy formation at low masses.
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All authors Benjamin N. Velguth, Burçin Mutlu-Pakdil, Erik Tollerud, Sarah Pearson, Kristine Spekkens, Amandine Doliva-Dolinsky, Michael G. Jones, Denija Crnojević, Jeffrey L. Carlin, David J. Sand, Paul Bennet, Guy Stringfellow, William Cerny, Alex Drlica-Wagner, Joanna D. Sakowska, Jaclyn Jensen, Laura C. Hunter, Eric F. Bell, David Martínez-Delgado, Anirudh Chiti, Adam Smercina, Nitya Kallivayalil, Deepthi S. Prabhu, Alexander H. Riley, Yumi Choi, Noelia E. D. Noël, Sasha N. Campana, Guinevere Herron, Alistair R. Walker, Andrew B. Pace, Clara E. Martínez-Vázquez, Clecio R. Bom, Julio A. Carballo-Bello, Pol Massana, Gustavo E. Medina

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

Resurrecting Electroweak Dark Matter via Type-II Seesaw in light of recent LZ Event

Partha Kumar Paul, Sujit Kumar Sahoo, Narendra Sahu et al. (+1 more)

The recent observation of the high-energy nuclear recoil event LZ230616 with a recoil energy around 248 keV provides an interesting possibility to probe inelastic doublet dark matter (iDM). However, the electroweak doublet DM scenarios face strong constraints from solar DM capture for DM masses around the TeV scale which give rise to correct thermal relic density. In this work, we revive the inelastic doublet DM (iDM) scenario via type-II seesaw. In particular, we consider an inert lepton doublet (ILD) DM. While the minimal ILD scenario gives the correct relic abundance around the TeV scale, it is strongly constrained by direct detection and solar DM capture. In the type-II seesaw, the presence of the scalar triplet generates the required mass splitting and provides additional annihilation channels, allowing the correct relic abundance for much larger DM masses. The larger DM mass also helps evade the solar capture and indirect detection constraints. Additionally, the scalar triplet gives sub-eV neutrino masses required by the oscillation data.
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All authors Partha Kumar Paul, Sujit Kumar Sahoo, Narendra Sahu, Shashwat Sharma

Cosmology and Nongalactic Astrophysics

Non-linear halo bias for accurate modelling of cosmic infrared background anisotropies

Baptiste Jego, Matthieu Béthermin, Katarina Kraljic et al. (+3 more)

Halo models provide the standard framework for interpreting cosmic infrared background (CIB) anisotropies and inferring the connection between dusty star-forming galaxies and their host dark matter halos. Recent studies have shown that inaccuracies in the modelling of halo clustering may bias the inferred parameters governing star formation in dark matter halos. In this work, we investigate whether a more detailed description of halo clustering can alleviate these shortcomings. We incorporate a scale-dependent, non-linear correction to the halo bias within a halo-model framework based on a simple SFR-halo mass parametrisation. We consider both a full mass-dependent implementation and a computationally efficient approximation. We also investigate the impact of updated (sub)halo mass functions. We validate the revised framework using mock observations derived from a dedicated simplified version of the SIDES-Uchuu simulation, combining the SIDES empirical galaxy model with the Uchuu N-body simulation, specifically designed to match the SFR prescriptions adopted in our halo-model. The corrections modify the predicted CIB clustering by up to 30% on intermediate scales, while the effective implementation reproduces the full treatment at the sub-percent level. The updated model removes the scale-dependent discrepancies previously identified and accurately reproduces the measured power spectra over the full multipole range. In MCMC analyses, the input SFR parameters are recovered with substantially reduced biases, with all input parameters recovered within their $1\sigma$ confidence intervals. Our results demonstrate that accurately modelling non-linear halo clustering is essential not only to reproduce CIB anisotropies, but also to reliably recover the underlying galaxy-halo connection. The framework presented here provides a validated foundation for future analyses of observational data.
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All authors Baptiste Jego, Matthieu Béthermin, Katarina Kraljic, Athanasia Gkogkou, Guilaine Lagache, Abhishek S. Maniyar

Earth and Planetary Astrophysics

Asteroids Impacting the Solar System Planets and the Moon. III. Real Impacts from Known Objects and LSST Discovery Predictions

