Papers for Thursday, May 16 2024

The effect of autoionizing resonances in atomic systems and processes is reviewed. Theoretical framework for treating resonances in the coupled channel approximation using the R-matrix method, as well as approximations related to plasma applications are described. The former entails large-scale atomic computations, and the latter is based on a new method for including collisional, Stark, thermal and other broadening mechanisms. We focus particularly on the problem of opacities calculations in high-energy-density (HED) plasmas such as stellar interiors and inertial confinement fusion devices. The treatment is generally relevant to radiative and collisional processes as the cross sections become energy-temperature-density dependent. While the computational difficulty increases considerably, the reaction rates are significantly affected. The related issue of the Boltzmann-Saha equation-of-state and its variants in local-thermodynamic-equilibrium (LTE) is also explored as the intermediary between atomic data on the one hand and plasma environments on the other.

Modern transient surveys now routinely discover flares resulting from tidal disruption events (TDEs) which occur when stars, typically $\sim0.5-2$ M$_{\odot}$, are ripped apart after passing too close to a supermassive black hole. We present three examples of a new class of extreme nuclear transients (ENTs) that we interpret as the tidal disruption of intermediate mass ($\sim3-10$ M$_{\odot}$) stars. Each is coincident with their host-galaxy nucleus and exhibits a smooth ($<10$% excess variability), luminous ($2-7\times10^{45}$ erg s$^{-1}$), and long-lived ($>150$ days) flare. ENTs are extremely rare ($\geq1\times10^{-3}$ Gpc$^{-1}$ yr$^{-1}$) compared to any other known class of transients. They are at least twice as energetic ($0.5-2.5\times 10^{53}$ erg) as any other known transient and these extreme energetics rule out stellar origins.

Numerical computations of stellar oscillations for models representative of B-type stars predict fewer modes to be excited than observations reveal from modern space-based photometric data. One shortcoming of state-of-the-art evolution models of B-type stars that may cause a lack of excited modes is the absence of microscopic diffusion in most such models. We investigate whether the inclusion of microscopic diffusion in stellar models of B-type stars, notably radiative levitation experienced by isotopes, leads to extra mode driving by the opacity mechanism compared to the case of models that do not include microscopic diffusion. We consider the case of slowly to moderately rotating stars and use non-rotating equilibrium models, while we account for (uniform) rotation in the computations of the pulsation frequencies. We calculate 1D stellar models with and without microscopic diffusion and examine the effect of radiative levitation on mode excitation, for both low-radial order pressure and gravity modes and for high-radial order gravity modes. We find systematically more modes to be excited for the stellar models including microscopic diffusion compared to those without it, in agreement with observational findings of pulsating B-type dwarfs. Furthermore, the models with microscopic diffusion predict that excited modes occur earlier on in the evolution compared to modes without it. In order to maintain realistic surface abundances during the main sequence, we include macroscopic envelope mixing by internal gravity waves. While radiative levitation has so far largely been neglected in stellar evolution computations of B-type stars for computational convenience, it impacts mode excitation predictions for stellar models of such stars. We conclude that the process of radiative levitation is able to reduce the discrepancy between predicted and observed excited pulsation modes in B-type stars.

High-resolution cross-correlation spectroscopy (HRCCS) combined with adaptive optics has been enormously successful in advancing our knowledge of exoplanet atmospheres, from chemistry to rotation and atmospheric dynamics. This powerful technique now drives major science cases for ELT instrumentation including METIS/ELT, GMTNIRS/GMT and MICHI/TMT, targeting biosignatures on rocky planets at 3-5 $\mu$m, but remains untested beyond 3.5 $\mu$m where the sky thermal background begins to provide the dominant contribution to the noise. We present 3.51-5.21 $\mu$m M-band CRIRES+/VLT observations of the archetypal young directly imaged gas giant $\beta$ Pictoris b, detecting CO absorption at S/N = 6.6 at 4.73 $\mu$m and H$_2$O at S/N = 5.7, and thus extending the use of HRCCS into the thermal background noise dominated infrared. Using this novel spectral range to search for more diverse chemistry we report marginal evidence of SiO at S/N = 4.3, potentially indicative that previously proposed magnesium-silicate clouds in the atmosphere are either patchy, transparent at M-band wavelengths, or possibly absent on the planetary hemisphere observed. The molecular detections are rotationally broadened by the spin of $\beta$ Pic b, and we infer a planetary rotation velocity of $v$sin(i) = 22$\pm$2 km s$^{-1}$ from the cross-correlation with the H$_2$O model template, consistent with previous K-band studies. We discuss the observational challenges posed by the thermal background and telluric contamination in the M-band, the custom analysis procedures required to mitigate these issues, and the opportunities to exploit this new infrared window for HRCCS using existing and next-generation instrumentation.

