Papers for Monday, Mar 17 2025

A high degree of linear polarization measured in the optical emission is an important observational feature of blazars. It provides strong evidence of the presence of relativistic particles and magnetic field ordering in the non-thermal emission regions of blazars owing to the synchrotron nature of low energy radiation. Thus, the polarization studies of blazars are emerging as a promising approach to probe the particle acceleration and the physical processes involved in their broadband emission. In this work, we investigate the behavior of the optical polarization of the blazar 1ES 1959+650 measured over a decade using the spectropolarimetry (SPOL) at the Steward Observatory. We use measurements of the degree of linear polarization and angle of polarization in the wavelength range 500 - 700 nm available during the period October 1, 2008 and June 30, 2018 (MJD 54739 - 58299) from the SPOL observations. Near simultaneous photometry data in the R and V bands are also used to study the optical emission from the source. The maximum degree of linear polarization, measured as $\sim$ 8.5$\%$, is significantly larger than the long term average value of $\sim$ 4.6$\%$. Analysis of the light curves indicates that the optical emission from the blazar 1ES 1959+650 is highly variable and variability in the degree of linear polarization can be quantified by a fractional variability amplitude of $\sim$ 39$\%$ over the period of about ten years. Long term optical emission in the R and V bands is very weakly anti-correlated with the degree of linear polarization. Modelling of the polarization due to the synchrotron emission suggests that the observed degree of linear polarization can be broadly reproduced by a power law distribution of relativistic electrons gyrating in a spherical emission region permeated with chaotic and ordered magnetic fields.

The computational expense of solving non-equilibrium chemistry equations in astrophysical simulations poses a significant challenge, particularly in high-resolution, large-scale cosmological models. In this work, we explore the potential of machine learning, specifically Neural Operators, to emulate the Grackle chemistry solver, which is widely used in cosmological hydrodynamical simulations. Neural Operators offer a mesh-free, data-driven approach to approximate solutions to coupled ordinary differential equations governing chemical evolution, gas cooling, and heating. We construct and train multiple Neural Operator architectures (DeepONet variants) using a dataset derived from cosmological simulations to optimize accuracy and efficiency. Our results demonstrate that the trained models accurately reproduce Grackle's outputs with an average error of less than 0.6 dex in most cases, though deviations increase in highly dynamic chemical environments. Compared to Grackle, the machine learning models provide computational speedups of up to a factor of six in large-scale simulations, highlighting their potential for reducing computational bottlenecks in astrophysical modeling. However, challenges remain, particularly in iterative applications where accumulated errors can lead to numerical instability. Additionally, the performance of these machine learning models is constrained by their need for well-represented training datasets and the limited extrapolation capabilities of deep learning methods. While promising, further development is required for Neural Operator-based emulators to be fully integrated into astrophysical simulations. Future work should focus on improving stability over iterative timesteps and optimizing implementations for hardware acceleration. This study provides an initial step toward the broader adoption of machine learning approaches in astrophysical chemistry solvers.

The most powerful cosmic engines in our universe are fueled by compact objects. These objects accrete large amounts of material and eject matter in the form of jets. Recent groundbreaking discoveries of gravitational waves from merging compact objects and the direct imaging of the black hole shadows with the Event Horizon Telescope represent major steps forward in our understanding of such systems. However, there exists a large population of stellar-mass compact objects in our own Galaxy, present in X-ray binaries (XRBs), which provide better laboratories with which to study the processes of accretion and ejection. XRBs produce highly variable emissions on timescales ranging from milliseconds (for light-travel time in the region close to the compact object) to weeks (governing the mass-inflow process). Therefore, high-time resolution observations can be a powerful tool to study these systems. However, as XRBs emit across the electromagnetic spectrum, a suite of facilities is needed to take full advantage of these techniques. The PRIMA Observatory (PRobe far-Infrared Mission for Astrophysics) will provide unique access to a wavelength range that has not been sampled in XRBs, representing an exciting new possibility for characterizing rapid time-domain phenomena of XRBs (and potentially other transient sources) in the far-infrared regime.

In classical diffusion, particle step-sizes have a Gaussian distribution. However, in superdiffusion, they have power-law tails, with transport dominated by rare, long Lévy flights. Similarly, if the time interval between scattering events has power-law tails, subdiffusion occurs. Both forms of anomalous diffusion are seen in cosmic ray (CR) particle tracking simulations in turbulent magnetic fields. They also likely occur if CRs are scattered by discrete intermittent structures. Anomalous diffusion mimics a scale-dependent diffusion coefficient, with potentially wide-ranging consequences. However, the finite size of galaxies implies an upper bound on step-sizes before CRs escape. This truncation results in eventual convergence to Gaussian statistics by the central limit theorem. Using Monte-Carlo simulations, we show that this occurs in both standard finite-thickness halo models, or when CR diffusion transitions to advection or streaming-dominated regimes. While optically thick intermittent structures produce power-law trapping times and thus subdiffusion, gaussianization also eventually occurs on timescales longer than the maximum trapping time. Anomalous diffusion is a transient, and converges to standard diffusion on the (usually short) timescale of particle escape, either from confining structures (subdiffusion), or the system as a whole (superdiffusion). Thus, standard assumptions of classical diffusion are physically justified in most applications, despite growing simulation evidence for anomalous diffusion. However, if escape times are long, this is no longer true. For instance, anomalous diffusion in the CGM or ICM would change CR pressure profiles. Finally, we show the standard diagnostic for anomalous diffusion, $\langle d^2 \rangle \propto t^{\alpha}$ with $\alpha \neq 1$, is not justified for truncated Lévy flights, and propose an alternative robust measure.

We present SIDM Concerto: $14$ cosmological zoom-in simulations in cold dark matter (CDM) and self-interacting dark matter (SIDM) models based on the Symphony and Milky Way-est suites. SIDM Concerto includes one Large Magellanic Cloud (LMC)-mass system (host mass $\sim 10^{11}~M_{\mathrm{\odot}}$), two Milky Way (MW) analogs ($\sim 10^{12}~M_{\mathrm{\odot}}$), two group-mass hosts ($\sim 10^{13}~M_{\mathrm{\odot}}$), and one low-mass cluster ($\sim 10^{14}~M_{\mathrm{\odot}}$). Each host contains $\approx 2\times 10^7$ particles and is run in CDM and one or more strong, velocity-dependent SIDM models. Our analysis of SIDM (sub)halo populations over seven subhalo mass decades reveals that: (i) the fraction of core-collapsed isolated halos and subhalos peaks at a maximum circular velocity corresponding to the transition of the SIDM cross section from a $v^{-4}$ to $v^0$ scaling; (ii) SIDM subhalo mass functions are suppressed by $\approx 50\%$ relative to CDM in LMC, MW, and group-mass hosts but are consistent with CDM in the low-mass cluster host; (iii) subhalos' inner density profile slopes, which are more diverse in SIDM than in CDM, are sensitive to both the amplitude and shape of the SIDM cross section. Our simulations provide a benchmark for testing SIDM predictions with astrophysical observations of field and satellite galaxies, strong lensing systems, and stellar streams. Data products are publicly available at this https URL.

We re-analysed ALMA observations of the [OIII]$\lambda$88$\mu$m emission line in JADES-GS-z14.0, so far the most distant spectroscopically confirmed galaxy at z=14.18. Our analysis shows a tentative detection of a velocity gradient of [OIII]$\lambda$88$\mu$m using three independent tests: 1) construction of moment maps; 2) extraction of integrated spectra from a grid of apertures; and 3) spectro-astrometry in both the image and uv planes. We performed kinematical fitting using the KinMS code and estimated a dynamical mass of log$_{10}$(M$_{\rm dyn}$/$\rm M_\odot$)= 9.4$^{+0.8}_{-0.4}$, with the bulk of the uncertainties due to the degeneracy between dynamical mass and inclination. We measure an upper limit on the velocity dispersion ($\sigma_{v}$) of $<40~$ km/s~which results in an estimate of V$_{\rm rot}/\sigma>$ 2.5. This result, if confirmed with higher-resolution observations, would imply that kinematically cold discs are already in place at $z\sim14$. Comparison with mock observations from the SERRA cosmological simulations confirms that even low-resolution observations are capable of detecting a velocity gradient in $z>10$ galaxies as compact as JADES-GS-z14.0. This work shows that deeper ALMA or JWST/NIRSpec IFS observations with high spatial resolution will be able to estimate an accurate dynamical mass for JADES-GS-z14.0, providing an upper limit to the stellar mass of this over-luminous galaxy.

Collisionless electron-ion shocks are fundamental to astrophysical plasmas, yet their behavior in strong magnetic fields remains poorly understood. Using Particle-in-Cell (PIC) simulations with the SHARP-1D3V code, we investigate the role of the ion magnetization parameter $\sigma_i$ in parallel shock transitions. Strongly magnetized converging flows ($\sigma_i > 1$) exhibit lower density compression ratios ($R \sim 2$), smaller entropy jumps, and suppressed particle acceleration, while maintaining pressure anisotropy stability due to conserved perpendicular temperatures across the shock, alongside increased parallel temperatures. In contrast, weakly magnetized shocks drive downstream mirror and firehose instabilities due to ion temperature anisotropy, which are suppressed in strongly magnetized cases. Additionally, weakly magnetized shocks exhibit the onset of a supra-thermal population induced by shock-drift acceleration, with most of the upstream kinetic energy thermalized for both electrons and ions in the downstream region. Our results demonstrate that perpendicular temperatures for both species are conserved in strongly magnetized cases and highlight deviations from standard ideal magnetohydrodynamic (MHD) behavior. These findings provide critical insights into the role of magnetic fields in parallel collisionless astrophysical shocks.

Since its inception, speckle interferometry has revolutionized high-resolution astronomical imaging, overcoming atmospheric challenges to achieve the diffraction limits of telescopes. Almost a decade ago, in 2018, a pair of speckle cameras -- 'Alopeke and Zorro -- were installed at the twin 8.1-meter Gemini North and South telescopes, two of the largest apertures in the world, in Hawai'i and Chile. Equipped with dual blue and red channels, 'Alopeke and Zorro deliver high-resolution imaging across optical bandpasses from 350 to 1000 nm, which has led to crucial discoveries in both stellar multiplicity and exoplanetary science. Furthermore, the broad and nonrestrictive access to these instruments, given by each Gemini Observatory partner and via the US NOIRLab open skies policy, has allowed our community to expand the applications of the instruments, supporting a wide range of scientific investigations from Solar System bodies, to morphological studies of stellar remnants, to evolved stars, to transient phenomena. This paper reviews the instrument technology and observational capabilities, and highlights key scientific contributions and discoveries of 'Alopeke and Zorro, emphasizing the enduring importance of speckle interferometry in advancing modern observational astronomy and expanding the frontiers of astronomical research.

