Papers for Thursday, Jan 22 2026

We present \textbf{DeepInflation}, an AI agent designed for research and model discovery in inflationary cosmology. Built upon a multi-agent architecture, \textbf{DeepInflation} integrates Large Language Models (LLMs) with a symbolic regression (SR) engine and a retrieval-augmented generation (RAG) knowledge base. This framework enables the agent to automatically explore and verify the vast landscape of inflationary potentials while grounding its outputs in established theoretical literature. We demonstrate that \textbf{DeepInflation} can successfully discover simple and viable single-field slow-roll inflationary potentials consistent with the latest observations (here ACT DR6 results as example) or any given $n_s$ and $r$, and provide accurate theoretical context for obscure inflationary scenarios. \textbf{DeepInflation} serves as a prototype for a new generation of autonomous scientific discovery engines in cosmology, which enables researchers and non-experts alike to explore the inflationary landscape using natural language. This agent is available at this https URL.

The AT2017gfo kilonova transient remains a unique multi-messenger event thanks to its proximity (z=0.00987) and the possibility to investigate time-resolved spectra, providing evidence of r-process nucleosynthesis. The kilonova signal was extensively studied in the spectral and time domains, giving key insights into the chemical composition and physical properties of the ejecta. Here, we report the discovery of a novel correlation between two fundamental observables: the peak energy of the EF_E spectrum, Ep, and the isotropic-equivalent luminosity, Liso. In particular, we show that up to about 2.5 days after the merger, the AT2017gfo spectrum evolves according to: log10[Ep/eV] = -0.13 (+0.02/-0.02) + 0.62 (+0.02/-0.02) * log10[Liso/(1e41 erg/s)] (68% C.L.) while in subsequent epochs, Ep remains almost constant with Liso, flattening around 1 eV. Exploiting simulations from a state-of-the-art radiative transfer code, we demonstrate that our kilonova model inherently predicts this peculiar correlation, suggesting a new diagnostic tool for comparing observables against simulations. Future kilonova observations will provide additional insight into the physics behind the Ep-Liso correlation.

We introduce $\texttt{WaveletNet}$, a wavelet-based neural network architecture to identify and reduce non-Gaussian noise in gravitational wave data. Traditionally, convolutional neural networks (CNNs) have been widely used as a flexible machine learning method to mitigate non-Gaussian noise. However, training CNNs requires many data samples, especially when the input data segments are long. Glitches that mimic high-mass black hole signals are empirically known to have a wavelet-like structure. We exploit this property in $\texttt{WaveletNet}$ by using simple neural networks to learn the best family of wavelets to model glitches in the LIGO-Virgo-KAGRA O3 data. Due to its simplicity, our framework is significantly more sample-efficient than CNNs. As a use case, we build upon the $\texttt{TIER}$ method and show how $\texttt{WaveletNet}$ can improve the performance of any search pipeline. We take potential GW candidates from the pipeline, and then downweight the candidates having noisy strain regions in their vicinity. We use our framework in a modular way: we provide an output score which can be added to the pipeline's existing detection statistic score for the candidates. We test our method using candidates from the $\texttt{IAS-HM}$ search pipeline and show that it improves the search sensitive volume by up to 15% for high-mass, asymmetric binaries.

The rapid expansion of the Fast Radio Burst (FRB) field has been accompanied by a simultaneous growth of FRB conferences. While these meetings are essential for interacting with other researchers and establishing collaborations, many remain only accessible to those with substantial travel funding, flexible schedules, or geographical proximity. This introduces barriers that predominantly affect early career researchers (ECRs) and people from under-resourced regions, limiting the growth, diversity, and sustainability of the community. To address these issues, the FRB 2025 conference, held in Montréal in July 2025 with over 200 participants, was designed to prioritize inclusivity and accessibility alongside scientific excellence. In this work, we describe how we implemented these goals, including: organizing committees spearheaded by ECRs, a fully hybrid format including YouTube livestreams, low registration fees, a pedagogical day at the beginning of the conference, local vegetarian catering, and the implementation of flash-talks instead of posters. From a post-conference survey of participants, we were able to assess the effectiveness of our initiatives. Notably, we received very positive feedback from the online participants, which amounted to roughly half of the attendees, especially regarding the livestreams and talk recordings. The pedagogical day was also greatly appreciated. The low registration fees naturally led to challenges, in particular with the audio-visual management, and although areas for improvement were noted, such as poster sessions and support for attendees requiring visas, the conference was generally viewed as a success. Our experience demonstrates that highly accessible, hybrid conferences are possible within modest budgets ($\$20$k CAD), and we outline recommendations for future conferences, both in the FRB field and in other domains.

A crucial physical quantity in determining the 21-cm signal during cosmic dawn is the inhomogeneous background of Ly$\alpha$ photons originating from the first galaxies. As these photons travel through the intergalactic medium, their scattering cross-section is often approximated as a delta function at resonance due to computational cost. That is, photons with emitted wavelengths between Ly$\alpha$ and Ly$\beta$ are assumed to travel in straight lines until they redshift into the Ly$\alpha$ resonance. However, due to the damping wing in the Ly$\alpha$ cross-section, this approximation fails as the frequency of the photon approaches the resonant frequency, resulting in multiple scatterings events that could be separated by non-negligible distances. Some previous works studied this effect of Ly$\alpha$ multiple scattering by running computationally heavy radiative-transfer simulations. However, robustly interpreting the cosmic 21cm signal requires exploring a large parameter space of astrophysical uncertainties, motivating more computationally-efficient approaches. Here we incorporate Ly$\alpha$ multiple scatterings in the public, semi-numerical simulation 21cmFAST. We employ Monte Carlo simulations to study the trajectories of Ly$\alpha$ photons on different scales. We find that the distance distributions of Ly$\alpha$ photons with respect to the absorption point can be modeled as analytical functions that are governed by a single parameter. Upon implementing the distance distributions in 21cmFAST, we find that the multiple scattering effect is important (about 50% difference in the 21-cm power spectrum) only at high redshifts before the spin temperature is fully coupled to the kinetic temperature. Furthermore, we find that Ly$\alpha$ multiple scattering does not enhance Ly$\alpha$ heating, and that the combined effect is negligible, especially under realistic X-ray heating scenarios.

One of the largest source of uncertainties in the predictions of stellar models comes from the internal transport mechanisms. In close massive binaries, previous theoretical studies suggest that tides systematically boost chemical mixing. However, observations do not reveal any clear period-nitrogen enrichment trend, challenging these predictions. In addition, comprehensive examinations of the interplay between tidal interactions, angular momentum and chemicals transport have so far been scarce. We investigate the interplay between tidal interactions and rotational mixing, and the impact of the angular moment transport (AMT) assumptions. We examine whether tidal interactions enhance or suppress chemical mixing by computing grids of genec binary models with various AMT treatments. In order to independently assess the role of tidal interactions, we systematically compute model variations of single stars with identical initial conditions. Our investigations reveal that tides can either enhance or suppress mixing relative to single-star models, and that the outcome is highly sensitive to the AMT assumptions. We identify a key contrast between the two types of computed models: in close systems subject to tides, magnetic models predict that the mixing efficiency is mostly determined by the orbital configuration, whereas in hydrodynamic models it also depends on the assumed initial velocity. As a result, hydro models may display non-monotonic period-enrichment trends, or even period-enrichment correlations. These results highlight the importance of the AMT assumptions in modeling binaries with tidal interactions. The sensitivity of the predictions of hydro models to initial conditions extends the size of the period-enrichment parameter space they cover, allowing them to accommodate for peculiar observed systems, i.e., with mild enrichment at short periods, or high enrichment at longer periods.

The origin of hot Jupiters is the oldest problem in exoplanet astrophysics. Hot Jupiters formed in situ or via disk migration should be in place just a few Myr after the formation of their host stars. On the other hand, hot Jupiters formed via eccentricity excitation and tidal damping as a result of planet--planet scattering or Kozai-Lidov oscillations may take 1 Gyr or more to arrive at their observed locations. We propose that the relative ages of hot Jupiters inside, near, and outside the bias-corrected peak of the observed hot Jupiter period distribution can be used to distinguish between these possibilities. Though the lack of precise and accurate age inferences for isolated hot Jupiter host stars makes this test difficult to implement, comparisons between the Galactic velocity dispersions of the hot Jupiter subpopulations enable this investigation. To transform relative age offsets into absolute age offsets, we calibrate the monotonically increasing solar neighborhood age--velocity dispersion relation using an all-sky sample of subgiants with precise ages and a metallicity distribution matched to that of hot Jupiter hosts. We find that the inside-peak and near-peak subpopulations are older than the outside-peak subpopulation, with the inside-peak subpopulation slightly older than the near-peak subpopulation. We conclude that at least 40\% but not more than 70\% of the hot Jupiter population must have formed via a late-time, peak-populating process like high-eccentricity migration that typically occurs more than 1.5 Gyr after system formation.

The discovery by JWST of a substantial population of compact "Little Red Dots" (LRDs) presents a major puzzle: their observed spectra defy standard astrophysical interpretations. Here, we show that LRD spectra are naturally reproduced by emission from an accreting Direct Collapse Black Hole (DCBH). Using radiation-hydrodynamic simulations, we follow the growth of the DCBH seed via a dense, compressionally heated, collisionally ionized accretion flow. The model self-consistently reproduces the screen responsible for the observed Balmer absorption, while allowing UV/optical emission to partially escape, along with reprocessed infrared radiation. Crucially, this structure is not a blackbody and requires no stellar contribution: the UV continuum originates entirely from reprocessed DCBH radiation, attenuated only by a small amount of dust with an extinction curve consistent with high-redshift galaxies. This single framework simultaneously explains the key observational puzzles of LRDs: (a) weak X-ray emission, (b) metal and high-ionization lines alongside absent star-formation features, (c) overmassive black holes, (d) compact morphology, (e) abundance and redshift evolution -- linking them directly to pristine atomic-cooling halos, (f) long-lived ($>100$ Myr), slowly variable phases driven by radiation pressure. Our findings indicate that JWST is witnessing the widespread formation of heavy black hole seeds in the early Universe.

eROSITA substantiated earlier indications that Loop-I is the northern part of an extended bipolar Galactic-bubble structure, but the southern bubble was not established in nonthermal emission and the shock strength was not robustly measured in either bubble. After using eROSITA data to map the bubble edges, we analyzed edge-adjacent radio and $\gamma$-ray data to remove foregrounds, test if the southern bubble can be detected in nonthermal emission, and measure the corresponding high-latitude spectra of both bubbles. Data were stacked parallel to the eROSITA bubble edges traced by an edge detector, in the same method used previously to pick up weak signals in the smaller, nested Fermi bubbles; the detected brightness jumps were then used to measure the spectrum. We detect ($>5\sigma$) both bubble tips in both radio and $\gamma$-rays, and find a radio spectrum corresponding to high, Mach $3$-$5$ shocks. The southern bubble is fainter, by $\sim$an order of magnitude in radio, its edge propagating into a medium roughly half as dense. The results indicate that these eROSITA bubbles are older, evolved counterparts of the Fermi bubbles, arising from an earlier collimated high-energy outburst from the Galactic center.

The rapid emergence of supermassive black holes (SMBHs) in the early Universe poses a challenge to current models of black hole growth. One promising formation pathway is the direct collapse black hole (DCBH) scenario, in which gas in pristine, low-metallicity halos forms supermassive (or quasi-) stars leading to massive black holes seeds under specific environmental conditions. In this work, we investigate the potential host environments of DCBHs by coupling a semi-analytic model tracing BH formation and galaxy co-evolution with high-resolution N-body dark matter merger trees. This allows us to trace the population of DCBHs formed during the hierarchical assembly of a $\sim 10^{12} ~\rm M_\odot$ dark matter halo hosting a bright $10^9 ~\rm M_\odot$ quasar at redshift $z \approx 7$. We find that, when accounting for local fluctuations in the UV radiation field within this early cosmic structure, massive BH seeds can form via direct collapse as early as $z \approx 22$. Even under more stringent conditions for heavy seed formation, tens of DCBHs are predicted to emerge within the simulated overdensity down to $z \sim 14$, at which point metal enrichment of the intergalactic medium inhibits further episodes of direct collapse. A significant fraction of the massive black hole population formed at $z > 14$ is expected to survive in satellite galaxies that do not merge with the central halo down to $z \approx 7$. We show that the existence of such a population of ungrown heavy BH seeds can be probed through deep JWST observations targeting regions surrounding bright high-redshift quasars, and we discuss tailored observational strategies to detect and identify these elusive systems.

Small asteroids and large meteoroids frequently impact the Earth, though their physical and material properties remain poorly understood. When observed as fireballs in Earth's atmosphere, these properties can be inferred from their ablation and fragmentation behavior. The 2022 release of previously classified United States Government (USG) satellite sensor data has provided hundreds of new fireball light curves, allowing for more detailed analysis. Here we present a new Bayesian inference method based on dynamic nested sampling that can robustly estimate these objects' physical parameters from their observed light curves, starting from relatively uninformative, flat priors. We validate our method against seven USG sensor-observed fireballs with independent ground-based observations and demonstrate that our results are consistent with previous estimates. We then apply our technique to $13$ decameter-size Earth impactors to conduct the most detailed population-level study of their structure and material strength to date. We identify three structurally distinct groups within the decameter impactors. The first group are primarily structurally homogeneous, weak objects which catastrophically disrupt below $\sim1.5$ MPa. The second group are heterogeneous objects which progressively fragment starting from $\sim1$ MPa typically up to $\sim3-8$ MPa. The third group are strong aggregates which remain mostly intact until $9-10$ MPa. Our results also suggest that decameter-size asteroids fragment in two distinct phases: an initial phase at $\sim0.04-0.09$ MPa and a second at $\sim1-4$ MPa. While decimeter- to meter-size objects typically lose most of their mass in the initial phase, larger decameter-size objects instead lose most of their mass in the second phase.

