Papers for Friday, Jun 13 2025

A core-corona decomposition of compact (neutron) star models was compared with the current mass-radius data of the outlier XTE~J1814-338. The corona (which may also be dubbed the envelope, halo or outer crust) is assumed to be of Standard Model matter, with an equation of state that is supposed to be faithfully known and accommodates nearly all other neutron star data. The core, solely parameterized by its mass, radius and transition pressure, presents a challenge regarding its composition. We derived a range of core parameters needed to describe the current data of XTE J1814-338.

Galaxy mergers play a critical role in driving galaxy evolution, especially by transforming galaxy morphology, redistributing the gas around galaxies, triggering AGN activity and star formation. We present the Cosmic Owl, a galaxy merger at $z=1.14$, identified in the COSMOS field. Deep imaging and spectroscopy from JWST, ALMA, and VLA reveal a complex system of twin collisional ring galaxies, exhibiting a nearly identical morphology. The grism spectra from the JWST COSMOS-3D program confirm that both galaxies host an AGN. A bipolar radio jet from one AGN extends to strike the merging front. In addition, we detect a starburst at the merging front, characterized by luminous extended nebular line emission and a massive cold gas reservoir. This starburst is likely triggered by interstellar shocks induced by galaxy collision and the AGN jet. The twin ring structure of the Cosmic Owl requires further numerical simulations to clarify the precise conditions that lead to the formation of this rare morphology. This system exemplifies how shock-induced star formation, driven by galaxy collision or AGN jet, can act as a previously underappreciated yet crucial mechanism for efficient gas-to-star conversion and rapid stellar mass assembly in the early Universe.

The 21cm signal from the Epoch of Reionization (EoR) is observed as a three-dimensional data set known as a lightcone, consisting of a redshift (frequency) axis and two spatial sky plane axes. When observed by radio interferometers, this EoR signal is strongly obscured by foregrounds that are several orders of magnitude stronger. Due to its inherently non-Gaussian nature, the EoR signal requires robust statistical tools to accurately separate it from these foreground contaminants, but current foreground separation techniques focus primarily on recovering the EoR power spectrum, often neglecting valuable non-Gaussian information. Recent developments in astrophysics, particularly in the context of the Galactic interstellar medium, have demonstrated the efficacy of scattering transforms - novel summary statistics for highly non-Gaussian processes - for component separation tasks. Motivated by these advances, we extend the scattering transform formalism from two-dimensional data sets to three-dimensional EoR lightcones. To this end, we introduce a 3D wavelet set from the tensor product of 2D isotropic wavelets in the sky plane domain and 1D wavelets in the redshift domain. As generative models form the basis of component separation, our focus here is on building and validating generative models that can be used for component separation in future projects. To achieve this, we construct maximum entropy generative models to synthesise EoR lightcones, and statistically validate the generative model by quantitatively comparing the synthesised EoR lightcones with the single target lightcone used to construct them, using independent statistics such as the power spectrum and Minkowski Functionals. The synthesised lightcones agree well with the target lightcone both statistically and visually, opening up the possibility of developing for component separation methods using 3D scattering transforms.

We present a probabilistic model for the QCD critical endpoint (CEP) and the equation of state (EOS) at $\beta$-equilibrium, constrained by neutron-star observations. Using a hybrid framework that combines the holographic V-QCD model with an effective van der Waals description of nuclear matter, we generate a large ensemble of EOSs incorporating nuclear theory uncertainties. Constraining this ensemble with neutron-star mass-radius data and tidal deformability measurements from gravitational waves, we identify a strong first-order deconfinement transition at zero temperature, with a transition strength of $\Delta n_{\rm{PT}}/n_0 = 3.75^{+0.70}_{-0.53}$ and onset density $n_{\rm{PT}}/n_0 = 4.9^{+1.33}_{-1.17}$. The resulting posterior yields $95\%$ credible intervals for the CEP location: $\mu_{\rm{crit}} = 626^{+90}_{-179}\,\rm{MeV}$, $T_{\rm{crit}} = 119^{+14}_{-6}\,\rm{MeV}$.

We present a hierarchical Bayesian framework designed to infer the luminosity function of any class of objects by jointly modeling data from multiple surveys with varying depth, completeness, and sky coverage. Our method explicitly accounts for selection effects and measurement uncertainties (e.g., in luminosity) and could be generalized to any extensive quantity, such as mass. We validate the model using mock catalogs, recovering how deep data reaching $\gtrsim 1.5$ dex below a characteristic luminosity $\tilde{L}^\star$ are essential to reduce biases at the faint end ($\lesssim 0.1$ dex), while wide-area data help constrain the bright end. As proof of concept, we consider a combined sample of 1176 Ly$\alpha$ emitters at redshift $3 < z < 5$ drawn from several MUSE surveys, ranging from ultra-deep ($\gtrsim 90$ hr) and narrow ($\lesssim 1$ arcmin$^2$) fields to shallow ($\lesssim 5$ hr) and wide ($\gtrsim 20$ arcmin$^2$) fields. With this complete sample, we constrain the luminosity function parameters $\log(\Phi^\star/\mathrm{Mpc^{-3}}) = -2.86^{+0.15}_{-0.17}$, $\log(L^\star/\mathrm{erg\,s^{-1}}) = 42.72^{+0.10}_{-0.09}$, and $\alpha = -1.81^{+0.09}_{-0.09}$, where the uncertainties represent the $90\%$ credible intervals. These values are in agreement with studies based on gravitational lensing that reach $\log(L/\mathrm{erg\,s^{-1}}) \approx 41$, although differences in the faint-end slope underscore how systematic errors are starting to dominate. In contrast, wide-area surveys represent the natural extension needed to constrain the brightest Ly$\alpha$ emitters [$\log(L/\mathrm{erg\,s^{-1}}) \gtrsim 43$], where statistical uncertainties still dominate.

We propose a new method to determine the dark matter density profile in the vicinity of distant supermassive black holes (SMBH) using reverberation mapping measurements of active galactic nuclei (AGN). For some AGN, the mapping of multiple emission lines allows us to measure the enclosed mass within different radii from the central SMBH, which allows us to infer or constrain the dark matter density profile on sub-pc scales. We find that for five out of fourteen AGN in our identified sample, the observed enclosed mass grows with radii, hinting evidence for the presence of a dark matter component at the 1-2 $\sigma$ level. For these sources, we find global evidence for a universal dark matter profile with a preferred radial steepness of index $\gamma \sim 1.6$, consistent with the scenario expected for a dark matter spike mildly relaxed by stellar heating processes. For the remaining AGN in our sample, we are able to derive upper limits on the dark matter density profile parameters. Interestingly, the strongest evidence for a dark matter component arises from the farthest object considered, 3C 390. This new method allows us to measure or constrain for the first time the dark matter density in the vicinity of extragalactic SMBHs, which is crucial to our understanding of the dynamics and nature of dark matter.

V455 Car is a southern oscillating eclipsing Algol-type system with an orbital period of 5.132888 days. Our first photometric solutions based on the Transiting Exoplanet Survey Satellite indicate that it is a semi-detached binary with the secondary star is almost filling its Roche lobe. The noticeable O'Connell effect in light curve could be explained by hot spot on the primary component, which may be attributed to the mass transfer from the secondary component to the primary one. The absolute parameters are determined as: $M_{1} = 5.30 \pm 1.10 \, \rm M_{\odot}$, $R_{1} = 3.17 \pm 0.22 \, \rm R_{\odot}$ for the primary, and $M_{2} = 1.58 \pm 0.32 \, \rm M_{\odot}$, $R_{2} = 6.66 \pm 0.46 \, \rm R_{\odot}$ for the secondary. \textbf{Based on $O-C$ analysis, we find a periodic variation of $P_3=26.62(\pm1.66)\,yr$. The periodic oscillation suggests a possible third body with a minimal mass of $0.59(\pm0.13)\,\rm M_{\odot}$}. It is speculated that the secondary star has undergone a longer evolution, leading to a mass ratio reversal being experienced in the binary system. Our frequency analysis finds that the primary of V455 Car may be an SPB/SLF star. This study reports a novel example of an oscillating eclipsing Algol-type system featuring an SPB/SLF primary star and a red giant star, which suggest that strong observational results for a high incidence of third bodies in massive binaries.

Bursts from the very early universe may lead to a detectable signal via the production of positrons, whose annihilation gives an observable X-ray signal. Using the absorption parameters for the annihilation photons of 511 keV, it is found that observable photons would originate at a red-shift around $z\approx$ 200-300, resulting in soft X-rays of energy $\sim$ 2-3 keV at present. Positrons are expected to be absent at these times or red-shifts in the standard picture of the early universe. Detection of the X-rays would thus provide dramatic support for the hypothesis of the bursts, explosive events at very early times. We urge the search for such a signal.