Qifeng Cheng and Daniel Scolnic

Impact rates predicted using pre-impact source-population models and those inferred from observations disagree by a factor of a few to $\sim200$ across the Solar System planets and the Moon. An exciting opportunity for an additional observational constraint is the discovery of asteroids before impact and their tracking until impact. We evaluate this prospect based on both known objects and forecasts of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). First, we identify impacts from known objects, confirming multiple past cases and predicting two coming impacts: 2015 FK488, a $\sim1.8$ km Centaur whose nominal orbit predicts an impact with Jupiter in $\sim200$ yr, and 2022 KG1, a $<10$ m NEO recently removed from the impact-risk lists but whose nominal trajectory leads to an Earth impact in $\sim260$ yr. Both orbits are poorly constrained. Second, assuming the model-based impact rate, we predict that LSST will discover 7 of the 59 synthetic impactors quantified in our previous analysis. All of the discovered impactors will impact Jupiter, and they have a size range of $\sim200-2000$ m and expected discovery-to-collision lead times of $1.94-257.4$ yr. Two of them are discovered inside Jupiter's Hill sphere, offering rare opportunities to observe the transition from a temporary bound orbit to impact before it happens. If instead we assume the observation-inferred impact rates, LSST will at most discover $\sim20$ future Earth impactors ($>10$ m) and $\sim300$ future Jupiter impactors ($>10$ m), with a wider range on both ends for discovery-to-collision lead times. These results demonstrate that LSST can identify a subset of planetary impactors years to centuries before collision, providing a new observational pathway for testing source-population models and the impact-rate mismatch.
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Earth and Planetary Astrophysics

Asteroids Impacting the Solar System Planets and the Moon. II: Comparison with Observational Impact Records

Qifeng Cheng and Daniel Scolnic

Planetary impact rates are difficult to infer from observations alone because impacts are rare, observational records are target-dependent, and converting observed flashes, bolides, and craters to an intrinsic impact rate depends on uncertain selection effects and conversion parameters. Building on the simulations in Paper I, we examine whether observational systematics can explain the order-of-magnitude mismatch between observed and modeled impact rates on Earth, and whether comparable discrepancies extend to other Solar System bodies. We convert 12 observed impact records for Earth, the Moon, Mars, and Jupiter to a common pre-atmospheric impact rate for $D>10$ m, propagate uncertainties through the conversion chain, and compare the resulting rates with the intrinsic rates derived in Paper I. We find discrepancies for Earth (observation-to-model median ratio $2.2-21.0$), the Moon ($3.4-132.1$), Mars ($14.2-118.6$), and Jupiter ($2.6-47.7$), with the dominant source of the discrepancy differing by body. The simulated Jupiter-family comet (JFC) contribution substantially reduces the Earth discrepancy, suggesting that an additional dynamical source may help explain the gap. The lunar records disagree with each other by two orders of magnitude, with the discrepancy dominated by size-extrapolation uncertainties. The Mars mismatch is dominated by crater-to-impactor conversion. The Jupiter comparison depends mainly on uncertainties in the inferred number of bound impactors and in the observational completeness thresholds. Further investigation of this mismatch requires incorporating cometary modeling and tighter constraints on size-extrapolation scaling and improved observational completeness.
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Earth and Planetary Astrophysics

Asteroids Impacting the Solar System Planets and the Moon. I. Collision Rates from N-body Simulations

Qifeng Cheng and Daniel Scolnic

Previous studies have shown a mismatch between the simulated rate of asteroids impacting the Earth and the observed rate, posing an important problem for planetary defense. Extending this analysis to other planets offers a new opportunity to examine minor body populations and impactor models. We present a unified simulation framework that estimates intrinsic $D\gtrsim10$~m impactor rates on the eight planets and the Moon. We construct size-calibrated source populations of Near Earth Objects (NEOs), Main Belt Asteroids (MBAs), Jupiter-family comets (JFCs), Centaurs, and scattering trans-Neptunian objects (TNOs), and propagate them with a 300-year $N$-body simulation. To avoid relying on black-box-like collision flags, we identify close encounters and estimate impact rates in two complementary ways: a direct count of realized impactors from object-level minimum-distance calculation and a collision expectation based on population-level impact parameter statistics. We predict over 300 years there will be $6.0^{+3.8}_{-2.7}$ impactors on Venus (all NEOs), $10.0^{+11.3}_{-4.9}$ on Earth (NEOs and JFCs), $\sim$$2981^{+481}_{-469}$ on Jupiter (mainly MBAs and JFCs), $1228^{+2759}_{-1017}$ on Saturn (mainly Centaurs), and none on the remaining planets with the $1\sigma$ upper limits spanning $<1.8$ (inner planets) to $<1\times10^{8}$ (outer planets; weak constraint). Jupiter uniquely receives both fast unbound impactors ($>50\, \mathrm{km\,s^{-1}}$) and slower bound ones reaching down to $\sim$$20\,\mathrm{km\,s^{-1}}$. In a companion paper, we compare our predictions with observations and test whether the gap extends across the Solar System and whether current telescopes can observe these collisions.
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Solar and Stellar Astrophysics

