Papers for Friday, May 30 2025

Massive black hole binaries (MBHBs) are a natural outcome of galaxy mergers, and they are expected to be among the loudest gravitational wave sources at low frequencies. SDSS J2320+0024 has been recently proposed as a promising MBHB candidate due to a possible periodicity in its light-curve and variability in the MgII emission line. In this work, we re-analyse the optical (g and r bands) light-curves of J2320+0024 within the framework of Bayesian model selection. When a periodicity is searched for together with red noise, the analysis of the g-band light-curve finds a peak in the posterior of the period at ~290 days. The posterior profile is too broad to result in a preference for the periodic models with respect to models including only red-noise. Furthermore, the same peak is not present in the analysis of the r-band light-curve. A periodic model without red-noise identifies a different (~1100 days) periodicity, and it is significantly statistically disfavoured with respect to the other tested models. In summary, no significant evidence in favour of a true periodic signal over red noise variability is found. Our analysis questions the robustness of the previously claimed periodicity and emphasizes the importance of rigorous statistical treatment. While our findings challenge the binary interpretation for J2320+0024, they do not rule it out. A statistically robust joint analysis of the photometric light-curves and of the evolving broad line profiles can shed further light on the real nature of this object.

We describe a new Python-based stand-alone halo finding algorithm, Haskap Pie, that combines several methods of halo finding and tracking into a single calculation. Our halo-finder flexibly solves halos for simulations produced by eight simulation codes (ART-I, ENZO, RAMSES, CHANGA, GADGET-3, GEAR, AREPO and GIZMO) and for both zoom-in or full-box N-body or hydrodynamical simulations without the need for additional tuning or user-specified modeling parameters. When compared to Rockstar and Consistent Trees, our halo-finder tracks subhalos much longer and more consistently, produces halos with better constrained physical parameters, and returns a much denser halo mass function for halos with more than 100 particles. Our results also compare favorably to recently described specialized particle-tracking extensions to Rockstar. Our algorithm is well-suited to a variety of studies of simulated galaxies and is particularly robust for a new generation of studies of merging and satellite galaxies.

Recent observations suggest a nearly constant gas-phase mass-metallicity relation (MZR) at $z \gtrsim 5$, in agreement with many theoretical predictions. This lack of evolution contrasts with observations at $z \lesssim 3$, which find an increasing normalization of the MZR with decreasing redshift. We analyze a high-redshift suite of FIRE-2 cosmological zoom-in simulations to identify the physical drivers of the MZR. Previous studies have explained the weak evolution of the high-redshift MZR in terms of weakly evolving or saturated gas fractions, but we find this alone does not explain the evolution in FIRE-2. Instead, stellar feedback following intense bursts of star formation drives enriched gas out of galaxies, resetting their interstellar medium and separating their histories into distinct ``burst cycles". We develop the ``Reduced Burst Model", a simplified gas-regulator model that successfully reproduces the simulated MZR and identifies the dominant drivers of its evolution. As redshift decreases, the metallicity of inflows within burst cycles increases at fixed stellar mass due to increased wind recycling of enriched gas. Meanwhile, the metal mass produced by stars per inflowing gas mass within these cycles decreases because of decreased star formation per gas mass inflowing into the galaxy. The effects of these two processes on the median metallicity largely cancel, holding the MZR constant for $z = 5 - 12$. At fixed stellar mass, the simulations predict lower gas metallicities at higher $\rm H\alpha$-derived star formation rates, in qualitative agreement with the fundamental metallicity relation (FMR), but this effect is reduced in rest UV-selected samples.

We study the effect of stellar mass segregation driven by collisional relaxation within the potential well of a smooth dark matter halo. This effect is of particular relevance for old stellar systems with short crossing times, where small collisional perturbations accumulate over many dynamical time scales. We run collisional $N$-body simulations tailored to the ambiguous stellar systems Ursa Major 3/Unions 1, Delve 1 and Eridanus 3, modelling their stellar populations as two-component systems of high- and low-mass stars, respectively. For Ursa Major 3/Unions 1 (Delve 1), assuming a dynamical-to-stellar mass ratio of 10, we find that after 10 Gyr of evolution, the radial extent of its low-mass stars will be twice as large (40 per cent larger) than that of its high-mass stars. We show that weak tides do not alter this relative separation of half-light radii, whereas for the case of strong tidal fields, mass segregation facilitates the tidal stripping of low-mass stars. We further find that as the population of high-mass stars contracts and cools, the number of dynamically formed binaries within that population increases. Our results call for caution when using stellar mass segregation as a criterion to separate star clusters from dwarf galaxies, and suggest that mass segregation increases the abundance of massive binaries in the central regions of dark matter-dominated dwarf galaxies.

The upcoming stage IV wide-field surveys will provide high precision measurements of the large-scale structure (LSS) of the universe. Their interpretation requires fast and accurate theoretical predictions including large scales. For this purpose, we introduce $\texttt{SwiftC}_\ell$, a fast, accurate and differentiable $\texttt{JAX}$-based pipeline for the computation of the angular power spectrum beyond the Limber approximation. It uses a new FFTLog-based method which can reach arbitrary precision and includes interpolation along $k$, allowing for $k$-dependent growth factor and biases. $\texttt{SwiftC}_\ell$ includes a wide range of probes and effects such as galaxy clustering, including magnification bias, redshift-space distortions and primordial non-Gaussianity, weak lensing, including intrinsic alignment, cosmic microwave background (CMB) lensing and CMB integrated Sachs-Wolfe effect. We compare our pipeline to the other available beyond-Limber codes within the N5K challenge from the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration. $\texttt{SwiftC}_\ell$ computes the 120 different angular power spectra over 103 $\ell$-multipoles in 5 ms on one GPU core. Using a pre-calculation, $\texttt{SwiftC}_\ell$ is thus about 40$\times$ faster than the winner of the N5K challenge with comparable accuracy. Furthermore, all outputs are auto-differentiable, facilitating gradient-based sampling and robust and accurate Fisher forecasts. We showcase a Markov Chain Monte Carlo on an LSST-like survey as well as a Fisher forecast, illustrating $\texttt{SwiftC}_\ell$'s differentiability, speed and reliability in measuring cosmological parameters. The code is publicly available at this https URL.

Extensive ground and space based surveys have now characterized the properties of thousands of exoplanets; their radii, masses, orbits around their host stars, and the beginnings of accurate measurements of the chemical compositions of their atmospheres and cores. How are these properties linked to their formation in physically and chemically evolving protoplanetary disks wherein they accrete pebbles, planetesimals, and gas as they undergo migration? To address this challenge, our review assembles a large and varied body of exoplanet observations as well as recent Atacama Large Millimeter Array (ALMA) and James Webb Space Telescope (JWST) observations of disk structure, chemistry, kinematics, and winds. The latest advances in theory and MHD simulations that bear on these issues are also reviewed and compared with the observations. Taken together, this review argues that a new dynamic paradigm for planet formation is emerging wherein MHD disk winds and not disk turbulence play a central role in disk evolution and planet formation including: angular momentum transport, gap and ring formation. disk astrochemistry, and planet formation and migration. These processes leave their mark on the resulting atmospheric composition, radii, and orbital characteristics of exoplanet populations, offering the possibility of future observational tests.