Passing stars (also called stellar flybys) have notable effects on the solar system's long-term dynamical evolution, injection of Oort cloud comets into the solar system, properties of trans-Neptunian objects, and more. Based on a simplified solar system model, omitting the Moon and the Sun's quadrupole moment J2, it has recently been suggested that passing stars are also an important driver of paleoclimate before ~50 Myr ago, including a climate event called the Paleocene-Eocene Thermal Maximum (~56 Myr ago). In contrast, using a state-of-the-art solar system model, including a lunar contribution and J2, and random stellar parameters (>400 simulations), we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr. Even in an extreme flyby scenario in which the Sun-like star HD 7977 (m = 1.07 M_Sun) would have passed within ~3,900 au about 2.8 Myr ago (with 5% likelihood), we detect no discernible change in Earth's orbital evolution over the past 70 Myr, compared to our standard model. Our results indicate that a complete physics model is essential to accurately study the effects of stellar flybys on Earth's orbital evolution.

Eccentric white dwarf-massive black hole binaries can potentially source some extreme X-ray transients, including the recently observed quasi-periodic X-ray eruptions and tidal disruption events at the galactic nuclei. Meanwhile, they are one of the target gravitational wave sources with extreme mass ratios for future millihertz gravitational wave missions. In this work, we focus on the tidal evolution and orbital dynamics of such binaries under the influence of the tidal backreaction and the dissipative effect from gravitational wave emission. We find that the latter can cause the dynamical tide to evolve chaotically after more than one orbital harmonics encounter the mode resonance through orbital decay. Different from the tidal-driven chaos, which only occurs for pericenter distances within around two times the tidal radius ($R_t$), this gravitational wave-driven chaos can happen at much larger pericenter distances. The growth scales similarly to a diffusive process, in which the tidal energy grows linearly with time on average over a long duration. If the tidal energy eventually approaches the stellar binding energy, achievable when the pericenter distance is less than $4R_t$, it can cause mass ejection as the wave breaks due to nonlinear effects. We show that this can potentially lead to the repeating partial tidal disruptions observed at galactic centers. That means these disruptions can occur at a much larger pericenter distance than previous analytical estimates. Furthermore, if the system can evolve to a close pericenter distance of about 2.7$R_t$, the white dwarf can further lose mass via tidal stripping at each pericenter passage. This provides a mechanism for producing the quasi-periodic eruptions.

We determine the contributions of the rapid (r) and slow (s) neutron capture processes to the Ba isotope mixture, along with Ba, Eu, and Sr NLTE abundances, in a sample of very metal-poor stars. The selected stars formed before the contribution from the main s-process in low- and intermediate-mass stars became significant. Some of our sample stars are enhanced in Sr, with [Sr/Ba] reaching up to 0.7. These stars gained their high Sr abundance from a poorly understood process, which may appear to be a weak s-process or a weak r-process. Our aim is to uncover the nature of this additional Sr source. The abundances derived from the resonance Ba II lines are influenced by the adopted Ba isotope mixture. We compute Ba isotope mixtures corresponding to different r- to s-process contributions and determine the corresponding abundances from the Ba II resonance lines in each sample star. Additionally, we determine Ba abundances from weak subordinate Ba II lines, which are unaffected by the adopted Ba isotope mixture. We then compare the Ba abundances derived from the subordinate lines with those from the Ba II resonance lines. We find a higher s-process contribution to Ba isotopes in stars with greater [Sr/Eu] and [Sr/Ba] overabundances, suggesting that the additional Sr synthesis was due to the early s-process occurring in massive stars. We estimate the [Sr/Ba] ratio produced by the early s-process and obtain [Sr/Ba]_earlyS = 1.1 +- 0.2. Regarding the potential synthesis of Sr and Ba in the i-process in massive stars, our results argue that there was no detectable contribution from this process within the error bars in our sample stars. In the early Galaxy, before significant main s-process enrichment, barium and strontium were produced primarily by the main r-process and the early s-process, which occurred in rapidly rotating massive stars.

The role of non-thermal proton energy transportation during solar and stellar flares is largely unknown; a better understanding of this physical process will allow us to rectify longstanding deficiencies in flare models. One way to detect the presence of non-thermal protons during flares is through the Orrall-Zirker (OZ) effect whereby an enhanced red wing appears in hydrogen emission lines (e.g., Lyman-$\alpha$ at 1215.67 Angstrom). We analyze archival Hubble Space Telescope/Cosmic Origins Spectrograph G130M (1060 - 1360 Angstrom) observations of the young M dwarf, AU Mic to search for evidence of OZ effect during the impulsive phase of six stellar flares with $E_\textrm{flare} \approx 10^{30 - 31}$ erg. While we found non-detections of the OZ effect, we note there is a pronounced blue enhancement in several C II and C III emission lines during one of the high-energy flares. We propose that either filament eruptions or chromospheric evaporation could be the mechanism driving this observed blue enhancement. We compare the far-ultraviolet (FUV) spectra to 1D radiative-hydrodynamic stellar flare models, which are unable to reproduce the blue enhancement and broadening in these cool flare lines. By completing a line-by-line analysis of the FUV spectrum of AU Mic, we provide further constraints on the physical mechanisms producing stellar flares on M dwarfs.

A unique linear trail of diffuse galaxies was recently identified in the NGC 1052 field. This trail includes the remarkable, ultra-diffuse galaxies DF2 and DF4 which lack dark matter and host unusually luminous globular clusters. It has been proposed that the trail formed via a high-speed collision between two gas-rich dwarf galaxies. This scenario predicts that the trail galaxies are kinematically connected and follow a specific trend in radial velocity as a function of position, based on the known velocities and positions of DF2 and DF4. To test this hypothesis, we measured radial velocities for seven additional galaxies on the trail. While the galaxies' low surface brightnesses presented observational challenges, we employ several methods to obtain measurements for galaxies with effective surface brightnesses up to 28.6 mag arcsec$^{-2}$, including a narrow slit placed over globular clusters and a novel wide slit mode on Keck/LRIS, as well as a 'light bucket' mode on Keck/KCWI. We find that five of our seven targets follow the precise velocity trend predicted by DF2 and DF4, to a degree with just a 2% chance of randomly occurring. Moreover, the trail galaxies' radial velocities are significantly higher than those of the NGC 1052 group, setting it apart as a separate, kinematically connected system. Our findings support the theory that this trail of galaxies, including DF2 and DF4, formed together in a single event. A 'bullet dwarf' collision remains the only known explanation for all the unusual properties of DF2, DF4, and the associated trail of galaxies.

In this paper we discuss the observational capabilities and sensitivity of the SQM-ISS detector to primordial black holes. The SQM-ISS experiment aims to detect slow, non relativistic massive particles within cosmic rays, using a detector on board the International Space Station. The device is designed to recognize the passage of highly penetrating and dense particles in a wide range of mass and charge states such as Strange Quark Matter (SQM). These particles, traveling at speeds typical of gravitationally bound objects in the galaxy - around 250 km/s - are also possible candidates of dark matter. The ability of SQM-ISS to identify penetrating, massive and slow-moving objects allows it also to be sensitive to the detection of primordial black holes. We discuss how black holes, traveling through the detector at velocities compatible with galactic orbital speeds, can be identified based on their interaction signatures.

The Galactic transient black hole candidate (BHC) MAXI~J1834-021 was detected for the first time by MAXI/GSC on February 05, 2023 and it was active for next $\sim 10$~months. A monotonic evolution of low-frequency QPOs from higher to lower frequencies is observed in the middle-phase of the outburst. We study this evolution of the QPO with the propagating oscillatory shock (POS) model, and it suggests the presence of a receding shock. The POS model fit also estimates the mass of the source to be $12.1\pm0.3~M_\odot$. We also study the boradband ($0.5$-$70$~keV) nature of the source using archival data of NICER and NuSTAR on March 10, 2023 with the both phenomenological (combined disk blackbody plus powerlaw) and physical (\textit{nthComp, kerrbb, TCAF}) models. The mass of the BHC estimated by the \texttt{kerbb} and \texttt{TCAF} models is found to be consistent with POS model fits as well as reported in our recent work. Combining all these methods, we predict mass of the source as $12.3^{+1.1}_{-2.0}~M_\odot$. The \texttt{kerbb} model fit also estimates the spin, distance, and inclination of the source to be $0.13^{+0.03}_{-0.02}$, $9.2^{+0.4}_{-0.9}$~kpc, and $80^\circ.0$$^{+2.7}_{-6.0}$, respectively. The combined spectral study suggests harder spectral state of the source with a higher dominance of the sub-Keplerian halo accretion rate over the Keplerian disk rate. The consistency of the observed frequency of the QPO with that of obtained from the \texttt{TCAF} model fitted shock parameters, confirms shock oscillation as the origin of the QPO.