We introduce the RIGEL model, a novel framework to self-consistently model the effects of stellar feedback in the multiphase ISM of dwarf galaxies with radiative transfer (RT) on a star-by-star basis. The RIGEL model integrates detailed implementations of feedback from individual massive stars into the RHD code, AREPO-RT. It forms individual massive stars from the resolved multiphase ISM by sampling the IMF and tracks their evolution individually. The lifetimes, photon production rates, mass-loss rates, and wind velocities of these stars are determined by their initial masses and metallicities based on a library that incorporates a variety of stellar models. The RT equations are solved in seven spectral bins accounting for the IR to HeII ionizing bands, using an M1 RT scheme. The thermochemistry model tracks the non-equilibrium H, He chemistry and the equilibrium abundance of CI, CII, OI, OII, and CO to capture the thermodynamics of all ISM phases. We evaluate the performance of the RIGEL model using $1\,{\rm M}_\odot$ resolution simulations of isolated dwarf galaxies. We found that the SFR and ISRF show strong positive correlations to the metallicity of the galaxy. Photoionization and photoheating can reduce the SFR by an order of magnitude by removing the available cold-dense gas fuel for star formation. The ISRF also changes the thermal structure of the ISM. Radiative feedback occurs immediately after the birth of massive stars and rapidly disperses the molecular clouds within 1 Myr. As a consequence, radiative feedback reduces the age spread of star clusters to less than 2 Myr, prohibits the formation of massive star clusters, and shapes the cluster initial mass function to a steep power-law form with a slope of $\sim-2$. The mass-loading factor of the fiducial galaxy has a median of $\sim50$, while turning off radiative feedback reduces this factor by an order of magnitude.

Black holes are believed to be crucial in regulating star formation in massive galaxies, which makes it essential to faithfully represent the physics of these objects in cosmological hydrodynamics simulations. Limited spatial and mass resolution and the associated discreteness noise make following the dynamics of black holes especially challenging. In particular, dynamical friction, which is responsible for driving massive black holes towards the centres of galaxies, cannot be accurately modelled with softened $N$-body interactions. A number of subgrid models have been proposed to mimic dynamical friction or directly include its full effects in simulations. Each of these methods has its individual benefits and shortcomings, while all suffer from a common issue of being unable to represent black holes with masses below a few times the simulated dark matter particle mass. In this paper, we propose a correction for unresolved dynamical friction, which has been calibrated on simulations run with the code KETJU, in which gravitational interactions of black holes are not softened. We demonstrate that our correction is able to sink black holes with masses greater than the dark matter particle mass at the correct rate. We show that the impact of stochasticity is significant for low-mass black holes ($M_{\rm BH} \leq 5 M_{\rm DM}$) and propose a correction for stochastic heating. Combined, this approach is applicable to next generation cosmological hydrodynamics simulations that jointly track galaxy and black hole growth with realistic black hole orbits.