(Abridged) The relations between stellar ($M_\ast$), gas ($M_{\rm gas}$), baryonic ($M_{\rm bar} = M_\ast + M_{\rm gas}$), and dark matter halo mass ($M_{200}$) provide unique constraints on galaxy formation and cosmology. The shape of the relations constrains how galaxies regulate their growth through gas accretion, star formation, and feedback; their scatter probes the stochasticity of galaxy assembly. Here, we assemble a sample of 49 nearby gas-rich dwarf and massive disc galaxies with unmatched ancillary data. We obtain their gas kinematics and derive their dark matter properties through rotation curve decomposition. Our sample allows us to study the galaxy-halo connection across nearly six orders of magnitude in $M_\ast$. We find that the $M_{\rm gas}-M_{200}$ relation rises monotonically, with galaxies having around 4 per cent of the average cosmological baryon fraction in cold gas. Contrastingly, the $M_\ast-M_{200}$ relation shows a more complex behaviour. A particularly interesting finding is that of a population of baryon-deficient' dwarfs (BDDs) with stellar masses $\sim 1-1.5$ orders of magnitude lower than expected from current models. Yet, baryon-rich galaxies also exist, and we find a large spread in the baryon retention fraction across our galaxies. We compare our findings with semi-analytic and hydrodynamical galaxy formation simulations. While the simulations broadly reproduce most observed features, they struggle to match the BDDs and do not capture the diversity in baryon fractions. Understanding these differences will shed new light on how feedback regulates galaxy formation. Finally, we study the dark matter halo concentration-mass relation. We find that below $M_{200} \sim 10^{11}\,M_\odot$, the concentrations are systematically lower than expected. We discuss whether these results stem from the influence of baryonic physics or the environment.

Circumbinary gas disks that are misaligned to the binary orbital plane evolve toward either a coplanar or a polar-aligned configuration with respect to the binary host. The preferred alignment depends on the dynamics of the disk: whether it undergoes librating or circulating nodal precession, with librating disks evolving to polar inclinations and circulating disks evolving to coplanar. We quantify the fraction of binary star systems whose disks are expected to have polar orbits $f_\text{polar}$, extending previous work to include disks with non-zero mass. Our results suggest that, for low mass disks, the polar fraction is highly sensitive to the distribution of binary eccentricity with a higher fraction expected for higher binary eccentricities, $f_{\rm polar}\sim e_{\rm b}$. However, for massive discs, the fraction is independent of the binary eccentricity and $f_{\rm polar}\approx 0.37$. The value of $f_\text{polar}$ is always reduced in a population with a greater preference for low initial mutual inclination. We also explore the consequences of the finite lifetime and non-zero radial extent of a real disk, both of which affect a disk's ability to complete its evolution to a stationary configuration. Our findings can be used to make predictions given populations with well-understood distributions of binary eccentricity, initial mutual inclination, and disk angular momentum.

We explore a theoretical framework in which Lorentz symmetry is explicitly broken by incorporating derivative terms of the extrinsic curvature into the gravitational action. These modifications introduce a scale-dependent damping effect in the propagation of gravitational waves (GWs), governed by a characteristic energy scale denoted as $M_{LV}$ . We derive the modified spectral energy density of GWs within this model and confront it with recent observational data from the NANOGrav 15-year dataset and the second data release of the International Pulsar Timing Array (IPTA). Our analysis yields a lower bound on the Lorentz-violating energy scale, finding $M_{LV} > 10^{-19}$ GeV at 68\% confidence level. This result significantly improves upon previous constraints derived from LIGO/VIRGO binary merger observations. Our findings demonstrate the potential of pulsar timing arrays to probe fundamental symmetries of spacetime and offer new insights into possible extensions of general relativity.

Even when used to describe the same phenomenon, equations, graphics and words each give different perspectives and lead to complementary insights. The basic elements of strong gravitational lensing are introduced here favoring words and graphics over equations whenever possible. Fermat's principle is the fundamental driver of strong lensing. Three "D's'' encapsulate the essential effects of lensing: Delay, Deflection and Distortion. Gravity and geometry both contribute to the delay of photons from a lensed source. Their interplay determines how the images of a source are deflected and how they are stretched or compressed. Caustics and critical curves are explained. Images of doubly, triply, quadruply and quintuply lensed sources are displayed. A table of symbols, their definitions and distinctions provides a summary of the basic elements of strong lensing.

Gravitational wave (GW) observations have significantly advanced our understanding of binary compact object (BCO) formation, yet directly linking these observations to specific formation scenarios remains challenging. The BCO phase space provides a robust and data-driven approach to discover the likely formation scenarios of these binaries. In this study, we expand the previously introduced binary black hole phase-space technique to encompass low-mass compact objects (LMCOs), establishing a novel framework to investigate their diverse formation mechanisms. Applying this approach to selected low-mass events $(\lesssim 5 M_\odot)$ from the GWTC-3 catalog and the recently observed GW230529 event, we show for the first time the phase-space demonstration of the LMCOs and find the associated probabilities for different formation scenarios including neutron stars, astrophysical black holes, or primordial black holes. Our analysis includes the astrophysical modelling uncertainties in and how it causes degeneracy between different formation scenarios. In future, with improvements in GW detector sensitivity and with detection of more GW events, the LMCO phase-space framework will significantly strengthen our capacity to associate more likely formation scenarios over the other, thereby refining our understanding of compact object formation for both astrophysical and primordial scenarios, and its evolution across the cosmic redshift.

It is necessary to understand the full accretion history of the Milky Way in order to contextualize the properties of observed Milky Way satellite galaxies and the stellar halo. This paper compares the dynamical properties and star-formation histories of surviving and disrupted satellites around Milky Way-like galaxies using the DC Justice League suite of very high-resolution cosmological zoom-in simulations of Milky Way analogs and their halo environments. We analyze the full census of galaxies accreted within the past 12 Gyrs, which including both surviving satellites at $z=0$, and dwarf galaxies that disrupted and merged with the host prior to $z=0$. Our simulations successfully reproduce the trends in $M_*$-[Fe/H]-[$\alpha$/Fe] observed in surviving Milky Way satellites and disrupted stellar streams, indicating earlier star-formation for disrupted progenitors. We find the likelihood and timescales for quenching and disruption are strongly correlated with the mass and time of infall. In particular, none of the galaxies accreted more than 12 Gyrs ago survived, and only 20% of all accreted galaxies with $M_*>10^8M_\odot$ survive. Additionally, satellites with highly radial trajectories are more likely to quench and disrupt. Disruption proceeds quickly for $\geq10^6M_\odot$ satellites accreted $10{-}12$ Gyr ago, often on timescales similar to the $\sim300$ Myr snapshot spacing. For high-mass satellites, the disruption timescale is faster than the quenching timescale. As a result, 92% of disrupted galaxies remain star-forming up until disruption. In contrast, Ultra Faint Dwarfs (UFDs) tend to quench prior to accretion, and 94% of UFDs accreted up to 12 Gyr ago survive at $z=0$.

The stochastic gravitational wave background (SGWB) in the nanohertz (nHz) regime, detectable by pulsar timing arrays (PTAs), offers a promising avenue to probe the cosmic population of supermassive black hole binaries (SMBHBs). These SMBHBs are expected to retain substantial eccentricity throughout their evolution due to their formation history. In this study, we propose a new modeling scenario of the nHz SGWB by incorporating the eccentricity of SMBHBs into a multi-scale adaptive simulation-based framework. We employ a time-domain eccentric waveform model, \esigmahm{}, to generate realistic gravitational wave (GW) signals from an astrophysical population of SMBHB, including physical effects from sub-parsec scales to Gpc scales. The eccentric inspiraling binary, unlike circular binaries, emits GW signal in multiple frequencies. As a consequence, the SGWB energy density in each frequency bin is not independent; instead, the presence of eccentricity introduces a spectral correlation between different frequencies. We show that these spectral correlations are absent for circular binaries but become increasingly significant for populations with higher eccentricities. Our novel approach can capture this effect and opens up the window towards measuring this with a high signal-to-noise ratio with future observations. This work develops the frontier of nHz signal modeling using eccentricity at small scales and can model realistic nHz signal, which will be essential for robust inference from future observations to shed light on the astrophysical properties of SMBHBs.

Exoplanetary systems that contain multiple planets on short-period orbits appear to be prevalent in the current observed exoplanetary population, yet the processes that give rise to such configurations remain poorly understood. A common prior assumption is that planetary accretion commences after the infall of gas and solids to the circumstellar disk ended. However, observational evidence indicates that accretion may begin earlier. We propose that compact systems are surviving remnants of planet accretion that occurred during the final phases of infall. In regions of the disk experiencing ongoing infall, the planetary mass is set by the balance between accretion of infalling solids and the increasingly rapid inward migration driven by the surrounding gas as the planet grows. This balance selects for similarly-sized planets whose mass is a function of infall and disk conditions. We show that infall-produced planets can survive until the gas disk disperses and migration ends, and that across a broad range of conditions, the mass of surviving systems is regulated to a few 10^{-5} to 10^{-4} times the host star's mass. This provides an explanation for the similar mass ratios of known compact systems.