Observations of galaxy-cluster cores reveal that AGN feedback is strongly associated with both a short central cooling time ($t_{\rm c} \lesssim 10^9 \, {\rm yr}$) and accumulations of cold gas ($\lesssim 10^4 \, {\rm K}$). Also, the central ratio of cooling time to freefall time is rarely observed to drop below $t_{\rm c}/t_{\rm ff} \approx 10$, and large accumulations of cold gas are rarely observed in environments with $t_{\rm c} / t_{\rm ff} \gtrsim 30$. Here we show that the critical range -- $10 \lesssim t_{\rm c}/t_{\rm ff} \lesssim 30$ -- plausibly results from magnetized thermal instability. We present numerical simulations of magnetized stratified atmospheres with an initially uniform magnetic field. Thermal instability in an otherwise static atmosphere with $t_{\rm c}/t_{\rm ff} \approx 10$ progresses to nonlinear amplitudes, causing cooler gas to accumulate, as long as the background ratio of thermal pressure to magnetic pressure is $\beta \lesssim 100$. And in atmospheres with $t_{\rm c}/t_{\rm ff} \approx 20$, cooler gas accumulates for $\beta \lesssim 10$. Magnetized atmospheres are therefore much more likely to precipitate than unmagnetized atmospheres with otherwise identical properties. We hypothesize that AGN feedback triggered by accumulations of cold gas prevents $t_{\rm c}/t_{\rm ff}$ from dropping much below 10, because cold gas inevitably precipitates out of magnetized galactic atmospheres with lower ratios, causing $t_{\rm c}/t_{\rm ff}$ to rise.

This study presents a detailed chemical, kinematic, and orbital dynamic analysis of five metal poor stars in the solar neighborhood: HD 2665, HD 5916, HD 122956, HD 189349, and HD 218857. Using high-resolution spectroscopic data from the ELODIE and ESPaDOnS instruments, we derived elemental abundances for 29 species (25 elements: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Sm) via LTE based analysis with ATLAS9 model atmospheres. Notably, we report first time detections of Ce and Nd in HD2665; Al, V, Sm, and Mn in HD5916; Al in HD 122956; and C, O, S, Sc, Mn, Co, Cu, Zn, Sr, Zr, Nd, and Sm in HD 189349. Dynamical and chemical diagnostics reveal distinct origins: HD 2665 shows strong orbital and chemical similarity to GC NGC 5139 ($\omega$ Cen), while HD 218857 exhibits chemodynamic signatures consistent with NGC 5634. HD 122956 aligns with NGC 6864 (M75), though intriguingly shares age, metallicity ([Fe/H]), and [Mg/Fe] ratios with NGC 6517, a cluster whose reported abundances are derived solely from one star with APOGEE $H$-band spectroscopic measurements, as no optical spectroscopic data exist for its members. In contrast, HD 5916 and HD 189349 exhibit kinematic and chemical properties consistent with the field-star population and are classified as thick disk members.

It has been suggested that Earth's present water budget formed from oxidation reactions between its initial hydrogen-rich primordial atmosphere and its magma ocean. Here we examine this hypothesis by building a comprehensive atmosphere-magma ocean model. We find that water formation is unlikely for two reasons. First, any water formed from oxidation reactions in the magma ocean would quickly outgass because of the water-poor atmosphere above. Second, the top boundary layer of the magma ocean becomes stable against convection because the oxidation reactions produce metallic iron, which sinks to the core of a growing Earth. This iron loss makes the top boundary layer significantly more buoyant than the rest of the magma, thus becoming stable against mixing. Our results suggest that hydrogen dissolution is unlikely to play a major role in the formation of Earth's oceans.

Statistical studies of protoplanetary disks and exoplanet populations often exhibit a "missing mass" problem, where observed dust masses in (sub-)millimeter surveys are significantly lower than expected when compared to the mass of evolved exoplanetary systems. We investigate how the streaming instability and subsequent planetesimal formation in protoplanetary disks might solve this missing mass problem when (sub-)millimeter observations are interpreted under the assumption of optically thin emission. We conduct hydrodynamical simulations of the streaming instability with self-gravity after which radiative transfer calculations with dust scattering are performed to measure the (sub-)millimeter intensity. The measured intensity is then used to estimate the disk mass under the assumption of optically thin emission and compared to the true mass in the simulation to calculate the observational bias via the mass excess. We find that the emission from overdense filaments that emerge due to the streaming instability are optically thick at (sub-)millimeter wavelengths, leading to mass excess factors of $\sim 2-7$, even when the optically thick fraction is low.

Gravitational waves from inspiraling compact binaries provide direct measurements of luminosity distances and serve as a powerful probe of the high-redshift Universe. In addition to their role as standard sirens, they offer an opportunity to constrain small-scale density fluctuations through the dispersion in the distance-redshift relation induced by gravitational lensing. We propose a method to constrain this lensing dispersion without requiring the redshift information by analyzing the angular clustering of gravitational wave sources. Our formalism incorporating second-order lensing effects in the luminosity distance shows that the amplitude of the auto-correlation angular clustering decreases with increasing lensing dispersion. While we show that the auto-correlation signal is detected with sufficient signal-to-noise ratios in future gravitational wave experiments, there exists a strong degeneracy between the lensing dispersion and the linear bias of gravitational wave sources. We demonstrate that this degeneracy is partially broken by a joint analysis of the auto-correlation of gravitational wave sources and the cross-correlation with galaxies whose redshifts are known. This approach enhances the use of gravitational waves as a cosmological probe at high redshifts.

Open clusters offer crucial insights into stellar nucleosynthesis and the chemical evolution of the Galactic disc, as their ages and distances can be determined with higher accuracy compared to field stars. In this study, we investigate the outermost regions of the Milky Way disc using two previously unstudied open clusters -Auner 1 and Berkeley 102- located at Galactocentric distances of approximately 14 kpc in largely uncharted areas of the Galaxy. We obtained medium-resolution spectra (R > 18,700) using the MEGARA integral-field unit (IFU) spectrograph on the 10.4 m Gran Telescopio Canarias (GTC), targeting red giant member stars in both clusters. From these spectra, we derived radial velocities, stellar atmospheric parameters, and chemical abundances for six elements: Fe, Ca, Co, Ni, Ba, and Eu. Additionally, we provide updated estimates of the clusters' ages and distances. Both clusters are old (3.2 +- 0.7 Ga), distant (d ~ 8 kpc), and lie below the Galactic plane (Z Gal ~ -0.7 kpc), with moderate extinction (AV ~ 1.3 mag). We find that Auner 1 has a metallicity of [Fe/H] = -0.30 +- 0.09 and Berkeley 102 of [Fe/H] = -0.35 +- 0.06, consistent with other clusters at similar Galactocentric radii and indicating minimal azimuthal variation in metallicity. The [X/Fe] abundance ratios align with expected trends, although [Ca/Fe] is slightly higher in both clusters, and [Eu/Fe] is notably enhanced in Berkeley 102 ([Eu/Fe] = 0.64 +- 0.05). Our findings highlight the effectiveness of GTC/MEGARA in IFU mode for Galactic archaeology and emphasize the need for further medium-to-high resolution spectroscopic studies of remote open clusters to refine models of the outer Galactic disc's chemical evolution.

How gas gets into, through, and out of galaxies is critical to understanding galactic ecosystems. The disk-CGM interface region is uniquely suited for studying processes that drive gas flows. Matter and energy that enter and leave a galaxy pass through this region; however, the precise pathways are yet to be explored. In this paper, we discuss future observations that will facilitate the discovery of the gas flow pathways in galaxies and the telescope parameters necessary for making those observations. We advocate for high spectral resolution ultraviolet spectroscopic capabilities on the Habitable Worlds Observatory (HWO) that will enable observations in a wavelength range of 940 - 3500 A (minimum range: 970 - 3000 A) and at a resolution of 100,000 (minimum of 50,000). We advocate 19 for a multi-object spectrograph with thousands of sub-arcsec slitlets and a field of view 6' x 6'. We also recommend that the spectrograph be sensitive enough to achieve a signal-to-noise ratio of 10 or higher within a few hours for a continuum source of 21 AB magnitude and estimate an optimal aperture size of 8 meters. These capabilities would enable the characterization of gas in the disk-halo interface, leading to breakthroughs in our understanding of the gas flows and galactic ecosystems.