Searching for Massive Remnant Planetary System Hosts with White Dwarf Gaia XP Spectra

Lou Baya Ould Rouis, J.J. Hermes, Pierre Bergeron et al. (+5 more)

Remnant planetary systems around massive white dwarfs ($M_{\rm WD} > 0.8\,{\rm M}_\odot$) are intrinsically rare and remain poorly characterized. As the evolutionary endpoints of intermediate-mass B- and A-type stars, these white dwarfs provide valuable constraints on the formation and survival of planetary systems around higher-mass progenitors. In the absence of large, dedicated spectroscopic surveys, extremely-low-resolution Gaia XP spectra provide a powerful means of identifying candidate metal-polluted white dwarfs. We obtained follow-up observations with low-resolution optical spectroscopy (R=500-4000) to search primarily for Ca II H & K absorption in massive, metal-polluted white dwarf candidates selected from Gaia XP spectra to increase the sample of massive remnant planetary system hosts among objects with effective temperatures below $\sim15{,}000$ K. We find that Gaia XP spectra recover metal-polluted white dwarfs efficiently, confirming 82$\pm$5% recovery of photospheric metals (59 of 72 targets) in high-confidence candidates of our sample (with classifier probability $P_{\rm DZ} > 0.65$). However, Gaia photometric masses derived from $G$, $G_{BP}$, and $G_{RP}$ broad-band photometry are not sufficient to identify the most massive systems, as reliable mass determinations require detailed metal-enriched atmospheric fits. We present a selection of cool white dwarfs confirmed to be both massive and metal polluted, demonstrating that Gaia XP spectra can substantially expand the sample of white dwarf exoplanet hosts. Our search led to the discovery of a new transiting debris system, SDSS J1624+5404, the 21st published system to date and eighth to show periodic transits.
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All authors Lou Baya Ould Rouis, J.J. Hermes, Pierre Bergeron, Simon Blouin, Stefan Arseneau, Tim Cunningham, Joseph A. Guidry, Ciarra Coston

Instrumentation and Methods for Astrophysics

The optical high-resolution spectral archive of the HERMES spectrograph mounted on the 1.2m Mercator telescope

Hans Van Winckel, Saskia Prins, Gert Raskin et al. (+13 more)

Context. The HERMES spectrograph is a high-resolution, fibre-fed optical spectrograph of the 1.2m Mercator telescope operated from the Roque de los Muchachos observatory in Spain. HERMES started its scientific operations in June 2009 and has been the workhorse instrument since then. Regular instrument updates have been crucial. They have helped to ensure the continued provision of high-quality spectra. This will continue both now and in the future. Aims. With this contribution we review over 16 years of HERMES operations and we launch and introduce the archive to the interna- tional community at large. We describe the overall performances of the HERMES spectrograph and list the most important instrument upgrades since the start of the operations. We release about 150 000 high-resolution spectra to the community and describe global properties of the datarelease. We use a standard propriety period of 1 year with some exceptions. Methods. We used the German Astrophysical Virtual Observatory (GAVO) DaCHS platform to present the archive in a Virtual Ob- servatory (VO) compatible form with both an access via a dedicated webinterface, and via VO-compliant tools like PyVO, TOPCAT, Aladin etc. We illustrate the use in several worked-out examples to search and download the fully wavelength-calibrated, cosmic- cleaned and barycentric corrected 1D spectra. Results. With this contribution we provide the needed information of the data product and offer a reference paper for the users of the HERMES archive.
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All authors Hans Van Winckel, Saskia Prins, Gert Raskin, Jesus Perez Padilla, Wim Pessemier, Wim De Meester, Maarten Dirickx, Yves Frémat, Alain Jorissen, Holger Lehmann, Kwinten Missiaen, Maddalena Reggiani, Hugues Sana, Andrew Tkachenko, Bart Vandenbussche, Christoffel Waelkens

Earth and Planetary Astrophysics

Rotational Mapping and Regional Atmospheric Retrievals of Variable Brown Dwarfs: Application to Luhman 16B and SIMP 0136

Ruizhe Wang, Heather A. Knuton, Julie Inglis et al. (+1 more)