The search for extraterrestrial life in the Solar System and beyond is a key science driver in astrobiology, planetary science, and astrophysics. A critical step is the identification and characterization of potential habitats, both to guide the search and to interpret its results. However, a well-accepted, self-consistent, flexible, and quantitative terminology and method of assessment of habitability are lacking. Our paper fills this gap based on a three year-long study by the NExSS Quantitative Habitability Science Working Group. We reviewed past studies of habitability, but find that the lack of a universally valid definition of life prohibits a universally applicable definition of habitability. A more nuanced approach is needed. We introduce a quantitative habitability assessment framework (QHF) that enables self-consistent, probabilistic assessment of the compatibility of two models: First, a habitat model, which describes the probability distributions of key conditions in the habitat. Second, a viability model, which describes the probability that a metabolism is viable given a set of environmental conditions. We provide an open-source implementation of this framework and four examples as a proof of concept: (a) Comparison of two exoplanets for observational target prioritization; (b) Interpretation of atmospheric O2 detection in two exoplanets; (c) Subsurface habitability of Mars; and (d) Ocean habitability in Europa. These examples demonstrate that our framework can self-consistently inform astrobiology research over a broad range of questions. The proposed framework is modular so that future work can expand the range and complexity of models available, both for habitats and for metabolisms.

Knowledge of the broad-band active galactic nuclei (AGN) spectral energy distribution (SED) that ionizes the gas-rich broad emission line region is key to understanding the various radiative processes at play and their importance that eventually leads to the emission line formation. We modeled a spectral energy distribution for highly accreting quasars, also known as extreme population A sources, based mainly on observational data available in astronomical databases, and on accretion disk models for the unobservable far-UV domain. Our selection criterion is the RFeII parameter - the ratio of the optical FeII emission between 4434 A and 4684 A to the H-beta 4861 A intensity, RFeII > 1. This criterion is satisfied by highly-accreting, possibly super-Eddington, black holes. We analyzed 155 sources up to a redshift of approximately 1, previously reported in the literature, to construct a median radio-quiet SED spanning from radio to X-ray wavelengths. We find that the SED of quasars exhibits distinct features compared to lower accreting AGN, including a pronounced big blue bump and strong optical/UV emission along with a steep X-ray continuum. We classify the sources into radio-quiet, radio-intermediate, and radio-loud categories, observing that radio-intermediate and a subsample of radio-quiet AGN show a significant far-IR excess over the radio-quiet SED and the far-IR excess appears to be related to the prominence of Feii emission. There is an overall consistency between the new SED and the one obtained for high Eddington ratio quasars in previous work. We provide the SEDs in digital format for eventual applications.

The light curves of the microlensing events MOA-2022-BLG-091 and KMT-2024-BLG-1209 exhibit anomalies with very similar features. These anomalies appear near the peaks of the light curves, where the magnifications are moderately high, and are distinguished by weak caustic-crossing features with minimal distortion while the source remains inside the caustic. To achieve a deeper understanding of these anomalies, we conducted a comprehensive analysis of the lensing events. We carried out binary-lens modeling with a thorough exploration of the parameter space. This analysis revealed that the anomalies in both events are of planetary origin, although their exact interpretation is complicated by different types of degeneracy. In the case of MOA-2022-BLG-091, the main difficulty in the interpretation of the anomaly arises from a newly identified degeneracy related to the uncertain angle at which the source trajectory intersects the planet-host axis. For KMT-2024-BLG-1209, the interpretation is affected by the previously known inner-outer degeneracy, which leads to ambiguity between solutions in which the source passes through either the inner or outer caustic region relative to the planet host. Bayesian analysis indicates that the planets in both lens systems are giant planets with masses about 2 to 4 times that of Jupiter, orbiting early K-type main-sequence stars. Both systems are likely located in the Galactic disk at a distance of around 4 kiloparsecs. The degeneracy in KMT-2024-BLG-1209 is challenging to resolve because it stems from intrinsic similarities in the caustic structures of the degenerate solutions. In contrast, the degeneracy in MOA-2022-BLG-091, which occurs by chance rather than from inherent characteristics, is expected to be resolved by the future space based Roman RGES microlensing survey.

Type Ia supernovae (SNe Ia) are powered by the radioactive decay of isotopes such as $^{56}$Ni and $^{56}$Co, making their $\gamma$-ray spectra useful probes of the explosion mechanism and ejecta structure. Accurate interpretation of $\gamma$-ray observables, including line ratios and continuum fluxes, requires a detailed understanding of the microphysical processes that shape the spectra. One such process is positronium formation during electron-positron annihilation, which can redistribute flux from the 511 keV line into the surrounding continuum. To assess the impact of positronium on the emergent spectra, we developed a new open-source module TARDIS-HE, for time-dependent three-dimensional $\gamma$-ray transport, integrated into the radiative transfer code TARDIS. The code simulates $\gamma$-ray spectra and light curves from one-dimensional supernova ejecta models and allows for flexible incorporation of decay chains and opacity treatments. Using TARDIS-HE, we explore the effect of positronium formation by varying the positronium fraction from 0 % to 100 %, and assuming an extreme case where 75 % of positronium decays result in three-photon emission. We find that full positronium formation can reduce the 511 keV line flux by approximately 70 % and modestly enhance energy deposition by up to 2 % at around 100 days post-explosion, compared to models without positronium. These results demonstrate that while the effect is not dominant, positronium formation introduces measurable changes to $\gamma$-ray observables. Future observations with missions such as the Compton Spectrometer and Imager (COSI) may offer constraints on positronium formation in SNe Ia and help refine models of their radioactive energy transport.

Galaxy cluster abundance measurements are a valuable tool for constraining cosmological parameters like the mass density ($\Omega_m$) and density fluctuation amplitude ($\sigma_8$). Wide area surveys detect clusters based on observables, such as the total integrated Sunyaev-Zel'dovich effect signal ($Y_{SZ}$) in the case of Planck. Quantifying the survey selection function is necessary for a cosmological analysis, with completeness representing the probability of detecting a cluster as a function of its intrinsic properties. Employing a Monte-Carlo method, we inject triaxial cluster profiles into random positions within the Planck all-sky maps, and subsequently determine the completeness of the Planck-selected CHEXMATE sample as a function of both geometry and SZ brightness. This is then used to generate 1000 mock CHEX-MATE cluster catalogs, and the distribution of shapes and orientations of the detected clusters, along with any associated bias in weak lensing-derived mass ($M_{WL}$) due to this orientation-dependent selection, denoted as $1 - b_{\chi}$, is obtained. We show that cluster orientation impacts completeness, with a higher probability of detecting clusters elongated along the line of sight (LOS). This leads to $1 - b_{\chi}$ values of $0-4\%$ for CHEXMATE clusters relative to a random population. The largest increase in $M_{WL}$ is observed in the lowest mass objects, which are most impacted by orientation-related selection bias. This bias is relevant for upcoming SZ surveys like CMB-S4, and should be considered for surveys utilizing other probes for cluster detection, such as Euclid.