Several observational studies suggest that the local few hundred Mpc around the Local Group are significantly underdense based on source number counts in redshift space across much of the electromagnetic spectrum, particularly in near-infrared galaxy counts. This ``Keenan--Barger--Cowie (KBC) void'', ``Local Hole'', or ``local supervoid'', would have significant ramifications for the Hubble tension by generating outflows that masquerade as an enhanced local expansion rate. We evaluate models for the KBC void capable of resolving the Hubble tension with a background Planck cosmology. We fit these models to direct distances from the Tully--Fisher catalogue of the CosmicFlows-4 compilation using a field-level forward model. Depending on the adopted void density profile, we find the derived velocity fields to prefer a void size of less than 70 Mpc, which is less than 10 per cent of the fiducial size found by Haslbauer et al. based on the KBC luminosity density data. The predicted local Hubble constant is $72.1^{+0.9}_{-0.8}$, $70.4^{+0.4}_{-0.4}$, or $70.2^{+0.5}_{-0.4}$ km/s/Mpc for an initial underdensity profile that is exponential, Gaussian, or Maxwell-Boltzmann, respectively. The latter two ameliorate the Hubble tension to within $3\sigma$ of the 4-anchor distance ladder approach of Breuval et al. giving $73.2 \pm 0.9$ km/s/Mpc. The exponential profile does achieve consistency with this measurement at just over $1\sigma$, but it is disfavoured by the Bayesian evidence. The preferred models produce bulk flow curves that disagree with recent estimates from CosmicFlows-4, despite the void models being flexible enough to match such estimates.

We present a fast and scalable estimator for the binned multi-frequency angular bispectrum (MABS) and the 3D bispectrum (BS) of the redshifted 21 cm signal from radio interferometric observations. The estimator operates on gridded visibilities and leverages the FFT-based acceleration to efficiently compute the MABS and the 3D BS covering all possible triangle configurations. We present the formalism and validate the estimator using simulated visibility data for a known input model BS, considering the Murchison Widefield Array (MWA) observations with a bandwidth of $30.72$ MHz centered at $154.25$ MHz. We consider two cases, namely, without flagging, and with flagging, which has exactly the same frequency channels flagged as the actual data. We obtain estimates of the BS for a wide range of triangle shapes covering the scales $0.003 ~\mathrm{Mpc}^{-1}\leq k_1 \leq 1.258 ~\mathrm{Mpc}^{-1}$. The estimated BS shows excellent agreement with analytical predictions based on the input model BS. We find that the deviations, which are below 20\% even in the presence of flagging, are mostly consistent with the expected statistical fluctuations. This work paves the way for reliable observational estimates of the 21 cm BS for the epoch of reionization, where the signal is predicted to be highly non-Gaussian.

We provide a meta-study of the statistical and individual properties of two volume-complete sets of evolved stars in the Solar Neighbourhood: (1) 852 stars from the Nearby Evolved Stars Survey (NESS), and (2) a partially overlapping set of 507 evolved stars within 300 pc. We also investigate distance determinations to these stars, their luminosity functions and their spatial distribution. Gaia APSIS GSP-Phot AENEAS temperatures of bright giant stars often appear to be underestimated. Existing literature on AGB stars under-samples both the most and least extreme nearby dust-producing stars. We reproduce the literature star-formation history of the solar neighbourhood, though stellar-evolution models over-predict the number of AGB stars of ages around 500 Myr. The distribution of AGB stars broadly matches the known 300 pc scale height of the Galactic disc and shows concentration in the direction of the Galactic centre. Most dust-producing carbon stars belong to the Galactic thick-disc population.

Here, the $\alpha$-attractor inflation is investigated within a framework incorporating a minimal measurable length, as implemented by the Generalized Uncertainty Principle (GUP). The GUP modifications to the Friedmann equations and cosmological perturbation parameters are employed to assess the model observational viability against recent high-precision data, primarily from the Atacama Cosmology Telescope Data Release 6 (ACT DR6) combined with Planck, DESI BAO, and BICEP/Keck 2018 observations (P-ACT-LB-BK18). Our results indicate that while the standard $\alpha$-attractor model ($\beta=0$) for $N_*=60$ lies near the $2\sigma$ boundary of the P-ACT-LB-BK18 dataset, the inclusion of GUP effects significantly shifts the predictions for the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$. Notably, for the GUP parameter $\beta$ values surpassing approximately $10^{13}$, the model predictions are shown to fall well within the 68\% CL region of this combined observational data, enhancing its consistency. The viable parameter space in the $\alpha-\beta$ plane is explored, revealing that a maximum $\alpha \simeq 0.74$ is consistent with the 68\% CL for $\beta \simeq 1.4\times 10^{13}$. In addition, for smaller values of $\alpha$, the predictions of the model remain inside the 68\% CL region for larger values of $\beta$.

We report multifrequency Very Long Baseline Array (VLBA) observations at 2.3 and 8.4GHz of three nearby ultraluminous infrared galaxies, identified via mid-infrared spectroscopic analyses as hosting deeply embedded active galactic nuclei (AGNs). Milliarcsecond-scale observations at both frequencies reveal compact continuum emission in IRAS F00188$-$0856 and IRAS F01298$-$0744, accounting for $\sim10$% of the flux density measured on arcsecond scales. The non-detection in IRAS F00091$-$0738 and the lower limit on the intrinsic 8.4 GHz brightness temperature of $10^{6.1}$ K in IRAS F01298$-$0744 yield no conclusive evidence of AGN-driven radio emission, whereas the measurement of $10^{7.8}$ K in IRAS F00188$-$0856 confirms an AGN origin. Thus, the mid-infrared AGN classification remains robust, with at least one object exhibiting compact radio emission indicative of AGN activity. We further investigate the high-frequency spectral steepening observed in all three galaxies. In each case, this steepening arises from spectral aging in diffuse kpc-scale emission, which is resolved out by the VLBA observations. One possible explanation for the steepening of the sample is merger-induced particle acceleration. IRAS F00188$-$0856 exhibits a peaked radio spectrum, characteristic of a young radio source, with the high-frequency steepening attributable to this AGN activity. Consequently, the spectral steepening at high frequencies arises from particles accelerated by merger dynamics or AGN activity.

We present periodicity and single-pulse searches at 1250 MHz for 22 radio-quiet gamma-ray pulsars, conducted using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). For PSR J1813$-$1246, we successfully detected pulsed signals with a spin period of 48.08 ms and a dispersion measure of 209.85 ${\rm pc cm^{-3}}$, consistent with the spin period measured at gamma-ray wavelengths. The estimated flux density is approximately 9 $\mu$Jy. For the remaining 21 sources, no radio emission was detected, with flux density upper limits of several $ \mu$Jy. The capability to detect pulsars with such low flux densities provides the opportunity to determine if and how these faint sources differ from much radio-brighter pulsars.

Physical problems with a solution that can be expressed analytically are scarce; this holds even more true for problems set in a cosmological context. Such solutions are, however, invaluable tools for making comparisons between theory, numerical experimentation and observations. In this work we present what to our knowledge is the first set of non-trivial closed-form expressions describing the behaviour of a system governed by the equations of non-ideal Magnetohydrodynamics (MHD), where the effects of Ohmic diffusion are considered, in a cosmologically expanding frame. We provide analytical solutions that describe the time evolution of linear perturbations to a homogeneous background in a radiation-dominated universe, yielding dissipative Alfvén waves. Although in our base framework solutions for any other cosmology of interest cannot be expressed in a closed form, they can still be obtained reliably through numerical integration of the coupled system of ordinary differential equations we provide. We compare our analytical solutions to numerical results obtained using our novel implementation of Smoothed Particle Magnetohydrodynamics (SPMHD) in the SWIFT astrophysical simulation code, to find good agreement between the two. We find the code to display good convergence behaviour, its predictions agreeing with theory to within 0.1% for a modest number of resolution elements and at a negligible computational cost. We aim this work as a companion and supplement to the cosmological ideal MHD wave tests recently presented in the literature, and suggest that it be adopted as part of standard testing of code implementations of MHD.