Axions or ALPs are hypothetical particles predicted by BSM theories, which make one of the dark matter candidates. These particles can convert into photons and vice-versa in the presence of magnetic field, with a probability decided by its coupling strength $\mathrm{g_{a\gamma}}$. One of the ways to detect these particles is using the CMB as a backlight. As the CMB photons pass through a galaxy cluster, they can get converted into ALPs in the mass range $10^{-15}$ eV to $10^{-11}$ eV through resonant conversion in the presence of cluster magnetic fields. This leads to a polarized spectral distortion ($\alpha$-distortion) in the CMB as the photon polarization parallel to the magnetic field in the galaxy cluster is involved in the conversion. The fluctuations in the magnetic field and electron density in a galaxy cluster lead to spatially varying $\alpha$-distortion around the cluster, with a power spectrum that is different from the lensed CMB polarization power spectrum for the standard model of cosmology. By measuring the difference in the polarization power spectrum around a galaxy cluster from the all-sky signal, one can find new $\alpha$-distortion in the sky. For galaxy clusters resolvable in multiple EM bands, one can measure the coupling strength $\mathrm{g_{a\gamma}}$ from the ALP power spectrum. Using multi-frequency techniques like ILC to clean the foregrounds, we show that the new power spectrum-based approach of the resolved galaxy clusters from upcoming CMB experiments such as Simons Observatory and CMB-S4 can detect (or put constraints) on the ALP-photon coupling strength of $\mathrm{g_{a\gamma} < 5.24 \times 10^{-12} \, GeV^{-1}}$ and $\mathrm{g_{a\gamma} < 3.61 \times 10^{-12} \, GeV^{-1}}$ at 95\% C.I. respectively for ALPs of masses $10^{-13}$ eV or for smaller $\mathrm{g_{a\gamma}}$ for lighter ALP masses (Abridged).

The nature of dark matter is an unsolved cosmological problem and axions are one of the weakly interacting cold dark matter candidates. Axions or ALPs (Axion-like particles) are pseudo-scalar bosons predicted by beyond-standard model theories. The weak coupling of ALPs with photons leads to the conversion of CMB photons to ALPs in the presence of a transverse magnetic field. If they have the same mass as the effective mass of a photon in a plasma, the resonant conversion would cause a polarized spectral distortion leading to temperature fluctuations with the distortion spectrum. The probability of resonant conversion depends on the properties of the cluster such as the magnetic field, electron density, and its redshift. We show that this kind of conversion can happen in numerous unresolved galaxy clusters up to high redshifts, which will lead to a diffused polarised anisotropy signal in the microwave sky. The spectrum of the signal and its shape in the angular scale will be different from the lensed CMB polarization signal. This new polarised distortion spectrum will be correlated with the distribution of clusters in the universe and hence, with the large-scale structure. The spectrum can then be probed using its spectral and spatial variation with respect to the CMB and various foregrounds. An SNR of $\sim$ 4.36 and $\sim$ 93.87 are possible in the CMB-S4 145 GHz band and CMB-HD 150 GHz band respectively for a photon-ALPs coupling strength of $\mathrm{g_{a \gamma} = 10^{-12} \, GeV^{-1}}$ using galaxy clusters beyond redshift z $= 1$. The same signal would lead to additional RMS fluctuations of $\sim \mathrm{7.5 \times 10^{-2} \, \mu K}$ at 145 GHz. In the absence of any signal, future CMB experiments such as Simons Observatory (SO), CMB-S4, and CMB-HD can put constraints on coupling strength better than current bounds from particle physics experiment CERN Axion Solar Telescope (CAST).

Future space missions that aim to detect and characterize Earth-like exoplanets will require an instrument that efficiently measures spectra of these planets, placing strict requirements on detector performance. The upcoming Roman Space Telescope will demonstrate the performance of an electron-multiplying charge-coupled device (EMCCD) as part of the coronagraphic instrument (CGI). The recent LUVOIR and HabEx studies baselined pairing such a detector with an integral field spectrograph (IFS) to take spectra of multiple exoplanets and debris disks simultaneously. We investigate the scientific impact of a noiseless energy-resolving detector for the planned Habitable Worlds Observatory's (HWO) coronagraphic instrument. By assuming higher quantum efficiency, higher optical throughput, and zero noise, we effectively place upper limits on the impact of advancing detector technologies. We find that energy-resolving detectors would potentially take spectra of hundreds of additional exoplanets "for free" over the course of an HWO survey, greatly increasing its scientific yield.