In this study, we investigate the effect of resistivity on the dynamics of global magnetohydrodynamic accretion flows (Res-MHD) around a spinning supermassive black hole. We perform a comparative study of 2D and 3D resistive models around black holes. We examine accretion flow dynamics considering globally uniform resistivity values, ranging from $\sim 0$ to 0.1. During the simulation time of $t \lesssim 1000~t_g$, we find that the mass accretion rate is comparable for both the 2D and 3D models. However, as the flow becomes increasingly turbulent, non-axisymmetric effects begin to dominate, resulting in significant differences in the mass accretion rates between the 3D and 2D. All the resistive models in a highly magnetized flow belong to the Magnetically Arrested Disk (MAD) state. We propose an efficient and physically motivated approach to examine the magnetic state by estimating the spatial average plasma beta parameter across the computational domain. We find that when the average plasma beta is close to or below unity $( \beta_{\text{ave}} \lesssim 1 )$, the accretion flow enters the MAD state. Additionally, we find that high-resistivity flow reduces magnetorotational instability (MRI) turbulence in the accretion flow, while the turbulence structures remain qualitatively similar in low-resistivity flows. Moreover, we observe indications of plasmoid formations in low-resistivity flow compared to high-resistivity flow. Furthermore, we do not find a clear relationship between the variability of the accretion rate, magnetic flux, and resistivity. Lastly, our findings suggest that low-resistivity models produce higher power jets than those with higher resistivity.

We present an investigation of the compact structure of the AGN 2021+317 based on multi-epoch Very Long Baseline Interferometry (VLBI) observations at 15, 22, and 43 GHz in the period from 2013 through 2024. The VLBI images show a core-jet structure extended to the south, with two stationary components in the northern region, one of which likely to be the core of the source. We also detected two new moving jet components (S4 and S5) in the observations of 2021. Based on these observational findings, we analyzed two distinctive jet models, involving one or another stationary component mentioned above as the jet core. One model assumes a moderate bulk motion velocity, a wider viewing angle, and a lower Doppler factor, with the magnetic field energy density significantly dominating over non-thermal particle energy density. The other model involves a higher bulk motion velocity, a narrower viewing angle, and a higher Doppler factor, with an even greater dominance of magnetic field energy in the core. The position angle of the jet ridge line rotates counter-clockwise over the observed period. The apparent kinematics of the jet components is more consistent with a model of the precessing jet, which has recently completed the first half of the precession cycle. Our results provide constraints on the dynamic evolution of the jet and its interaction with the surrounding medium.

The observed exoplanet population exhibits a scarcity of short-period Saturn-mass planets, a phenomenon referred to as the ``hot Saturn desert". This observational scarcity can be utilized to validate the theories regarding the formation and evolution of gas planets. In this study, we conduct large-scale numerical simulations to explore how the initial conditions of gas planets orbiting solar-type and M-dwarf stars influence their evolutionary trajectories in the semi-major axis versus planetary radius ($a$-$R$) parameter space. We generate a synthetic population of 10,000 short-period gaseous planets by systematically varying their initial planetary masses ($M_{\rm p}$), initial planetary luminosities ($L_{\rm p}$), initial core mass fractions ($f_{\rm core}$), and semi-major axis ($a$). Furthermore, we assume these gaseous planets have ceased orbital migration and model their long-term thermal evolution, taking into account the impacts of atmospheric evaporation. Our results show that the initial mass, $L_{\rm p}$, and $f_{\rm core}$ are the dominant factors controlling radius evolution for short-period gas planets. The key to survival as a hot Saturn analogue appears to be having just the right combination of properties after gas disk dissipation: an $M_{\rm p}$ below 0.5 Jupiter Mass ($M_{\rm Jup}$), a substantial $f_{\rm core}$ of $\geq$ 30%, and relatively low $L_{\rm p}$ on the order of $10^{-6}$ solar luminosity ($L_{\odot}$) or less. The survival criteria for hot Saturn analogs align with theoretically unfavorable initial conditions of gas planets formed via core accretion scenario, naturally explaining the observed boundaries of the hot Saturn desert.

Binary systems consisting of an early type star and a black hole (BH) are crucial for understanding various astrophysical phenomena, particularly the origins of detected gravitational wave sources. Be binary systems are expected to represent a key evolutionary stage in hosting BHs. However, while hundreds of Be X-ray binaries are known, the only confirmed BH candidate in a Be binary remains highly controversial. We report the discovery of ALS 8814, a Be star-BH binary with a moderately eccentric ($e = 0.23$) and wide orbit ($P = 176.6$ days), revealed by the radial velocity (RV) measurement of the visible Be star. Our analysis, combining flux-calibrated spectra in the Balmer discontinuity region and spectral template matching, yields a mass of $11.2^{+1.4}_{-1.2}$ $M_\odot$ for the Be star. The minimum mass of the unseen companion, assuming an edge-on inclination ($i = 90^{\circ}$), is $9.8\pm 0.7\,M_\odot$. We rule out the presence of non-degenerate companions in ALS 8814, indicating that it can only be a BH. This discovery represents a robust case of a Be-BH binary, identified purely through precise RV measurements from a single set of lines. The extremely low peculiar velocity of ALS 8814 suggests that the BH is formed via a direct core-collapse with a negligible natal kick, implying an almost perfect alignment between the Be star's spin and the orbital plane. In this context, the binary's inclination angle is estimated to be 22$^{\circ}$-49$^{\circ}$ by analyzing the shallow double-peaked profile of the H$\alpha$ emission line. This inclination range corresponds to a BH mass estimate between $15\,M_\odot$ and $58\,M_\odot$. As the only unambiguous Be-BH binary system known to date, ALS 8814 provides valuable constraints on the BH formation in a binary system with a high-mass companion.

Using the IRAM 30 m telescope, we presented observations of N2H+ J = 1-0, CCS JN = 87-76 and 77-66 lines toward a large sample of ultracompact HII regions (UC HIIs). Among our 88 UC HIIs, 87 and 33 sources were detected in the N2H+ J = 1-0 and CCS JN = 87-76 lines, respectively. For the CCS 77-66 transition, we detected emission in 10 out of 82 targeted sources, all of which also exhibited emission in the CCS JN = 87-76 line. Physical parameters are derived for our detections, including the optical depth and excitation temperature of N2H+, the rotational temperature of CCS and the column density. Combining our results and previous observation results in different stages of high-mass star-forming regions (HMSFRs), we found that the column density ratio N(N2H+)/N(CCS) increases from high-mass starless cores (HMSCs) through high-mass protostellar cores (HMPOs) to UC HIIs. This implies that N(N2H+)/N(CCS) can trace the evolution process of HMSFRs. It was supported by our gas-grain chemical model, which shows that N(N2H+)/N(CCS) increases with the evolution age of HMSFRs. The temperature, density and chemical age were also constrained from our best-fit model at each stage. Thus, we propose N(N2H+)/N(CCS) as a reliable chemical clock of HMSFRs.

Identifying key observables is essential for enhancing our knowledge of exoplanet habitability and biospheres, as well as improving future mission capabilities. While currently challenging, future observatories such as the Large Interferometer for Exoplanets (LIFE) will enable atmospheric observations of a diverse sample of temperate terrestrial worlds. Using thermal emission spectra that represent conventional predictions of atmospheric CO2 variability across the Habitable Zone (HZ), we assess the ability of the LIFE mission - as a specific concept for a future space-based interferometer - to detect CO2 trends indicative of the carbonate-silicate (Cb-Si) weathering feedback, a well-known habitability marker and potential biological tracer. Therefore, we explore the feasibility of differentiating between CO2 trends in biotic and abiotic planet populations. We create synthetic exoplanet populations based on geochemistry-climate predictions and perform retrievals on simulated thermal emission observations. The results demonstrate the robust detection of population-level CO2 trends in both biotic and abiotic scenarios for population sizes as small as 30 Exo-Earth Candidates (EECs) and the lowest assessed spectrum quality in terms of signal-to-noise ratio, S/N = 10, and spectral resolution, R = 50. However, biased CO2 partial pressure constraints hinder accurate differentiation between biotic and abiotic trends. If these biases were corrected, accurate differentiation could be achieved for populations with $\geq$ 100 EECs. We conclude that LIFE can effectively enable population-level characterization of temperate terrestrial atmospheres and detect Cb-Si cycle driven CO2 trends as habitability indicators. Nevertheless, the identified biases underscore the importance of testing atmospheric characterization performance against the broad diversity expected for planetary populations.