We present observations of SN 2023xgo, a transitional Type Ibn/Icn SN, from $-5.6$ to 63 days relative to $r$-band peak. Early spectra show CIII $\lambda$5696 emission like Type Icn SNe, shifting to Type Ibn features. The He I velocities (1800-10000 km s$^{-1}$) and pseudo-equivalent widths are among the highest in the Ibn/Icn class. The light curve declines at 0.14 mag d$^{-1}$ until 30 days, matching SNe Ibn/Icn but slower than fast transients. SN 2023xgo is the faintest in our SN Ibn sample (M$_{r}$ = -17.65 $\pm$ 0.04) but shows typical colour and host properties. Semi-analytical modelling of the light curve suggests a compact CSM shell (10$^{12}$-10$^{13}$ cm), mass-loss rate between 10$^{-4}$-10$^{-3}$ M$_{\odot}$ yr$^{-1}$ with CSM and ejecta masses of $\sim$0.22 and 0.12 M$_{\odot}$, respectively. Post-maximum light-curve, spectral modelling favours a $\sim$3 M$_{\odot}$ helium star progenitor with extended ($\sim$10$^{15}$ cm), stratified CSM (density exponent of 2.9) and mass-loss rate of 0.1-2.7 M$_{\odot}$ yr$^{-1}$. These two mass-loss regimes imply a radially varying CSM, shaped by asymmetry or changes in the progenitors mass loss over time. This mass-loss behavior fits both binary and single-star evolution. Early Icn-like features stem from hot carbon ionization, fading to Ibn-like with cooling. SN 2023xgo thus offers rare insight into the connection between SNe Icn, Ibn, and SNe Ibn with ejecta signatures.

We present the ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO), a Large Program of the Atacama Large Millimeter/submillimeter Array (ALMA). AGE-PRO aims to systematically trace the evolution of gas disk mass and size throughout the lifetime of protoplanetary disks. It uses a carefully selected sample of 30 disks around M3-K6 stars in three nearby star-forming regions: Ophiuchus (0.5-1 Myr), Lupus (1-3 Myr), and Upper Sco (2-6 Myr). Assuming the three regions had similar initial conditions and evolutionary paths, we find the median gas disk mass appears to decrease with age. Ophiuchus disks have the highest median gas mass (6 M$_{\rm Jup}$), while the Lupus and Upper Sco disks have significantly lower median masses (0.68 and 0.44 M$_{\rm Jup}$, respectively). Notably, the gas and dust disk masses appear to evolve on different timescales. This is evidenced by the median gas-to-dust mass ratio, which decreases from 122 in the youngest disks ($<$1 Myr) to 46 in Lupus disks, and then increases to 120 in the Upper Sco disks. The median gas disk sizes range between 74-110 au, suggesting that typical gas disks are much smaller than those of well-studied, massive disks. Population synthesis models suggest that magneto-hydrodynamic wind-driven accretion can reproduce median disk properties across all three regions, when assuming compact disks with a declining magnetic field over time. In contrast, turbulent-driven models overestimate gas masses of $>$1 Myr disks by an order of magnitude. Here we discuss the program's motivation, survey design, sample selection, observation and data calibration processes, and highlight the initial results.

We present Band 6 and Band 7 observations of 10 Lupus disks around M3-K6 stars from the ALMA survey of Gas Evolution in PROtoplanetary disks (AGE-PRO) Large Program. In addition to continuum emission in both bands, our Band 6 setup covers the $\mathrm{{}^{12}CO}$, $\mathrm{{}^{13}CO}$ and $\mathrm{C^{18}O}\,J$=2-1 lines, while our Band 7 setup covers the $\mathrm{N_2H^+}\,J$=3-2 line. All of our sources are detected in $\mathrm{{}^{12}CO}$ and $\mathrm{{}^{13}CO}$, 7 out of 10 are detected in $\mathrm{C^{18}O}$, and 3 are detected in $\mathrm{N_2H^+}$. We find strong correlations between the CO isotopologue line fluxes and the continuum flux densities. With the exception of one disk, we also identify a strong correlation between the $\mathrm{C^{18}O}\,J$=2-1 and $\mathrm{N_2H^+}\,J$=3-2 fluxes, indicating similar CO abundances across this sample. For the two sources with well-resolved continuum and $\mathrm{{}^{12}CO}\,J$=2-1 images, we find that their gas-to-dust size ratio is consistent with the median value of $\sim 2$ inferred from a larger sample of Lupus disks. We derive dust disk masses from continuum flux densities. We estimate gas disk masses by comparing $\mathrm{C^{18}O}\,J$=2-1 line fluxes with those predicted by the limited grid of self-consistent disk models of Ruaud et al. (2022). A comparison of these mass estimates with those derived by Trapman et al. (2025), using a combination of CO isotopologue and $\mathrm{N_2H^+}$ line emission, shows that the masses are consistent with each other. Some discrepancies appear for small and faint disks, but they are still within the uncertainties. Both methods find gas disk masses increase with dust disk masses, and gas-to-dust mass ratios are between $10-100$ in the AGE-PRO Lupus sample.

The Atacama Large Millimeter/submillimeter Array (ALMA) large program AGE-PRO explores protoplanetary disk evolution by studying gas and dust across various ages. This work focuses on ten evolved disks in Upper Scorpius, observed in dust continuum emission, CO and its isotopologues, and N$_2$H$^+$ with ALMA Bands 6 and 7. Disk radii, from the radial location enclosing 68% of the flux, are comparable to those in the younger Lupus region for both gas and dust tracers. However, solid masses are about an order of magnitude below those in Lupus and Ophiuchus, while the dust spectral index suggests some level of dust evolution. These empirical findings align with a combination of radial drift, dust trapping, and grain growth into larger bodies. A moderate correlation between CO and continuum fluxes suggests a link between gas and dust content, through the increased scatter compared to younger regions, possibly due to age variations, gas-to-dust ratio differences, or CO depletion. Additionally, the correlation between C$^{18}$O and N$_2$H$^+$ fluxes observed in Lupus persists in Upper Sco, indicating a relatively stable CO gas abundance over the Class II stage of disk evolution. In conclusion, the AGE-PRO survey of Upper Scorpius disks reveals intriguing trends in disk evolution. The findings point towards potential gas evolution and the presence of dust traps in these older disks. Future high-resolution observations are needed to confirm these possibilities and further refine our understanding of disk evolution and planet formation in older environments.

The evolution of the gas mass of planet-forming disks around young stars is crucial for our understanding of planet formation, yet it has proven hard to constrain observationally, due both to the difficulties of measuring gas masses and the lack of a homogeneous sample. Here we present a large grid of thermochemical models which we use to measure protoplanetary gas disk masses of AGE-PRO, the ALMA survey of Gas Evolution in PROtoplanetary disks. AGE-PRO covers a sample of 30 disks around similar spectral type (M3-K6) stars with ages between 0.1 and 10 Myr. Our approach is to simultaneously fit observations of CO isotopologues and N2H+, a complementary molecule produced when CO freezes out. We find that the median gas mass of the three regions decreases over time, from 7.0(+4.4,-2.6)x10^-3 Msun in Ophiuchus (<1 Myr) to 9.4(+5.4,-3.4)x10^-4 Msun for Lupus (~1-3 Myr) and 6.8(+5.1,-2.8)x10^-4 Msun for Upper Sco (~2-6 Myr), with ~1 dex scatter in gas mass in each region. We note that the gas mass distributions for Lupus and Upper Sco look very similar, which could be due to survivorship bias for the latter. The median bulk CO abundance in the CO emitting layer is found to be a factor ~10 lower than the ISM value but does not significantly change between Lupus and Upper Sco. From Lupus to Upper Sco the median gas-to-dust mass ratio increases by a factor ~3 from ~40 to ~120, suggesting efficient inward pebble drift and/or the formation of planetesimals.

The potential for planet formation of a circumstellar disk depends on the dust and gas reservoirs, which evolve as a function of the disk age. The ALMA Large Program AGE-PRO has measured several disk properties across three star-forming regions of different ages, and in this study we compare the observational results to dust evolution simulations. Using DustPy for the dust evolution, and RADMC-3D for the radiative transfer, we ran a large grid of models spanning stellar masses of 0.25, 0.50, 0.75, and 1.0 $M_\odot$, with different initial conditions, including: disk sizes, disk gas masses, and dust-to-gas ratio, and viscosity. Our models are performed assuming smooth, weakly, or strongly substructured disks, aiming to investigate if any observational trend can favor or exclude the presence of dust traps. The observed gas masses in the disks of the AGE-PRO sample are not reproducible with our models, which only consider viscous evolution with constant $\alpha$, suggesting that additional physical mechanisms play a role in the evolution of the gas mass of disks. When comparing the dust continuum emission fluxes and sizes at 1.3 mm, we find that most of the disks in the AGE-PRO sample are consistent with simulations that have either weak or strong dust traps. The evolution of spectral index in the AGE-PRO sample is also suggestive of an unresolved population of dust traps. Future observations at high angular resolution are still needed to test several hypotheses that result from comparing the observations to our simulations, including that more massive disks in gas mass have the potential to form dust traps at larger disk radii.