Modern studies of galaxy formation rely heavily on numerical simulations, which in turn require tools to identify and track self-bound structures in stars and dark matter. In this paper, we present Bloodhound, a new halo tracking algorithm optimized to track and characterize substructure in cosmological simulations, a regime that is crucial for studies of the nature of dark matter but where standard methods often have difficulties. Using simulations of Milky Way-mass haloes, we demonstrate that Bloodhound extends subhalo tracking by $3-4\, \mathrm{Gyr}$ on average, and significantly longer for subhaloes with small pericentres, relative to the widely used ROCKSTAR $+$ consistent-trees halo tracking pipeline. We also show that Bloodhound provides continuous tracking, mitigating an issue for the standard technique where subhaloes can be lost and then found again -- but assigned to a new merger tree -- after several snapshots. This improved tracking leads to a substantially larger number of surviving subhaloes in the inner regions of dark matter haloes, which has several implications for studies of the Milky Way's satellite galaxy system and its use for constraining properties of dark matter. For example, within the radius where current surveys are complete to ultra-faint galaxies ($D_{\rm MW} \lesssim 50$ kpc), Bloodhound finds more than twice as many subhaloes above the atomic cooling scale relative to the standard tracking method. Our results underscore the importance of robust subhalo tracking techniques in advancing our understanding of galaxy formation and cosmological models.

Quasar absorption lines provide a unique window to the relationship between galaxies and the intergalactic medium during the Epoch of Reionization. In particular, high redshift quasars enable measurements of the neutral hydrogen content of the universe. However, the limited sample size of observed quasar spectra, particularly at the highest redshifts, hampers our ability to fully characterize the intergalactic medium during this epoch from observations alone. In this work, we characterize the distributions of mean opacities of the intergalactic medium in simulations from the Cosmic Reionization on Computers (CROC) project. We find that the distribution of mean opacities along sightlines follows a non-trivial distribution that cannot be easily approximated by a known distribution. When comparing the cumulative distribution function of mean opacities measurements in subsamples of sample sizes similar to observational measurements from the literature, we find consistency between CROC and observations at redshifts $z\lesssim 5.7$. However, at higher redshifts ($z\gtrsim5.7$), the cumulative distribution function of mean opacities from CROC is notably narrower than those from observed quasar sightlines implying that observations probe a systematically more opaque intergalactic medium at higher redshifts than the intergalactic medium in CROC boxes at these same redshifts. This is consistent with previous analyses that indicate that the universe is reionized too early in CROC simulations.

To study stars analogous to those in the early Universe with redshift z > 3, we need to probe environments with low metallicities. Until recently, massive O-type stars with metallicities lower than that of the Small Magellanic Cloud (SMC, Z < 20%Z_sol) were only known in compact dwarf galaxies. Observations of stars in such distant galaxies (> 1 Mpc) suffer from limited S/N ratios and spatial resolution. Recently, a few O-type stars were identified in the nearby Magellanic Bridge which offers a unique laboratory with low gas density and metal content. We acquired high-resolution HST-COS FUV spectra of two O-type stars in the Magellanic Bridge. Using the UV forest of iron lines from these observations, we aim to precisely measure the inherent iron abundances and determine the metallicity of the stars. Using detailed expanding non-LTE atmosphere models, we generate synthetic spectra for different iron abundances and for a range of microturbulent velocities. We use Bayesian posterior sampling to measure the iron abundance and compute uncertainties based on the possible range of microturbulent velocities. The O stars in the Magellanic Bridge have severely sub-SMC Fe abundances, reaching as low as 10.8% and 3.6% Fe_sol. The most Fe-deficient star also shows alpha-enhancement. These stars are the nearest extremely metal-poor O stars discovered to date. Our finding marks the first robust determination of O-star iron abundances in a metallicity regime comparable to dwarf galaxies like Sextans A and Leo P. The iron abundances of the stars do not correlate with their oxygen abundances. Our results highlight the problem of using oxygen-based metallicities. The proximity of the stars in the Bridge combined with their different abundance patterns underlines that the ISM of the Magellanic Bridge must be highly inhomogeneous and is not properly mixed.

We propose that a hierarchical shock model$\unicode{x2014}$including supernova remnant shocks, galactic wind termination shocks, and accretion shocks around cosmic filaments and galaxy clusters$\unicode{x2014}$can naturally explain the cosmic ray spectrum from ~1 GeV up to ~200 EeV. While this framework applies to the entire cosmic ray spectrum, in this work, we focus on its implications for ultra-high-energy cosmic rays (UHECRs). We perform a hydrodynamic cosmological simulation to investigate the power processed at shocks around clusters and filaments. The downstream flux from nearby shocks around the local filament accounts for the softer, lower-energy extragalactic component around the ankle, and the upstream escaping flux from nearby clusters accounts for the transition to a hard spectral component at the highest energies. This interpretation is in agreement with UHECR observations. We suggest that a combination of early-Universe galactic outflows, cosmic ray streaming instabilities, and a small-scale turbulent dynamo can increase magnetic fields enough to attain the required rigidities. Our simulation suggests that the available volume-averaged power density of accretion shocks exceeds the required UHECR luminosity density by three orders of magnitude. We show that microgauss magnetic fields at these shocks could explain both the origin of UHECRs and the as-yet unidentified source of the diffuse radio synchrotron background below 10 GHz. The shock-accelerated electrons produce a hard radio background without overproducing diffuse inverse Compton emission. These results motivate further observational tests with upcoming facilities to help distinguish accretion shocks from other UHECR sources.

The metal enrichment of a galaxy is determined by the cycle of baryons in outflows, inflows, and star formation. The relative contribution and timescale of each process sets the relationship between stellar mass, metallicity, and the star formation rate (SFR). In the local universe, galaxies evolve in an equilibrium state where the timescales on which SFR and metallicity vary are comparable, and define a surface in mass-metallicity-SFR space known as the Fundamental Metallicity Relation (FMR). However, high-redshift observations suggest that this state of equilibrium may not persist throughout cosmic time. Using galaxies from the Keck Baryonic Structure Survey (KBSS) observed with MOSFIRE, we explore the relationship between stellar mass, gas-phase oxygen abundance, and SFR at $z \sim 2.3$. Across strong-line calibrations and SFR calculation methods, KBSS galaxies are inconsistent with the locally-defined FMR. We use both parametric and non-parametric methods of exploring a mass-metallicity-SFR relation. When using a parametric approach, we find no significant reduction mass-metallicity relation scatter when folding in SFR as a third parameter, although a non-parametric approach reveals that there could be a weak, redshift-dependent anticorrelation between residual gas-phase oxygen abundance, and SFR. Injection-recovery tests show that a significant reduction in scatter requires a stronger anticorrelation between SFR and residual metallicity. Our results suggest that the local FMR may not persist to $z \sim 2.3$, implying that $z \sim 2.3$ galaxies may not be in the equilibrium state described by the FMR and are more similar to higher redshift galaxies.

Blast wave models are commonly used to model relativistic outflows from ultra-relativistic gamma-ray bursts (GRBs), but are also applied to lower Lorentz factor ejections from X-ray binaries (XRBs). Here we revisit the physics of blast waves and reverse shocks in these systems and explore the similarities and differences between the ultra-relativistic ($\Gamma \gg 1$) and moderately relativistic ($\Gamma \sim$ a few) regimes. We first demonstrate that the evolution of the blast wave radius as a function of the observer frame time is recovered in the on-axis ultra-relativistic limit from a general energy and radius blast wave evolution, emphasizing that XRB ejections are off-axis, moderately relativistic cousins of GRB afterglows. We show that, for fixed blast wave or ejecta energy, reverse shocks cross the ejecta much later (earlier) on in the evolution for less (more) relativistic systems, and find that reverse shocks are much longer-lived in XRBs and off-axis GRBs compared to on-axis GRBs. Reverse shock crossing should thus typically finish after $\sim10-100$ days (in the observer frame) in XRB ejections. This characteristic, together with their moderate Lorentz factors and resolvable core separations, makes XRB ejections unique laboratories for shock and particle acceleration physics. We discuss the impact of geometry and lateral spreading on our results, explore how to distinguish between different shock components, and comment on the implications for GRB and XRB environments. Additionally, we argue that identification of reverse shock signatures in XRBs could provide an independent constraint on the ejecta Lorentz factor.

Black hole X-ray binaries in outburst launch discrete, large-scale jet ejections which can propagate to parsec scales. The kinematics of these ejecta appear to be well described by relativistic blast wave models original devised for gamma-ray burst afterglows. In previous kinematic-only modelling, a crucial degeneracy prevented the initial ejecta energy and the interstellar medium density from being accurately determined. In this work, we present the first joint Bayesian modelling of the radiation and kinematics of a large-scale jet ejection from the X-ray binary MAXI J1535-571. We demonstrate that a reverse shock powers the bright, early ejecta emission. The joint model breaks the energetic degeneracy, and we find a conservative initial ejecta energy of $E_{0} \sim 4 \times 10^{43} \, {\rm erg}$, consistent with the disc luminosity integrated over a flare-informed launching timescale, and a low interstellar medium density of $n_{\rm ism} \sim 5 \times 10^{-5} \, {\rm cm^{-3}}$. This work lays the foundation for future parameter estimation studies using all available data of X-ray binary jet ejecta.

Pulsar Timing Arrays are playing a crucial role in the ongoing gravitational wave astronomy revolution. The current evidence for a stochastic gravitational wave background (SGWB) at nHz frequencies offers an opportunity to discover cosmological signals and threatens the observability of other subdominant GWs. We explore prospects to constrain second-order scalar-induced GWs (SIGWs) associated with enhanced curvature perturbations in the primordial universe, forecasting realistic future PTA datasets. We assess how the currently observed signal could eventually limit future capabilities to search for GW relics of primordial phenomena and associated phenomenological consequences such as primordial black hole (PBH) formation. Given the sensitivity of PBH abundance to spectral parameters, measuring it remains a challenge for realistic signals. However, future observation could still rule out nearly subsolar mass PBHs formed through standard formation scenarios in some cases. Future progress in constraining PBH models is expected to stem from theoretical advancements in PBH computations, which should help resolve the tension between different computational methods. The analysis is based on and extends the Python code $\texttt{fastPTA}$.

We investigate a scenario where a dark energy quintessence field $\phi$ with positive kinetic energy is coupled with dark matter. With two different self-interaction potentials for the field and a particular choice of the coupling function, we show explicitly how the observable effective equation of state parameter $w_{\rm eff}$ for the dark energy field crosses the phantom barrier ($w_{\rm eff} = -1$) while keeping the equation of state of the quintessence field $w_\phi > -1$. With appropriate choices of parameters, $w_{\rm eff}$ crosses the phantom divide around redshift $z\sim 0.5$, transitioning from $w_{\rm eff} <-1$ in the past to $w_{\rm eff}>-1$ today. This explains DESI observations well. Our analysis reveals that the model remains consistent within the $2\sigma$ confidence intervals provided by DESI for several combinations of the scalar field parameters, highlighting its potential in explaining the dynamics of dark energy arising from a simple Yukawa-type long-range interaction in the dark sector. While the current findings offer a promising framework for interpreting DESI observations, future work, including a comprehensive Markov Chain Monte Carlo (MCMC) analysis, is necessary to constrain the parameter space further and strengthen the statistical significance of the results.