We present a Bayesian framework for converting time-resolved spectroscopy into rotation-inferred regional spectra and atmospheric constraints for variable brown dwarfs. We derive an analytic mapping framework with evidence-optimized regularization and uncertainty propagation by marginalizing over physical parameters and model complexities. We provide methods for selecting characteristic spectral end-members from the inferred surface maps, and highlight the advantage of analyzing these rotation-inferred regional spectra over the disk-integrated time-resolved observations, while explicitly accounting for the geometric degeneracies inherent to rotational mapping. We apply this framework to published JWST/NIRSpec rotational monitoring of Luhman 16B and SIMP 0136. For both objects, we identify dominant spectral regions and retrieve regional variations in cloud structure, thermal gradients, and chemistry that are consistent with cloud radiative feedback. In addition, we demonstrate the importance of limb darkening in deriving surface maps. These results establish a statistically controlled method for linking rotational spectral variability to atmospheric heterogeneity and enable future rotational mapping and regional atmospheric studies of giant planet atmospheres.
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All authors Ruizhe Wang, Heather A. Knuton, Julie Inglis, Xianyu Tan

Earth and Planetary Astrophysics

Multiband Color Monitoring of 3I/ATLAS through Ground-Based Relay Observations

Ariel Graykowski, Bryce Bolin, Laura-May Abron et al. (+140 more)

We present multiband, long-baseline photometric observations of interstellar comet 3I throughout its 2025–2026 apparition using coordinated ground-based global relay observations. Our dataset combines measurements from professional observatories and citizen-operated Unistellar eVscopes distributed worldwide, providing dense temporal coverage from 2025 July 2 through 2026 April 1 and spanning the comet's pre- and post-perihelion trajectory. Broadband photometry was obtained in bandpasses equivalent to the Johnson–Cousins $B$ (436 nm), $V$ (545 nm), and $R$ (641 nm) filters and the Sloan $g$ (477 nm), $r$ (623 nm), and $i$ (763 nm) filters. The photometry was measured using projected aperture radii of approximately 10{,}000~km to provide a consistent probe of the inner coma across the heterogeneous dataset. We measure representative mean colors of $B-V=0.86\pm0.06$, $V-R=0.50\pm0.03$, $B-R=1.36\pm0.08$, and $g-r=0.58\pm0.08$, demonstrating a persistently red optical coma. Constant-color models provide an adequate description of the data, with little evidence for long-term color evolution with time or heliocentric distance despite substantial changes in the coma's brightness, gas production, and volatile composition. This suggests that the ensemble-averaged optical scattering properties of the coma remained relatively stable over the period sampled by our observations, even as other properties of the coma evolved. These observations provide the first densely sampled, apparition-long characterization of the broadband optical colors of an interstellar comet and establish a benchmark for comparison with future interstellar objects.
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All authors Ariel Graykowski, Bryce Bolin, Laura-May Abron, Franck Marchis, Martin Mašek, Filipp D. Romanov, Ahmed M. Abdelaziz, Dimitrios Athanasopoulos, Matthew Belyakov, Luca Buzzi, Michael W. Coughlin, Ergün Ege, Nicolas Erasmus, Thomas M. Esposito, Christoffer Fremling, Josep M. L. Garcia, Marek Husárik, Oleksandra Ivanova, Tarek M. Kamel, Sergey Karpov, Myung-Jin Kim, Tomasz Kwiatkowski, H.-J. Lee, Sofiia Mykhailova, Alessandro Nastasi, Dagmara Oszkiewicz, John W. Pickering, Alexey Sergeyev, Roman Telesnikov, Josep M. Trigo-Rodríguez, Al Alicea, Jin Beniyama, Otabek A. Burkhonov, Kamoliddin E. Ergashev, Y.H.M. Hendy, Jeong-Han Kim, Cheng-Han Hsieh, M. Emir Kenger, Thomas Lehmann, Igor Luk'yanyk, Ali Takey, Dušan Tomko, Murat Tekkesinoglu, Shane Winter, Joel Alonzo, Michael Beddo, Axel Bienefeld, Mario Billiani, John K. Bradley, Olivier Clerget, Sabine Cremer, Nicolas Delaunoy, José Donas, John Dunn, Jiří Dvořáček, Michael Edwards, Taj Entabi, Raffaele Esposito, Karen Fischer, Robert Foster, Edward Friday, Keiichi Fukui, Francois Gagnon, Matthieu Garisson, George Ghreichi, Patrice Girard, Tateki Goto, Michael Grant, Chris Greenfield, Bruno Guillet, Josef Hanus, John Harrison, David Havell, Kevin Heider, Kirt Hufstedler, Kachi Iwai, Maxime Johnson, Christian Joisten, Scott Kardel, Suzanne Kavic, Vamshi Kesireddy, Rachel Knight, David Koster, Jericho Kuehl, Ryuichi Kukita, Jan Kunc, Petri Kuossari, Alain Lambert, Scott Lancelle, Jean-Marie Laugier, Stephen Lawrence, Pedro Lemos, Jeffrey Linn, Joseph Llanes, Steeve Loisel, Gaël Lombart, Margaret A. Loose, Yohann Lorand, Chris Mahar, Scott Manley, Vincent Marcouiller, Sevastos Mastrogiorgis, Nicola Meneghelli, Mike Mitchell, Iaroslav Mokroguz, Jacques Molne, Fabrice Mortecrette, Ioannis Mytakos, Anouchka Nardi, Wataru Ono, James Owen, Larry Parchman, Bruce Parker, Michael Primm, Darren Rivett, Facundo Robles, Van Ruckman, Matthew Ryno, Nikolaj Schraufl, Jean-Pierre Schulz, Christoph Seidler, Lauren A. Sgro, Masao Shimizu, Francois Simard, Georges Simard, Bran Solo, Grant Sorenson, Marcelo Souza, David Swalander, Akimitsu Takahashi, Lydia Tamez, Petri Tikkanen, Bryan Tobias, Ian Transom, William Turnipseed, Charles Urban, Claudio Vantaggiato, Aad Verveen, Andrew Wendelborn, Stefan Will, Mark Wilson, Neil Yoblonsky, Wai-Chun Yue