The architecture of planetary systems depends on the evolution of the disks in which they form. In this work, we develop a population synthesis approach to interpret the AGE-PRO measurements of disk gas mass and size considering two scenarios: turbulence-driven evolution with photoevaporative winds and MHD disk-wind-driven evolution. A systematic method is proposed to constrain the distribution of disk parameters from the disk fractions, accretion rates, disk gas masses, and CO gas sizes. We find that turbulence-driven accretion with initially compact disks ($R_0 \simeq 5-20~$au), low mass-loss rates, and relatively long viscous timescales ($t_{\nu,0} \simeq 0.4-3~$Myr or $\alpha_{SS} \simeq 2-4 \times 10^{-4}$) can reproduce the disk fraction and gas sizes. However, the distribution of apparent disk lifetime defined as the $M_D/\dot{M}_*$ ratio is severely overestimated by turbulence-driven models. On the other hand, MHD wind-driven accretion can reproduce the bulk properties of the disk populations from Ophiuchus to Upper Sco assuming compact disks with an initial magnetization of about $\beta \simeq 10^5$ ($\alpha_{DW} \simeq 0.5-1 \times 10^{-3}$) and a magnetic field that declines with time. More studies are needed to confirm the low masses found by AGE-PRO, notably for compact disks that question turbulence-driven accretion. The constrained synthetic disk populations can now be used for realistic planet population models to interpret the properties of planetary systems on a statistical basis.

Protoplanetary disk evolution can be deeply influenced by the UV radiation emitted by neighboring massive stars (mainly of spectral type O and B). We show that the process of external photoevaporation, which causes an outside-in depletion of disk material due to environmental UV radiation, can lead to a significant decrease in disk size, and moderate in disk mass and lifetime even at moderate irradiation levels (1-10 G$_{0}$). In this work we investigate the role of external photoevaporation in shaping the masses and sizes of the ten AGE-PRO disks in the Upper Scorpius region, which we estimate to be subject to FUV fluxes ranging between 2 and 12 G$_{0}$, on average. We compare the disk masses and sizes resulting from 1D numerical viscous evolution simulations in which the effect of external photoevaporation is included, to the values retrieved from the AGE-PRO observations. While the pure viscous framework fails in adequately explaining the observed disk properties in Upper Scorpius, with the inclusion of external photoevaporation we can successfully reproduce gas disk sizes for 7 out of 10 sources within a factor <2, when the initial disk mass is 1-10% of the stellar mass. We emphasize the importance of accounting for the environmental irradiation when comparing star-forming regions of different ages, even when moderate FUV irradiation fields are experienced, as in the case of Upper Scorpius.

We perform visibility fitting to the dust continuum Band 6 1.3 mm data of the 30 protoplanetary disks in the AGE-PRO ALMA Large Program. We obtain disk geometries, dust-disk radii, and azimuthally symmetric radial profiles of the intensity of the dust continuum emission. We examine the presence of continuum substructures in the AGE-PRO sample by using these radial profiles and their residuals. We detect substructures in 15 out of 30 disks. We report five disks with large ($>$15 au) inner dust cavities. The Ophiuchus Class I disks show dust-disk substructures in $\sim80\%$ of the resolved sources. This evidences the early formation of substructures in protoplanetary disks. A spiral is identified in IRS 63, hinting to gravitational instability in this massive disk. We compare our dust-disk brightness radial profiles with gas-disk brightness radial profiles and discuss colocal substructures in both tracers. In addition, we discuss the evolution of dust-disk radii and substructures across Ophiuchus, Lupus, and Upper Scorpius. We find that disks in Lupus and Upper Scorpius with large inner dust cavities have typical gas-disk masses, suggesting an abundance of dust cavities in these regions. The prevalence of pressure dust traps at later ages is supported by a potential trend with time with more disks with large inner dust cavities (or "transition disks") in Upper Scorpius and the absence of evolution of dust-disk sizes with time in the AGE-PRO sample. We propose this is caused by an evolutionary sequence with a high fraction of protoplanetary disks with inner protoplanets carving dust cavities.

One important key in understanding a galaxy's evolution is to study the consequences of its past dynamical interactions that influenced its shape. By measuring the metallicity distribution of stellar populations with different ages, one can learn about these interactions. The Magellanic Clouds, being the nearest pair of interacting dwarf galaxies with a morphology characterised by different tidal and kinematic sub-structures as well as a vast range of stellar populations, represent an excellent place to study the consequences of dwarf-dwarf galaxy interactions and with their large host, the Milky Way. We aim to determine the metallicities ([Fe/H]) of red giant branch (old) and supergiant (young) stars covering the entire galaxies, estimate their radial metallicity gradients and produce homogeneous metallicity maps. We use the XP spectra from Gaia Data Release 3 to calculate synthetic Strömgren magnitudes from the application of the GaiaXPy tool and adopt calibration relations from the literature to estimate the metallicities. We present photometric metallicity maps for ~90,000 young stars and ~270,000 old stars within ~11 deg of the Small Magellanic Cloud and ~20 deg of the Large Magellanic Cloud from a homogeneous dataset. We find that the overall radial metallicity gradients decrease linearly in agreement with previous studies. We apply piecewise-regression fitting to derive the gradients within different radial regions. The overall metallicity gradients, traced by young and old stars, decrease from the centre to the outskirts of both galaxies. However, they show multiple breakpoints depicting regions following different and sometime opposite trends. These are associated to the structure of the galaxies, their history of star formation and chemical evolution but may be influenced by a low number of sources, especially at the centre (due to crowding) and in the outermost regions.

The inward drift of mm-cm sized pebbles in protoplanetary disks has become an important part of our current theories of planet formation and, more recently, planet composition as well. The gas-to-dust size ratio of protoplanetary disks can provide an important constraint on how pebbles have drifted inward provided that observational effects, especially resolution, can be accounted for. Here we present a method for fitting beam-convolved models to integrated intensity maps of line emission using the astropy python package and use it to fit 12 CO moment zero maps of ten Lupus and ten Upper Scorpius protoplanetary disks from the AGE-PRO ALMA Large Program, a sample of disks around M3-K6 stars that cover the ~1 to 6 Myr of gas disk evolution. From the unconvolved best fit models we measure the gas disk size (RCO,90%[model]), which we combine with the dust disk size (Rdust,90%[FRANK]) from continuum visibility fits from Vioque et al. (2025, in press.) to compute beam-corrected gas-to-dust size ratios. In our sample we find gas-to-dust size ratios between ~1 and ~5.5, with a median value of 2.78(+0.37,-0.32). Contrary to models of dust evolution that predict an increasing size ratio with time, we find that the younger disks in Lupus have similar (or even larger) median ratios (3.02(+0.33,-0.33)) than the older disks in Upper Sco (2.46(+0.53,-0.38)). A possible explanation to this discrepancy is that pebble drift is halted in dust traps combined with truncation of the gas disk by external photo-evaporation in Upper Sco, although survivorship bias could also play a role.

Cold gaseous systems play important roles in galaxy evolution by possibly providing fuel to ignite active galactic nuclei (AGN) activity and star-formation. In this work, we analyze [CII]$158\rm \mu m$ and continuum observations from ALMA for a sample of four radio AGN at $z \approx 3.5$, focusing on eight associated companion cloud systems discovered within projected distances of tens of kiloparsecs or less. The spatial distribution of these companions indicates that the majority of cold gas is not located at the AGN position, i.e., not in their host galaxies. With the assistance of [CII] at 0.2" resolution, we further confirm the gas-poor nature of the hosts by re-analyzing archival [CI] (a tracer of H$_{2}$) at $\sim2"$ resolution. Our sample has [CII] luminosities in a range of $2.8\times10^{8}<L_{\rm [CII]}/L_{\odot}<4.2\times10^{9}$. The $L_{\rm [CII]}/L_{\rm IR}$ ratio, $\sim 9.4\times10^{-4}$, is consistent with sources discussed in the literature. Our findings show the gas-poor radio AGN hosts have nearby gas-rich companions. We propose that these companions, which may be stripped clouds in merger process and by interaction with the energy output from the AGN, could also be a trigger of radio-loud AGN. They may also be a signature of negative AGN feedback (e.g., shock heating) on these infalling companions and on the host galaxy. In general, our analysis shows that powerful AGN at and before Cosmic Noon are impacting and being impacted by cold gaseous clouds in their circum-galactic or proto-intracluster media.