Multiple observations now suggest that the hydrogen reionization may have ended well below redshift six. While there has previously been no conclusive proof of extended neutral islands in the $z < 6$ intergalactic medium, it is possible that such islands give rise to the giant Ly$\alpha$ absorption troughs seen in the spectra of high-redshift quasars. Here we present evidence that the deepest and longest-known Ly$\alpha$ trough at $z < 6$, towards ULAS J0148+0600 (J0148), is associated with damping wing absorption. The evidence comes from a window of strong Ly$\alpha$ transmission at the edge of the J0148 proximity zone. We show that the relatively smooth profile of this transmission window is highly unlikely to arise from resonant absorption alone, but is consistent with the presence of a damping wing. We further argue that the damping wing is unlikely to arise from a compact source due to the lack of associated metal lines, and is more likely to arise from an extended neutral island associated with the giant Ly$\alpha$ trough. We investigate the physical conditions that may give rise to the strong transmission window, and speculate that it may signal an usually deep void, nearby ionizing sources, and/or the recent passage of an ionization front.

The Kepler mission reveals a peculiar trough-peak feature in the orbital spacing of close-in planets near mean-motion resonances: a deficit and an excess that are a couple percent to the narrow, respectively wide, of the resonances. This feature has received two main classes of explanations, one involving eccentricity damping, the other scattering with small bodies. Here, we point out a few issues with the damping scenario, and study the scattering scenario in more detail. We elucidate why scattering small bodies tends to repel two planets. As the small bodies random-walk in energy and angular momentum space, they tend to absorb, fractionally, more energy than angular momentum. This, which we call "ping-pong repulsion", transports angular momentum from the inner to the outer planet and pushes the two planets apart. Such a process, even if ubiquitous, leaves identifiable marks only near first-order resonances: diverging pairs jump across the resonance quickly and produce the MMR asymmetry. To explain the observed positions of the trough-peaks, a total scattering mass of order a few percent of the planet masses is required. Moreover, if this mass is dominated by a handful of Mercury-sized bodies, one can also explain the planet eccentricities as inferred from transit-time-variations. Lastly, we suggest how these conditions may have naturally arisen during the late stages of planet formation.

The density fields constructed by traditional mass assignment methods are susceptible to irritating discreteness, which hinders morphological measurements of cosmic large-scale structure (LSS) through Minkowski functionals (MFs). For alleviating this issue, fixed-kernel smoothing methods are commonly used in literatures, at the expense of losing substantial structural information. In this work, we propose to measure MFs with Delaunay tessellation field estimation (DTFE) technique, with the goal to maximize extractions of morphological information from sparse tracers. We perform our analyses starting from matter fields and progressively extending to halo fields. At matter field level, we elucidate how discreteness affects the morphological measurements of LSS. Then, by comparing with traditional Gaussian smoothing scheme, we preliminarily showcase the advantages of DTFE for enhancing measurements of MFs from sparse tracers. At halo field level, we first numerically investigate various systematic effects on MFs of DTFE fields, which are induced by finite voxel sizes, halo number densities, halo weightings, and redshift space distortions (RSDs), respectively. Then, we explore the statistical power of MFs measured with DTFE for extracting cosmological information encoded in RSDs. We find that MFs measured with DTFE exhibit improvements by $\sim$ $2$ orders of magnitude in discriminative power for RSD effects and by a factor of $\sim$ $3$-$5$ in constraining power on structure growth rate over the MFs measured with Gaussian smoothing. These findings demonstrate the remarkable enhancements in statistical power of MFs achieved by DTFE, showing enormous application potentials of our method in extracting various key cosmological information from galaxy surveys.

Seasonal variations of atmospheric muons are traditionally interpreted in terms of an effective temperature that relates the atmospheric temperature profile at a given time to the dependence of muon production on atmospheric depth. This paper aims to review and generalize the treatment of muon production and effective temperature that has been used to interpret seasonal variations of atmospheric muons by many experiments. The formalism is developed both in integral form -- for application to compact detectors at a fixed depth that record all muons with $E_\mu > E_\mu^\mathrm{min}$ -- and in differential form -- for application to extended detectors like IceCube, KM3NeT, and Baikal-GVD, where the rates are proportional to energy-dependent effective areas.