Earth and Planetary Astrophysics

Comparative analysis of Neural Networks approaches for Initial Orbit Determination of Near-Earth Objects

Francesco Geroni, Roberto Paoli, Riccardo Massidda et al. (+1 more)

Initial Orbit Determination (IOD) from Very Short Arcs (VSAs) remains one of the most challenging open problems in asteroid surveillance and celestial mechanics. Classical methods require angular observations spanning a sufficient fraction of the orbit, and become ill-conditioned or fail outright when only a single observing night is available, as is the case for most newly discovered Near-Earth Objects (NEOs). We present a comparative analysis of two Neural Network (NN) models that attack the ranging problem directly: both ingest a triplet of time-tagged angular measurements $(t_i,\alpha_i,\delta_i)$, $i=1,2,3$, from a single VSA and predict the geocentric range and range-rate $(\rho,\dot\rho)$, thus completing the orbital state vector. The first is a Multi-Layer Perceptron trained on a purely data-driven objective; the second augments it with a physics-informed loss. Both are trained, under an object-disjoint partition, on a sample of the $568\,127$ VSAs of $39\,031$ real NEOs available in the NEODyS-2 catalogue. Each model returns an estimate on every arc by construction, so we assess instead whether that estimate is dynamically admissible: on a held-out test set of $56\,773$ arcs the physics-informed model places $85.1\%$ of its predictions inside the admissible region, against $76.5\%$ for the data-driven baseline, whereas Gauss's and Laplace's methods return a solution on only $45.0\%$ and $47.3\%$ of the same arcs and collapse onto the degenerate root in about nine of those cases out of ten. A stratified analysis over proper motion and true range shows that the physics-informed objective is not uniformly superior to the baseline: it trades a longer error tail for admissibility and for a marked advantage on the fast, nearby arcs that are operationally the most relevant.
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All authors Francesco Geroni, Roberto Paoli, Riccardo Massidda, Giacomo Tommei

Astrophysics of Galaxies

Stochastic black hole growth tracks stellar mass in ultramassive galaxies

Michele Cappellari, Dieu D. Nguyen and Susan A. Kassin

Over the past three decades, it has been established that galaxy spheroids contain supermassive black holes (BHs) whose masses correlate tightly with the properties of their host galaxies. The most predictive of these correlations is between BH mass and stellar velocity dispersion (the $M_{\rm BH}-\sigma$ relation), alongside a relation with bulge luminosity or stellar mass (the $M_{\rm BH}-M_\star$ relation). Theoretical models of galaxy evolution predict that for the most massive galaxies, whose late-time growth proceeds mainly via gas-poor `dry' mergers, $M_\star$ should become a better predictor of BH mass than $\sigma$. However, genuine deviations from the $M_{\rm BH}-\sigma$ relation have remained difficult to observe due to the extreme rarity and low central surface brightness of such galaxies. Here we report James Webb Space Telescope (JWST) measurements of central BHs in a sample of eight ultramassive galaxies. We find the largest deviations from the $M_{\rm BH}-\sigma$ relation ever reported, with most BH masses exceeding $10^{10}$ solar masses. In this extreme mass regime, the galaxies tightly follow the $M_{\rm BH}-M_\star$ relation with minimal scatter, successfully confirming theoretical predictions. Furthermore, we observe significant stochasticity: For one ultramassive galaxy, the central dispersion drops rather than peaks, revealing no evidence for a central mass; while we can formally only place an upper limit, the data are entirely consistent with no BH at all. Crucially, this physical dichotomy is already evident directly in the raw kinematic maps prior to any fitting, and is robustly confirmed by our dynamical modelling. This unexpected diversity suggests that extreme multi-body dynamical processes, such as gravitational recoil or three-body ejections, significantly disrupt BH growth in the Universe's most massive galaxies.
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Astrophysics of Galaxies