Molecular oxygen (O2) will be an important molecule in the search for biosignatures in terrestrial planetary atmospheres in the coming decades. In particular, O2 combined with a reducing gas is thought to be strong evidence for disequilibrium caused by surface life. However, there are circumstances where it would be very difficult or impossible to detect O2, in which cases it has been suggested that ozone (O3), the photochemical product of O2, could be used instead. Unfortunately, the O2-O3 relationship is highly nonlinear and dependent on the host star, as shown in detail in the first paper in this series. We explore the O2-O3 relationship around G0V-M5V host stars, using climate/photochemistry modeling to simulate atmospheres while varying abundances of O2 and nitrous oxide (N2O). N2O is of particular importance to the O2-O3 relationship not just because it is produced biologically, but because it is the primary source of nitrogen oxides (NOx), which fuel the NOx catalytic cycle which destroys O3, and the smog mechanism that produces O3. We vary the O2 mixing ratio from 0.01-150% present atmospheric level (PAL), and N2O abundances of 10% and 1000% PAL. We find that varying N2O impacts the O2-O3 relationship differently depending strongly on both the host star and the amount of atmospheric O2. Planets orbiting hotter hosts with strong UV fluxes efficiently convert N2O into NOx, often depleting a significant amount of O3 via faster NOx catalytic cycles. However, for cooler hosts and low O2 levels we find that increasing N2O can lead to an increase of overall O3 due to the smog mechanism producing O3 in the lower atmosphere. Variations in O3 result in significant changes in the amount of harmful UV reaching the surfaces of the model planets as well as the strength of the 9.6 $\mu$m O3 emission spectral feature, demonstrating potential impacts on habitability and future observations.

We consider a non-linear interaction between the dark matter and dark energy components of the universe. In particular, within the FLRW geometry, where dark matter is described by a dust fluid and dark energy by an ideal gas with a constant equation of state parameter, we introduce energy transfer between the two fluids. The effective cosmological fluid leads to a unified dynamical dark energy model with the feature that the Hubble function admits an analytic expression. We study this model using the DESI DR2 Baryonic Acoustic Oscillations data and the Supernova data from Pantheon+. The interacting model fits the data better than the $\Lambda$CDM model, with $\chi_{\text{model}}^{2}-\chi_{\Lambda\text{CDM}}^{2}=-5$. Using the Akaike Information Criterion to compare the two models, we derive $\text{AIC}_{\operatorname{model}}-\text{AIC}_{\Lambda\text{CDM}}=-1$, from which we conclude that the interacting model is marginally better supported by the data than the $\Lambda$CDM, but the difference is not statistically significant.

Intensive reverberation mapping monitoring programs combine ground-based photometric observations from different telescopes, requiring intercalibration of lightcurves to reduce systematic instrumental differences. We present a new iterative algorithm to calibrate photometric time-series data of active galactic nuclei (AGN) using 100s of comparison stars on the same images, building upon the established method of ensemble photometry. The algorithm determines telescope-specific and epoch-specific correction parameters, and simultaneously computes a multi-component noise model to account for underestimated uncertainties based on the scatter in the comparison star data, effectively identifying problematic epochs, telescopes, and stars. No assumptions need to be made about the AGN variability shape, and the algorithm can in principle be applied to any astronomical object. We demonstrate our method on lightcurves taken with ten 1-m telescopes from the Las Cumbres Observatory (LCO) robotic telescope network. Comparing our results to other intercalibration tools, we find that the algorithm can more accurately quantify the uncertainties in the data. We describe additional corrections that can be made for particularly bluer AGNs like Fairall 9, arising due to systematic effects dependent on star colour.

This study examines the flux and photon index distributions of 11 Very High Energy (VHE) Flat Spectrum Radio Quasars (FSRQs) using over 16 years of Fermi-LAT $\gamma$-ray data. The distributions reveal double lognormal profiles in both flux and index, primarily in the 3-day and 7-day binnings, supporting the ``two-flux-state hypothesis" for blazars. These profiles, which become insignificant at 30-day binning, suggest that shorter timescales are better at capturing distinct states, while longer timescales smooth out shorter variations. Most VHE FSRQs exhibit a ``harder-when-brighter" trend, where the photon index decreases during high-flux states, suggesting efficient particle acceleration and possibly reduced radiative cooling. In contrast, two sources display a ``softer-when-brighter" behavior, likely due to enhanced radiative cooling in high photon density environments. Additionally, we observe that the Spearman rank correlation between flux and photon index strengthens with increasing time bin sizes, indicating more pronounced correlations over longer timescales. This possibly indicates that, on shorter timescales, flux variations are driven by a combination of photon index changes and normalization effects. Averaging flux over longer durations minimizes the effect of normalization variation, thereby enhancing the observed correlation. We also compare the flux and index distributions of VHE and non-VHE FSRQs, emphasizing the differences in their variability and emission patterns.

The tension between the Hubble constant ($H_0$) inferred from the cosmic microwave background (CMB) and that measured from late-time observations, such as the local distance ladder, is a major challenge in modern cosmology. Early dark energy (EDE) has been proposed as a possible resolution to the $H_0$ tension, but it typically worsens the $S_8$ tension by enhancing the small-scale matter power spectrum due to an increased cold dark matter density. To address this issue, we propose a model that combines EDE with an interacting dark energy-dark matter (iDEDM) scenario, and investigate whether this mixed model can simultaneously resolve both tensions. We find that the DE-DM interaction suppress the growth of structure and reduce $S_8$, while EDE contributes to increase $H_0$, although less effectively than in the EDE-only case. Our MCMC analysis using Planck 2018, DESI BAO, DES, Pantheon+, and SH0ES data shows that the mixed model provides modest improvements in both tensions, although it does not fully resolve either. This limitation appears to stem from the fact that both EDE and iDEDM independently favor a higher present-day matter density, which reduces the angular diameter distance and limits the degree to which EDE can lower the sound horizon.

The galaxy cluster CIZA J2242.8+5301 is a well-studied merging galaxy cluster that hosts prominent double radio relics including the famous sausage relic, as well as other diffuse radio sources. Observations at frequencies below 100 MHz are essential for investigating the physics of radio relics as they provide unique access to the low-energy population of cosmic-ray electrons. We aim to study the morphology, spectral characteristics, and physical processes that produce relics. We present the first observations of the Sausage cluster at 45 MHz, the lowest radio frequency at which this cluster has been studied to date, using the Low Band Antenna (LBA) of the LOFAR radio interferometer. We made use of ten hours of LOFAR LBA observations, from which we achieved a thermal-noise limited radio image with a noise level of 1.5 mJy/beam at a resolution of 15 arcsec. These data were combined with existing multi-frequency measurements at higher frequencies: LOFAR High Band Antenna, Giant Metrewave Radio Telescope, Westerbork Synthesis Radio Telescope, and Karl G. Jansky Very Large Array. This broad frequency coverage allowed us to derive integrated spectral indices, spectral index and curvature maps, and Mach number distributions across the relics. We derived Mach numbers from the local injection index measure using low-frequency data with M_N = 2.9 +-0.5 for the northern relic and M_S = 2.9+-0.8 for the southern relic. LOFAR LBA observations reveal a remarkably symmetric surface brightness profile across the eastern part of the northern relic, with wings extending on either side of the peak. This discovery is contrary to the expectation of particle acceleration at a single, sharp shock and the subsequent downstream advection of accelerated electrons. We modelled the surface brightness profile, including the effects of projection, magnetic field variation, and shock deformation.

The stability of an accretion disc surrounding a millisecond pulsar is analysed from an energetic point of view, using magnetohydrodynamic simulations that consider realistic disc structures and a variety of magnetic field inclination angles. The time-averaged components of the magnetic field interact with the disc through ohmic dissipation, which causes heating and partial evaporation of its innermost region. The stability of the disc right after the magnetic field is turned on is analysed as a function of the location of the inner radius of the disc and the magnetic inclination angle. Our results show that the disc is severely altered in those cases where its inner radius lies well beyond the light cylinder and the magnetic axis is not totally aligned with the neutron star spin axis. Overall, the results of the simulations agree with those obtained in previous works where analytical or semi-analytical energy models were also used to discuss the stability of the disc. The implications for the understanding of the transitional millisecond pulsars are discussed. We briefly mention implications of our results for low-mass X-ray binaries and supernova fallback discs.