Context. The chemically peculiar (CP) stars of the upper main sequence are defined by spectral peculiarities that indicate unusual elemental abundance patterns in the presence of diffusion in the calm, stellar atmospheres. Some of them have a stable local magnetic field of up to several kiloGauss. The pre-main-sequence evolution of these objects is still a mystery and contains many open questions. Aims. We identify CP stars on the pre-main sequence to determine possible mechanisms that lead to the occurrence of chemical peculiarities in the (very) early stages of stellar evolution. Methods. We identified likely pre-main-sequence stars by fitting the spectral energy distributions. The subsequent analysis using stellar spectra and photometric time series helped us to distinguish between CP and non-CP stars. Additionally, we compared our results to the literature to provide the best possible quality assessment. Results. Out of 45 candidates, about 70 % seem to be true CP stars or CP candidates. Furthermore, 9 sources appear to be CP stars on the pre-main sequence, and all are magnetic. We finally report a possible CP2 star that is also a pre-main-sequence star and was not previously in the literature. Conclusions. The evolution of the peculiarities seems to be related to the (strong) magnetic fields in these CP2 stars.

Partially-ionized plasmas consist of charged and neutral particles whose mutual collisions modify magnetic reconnection compared with the fully-ionized case. The collisions alter the rate and locations of the magnetic dissipation heating and the distribution of energies among the particles accelerated into the non-thermal tail. We examine the collisional regimes for the onset of fast reconnection in two environments: the partially-ionized layers of the solar atmosphere and the protoplanetary disks that are the birthplaces for planets around young stars. In both these environments, magnetic nulls readily develop into resistive current sheets in the regime where the charged and neutral particles are fully coupled by collisions, but the current sheets quickly break down under the ideal tearing instability. The current sheets collapse repeatedly, forming magnetic islands at successively smaller scales, till they enter a collisionally-decoupled regime where the magnetic energy is rapidly turned into heat and charged-particle kinetic energy. Small-scale, decoupled fast reconnection in the solar atmosphere may lead to preferential heating and energization of ions and electrons that escape into the corona. In protoplanetary disks such reconnection causes localized heating in the atmospheric layers that produce much of the infrared atomic and molecular line emission observed with the Spitzer and James Webb Space Telescopes.

With the next generation of interferometric telescopes, such as the Square Kilometre Array (SKA), the need for highly computationally efficient reconstruction techniques is particularly acute. The challenge in designing learned, data-driven reconstruction techniques for radio interferometry is that they need to be agnostic to the varying visibility coverages of the telescope, since these are different for each observation. Because of this, learned post-processing or learned unrolled iterative reconstruction methods must typically be retrained for each specific observation, amounting to a large computational overhead. In this work we develop learned post-processing and unrolled iterative methods for varying visibility coverages, proposing training strategies to make these methods agnostic to variations in visibility coverage with minimal to no fine-tuning. Learned post-processing techniques are heavily dependent on the prior information encoded in training data and generalise poorly to other visibility coverages. In contrast, unrolled iterative methods, which include the telescope measurement operator inside the network, achieve state-of-the-art reconstruction quality and computation time, generalising well to other coverages and require little to no fine-tuning. Furthermore, they generalise well to realistic radio observations and are able to reconstruct the high dynamic range of these images.

Spectral energy distribution (SED) fitting is one of most commonly used techniques to study the dust properties in Active Galactic Nuclei (AGN). Works implementing this technique commonly use radiative transfer models that assume a variety of dust properties. Despite the key role of this aspect, limited effort has been put forward to explore the chemical composition, the role of different optical properties, and the grain size distribution of dust, all of which can have a substantial impact on the theoretical radiative transfer calculations. In this work, we explore the role of the dust chemical composition in the AGN dusty torus through SED fitting to \emph{Spitzer}/IRS spectra of a sample of 49 nearby AGN with silicate features in emission. We implement a mineralogy model including the popular astronomical silicates and a set of oxides and amorphous silicates with different grain sizes. We find that best fits use principally porous alumina, periclase, and olivine. In terms of mass fractions, $\sim99\%$ of the dust is composed of dust grains of size $\rm{0.1 \mu m}$, with a $<1\%$ contribution from $\rm{3 \mu m}$ grains. Moreover, the astronomical silicates have a very low occurrence in the best fits, suggesting that they are not the most suited dust species to reproduce the silicate features in our sample.