Pulsar Timing Array (PTA) projects have reported various lines of evidence suggesting the presence of a stochastic gravitational wave (GW) background in their data. One key line of evidence involves a detection statistic sensitive to inter-pulsar correlations, such as those induced by GWs. A $p$-value is then calculated to assess how unlikely it is for the observed signal to arise under the null hypothesis $H_0$, purely by chance. However, PTAs cannot empirically draw samples from $H_0$. As a workaround, various techniques are used in the literature to approximate $p$-values under $H_0$. One such technique, which has been heralded as a model-independent method, is the use of ``scrambling'' transformations that modify the data to cancel out pulsar correlations, thereby simulating realizations from $H_0$. In this work, scrambling methods and the detection statistic are investigated from first principles. The $p$-value methodology that is discussed is general, but the discussions regarding a specific detection statistic apply to the detection of a stochastic background of gravitational waves with PTAs. All methods in the literature to calculate $p$-values for such a detection statistic are rigorously analyzed, and many analytical expressions are derived. All this leads to the conclusion that scrambling methods are \emph{not} model-independent and thus not completely empirical. Rigorous Bayesian and Frequentist $p$-value calculation methods are advocated, the evaluation of which depend on the generalized $\chi^2$ distribution. This view is consistent with the posterior predictive $p$-value approach that is already in the literature. Efficient expressions are derived to evaluate the generalized $\chi^2$ distribution of the detection statistic on real data. It is highlighted that no Frequentist $p$-values have been calculated correctly in the PTA literature to date.

Planet-forming discs often contain structures like spiral arms, typically linked to the disc's gravitational forces. In 2D models, an ad hoc softening prescription is commonly used for self-gravity, but this overlooks the vertical structure's impact, suppresses the Newtonian nature of gravity at short distances and doesn't respect Newton's third law. To address these issues, associated with a Plummer potential approximation, we developed an exact self-gravity kernel for thin, hydrostatically supported discs, including a dust fluid component. Our analytical framework provides a precise 2D self-gravity prescription validated by benchmarks and 2D/3D numerical tests. The derived kernel, based on modified Bessel functions, maintains Newtonian gravitation features, such as point-wise symmetry, a smooth transition from light to massive discs and a singularity at zero distance, among others. In contrast to other prescriptions found in the literature, it proves capable of leading to an additional, and previously unnoticed, source of gravitational runaway discernible only at infinitesimal distances. We finally note that our new prescription remains compatible with methods based on the fast Fourier transform, affording superior computational efficiency. Our exact kernel formulation overcomes substantial limitations inherent in the smoothing-length approach. It permits a novel, fully consistent treatment of self-gravity in Gaussian-stratified thin discs. The approach, that makes the usage of the Plummer potential obsolete, will prove useful to studying all common planet formation scenarios, which are often backed by 2D-flat numerical simulations. Accordingly, in an accompanying paper, we will investigate how the occurence of the gravitational instability is affected.

The Legacy Survey of Space and Time (LSST) is expected to observe up to ${\sim}100$ million quasars in the next decade. In this work, we show that it is possible to use such data to measure the characteristic frequency evolution of a "chirp" induced by gravitational waves, which can serve as robust evidence for the presence of a compact supermassive black-hole binary. Following the LSST specifications, we generate mock lightcurves consisting of (i) a post-Newtonian chirp produced by orbital motion through, e.g., relativistic Doppler boosting, (ii) a damped random walk representing intrinsic quasar variability, and (iii) Gaussian photometric errors, while assuming non-uniform observations with extended gaps over a period of 10 yr. Through a fully-Bayesian analysis, we show that we can simultaneously measure the chirp and noise parameters with little degeneracy between the two. For chirp signals with an amplitude of $A = 0.5$ mag and a range of times to merger ($t_m = 15{-}10^4$ yr), we can typically measure a non-zero amplitude and positive frequency derivative with over $5\sigma$ credibility. For binaries with $t_m = 50$ yr, we achieve $3\sigma$ ($5\sigma$) confidence that the signal is chirping for $A \gtrsim 0.1$ ($A > 0.2$). Our analysis can take as little as 35 s (and typically $<$ 10 min) to run, making it scalable to a large number of lightcurves. This implies that LSST could, on its own, establish the presence of a compact supermassive black-hole binary, and thus discover gravitational wave sources detectable by LISA and by Pulsar Timing Arrays.

On 2024 December 28, CHIME/FRB detected the thus-far non-repeating FRB 20241228A with a real-time signal-to-noise ratio of $>50$. Approximately 112~s later, the X-ray Telescope onboard the Neil Gehrels Swift Observatory was on source, the fastest follow-up to-date of a non-repeating FRB (Tohuvavohu et al. in prep.). Using CHIME/FRB and two of the three CHIME/FRB Outriggers, we obtained a Very Long Baseline Interferometry localization for FRB 20241228A with a 1$\sigma$ confidence ellipse of 11$^{\prime\prime}$ by 0.2$^{\prime\prime}$. This represents the first published localization using both the CHIME-KKO and CHIME-GBO Outriggers. We associate FRB 20241228A with a star-forming galaxy at a redshift of $z = 0.1614\pm0.0002$. The persistent X-ray luminosity limit at this source's location and distance is $<1.2 \times 10^{43}$ erg s$^{-1}$ in the $0.3-10$ keV band, the most stringent limit of any non-repeating FRB to-date (Tohuvavohu et al. in prep.). The stellar mass ($\sim 2.6 \times 10^{10}\,M_{\odot}$) and star formation rate ($\sim 2.9\,M_{\odot}$~yr$^{-1}$) of the host galaxy of FRB 20241228A are consistent with the broader FRB host galaxy population. We measure significant scattering ($\sim$1ms) and scintillation ($\sim$20 kHz at 600 MHz) along the line of sight to this source, and suggest the scintillation screen is Galactic while the scattering screen is extragalactic. FRB 20241228A represents an exciting example of a new era in which we can harness VLBI-localizations and rapid high-energy follow-up to probe FRB progenitors.

We present a general analysis of the role of shear viscosity in cosmological backgrounds, focusing on isotropic space-time in both Einstein and $f(R)$ gravity. By computing the divergence of the stress-energy tensor in a general class of isotropic (but not necessarily homogeneous) geometries, we show that shear viscosity does not contribute to the background dynamics when the fluid is comoving. This result holds in both the Jordan and Einstein frames, and implies that shear viscosity cannot affect the electromagnetic luminosity distance which is determined by the background light-like geodesics. As an application of our results, we critically examine recent claims that shear viscosity can alter the Hubble evolution and the electromagnetic luminosity distance in Starobinsky gravity. We demonstrate that the continuity equation used in that work is at odds both with the covariant conservation of the stress-energy tensor and the local second law of thermodynamics. We further show that even in models where such modifications could mimic bulk viscosity, the resulting entropy evolution is inconsistent with standard thermodynamic expectations.

In this work, we consider the possibility that the dynamical dark energy hinted at by recent DESI data may be mimicked by the effects of additional components in the universe, potentially arising from topological defects. We find that the data does not show a particular preference for the existence of cosmic strings. However, a domain wall contribution at the percent level can improve the fit, yielding a $\Delta \chi^2= -1.72$ compared to the $\Lambda \rm{CDM}$ model. The improvement indicates that topological defects remain a viable and interesting extension to $\Lambda\rm{CDM}$, meriting further investigation with future cosmological data.

Starobinsky's $R+\alpha R^2$ inflation provides a compelling one-parameter inflationary model that is supported by current cosmological observations. However, at the same order in spacetime derivatives as the $R^2$ term, an effective theory of spacetime geometry must also include the Weyl-squared curvature invariant $W^2$. In this paper, we study the inflationary predictions of the gravitational theory with action of the form $R+\alpha R^2 - \beta W^2$, where the coupling constant $\alpha$ sets the scale of inflation, and corrections due to the $W^2$ term are treated self-consistently via reduction of order in an expansion in the coupling constant $\beta$, at the linear order in $\beta/\alpha$. Cosmological perturbations are found to be described by an effective action with a non-trivial speed of sound $c_{\textrm{s}}$ for scalar and $c_{\textrm{t}}$ for tensor modes, satisfying the relation $c_{\textrm{t}}/c_{\textrm{s}} \simeq 1+ \frac{\beta}{6\, \alpha}$ during the inflationary phase. Within this self-consistent framework, we compute several primordial observables up to the next-to-next-to-next-to leading order (N3LO). We find the tensor-to-scalar ratio $r \simeq 3(1-\frac{\beta}{6\alpha})(n_\textrm{s}-1)^2$, the tensor tilt $n_{\textrm{t}}\simeq-\frac{r}{8}$ and the running of the scalar tilt $\mathfrak{a}_{\textrm{s}}\simeq-\frac{1}{2} (n_{\textrm{s}} - 1)^2$, all expressed in terms of the observed scalar tilt $n_{\textrm{s}}$. We also provide the corresponding corrections up to N3LO, $\mathcal{O}((n_{\textrm{s}} - 1)^3)$.