This work investigates the multi-wavelength properties of 165 4FGL blazars from the Fermi-LAT fourth source catalogue, looking for with counterparts in the Australian SKA Pathfinder (ASKAP) First Large Absorption Survey in HI (FLASH) continuum. Using high-resolution data from FLASH and complementary radio datasets, combined with archival Atacama Large Millimeter Array (ALMA) observations, we perform detailed spectral energy distribution (SED) analyses across cm-to-mm wavelengths. Our findings reveal that most blazars exhibit re-triggered peaked spectra, indicative of emission dominated by a single emitting region. Additionally, we identify strong correlations between radio and gamma-ray luminosities, highlighting the significant role of relativistic jets in these active galactic nuclei. The inclusion of spectroscopic redshifts from Sloan Digital Sky Survey (SDSS) and Gaia enables a comprehensive analysis of the evolutionary trends and physical characteristics of the sources. Furthermore, we report a tight Radio-X-ray Correlation for Flat Spectrum Radio Quasars, contrasting with the more scattered behaviour observed in BL-Lacs, reflecting their distinct accretion and jet-driving mechanisms. These results provide critical insights into the physics of blazars and their environments, paving the way for future studies with next-generation facilities like the SKA Observatory (SKAO) for radio observations and Cherenkov Telescope Array for gamma-ray studies.

In the cosmic web, filaments play a crucial role in connecting walls to clusters and also act as an important stage for galaxy formation and evolution. Recent observational studies claim that filaments have spin. In this study, we examined the potential impact of diversity in filament identification algorithms and galaxy survey datasets on the quantification of filament spin. The results of this study demonstrate qualitative agreement with previous research, suggesting that a reliable filament spin signal is detectable when the viewing angle of filament spine larger than 80 degrees under a rough estimation. The detected filament spin signal is intricately linked to the viewing angle, dynamic temperature, etc. The quantitative difference of filament spin signal among samples is slightly dependent on the filament identification algorithms, while the value is relatively greater dependent on the redshift space distortion effect in the galaxy sample.

Observational studies have reported that cosmic filaments on the megaparsec scale exhibit rotational motion. Subsequent simulation studies have shown qualitative agreement with these findings, but quantitative discrepancies remain due to differences in data and methods, which require verification. To address this issue, we adopt the same methodology as used in the observations to identify filament spin from the galaxy distribution constructed from a hydrodynamic simulation. Using the same approach to measure filament spin, we find that the simulation results closely match the observational findings, with only minor discrepancies arising from slight differences in the fraction of filaments classified as dynamically cold or hot based on their dynamic temperature. Additionally, an analysis of how filament spin affects the galaxy spin-filament correlation shows that filaments with strong spin signals and dynamically cold have a greater impact on the galaxy spin-filament correlation than those with weaker spin signals and dynamically hot filaments. These results not only provide further evidence that cosmic filaments exhibit spin, but also highlight the importance of this rotation in the acquisition of angular momentum by individual galaxies. Future studies exploring the influence of filament spin on galaxy spin may shed light on the physical origins of filaments and the angular momentum of galaxies.

We present a publicly available, high-resolution, filled-parameter-space synthetic distribution of the Plutinos, trans-Neptunian Objects (TNOs) librating in the 3:2 mean-motion resonance with Neptune, with particular focus on the Plutinos simultaneously Kozai-librating. This synthetic distribution was built in preparation for results from the Large inclination Distant Objects (LiDO) Survey, which pointed at locations on the sky where Kozai Plutinos are predicted to come to pericenter and are thus most easily detected in magnitude-limited surveys. Although we do not expect the full stable parameter-space presented here to be populated with real TNOs, it provides a useful starting point for comparison with Neptune migration simulations and debiased observational results. Our new stable parameter space synthetic distribution of fictitious Plutinos is consistent with previous works, and we build on past results by focusing on the behavior of Kozai Plutinos over 4Gyr integrations. We find that 95% of 4Gyr stable Kozai Plutinos remain in the same omega-libration island for the entire integration. This provides an interesting diagnostic opportunity: any asymmetry in the true number of 4Gyr stable Kozai Plutinos in the two omega-libration islands must be caused by the details of emplacement during giant planet migration. Through analysis of previously published Neptune migration models, we show that the intrinsic fraction of Plutinos captured into Kozai depends on Neptune's migration speed and mode. Combining the filled-parameter-space synthetic distribution with future migration simulations and the results of the carefully characterized LiDO survey will enable interpretation of the intrinsic orbital distribution of the Kozai and non-Kozai Plutinos.

We present a framework for dark matter (DM) halo formation based on a kinetic theory of self-gravitating fermions together with a solid connection to thermodynamics. Based on maximum entropy arguments, this approach predicts a most likely phase-space distribution which takes into account the Pauli exclusion principle, relativistic effects, and particle evaporation. The most general equilibrium configurations depend on the particle mass and develop a degenerate compact core embedded in a diluted halo, both linked by their fermionic nature. By applying such a theory to the Milky Way we analyze the stability of different families of equilibrium solutions with implications on the DM distribution and the mass of the DM candidate. We find that stable core-halo profiles, which explain the DM distribution in the Galaxy, exist only in the range $mc^2 \approx 194 - 387\,\rm{keV}$. The lower bound is a consequence of imposing thermodynamical stability on the core-halo solutions having a $4.2\times 10^6 M_\odot$ quantum core mass alternative to the black hole hypothesis at the Galaxy center. The upper bound is solely an outcome of general relativity when the quantum core reaches the Oppenheimer-Volkoff limit and undergoes gravitational collapse towards a black hole. We demonstrate that there exists a set of stable core-halo profiles which are astrophysically relevant in the sense that their total mass is finite, do not suffer from the gravothermal catastrophe, and agree with observations. The morphology of the outer halo tail is described by a polytrope of index $5/2$, developing a sharp decline of the density beyond $25\,\rm{kpc}$ in excellent agreement with the latest Gaia DR3 rotation curve data. Moreover, we obtain a total mass of about $2\times 10^{11} M_\odot$ including baryons and a local DM density of about $0.4\,\rm{GeV}\,c^{-2}\,\rm{cm}^{-3}$ in line with recent independent estimates.

We present particle-in-cell simulations of one dimensional relativistic electromagnetic shocks in a uniform magnetic field, for a range of magnetic field strengths, plasma temperatures and numerical initial conditions. We show that the particle energy distributions of these shocks can develop a state of population inversion in the precursor and shock regions, which may allow for synchrotron maser (or maser-like, coherent) emission. Our set-up is applicable to conditions expected in models of fast radio bursts and therefore lends credence to the synchrotron maser model for these transients. We also show, for the first time, how a newly developed ``analytic particle pusher'' for kinetic simulations gives similar results to the commonly-used Boris pusher, but for larger timesteps and without the need to resolve the gyro-radius and gyro-period of the system. This has important implications for modeling astrophysical plasmas in extreme magnetic fields as well as for bridging scales between kinetic and fluid regimes.

Context. Planetary migration models predict multiple planets captured into a chain of mean-motion resonances during the disk phase. Over a dozen systems have been observed in these configurations, nearly all close-in planets, with a lack of resonant chains for planets with orbital periods larger than ~300 days. Aims. Dynamical studies often overlook the fact that stars do not evolve in isolation. In this work, we explore the possibility that the absence of giant planets in long-period resonant chains may be due to post-formation disruption caused by stellar flybys. Methods. For planets in the 2:1-2:1 and 3:2-3:2 resonant chains, we evaluate the long-term stability after varying parameters such as the planet masses, as well as the inclination, pericentric distance, and mass of the flyby star. Results. Our integrations show that the 2:1-2:1 resonant chain is significantly more resilient to a stellar flyby than for the 3:2-3:2 configuration. The nature of the instability is different in both scenarios, the 2:1-2:1 becomes unstable quickly, soon after a penetrative close encounter. Instead, planets in the 3:2-3:2 chain become unstable in long timescales due to more distant flybys (up to q/a_out ~ 25 for Jupiter-mass planets) that only provide small perturbations for the system to chaotically dissolve. Conclusions. If an encounter occurs between a star hosting planets and a passing star, Jupiter-mass systems with 3 planets in a 3:2-3:2 resonant chain or more compact initial configurations are likely to be disrupted.

Freshly injected interstellar Pickup Ions (PUIs) are expected to exhibit a simple, torus-shaped velocity distribution function. The PUI velocity in the solar wind frame depends on the velocity of the interstellar neutral (ISN) population at the pick-up position. In this study, we compare PUI velocity distributions measured by the PLasma And SupraThermal Ion Composition (PLASTIC) instrument over the full orbit of Solar TErestrial RElations Observatory-Ahead (STEREO-A) directly. We define a new position-independent velocity measure for PUIs that takes the local direction of the interstellar neutral inflow into account. The resulting new PUI velocity measure corrects thereby for the position-dependent contribution of the ISN velocity. Pitch-angle distributions are then analysed depending on the magnetic-field azimuthal angle for different orbital positions and different values of the PUI velocity measure. The new PUI velocity measure shows an approximately constant cut-off over the complete orbit of STEREO-A. A torus signature is visible everywhere. Therein, a broadening of the torus signature outside the focusing cone and crescent regions and for lower velocity measure observed. In addition, we illustrate the symmetry between the primary and secondary ISN trajectory in the vicinity of the focusing cone. A torus signature associated with freshly injected PUIs is visible over the complete orbit of STEREO-A with increased density in the focusing cone. At least remnants of a torus signature remain for smaller values of the PUI velocity measure. The new velocity measure also prepares for PUI studies with Solar Orbiter.

While about 20 Type II supernova progenitors have been identified using optical data from the Hubble Space Telescope (HST), direct detection of type Ib/Ic supernova (SN Ib/Ic) progenitors remains challenging due to their faint optical brightness and highly obscured environments. This study aims to investigate the detection limits and advantages of near-infrared (near-IR) observations with the James Webb Space Telescope (JWST) and the Nancy Grace Roman Space Telescope (NGRST) for the detection of SN Ib/Ic progenitors. The spectral energy distributions of SN Ib/Ic progenitor models with various masses, chemical compositions, and mass-loss rates are calculated with the non-LTE radiative transfer code CMFGEN. We then assess the detectability of SN Ib/Ic progenitors using near-IR filters from the JWST and the NGRST, comparing the results to the capabilities of the HST. Our analysis indicates that near-IR observations significantly outperform the HST in detecting SN Ib/Ic progenitors when considering the effect of extinction. Near-IR magnitudes also provide better constraints on the mass-loss rates of progenitors because of the free-free emission from the wind matter. Additionally, near-IR magnitudes and color-color diagrams are effective in distinguishing SN Ib/Ic progenitors from possible companion and/or background objects. This study suggests that the JWST and the NGRST can play a crucial role in advancing our understanding of SN Ib/Ic progenitors by improving detectability and offering better constraints on progenitor properties. We emphasize that observations with exposure times exceeding 1 hour would be needed to detect typical SNe Ib/Ic progenitors at distances greater than 10 Mpc.