The JWST Ultramassive Galaxy Sample – II. Supermassive Black Hole Masses for 8 Extreme Early-Type Galaxies via Jeans Anisotropic Modelling of High-Resolution Integral-Field NIRSpec Stellar Kinematics

Michele Cappellari, Dieu D. Nguyen and Susan A. Kassin

We present central supermassive black hole (BH) mass measurements for the JWST Ultramassive Galaxy Sample, comprising 8 galaxies selected from a complete sample of the most massive early-type galaxies in the nearby Universe ($M_\star \gtrsim 2\times10^{12} M_\odot$). Building on the MGE photometric profiles and JWST/NIRSpec stellar kinematics from Paper I, we use the Jeans Anisotropic Modelling (JAM) framework to reconstruct the nuclear dynamics. Given the unique structural properties of these dry-merger-dominated systems, our Bayesian MCMC analysis explicitly tests both oblate and prolate intrinsic geometries. By marginalizing over classical dynamical degeneracies (including orbital velocity anisotropy, mass-to-light ratios, and inclination), we extract robust BH masses. We demonstrate that JWST's exceptional resolution allows JAM to tightly constrain the central potential using nuclear kinematics alone. Crucially, not all ultramassive galaxies host ultramassive BHs: while most display a classic central velocity dispersion peak, notable exceptions emerge, including a clear central dispersion drop in one galaxy and a subdued peak in another. These kinematic differences yield distinct BH masses, suggesting BH growth at extreme mass scales is highly stochastic. This stochasticity may be driven by three-body ejections during hierarchical mergers or gravitational recoil kicks from coalescing binaries. In the latter case, the kicked BH may be displaced and wandering outside the compact NIRSpec field of view. Our derived BH masses populate the historically sparse upper envelope of the galaxy mass hierarchy, providing the critical foundation for Paper III to investigate extreme-mass BH scaling relations and test models of galaxy-BH co-evolution.
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Astrophysics of Galaxies

The JWST Ultramassive Galaxy Sample – I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization

Michele Cappellari, Dieu D. Nguyen and Susan A. Kassin

We introduce the JWST Ultramassive Galaxy Sample, comprising 8 extreme early-type galaxies ($M_\star \gtrsim 2\times10^{12}\,\mathrm{M}_\odot$) drawn as a representative subset from a comprehensive full-sky census of over 100 such objects. This program aims to dynamically measure their central supermassive black holes (BHs) to probe the extreme high-mass end of BH–galaxy scaling relations, a critical regime where the physical mechanisms governing BH growth and host-galaxy co-evolution are expected to fundamentally change. In this first paper, we present the foundational data products: detailed photometric models and spatially resolved nuclear stellar kinematics. To accurately map the stellar mass distribution from the BH sphere of influence out to the extended halo, we combine diffraction-limited JWST/NIRCam imaging with wide-field DESI Legacy Surveys data, parametrizing the surface brightness using Multi-Gaussian Expansion (MGE). We extract stellar kinematics from JWST/NIRSpec integral-field observations using the penalized pixel-fitting (pPXF) method. To fully exploit the continuous $1.66-3.17\,\mu\mathrm{m}$ wavelength coverage—avoiding the telluric gaps of ground-based empirical libraries and the computational burden of massive theoretical grids—we introduce the use of near-separable Non-Negative Matrix Factorization (NMF). This algorithm identifies an optimal, highly compressed subset of synthetic spectra from the updated BOSZ library, perfectly capturing its spanning power at a fraction of the computational cost. The resulting kinematic maps reveal that these ultramassive systems are overwhelmingly slow rotators, frequently harboring kinematically decoupled cores. These high-quality photometric and kinematic data provide the inputs required for the robust Jeans Anisotropic Modelling (JAM) of the central BH masses in Paper II.
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Astrophysics of Galaxies

Stellar Yields of Rapidly Rotating Population III Stars for the High Redshift Universe

Devesh Nandal, Konstantinos Topalakis, Vasilisa Sergienko et al. (+6 more)