By ``nethotrons'', from the ancient Greek verb for to ``spin'', it is meant here a natural or artificial rotating object, like a pulsar or an artificial satellite, whose rotational axis is cumulatively displaced by the post-Newtonian static (gravitoelectric) and stationary (gravitomagnetic) components of the gravitational field of some massive body around which it freely moves. Until now, both relativistic effects have been measured only by the dedicated space-based mission Gravity Probe B in the terrestrial environment. It detected the gravitoelectric de Sitter and gravitomagnetic Pugh-Schiff spin precessions of four superconducting gyroscopes accumulated in a year after about 50 years from conception to completion of data analysis at a cost of 750 million dollars to $0.3$ and $19$ per cent accuracy, respectively. The perspectives to measure them also with long-lived Earth's laser-ranged geodetic satellites, like those of the LAGEOS family or possibly one or more of them to be built specifically from scratch, and pulsars orbiting the supermassive black hole in the Galactic Centre, yet to be discovered, are preliminarily investigated. The double pulsar PSR J0737-3039A/B is examined as well.

Laser-ranging satellites have proved their efficiency in high precision testing of General Relativity and constraining modified gravity theories proposed to explain the dark sector and the cosmological tensions. The LARES 2 satellite launched in 2022, is currently providing improved information regarding the frame-dragging effect predicted by General Relativity, as well as the geodesy, thus essentially complementing the data of already existing laser-ranging satellites. The proper knowledge of the Earth's tidal perturbation modes is essential for accurately extracting the sought frame-dragging signal. We present the results of computation of 110 significant modes in Doodson number classification for the parameters of LARES 2 satellite, continuing our previous study on those obtained for the LARES satellite.

Black hole shadows are a widespread topic in astrophysics. This paper searches for an optical view of the black hole and the relationship between black hole shadow and photon sphere with curvature. We were inspired by the observations of Sagittarius $A^*$ and supermassive black hole M87$*$ through the Event Horizon Telescope. We have found the signature of the modified theory of gravity on the photon sphere and shadow. We considered $f(R)$ modified theory of gravity and new scalar degree of freedom $F$ appears in the expressions of photon sphere and shadow.

The difference ("mismatch") between two gravitational-wave (GW) signals is often used to estimate the signal-to-noise ratio (SNR) at which they will be distinguishable in a measurement or, alternatively, when the errors in a signal model will lead to biased measurements. It is well known that the standard approach to calculate this "indistinguishability SNR" is too conservative: a model may fail the criterion at a given SNR, but not necessarily incur a biased measurement of any individual parameters. This problem can be solved by taking into account errors orthogonal to the model space (which therefore do not induce a bias), and calculating indistinguishability SNRs for individual parameters, rather than the full $N$-dimensional parameter space. We illustrate this approach with the simple example of aligned-spin binary-black-hole signals, and calculate accurate estimates of the SNR at which each parameter measurement will be biased. In general biases occur at much higher SNRs than predicted from the standard mismatch calculation. Which parameters are most easily biased depends sensitively on the details of a given waveform model, and the location in parameter space, and in some cases the bias SNR is as high as the conservative estimate. We also illustrate how the parameter bias SNR can be used to robustly specify waveform accuracy requirements for future detectors.

The data analysis of space-based gravitational wave detectors like Taiji faces significant challenges from non-stationary noise, which compromises the efficacy of traditional frequency-domain analysis. This work proposes a unified framework based on short-time Fourier transform (STFT) to enhance parameter estimation of Galactic binary and characterization of instrumental noise under non-stationarity. Segmenting data into locally stationary intervals, we derive STFT-based models for signals and noises, and implement Bayesian inference via the extended Whittle likelihood. Validated through the analysis of verification Galactic binaries and instrumental noises, our STFT approach outperforms frequency-domain methods by reducing the uncertainty and bias of estimation, successfully recovering low signal-to-noise ratio signals missed by frequency-domain analysis, and mitigating the degeneracy among noise parameters. The framework's robustness against noise drifts and computational efficiency highlight its potential for integration into future global analysis pipelines.

Vortex-magnetic interactions shape magnetohydrodynamic (MHD) turbulence, influencing energy transfer in astrophysical, geophysical, and industrial systems. On the Sun, granular-scale vortex flows couple strongly with magnetic fields, channelling energy into the corona. At high Reynolds numbers, vorticity and magnetic fields are nearly frozen into the charged fluid, and MHD flows emerge from the interplay between vortex dynamics and Lorentz forces. To probe this competition in a controlled setting, we revisit the canonical problem of two antiparallel flux tubes. By varying the magnetic flux threading each tube--and thus sweeping the interaction parameter $N_i$, which gauges Lorentz-to-inertial force balance--we uncover three distinct regimes: vortex-dominated joint reconnection, instability-triggered cascade, and Lorentz-induced vortex disruption. At low $N_i$, classical vortex dynamics dominate, driving joint vortex-magnetic reconnection and amplifying magnetic energy via a dynamo effect. At moderate $N_i$, the system oscillates between vorticity-driven attraction and magnetic damping, triggering instabilities and nonlinear interactions that spawn secondary filaments and drive an energy cascade. At high $N_i$, Lorentz forces suppress vortex interactions, aligning the tubes axially while disrupting vortex cores and rapidly converting magnetic to kinetic energy. These findings reveal how the inertial-Lorentz balance governs energy transfer and coherent structure formation in MHD turbulence, offering insight into vortex-magnetic coevolution in astrophysical plasmas.

Our previous investigation within the time-dependent nuclear energy-density functional theory showed that the nuclear superfluids contained inside cold neutron stars could become gapless under certain circumstances. The absence of a gap in the energy spectrum of quasiparticle excitations leads to a specific heat that is comparable to that in the normal phase in sharp contrast with the exponential suppression in the BCS phase of type $^1S_0$ pairing. Here, we further study gapless superfluidity within the same microscopic framework focusing on hydrodynamic properties. In particular, we calculate the mass fraction transported by the normal fluid of quasiparticle excitations, and we find that it can be finite even at zero temperature. We derive an approximate analytical formula for arbitrary neutron-proton superfluid mixtures. We also present numerical results for neutron stars. Our study suggests that the dynamics of neutron stars may be much more complicated than previously thought. The realization of gapless superfluidity in neutron stars and its implications are discussed.

We present a microscopic calculation of the electric conductivity and net-particle diffusion coefficients for a viscous and resistive ultra-relativistic plasma. Our results might be of interest for several astrophysical and cosmological problems, but the main physical application we have in mind is the hot deconfined matter produced in relativistic heavy-ion collisions. Accordingly, as charged particles of the medium we take three species (flavors) of light (massless for the sake of simplicity) quarks -- $u$, $d$ and $s$ -- and antiquarks, entailing the existence of three macroscopic conserved charges: baryon number ${\cal B}$, electric charge $Q$ and strangeness $S$. Our results are valid both in a weakly and in a strongly-magnetized plasma, where the energy stored in the magnetic field is comparable to the one carried by the medium particles. Actually, for a conformal fluid, the behavior of the system only depends on the ratio between the thermal and the magnetic pressure, the so-called plasma beta-parameter, acting as a scaling variable. Our calculation, starting from a relativistic Boltzmann-Vlasov equation, is based on a generalized Chapman-Enskog approach in which space-time gradients and the local electric field are treated as first-order quantities in a perturbative expansion, while terms containing magnetic corrections are considered of zeroth order and hence self-consistently resummed. We find that, also in the strong-field limit, for each conserved charge a generalized Wiedemann-Franz law, connecting charge conductivity and diffusion coefficient, exists. However these transport coefficients acquire a non-trivial tensor structure, reflecting the development of a longitudinal, a transverse and a Hall current as a response to electric fields or density gradients.

The similarity between dark matter and baryon energy densities suggests the existence of a dark sector analogous to the visible QCD sector. In addition, small-scale structure issues can be addressed by dark matter self-interactions with a cross section comparable to that of QCD. Both observations point to a GeV-scale dark QCD sector. In this letter, guided by these two coincidences, we investigate how a chiral dark QCD model with a MeV-scale dark photon can resolve the core-cusp problem. A potential third coincidence, associated with the latest measurement of $N_{\rm eff}$ being lower than the Standard Model prediction, is also discussed. Current constraints leave a finite window in the parameter space, which can be tested by future experiments such as Gamma Factory.