We present a reanalysis of the water maser system in NGC 4258 to reassess its geometric distance, commonly reported as approximately 7.6 Mpc with percent-level accuracy, a key anchor in extragalactic distance ladder calibrations and recent determinations of the Hubble constant. We introduce a method that relies exclusively on tracking individual maser components, rather than assuming a single averaged trajectory as in previous works, thereby avoiding arbitrary data averaging that can bias interpretations of the disk's geometry and dynamics. This approach requires spatially resolved individual maser components; consequently, the majority of observational epochs were excluded, as they lack sufficient spatial resolution to localize the maser position. We track individual maser components across multiple epochs and introduce an efficient marginalization method over nuisance parameters (angular radius and azimuth of each maser), reducing the number of free parameters from hundreds to 14. Our analysis reveals that the current observational cadence is insufficient to reliably track the individual masers, which our method relies on, given their intrinsic variability. Across a range of maser selections and model configurations, inferred distances span approximately between 6.7 to 8.1 Mpc, demonstrating significant sensitivity to how our method selects individual masers. Even visually and statistically robust fits can differ by several standard deviations, reflecting ambiguity in component identification across sparsely sampled epochs. We evaluate the impact of observational cadence on tracking fidelity and distance precision, and show that high-cadence monitoring is needed for our method to track individual masers and produce a robust anchor for cosmology.

Fast X-ray transients (FXTs) are flashes of X-rays that last for a few hundreds of seconds to a few hours. An enigmatic population of these transients that did not have a clear origin has been known for several decades, mostly found serendipitously in soft X-ray imaging observations. Recent progress in this field by Einstein Probe has found that many FXTs are associated with gamma-ray bursts and the collapse of massive stars. Motivated by this, we searched the NuSTAR archive in the harder 3--79 keV band for $\sim1000$ s duration transients. From 204 Ms of exposure we present five candidate FXTs, four of which are spectrally hard, with power-law indices $-3<\Gamma<0$, standing them apart from FXTs discovered in the soft band. Three have potential associations with galaxies at $z=0.1-2$, implying 3--79 keV luminosities of $10^{43}$ to $10^{48}$ erg s$^{-1}$ and volumetric event rates of 125--2900 Gpc$^{-3}$ yr$^{-1}$. The properties of these NuSTAR FXTs most resemble low-luminosity gamma-ray bursts, and would be much more common than their higher-luminosity counterparts in this redshift range.

We demonstrate the capabilities of probabilistic diffusion models to reduce dramatically the computational cost of expensive hydrodynamical simulations to study the relationship between observable baryonic cosmological probes and dark matter at field level and well into the non-linear regime. We introduce a novel technique, Cosmo-FOLD (Cosmological Fields via Overlap Latent Diffusion) to rapidly generate accurate and arbitrarily large cosmological and astrophysical 3-dimensional fields, conditioned on a given input field. We are able to generate TNG300-2 dark matter density and gas temperature fields from a model trained only on ~1% of the volume (a process we refer to as `upscaling'), reproducing both large scale coherent dark matter filaments and power spectra to within 10% for wavenumbers k <= 5 h Mpc^-1. These results are obtained within a small fraction of the original simulation cost and produced on a single GPU. Beyond one and two points statistics, the bispectrum is also faithfully reproduced through the inclusion of positional encodings. Finally, we demonstrate Cosmo-FOLD's generalisation capabilities by upscaling a CAMELS volume of 25 (Mpc h^-1)^3 to a full TNG300-2 volume of 205 (Mpc h^-1)^3$ with no fine-tuning. Cosmo-FOLD opens the door to full field-level simulation-based inference on cosmological scale.

We provide a detailed characterization of 2M07515777+1807352, a post-common envelope eclipsing binary system with a 10.3 d, nearly, but not quite, circular orbit (e = 0.02). This system consists of a massive white dwarf (WD) ($1.08$ M$_{\odot}$) and a 4400 K main-sequence companion (0.66 M$_{\odot}$). This WD is among the most massive known within post-common envelope binary systems. We also find, through both spectral energy distribution and $\it{TESS}$ light curve analyses, that the WD has a radius of $1.54 R_{\earth}$, roughly $12\sigma$ larger than the expected value from WD mass-radius relationships. Both the Lomb-Scargle analysis and the $v \sin{i}$ of the system indicate the main-sequence companion to be super-synchronously rotating at a period of $\sim$6 days, which may suggest accretion occurred during the evolution of the system. This binary also shares similar physical characteristics with six other post-common envelope systems hosting massive WDs, which may point to a shared formation pathway. We model the history of this system with COSMIC and find that it likely formed through an episode of common envelope evolution following the onset of mass transfer when the progenitor primary was on either the early or the thermally pulsing stages of the asymptotic giant branch. As a result of its properties, the study of 2M07515777+1807352 can provide new insights regarding many key outstanding questions in our understanding of common envelope evolution.

Conduction as a mechanism for explaining the disrupted cooling-flow in galaxy clusters has been mostly discounted, as the process is inefficient at transporting heat all the way from the cluster into the core. However, thermal conduction can be strongly enhanced when materials of significantly different temperature are brought into proximity, and thus into close thermal contact. Jets of active galactic nuclei may act as heat pumps by bringing low-entropy gas from the cluster core into thermal contact with the hot outer atmosphere of the cluster, significantly increasing the feedback efficiency of active galactic nuclei. We test this hypothesis by running a suite of 3D magnetohydrodynamic simulations of active galactic nuclei jets in a Perseus-like cluster, including anisotropic conduction. We find that the heat pump efficiency $\eta$ can reach up to 50\% of the maximum possible efficiency $\eta_{\rm max}$ if conduction operates near the Spitzer-Braginskii limit, while $\eta\approx f_{\rm sp}\eta_{\rm max}$ if conduction along the field lines is substantially suppressed below the Spitzer-Braginskii value by a factor $f_{\rm sp}$ by kinetic effects, as recently suggested. We further find that jet-induced thermal conduction is self-limiting: Magnetic draping during the uplift results in a magnetic field orientation close to perpendicular to the induced temperature gradients, significantly reducing conduction along the ideal conductive pathways. Thus, for conservative assumptions about thermal conduction suppression by $f_{\rm sp} \lesssim 0.1$, the heat pump effect leads to only marginal heat transfer and, correspondingly, to immaterial changes in the overall thermal evolution of cool core clusters beyond the isolated effects of conduction and jet-induced heating alone.

Strongly lensed star clusters have recently been detected up to redshift $z\approx 10$ in galaxy cluster fields using the James Webb Space Telescope (JWST). When pairs of mirror images of such star clusters appear across the lensing critical curve, it is usually assumed that both images will display identical spectral energy distributions (SEDs). However, this assumption may be invalidated in the presence of gravitational microlensing from stars or other compact objects in the lens, since microlensing will affect the SED contribution from bright stars within the star cluster independently in the two mirror images. Here, we explore under what circumstances mismatched mirror-image SEDs are likely to be observable, and argue that SED differences detectable in JWST observations of lensing-cluster fields will be limited to star clusters of mass $< 10^5\ M_\odot$ and ages $\lesssim 5$ Myr. The probability of severely mismatched mirror-image SEDs increases if the stellar initial mass function is very top-heavy and extends to stellar masses $\gg 100\ M_\odot$, as has been suggested to be the case for Population III stars. The prevalence of lensed star clusters with highly discrepant mirror-image SEDs could therefore serve as a probe of very massive stars and extreme stellar populations in the early Universe.

The central compact object (CCO) in the Vela Junior supernova remnant is a young neutron star whose relatively low X-ray flux and small distance suggest it has a mass high enough to activate fast neutrino cooling processes. Here we analyse all XMM-Newton MOS and pn and Chandra ACIS-S spectra of the Vela Junior CCO, with observations taking place over the 9 years from 2001 to 2010. We find that the best-fit flux and spectral model parameters do not vary significantly when treating each observation independently, and therefore we fit all the spectra simultaneously using various spectral models to characterize the predominantly thermal emission from the neutron star surface. Our results indicate the Vela Junior CCO has an atmosphere composed of hydrogen, a hot spot temperature (unredshifted) of 3.5x10^6 K, and a colder surface temperature of (6.6-8.8)x10^5 K. Possible absorption lines at ~0.6 keV and 0.9 keV provide evidence for the first-time of an average surface magnetic field B~3x10^10 G for this CCO, which is similar to the magnetic field of other CCOs. At the accurate new Vela Junior distance of 1.4 kpc, the observed luminosity that is dominated by the hot spot is ~5x10^32 erg s^-1. The luminosity from the rest of the colder surface is (1.3-4.0)x10^32 erg s^-1. The cool luminosity and temperature imply the Vela Junior CCO is indeed colder than many other young neutron stars and probably has a high mass that triggered fast neutrino cooling.

Extended warm and cold gas nebulae, with complex morphologies and kinematics, have been observed in the centres of cool-core galaxy clusters. Their origin within the hot intracluster medium (ICM) is still puzzling, and among many mechanisms, positive feedback from the central active galactic nucleus (AGN) has been proposed. In this work, we performed a suite of very high-resolution hydrodynamic simulations of a Perseus-like cool-core galaxy cluster subject to self-regulated AGN jet feedback, which leads to realistic ICM properties. By explicitly following warm ionized, neutral, and molecular gas phases, we studied the complex interplay between AGN activity and the multi-phase ICM. While AGN feedback globally heats the ICM, we find that during the individual AGN jet bursts, hot material is also injected laterally to the jet axis, within the turbulent mixing layer. This material, as it expands, compresses the surrounding hot ICM, reducing the local cooling time, and leads to the formation of cold clumps on a characteristic timescale of $\sim 30$ Myr. By employing tracers, we explicitly track cooling within the affected regions, finding that very hot gas identified in high-compression, low-vorticity zones condenses in situ to form cold clumps. A statistical analysis reveals that the condensation of cold gas is highly promoted once the local turbulent Mach number, $\sigma_{hot}/c_{s,hot}$, in the hot gas component ($T \geq 10^7$ K) takes values around ~0.3. The presented process is a further important step in understanding the physical mechanisms that lead to the formation of cold gas in the cluster core. Our measured values of the characteristic turbulent Mach number, together with detailed multi-phase gas kinematics predictions, provide important theoretical tools to interpret future X-ray spectroscopy and deep radio data, ultimately to constrain the origin of cool-core cluster nebulae.

We present a detailed analysis of sloshing cold fronts in a sample of three nearby galaxy clusters (Abell 496, Abell 2029, and Abell 1644) observed with the Chandra X-ray Observatory. Cold fronts manifest as sharp edges in the X-ray surface brightness of the intracluster medium (ICM) in galaxy clusters. In the residual X-ray surface brightness maps, where the global ICM distribution has been subtracted, cold fronts generated by gas sloshing are observed at the boundaries of the spiral excesses. We perform a systematic and comprehensive study of the surface brightness edges along the spiral excesses. We find the deficit of the thermal pressure radially inward of the brightness edges, in contrast to stripping cold fronts that typically exhibit higher thermal pressure in brightness edges. Assuming that the sharp edges in the X-ray surface brightness distributions are sustained entirely by the gas bulk motions, we estimate the velocity gradients across the edges that are required to compensate for the deficit of the thermal pressure. We do not find statistically significant velocity gradients along the azimuthal direction. Our results suggest that alternative mechanisms such as magnetic fields and viscosity are necessary to maintain the sharpness of sloshing cold fronts.

A small fraction of X-ray photons from gamma-ray bursts (GRBs), after escaping the relativistic jet, are scattered by electrons in the circumburst medium. Subsequent photon-photon absorption between the incoming MeV $\gamma$-rays and the back-scattered X-rays generate electron-positron pairs, enriching the surrounding medium with leptons. We investigate how these back-scattered photons modify the prompt GRB spectrum through $\gamma-\gamma$ absorption. In a dense and pair-loaded wind environment, the emerging spectra exhibit a broad attenuation structure, whose morphology is sensitive to the low-energy spectral index $\alpha$. In particular, spectra with $\alpha > -1$ develop a pronounced, saddle-shaped absorption between 1 and 100 MeV (rest frame). Such external MeV absorption could account for the spectral curvature seen in some bright GRBs, and may point to enhanced mass loss from their progenitor stars, consistent with early observations of core-collapse supernovae.

Observations from the James Webb Space Telescope (JWST) have uncovered supermassive black holes (SMBHs) with masses exceeding $10^6 \mathrm{M}_{\odot}$ at redshifts $z > 8$, posing significant challenges to existing models of early black hole formation and growth. Here we show, in a fully cosmological setting, that light seed black holes (LSBHs), remnants of Population III stars, can grow rapidly to $\sim10^4 \mathrm{M}_{\odot}$ in the early Universe. This growth is enabled by our novel black hole seeding prescription and the unprecedented resolution of our zoom-in cosmological simulations, which resolve the dense environments necessary for efficient accretion. Our results provide robust evidence that LSBHs can attain the masses required to serve as the dominant progenitors of the SMBH population observed at later cosmic epochs. These findings have far-reaching implications for the interpretation of JWST observations and future gravitational wave detections with LISA.

We investigate erythrohenosis -- the collision and merger of two red giants -- establishing an end-to-end model for this fundamental evolutionary channel in dense stellar environments. Combining three-dimensional SPH simulations of a binary with analytical modeling, we characterize the event from initial encounter to terminal explosion. We demonstrate that grazing encounters induce tidal capture and rapid orbital decay, accompanied by large-amplitude, nonlinear stellar oscillations. The subsequent inspiral spins up the common envelope into a stable, non-spherical equilibrium, powering a luminous precursor with quasi-periodic bursts. The terminal explosion, modeled with angular momentum conservation, produces an intrinsically flattened remnant that preserves a geometric memory, or morphomnesia, of its binary origin. The associated gravitational wave signal features a rapid, drag-dominated frequency evolution, identifiable by a unique time-varying apparent chirp mass. These results define a distinctive multi-stage observational fingerprint -- linking transient optical precursors, asymmetric nebulae, and anomalous gravitational wave chirps -- to guide identification in current and future multi-messenger surveys.

The stellar halo of the Milky Way contains the remnants of past accretion events, which could be detectable as substructures in the classical integrals of motion space, such as energy and angular momentum (E-Lz). However, our galaxy also contains a non-axisymmetric stellar bar, which traps stars in resonant orbits, leading to substructures in phase-space. Using a high-resolution magneto-hydrodynamic cosmological zoom-in simulation of a Milky Way analogue, we explore the connection between the bar and the accreted stellar halo. We find that the bar induces prominent substructures, or "ridges", in E-Lz, caused by the resonances. The most pronounced of these is caused by the corotation and the retrograde 1:1 resonances, with weaker ridges visible due to the prograde 1:1 and outer Lindblad resonance. The ridges are present across much of the stellar halo, with variations in radius due to the morphology of different orbital families. We explore the scattering of orbits at the resonances, finding that stars trapped at the 1:1 retrograde resonance become more circularised and have more negative angular momentum. Additionally, stars can move between the corotation and retrograde 1:1 families, thus alternating between prograde and retrograde motion. Due to these scatterings and the pre-existing metallicity gradients in the accreted population, the bar-induced substructures have distinct metallicities compared to stars in the surrounding phase-space. Our results suggest the need for caution when searching the Milky Way stellar halo for accreted substructures in both integral of motions and chemical spaces, since these can be induced by internal perturbations.