JWST has revealed rapid nitrogen enrichment in high redshift galaxies, renewing the need for stellar yields that follow metal free stars beyond the main sequence and across their final fates. We present Geneva stellar evolution models of rapidly rotating Pop~III stars with $5 \leq M_{\rm ini}/M_\odot \leq 200$ and $\upsilon_{\rm ini}/\upsilon_{\rm crit}=0.7$, evolved to the end of core O-burning. We calculate gross adopted ejecta masses using fate dependent remnant prescriptions spanning core collapse, pulsational pair instability, and complete pair instability. Our quantitative results focus on hydrostatically produced CNO material, while heavier species are treated as final-model reservoirs. Rotation produces primary CNO material by mixing newly synthesized C and O into H-burning layers, where CNO cycling generates nitrogen. The resulting abundance signature depends strongly on which stellar layers escape. Models leaving compact remnants can reach $\log({\rm N/O})=-0.49$ while remaining poor in Si/S/Ar/Ca-rich material. PISN models eject the largest nitrogen masses, $M_{\rm N}=1.8$–$2.5,M_\odot$, but also release $57$–$65,M_\odot$ of oxygen, lowering $\log({\rm N/O})$ to $-1.44$ to $-1.29$. Thus, high nitrogen yields do not imply high N/O ratios. This trend persists after IMF weighting, as increasingly top-heavy populations add oxygen and deep alpha material faster than they build a nitrogen dominated mixture. Our grid provides a new CNO-focused prompt-enrichment dataset for interpreting nitrogen-rich systems including GN-z11, CEERS-1019, and GS~3073.
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All authors Devesh Nandal, Konstantinos Topalakis, Vasilisa Sergienko, Doga Eker, Efe K. Celep, Danielle A. Berg, Daniel J. Whalen, Sophie Tsiatsiou, Raphael Hirschi

High Energy Astrophysical Phenomena

Euclid: Quick Data Release (Q1) – Optical hotspots in powerful radio galaxies

M. J. Hardcastle, L. Bisigello, M. Bondi et al. (+154 more)

The hotspots of powerful radio galaxies are the sites of high-energy particle acceleration, but radio observations give us limited information on the electron energy distributions that they generate, which affects our overall understanding of their physics and energetics. Optical synchrotron counterparts to radio galaxy hotspots, which probe high electron energies, have been known for many years, but have only been studied in a small number of objects selected as being very bright in the radio. By combining Low-Frequency Array (LOFAR) observations with the Euclid Q1 data release in the Euclid Deep Field North, we identify 77 powerful radio galaxies with hotspots and show that a small but significant fraction of them, 7–15%, may have detected infrared and optical counterparts to their hotspots. The hotspot spectral energy distributions in our clearest cases are consistent with particle acceleration up to (but not beyond) 1\,TeV in energy on the assumption of field strengths close to equipartition, whereas non-detected hotspots either do not reach such high electron energies or would have to have very different electron energy spectra or significantly sub-equipartition magnetic field strengths. Two new candidate optical hotspots are clearly detected matching high-resolution LOFAR data; one is remarkable as both the highest-redshift optical hotspot known to date ($z \approx 1.6$) and also the first optical detection of the hotspot of the inner lobe of a restarting source. We discuss approaches to performing a large-scale study of hotspots with the full wide-area Euclid surveys, particularly when combined with the international baselines of LOFAR, enabling for the first time a statistical analysis of high-energy particle acceleration in hotspots.
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All authors M. J. Hardcastle, L. Bisigello, M. Bondi, M. Magliocchetti, L. K. Morabito, J. Petley, F. Ricci, H. J. A. Rottgering, K. Rubinur, D. J. B. Smith, D. Stern, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, M. Cropper, J.-G. Cuby, A. Da Silva, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, F. Dubath, X. Dupac, M. Farina, R. Farinelli, S. Ferriol, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, J. Hoar, W. Holmes, I. M. Hook, 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, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, A. Secroun, G. Seidel, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, J. Skottfelt, L. Stanco, P. Tallada-Crespí, A. N. Taylor, H. I. Teplitz, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, O. R. Williams, A. Zacchei, G. Zamorani, F. M. Zerbi, E. Zucca, J. García-Bellido, V. Scottez, F. Tarsitano, J. H. Knapen

Astrophysics of Galaxies

Stellar ages from [C/N] in giant stars: applicability and limitations

Giada Casali, Luca Casagrande, Fiorenzo Vincenzo et al. (+5 more)