Time-correlated variations in the pulse profiles of radio pulsars provide insights into changes in their magnetospheres. For a small number of pulsars (~20), these variations have been shown to correlate with spin-down rate. Many of these profile changes involve small (few percent) variations in the relative intensity of different profile components, and hence tools such as Gaussian process regression have been employed to separate the time-correlated profile variation from intrinsic noise. In this paper, we present a computationally efficient approximation of a 2-D Gaussian process model that enhances sensitivity by simultaneously tracking time- and phase-correlated signals. Applying this model to 26 pulsars observed at the Jodrell Bank Observatory, we detect significant profile shape variations in 21 pulsars. Using principal component analysis, we confirm spin-down correlated shape variations in 11 pulsars where this had been previously observed. Additionally, we find evidence of spin-down correlated shape changes in 7 pulsars for the first time (PSRs B0105+65, B0611+22, B0626+24, B1740-03, B1826-17, B1917+00, and B2148+63). We look in greater detail at PSR B0740-28, where the correlation between profile shape and spin-down itself seems to switch between quasi-stable states. Notably the profile shape associated with greater spin-down seems to invert at times, presenting a challenge to our understanding of the physical processes at work.

Universal Design (UD), an approach to accessibility that was first conceptualized in architecture to make buildings physically accessible, has since been applied to curriculum design to make classrooms accessible for a larger range of learning needs. In this paper, we illustrate how the concepts of UD are relevant outside of architecture and the creation of curricula by highlighting examples of norms that exist in the field of astronomy that create barriers for disabled folks. we discuss ways the foundations of UD can be applied more generally to department culture, conferences, outreach events, and academia as a whole to make STEM fields more inclusive. In order to implement UD in these sectors, one must create multiple pathways or options for folks to engage with and show their success in astronomy. While UD is critical for disabled folks, it can easily be expanded to include the promotion of people whose backgrounds and/or identities are currently underrepresented or under-supported in STEM. Lastly, we introduce guiding questions and tools for departments and institutions to evaluate the accessibility of their activities and traditions to disabled individuals. In summary, we aim to show the importance of increased accessibility and provide some strategies to make STEM more inclusive to disabled people by using the mindset and principles of UD.

Primordial scalar curvature perturbations ($\zeta$), typically probed on large cosmological scales via CMB and LSS observations, can be significantly enhanced on smaller scales by various early Universe mechanisms, for instance, non-minimal inflationary models. While decoupled at linear order, scalar and tensor perturbations, i.e., Gravitational Waves (GWs), interact at second order. As a consequence, an enhanced primordial scalar power spectrum $P_\zeta(k)$ can source a sizable stochastic GW background (SGWB). In these proceedings, we briefly review the generation mechanism of such signals, typically referred to as scalar-induced GWs (SIGWs), and discuss the prospects of measuring them with present and future Pulsar Timing Arrays datasets and future GW observatories like the Laser Interferometer Space Antenna LISA.

The Cosmological Principle, which states that the Universe is homogeneous and isotropic (when averaged on large scales), is the foundational assumption of Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmologies such as the current standard Lambda-Cold-Dark-Matter ({\Lambda}CDM) model. This simplification yields an exact solution to the Einstein field equations that relates space and time through a single time-dependent scale factor, which defines cosmological observables such as the Hubble parameter and the cosmological redshift. The validity of the Cosmological Principle, which underpins modern cosmology, can now be rigorously tested with the advent of large, nearly all-sky catalogs of radio galaxies and quasars. Surprisingly, the dipole anisotropy in the large-scale distribution of matter is found to be inconsistent with the expectation from kinematic aberration and Doppler boosting effects in a perturbed FLRW universe, which is the standard interpretation of the observed dipole in the cosmic microwave background (CMB). Although the matter dipole agrees in direction with that of the CMB dipole, it is anomalously larger, demonstrating that either the rest frames in which matter and radiation appear isotropic are not the same, or that there is an unexpected intrinsic anisotropy in at least one of them. This discrepancy now exceeds 5{\sigma} in significance. We review these recent findings, as well as the potential biases, systematic issues, and alternate interpretations that have been suggested to help alleviate the tension. We conclude that the cosmic dipole anomaly poses a serious challenge to FLRW cosmology, and the standard {\Lambda}CDM model in particular, as an adequate description of our Universe.

In developing a deeper understanding of the Circumgalactic Medium, one feature that is poorly understood is the nature of the ultraviolet background (UVB) and its impact on observed column densities. A wide array of UVB models have been created over the years by many different authors, each based on the latest observational data available at the time. In addition to having a large variance between model properties, the formatting between released models is also inconsistent. This data release provides reformatted versions of several widely-used ultraviolet background models-Faucher-Giguère et al. 2009, Haardt and Madau 2012, Puchwein et al. 2019, and Faucher-Giguère 2020-such that each model is in the same units and thus can be utilized to directly compare these models over a wide redshift range. This release also includes code to run a 'cloudy_cooling_tools' pipeline to generate ionization tables for different UVB models.

Intracluster light, the diffuse glow of stars stripped from galaxies during a cluster's formation, is an established tracer of a cluster's dynamical history. The upcoming Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) is set to revolutionize studies of intracluster light by imaging the entire southern sky down to a limiting surface brightness $\mu \gtrsim 30\text{mag}/\text{arcsec}^2$ by year ten. In this letter, we create a precursor LSST dataset (reaching the equivalent of year eight depth) using DECam observations of Abell 3667 and study its intracluster light. We have discovered a low surface brightness ($ \mu \gtrsim 26\text{mag}/\text{arcsec}^2 $) optical bridge extending over $\sim 400\text{ kpc}$ which connects the two brightest galaxies (BCG1 and BCG2) in the cluster; the color and surface brightness of the bridge is consistent with formation via a major merger. The inner regions of BCG1 ($r < 200\text{ kpc}$) and BCG2 ($r < 50\text{ kpc}$) are consistent with formation via gradual stripping of satellite galaxies, but BCG2's outer profile appears disrupted by a recent merger. We hypothesize that the bridge is a relic of a recent first-pass between the two brightest galaxies and is composed of stars being stripped from BCG2. Future studies of intracluster light with LSST will discover new features such as the bridge in local clusters while enabling detailed studies of the stellar populations of these features with its six photometric bands.

In this study, we conducted a systematic analysis of long-term Fermi-LAT \gamma-ray data for a sample of blazars, including FSRQs, BL\,Lacs, and BCUs, to investigate their $\gamma$-ray variability. We focused on light curves binned in 3-, 7-, and 30-day intervals to assess the impact of binning, using data with TS >4 as a detection threshold. We calculated fractional variability ($F_{\rm var}$) for each category and found that FSRQs exhibit higher mean variability compared to BL\,Lacs and BCUs, with BCUs displaying intermediate variability closer to BL\,Lacs. The KS test on the variability distributions indicates that FSRQs differ from both BL Lacs and BCUs, whereas BCUs are more similar to BL Lacs. The higher variability in FSRQs is likely linked to more powerful jets and accretion. The correlation between \gamma-ray flux and spectral index suggests a moderate positive correlation for BL Lacs and BCUs, indicating a "softer when brighter" behavior. FSRQs displayed a mild anticorrelation, suggesting these sources tend to become harder as their flux increases. Analysis of flux distributions revealed log-normal behavior in many sources, consistent with multiplicative variability in blazar jets. Some sources show bimodal distributions, implying transitions between emission states. Binning affects the observed variability, with longer bins smoothing short-term fluctuations. Power spectral density analysis suggests FSRQs exhibit steeper slopes, reflecting structured variability, while BL Lacs display shallower slopes, dominated by stochastic processes. The absence of PSD breaks suggests no dominant timescale within the Fermi window. Spectral index distributions further highlight complexity, often requiring multi-component models.