We combine stellar orbits with the abundances of the heavy, $r$-process element europium and the light, $\alpha$-element, silicon to separate in-situ and accreted populations in the Milky Way across all metallicities. At high orbital energy, the accretion-dominated halo shows elevated values of [Eu/Si], while at lower energies, where many of the stars were born in-situ, the levels of [Eu/Si] are lower. These systematically different levels of [Eu/Si] in the MW and the accreted halo imply that the scatter in [Eu/$\alpha$] within a single galaxy is smaller than previously thought. At the lowest metallicities, we find that both accreted and in-situ populations trend down in [Eu/Si], consistent with enrichment via neutron star mergers. Through compiling a large dataset of abundances for 46 globular clusters (GCs), we show that differences in [Eu/Si] extend to populations of in-situ/accreted GCs. We interpret this consistency as evidence that in $r$-process elements, GCs trace the star formation history of their hosts, motivating their use as sub-Gyr timers of galactic evolution. Furthermore, fitting the trends in [Eu/Si] using a simple galactic chemical evolution model, we find that differences in [Eu/Si] between accreted and in-situ MW field stars cannot be explained through star formation efficiency alone. Finally, we show that the use of [Eu/Si] as a chemical tag between GCs and their host galaxies extends beyond the Local Group, to the halo of M31 - potentially offering the opportunity to do Galactic Archaeology in an external galaxy.

We present the largest extragalactic survey of supernova remnant (SNR) candidates in nearby star-forming galaxies using exquisite spectroscopic maps from MUSE. Supernova remnants exhibit distinctive emission-line ratios and kinematic signatures, which are apparent in optical spectroscopy. Using optical integral field spectra from the PHANGS-MUSE project, we identify SNRs in 19 nearby galaxies at ~ 100~pc scales. We use five different optical diagnostics: (1) line ratio maps of [SII]/H$\alpha$; (2) line ratio maps of [OI]/H$\alpha$; (3) velocity dispersion map of the gas; (4) and (5) two line ratio diagnostic diagrams from BPT diagrams to identify and distinguish SNRs from other nebulae. Given that our SNRs are seen in projection against HII regions and diffuse ionized gas, in our line ratio maps we use a novel technique to search for objects with [SII]/H$\alpha$ or [OI]/H$\alpha$ in excess of what is expected at fixed H$\alpha$ surface brightness within photoionized gas. In total, we identify 2,233 objects using at least one of our diagnostics, and define a subsample of 1,166 high-confidence SNRs that have been detected with at least two diagnostics. The line ratios of these SNRs agree well with the MAPPINGS shock models, and we validate our technique using the well-studied nearby galaxy M83, where all SNRs we found are also identified in literature catalogs and we recover 51% of the known SNRs. The remaining 1,067 objects in our sample are detected with only one diagnostic and we classify them as SNR candidates. We find that ~ 35% of all our objects overlap with the boundaries of HII regions from literature catalogs, highlighting the importance of using indicators beyond line intensity morphology to select SNRs. [OI]/H$\alpha$ line ratio is responsible for selecting the most objects (1,368; 61%), (abridged).