Studies of galactic bars have primarily focused on stellar bars, since they can be directly observed through ultraviolet to infrared wavebands. Cosmological as well as idealised simulations reveal that the dark matter (DM) haloes interact with baryonic matter, primarily the stellar bars, dynamically by means of the exchange of angular momentum. In these simulations, the spherical DM halo dynamically responds to interaction with the stellar bar by reshaping its orbital structure in the proximity of the stellar bar, forming a bar-like configuration, called as the Dark Matter (DM) bar. Using N-body simulations of Milky Way analogs we discuss the role of inner halo angular momentum, measured as halo spin parameter {\lambda} of the dark matter halo, on formation and evolutionary characteristics of the DM bars. Our systematic study involves haloes with initial spin configurations ranging from {\lambda} = 0 to 0.1. The result conveys that DM bar formation and its characteristics are extensively dependent on the initial spin parameter {\lambda} of the DM halo. We demonstrate that the strength of the dark matter bar gradually increases with an increase in halo spin in long-term evolution, with a significant impact of stellar bar buckling on dark matter bar strength. The evolutionary characteristics of the DM bar are strongly influenced by the initial spin of the host halo.

We present a spectroscopic survey of field galaxies and lensed sources in the vicinity of the strong lensing galaxy cluster known as the Carousel lens at z=0.49. Using both Gemini/GMOS slitmask spectra and deep VLT/MUSE observations, we bring the total number of lensed sources up to 13, including three which were not previously known from imaging observations but are apparent in the MUSE data as emission-line sources. Of these sources, 10 have confident redshifts, and an additional 2 have tentative redshifts from likely Ly$\alpha$ emission (including seven new redshifts determined here adding to those presented previously in Sheu et al. (2024)). The lensed sources span a redshift range from z=0.96 to 4.09 with most of them showing 3-5 images, including four sources displaying central or radial images. In total, we identify 43 images of these 13 sources. This lens system is remarkably symmetric and well-modeled by a simpler lens model than typical cluster lenses, and the large number of sources and their large range of redshifts make this cluster ideal for constraining cosmological parameters such as $w$ and $\Omega_m$ as well as the cluster density profile. Additionally, we present a catalog of 57 unlensed field galaxies with confident redshifts, of which 49 are associated with the cluster. We measure a cluster velocity dispersion of about 1100 km s$^{-1}$ from which we estimate a halo mass $M_{200c} \approx 1.2 \times 10^{15} M_\odot$.

Galaxy clusters serve as a unique and valuable laboratory for probing cosmological models and understanding astrophysics at the high-mass limit of structure formation. Clusters that are dynamically relaxed are especially useful targets of study because of their morphological and dynamical simplicity. However, at redshifts z > 1, very few such clusters have been identified. We present results from new Chandra observations of the cluster SPT-CL J2215-3537 (hereafter SPT J2215), at z = 1.16, the second most distant relaxed, cool-core cluster identified to date. We place constraints on the cluster's total mass profile and investigate its thermodynamic profiles, scaling relations (gas mass, average temperature, and X-ray luminosity), and metal enrichment, resolving the cool core and providing essential context for the massive starburst seen in its central galaxy. We contextualize the thermodynamic and cosmological properties of the cluster within a sample of well-studied, lower-redshift relaxed systems. In this way, SPT J2215 serves as a powerful high-redshift benchmark for understanding the formation of cool cores and the evolution of massive clusters of galaxies.

Accurate estimation of meteoroid bulk density is crucial for assessing spacecraft impact hazards from sub-millimeter to millimeter-sized meteoroids. Previous studies often used manual tuning or optimization methods to fit ablation and fragmentation models to optical meteor data, but subjective choices made physical properties and uncertainties difficult to compare. We develop a global, statistically robust method that uses Dynamic Nested Sampling to fit an erosion-fragmentation model to meteor light curves and deceleration measured by the Canadian Automated Meteor Observatory (CAMO) mirror tracking system and Electron-Multiplied CCD (EMCCD) cameras. Applied to 15 shower meteors, the method returns posterior distributions and Bayesian evidences for single- and double-fragmentation scenarios. Tests on four synthetic cases recover the known inputs, with best-guess solutions matching the true parameters. For 9 Orionids and 6 Alpha Capricornids with masses 1e-6 to 1e-5 kg, the median bulk density is 159 (+558/-57) kg/m3 for Orionids and 333 (+1089/-114) kg/m3 for Alpha Capricornids. Orionids are consistent with low-density cometary material, while Alpha Capricornids are systematically denser and show a second density cluster near 1300 kg/m3, consistent with higher-density asteroidal material. This framework enables automated, statistically rigorous characterization of meteoroid properties and will be extended to larger samples of shower and sporadic meteors across orbital classes.

The Habitable Worlds Observatory (HWO) will be a large ultraviolet/optical/near-infrared space telescope operating at the Sun-Earth Lagrange point L2. HWO was highly recommended by the National Academies` 2020 decadal survey and will be the first telescope designed specifically to search for life on planets orbiting other stars. HWO will also be able to perform a host of other transformational astrophysics, including cosmology, galaxy evolution, solar system science, and beyond. The development of the telescope and instrument suite is an iterative process. Example observatory architectures, called exploratory analytic cases (EACs) by the HWO Technology Maturation Project Office (TMPO), are modeled end-to-end to explore the engineering and science trade space. Recently, an ultraviolet Integral Field Spectrograph (UV IFS) was added to HWO's instrument suite for the EACs 4 and 5. To explore the science and engineering trade space for this specific instrument, we developed a high-fidelity UV IFS simulation tool, PyISH. The UV IFS simulation tool is designed to be used by scientists to model specific science cases as seen by a UV IFS on HWO, as well as engineers to explore the trade space when developing potential instrument architectures. The modular components, deliverables, and an example of the tool simulating a specific science case proposed for HWO are described in this paper.

Astrometry from the Gaia satellite and from the long-term combination of Hipparcos and Gaia are now sensitive to sky-plane accelerations as low as $\approx$1 m/s/yr. This paper quantifies and explores an important caveat: apparent nonlinear motion due to a star's nonzero radial velocity can be indistinguishable from real astrometric acceleration. This nonlinear motion is parallel to the proper motion, so it can be both quantified and avoided by projecting apparent astrometric accelerations into components parallel and perpendicular to the proper motion. We illustrate this distinction for a sample of very nearby, fast-moving stars from the Hipparcos-Gaia Catalog of Accelerations (HGCA). We then generalize the effect of stellar radial velocity and projections of the astrometric acceleration to binary stars in which we observe the acceleration of both components. Finally, we demonstrate that the proper motion differences in the HGCA are statistically well-behaved even for the nearest and fastest-moving stars, at least in the component perpendicular to the proper motion. This distinction -- between astrometric acceleration parallel and perpendicular to proper motion -- could have important consequences for future missions reaching extreme astrometric sensitivities around nearby stars.

The dominant radiation mechanism that powers the prompt $\gamma$-ray emission in gamma-ray bursts (GRBs) remains poorly understood. High quality, time- and energy-resolved linear polarization measurements of prompt $\gamma$-ray photons can distinguish between synchrotron and inverse-Compton processes and provide crucial constraints on the outflow properties. This will be achieved by POLAR-2 that is proposed as a dedicated GRB polarimeter and successor to POLAR. The High-energy Polarimetry Detector (HPD) is one of the three instruments of POLAR-2 that features significantly improved sensitivity in the $(40-1000)$\,keV energy range and a detection area four times larger than that of POLAR. Here we demonstrate the capabilities of the HPD to constrain key physical model parameters by creating and fitting to synthetic sources using a time-resolved spectro-polarimetric theoretical model of prompt GRB emission. The time-resolved spectral and polarization fits are performed using a novel technique featuring maximum likelihood over an unbinned (in time and energy) list of detected events. The constrained model parameters directly relate to the underlying source physics that would reveal an accelerating, coasting or decelerating emission region. For a pulse fluence of $\mathcal{F}=10^{-5}\mathcal{F}_{-5}\,{\rm erg\,cm^{-2}}$ we can constrain the time-integrated polarization degree to an absolute accuracy ($1\,\sigma$) of about $2.5\mathcal{F}_{-5}^{\,-1/2}$ per cent, as long as source photons dominate over the background. In bright GRBs, such unprecedented accuracy at these energies will allow to distinguish between different models for the prompt GRB emission mechanism and constrain the magnetic field geometry, jet angular structure and outflow composition.

Tidal disruption events (TDEs) represent a truly unique, and potentially very powerful, probe of the quiescent supermassive black hole (SMBH) population. Given current observational survey capabilities the vast majority of the TDEs discovered in the next decade will be observed only across optical-UV wavelengths. A set of questions of broad scientific interest relating to SMBH demographics and SMBH-galaxy correlations could in principal be answered by using TDE emission as an efficient means to constrain SMBH masses. In this paper we argue for using well-understood elements of TDE emission (the thermal X-ray continuum and late-time UV plateau) to derive empirical relationships between the more poorly understood early optical/UV flare and the black hole mass, before using these empirical relationships to measure TDE black hole masses simply and rapidly. We provide a publicly available code TDEFLARE which does this, showing (i) it produces results consistent with disk codes containing far more physics, (ii) it reproduces galactic scaling relationships at high ($>5\sigma$) significance, (iii) it produces reliable mass estimates for both partial and full disruptions, and (iv) it does not require late time data to derive mass constraints. We provide 89 TDE black hole mass constraints, derive the intrinsic black hole mass function implied by the current TDE population, and discuss the Malmquist-Hills bias, an important confounding factor in TDE science.

I examine a recently proposed failed-supernova scenario for the fading of the yellow supergiant event M31-2014-DS1, and find that it requires unlikely fine-tuned parameters to work, if at all. In the failed-supernova scenario, most of the yellow supergiant collapsed to form a black hole. Due to the energy carried by neutrinos from the cooling, collapsing core, gravity decreases, leading to the ejection of a small fraction of the outer envelope, some of which remains bound. The fallback accreted gas possesses large angular-momentum fluctuations due to the pre-collapse envelope convection. The fallback material forms intermittent accretion disks around the black hole that launch jets (or disk wind), which unbind most of the bound material. The failed-supernova scenario for M31-2014-DS1 requires that only <1% of the bound material be accreted by the black hole, but the jets do not shut down the backflow for over 10 years. I find this fine-tuned requirement unlikely. I also find that, due to the rapid radiative cooling of the outflow interaction zone with the outer gas, the expected radiation is about an order of magnitude or more above the observed value. These, as well as earlier challenges raised against the failed-supernova scenario, make the alternative type II intermediate-luminosity optical transient scenario, in which fading is due to dust ejection in a violent binary interaction, more likely. The fading event M31-2014-DS1 does not support the failed-supernova scenario predicted by the neutrino-driven explosion mechanism of core-collapse supernovae.

Theoretical models predict that the Galaxy hosts $10^8$-$10^9$ black holes formed from the complete gravitational collapse of heavy stars and that most of these black holes are isolated, without any companion. Within 15 pc of the Solar System ($\sim 50$ ly), there may be a few black holes. If located inside one of the Local Interstellar Clouds - which occupy 5-20% of this local volume - an isolated black hole could produce detectable electromagnetic emission via accretion from the interstellar medium, given the capabilities of current or near-future observatories. However, precise predictions remain challenging due to large uncertainties in the expected accretion spectra. Outside these clouds, the accretion rate would be too low in any standard model to yield a detectable electromagnetic signal. While astrometric detection via gravitational perturbation of nearby stars is conceivable, the local stellar density is too low for this method to be realistically successful. We have searched the Gaia DR3 catalog for candidate isolated black holes accreting from the interstellar medium and identified five sources. All candidates lie close to the Galactic plane, making them likely spurious astrometric solutions, for instance caused by unmodelled background sources (crowding) and/or unmodelled binarity; nevertheless, they cannot be definitively ruled out without follow-up observations.

Dipole mixed modes observed in the oscillation pattern of red giant stars probe the radiative regions in the stellar core. Oscillation spectra of helium-core-burning stars sometimes show extra peaks that remain unexplained by the dipole mixed-mode pattern expected from the coupling of a radiative cavity in the stellar core and a pressure cavity in the stellar envelope. We use the asymptotic expansion developed for a multi-cavity star in order to characterize these extra peaks. The analytical resonance condition of the multi-cavity gravito-acoustic modes, with two inner gravity cavities and an outer pressure cavity, helps us explain that the apparent extra peaks are dipole mixed modes that follow the 3-cavity oscillation pattern. The derivation of the two asymptotic period spacings associated with the two distinct regions in the radiative core provides an estimate of the full radiative cavity. Our results provide new constraints for analysing the overshoot or mixing in the core of helium-core-burning stars. An important structure discontinuity inside the radiative core may explain the larger than expected observed period spacings.

High-contrast imaging systems using active control with adaptive optics (AO) are often limited by non-common path (NCP) aberrations that are seen only at the final science image. AO systems employing focal-plane wavefront sensors (FP-WFSs) are able to simultaneously correct NCP aberrations and measure science images, but they typically require a second stage of control that adds system cost and complexity. We present control algorithms to augment AO systems with FP-WFSs within their existing control setup. We demonstrate inter-arm NCP aberration transfer can be mitigated through temporal filtering, present frequency- and time-domain validation of controller stability and performance, and discuss the optimality of the chosen controllers. This work will enable the development, testing, and installation of FP-WFS technologies for direct imaging of exoplanets.

The paper presents the results of long-term homogeneous spectroscopic studies of the Herbig Ae/Be star HD 141569A obtained in the optical range. We detect spectral variability on timescales of months to years, including changes in the spectrophotometric parameters of the Halpha emission line, as well as other hydrogen absorption lines. Based on the derived physical parameters and age, the star appears to be in a transitional evolutionary stage from a protoplanetary disk to a debris disk. We determine that the star axial rotation period is approximately 12 hours, and its equatorial velocity is significantly below the critical rotation velocity. The observed spectral variability is likely caused by partial obscuration of the central star radiation by extended fragments of the disrupted disk.