High-redshift little red dots (LRDs) detected with the James Webb Space Telescope are considered the cores of emerging galaxies. For the first time, we compare LRDs in $M_{\rm bh}$-$M_{\star}$ diagrams with an array of $z=0$ galaxy-morphology-dependent scaling relations, along with the $M_{\rm bh}$-$M_{\rm \star,nsc}$ relation for nuclear star clusters. The $M_{\rm bh}$-$M_{\rm \star,sph}$ relations for spheroidal stellar systems are characterised by a nearly parallel set of quasi-quadratic (or steeper) distributions that are known to trace the `punctuated equilibrium' of galaxies, reflecting their stepwise growth in black hole mass and merger-built bulge/spheroid mass. We show that LRDs are not equivalent to nuclear star clusters, with the latter having higher $M_{\rm bh}/M_{\star}$ ratios. However, the least massive LRDs exhibit similar $M_{\rm bh}$ and $M_{\rm \star,gal}$ values as ultracompact dwarf (UCD) galaxies. We show that the LRDs span the $M_{\rm bh}$-$M_{\rm \star,gal}$ diagram from UCD galaxies to primaeval lenticular galaxies. In contrast, spiral galaxies and the subset of major-merger-built early-type galaxies define offset relations. Additionally, we observe that low-$z$ galaxies with active galactic nuclei align with the steep black hole scaling relations for disc galaxies defined by primarily inactive galaxies with directly measured black hole masses. Collectively, this highlights the benefits of considering galaxy morphology, which reflects their accretion and merger history, to understand the coevolution of galaxies and their black holes.

The 8 April 2024 total solar eclipse (TSE) provides a unique opportunity to study the solar corona. This work presents our prediction of the solar corona at the time of the eclipse based on magnetohydrodynamic (MHD) modeling performed with the Alfvén Wave Solar Model-Realtime (AWSoM-R) in the Space Weather Modeling Framework, developed at the University of Michigan. We performed multiple simulations made with data input in the form of synchronic magnetograms from four sources, i.e., ADAPT-GONG, Lockheed Martin ESFAM, HipFT and NSO-NRT magnetograms. Simulations also include a higher-resolution model and a post-eclipse model incorporating newly emerged active regions. Our study fundamentally focuses on the limitations imposed by the lack of global solar observations, particularly on how these limitations affect coronal simulations. Specifically, we examine how differences among the magnetograms and the absence of observations from the east limb, due to the Sun's rotation, impact the accuracy of the predicted coronal structures. We synthesized a variety of representative observables, including the white-light and extreme-ultraviolet images from each model, and compared them with observations. The synthesized observables show remarkable differences because of the distinct magnetic coronal topologies, which stem from the varied magnetic flux distributions and the gaps in observational coverage. Our findings emphasize the need for comprehensive and multi-satellite magnetic field observations to improve future solar corona predictions.

We present an empirical chemical evolution model that explains the distribution of metals in the interstellar medium (ISM) and the circumgalactic medium (CGM) of galaxies based on the UniverseMachine and NeutralUniverseMachine models in the framework of $\Lambda$CDM structure formation. We parameterize the fractions of outflowing metals returned and mixed into the multi-phase ISM of the star-forming regions ($f_{\rm H2}$) and into the neutral gas regions ($f_{\rm HI}$); metal production, transfer, and dilution are caused by star formation, galaxy mergers, and gas inflow from the inter-galactic medium, respectively, with rates determined by the (Neutral)UniverseMachine models. Using a Markov Chain Monte Carlo algorithm, we explore the posterior distributions of metal return and mixing consistent with observed mass-metallicity relations in HII regions (at $0<z<5$), HI damped Lyman-alpha systems (at $1<z<4$), and the CGM (at $z=0$). We find that the fraction of metals present in the ISM, $f_{\rm H2}+f_{\rm HI}$, increases with halo mass from $\sim20$\% at $10^{10}M_\odot$ to $\sim80$\% at $10^{13}M_\odot$. These fractions increase mildly at higher redshifts, to $\sim30$\% at $10^{10}M_\odot$ and $\sim80$\% at $10^{13}M_\odot$ at $z=5$. Interestingly, there is no significant redshift evolution of $f_{\rm H2}+f_{\rm HI}$ at fixed circular velocity, suggesting that metal distribution between the ISM and CGM is universally determined by the halo potential well depth. CGM metal enrichment is thus slow in high-$z$ halos with deep potential wells. While $f_{\rm H2}$ monotonically increases with halo mass, $f_{\rm HI}$ peaks at $\sim10^{12}-10^{13} M_\odot$, suggesting that reinfall may be inefficient in larger-mass halos.

Image alignment plays a crucial role in solar physics research, primarily involving translation, rotation, and scaling. \G{The different wavelength images of the chromosphere and transition region have structural complexity and differences in similarity, which poses a challenge to their alignment.} Therefore, a novel alignment approach based on dense optical flow (OF) and the RANSAC algorithm is proposed in this paper. \G{It takes the OF vectors of similar regions between images to be used as feature points for matching. Then, it calculates scaling, rotation, and translation.} The study selects three wavelengths for two groups of alignment experiments: the 304 Å of the Atmospheric Imaging Assembly (AIA), the 1216 Å of the Solar Disk Imager (SDI), and the 465 Å of the Solar Upper Transition Region Imager (SUTRI). Two methods are used to evaluate alignment accuracy: Monte Carlo simulation and Uncertainty Analysis Based on the Jacobian Matrix (UABJM). \G{The evaluation results indicate that this approach achieves sub-pixel accuracy in the alignment of AIA 304 Å and SDI 1216 Å, while demonstrating higher accuracy in the alignment of AIA 304 Å and SUTRI 465 Å, which have greater similarity.

Dust concentration in protoplanetary disks (PPDs) is the first step towards planetesimal formation, a crucial yet highly uncertain stage in planet formation. Although the streaming instability (SI) is widely recognized as a powerful mechanism for planetesimal formation, its properties can be sensitive to the gas dynamical environment. The outer region of PPDs is subject to the vertical shear instability (VSI), which could further induce the Rossby wave instability (RWI) to generate numerous vortices. In this work, we use the multifluid dust module in Athena++ to perform a 3D global simulation with mesh refinement to achieve adequate domain size and resolution to resolve and accommodate all these instabilities. The VSI mainly governs the overall gas dynamics, dominated by the breathing mode due to dust mass loading. The dust strongly settles to the midplane layer, which is much more densely populated with small vortices compared to the dust-free case. Strong dust clumping is observed, which is likely owing to the joint action of the SI and dusty RWI, and those sufficient for planetesimal formation reside only in a small fraction of such vortices. Dust clumping becomes stronger with increasing resolution, and has not yet achieved numerical convergence in our exploration. In addition, we find evidence of the Kelvin-Helmholtz instability (KHI) operating at certain parts of the dust-gas interface, which may contribute to the temporary destruction of dust clumps.

Radiative transfer effects need to be taken into account when analysing spectral line observations. When the data are not sufficient for detailed modelling, simpler methods are needed. The escape probability formalism (EPF) is one such tool. We wish to quantify the model errors in the EPF analysis of interstellar clouds and cores. We introduce PEP, a parallel program for calculating fast EPF parameters quickly. We model full radiative transfer to generate synthetic observations for various cloud models. These are examined with the PEP program, and their results are compared to the actual beam-averaged kinetic temperatures, column densities, and volume densities. PEP enables the calculations of even millions of parameter combinations in a matter of seconds. However, the simple assumptions of EPF can lead to significant errors. In the tests the errors were typically within a factor of two, but could in some cases reach an order of magnitude. The model errors are thus similar or even larger than the statistical errors caused by the typical observational noise. Due to degeneracies, parameter combinations are better constrained than the individual parameters. The model errors could be reduced by using full radiative transfer modelling. However, in the absence of full knowledge of the source structure, the errors are difficult to quantify. We also present a method for approximate handling of hyperfine structure lines in EPF calculations. Both the observational statistical errors and the model errors need to be considered when estimating the reliability of EPF results. Full radiative transfer modelling is needed to better understand the true uncertainties.

We investigate the relationships between the properties of the cool circumgalactic medium (CGM), traced by Ca II absorption lines, and those of galaxies at $z<0.4$ by utilizing a galaxy-quasar pair sample compiled from the Year 1 data of the Dark Energy Spectroscopic Instrument (DESI). This large dataset, containing $\sim 900,000$ galaxy-quasar pairs within $200\,\rm kpc$, enables us to obtain composite spectra with sensitivity reaching to $\text{mÅ}$ level and to explore the Ca II absorption as a function of stellar mass, SFR, redshift, and galaxy types, including AGNs. Our results show a positive correlation between the absorption strength and stellar mass of star-forming galaxies with $\langle W_{0}^{\rm Ca\ II}\rangle \propto M_{*}^{0.5}$ over three orders of magnitude in stellar mass from $\sim 10^{8}$ to $10^{11} \, M_{\odot}$, while such a mass dependence is weaker for quiescent galaxies. For galaxies with similar mass, we find that Ca II absorption is stronger around star-forming galaxies than around quiescent galaxies especially within the inner regions ($<30\,\rm kpc$) of the halos. Among star-forming galaxies, the Ca II absorption further correlates with SFR, following $\propto \mathrm{SFR^{0.3}}$. However, in contrast to the results at higher redshifts, we find that stronger absorption around star-forming galaxies is not preferentially observed along the minor axis of galaxies, indicating a possible redshift evolution of CGM dynamics resulting from galactic feedback. Moreover, no significant difference between the properties of the cool gas around AGNs and galaxies is detected. Finally, we measure the absorption profiles with respect to the virial radius of dark matter halos and estimate the total Ca II mass in the CGM. The results show that the CGM contains a metal mass comparable to the metal mass in the ISM of galaxies.

Aims. Asteroseismic radius and Gaia distance (ARD) method has been proposed to establish the SBCRs for late-type stars. Methods. We select Kepler RGB stars with high-precision asteroseismic radii (uncertainties < 1%) and cross-match them with 2MASS, APASS, and Gaia to obtain Johnson-B, Johnson-V, G, J, H, and Ks-band photometric data. After applying selection criteria, we obtain 626 RGB stars to build the SBCR. Among these, 100 RGBs are used as independent validation for the distance, and the remaining samples are used to fit the SBCR. Results. First, using 526 targets with asteroseismic radii and Gaia distances, nine SBCRs are proposed based on 2MASS (J, H, Ks), APASS (Johnson-B, Johnson-V), and Gaia (G) photometry. The average rms scatter in these relations is 0.075 mag, which corresponds to an uncertainty of approximately 3.5% in distance. These relations are further validated using 100 independent samples with Gaia distances, showing no bias, with a dispersion of approximately 3%. Compared to interferometric measurements, a systematic underestimation of 2.3% was observed, and the discrepancy decreases as the angular diameter increases. Additionally, the distances of eclipsing binaries in the Large Magellanic Cloud and Small Magellanic Cloud obtained using our SBCRs are generally consistent with those measured in the literature, with a dispersion of 1% and a slight overestimation of 1% to 2.5%. Conclusions. The ARD method capitalizes on two key advantages for precise stellar distance determination: a statistically robust sample of homogeneous RGB stars with low observational costs, and independent distance verification through Gaia data. Such SBCRs can be further calibrated and expanded more efficiently and effectively.