We present constraints on the spacetime variation of the fine-structure constant $\alpha$ at redshifts $3<z<10$ using JWST emission-line galaxies. The galaxy sample consists of 572 high-quality spectra with strong and narrow [O III] $\lambda\lambda$4959,5007 doublet emission lines from 522 galaxies, including 267 spectra at $z>5$. The [O III] doublet lines are arguably the best emission lines to probe the variation in $\alpha$. We divide our sample into 5 subsamples based on redshift and calculate the relative variation $\Delta\alpha/\alpha$ for the individual subsamples. The calculated $\Delta\alpha/\alpha$ values are consistent with zero within $1\sigma$ at all redshifts, suggesting no time variation in $\alpha$ above a level of $(1-2) \times10^{-4}$ ($1\sigma$) in the past 13.2 billion years. When the whole sample is combined, the constraint is improved to be $\Delta\alpha/\alpha = (0.4\pm0.7) \times10^{-4}$. We further test the spatial variation in $\alpha$ using four subsamples of galaxies in four different directions on the sky. The measured $\Delta\alpha/\alpha$ values are consistent with zero at a $1\sigma$ level of $\sim10^{-4}$. While the constraints in this work are not as stringent as those from lower-redshift quasar absorption lines in previous studies, this work uses an independent tracer and provides the first constraints on $\Delta\alpha/\alpha$ at the highest redshifts. Our analyses also indicate that the relative wavelength calibration of the JWST spectra is robust. With the growing number of emission-line galaxies from JWST, we expect to achieve stronger constraints in the future.

We present the analysis of publicly available NuSTAR, Suzaku and XMM-Newton observations of the recurrent symbiotic system T CrB covering the 2006.77-2022.66 yr period. The X-ray spectra are analysed by adopting a model that includes a reflection component produced by the presence of the accretion disk. Our best-fit model requires a disk with a radius of 100 AU, effective thickness of 10 AU, averaged column density 10$^{25}$ cm$^{-2}$ and orientation of 50$^{\circ}$ with respect to the line of sight that contributes significantly to the total X-ray flux detected from T CrB, in addition to naturally producing the emission of the 6.4 keV Fe line. The spectral analysis suggests that the temperature of the boundary layer evolved from 14.8 keV in the steady-state phase (before 2016), to 2.8 keV in the 2017.24 epoch, to finally stabilise to about $\sim$8 keV in the subsequent epochs. Variations in the plasma temperature of the boundary layer are attributed to the evolution of the mass accretion rate using theoretical interpretations from an accretion disk model. The presence of emission lines in the high-resolution XMM-Newton RGS spectrum of 2017.24 prevents from adopting a black body emission model to fit the soft X-ray range. Instead, we use plasma emission models that suggest the presence of adiabatically-shocked gas produced by gas velocities of 110-200 km s$^{-1}$, very likely tracing jet-like ejections similar to what is found in other symbiotic systems. Given the the analysis of X-ray and optical data together, we show that T CrB has a similar evolution as black hole binaries, accreting neutron stars and AGN in the hardness-intensity diagram.

The structure and kinematics of the old component of the Galactic bulge are still a matter of debate. The bulk of the bulge as traced by red clump stars includes two main components, which are usually identified as the metal-rich and metal-poor components. They have different shapes, kinematics, mean metallicities, and alpha-element abundances. It is our current understanding that they are associated with a bar and a spheroid, respectively. On the other hand, RR Lyrae variables trace the oldest population of the bulge. While it would be natural to think that they follow the structure and kinematics of the metal-poor component, the data analysed in the literature show conflicting results. We aim to derive a rotation curve for bulge RR Lyrae stars in order to determine that the old component traced by these stars is distinct from the two main components observed in the Galactic bulge. This paper combines APOGEE-2S spectra with OGLE-IV light curves, near-IR photometry, and proper motions from the VISTA Variables in the Ví a L\' actea survey for 4197 RR Lyrae stars. Six-dimensional phase-space coordinates were used to calculate orbits within an updated Galactic potential and to isolate the stars. The stars that stay confined within the bulge represent 57% of our sample. Our results show that bulge RR Lyrae variables rotate more slowly than metal-rich red clump stars and have a lower velocity dispersion. Their kinematics is compatible with them being the low-metallicity tail of the metal-poor component. We confirm that a rather large fraction of halo RR Lyrae stars pass by the bulge within their orbits, increasing the velocity dispersion. A proper orbital analysis is therefore critical to isolate bona fide bulge variables. Finally, bulge RR Lyrae seem to trace a spheroidal component, although the current data do now allow us to reach a firm conclusion about the spatial distribution.