IGR J17091-3624 is a distinctive black hole X-ray binary exhibiting exotic variability, including complex "heartbeat" oscillations in its X-ray light curves, similar to those observed in GRS 1915+105, a system renowned for its structured, rapid X-ray variability but heavily obscured at optical wavelengths. In contrast, IGR J17091-3624 is less obscured, making it a more accessible target for optical investigations. Due to its weak radio emission, optical and infrared data are essential to probe the jet and outer disc behavior of IGR J17091-3624. This study presents the first long-term optical monitoring of IGR J17091-3624, using data from the Las Cumbres Observatory (LCO) over its 2011, 2016, and 2022 outbursts. We combine these observations with quasi-simultaneous X-ray data from Swift/XRT, RXTE, and NICER, employing light curve and variability analysis, spectral energy distributions, color-magnitude diagrams, and optical/X-ray correlations to investigate optical emission mechanisms. We find that the optical and X-ray fluxes are significantly correlated, following a power-law relation with the index 0.40\pm0.04, suggesting that the optical emission in IGR J17091-3624 is dominated by an X-ray-irradiated accretion disk. Based on optical spectral slope constraints, we estimate the extinction toward IGR J17091-3624 A_V = 4.3 to 6.6 mag. The global optical/X-ray correlation suggests a distance estimate of 8-17 kpc, in line with previous findings. High-cadence optical observations show tentative evidence of optical oscillations that may arise from reprocessed X-ray modulations, although confirming this will require higher time-resolution optical data.

Understanding the connection between active galactic nuclei and star-formation (the AGN-SF connection) is one of the longest standing problems in modern astrophysics. In the age of large Integral Field Unit (IFU) surveys, studies of the AGN-SF connection greatly benefit from spatially resolving AGN and SF contributions to study the two processes independently. Using IFU data for 54 local active galaxies from the S7 sample, we present a new method to separate emission from AGN activity and SF using mixing sequences observed in the [NII]$\lambda 6584$/H$\alpha$ vs. [OIII]$\lambda 5007$/H$\beta$ Baldwin-Phillips-Terlevich (BPT) diagram. We use the new decomposition method to calculate the H$\alpha$ star-formation rate and AGN [OIII] luminosity for the galaxies. Our new method is robust to outliers in the line-ratio distribution and can be applied to large galaxy samples with little manual intervention. We infer star-formation histories (SFHs) using pPXF, conducting detailed recovery tests to determine the quantities that can be considered robust. We test the correlation between the AGN Eddington ratio, using the proxy L[OIII]/$\sigma_*^4$, and star-formation properties. We find a moderately strong correlation between the Eddington ratio and the star-formation rate (SFR). We also observe marginally significant correlations between the AGN Eddington ratio and the light-weighted stellar age under 100 Myr. Our results point to higher AGN accretion being associated with young nuclear star formation under 100 Myr, consistent with timelines presented in previous studies. The correlations found in this paper are relatively weak; extending our methods to larger samples, including radio-quiet galaxies, will help better constrain the physical mechanisms and timescales of the AGN-SF connection.

We introduce IRMaGiC, an algorithm built based on RedMaGiC desgined to enhance the selection of Luminous Red Galaxies (LRGs) across the redshift range $1 \leq z \leq 2$. We show that this method extends the capabilities of the redMaGiC algorithm by applying it to simulated photometric data from the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) and the Nancy Grace Roman Space Telescope's High Latitude Wide Area Survey (HLWAS). By integrating infrared band coverage from Roman HLWAS with LSST's optical bands, IRMaGiC enables red-sequence calibration at higher redshifts. We demonstrate that IRMaGiC reduces scatter and bias in photometric redshift estimates for LRGs at higher redshift, providing more accurate redshift assessments compared to existing methods. Our findings suggest that incorporating infrared data can considerably improve the selection and redshift estimation of LRGs at higher redshift, offering substantial benefits for future cosmological surveys.

Using the Dark Energy Spectroscopic Instrument Milky Way Survey (DESI MWS), we examine the 6D space of the anticenter region of the stellar disk (150$^\circ$ $<$ Galactic longitude $<$ 220$^\circ$) using 61,883 main sequence turn-off stars. We focus on two well-known stellar overdensities in the anticenter, the Monoceros Ring (MRi) and Anticenter Stream (ACS). We find that the MRi overdensity has kinematics consistent with a tidally induced spiral arm, a type of dynamic spiral arm created by an interaction with a satellite galaxy, most likely the Sagittarius Dwarf Spheroidal galaxy (Sgr). We use the kinematics of the MRi to calculate the two most recent passage times of Sgr are 0.25 $\pm$ 0.09 Gyrs and 1.10 $\pm$ 0.23 Gyrs from the present day. We validate that the ACS is kinematically decoupled from the MRi because they are moving in opposite radial and vertical directions. We find that the kinematics associated with the ACS are not confined to our defined overdensity. The features we see in the ACS region are likely part of a broader distribution of stars with the same kinematic signature as detected in other places, like the vertical wave in the outer disk and phase spiral.

Convection is ubiquitous in stellar and planetary interiors where it likely plays an integral role in the generation of magnetic fields. As the interiors of these objects remain hidden from direct observation, numerical models of convection are an important tool in the study of astrophysical dynamos. In such models, unrealistic large values of the viscous ($\nu$) and thermal ($\kappa$) diffusivity are routinely used as an ad-hoc representation of the effects of subgrid scale turbulence which is otherwise too small-scale to resolve numerically. However, the functional forms of these diffusion coefficients can vary greatly between studies, complicating efforts to compare between results and against observations. We explore this issue by considering a series of non-rotating, non-magnetic, solar-like convection models with varying radial functions for the diffusivities and differing boundary conditions. We find that the bulk kinetic energy scales similarly regardless of the diffusivity parameterization. This scaling is consistent with a free-fall scaling, wherein viscosity plays a subdominant role in the force balance. We do not, however, observe such diffusion-free behavior in the convective heat transport. Our results also indicate that the functional form adopted for the diffusion coefficients can impact the distribution of turbulence within the convective shell. These results suggest that some care should be taken when comparing solar convection models directly against helioseismic observations.

As radio emission from normal galaxies is a dust-free tracer of star formation, tracing the star formation history of the Universe is a key goal of the SKA and ngVLA. In order to investigate how well radio luminosity traces star formation rate (SFR) in the early Universe, we have examined the radio properties of a JWST Paschen-alpha sample of galaxies at 1.0<=z<=1.8. In the GOODS-S field, we cross-matched a sample of 506 FRESCO Paschen-alpha emitters with the 1.23 GHz radio continuum data from the MeerKAT MIGHTEE survey finding 47 detections. After filtering for AGN (via X-ray detections, hot mid-infrared dust and extended radio emission), as well as blended sources, we obtained a sample of SFGs comprising: 11 cataloged radio detections, 18 non-cataloged detections (at ~3-5sigma) and 298 undetected sources. Stacking the 298 undetected sources we obtain a 3.3sigma detection in the radio. This sample, along with a local sample of Paschen-alpha emitters, lies along previous radio luminosity/SFR relations from local (z<0.2) to high redshift (z~1). Fitting the FRESCO data at 1.0<=z<=1.8 we find log(L_1.4GHz) = (1.31+/-0.17) x log(SFR_Pa-alpha) + (21.36+/-0.17) which is consistent with other literature relations. We can explain some of the observed scatter in the L_1.4GHz/SFR_Pa-alpha correlation by a toy model in which the synchrotron emission is a delayed/averaged tracer of the instantaneous Paschen-alpha SFR by ~10/75 Myr.

We report a radio SETI search for periodic, kHz-wide signals from five of the nearest stars observable with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using the 19-beam L-band receiver (1.05-1.45 GHz), we obtained 1200 s tracking observations of Groombridge 34 A/B, Ross 248, 61 Cygni B, and Ross 128. Dynamic spectra from all beams and both linear polarisations were searched channel by channel with a fast-folding algorithm sensitive to periods between 1.1 and 300 s. A multi-layer RFI-mitigation pipeline exploits multi-beam occupancy, cross-target bad-channel statistics, XX/YY polarisation coincidence, broad frequency masks, and narrow site-specific RFI exclusion zones, followed by clustering in period-frequency space. The pipeline is validated on FAST observations of PSR B0329+54, where we recover the known 0.714 s spin period and harmonic structure in the expected beam. For the stellar sample, successive cuts reduce the raw FFA hit lists (> 10^6 hits per target) to a small number of cluster-level candidates, all of which exhibit clear radio-frequency interference signatures in phase-time and phase-frequency diagnostics. We therefore report no convincing detections of periodic transmitters in our searched parameter space. Using the radiometer equation with our adopted detection threshold (S/N = 25) and assuming a duty cycle delta = 0.1, we obtain upper limits of approximately (7-9) x 10^9 W on the isotropic-equivalent EIRP of kHz-wide periodic beacons at these stars, among the most stringent constraints to date on periodic radio emission from nearby stellar systems.

We present a new framework for multi-line analysis that combines kernel principal component analysis (Kernel PCA), an unsupervised machine-learning method, and Kernel SHapley Additive exPlanations (Kernel SHAP), an explainable artificial intelligence (XAI) technique. To enable a comparison with PCA-based studies, which have been widely used in multi-line analyses, we apply our framework to integrated intensity maps of 13 molecular lines from Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 archival data of the nearby galaxy NGC 1068. Previous PCA-based studies of NGC 1068 reported that physically meaningful structures are mainly captured up to the second component. In contrast, our framework can interpret physically meaningful features up to the fourth component. Furthermore, by comparing the results obtained from our framework with molecular column densities derived from local thermodynamical equilibrium (LTE) analysis, we suggest that the abundance of HCO+ is relatively enhanced in the molecular outflow region extending to a radius of about 400 pc from the galactic center, likely due to the effects of ultraviolet radiation and highly dense gas. These results show that our framework can provide data-driven insights into physical and chemical features that have not been clearly identified in previous studies. It also provides an efficient tool for interpreting the rapidly increasing amount of multi-line observational data.

Determining how galaxies accumulate stellar mass is paramount to understanding the Universe. Two primary mechanisms drive this process: star-formation (SF) & mergers. Our understanding of star formation, and to some degree the processes that influence the baryon cycle (environment, gas supply, feedback, etc), are either relatively well constrained or will develop significantly over the coming decades via upcoming facilities (i.e. through their imprint on galaxy properties measured with deep multi-wavelength and spectroscopic data). However, the same can not be said for mergers. It is telling that we indirectly know hierarchical assembly through mergers is one of the most crucial processes that shape our Universe, but the robust observational measurement of mergers is almost non-existent outside of the local Universe - let alone how these mergers impact galaxy properties. This is not likely to significantly change in the coming decades as existing or approved facilities/surveys are inadequate in charactering mergers in the distant Universe. Motivated by this, we discuss an ambitious study to first explore mergers, and then the co-dependent astrophysical process that govern the accumulation of stellar mass over the last ~10billion years, and highlight the essential need for a 10m+ class multi-object spectroscopic facility.

Double source plane strong lensing (DSPL) systems offer a robust, independent probe of cosmological parameters. The Chinese Space Station Telescope (CSST) is expected to discover hundreds of DSPLs, yet the survey modes and system configurations that best enable cosmological inference remain uncertain. To investigate the impact of varying signal-to-noise ratios (SNR) and Einstein radius ratios of DSPLs (denoted as $\beta^{-1}$ parameters) on cosmographic inference under different CSST survey modes (Wide Field (WF), Deep Field (DF), and Ultra-Deep Field (UDF)), we simulate and model mock lenses with Singular Isothermal Ellipsoid (SIE) mass profiles and Sérsic sources whose image properties are tailored to CSST specifications. Assuming a flat $w$CDM universe with fiducial values $\Omega_{\rm m} = 0.30966$ and $w = -1$, and uniform priors of $\Omega_{\rm m} \in [0, 1]$ and $w \in [-2, -1/3$), we find that the constraining power on cosmological parameters for a given DSPL system increases significantly with survey depth. For a representative DSPL system with two prominent arcs and a moderate $\beta^{-1}=1.17$, the constraints on ($w, \Omega_{\rm m}$) improve from ($-1.28_{-1.00}^{+0.64}, 0.50_{-0.32}^{+0.28}$) in the WF to ($-1.59_{-0.32}^{+0.63}, 0.42_{-0.06}^{+0.15}$) in the UDF. Furthermore, we find that systems with smaller $\beta$ values yield tighter cosmographic constraints. We conclude that DSPL systems identified in UDF observations, particularly those with small $\beta$, are the most promising candidates for early-stage cosmological studies with CSST.

The formation mechanisms of intensely starbursting galaxies at high redshift remain unknown. One possible mechanism for triggering these starbursts is mergers and interactions, but detecting these at high redshift remains a challenge. Observations of high-redshift gravitationally lensed galaxies enable studies of the interstellar medium and environment of these extreme starbursts in detail. We used high angular resolution observations of dust continuum, CO(6-5), H2O(211-202), and H2O+(202-111) emission to constrain the ongoing processes in the z = 3.63 gravitationally lensed submillimeter galaxy H-ATLAS J083051.0+013224 (G09v1.97). We used PyAutoLens to create a de-magnified source plane CO(6-5) emission line cube and performed kinematic modeling using 3DBarolo. Additionally, we investigated the properties of the continuum and molecular line emission in the source plane. We find that the regions of CO(6-5) and H2O(211-202) emission match closely in the source plane but that the dust continuum emission is more compact. We find that our lens modeling results do not require more than one source, contrary to what has been found in previous studies. Instead, we find that G09v1.97 resembles a rotating disk with Vmax/sigma = 2.8 +/- 0.4 with evidence for residual emission indicative of non-circular motions such as outflows, tidal tails, or an additional background galaxy. We suggest that the origin of the non-circular motions may be associated with a bi-conical outflow, a tidal tail from an interaction, or indicate the possible presence of an additional galaxy. We calculate the dynamical mass, gas mass, star-formation rate, and depletion time for G09v1.97 and find a high star-formation rate and low gas depletion time. In combination, this suggests that G09v1.97 has recently undergone an interaction, triggering intense star formation, and is in the process of settling into a disk.