OT 355 (4FGL J1734.3 + 3858) is a relatively rarely studied but highly variable, moderate-redshift (z = 0.975) flat-spectrum radio quasar (blazar). With this work, we aim to study its optical variability on different timescales, which can help us to better understand the physical processes in relativistic jets operating in blazar-type active galactic nuclei. OT 355 was observed in four colors (BVRI) during 41 nights between 2017 and 2023 using three 1 and 2 m class telescopes. The object was also monitored on intra-night timescales, for about 100 h in total. In addition, secondary standard stars in the field of OT 355 were calibrated in order to facilitate future photometric studies. We detected significant intra-night and night-to-night variations of up to 0.5 mag. Variability characteristics, color changes, and a possible ``rms-flux'' relation were studied and discussed. Using simple arguments, we show that a negative ``rms-flux'' relation should be expected if many independent processes/regions drive the short-term variability via Doppler factor changes, which is not observed in this and other cases. This finding raises arguments for the idea that more complex multiplicative processes are responsible for blazar variability. Studying blazar variability, especially on the shortest possible timescales, can help to estimate the strength and geometry of their magnetic fields, the linear sizes of the emitting regions, and other aspects, which may be of importance for constraining and modeling blazars' emitting mechanisms.

A comprehensive analysis of quasi-periodic oscillations (QPOs) in the gamma-ray emissions of blazars. Utilizing 15 years of Fermi-LAT observations of seven blazars in our sample, we identify both long-term and transient quasi-periodic oscillations in the gamma-ray light curves, with timescales ranging from a few months to years. These periodicities were detected using the Lomb-Scargle periodogram and REDFIT techniques. To robustly evaluate the statistical significance of the quasi-periodic signals observed in the Lomb-Scargle Periodograms, 30,000 synthetic $\gamma$-ray light curves were generated for each source using a stochastic model known as the Damped Random Walk (DRW) process. To investigate the physical origin of the observed gamma-ray QPOs with different timescales, we explore several plausible scenarios, with particular emphasis on a relativistic jet hosted by one of the black holes in a supermassive binary black hole system, jet precession, and helical motion of magnetized plasma blob within the jet. The $\gamma$-ray light curves exhibiting long-timescale quasi-periodic oscillations (QPOs) are analyzed within the framework of a supermassive binary black hole (SMBBH) model, employing a Markov Chain Monte Carlo (MCMC) approach, allowing us to constrain key physical parameters such as the jet Lorentz factor ($\Gamma$) and the viewing angle between the observer's line of sight ($\psi$) relative to the spin axis of SMBH.

AT2022rze is a luminous, ambiguous transient located South-East of the geometric center of its host galaxy at redshift z = 0.08. The host appears to be formed by a merging galaxy system. The observed characteristics of AT2022rze are reminiscent of active galactic nuclei (AGN), tidal disruption events (TDEs), and superluminous supernovae (SLSNe). The transient reached a peak absolute magnitude of -20.2 +- 0.2 mag, showing a sharp rise (trise,1/e = 27.5 +- 0.6 days) followed by a slow decline (tdec,1/e = 382.9 +- 0.6). Its bumpy light curve and narrow Balmer lines indicate the presence of gas (and dust). Its light curve shows rather red colors, indicating that the transient could be affected by significant host extinction. The spectra reveal coronal lines, indicative of high-energy (X-ray/UV) emission. Archival data reveal no prior activity at this location, disfavoring a steady-state AGN, although an optical spectrum obtained prior to the transient is consistent with an AGN classification of the host. Based on this, we conclude that the transient most likely represents a Changing-look AGN at the center of the smallest component of the merging system.

Pre-impact detection asteroids (PIDAs) may be detected only a few hours before their impact with Earth, providing a brief opportunity to characterize them before impact. We describe the characterization of PIDA 2024 RW$_1$, which was discovered by the Catalina Sky Survey on 2024 September 4 at 05:43 UTC, before it entered the atmosphere near the northern Philippines at 16:39 UTC. We observed 2024 RW$_1$ with the Astrophysical Research Consortium Telescope Imaging Camera on the Apache Point Astrophysical Research Consortium's 3.5-m telescope on 2024 September 4 10:16 UTC. We obtained g, r, i, and z photometry of 2024 RW$_1$, yielding color indices of g-r = 0.47$\pm$0.04, r-i = 0.13$\pm$0.04, i-z = -0.11$\pm$0.07, and g-i = 0.60$\pm$0.04, corresponding to a spectral slope of 0.67$\pm$0.40~$\%$/100 nm. The closest match to an asteroid spectral type is with B-type asteroids from the C-complex. We detect variations in the time series photometry of the asteroid with an amplitude of $\sim$0.75, and a double-peaked rotation period of $\sim$1900 s. Assuming a visible albedo of 0.07 and a density of $\sim$1500 kg/m$^3$, and using the derived absolute magnitude of 32.2$\pm$0.5, we calculate that the asteroid has a diameter of 1.8$\pm$0.4 m and a total mass of $\sim$5000 kg. The most likely source of 2024 RW$_1$ is the 3:1 mean motion resonance followed by the $\nu_6$ resonance, according to NEOMOD3.

The frequency of compact object interactions in AGN discs is naturally tied to the number of objects embedded within it. We investigate the evolution of black holes in the nuclear stellar cluster on inclined orbits to the AGN disc by performing adiabatic hydrodynamical simulations of isolated black hole disc crossings over a range of disc densities and inclinations $i\in[2^\circ,15^\circ]$. We find radiation dominates the pressure in the wake that forms around the BH across the full inclination and disc density range. We identify no well defined steady state wake morphology due to the thin geometry of the disc and the vertical exponential density drop off, where the wake morphology depends on the vertical depth of the transit within the disc. The inclination damping $\Delta i$ relative the pre-transit inclination behaves as a power law in $\sin(i)$ and the ambient Hill mass $m_\text{H,0}$ as $\Delta i/i \propto m_{\rm H,0}^{0.4} \sin(i)^{-2.7}$. The drag on the BH is dominated by the gravity of the wake for the majority of our inclination range until accretion effects become comparable at $\sin(i)\gtrsim30H_0/R_0$, where $H_0/R_0$ is the disc aspect ratio. At low inclinations ($\sin(i)\lesssim3H_0/R_0$) the wake morphology becomes more spherical, leading to a regime change in the inclination damping behaviour. Our results suggest that the inclination damping timescale is shorter than expected from only episodic Bondi-Hoyle-Lyttelton accretion events during each transit, implying inclined objects may captured by the AGN disc earlier in its lifetime than previously thought.

This work presents a formalism for deriving likelihoods of the cosmological density field directly from first principles within Perturbation Theory (PT). By assuming a perturbative expansion around the Gaussian initial density field and additional stochastic components, we analytically compute two forms of the likelihood. Full marginalization over all underlying fields yields the likelihood of the observed density field, expressed in terms of its summary statistics (such as the power spectrum and bispectrum), which are naturally given by the formalism, and conditioned on model parameters. Marginalizing only over the stochastic fields results in the field-level likelihood. A key strength of this method is its ability to automatically specify the precise combinations of initial field covariances and PT expansion kernels required at each perturbative order (e.g., tree-level power spectrum and bispectrum, and the 1-loop power spectrum). This guarantees that the resulting likelihoods are fully consistent with PT at the chosen order of accuracy, avoiding ad-hoc choices in constructing the statistical model.

We present high-resolution simulations of the first star-forming clouds in 15 minihalos with masses ranging from $\sim 10^5$ to $10^7\ \text{M}_{\odot}$ at redshifts $z \sim 17 - 20$, using the \texttt{GIZMO} code. Our simulations incorporate detailed primordial gas physics and adopt initial conditions from the state-of-the-art TNG cosmological simulations. To achieve the required resolution, we apply a particle-splitting technique that increases the resolution of the original TNG data by a factor of $\sim 10^5$, reaching gas and dark matter particle masses of $0.2\ \text{M}_{\odot}$ and $80\ \text{M}_{\odot}$, respectively. This enables us to resolve gas accretion during the early assembly of minihalos and to capture the emergence of strong turbulent flows. We find that turbulence, driven by gas infall into the dark matter potential wells, is predominantly supersonic, with characteristic Mach numbers ranging from $1.8$ to $4.2$, increasing with halo mass. The supersonic turbulence effectively fragments the central gas cloud into multiple dense clumps, some of which form gravitationally bound cores and begin to collapse into the first stars. Our results suggest that supersonic turbulence is a common feature in minihalos and plays a key role in generating clumpy star-forming clouds, with important implications for the initial mass function of the first stars.