The [C/N] abundance ratio is a powerful age indicator for giant stars, enabling age estimates for spectroscopic samples where traditional methods are limited. We calibrate a multivariate [C/N]-age-[Fe/H] relationship using 9,122 giant stars observed by Kepler, with asteroseismic ages and APOGEE DR17 abundances. The calibration is performed separately for lower red giant branch (LRGB), upper RGB (URGB), and red clump (RC) stars. We validate the relationships using independent samples from K2, TESS, and open clusters, finding good agreement with reference ages, particularly for LRGB stars, with typical precision of ~30% for ages between ~2 - 10 Gyr. The performance degrades for URGB and RC stars and low metallicities, likely due to extra mixing processes, for young (<2 Gyr) and old (>10 Gyr) stars, where the [C/N]-age correlation weakens. We show that the [C/N]-based ages reproduce known Milky Way features, including the age distribution across the [alpha/Fe]-[Fe/H] plane and the flaring of the Galactic disc. Compared to other chemical clocks, [C/N] provides more robust and precise age estimates within its domain of validity. Our results demonstrate that [C/N], combined with metallicity, is an effective empirical tool for deriving stellar ages of giant stars from spectroscopic surveys, particularly for LRGB stars with [Fe/H] > -1, enabling Galactic archaeology studies beyond the reach of current asteroseismic samples.
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All authors Giada Casali, Luca Casagrande, Fiorenzo Vincenzo, Andrea Miglio, Melissa Ness, Grazina Tautvaišiene, Laura Magrini, Sven Buder

High Energy Astrophysical Phenomena

Nonlinearly Causal General-Relativistic Two-Fluid Dissipative Magnetohydrodynamics

Elias R. Most and Samuel J. Dunham

We present a formulation of general-relativistic (GR) 19-moment dissipative magnetohydrodynamics (MHD), capable of handling all first-order dissipative terms (viscosity, heat conductivity, resistivity and Hall terms), as well as all ideal electron degrees of freedom (number density, momentum and energy) in a GR astrophysical two-fluid plasma. We derive necessary and sufficient nonlinear causality conditions for the constrained first-order 19-moment system, as well as both necessary and sufficient conditions for strong hyperbolicity. To assess the formulation numerically, we develop a high-resolution shock-capturing scheme that solves these equations in a performance-portable fashion. The scheme expresses all evolution equations, including the dissipative and electron sectors, in flux-divergence form, allowing us to model systems with scales separated by orders of magnitude without resolving kinetic scales everywhere on the grid. In addition, we use implicit integration methods to systematically overstep kinetic scales in MHD regions, such as cyclotron and plasma frequencies. To make the scheme as robust as GRMHD codes, we construct necessary and sufficient conditions for a conserved state to be physically admissible, and based on these construct a new physicality-enforcement scheme. As an exact validation comparison, we formulate and derive a full solution to dissipative two-fluid Bondi accretion in general relativity. We then validate the equations against a series of results from kinetic particle-in-cell models of black hole accretion and magnetospheric dynamics, demonstrating that our formulation and scheme can correctly capture major features relevant for feedback on global scales of these solutions, including dimensionless reconnection rates of order $0.1$ and Braginskii-like anisotropic pressures and heat fluxes.
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Cosmology and Nongalactic Astrophysics

Modified Gravity from growth data: goodness-of-fit and gravitational coupling

Manoel V. S. Filho, Fernanda Oliveira, Wiliam S. Hipólito-Ricaldi et al. (+2 more)

While background expansion data alone cannot discriminate among cosmological models, the growth of large-scale structures directly probes the underlying theory of gravity, offering a path to distinguish General Relativity from its modifications. In this work, we constrain three representative $F(R)$ modified gravity models (Starobinsky, Hu-Sawicki, and $R^2$-corrected Appleby-Battye) using measurements of the growth rate $f(z)$ and the matter fluctuation amplitude $\sigma_8(z)$. Our analyses combine MCMC parameter estimation, Gaussian Process reconstructions, and goodness-of-fit statistics including Akaike information criterion (AIC) and Bayesian information criterion (BIC). All investigated models provide statistically comparable fits to the current growth data, with information criteria differences too small to establish a preference for any particular scenario. To overcome this degeneracy, we reconstruct the effective gravitational coupling $\mu(z)$ from the MCMC posterior samples, providing a physically motivated diagnostic that complements standard goodness-of-fit criteria. The Starobinsky and Hu-Sawicki models predict moderate departures from General Relativity, remaining compatible with constraints on both $\mu(z)$ and $S_8$. In contrast, the $R^2$-AB model predicts $\mu_0 \sim 3.5$ and $S_8 = 0.638$, a $3.2\sigma$ tension with Planck 2018, rendering it physically disfavored despite its competitive statistical performance.
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All authors Manoel V. S. Filho, Fernanda Oliveira, Wiliam S. Hipólito-Ricaldi, Felipe Avila, Armando Bernui