I derive the statistical relationship between a radial velocity or astrometric acceleration (a trend), a companion's mass, and the projected separation of the companion. These relationships, expressed as probability density functions, are analytic and independent of all Keplerian orbital elements so long as orbits are randomly oriented in space. I also derive a closed-form expression for the probability distribution of the ratio of the projected separation to the semimajor axis at fixed eccentricity. This expression can be numerically integrated over eccentricity for an arbitrary distribution of eccentricities. I verify my results with empirical comparisons to equivalent but more complex expressions in the literature based on the equations of Keplerian orbits. The closed-formed expressions derived here would be especially useful for any calculation that requires derivatives, e.g., Hamiltonian Monte Carlo. I also provide a Jupyter notebook including all figures and calculations.

We present a unified framework that combines early- and late-Universe observations to constrain three functional realizations of f(T,B) gravity: the linear, quadratic, and general power-law models. First, constraints on deviations from the standard weak interaction freeze-out temperature are derived using the most recent measurements of the primordial helium-4 mass fraction. Second, we perform a joint analysis incorporating five priors: Type Ia supernovae, baryon acoustic oscillations, cosmic chronometers, Big Bang Nucleosynthesis, and Cosmic Microwave Background in order to place bounds on the model parameters. The joint likelihood analysis significantly tightens the constraints compared to individual datasets. Third, we test the null, strong, and dominant energy conditions to evaluate the physical viability of the best-fit solutions across the cosmic redshift range. Our results show that all three f(T,B) models are consistent with current observations and exhibit stable behavior under the energy-condition criteria, supporting torsion-boundary modified gravity as a robust and viable alternative to General Relativity.

The results of a study of the cosmic ray composition in individual events in the energy range (2-12.5) EeV using the muon correlation method is presented. The considered sample included showers with zenith angles less than 60 degrees recorded in the period 1974-2018. The existence of four separate groups of primary particles with different origins is confirmed. The obtained results have potential importance for understanding the composition of cosmic rays in the specified primary energy range.

Accretion onto black holes often leads to the launch of outflows that significantly influence their surrounding environments. The two primary forms of these outflows are X-ray disk winds-hot, ionized gases ejected from the accretion disk-and relativistic jets, which are collimated streams of particles often expelled along the rotational axis of the black hole. While previous studies have revealed a general association between spectral states and different types of outflows, the physical mechanisms governing wind and jet formation remain debated. Here, using coordinated NICER and MeerKAT observations of the recurrent black hole X-ray binary 4U 1630-472, we identify a clear anti-correlation between X-ray disk winds and jets: during three recent outbursts, only one type of outflow is detected at a time. Notably, this apparent exclusivity occurs even as the overall accretion luminosity remains within the range expected for a standard thin disk, characteristic of the canonical soft state. These results suggest a competition between outflow channels that may depend on how the accretion energy is partitioned between the disk and the corona. Our findings provide new observational constraints on jet and wind formation in X-ray binaries and offer a fresh perspective on the interplay between different modes of accretion-driven feedback.

Changing-look active galactic nuclei (CLAGNs) represent a rare class of AGNs that undergo transitions from type 1 (characterized by the presence of broad emission lines in their spectra) to type 2 (absence of broad emission lines) or vice versa, over timescales ranging from months to years. Since normal type 1 and type 2 AGNs are known to show different polarization properties, detailed investigations of the CLAGN polarization can shed light on the underlying mechanisms responsible for the changing-look phenomenon. We present new (spectro)polarimetric observations of two changing-look AGNs located in the core of the inclined spiral galaxies NGC 1365 and NGC 2992. Both AGNs are radio emitters, thereby enabling a comparison of their polarization to the radio jet axis, which defines the accretion disk geometry. In the case of NGC 1365, the AGN shows polarization characteristics consistent with those observed in type 1 Seyferts, in particular polarization parallel to the radio jet. This intrinsic polarization is modified by the wavelength-dependent dichroic extinction that occurs in the galaxy bar and that rotates the polarization angle at the shortest wavelengths. NGC 2992, on the other hand, is so inclined that dichroic dust extinction in the disk completely dominates the polarization of the AGN, thus overwhelming any polarization due to scattering. Consequently, the polarization properties remain essentially constant between the different AGN states, and the faint broad lines observed in the polarized flux are most likely not scattered light. Differential dilution between the continuum and the narrow-line polarizations can explain the unusually high polarization measured in the emission lines.

G284.3$-$1.8 is a supernova remnant with a radio shell and thermal X-ray emission. Located near its center is the gamma-ray binary 1FGL J1018.6$-$5856, although the physical association between the two systems is not clear yet. Our X-ray spectroscopy with Suzaku reveals that G284.3$-$1.8 and 1FGL J1018.6$-$5856 have compatible absorption column densities of $N_\mathrm{H} = 6\textrm{--}7 \times 10^{21}~\mathrm{cm}^{-2}$, indicating that the two systems have similar distances. The actual distance is determined as $3~\mathrm{kpc}$ using $\mathrm{^{12}CO}$ ($J=1\textrm{--}0$) data obtained with NANTEN. The X-ray spectrum of G284.3$-$1.8 shows a strong K-shell emission line of Mg, confirming that the earlier claim that the SNR is one of the few Mg-rich SNRs. Comparing recent stellar models taking into account the "shell merger" processes, we find that the obtained Mg-to-Ne mass ratio of $M_\mathrm{Mg}/M_\mathrm{Ne} = 0.73^{+0.07}_{-0.03}$ and Si-to-Mg mass ratio of $M_\mathrm{Si}/M_\mathrm{Mg} = 0.44\pm0.03$ suggest a supernova explosion that would have left a neutron star. The characteristics of 1FGL J1018.6$-$5856, on the other hand, are better explained with a model in which its compact object is neutron star. The present results, therefore, would suggest a possible scenario where G284.3$-$1.8 and 1FGL J1018.6$-$5856 are both remnants of a common supernova explosion although further observational tests are necessary.

We present a detailed photometric and spectroscopic analysis of the Type IIP supernova SN~2023zcu, which exploded in the galaxy NGC~2139 (redshift $z$ = 0.006). SN~2023zcu exhibits a well-sampled light curve covering the rise, plateau, and nebular phases. It has an optically thick phase of $100.6 \pm 0.6$ d with a magnitude drop of $\sim$1.7 mag in the {\em V} band during the transition between the plateau and the nebular phases. Weak emission features in the early-time spectra indicate a low-level interaction between circumstellar material (CSM) and the SN ejecta. The spectral evolution is well sampled and exhibits a prominent P-Cygni profile of H$\alpha$, a defining characteristic of Type IIP SNe. Signatures of metal-line formation (e.g., \ion{Fe}{2}, \ion{Ca}{2} near-infrared triplet) are also evident in the spectra as the SN evolves. Spectral modeling with the radiative-transfer code \texttt{TARDIS} during the early photospheric phase (8.7--35.5 d since explosion) yields photospheric temperatures decreasing from $\sim$9,000 to $\sim$6,000 K and expansion velocities declining from $\sim$10,000 to $\sim$5,400 km s$^{-1}$. A tailored expanding photosphere method (EPM) fit based on the \texttt{TARDIS} models provides a distance estimate of $27.8 \pm 2.0$ Mpc. Nebular-phase spectra and bolometric light-curve modeling suggest a progenitor mass in the range 12--15 M$_\odot$. This thorough analysis helps to constrain progenitor properties and explosion parameters, thereby strengthening our understanding of Type IIP SNe.

Returning radiation is thought to play a key role in disk illumination of black hole X-ray binaries in the high-soft state, yet it has not been fully incorporated into XSPEC reflection models. We present a new table model for reflection spectroscopy that, for the first time, self-consistently accounts for the returning radiation. To isolate this effect, we adopt the standard disk-corona configuration but disable the corona, allowing the reflection spectrum to be produced solely by self-irradiation of the disk. Applying our model to the black hole X-ray binary 4U 1630$-$47, we report a rapidly spinning black hole ($a_* \sim 0.99$), a disk inclination of $i \sim 53^\circ$, a mass accretion rate of $\dot{M}_{\rm BH} \sim 15\% \, {\rm \dot{M}_{Edd}}$, and an electron density of $n_{\rm e} \sim 10^{21} \,\mathrm{cm^{-3}}$ to reproduce the observed reflection features. The model also yields a source distance of $D\sim 8.2 \, {\rm kpc}$, slightly below the commonly adopted value of $10 \, {\rm kpc}$ in the literature. Compared to the widely used relxillNS, our model naturally produces a harder high-energy reflection spectrum, fitting the data without invoking a Comptonized component.

The recent detection of a common-spectrum stochastic signal by multiple pulsar timing array (PTA) collaborations has provided tentative evidence for a nanohertz (nHz) stochastic gravitational-wave background (SGWB). This signal can be widely interpreted as originating from a cosmic population of inspiraling supermassive black hole binaries (SMBHBs). Current PTA analyses primarily constrain the SGWB power spectrum and its auto-angular power spectrum. However, the supermassive black holes will produce an underlying correlation with the large-scale structure of the Universe, which can help in understanding the formation and evolution of the binaries. In this work, we develop a new analysis pipeline PyGxGW-PTA for studying the cross-correlation of nHz GW signal with galaxy surveys ($C^{\rm g\, GW}_\ell$) and obtain the first constraint on the SGWB and galaxy distribution cross-correlation using the NANOGrav 15-year dataset in combination with the DESI galaxy catalog. We find no statistically significant correlation between the SGWB and the large-scale distribution of DESI galaxies and using an optimal estimator we put an upper bound on $C^{\rm g\, GW}_{\ell=8} < 0.0083$ at $95\%$ C.I. This yields the first observational upper limit on the spatial correlation between the nHz SGWB and the large-scale structure of the Universe, establishing the observational groundwork for future multi-tracer analyses that will combine PTA data with next-generation galaxy surveys to unveil the SMBHB-galaxy correlation.

The Transiting Exoplanet Survey Satellite (TESS) Full-Frame Images (FFIs) provide photometric time series for millions of stars, enabling transit searches beyond the limited set of pre-selected 2-minute targets. However, FFIs present additional challenges for transit identification and vetting. In this work, we apply ExoMiner++ 2.0, an adaptation of the ExoMiner++ framework originally developed for TESS 2-minute data, to FFI light curves. The model is used to perform large-scale planet versus non-planet classification of Threshold Crossing Events across the sectors analyzed in this study. We construct a uniform vetting catalog of all evaluated signals and assess model performance under different observing conditions. We find that ExoMiner++ 2.0 generalizes effectively to the FFI domain, providing robust discrimination between planetary signals, astrophysical false positives, and instrumental artifacts despite the limitations inherent to longer cadence data. This work extends the applicability of ExoMiner++ to the full TESS dataset and supports future population studies and follow-up prioritization.

Recently, Goldman (2024) obtained evidence for a large scale compressible, Burgers turbulence in the ism of a gravitationally lensed, star-forming galaxy at $z = 1.87$, with an outflowing wind. The turbulent timescale on the largest spatial scale has been found to be ~500 Myr . This together with the large spatial scale of~ 6.4 kpc suggest a large scale generating mechanism (such as tidal interaction or merger) that lasted for ~500 Myr. On the other hand, the outflowing wind is much younger and is probably the result of the intense star formation. Therefore, could it be that the star formation drives also turbulence on small scales? In the present work we utilize multi-point second order structure functions to find whether there exists also a small scale turbulence in this galaxy, and if so, try to identify its drivers. We obtained evidence for small scale turbulence whose largest spatial scale ~240 pc for the nebular gas velocity field and ~ 290 pc$ for the outflowing wind velocity field. These values suggest that stellar sub clumps or giant star clusters with an high concentration of young massive stars could be responsible for both the outflow and for the small scale turbulence.

Context. The European Archive of the James Webb Space Telescope (eJWST) provides access to all data collected by the James Webb Space Telescope (JWST). JWST's capabilities span from studying early universe galaxy formation to probing exoplanet atmospheres. Specifically, for Active Galactic Nuclei (AGN), JWST offers unparalleled opportunities, enabling investigation into AGN phenomena with unprecedented detail through high-resolution imaging, spectroscopy, and photometric data. Aims. This study aims to compile and release a catalogue of all AGN observations conducted with JWST. Using eJWST, we systematically filter and organize these observations to facilitate access and retrieval of all of JWST's data products related to AGNs. Our goal is to provide the community with a valuable resource for their research. Methods. We compiled the AGN observations in eJWST using specific keywords set by the principal investigators in their proposals, manually reviewing the approved programs of JWST, as well as cross-matching all available observations with available AGN catalogues such as the Million Quasar catalogue, the SDSS MaNGA AGN catalogue, the CDFS catalogue, and others. Results. The resulting catalogue contains a total of 3,242 individual AGNs included in JWST observations. This is one of the first extensive collections of AGN observations from the JWST. It includes detailed information about the targets (name, coordinates, redshift), specifics of the JWST observations (instrument, aperture, filter, etc.), and provides links for data downloads.

A key question in extragalactic astronomy is how the star-formation rate density (SFRD) evolves over cosmic time. A powerful way of addressing this question is using radio-continuum observations, where the radio waves are unaffected by dust and are able to reach sufficient resolution to resolve individual galaxies. We present an investigation of the 1.4 GHz radio luminosity functions (RLFs) of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) using deep radio continuum observations in the COSMOS and XMM-LSS fields, covering a combined area of $\sim 4\,\mathrm{deg}^2$. These data enable the most accurate measurement of the evolution in the SFRD from mid-frequency radio continuum observations. We model the total RLF as the sum of evolving SFG and AGN components, negating the need for individual source classification. We find that the SFGs have systematically higher space densities at fixed luminosity than found in previous radio studies, but consistent with more recent studies with MeerKAT. We attribute this to the excellent low-surface brightness sensitivity of MeerKAT. We then determine the evolution of the SFRD. Adopting the far-infrared - radio correlation results in a significantly higher the SFRD at $z > 1$, compared to combined UV and far-infrared measurements. However, using more recent relations for the correlation between star-formation rate and radio luminosity, based on full spectral energy distribution modelling, can resolve this apparent discrepancy. Thus radio observations provide a powerful method of determining the total SFRD, in the absence of dust-sensitive far-infrared data.