We consider the formation of Q-balls in false vacuum remnants during a cosmological first-order phase transition. We find that under certain circumstances Q-balls can collapse to form primordial black holes. This scenario can produce multimessenger signals that may be observed at upcoming experiments, including 1-100 nHz gravitational waves from the phase transition, and gamma-rays emitted from primordial black holes as Hawking radiation and as superradiance. These signals are quite distinctive, and differ markedly from signals expected from Fermi-balls. The reheating of the dark sector from the phase transition may address the Hubble tension.

Ultralight vector dark matter induces metric fluctuations that generate timing residuals in the arrival times of pulsar emissions through two distinct modes: a fast mode, sourced by coherent field oscillations, and a slow mode, arising from interference patterns. These modes enable the detection of vector dark matter with masses $m \sim 10^{-24} - 10^{-22}\ \mathrm{eV}$ and $m \sim 10^{-18} - 10^{-16}\ \mathrm{eV}$, respectively, using pulsar timing arrays. While previous studies have explored the fast mode, they neglect the full statistical treatment of the vector field and a precise treatment of its polarization structure. In this work, we investigate the timing residuals from both modes, fully accounting for the statistical properties of ultralight vector dark matter, assuming equipartition among its three polarization states. The two-point correlation functions of timing residuals that we derive serve as direct tools for identifying vector dark matter signatures as a stochastic background in pulsar timing data.

The KM3NeT experiment has recently observed a neutrino with an energy around 100 PeV, and IceCube has detected five neutrinos with energies above 1 PeV. While there are no known astrophysical sources, exploding primordial black holes could have produced these high-energy neutrinos. For Schwarzschild black holes this interpretation results in tensions between the burst rates inferred from the KM3NeT and IceCube observations, and with indirect constraints from the extragalactic gamma ray background. In this letter we show that if there is a population of primordial black holes charged under a new dark $u(1)$ symmetry which spend most of their time in a quasi-extremal state, the neutrino emission at 1 PeV may be more suppressed than at 100 PeV. The burst rates implied by the KM3NeT and IceCube observations and the indirect constraints can then all be consistent at $1\sigma$. Furthermore, these black holes could constitute all of the observed dark matter in the universe.

We show that Langer's rate of bubble nucleation is quantitatively correct up to small higher-loop corrections, in comparison to lattice simulations. These results are a significant advancement on decades of lattice studies showing only qualitative trends, and the first showing agreement for any conservative system. We confirm that the failure to fully thermalize the metastable phase explains discrepancies with recent lattice studies that found disagreement with Langer's rate. The key theoretical development is the translation of Langer's perturbative definition of a thermal metastable phase into a nonperturbative statement that can be implemented on the lattice. Our statistical and systematic errors are small enough to allow us to measure on the lattice the coefficient of the two-loop contribution, missing from the perturbative prediction. Our conclusions also exclude a possible systematic uncertainty in $^3$He experiments.

Some recent studies based on numerical relativity simulations claim that slow contraction/ekpyrosis is strongly preferred over inflation as the smoothing mechanism that brought the universe into the homogeneous, isotropic and flat state we observe today on large scales. In this paper, we evaluate the likelihood of the initial conditions employed in the aforementioned simulations by estimating the probability that a free scalar field dominating the universe at the beginning of inflation or ekpyrosis will be sufficiently homogeneous on scales comparable to the Hubble radius at that time. We explore the space of parameters that characterize the initial power spectrum of the scalar field, finding that either can be more likely than the other for a fixed choice of parameters. On the other hand, when we extremize over these parameters, we find that the maximal probability for inflation is much higher than that of ekpyrosis.

In various of particle accelerator designs, amplitude and phase modulation methods are commonly applied to shape the RF pulses for implementing pulse compressors or compensating for the fluctuations introduced by the high-power RF components and beam loading effects. Phase modulations are typically implemented with additional phase shifters that require drive or control electronics. With our recent next-generation LLRF (NG-LLRF) platform developed based on direct RF sampling technology of RF system-on-chip (RFSoC) devices, RF pulse shaping can be realized without the analogue phase shifters, which can significantly simplify the system architecture. We performed a range of high-power experiments in the C-band to evaluate the RF pulse-shaping capabilities of the NG-LLRF system at different stages of the RF circuits. In this paper, the high-power characterization results with the Cool Copper Collider (C3) structure driven by RF pulses with different modulation schemes will be described. With the pulse modulation and demodulation completely implemented in the digital domain, the RF pulse shaping schemes can be rapidly adapted for X-band structures simply by adding analogue mixers.

The low-level RF (LLRF) systems for S-band linear accelerating structures are typically implemented with heterodyne base architectures. We have developed and characterized the next generation LLRF (NG-LLRF) based on the RF system-on-chip (RFSoC) for C-band accelerating structures, and the platform delivered the pulse-to-pulse fluctuation levels considerably better than the requirement of the targeted applications. The NG-LLRF system uses the direct RF sampling technique of the RFSoC, which significantly simplified the architecture compared to the conventional LLRF. We have extended the frequency range of the NG-LLRF to S-band and experimented with different RFSoC devices and system designs to meet the more stringent requirements for S-band LLRF applications. In this paper, the characterization results of the platform with different system architectures will be summarized and the high-power test results of the NG-LLRF with the S-band accelerating structure in the Next Linear Collider Test Accelerator (NLCTA) test facility at the SLAC National Accelerator Laboratory will be presented and analyzed.

A silicon microstrip detector (SSD) has been developed to have state of the art spatial resolution and a large sensitive area under stringent power constraints. The design incorporates three floating strips with their bias resistors inserted between two aluminum readout strips. Beam test measurements with the single sensor confirmed that this configuration achieves a total detection efficiency of $99.8 \, \%$ and spatial resolution $7.6 \, \mathrm{\mu m}$ for MIPs. A double-$\eta$ algorithm was developed to optimize hit position reconstruction for this SSD. The design can be adapted for large area silicon detectors.

We show that the coexistence of a non-minimal coupling to gravity fR=1+cR phi^(n/2) with a kinetic mixing of the form fk=fR^m -- where n=2 and 4 and 0.5<m<10 -- reconciles chaotic inflation based on the phi^n potential with the recent ACT results, if we adopt the Palatini formulation of gravity. The attainment of inflation allows for subplanckian inflaton values and energy scales below the cut-off scale of the corresponding effective theory. The model can be also embedded in supergravity by introducing two chiral superfields and a monomial superpotential, linear with respect to the inflaton-accompanying field. Its stabilization is achieved thanks to a compact contribution to the Kaehler potential, whose the inflationary part includes an holomorphic logarithmic term and a real one multiplying a shift-symmetric quadratic polynomial term.

We study static, spherically symmetric neutron stars in a class of scalar-tensor theories with non-canonical kinetic terms (K-essence) obeying all causality and hyperbolicity conditions. These models have non-trivial dynamics that lead to a type of anti-screening of the scalar. They lead to small corrections in the solar system due to a small coupling, but can lead to large corrections in regimes of high densities, especially neutron stars. We solve the modified Tolman-Oppenheimer-Volkoff equations numerically using realistic equations of state (SLy4, WFF1, MS1, MPA1). For a given central density, we find that two distinct configurations may exist, forming two separate branches of solutions. We find that above a certain critical central density solutions with the correct asymptotic behavior at spatial infinity cannot be obtained. We obtain precise predictions for the mass-radius relation for neutron stars for different values of the parameters in the model and we compare to data.