We propose a new method for extracting bulk motion gases in the disk of a galaxy from HI data cubes, offering improvements over classical techniques like moment analysis and line profile fitting. Our approach decomposes the line-of-sight velocity profiles into multiple Gaussian components, which are then classified into (underlying and dominant) bulk and non-bulk motion gases based on criteria such as HI surface density, velocity dispersion, kinetic energy, and rotation velocity. A 2D tilted-ring analysis is employed to refine the kinematical parametres of the galaxy disk, ensuring robust extraction of the bulk motion gases. We demonstrate the effectiveness of this method using the HI data cubes of NGC 4559 from the WSRT-HALOGAS survey, distinguishing between bulk and non-bulk gas components. From this, we find that approximately 50% of the HI gas in NGC 4559 is classified as non-bulk, possibly linked to processes such as stellar feedback. This work provides a robust framework for analysing HI kinematics of galaxies from high sensitivity HI observations of galaxies like MeerKAT-MHONGOOSE and FAST-FEASTS and allows us to best exploit the kinematic information of the complex gas dynamics within galaxy disks.

In this work we provide a detailed derivation of the observed galaxy number over-density obtained by computing cosmological perturbations up to third order in redshift space and on very large scales. We compute all the relativistic and projection effects, arising from the observation of galaxies on the past light cone, including all redshift effects, i.e. peculiar velocities, Sachs-Wolfe (SW) effects, integrated SW effects, gravitational lensing and time delay terms. Moreover, we have considered all post- and post-post-Born contributions from the photon geodesic equations in order to take into account all possible effects due to the lensing distortions. The derivation is performed in the Poisson gauge. This work largely follows the formalism used in (Bertacca et al. 2014a, Bertacca et al. 2014b, Bertacca 2015, Bertacca et al. 2020), pushing it for the first time up to the third perturbative order. This result will be important for a variety of applications, such as a complete estimation of projection effects and the investigation of possible parity violation signatures in the 3- and 4-point galaxy correlation functions.

Quiescent galaxies (QGs) typically have little cold gas to form stars. The discovery of gas-rich QGs challenges our conventional understanding of the evolutionary paths of galaxies. We take advantage of a new catalog of nearby, massive galaxies with robust, uniformly derived physical properties to better understand the origin of gas-rich QGs. We perform a comparative analysis of the cold interstellar medium and star formation properties of carefully matched samples of galaxies with varying degrees of star formation activity and gas richness. QGs with different gas content have virtually identical morphological types, light concentration, mass-size relation, stellar age, dark matter halo mass, and black hole activity. The only distinguishing characteristic is the environment. Gas-rich satellite QGs reside in a lower-density environment than their gas-poor counterparts, as a consequence of which they manage to retain their gas and experience a higher probability of cold gas accretion or gas-rich mergers. The environmental densities of central QGs are similar regardless of their gas content. We suggest that the cold gas resides mainly in the outskirts of the gas-rich QGs, where bars, if present, cannot transport it inward efficiently to fuel central star formation. The prominent bulges in gas-rich QGs stabilize the cold gas from fragmentation and leads to low star formation efficiency.

This document presents a novel method for the intra-field calibration and imaging of the radio source SgrA$^*$, observed with the Atacama Large Millimeter/submillimeter Array (ALMA). SgrA$^*$ is a complex source comprising two components: the compact core (which exhibits high variability) and the extended minispiral (which is relatively stable over short timescales). The novel approach consists in a self-calibration method that employs the extended structure of the source (the minispiral) to calibrate the flux variability of the compact core. The algorithm involves several steps: (1) an initial CLEAN image is generated for the entire source; (2) the core is subtracted, leaving only the minispiral; (3) a two-component visibility model is constructed, comprising the minispiral and the core; (4) the model is fitted to the data, retrieving flux density parameters for each integration time; and (5) the data are scaled and calibrated, resulting in nearly constant brightness for the minispiral and variable flux for the core. The implementation of this algorithm through a script in the CASA package is described, detailing the configuration parameters and the steps involved. The success of the method is demonstrated through light curves of SgrA$^*$ observed on day 21 April 2018 in Band 6, as part of the 2018 EHT campaign. The light curves have been produced for Stokes I (total intensity), linear polarized intensity, EVPA (electric vector position angle), and Stokes V (circular polarization), providing valuable insights into the variability of this radio source.

The optical depth to reionization, a key parameter of the $\Lambda$CDM model, can be computed within astrophysical frameworks for star formation by modeling the evolution of the intergalactic medium. Accurate evaluation of this parameter is thus crucial for joint statistical analyses of CMB data and late-time probes such as the 21 cm power spectrum, requiring consistent integration into cosmological solvers. However, modeling the optical depth with sufficient precision in a computationally feasible manner for MCMC analyses is challenging due to the complexities of the nonlinear astrophysics. We introduce NNERO (Neural Network Emulator for Reionization and Optical depth), a framework that leverages neural networks to emulate the evolution of the free-electron fraction during cosmic dawn and reionization. We demonstrate its effectiveness by simultaneously constraining cosmological and astrophysical parameters in both standard cold dark matter and non-cold dark matter scenarios, including models with massive neutrinos and warm dark matter, showcasing its potential for efficient and accurate parameter inference.

We present photometric observations of the BL Lacertae object S5 0716+714 with a temporal resolution of 120 s in the Sloan i' and r' bands. These observations were conducted using the Comet Search Program telescope at Xingming Observatory from 2018 December 22 to 2020 February 15, and more than 5600 effective images were obtained on each filter across 79 nights. Additionally, we compiled long-term variability data spanning 34 yr in the optical UBVRI bands. Using the power-enhanced F-test and nested ANOVA test, we found intraday variability (IDV) on 31 nights and possible IDV on 20 nights in the i' band. Similarly, IDV was detected on 35 nights in the r' band, while possible IDV was observed on 22 nights. The minimum variability timescale is 7.33 minutes, and the estimated black hole masses are (0.68- 5.12)*10^8 Msun. The spectral variability and long-term optical light curves reveal a bluer-when-brighter trend on intraday timescales. The long-term optical flux density and spectral index exhibit periodic variability with a timescale of about 1038 days. An anticorrelation between optical flux and spectral index was observed, with a time delay of -140 days. Variability across different optical bands exhibited a strong correlation, with no discernible time lag. From the IDV, spectral variability, correlation, and time delays between different bands, we conclude that these radiation characteristics may result from the shock-in-jet model scenario.

Coronal lines are forbidden emission lines with a ionisation potential $\chi\gtrsim100\,{\rm eV}$. They are linked to energetic phenomena triggered by AGNs in the circumnuclear medium. We present the first high-angular-resolution integral-field analysis of the $[{\rm Fe\,VII}]\,\lambda6087$ coronal line in a sample of four nearby low-inclination Seyfert galaxies (three of Type 1 and one of Type 2). The data were obtained with the adaptive-optics-assisted mode of MUSE, and have angular resolutions of $0.06-0.18\,{\rm arcsec}$, allowing us to probe regions down to a few tens of parsecs in size. In three of the objects, we find a resolved coronal emission in a relatively compact configuration ($\lesssim200\,{\rm pc}$ in radius). The coronal emission is smooth and symmetric with respect to the centre of the galaxy, except for one object where an off-nucleus clump of emission is detected. Through the use of spectroastrometry we find that the $[{\rm Fe\,VII}]$ outflow of the Type 2 AGN host has a redshifted and a blueshifted component whose centroids are separated by $\sim20\,{\rm pc}$. We interpret this as evidence that some of the coronal emission comes from the inner part of a biconic outflow, also seen in low-ionisation lines. Similar $[{\rm Fe\,VII}]$ properties are found in two of the Type 1 AGN hosts, but with a much smaller separation between the centroids of the lobes of the outflow ($<7\,{\rm pc}$). This could be due to the foreshortening of the axis of the bicone in Type 1 objects. We also studied the spectrum of the unresolved nuclear source and found that in three out of four galaxies a fraction of at least $\sim60\%$ of the $[\textrm{Fe VII}]$ emission has kinematics similar to those of $[{\rm O\,III}]$. We conclude that part of the coronal emission within the inner few tens of parsecs is co-spatial and shares kinematics with the outflows as traced by lower-ionisation lines.

Observations and simulations of coronal rain show that as cold and dense plasma falls through the corona it initially undergoes acceleration by gravity before the downward velocity saturates. Simulations have shown the emergence of an unexpected relation between terminal velocity of the rain and density ratio that has not been explained. Our aim is to explain this relation. In this paper we develop a simple point-mass model to understand how the evolution of the ambient corona moving with the coronal rain drop can influence the falling motion. We find that this simple effect results in the downward speed reaching a maximal value before decreasing, which is consistent with simulations with realistic coronal rain mass. These results provide an explanation for the scaling of the maximum downward speed to density ratio of the rain to the corona and as such provide a new tool that may be used to interpret observations.

The Central Molecular Zone (CMZ) of the Galactic Center (GC) region of the Milky Way contains a substantial fraction of the molecular mass of the Galaxy >10e7 solar masses yet exhibits an order of magnitude lower star formation efficiency (SFE) than expected given the high densities found in this region. There are multiple possible explanations for the depressed SFE in the CMZ, like feedback, strong turbulence, longer free-fall timescales, and high magnetic field strengths. It is currently unclear which of these mechanisms is the dominant inhibitor of star formation in the CMZ. It is important to understand the star formation process in the extreme environment of the CMZ because it is the only Galactic nuclear region we are able to study at high spatial resolutions with current observatories. One way to determine the relative importance of the different SFE inhibiting mechanisms is through multi-spatial and multi-frequency polarimetric observations of the CMZ. Such observations will provide insight into the behavior of the magnetic field in this unique environment. These observations will complement radio observations of non-thermal structures revealing the magnetic field morphology and polarization. The PRobe far--Infrared Mission for Astrophysics (PRIMA) will be uniquely capable of contributing to such explorations by providing unique resolutions and frequencies for polarimetric observations. The PRIMAger instrument will yield polarimetric observations covering the wavelength range 80 -- 261 um with beam sizes ranging from 11 -- 28'', capabilities that complement existing and upcoming observatories.

We have presented a new approach to separate small spectral $\mu$ and $y$ distortions of the CMB from foreground components with poorly defined spectral shapes. Our linear method, called the Least Response Method (LRM), is based on the idea of simultaneously minimizing the response to all possible foregrounds and photon noise while maintaining a constant response to the useful signal. We compared our approach with the mILC method, which is a modification of the Internal Linear Combination previously used for CMB anisotropy maps, and proved the advantages of LRM. In addition, we found the optimal temperature of the telescope optical system for any experiments related to the study of the CMB $\mu$ distortions.

Astrophysical masers are widely used in star formation studies. In particular, they are valuable in investigations of high-mass star-forming regions that are difficult to observe at optical frequencies. We used multi-transition data to derive physical conditions in the immediate environment of forming high-mass stars. Simultaneous observations of two maser transitions, excited OH at 6.035 GHz and methanol at 6.668 GHz, were made using e-Merlin. Both transitions are radiatively pumped but prefer diverse physical conditions. We imaged ten high-mass star-forming sites with milliarcsecond angular resolution, identifying regions where excited OH and methanol masers coexist and where they avoid each other. Moreover, we identified circularly polarized Zeeman splitting pairs of the OH transition, estimating magnetic field strengths in the range from 0.2 to 10.6~mG. The detection of linearly polarized components enabled us to compare the directions of magnetic field vectors with the outflows coming from the young star-forming objects. We found that the two maser lines appeared to coexist in six high-mass star-forming regions, in cloudlets separated by up to 205~au. Where the lines show avoidance, this can be related to changes in dust and gas temperatures; we also found a few examples suggestive of a high gas density. In seven sources, Kolmogorov-Smirnov tests show the nonrandom relationship between the position angles of distribution of the two maser transitions. We did not obtain consistent results regarding the direction of the magnetic field and outflow.