We introduce a complete model for dephasing due to line-of-sight acceleration (LOSA) in gravitational wave (GW) signals from stellar-mass binary black holes (BBHs) in three-body systems. Our prescription provides curvature- and projection-dependent phase features that are not recovered by local-expansion-based treatments. We perform parameter-space surveys and mock parameter inferences assuming the nominal sensitivity of the Einstein Telescope (ET) to identify the regime where the time-varying LOSA allows for separate constraints on the outer orbital parameters, in particular the tertiary mass and distance. We estimate that ET may detect a few to tens of such systems per year, provided that all binaries merge dynamically, and demonstrate that these constraints can be used to directly discriminate between a dynamical and AGN origin for BBHs. Finally, we reanalyse the GW190814 event and four O4a events finding no evidence for LOSA, with the previously claimed LOSA in GW190814 disappearing when a sufficiently long data segment is used.

We present a detailed temporal and spectral analysis of the blazar S5\,1044+71 using multi-wavelength data obtained from the \emph{Fermi}-LAT and Swift-XRT/UVOT telescopes. Applying the Bayesian block algorithm to the 3-day binned $\gamma$-ray lightcurve, we identify pronounced variability, including four major outbursts marked by significant flux enhancements. The highest flux recorded was $(1.1 \pm 0.2)\times 10^{-6}\,\text{ph}\,\text{cm}^{-2}\,\text{s}^{-1}$ on 57868.5 MJD. Each outburst comprises multiple components, and lightcurve profile analysis indicates predominantly symmetric temporal structures. The shortest variability timescale of 4.5 hours constrains the emission region to be located within 0.03 pc of the central engine, likely near the broad-line region (BLR). Additionally, two highest-energy photons were detected with energies of 46.4 GeV (on 57739.6 MJD) and 42.5 GeV (on 59161.9 MJD), observed outside the peak flaring activity. The fractional variability shows an overall increasing trend from UV/optical to $\gamma$-ray bands, with a noticeable dip in the X-ray range, consistent with the shape of the broadband spectral energy distribution (SED). The flux distributions during flares exhibit log-normal or double log-normal behavior, suggesting multiplicative variability processes and evolving emission zones. Cross-correlation analysis reveals a strong positive correlation between the $\gamma$-ray and X-ray bands, with X-rays lagging by 42.5 days. Broadband SED modeling across different flux states supports a one-zone leptonic scenario, with $\gamma$-ray emission produced via external Compton scattering of IR and BLR photons. High-flux states show harder electron spectra, elevated break energies, and reduced magnetic fields-features consistent with efficient particle acceleration and Compton dominance.

The Gaia Alerts system is providing alerts on a variety of objects displaying a significant photometric change detected by the Gaia satellite from one passage to the next one over the same region of the sky. Among the over 22000 alerts published until the end of 2022, around 13 percent concern AGN or quasar candidates. We have embarked on a spectroscopic ground-based follow-up of some of those (including some selected by a different method specifically in galactic nuclei), to establish their true nature, and reveal the various phenomena leading to a change in magnitude of those AGN. The present paper deals with radio-quiet objects, while the radio-loud ones will be described in a companion paper. We confirm, on one hand, the AGN/quasar nature of 64 new candidates alerted by Gaia, and, on the other hand, obtained second-epoch spectra of over 200 known AGN also alerted for large photometric variations. The observed phenomena show a large variety: from Flares to Tidal Disruption Events (TDEs) and a large number of Changing Look Quasars (CLQs, 56 secure ones, plus 23 probable ones), not forgetting some rarer events like SNe, microlensing events or Extreme Coronal Line Emitters. This sample shows that variability is an excellent tool to detect new quasars, especially radio-quiet ones that otherwise would be undetected, and that a significant fraction of variable AGN/quasars, around 10 percent, presents the CLQ phenomenon. Some of the new CLQs are followed-up to monitor further changes and measure time scales.

Earth's ionosphere is a perpetual detector of ionizing radiation received from celestial objects, particularly the Sun. Solar ionizing radiation in the form of extreme ultraviolet (EUV) and X-rays during both quiet and active phase of the Sun, and charged particles associated with a solar wind imprint their ionization signatures on the ionosphere. Although due to the bipolar nature of the geomagnetic field, the events, such as the solar coronal mass ejections (CMEs) and associated solar wind enhancement, usually disturb the polar ionosphere only, the UV and X-rays from the solar flares produce sudden ionospheric disturbances (SIDs) in low-mid-latitude part of the earth's ionosphere. Such ionospheric disturbances are studied with the help of the influence they exert on radio waves propagating through earth- ionosphere waveguide. For the lower part of the ionosphere, called the D region, prominent modification in electron-ion density during solar flares can be observed via deviation in earth bound Very Low Frequency (VLF) wave signal from its ambient diurnal profile. In earlier work, successful model of the deviation in VLF amplitude due to different classes of solar flares was formulated. There, calculation of rate of ionization with Monte Carlo simulation and ion-chemistry evaluation of plasma density enhancement followed by a radio propagation simulation was used. Presently, we attempt to numerically reconstruct the modulation in VLF signal from its diurnal pattern produced by multiple solar flares occurring over a single day. Successful reconstruction of the VLF signal modulation for such a complex flaring scenario points to the accuracy of our understanding of the ionization effect due to solar activity on the lower ionosphere, and strengthen our claim to use earth's ionosphere as a high energy space transient event detector.

Aims. Massive stars impact their surrounding initiating star-formation along their photo-dissociation region. Once the HII region is formed it is unclear if and how the second generation of stars impacts its aspect and evolution. Methods. We performed high spectral resolution (R ~ 23400) Ha Fabry-Perot observations in five fields covering the Galactic HII region NGC 7538 and lead profiles multi-gaussian fitting to extract the parameters as peak intensity, width and velocity. We then analyse the kinematics of the ionised gas building kinematic diagrams and second order structure functions for every field. Results. The observations reveal a general blue-shifted ionised gas flow larger than 11 km s-1 in NGC 7538, consistent with previous studies. Profiles originating from features that are dark in Ha due to extinction or from outside the region show velocity dispersion larger than the one typically found for the Warm Interstellar Medium. The analysis of kinematic diagrams and second-order structure functions reveals non-thermal motions attributed to turbulence and large-scale velocity gradients. In the direction of the HII region itself the turbulence seems to be shock-dominated, with a characteristic scale length between ~ 0.72 and 1.46 pc. In this context, we propose that the kinematics of the central part of the region could be explained by the superposition of the outflow coming from IRS1 and a wind bow shock formed ahead IRS6.

We investigate the connection between ionized gas kinematics and gas-phase metallicity gradients in 21 star-forming galaxies at $0.5 < z < 1.7$ from the MSA-3D survey, using spatially resolved JWST/NIRSpec slit-stepping observations. Galaxy kinematics are characterized by the ratio of rotational velocity to intrinsic velocity dispersion, $v/\sigma$, measured at $1.5\,R_e$, where $R_e$ is the effective radius. We find that dynamically hotter disks exhibit systematically flatter metallicity gradients, with a moderate anti-correlation between metallicity gradient and $v/\sigma$ (Pearson $r=-0.43$, $p=0.05$) and a linear fit yields a slope of $\sim 0.005$ dex per dex in $v/\sigma$, weaker than the dependence on stellar mass. A significantly stronger anti-correlation is observed with $R_e/\sigma$, interpreted as a proxy for the radial mixing timescale ($r=-0.59$, $p=0.005$), indicating that cumulative radial mixing more directly regulates chemical stratification. The metallicity gradients in our sample are uniformly shallow, indicating that efficient turbulent mixing in kinematically settled disks regulates the chemical structure of typical star-forming galaxies at $z\sim1$.

Approximately 25-50% of white dwarfs (WDs) exhibit metal absorption lines in their photospheres, which are attributed to accretion from their remnant planetary systems. Although white dwarfs with detected planetary systems are more likely to show photospheric pollution, one notable exception - WD 1856+534 - hosts a close-in giant planet yet exhibits no detectable photospheric metal pollution. Previous studies have proposed that massive, close-in planets can block inward transport of small particles driven by radiative forces (e.g., Poynting-Robertson drag and the Yarkovsky effect). However, it remains unclear whether the close-in planet can similarly prevent delivery of larger bodies via dynamical interactions. We aim to quantify the protective influence of close-in planets on white-dwarf pollution by asteroids approaching on near-parabolic orbits, and to explore the planetary masses and orbital separations required to provide effective protection. We perform ensembles of short-term N-body integrations, sampling a range of planet masses and orbital separations and initializing asteroids on highly eccentric orbits with periapses near the WD Roche radius, in order to measure scattering, capture, and ejection outcomes and quantify the planet's shielding efficiency. For WD1856+534b-like configurations (a_p = 0.02 au), giant planets with masses greater than 0.5 Jupiter masses are sufficient to clear over 80% of highly eccentric small-body contaminants. The effectiveness of the protective effect diminishes with decreasing planetary mass and increasing semi-major axis. These findings help explain why some white dwarfs that host close-in giant planets do not show the photospheric metal pollution commonly observed in other systems.

We investigate collapsar models with and without self-gravity under identical initial conditions to directly compare the effects of self-gravity on jet properties, such as opening angle, jet power, terminal Lorentz factor, and its variability. We compute a suite of time-dependent, three-dimensional GRMHD simulations of collapsars in evolving spacetime. We update the Kerr metric components due to the growth of the black hole mass and changes its angular momentum. The self-gravity is considered via perturbative terms. We present for the first time the process of jet formation in self-gravitating collapsars. We find that self-gravity leads to temporary jet quenching, which can explain some features in the gamma-ray burst prompt emission. We find no substantial difference in jet launching times between models with and without self-gravity. We observe that in the absence of self-gravity, the jet can extract more rotational energy from the black hole, while self-gravitating models produce narrower jet opening angles. We show that under certain conditions, self-gravity can interrupt the jet formation process, resulting in a failed burst. Our computations show that self-gravity significantly modifies the process of jet propagation, resulting in notably different jet properties. We show that the timescales, variability, and opening angle of jet depend on whether self-gravity is included or not. We argue that self-gravity can potentially explain certain prompt emission properties due to the jet quenching.

Surface chemistry on interstellar dust grains is recognized as a central component in astrochemical models, representing a plausible formation route for many of the observed complex molecular species. However, key parameters governing interstellar surface chemistry, such as diffusion energy barriers, remain poorly constrained. In particular, surface diffusion constitutes a fundamental step for the synthesis of complex organic molecules and plays a crucial role in understanding the desorption process. In this paper, the diffusion dynamics of carbon monoxide (CO) on amorphous solid water (ASW) surfaces, representative of interstellar ices, is modeled with quantum-chemical methods. Employing a representative ensemble of water clusters, each made by 22 molecules, diffusion energy barriers between the binding sites are computed using Density Functional Theory. Diffusion rate coefficients are then determined by applying the harmonic approximation of Transition State Theory. The results, in agreement with experimental studies, revealed a wide distribution of diffusion energies. This reflects the intrinsic topological heterogeneity of ASW surfaces, and highlights how surface mobility significantly influences CO's desorption dynamics and, as a consequence, surface-mediated reactivity in interstellar environments. We show that key parameters commonly employed in astrochemical models, like the ratio between binding and diffusion energy, should be carefully revised.

In a recent publication [R. C. Tautz and I. Lerche, Res. Astron. Astrophys. 16, 162 (2016); arXiv:1606.08272], the authors present a derivation of the Green's function for the three-dimensional telegraph equation (also known as the heat wave equation, or relativistic heat conduction equation). We demonstrate that the closed-form expression derived in their Appendix A is incorrect. Specifically, the published solution lacks a Dirac delta term representing the ballistic wavefront and contains an algebraic error in the prefactor of the wake term. These omissions arise from the neglect of distributional derivatives when differentiating a Heaviside step function. We provide a rigorous derivation of the Green's function using the Fourier transform method, verify the correct limiting behavior as the damping vanishes, and pinpoint the exact mathematical step where the original derivation failed.

Transmission spectroscopy is a key technique in the characterization of exoplanet atmospheres and has been widely applied to planets undergoing hydrodynamic escape. While a robust analytic theory exists for transmission spectra of hydrostatic atmospheres, the corresponding interpretation for escaping atmospheres has so far relied on numerical modeling. In this work, we develop a theory of transmission spectroscopy in hydrodynamically escaping atmospheres by coupling the standard transmission geometry to a steady-state, spherically symmetric, isothermal outflow. This approach yields closed-form expressions and allows the optical depth inversion problem to be examined. The analytic solution reveals that transmission spectroscopy of planetary winds naturally separates into two regimes. In an opacity-limited regime, transmission depths retain sensitivity to the atmospheric mass-loss rate. Beyond a critical threshold, however, spectral-line cores become saturated and no longer provide a unique constraint on the mass flux. This transition is marked by a sharp analytic boundary of the form $\sigma(\lambda)\times \dot M \le C_{sat}$, where $C_{sat}$ is a constant set by the thermodynamic and geometric properties of the wind. This condition specifies when the inversion between transmission depth and mass-loss rate admits a real solution. Once it is violated, the effective transit radius is no longer controlled by opacity or mass loss, but by the geometric extent of the absorbing wind. These results demonstrate that spectral-line saturation in transmission spectroscopy corresponds to a fundamental loss of invertibility between absorption and atmospheric mass loss, rather than a gradual weakening of sensitivity. The theory provides a physically transparent explanation for why strong transmission line cores often fail to constrain mass-loss rates, while weaker lines and line wings remain diagnostic.

With recent observational advancements, exocomet studies have entered a new era: we have moved from an epoch where exocomets' signatures were analysed to identify their true nature to a new epoch where individual exocomets' detections are studied in detail to characterise the observed bodies. In this context, as with other astronomical objects such as exoplanets and minor bodies in the solar system, a nomenclature system is needed to uniquely identify any observed exocometary body. Here, after outlining the purpose of a nomenclature and its required characteristics, we review the information on exocomets that can be included in the nomenclature. Finally, we propose an exocomet nomenclature scheme to identify the individual exocomets that have been discovered or yet to be discovered. Examples of nomenclature names of a few archetypal exocomets are provided.

The study of heavily obscured supermassive black hole (SMBH) growth in late-stage galaxy mergers is challenging: column densities $N_{\mathrm{H}}>10^{24},\mathrm{cm}^{-2}$ can block most nuclear emission, leaving significant gaps in the SMBH growth census. Millimeter-wave continuum emission offers a potential window into this obscured phase, as it can trace Active Galactic Nuclei (AGN) activity through mechanisms less affected by dust extinction. In this work, we test whether the observed correlation between millimeter ($\sim200,\mathrm{GHz}$) and hard X-ray (14 - 150,keV) luminosities can be used to plausibly identify hidden AGN in local (Ultra)Luminous Infrared Galaxies (U)LIRGs, including systems hosting confirmed dual AGN. We identify three sources -- one confirmed AGN and two strong candidates -- presenting significant evidence of AGN activity. The confirmed dual AGN lie within $\sim3\sigma$ of the mm--X-ray correlation, suggesting this relation can be used to identify hidden pairs. By combining the position of each source relative to this correlation with independent star formation rate constraints, we propose a method to disentangle AGN and star formation contributions for sources with measured column densities. While our analysis is based on a small, heterogeneous local sample and relies on empirical scaling relations, these results indicate that millimeter continuum emission may provide a useful complementary diagnostic for obscured SMBH growth. ALMA observations at high angular resolutions are particularly valuable for this approach, while future facilities such as the ngVLA will be essential to test its robustness in larger and more distant samples.

I compare seven actively studied r-process nucleosynthesis scenarios against observed properties of r-process elements in the early Universe, and conclude that the most likely scenario to contribute to the site of elements below the third r-process peak is the magnetorotational r-process scenario, and that of the third peak is the common envelope jets supernova (CEJSN) r-process scenario. The collapsar and CEJSN r-process scenario might also contribute to the lighter r-process elements, and the binary neutron star (NS-NS) merger r-process scenario might contribute to the third r-process peak. The magnetar, the wind from the newly born NS, and the accretion-induced collapse of a white dwarf r-process scenarios fall short in explaining observations. They might exist, but cannot be major contributors to the r-process in the early Universe. To constrain r-process scenarios in the early Universe, I require that they explain the large scatter in the r-process abundances of very metal-poor stars, account for the correlation between light r-process nucleosynthesis and iron production, and the lack of correlation between the third peak r-process production and iron production, as inferred from very metal-poor stars. I discuss the diversity of the CEJSN r-process scenario and encourage extending its exploration.

Aims. We investigate the radio loudness ($\mathcal{R}$) distribution in a large, homogeneous sample of radio galaxies. Methods. The sample is composed of galaxies from the ROGUE I/II catalogue belonging to the SDSS MGS and is divided into optically inactive radio galaxies (OPIRGs), optically active ones (OPARGs) and radio Seyferts. We use optical, mid-infrared and radio data to calculate the AGN bolometric luminosities, accretion rate ($\lambda$), black-hole mass ($M_{BH}$) and $\mathcal{R}$. Results. Contrary to some previous studies based on restricted samples, using our complete sample of objects with redshifts $z < 0.4$, we find no evidence of bimodality in $\mathcal{R}$. The highest $\mathcal{R}$ values are associated with extended radio structures. $\mathcal{R}$ is anti-correlated with $\lambda$, and spans about 2 dex at fixed $\lambda$. Radio Seyferts, OPARGs and OPIRGs form a sequence of increasing $M_{BH}$ with substantial overlap. Radio Seyferts show no $\mathcal{R}$-$M_{BH}$ correlation, whereas OPARGs and OPIRGs show a weak positive trend. From theoretical considerations, the observed two-dex spread in radio luminosity and $\mathcal{R}$ can be reproduced by a four-fold variation in the dimensionless magnetic flux $\varphi$ assuming realistic black-hole spins. Conclusions. The smooth distribution of radio loudness supports a common evolutionary path for all radio sources, with black-hole spin and magnetic field varying continuously. The radio loudness depends on black-hole mass and accretion rate, while moderate variations in $\varphi$ may account for the observed scatter in this relation.

While sub-mm melt droplets should rapidly lose alkali elements in a vacuum at liquidus temperatures, chondrules are only modestly depleted in them (by less than one order of magnitude). The detection of sodium in olivine cores has previously suggested very high saturating partial pressures of gaseous sodium, but we show that alkalis were lost during heating and recondensed at lower temperatures, essentially in the present-day chondrule mesostases. This recondensation was accompanied by mass-dependent enrichment in light isotopes (for multi-isotope alkalis such as K and Rb), but its limited extent indicates a cooling acceleration (or "quenching"). The isotopic fractionation also constrains the ratio of the chondrule density and the cooling rate prior to the quench around $10^{-6}\:\mathrm{kg.m^{-3}.K^{-1}.h}$ suggesting densities above $\sim 10^{-6}\:\mathrm{kg/m^3}$. In a nebular context, this is achievable by radial and vertical concentrations near pressure bumps.

Gravitational waves from extreme mass-ratio inspirals (EMRIs) will enable sub-percent measurements of massive black hole parameters and provide access to the demographics of compact objects in galactic nuclei. During the LISA mission, multiple EMRIs are expected to be detected, allowing statistical studies of massive black hole populations and their formation pathways. We perform hierarchical Bayesian inference on simulated EMRI catalogues to assess how well LISA could constrain the astrophysical population using parametrised population models. We test our inference framework on a variety of populations, including heterogeneous and homogeneous mixtures of parametrised subpopulations, and scenarios in which the assumed model is deliberately misspecified. Our results show that population parameters governing distributions with sharp features can be tightly constrained. Mixed populations can be disentangled with as few as $\sim20$ detections, and even with model misspecification, the inference retains sensitivity to key population features. These results demonstrate the capabilities and limitations of EMRI population inference, providing guidance for constructing realistic astrophysical population models for LISA analysis.

The detection of strong, large-scale magnetic fields at the surface of only the oldest population of white dwarfs might point towards a hidden internal magnetic field slowly rising to the surface. In addition, strong magnetic fields have recently been measured through asteroseismology in the radiative interiors of red giant stars, the progenitors of white dwarfs. To investigate the potential connection between these observations, we revisit the fossil field framework by using the asteroseismic detections to constrain the strength of such magnetic fields as they evolve to the white dwarf stage. We assume that the magnetic field was either created during the main sequence core convection or that it fills the radiative interior as the star evolves on the red giant branch. From these, we evolve the magnetic flux, allowing for magnetic diffusion along the evolution of a 1.5Msun modelled star. We find that measured field strengths in red giants attributed to the hydrogen-burning shell are compatible with the field amplitudes and emergence timescales of magnetized white dwarfs. On the contrary, magnetic fields generated solely from a convective-core dynamo on the main-sequence and detectable during the red giant branch would be buried too deep in the star and not match the breakout timescales and the field strengths of magnetic white dwarfs. A broadly magnetized internal radiative zone during the red giant branch is therefore key for the fossil field theory to connect magnetic fields observed along the late evolution of stars.

Recent JWST observations indicate that massive quiescent galaxies (stellar mass $M_{*}\gtrsim 10^{10}~\mathrm{M_\odot}$) at high redshift ($z\gtrsim 6$) are more abundant than predicted by most existing galaxy formation simulations and semi-analytic models. Notably, the new COLIBRE simulations have succeeded in reconciling this tension, though the precise reason for their improved agreement with JWST data remains unclear. We demonstrate that the improved agreement is largely due to super-Eddington growth of supermassive black holes (BHs) at high redshift. We run a series of $(100~\mathrm{cMpc})^{3}$ simulations with the COLIBRE subgrid physics, varying the maximum allowed BH accretion rate in units of the Eddington rate. We show that only the fiducial COLIBRE model, which permits super-Eddington accretion, is consistent with the JWST constraints at $z \gtrsim 6$. Moreover, we find that in COLIBRE about $50$ per cent of BH mass growth at high redshift occurs in the super-Eddington regime, even though such events are extremely rare in time. Our work highlights the important role of super-Eddington accretion in simulations of galaxy formation for reproducing the observed early emergence of quenching of massive galaxies.

$\beta$ Pictoris is a young nearby A5V star, about 20 Myr old, embedded in a prominent debris disc. For the past 40 years, variable absorption features have been observed in the stellar spectrum, produced by the gaseous tails of exocomets transiting the star. Yet, despite the large number of observations available, the origin and dynamical evolution of the exocomets remain poorly understood. Here we present new spectroscopic observations of $\beta$ Pic, obtained on April 29, 2025, with the Hubble Space Telescope and the HARPS spectrograph. We report the detection of three strong exocomet signatures at low radial velocities (-7.5, +2.5 and +10 km/s), in a large set of lines from various species and excitation levels. We show that the three exocometary tails have different excitation states, indicating that they are located at different distances from the star. Using a detailed modelling of the excitation state of the transiting gas, which includes both radiative and collisional excitation, we derive the transit distance of the three exocometary gaseous tails to be $0.88 \pm 0.08$, $4.7 \pm 0.3$, and $1.52 \pm 0.15$ au. These values are much larger than previous estimates, which generally placed the transient features within 0.2 au. This reveals that gaseous tails produced by exocomets sublimating close to the star can expand and migrate over large distances, while still remaining detectable in absorption spectroscopy. Our study provides a new method to measure the transit distance of exocomets, based on excitation modelling, complementing the acceleration method only applicable for high-velocity objects.

Recent cosmological data favour phantom-crossing dark energy, motivating models with non-minimal couplings that induce a fifth force on structure formation. Reconciling these models with local tests often requires strong screening, leading to environment-dependent clustering. We investigate such effects via a late-time structure-induced phase transition driven by a non-minimally coupled scalar field. For this purpose, we introduce norns, a fully relativistic cosmological particle-mesh code that self-consistently evolves a complex scalar field - a generalisation of the symmetron producing global U(1) strings rather than domain walls. Using simulations, we compare string and wall-forming models, quantifying impacts on the matter power spectrum, halo mass function, and defect dynamics. Strong environment-dependent effects can generate significant departures from LCDM in underdense regions while keeping the overall power spectrum changes modest (~ 4-15% at k~0.3-0.5 h Mpc^-1, sub-percent for z > 0.2). We find that an attractive fifth force can locally suppress structure growth in voids while enhancing it in surrounding overdense regions by driving outflows from the voids. These effects leave distinctive signatures in the matter density probability density function and in marked halo power spectra, which are likely detectable in low-redshift data.

We present the first high-resolution ($\sim$ 0.14") Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 dust continuum and CO molecular line emission observations of the quadruple system HD 34700. In particular, HD 34700AaAb is a spectroscopic binary ($M_{\rm{bin}}=4\,M_\odot$) surrounded by two low-mass companions at large separations. Its circumbinary disk is highly substructured, featuring numerous spiral arms and a large cavity observed in infrared (IR) scattered light. We analyzed the CO line channel and intensity moment maps. By fitting a Keplerian model to the line channel emission, we identified the residual motions and conducted a line spectra analysis. We resolved an asymmetric continuum crescent on top of a dust ring at 0.39" (138 au), colocated with the IR ring. The CO molecule line emissions trace a smaller cavity in gas, whose edge aligns with the inner rim of the ring detected in H$\alpha$ emission at 0.20" (65 au). The $^{12}$CO line emission and kinematics trace highly non-Keplerian motions ($\sim0.1\Delta\upsilon_{\rm kep}$), and these CO spiral features align well with the spiral structures in scattered light. The $^{12}$CO line spectra analysis reveals a streamer above the southeastern disk plane, likely falling onto the disk. The $^{13}$CO and C$^{18}$O kinematics largely follow the disk's underlying Keplerian rotation, while $^{13}$CO exhibits tentative signs of anticyclonic vortex flows at the continuum crescent location. Our multimolecular line study suggests that the circumbinary disk of HD 34700A is highly perturbed in its upper layers, possibly warped and influenced by infalling material. While late-stage infall may account for the IR spirals and the formation of the vortex through Rossby wave instability, an embedded massive companion within the cavity may also contribute to these features.

The baryonic mass-size relation of galaxies links the total baryonic mass (stars plus gas) to the baryonic half-mass radius. In the first paper of this series, we showed that star-forming galaxies from the SPARC sample follow two distinct relations in the baryonic mass-size plane: one defined by high-surface-density (HSD), star-dominated, Sa-to-Sc galaxies, and one defined by low-surface-density (LSD), gas-dominated, Sd-to-dI galaxies. In this second paper, we study the structural relations between baryonic mass, half-mass radius, and mean surface density to constrain possible morphological transformations between star-forming and passive galaxies. We complemented the SPARC sample with $\sim$1200 passive galaxies that are nearly devoid of gas: ellipticals (Es), lenticulars (S0s), dwarf ellipticals (dEs) or dwarf spheroidals (dSphs), and the so-called `ultra-diffuse galaxies' (UDGs). Our results can be summarised as follows: (1) passive stellar components follow four distinct relations at high statistical significance, namely (i) ellipticals plus bulges, (ii) S0 disks, (iii) non-nucleated dwarfs (dEs, dSphs, UDGs), and (iv) nucleated dEs; (2) star-forming HSD disks (mostly Sa to Sc) overlap with S0 disks within 2$\sigma$ in the baryonic relations and within 1$\sigma$ in the stellar ones, so present-day spirals may simply evolve into lenticulars as they run out of gas; (3) star-forming LSD disks (mostly Sd to dI) are offset from non-nucleated passive dwarfs at more than 3$\sigma$ in the baryonic relations, but the two galaxy populations overlap within 1$\sigma$ in the stellar relations, suggesting that non-nucleated passive dwarfs may form from star-forming dwarfs only after gas removal; (4) UDGs extend the sequence of non-nucleated dEs/dSphs and may originate from the most diffuse star-forming LSD galaxies with no need for a substantial expansion of the stellar component.

The A1V star $\gamma$ Oph, at a distance of 29.7 pc, is known from Spitzer imaging to host a debris disk with a large radial extent and from its spectral energy distribution to host inner warm dust. We imaged $\gamma$ Oph with JWST/MIRI at 15 and 25.5 microns, which reveal smooth and radially broad emission that extends to a radius of at least 250 au at 25.5 microns. In contrast to JWST findings of an inner small-grain component with distinct ringed substructures in Fomalhaut and Vega, the mid-infrared radial profile combined with prior ALMA imaging suggests a radially broad steady-state collisional cascade with the same grain size distribution throughout the disk. This further suggests that the system is populated by a radially broad planetesimal belt from tens of au or less to well over 200 au, rather than a narrow planetesimal belt from which the observed dust is displaced to appear broad. The disk is also found to be asymmetric, which could be modelled by a stellocentric offset corresponding to a small eccentricity of $\sim$0.02. Such a disk eccentricity could be induced by a mildly eccentric $<$$10\,M_\mathrm{Jup}$ giant planet outside 10 au, or a more eccentric companion up to stellar mass at a few au, without producing a resolvable radial gap in the disk.