Spiral jets are impulsive plasma ejections that typically show an apparent rotation motion. Their generation, however, is still nont understood thoroughly. Based on a high-resolution vector magnetogram form the Polarimetric and Helioseismic Imager onboard Solar Orbiter, we constrcut a data-constrained three-dimensional (3D) MHD model, aiming to disclose the eruption mechanism of a tiny spiral jet at a moss region observed on March 3 2022. The initial configuration of the simulation consists of an extrapolated coronal magnetic field based on the vector magnetogram and an inserted unstable flux rope constructed by the Regularized Biot-Savart Laws method. Our results highlight the critical role of the fan-spine configuration in forming the spiral jet and confirm the collapse of the pre-existing magnetic null to a curved 3D current sheet where external reconnection takes places. It is further disclosed that the flux rope quickly moves upward, reconnecting with the field lines near the outer spine, thereby enabling the transfer of twist and cool material from the flux rope to the open field, giving rise to the tiny spiral jet we observed. The notable similarities between these characteristics and those for larger-scale jets suggest that spiral jets, regardless of their scale, essentially share the same eruption mechanism.

We explore the hypothesis that the weak emission lines observed in some early-type galaxies (ETGs) are due to ionization by hot low-mass evolved stars (HOLMES) and analyze the pros and cons.

The high-mass X-ray binary Cygnus X-3 has been suggested for a long time to be a source of high-energy photons and neutrinos. In view of the increased sensitivity of current experiments, we examine the acceleration and interactions of high-energy cosmic rays (CRs) in this binary system, assuming that the compact object is a black hole. Using a test-particle approach in a Monte-Carlo framework, we employ as the basic CR acceleration mechanisms magnetic reconnection or this http URL order Fermi acceleration and diffusive shock acceleration. We find that in all three scenarios CRs can be accelerated beyond PeV energies. High-energy photons and neutrinos are produced as secondaries in photo-hadronic interactions of CRs on X-ray photons and in the scattering on gas from the wind of the companion star. Normalising the predicted photon flux to the excess flux observed by LHAASO at energies above PeV in the direction of Cygnus X-3, a CR acceleration efficiency of $10^{-3}$ is sufficient to power the required CR luminosity. Our results suggest that the PeV photon flux from Cygnus X-3 could be in a bright phase significantly increased relative to the average flux of the last years.

Strong magnetic fields in the core of red-giant branch stars are expected to suppress the amplitudes of the multipole modes. This occurs when the strength of the internal magnetic field approaches the critical field strength, at which the magnetic forces become comparable to the buoyancy. We performed Hamiltonian ray tracing simulations of magneto-gravity waves to investigate the suppression of the multipole modes in the presence of an internal dipole-like magnetic field. We took into account different stellar masses, metallicities, and ages, as well as various oscillation frequencies and spherical degrees. In particular, we estimated the trapped fraction, a measure of multipole mode suppression, which quantifies the fraction of mode energy in the core that is dissipated by the interaction with the magnetic field. Our results indicate that the trapped fraction can be described by a simple expression, which smoothly connects the regime without multipole mode suppression with the regime with complete suppression of the multipole modes. Crucially, the trapped fraction depends only on the ratio between the strength of the internal magnetic field and the critical field strength. Therefore, our expression for the trapped fraction provides a flexible tool that can be used, for example, to estimate the amount of multipole mode suppression as a star ascends the red-giant branch or to investigate the onset of the suppression in observed power spectral densities.

We derive Fe-abundance ratios of 6 galaxies at $z=9-12$ with $-22<M_{\mathrm{UV}}<-19$ whose JWST/NIRSpec spectra achieve very high signal-to-noise ratios, $\mathrm{SNR}=40-230$, at the rest-frame UV wavelength. We fit stellar synthesis model spectra to these JWST spectra, carefully masking out nebular emission, interstellar absorption, and non-iron stellar absorption lines, and obtain Fe-abundance ratios of $\mathrm{[Fe/H]}=-2-0$ for 4 galaxies and upper limits of $\mathrm{[Fe/H]}\sim-1$ for 2 galaxies. We compare these [Fe/H] values with the oxygen abundances of these galaxies ($7.2<12+\log{\mathrm{(O/H)}}<7.9$) in the same manner as previous studies of low-$z$ galaxies, and derive oxygen-to-iron abundance ratios [O/Fe]. We find that majority of (4 out of 6) galaxies are consistent with iron-poor abundance ratios ($\mathrm{[O/Fe]}\gtrsim0$) while that 2 out of 6 galaxies, GS-z11-0 and GN-z11, show Fe enhancements ($\mathrm{[O/Fe]}<0$), especially GS-z11-0 ($z=11.12$) with a Fe enhancement ($\mathrm{[O/Fe]}=-0.91_{-0.42}^{+0.35}$) beyond the solar-abundance ratio at $\sim3\sigma$. Because, unlike GS-z11-0, GN-z11 ($z=10.60$) may be an AGN, we constrain [O/Fe] via FeII emission under the assumption of AGN and confirm that the Fe enhancement is consistent even in the case of AGN. While [O/Fe] values of the majority of the galaxies are explained by the chemical enrichment of core-collapse supernovae (CCSNe), the Fe enhancements of GS-z11-0 and GN-z11 are puzzling. We develop chemical evolution models, and find that the iron enhancements against oxygen in GS-z11-0 and GN-z11 can be explained by 1) pair-instability supernovae/bright hypernovae with little contribution of CCSNe or 2) Type-Ia supernovae with short delay time ($\sim30-50$ Myr) with a top-light initial mass function.

Solar microflares are ubiquitous in the solar corona, yet their driving mechanisms remain a subject of ongoing debate. Using high-resolution coronal observations from the Solar Orbiter's Extreme Ultraviolet Imager (EUI), we identified about a dozen distinct moving plasma structures (hereafter, `` tiny ejections'') originating from the centers of three homologous microflares out of four successive events. These tiny ejections propagate roughly perpendicular to the flaring loops. They often originate as dot-like structures with a length scale of approximately $10^{3}$ km. While these initial dot-like shapes are observable in EUI images, they remain undetectable in the images captured by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. As they propagate, these dot-like structures consistently evolve into loop-like formations, possibly due to the heating of the surrounding magnetic field. Rather than being generated by a series of flux rope eruptions, the tiny ejections appear to result from small-angle magnetic reconnections within a bipolar field. Thus, the microflares associated with these ejections may be driven by magnetic reconnection within braided fields, a process similar to the proposed nanoflare mechanism and distinct from the standard large-scale flare model.

The detection of spectral bands at 3.06 um by MicrOmega, combined with the chemical identification of other NH-containing organic molecules in Ryugu samples, suggests the presence of potential NH-bearing compounds. However, the chemical forms of these NH-rich compounds, whether associated with N-rich organics, ammonium (NH4+) salts, NH4 or NH-organics-bearing phyllosilicates, or other forms, remain to be better understood. In this study, we report the characterization of two Ryugu particles (C0050 and C0052) using multi-scale infrared (mm-reflectance, micro-FTIR, and nano-AFM-IR) and NanoSIMS techniques to constrain the nature and origin of NH-bearing components in the Ryugu asteroid. Our findings show that Ryugu's C0052 particle contains rare, micrometer-sized NH-rich organic compounds with peaks at 1660 cm-1 (mainly due to C=O stretching of the amide I band) and 1550 cm-1 (mainly due to N-H bending vibration mode of the amide II band), indicative of amide-related compounds. In contrast, these compounds are absent in C0050. Notably, nitrogen isotopic analysis reveals that these amides in C0052 are depleted in 15N (d15N = -215 +/- 92 permil), confirming their indigenous origin, while carbon and hydrogen isotopic compositions are indistinguishable from terrestrial values within errors (d13C = -22 +/- 52 and dD = 194 +/- 368 permil). The amides detected in C0052 could have formed through hydrothermal alteration from carboxylic acids and amines precursors on the Ryugu's parent planetesimal. Alternatively, they could have originated from the irradiation of 15N-depleted N-bearing ice by UV light or galactic cosmic rays, either at the surface of the asteroid in the outer Solar System or on mantle of interstellar dust grains in the interstellar medium. Amides delivered to early Earth by primitive small bodies, such as asteroid Ryugu, may have played a crucial role in prebiotic chemistry.

Abundances of five elements, Na, Mg, Al, Si, and Sr, are investigated for 44 very metal-poor stars (-4.0 < [Fe/H] < -1.5) in the Galactic halo system based on an Local Thermodinamic Equilibrium (LTE) analysis of high-resolution near-infrared spectra obtained with the Infrared Doppler instrument (IRD) on the Subaru Telescope. Mg and Si abundances are determined for all 44 stars. The Si abundances are determined from up to 29 lines, which provide reliable abundance ratios compared to previous results from a few optical lines. The Mg and Si of these stars are over-abundant, relative to iron, and are well-explained by chemical-evolution models. No significant scatter is found in the abundance ratios of both elements with respect to iron, except for a few outliers. The small scatter of the abundance ratios of these elements provides constraints on the variations of stellar and supernova's yields at very low metallicity. Al abundances are determined for 27 stars from near-infrared lines (e.g., 1312nm), which are expected to be less affected by non-LTE (NLTE) effects than optical resonance lines. The average of the [Al/Fe] ratios is close to the solar value, and no dependence on metallicity is found over -3.0 < [Fe/H] < -2.0. Na abundances are determined for 12 stars; they exhibit Solar abundance ratios and no dependence on metallicity. The Sr abundances determined from the Sr II triplet are significantly higher than those from the optical resonance lines obtained by previous studies for our sample. This discrepancy shows a clear dependence on temperature and surface gravity, supporting models that predict large NLTE effects on the near-infrared lines for metal-poor red giants.