We report a detailed investigation of three intermediate-to-old age open clusters, Berkeley 17, Berkeley 18, and Berkeley 39, utilizing precise astrometric and photometric data from Gaia DR3. Cluster membership was robustly determined through a probabilistic proper-motion analysis, yielding statistically significant samples of 600, 1042, and 907 stars, respectively. From the mean parallaxes of these members, we determine astrometric distances ranging from approximately 3.40 kpc for Berkeley 17 to 5.80 kpc for Berkeley 18. Isochrone fitting applied to the decontaminated color-magnitude diagrams constrains the cluster ages to 9.12 +/- 1.00 Gyr, 3.36 +/- 0.50 Gyr, and 5.10 +/- 0.50 Gyr, respectively. Interstellar reddening spans a wide range, from E(B-V) = 0.17 mag in Berkeley 39 to 0.58 mag in Berkeley 17. Structural parameters derived from King model fits to the radial density profiles, combined with mass function analyses, indicate that the clusters are dynamically relaxed systems with mass distributions broadly consistent with the canonical Salpeter slope. Our kinematic analysis reveals that Berkeley 17, Berkeley 18, and Berkeley 39 are part of the outer disk population.

Ten high resolution Fourier transform spectra of the pentad region near 3.3 {\mu}m of methane diluted in carbon dioxide at total pressures up to 800 hPa have been recorded at 296.5(5) K. Including a high resolution spectrum of pure methane at low pressure, these spectra have been analyzed using multi-spectrum fitting techniques. The methane lines were modeled using hard-collision speed-dependent line profiles and line mixing was included in the strongest absorption regions, considering the first order Rosenkranz approximation and the relaxation matrix formalism. CO$_2$ broadening and shift coefficients have been measured, together with the speed dependence of broadening. Results obtained using the two line mixing models are intercompared and compared with previous work.

We investigate the excitation of quasi-normal modes (QNMs) in gravitational lensing by a Schwarzschild black hole using a scalar field model. By employing a time-domain mode-sum method, we analyze the complex interplay between an incident burst signal and the black hole spacetime. We find that the incident waves can non-resonantly excite a substantial number of high-$l$ modes, with amplitudes for modes as high as l=20 remaining significant compared to the fundamental l=0 mode. We confirm through QNM template fitting that the late-time behaviors of these excited modes are indeed QNMs. After passing through the black hole, we find that the lensed waves form a highly directional and coherent Gaussian beam whose cross-sectional intensity profile is well-described by a Gaussian profile. Unlike spherical waves, this beam's amplitude does not decrease with distance from the black hole but remains nearly constant in the near-field region. Moreover, due to the superposition of numerous QNMs, oscillations largely cancel each other out. The lensed temporal waves do not exhibit typical oscillatory patterns.

We propose a novel origin for the disparity between quark and lepton flavor mixing based on the refractive nature of neutrino masses. We postulate that the fundamental mixing in both the quark and lepton sectors is CKM-like, together with tiny vacuum neutrino masses, while the observed PMNS mixing matrix emerges dynamically from coherent forward scattering of neutrinos on an ultralight dark matter background. The resulting in-medium Hamiltonian rotates CKM mixing angles into large effective lepton mixings, naturally realizing quark--lepton complementarity without invoking new flavor symmetries. This framework links neutrino mass generation, flavor mixing, and dark matter, and predicts environment-dependent neutrino oscillation effects testable in current and future experiments.

We review the main neutrino emission mechanisms operating in dense quark matter under strong magnetic fields, with particular emphasis on conditions expected in the interiors of compact stars. We discuss the direct Urca and neutrino synchrotron processes in unpaired quark matter, incorporating the effects of Landau-level quantization. For the direct Urca process, the quantization of the electron energy spectrum plays a critical role, whereas quark quantization can often be neglected at sufficiently high baryon densities. The resulting field-dependent neutrino emissivity is anisotropic and exhibits an oscillatory behavior as a function of magnetic-field strength. We explore the implications of these effects for magnetar cooling and for possible anisotropic neutrino emission that could contribute to pulsar kicks. In addition, we review the $\nu\bar{\nu}$ synchrotron emission process, which, although subdominant, provides valuable insights into the interplay between magnetic fields and weak interactions in dense quark matter. Overall, our analysis highlights the nontrivial influence of strong magnetic fields on neutrino production in magnetized quark cores, with potential consequences for the thermal and dynamical evolution of compact stars.

We investigate the detectability of post-Newtonian higher harmonics from Galactic double white dwarfs in the centihertz band ($\sim 0.01$ Hz). Using a synthetic population, we show that, unlike the quadrupole mode, higher harmonics remain undetectable with LISA except for rare nearby systems. In contrast, planned mid-band (decihertz) observatories such as DECIGO and BBO will be able to detect the third harmonic for about 10\% of inspiral binaries above $\sim 5$ mHz, enabling statistical constraints on mass ratios. These results highlight the successive roles of LISA and future decihertz missions in establishing a coherent strategy for space-based gravitational-wave astronomy.

We examine the role of angular momentum in general relativity from both heuristic and fully covariant perspectives, with the aim of clarifying conceptual ambiguities that arise when Newtonian intuition is extrapolated into the relativistic regime. Focusing on free--fall dynamics in the Schwarzschild and Kerr spacetimes in the test--particle limit, we employ an effective--potential heuristic approach to isolate the roles of the specific energy $E$, specific angular momentum $L$, and black--hole spin $a$. Within this framework, we identify well--defined regions of parameter space in which the Kerr spacetime leads to stronger or weaker local radial infall than the Schwarzschild case at the same radius. By analysing the kinematics of infalling geodesic congruences, we show how these local regimes combine along complete trajectories to either enhance or reduce gravitational focusing. We then interpret these results within a covariant 1+3 description of general relativity, in terms of the expansion, shear and Raychaudhuri evolution of timelike congruences. We demonstrate that black--hole rotation systematically modifies the shear of infalling irrotational flows, even when the magnitude of the local expansion is reduced, and that this shear modulation governs the overall rate of focusing. Our work complements previous studies of relativistic infall by providing a unified energetic and geometric interpretation of how angular momentum and rotation can strengthen or weaken gravitational collapse relative to the non--rotating case.

In this work, we present a novel compact particle identification (PID) detector concept based on Silicon Photomultipliers (SiPMs) optimized to perform combined Ring-Imaging Cherenkov (RICH) and Time-of-Flight (TOF) measurements using a common photodetector layer. The system consists of a Cherenkov radiator layer separated from a photosensitive surface equipped with SiPMs by an expansion gap. A thin glass slab, acting as a second Cherenkov radiator, is coupled to the SiPMs to perform Cherenkov-based charged particle timing measurements. We assembled a small-scale prototype instrumented with various Hamamatsu SiPM array sensors with pixel pitches ranging from 2 to 3 mm and coupled with 1 mm thick fused silica window. The RICH radiator consisted of a 2 cm thick aerogel tile with a refractive index of 1.03 at 400 nm. The prototype was successfully tested in beam test campaigns at the CERN PS T10 beam line with pions and protons. We measured a single-hit angular resolution of about 4 mrad at the Cherenkov angle saturation value and a time resolution better than 50 ps RMS for charged particles with Z = 1. The present technology makes the proposed SiPM-based PID system particularly attractive for space applications due to the limited detector volumes available. In this work, we present beam test results obtained with the detector prototype and we discuss possible configurations optimized for the identification of ions in space applications.

Neutrino physics offers unique insights into phenomena beyond the Standard Model (BSM). This thesis presents phenomenological investigations organized around three pillars: consolidation of the three-flavor oscillation paradigm, exploration of new physics viability, and precise determination of solar neutrino fluxes. The theoretical framework introduces massive neutrinos, leptonic mixing, and flavor transitions, followed by experimental results emphasizing Borexino and NOvA data analyses. The first pillar establishes the three-flavor framework through global analysis of solar, atmospheric, reactor, and accelerator data, providing updated determinations of mixing angles ($\theta_{12}$, $\theta_{13}$, $\theta_{23}$) and mass-squared differences ($\Delta m^2_{21}$, $\Delta m^2_{31}$), while quantifying ambiguities in mass ordering and $\theta_{23}$ octant. The second pillar investigates Non-Standard Interactions (NSI) with electrons and quarks, combining Borexino data with COHERENT's CE$\nu$NS measurements to establish bounds on propagation and detection couplings, excluding viable NSI parameter regions including potential LMA-D solutions. The third pillar advances solar neutrino physics through precision flux determinations, integrating pp-chain and CNO-cycle measurements. Results show preference for high-metallicity Standard Solar Models and incompatibility between $3+1$ mixing parameters favored by Gallium experiments and solar observations. This synthesis guides future experiments toward resolving mass ordering, CP violation, and dark sector interactions.

We investigate the geometry of a tidally deformed, rotating black hole and timelike geodesics in its vicinity. Our framework provides a local picture of the structural evolution of a relativistic restricted three-body problem around a deformed black hole in an adiabatically evolving binary, motivated by various astrophysical settings including disk dynamics and extreme mass-ratio inspirals. As the tidal-field strength is increased, initially regular, bound geodesics undergo four stages: (i) weak chaos emerges within the bound motion; (ii) a subset of trajectories plunges into the black hole; (iii) a fraction of the remaining trajectories becomes unbound; and (iv) no bound trajectories persist. We provide semi-analytic estimates for the critical tidal amplitudes associated with each transition. Our estimates indicate that, within the frequency band of ground-based gravitational-wave detectors, the matter flow around black holes may already be depleted, whereas LISA and (B-)DECIGO could probe the earlier stages. Our results suggest that an object orbiting a tidally deformed massive BH may remain near resonances over a wide range of separations, indicating an accumulated, non-negligible impact on the gravitational-wave phase. Tidal perturbations can also introduce nonlinear couplings among epicyclic oscillations of geodesics, offering a potential avenue to resonant excitation of quasi-periodic oscillations in X-ray light curves from accreting black holes.

We investigate a dark sector coupled to the Standard Model (SM) through a kinetically mixed dark photon $U$ associated with a new $U(1)'$ gauge symmetry. Kinetic mixing $\varepsilon$ induces an effective coupling to the electromagnetic current, while $U$ interacts with stable dark matter (DM) $\chi$ via a dark gauge coupling $g_\chi$. Our analysis is based on the parton-hadron-string dynamics (PHSD) transport approach, extended to include dark photon production and decay into dileptons ($U\!\to e^+e^-$). In PHSD, dark photons are produced in high-energy collisions through Dalitz decays of light mesons ($\pi^0,\eta,\eta',\omega$), Delta-resonances ($\Delta\!\to N U$), direct vector meson decays ($\rho,\omega,\phi\!\to U$), kaon decays, and $q\bar q\!\to U$ annihilation. Building on previous PHSD benchmarks against dilepton data, we extract upper limits on $\varepsilon^2(m_U,m_\chi,\alpha_\chi)$ in both the visible regime ($m_U<2m_\chi$), where $U\!\to e^+e^-$ dominates, and the invisible regime ($m_U>2m_\chi$), where $U\!\to\chi\bar\chi$ is kinematically open. Cosmological and astrophysical constraints are incorporated in two complementary ways. First, we compute the velocity-dependent self-interaction cross section $\sigma/m_\chi$ for Yukawa-mediated SIDM and confront it with bounds from dwarf galaxies, galaxy groups, and clusters. Second, we determine thermal relic target curves by computing the relic abundance and requiring $\Omega_{\rm DM}h^2\simeq 0.12$, consistent with \textit{Planck} measurements of the cosmic microwave background. Combining PHSD limits on $\varepsilon^2$ with relic density and self-interaction requirements, we exclude regions of the $(m_\chi,m_U)$ plane for each DM realization (Dirac, Majorana, or complex scalar) and identify benchmark scenarios in which heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied.

Bayesian model comparison implements Occam's razor through its sensitivity to the prior. However, prior-dependence makes it important to assess the influence of plausible alternative priors. Such prior sensitivity analyses for the Bayesian evidence are expensive, either requiring repeated, costly model re-fits or specialised sampling schemes. By exploiting the learned harmonic mean estimator (LHME) for evidence calculation we decouple sampling and evidence calculation, allowing resampled posterior draws to be used directly to calculate the evidence without further likelihood evaluations. This provides an alternative approach to prior sensitivity analysis for Bayesian model comparison that dramatically alleviates the computational cost and is agnostic to the method used to generate posterior samples. We validate our method on toy problems and a cosmological case study, reproducing estimates obtained by full Markov chain Monte Carlo (MCMC) sampling and nested sampling re-fits. For the cosmological example considered our approach achieves up to $6000\times$ lower computational cost.

According to modern physics, our Universe is baryon-asymmetric. That phenomenon can not be described in the frameworks of the Standard Model of particle physics. Globally, the Universe consists of baryon matter. However, some scenarios can lead to the existence of local antimatter domains. In the research, the chemical evolution of such an isolated antimatter domain, surrounded by baryonic matter, is studied. The size of the domain is estimated according to the conditions of its survival in baryon surrounding, and the process of annihilation at its border is taken into account.

We derive exact general solutions (as opposed to attractor particular solutions) for the evolution of a scalar field $\phi$ in a universe dominated by a background fluid with equation of state parameter $w_B = -1$, extending earlier work on exact solutions with $w_B > -1$. Straightfoward exact solutions exist when the evolution is described by a linear differential equation, corresponding to constant, linear, and quadratic potentials. In the nonlinear case, exact solutions are derived for $V = V_0\ln \phi$, $V = V_0 \phi^{1/2}$ and $V = V_0/\phi$, and the logarithmic potential also yields an exact first integral. These complicated parametric solutions are considerably less useful than those derived previously for a universe dominated by a barotropic fluid such as matter or radiation with $w_B > -1$. However, we generalize the slow-roll approximation and show that it applies to all sufficiently flat potentials in the case of a vacuum-dominated expansion, while it never applies when the universe is dominated by a background fluid with $w_B > -1$.