Context. The solar corona maintains temperatures of a million Kelvin or more. The plasma heating mechanisms responsible for these extreme temperatures are still unclear. Large regions of magnetic activity in the photosphere cause extreme ultraviolet (EUV) emission in the corona. Even smaller regions with bipolar and multipolar magnetic fields can generate coronal bright points (CBPs). Aims. We performed a statistical analysis of 346 CBPs. We used Solar Dynamics Observatory (SDO) images to track CBPs on a continuous basis. Therefore, we were able to collect a database of information on the CPB's lifetime, shape, polarity, flux emergence, and merging behavior, as well as their magnetic evolution, using the SDO Helioseismic and Magnetic Imager (SDO-HMI) instrument. Methods. We searched the SDO data archive for the longest continuous interval of uninterrupted observations in 2015. The longest such interval contains 12 consecutive days of full-disk images from the EUV channels of the SDO-AIA instrument. To analyze the properties of CBPs, we employed an automated tracking algorithm to follow the evolution of the CBPs. Furthermore, we manually checked the shape, underlying magnetic polarities, and merging behavior of each CBP. Results. We provide statistics on the magnetic polarity, emergence, and merging of CBPs. We established a relationship between the CBP's merging behavior and both its shape and magnetic polarities. Brighter CBPs are visible in all SDO-AIA channels and exhibit strong radiative energy losses. The category of CBPs with a bipolar field has the highest probability of being emissive in all SDO-AIA channels. The majority of CBPs have two opposite polarities below them. Conclusions. The merging of two CBPs is an unusual phenomenon that is related to complex multipolar magnetic regions. Moreover, loop-shaped CBPs usually appear above bipolar fields... (see full abstract in pdf)

This paper addresses the evolution of an axially symmetric magnetic field in the core of a neutron star. The matter in the core is modeled as a system of two fluids, namely neutrons and charged particles, with slightly different velocity fields, controlled by their mutual collisional friction. This problem was addressed in our previous work through the so-called ``fictitious friction'' approach. We study the validity of our previous work and improve it by comparing the fictitious friction approach to alternatives, making approximations that allow it to be applied to arbitrary magnetic field strengths and using realistic equations of state. We assume the neutron star crust to be perfectly resistive, so its magnetic field reacts instantaneously to changes in the core, in which we neglect the effects of Cooper pairing. We explore different approaches to solve the equations to obtain the velocities and chemical potential perturbations induced by a given, fixed magnetic field configuration in the core. We also present a new version of our code to perform time-evolving simulations and discuss the results obtained with it. Our calculations without fictitious friction further confirm that bulk velocity is generally much greater than ambipolar velocity, leading to faster evolution. These findings align with those with fictitious friction, validating this approach. We also find that, in the long term, the star evolves towards a barotropic ``Grad-Shafranov equilibrium,'' where the magnetic force is fully balanced by charged particle fluid forces. Qualitatively, the evolution and the final equilibrium are independent of the magnetic field strength $B$ and the equation of state considered. The timescale to reach this equilibrium is proportional to $B^{-2}$ and becomes shorter for equations of state with a smaller gradient of the ratio between the densities of protons and neutrons.

VERITAS began full-scale operations in 2007 and it remains one of the world's most sensitive very-high-energy (VHE; E >100 GeV) gamma-ray observatories. More than 8,300 hours (~50%) of its good-weather data were targeted on active galactic nuclei (AGN). Many of these observations were taken as part of an ongoing comprehensive program to discover new VHE AGN. Upon discovery, the VERITAS collaboration leverages VHE spectral and variability measurements, and accompanying broadband observations to probe the underlying jet-powered processes in AGN. Recent scientific highlights from the VERITAS AGN discovery program, including the VHE discoveries of B2 0912+29, 1ES 1028+511, 1ES 1118+424 and RBS 1366, are presented.

We present metallicities derived from a sample of eleven M dwarfs belonging to wide binary systems with warmer FG primary companions observed by the high-resolution (R=22,500) near-infrared SDSS-IV APOGEE spectra. Using a plane-parallel one-dimensional local thermodynamic equilibrium (LTE) abundance analysis, we determine effective temperatures ($T_{\rm eff}$) based on the abundance equilibrium from the Fe I, FeH, OH, and H$_2$O spectral lines. We obtained three $T_{\rm eff}$ scales based on these lines and found that, regardless of the chosen $T_{\rm eff}$ scale, the M dwarf metallicities agree well with those of the warmer primaries, where the upper mean abundance difference limit is 0.04 $\pm$ 0.06. This good agreement confirms that FeH lines are a reliable indicator of $T_{\rm eff}$ in the $H-$band spectra.

The light that we receive from clusters of galaxies is redshifted by the presence of the clusters' gravitational potential. This effect, known as gravitational redshift, is an early prediction of Einstein occurring in any metric theory of gravity. As a direct consequence, the central galaxy, located near the bottom of the gravitational potential, is observed to be more redshifted than the cluster members. In 2011, a first detection of this redshift difference on cluster scales was achieved and compared with theoretical predictions for gravitational redshift in various theories of gravity. However, the interpretation of this result has been challenged by several later studies, which emphasised the possible influence of additional kinematic effects on the observed signal from stacked clusters. In this work, we present the first derivation of all such effects within a relativistic framework, accurate to third order in the weak-field approximation. This framework allows us to correctly capture the hierarchy of terms at the scale of clusters, while accounting for all relativistic effects. We compare our result with previous literature and show that some terms were not properly included, leading to an overestimation of the kinematic contamination.

The mass function (MF) of isolated objects measured by microlensing consists of both a stellar and a planetary component. We compare the microlensing MFs of Gould et al (2022) and Sumi et al (2023) to other measurements of the MF. The abundance of brown dwarfs in the Sumi et al (2023) stellar MF is consistent with measurements from the local solar neighborhood (Kirkpatrick et al 2024). Microlensing free-floating planets ($\mu$FFPs) may may be free-floating or orbit host stars with semimajor axes $a\gtrsim 10~\mathrm{au}$ and therefore can constrain the populations of both free-floating planetary-mass objects and wide-orbit planets. Comparisons to radial velocity and direct imaging planet populations suggest that either most of the $\mu$FFP population with masses $>1~M_{\rm Jup}$ is bound to hosts more massive than M dwarfs or some fraction of the observed bound population actually comes from the low-mass tail of the stellar population. The $\mu$FFP population also places strong constraints on planets inferred from debris disks and gaps in protoplanetary disks observed by ALMA.

Titan has a climate system with similarities to Earth, including the presence of a thick atmosphere made up of several atmospheric layers. As on Earth, Titan's climate is influenced by several factors: the gaseous species making up the atmosphere, the energy deposited on the satellite, and solid organic aerosols. Indeed, numerous observations have revealed the presence of solid particles in the form of an opaque orange haze in Titan's atmosphere, influencing radiation balance and atmospheric dynamics, for example. However, the influence of these suspended solid particles seems to evolve according to the atmospheric altitude where they are located, certainly testifying to the presence of organic solids with different physico-chemical properties. At present, it is suspected that several populations/classes of atmospheric aerosols may form following different chemical pathways, and that aerosols undergo growth processes that modify their properties. We propose the calculation of an uptake coefficient between six neutral gaseous products (C2H2, HCN, C2H6, C2H3N, HC3N, C2N2) and the surface of the Titan aerosol analogues produced in this study.

Characterizing the growth of supermassive Black Holes (SMBHs) is critical to the evolution of galaxies, however the majority of this activity is obscured, rendering traditional tracers of active SMBHs, such as in the restframe optical/UV, ineffective. The mid-infrared has been particularly successful in revealing obscured AGN activity however much of this work is confined to the local universe due to the lack of a far-IR telescope with the required sensitivity and wavelength coverage. In this work we demonstrate the effectiveness of PRIMA (PRobe far-Infrared Mission for Astrophysics), a concept 1.8m far-IR observatory, to detect and characterize deeply obscured galaxy nuclei over cosmic time. With the PRIMAger instrument covering 25 - 235 $\mu$m, we find that we can accurately detect obscured nuclei via the deep silicate absorption at restframe $9.8 \mu$m between $z=2-7$. Additionally, the FIRESS spectrograph can produce R$\sim$100 spectra of obscured nuclei out to $z\sim7$, detecting Polycyclic Aromatic Hydrocarbons (PAHs), ices, ionized and molecular gas. With the large number of deeply obscured nuclei PRIMA can detect and characterize, such a mission is critical to understanding the growth of SMBHs.

The Central Molecular Zone (CMZ), a star-forming region rich in molecular clouds located within hundreds of parsecs from the centre of our Galaxy, converts gas into stars less efficient than anticipated. A key challenge in refining star-formation models is the lack of precise mapping of these dense molecular hydrogen clouds, where traditional tracers often yield inconsistent results due to environmental limitations. We demonstrate how, in the not-so-far future, neutrinos will emerge as a robust mass tracer thanks to advancements in neutrino telescopes. Since neutrinos are produced alongside gamma-rays when cosmic-rays interact with molecular clouds, they offer a complementary, systematics-independent measurement of the gas density. In an optimistic case where most gamma-ray emission from the Galactic Centre region originates from pion decays, we expect several tens of muon neutrinos to be detected in about two decades by KM3NeT, Baikal-GVD, and P-ONE combined, which will enable a better determination of the baryonic content in the Galactic Centre region. The CMZ will serve as a testbed to calibrate conventional tracers against neutrinos, ultimately improving gas measurements in distant galaxies, where neutrinos are undetectable, but traditional tracers remain available.

Recent cosmological observations suggest that the dark energy equation of state may have changed in the latter stages of cosmic history. We introduce a quintessence scenario, termed bounded dark energy, capable of explaining this feature in a technically natural way. Our approach is motivated from a bottom-up perspective, based on the concept of mirage cut-off, where we demonstrate the stability of the quintessence potential against large quantum corrections. At the same time, the bounded dark energy framework aligns well with top-down considerations motivated from quantum gravity arguments. We employ both human-driven insights and machine learning techniques to identify explicit realizations of bounded dark energy models. We then perform an analysis based on Markov Chain Monte-Carlo to assess their predictions against CMB, galaxy surveys, and supernova data, showing that bounded dark energy provides a good fit to current observations. We also discuss how upcoming measurements can further test and refine our proposal.

We introduce a novel, fast, and efficient generative model built upon scattering covariances, the most recent iteration of the scattering transforms statistics. This model is designed to augment by several orders of magnitude the number of map simulations in datasets of computationally expensive CMB instrumental systematics simulations, including their non-Gaussian and inhomogeneous features. Unlike conventional neural network-based algorithms, this generative model requires only a minimal number of training samples, making it highly compatible with the computational constraints of typical CMB simulation campaigns. We validate the method using realistic simulations of CMB systematics, which are particularly challenging to emulate, and perform extensive statistical tests to confirm its ability to produce new statistically independent approximate realizations. Remarkably, even when trained on as few as 10 simulations, the emulator closely reproduces key summary statistics -- including the angular power spectrum, scattering coefficients, and Minkowski functionals -- and provides pixel-to-pixel covariance estimates with substantially reduced sample noise compared to those obtained without augmentation. The proposed approach has the potential to shift the paradigm in simulation campaign design. Instead of producing large numbers of low- or medium-accuracy simulations, future pipelines can focus on generating a few high-accuracy simulations that are then efficiently augmented using such generative model. This promises significant benefits for current and forthcoming cosmological surveys such as $Planck$, $LiteBIRD$, Simons Observatory, CMB-S4, Euclid and Rubin-LSST. We make both the general framework for scattering transform statistics available at this https URL and the emulator available at this https URL.

X-ray polarimetry offers a unique window into neutron star physics and can provide answers to questions that cannot otherwise be probed. The up-and-coming REDSoX sounding rocket mission will be the first experiment equipped with a detector able to explore polarized X-rays below 1 keV, observing in the 0.2-0.4 keV range. Although REDSoX will only be capable of short, one-off observations, it will crucially test the instrument performance. In this paper we investigate how a fully-fledged orbital mission with longer lifetime, based on an instrument design similar to REDSoX, will allow us to study thermal emission from the X-ray dim isolated neutron stars (XDINSs) and magnetars, probing their magnetic field and the physics of their outer surface layers, including vacuum effects and QED mode conversion at the vacuum resonance. We discuss the potentially observable features for promising values of the star's surface temperature, magnetic field, and viewing geometry. Assuming emission from the whole surface, we find that, for a source with a magnetic field B=5x10^{13} G and surface temperature T~10^7 K, the instrument can resolve a proton-cyclotron absorption feature in the spectrum with high significance when collecting ~25,000 counts across a single observation. Similarly, for a source with B=10^{14} G and T~10^7 K, a switch in the dominant polarization mode, caused by mode conversion at the vacuum resonance, can be detected by collecting ~25,000 counts, allowing for a long-sought observational test of the presence of QED effects. We then present two case studies for XDINS targets: RX J1856.5-3754 and RX J0720.4-3125.

We study dark matter halos modeled by general relativistic polytropic spheres in spacetimes with the repulsive cosmological constant representing vacuum energy density, governed by a polytropic index $n$ and a relativistic (cosmological) parameter $\sigma$ ($\lambda$) determining the ratio of central pressure (vacuum energy density) and central energy density of the fluid. To give mapping of the polytrope parameters for matching extension and mass of large dark matter halos, we study properties of the polytropic spheres and introduce an effective potential of the geodesic motion in their internal spacetime. Circular geodesics enable us to find the limits of the trapping polytropes with central regions containing trapped null geodesics; supermassive black holes can be formed due to the instability of the central region against gravitational perturbations. Stability of the polytropic spheres relative to radial perturbations is determined. We match extension and mass of the polytropes to those of dark matter halos related to large galaxies or galaxy clusters, with extension $100 < \ell/\mathrm{kpc} < 5000$ and gravitational mass $10^{12} < M/M_\odot < 5 \times 10^{15}$. The observed velocity profiles simulated by the phenomenological dark matter halo density profiles can be well matched also by the velocity profiles of the exact polytrope spacetimes. The matching is possible by the non-relativistic polytropes for each value of $n$, with relativistic parameter $\sigma \leq 10^{-4}$ and very low central energy density. Surprisingly, the matching works for ``spread'' relativistic polytropes with $n > 3.3$ and $\sigma \geq 0.1$ when the central density can be much larger. The trapping polytropes forming supermassive black holes must have $n > 3.8$ and $\sigma > 0.667$.

Binary black hole systems are typically assumed to evolve in vacuum. However, the environment surrounding the binary components can influence their properties, such as their tidal deformability, affecting the gravitational waveform produced by the binary and its interpretation in gravitational wave data analysis. In this work we focus on next-generation experiments, such as the Einstein Telescope and LISA, and we quantify the systematic biases in gravitational wave observations that arise when tidally deformed binaries are interpreted as occurring in vacuum. We consider binaries over a range of masses and we compare different phenomenological models for the dynamical evolution of the tidal deformability. We find that systematic biases could significantly affect the measurability of the binary parameters if tidal effects are not carefully modeled.

Observation of an exploding black hole would provide the first direct evidence of primordial black holes, the first direct evidence of Hawking radiation, and definitive information on the particles present in nature. However, indirect constraints suggest that direct observation of an exploding Schwarzschild black hole is implausible. We introduce a dark-QED toy model consisting of a dark photon and a heavy dark electron. In this scenario a population of light primordial black holes charged under the dark $u(1)$ symmetry can become quasi-extremal, so they survive much longer than if they were uncharged, before discharging and exhibiting a Schwarzschild-like final explosion. We show that the answer is "yes", in this scenario the probability of observing an exploding black hole over the next $10$ years could potentially be over $90\%$.

We investigate a novel gravitational wave (GW) production mechanism from gravitons generated during the pre-thermal phase of cosmic reheating, where the energy density is dominated by non-thermalized inflaton decay products, dubbed reheatons. We consider multiple production channels, including: $i)$ pure inflaton-inflaton annihilation, $ii)$ graviton Bremsstrahlung from inflaton decay, $iii)$ scatterings between an inflaton and a reheaton, and $iv)$ scatterings among reheatons. To determine the resulting GW spectrum, we solve the Boltzmann equation to obtain the graviton phase-space distribution for each channel. We find that the third channel, $iii)$, dominates due to the large occupation number of reheatons at highly-energetic states during the pre-thermalization phase. Notably, in scenarios with a low inflaton mass, the GW spectrum could fall within the sensitivity range of future experiments such as the Einstein Telescope, the Cosmic Explorer, the Big Bang Observer, and ultimate DECIGO.

We present a new methodology in optical aperture masking interferometry involving Fourier analysis of the complex visibilities (real and imaginary, or amplitude and phase), derived from the interferometric images. The analysis includes use of a non-redundant aperture mask, and self-calibration of the hole-based complex voltage gains to correct for non-uniform illumination and phase fluctuations across the mask. The technique is demonstrated using the Synchrotron Radiation Interferometry (SRI) facility at the ALBA synchrotron light source. Application of the technique results in a joint derivation of the Gaussian shape of the electron beam, and of the hole-based voltage gain amplitude and phase distribution over the mask area. The gain phases are linearly related to the photon path-lengths through the optical system for the ray to each hole, and hence represent an accurate wavefront sensor (WFS) determining the path-length distortions across the wavefront. Wavefront sensing is a vital technology in fields ranging from adaptive optics to metrology to optometry. We calculate that the rms precision of this WFS method is better than 1~nm per frame in the current experiment. We compare the technique to the standard Shack-Hartman WFS. We also show that a structure-agnostic imaging and deconvolution process can be used with the visibility data to determine the beam shape without assuming a Gaussian model, and hence the technique is generalizable to more complex source morphologies.

We present exact solutions to the Nambu-Goto equations for thin vortons stabilized by chiral currents. The solutions describe a class of non-self-intersecting, stationary loops with arbitrary shapes. In addition to the trivial circular and the Kibble-Turok vortons, we also derive a two-parameter family that incorporates the first, second, and third harmonic modes. We found that, in general, the vorton's constraints allow for constructing families of solutions with arbitrary harmonic modes. We further investigate the gravitational lensing effects associated with these solutions under the weak-field and thin-lens approximations. For circular vortons, the lensing exhibits a sharp discontinuity separating two regions with distinctly different distortions. The corresponding Einstein ring co-exist alongside an almost undistorted source image. This effect is significantly amplified in the case of non-circular vortons, highlighting their potential observational signatures.

We find a connection between relativistic Modified Newtonian Dynamics (MOND) theories and (scalar) mimetic gravity. We first demonstrate that any relativistic MOND model featuring a unit-timelike vector field, such as TeVeS or Aether-scalar-tensor theory, can be embedded within a conformal/disformal-invariant framework. Gauge fixing the conformal/disformal symmetry amounts to imposing a constraint on the norm of the vector, the scalar field or the cross contraction. Notably, we find that these constraints can be interchanged as long as the vector and scalar fields remain timelike. This means that relativistic MOND theories may be recasted as a mimetic gravity theory. Lastly, by constructing the fundamental building blocks of a conformal-invariant scalar-vector-tensor theory, we establish a new framework for developing relativistic MOND theories. This perspective offers deeper insight into how non-invertible disformal transformations and conformal/disformal symmetries serve as fundamental principles in constructing viable alternatives to dark matter.

A novel mechanism for the production of a cosmic network of fundamental superstrings based on a time-varying string tension has been recently proposed in the context of a kinating background driven by the volume modulus of string compactifications. In this paper, we generalise the analysis of this growth mechanism by using dynamical system techniques. We first study the cosmological growth of strings in a spatially-flat Universe filled with a perfect fluid and a field-dependent tension, finding the fixed points of the phase space of this system. We then apply this analysis to fundamental strings and EFT strings obtained from wrapping $p$-branes on $(p-1)$-cycles. We find a cosmological growth for fundamental strings even without kination, as in scaling fixed points, and for EFT strings arising from D3- and NS5-branes wrapped around fibration cycles.

The observed cosmological constant may originate as the minimum value $U_{min}$ of a scalar field potential, where the scalar field is frozen due to a large mass. If this vacuum is metastable, it may decay to a true vacuum either at present or in the future. Assuming its decay rate $\Gamma$ is comparable to the Hubble expansion rate $H_0$, we estimate the scale of true vacuum bubbles and analyze their evolution. We find that their initial formation scale is sub-millimeter and their tension causes rapid collapse if $m \gtrsim 1.7 \cdot 10^{-3}\, eV$. For smaller masses, the bubbles expand at the speed of light. We extend our analysis to scalar-tensor theories with non-minimal coupling, finding that the nucleation scale of gravitational constant bubbles remains consistent with the sub-millimeter regime of General Relativity. The critical mass scale remains around $10^{-3}\,eV$. A theoretical estimate at redshift $z_{obs} \sim 0.01$ suggests an observable bubble radius of $\sim 50$ Mpc, implying a gravitational transition triggered $\sim 300$ Myr ago, with a present-day size approaching $100$ Mpc. Additionally, we explore mass ranges ($m < 10^{-3}\,eV$) and non-minimal coupling $\xi$ ranges ($10^{-8}\,eV^{2-n} - 10^{-1}\,eV^{2-n}$) that lead to a variation $\Delta G/G_N$ within the $1\%-7\%$ range. We assume non-minimal coupling of the form $F(\phi)=1/\kappa - \xi \phi^n$, with $\kappa=8\pi G_N$ and $2 \leq n \leq 9$. Finally, we review various local physics or/and transition based proposed solutions to the Hubble tension, including ultra-late-time transitional models (\(z \sim 0.01\)), screened fifth-force mechanisms, and the \(\Lambda_s\)CDM model, which features a transition at \(z \sim 2\). We discuss observational hints supporting these scenarios and the theoretical challenges they face.

It is well known that alternative theories to the Standard Model allow -- and sometimes require -- fundamental constants, such as the fine-structure constant, $\alpha$, to vary in spacetime. We demonstrate that one way to investigate these variations is through the Mass-Radius relation of compact astrophysical objects, which is inherently affected by $\alpha$ variations. We start by considering the model of a polytropic white dwarf, which we perturb by adding the $\alpha$ variations for a generic class of Grand Unified Theories. We then extend our analysis to neutron stars, building upon the polytropic approach to consider more realistic equations of state, discussing the impact of such variations on mass-radius measurements in neutron stars. We present some constraints on these models based on current data and also outline how future observations might distinguish between extensions of the Standard Model.

We present the full release of the atlas of continuous gravitational waves, covering frequencies from 20 Hz to 1700 Hz and spindowns from -5e-10 to 5e-10 Hz/s. Compared to the early atlas release, we have extended the frequency range and have performed follow-up on the outliers. Conducting continuous wave searches is computationally intensive and time-consuming. The atlas facilitates the execution of new searches with relatively minimal computing resources.

We derive scaling laws that connect certain macroscopic observables of strange quark stars with key microscopic properties of self-bound quark matter, such as the energy per baryon at zero pressure and the strength of repulsive interactions. We also identify universal relations linking global properties of strange quark stars - specifically, their moment of inertia, tidal deformability, and both gravitational and baryonic compactness. Remarkably, these relations hold for two substantially different microscopic models - the quark-mass density-dependent model with excluded-volume corrections and the vector MIT bag model - underscoring their robust, model-independent nature. We demonstrate that the universal relations for strange quark stars differ significantly from those previously established for neutron stars composed of hadronic matter, thus enabling discrimination between the two types of objects without requiring detailed knowledge of their equations of state. Moreover, observational constraints on the maximum mass of compact stars could place bounds on both the depth of quark-matter self-binding and the strength of quark repulsive interactions.