The recent advancements in exoplanet observations enable the potential detection of exo-Venuses, rocky planets with carbon-rich atmospheres. How extended these atmospheres can be, given high carbon abundances, has not been studied. To answer this, we present a model for a theoretical class of exoplanets - puffy Venuses - characterized by thick, carbon-dominated atmospheres in equilibrium with global magma oceans. Our model accounts for carbon and hydrogen partition between the atmosphere and the magma ocean, as well as the C-H-O equilibrium chemistry throughout a semi-grey, radiative-convective atmosphere. We find that radius inflation by puffy Venus atmospheres is significant on small and irradiated planets: carbon content of 1200 ppm (or that of ordinary chondrites) can generate an atmosphere of ~0.16 - 0.3 $R_{\oplus}$ for an Earth-mass planet with equilibrium temperatures of 1500 to 2000 K. We identify TOI-561 b as an especially promising puffy Venus candidate, whose under-density could be attributed to a thick C-rich atmosphere. We also advocate for a puffy Venus interpretation of 55 Cancri e, where recent JWST observation indicates the presence of a CO/CO2 atmosphere. Puffy Venuses may thus constitute a testable alternative interpretation for the interior structure of underdense low-mass exoplanets.

The HNC/HCN ratio is observationally known as a thermometer in Galactic interstellar molecular clouds. A recent study has alternatively suggested that the HNC/HCN ratio is affected by the ultraviolet (UV) field, not by the temperature. We aim to study this ratio on the scale of giant molecular clouds in the barred spiral galaxy M83 towards the southwestern bar end and the central region from ALMA observations, and if possible, distinguish the above scenarios. We compare the high (40-50 pc) resolution HNC/HCN ratios with the star formation rate from the 3-mm continuum intensity and the molecular mass inferred from the HCN intensities. Our results show that the HNC/HCN ratios do not vary with the star formation rates, star formation efficiencies, or column densities in the bar-end region. In the central region, the HNC/HCN ratios become higher with higher star formation rates, which tend to cause higher temperatures. This result is not consistent with the previously proposed scenario in which the HNC/HCN ratio decreases with increasing temperature. Spectral shapes suggest that this trend may be due to optically thick HCN and optically thin HNC. In addition, we compare the large-scale ($\sim 200$ pc) correlation between the dust temperature from the FIR ratio and the HNC/HCN ratio for the southwestern bar-end region. The HNC/HCN ratio is lower when the dust temperatures are higher. We suggest from the above results that the HNC/HCN ratio depends on the UV radiation field that affects the interstellar medium on the $\sim100\,$pc scale where the column densities are low.

Gravitational wave signals from core-collapse supernovae are one of the important observables for extracting the information of dense matter. To extract the properties of proto-neutron stars produced via core-collapse supernovae by asteroseismology, we perform a linear perturbation analysis using data obtained from two-dimensional numerical simulations. We employ 12 and 20 solar-mass progenitors and compare two different treatments of gravity. One is a general relativistic one with a conformal flatness condition and the other is an effective gravitational potential mimicking the Tolman-Oppenheimer-Volkoff solution. We discuss how the frequencies of the proto-neutron star oscillations corresponding to the gravitational wave signals in the simulations depend on the proto-neutron star properties. In our models, we find that the gravitational wave frequencies of the proto-neutron stars determined with the Cowling approximation can be expressed to very good approximation as a function of the proto-neutron star average density almost independently of the progenitor mass, treatment of gravity in the simulations, and the interpolations in the simulations. On the other hand, if one considers the gravitational wave frequencies as a function of the surface gravity of proto-neutron stars, such a relation appears sensitive to the treatment of gravity and other numerical details in the simulations. Thus, the average density of proto-neutron stars seems more suitable for universally expressing the supernova gravitational wave frequencies, instead of the surface gravity.

In Papers I-III, we use the flat-sky and distant-observer approximations to develop a formalism with which the correlation statistics of cosmological tensor fields are calculated by the nonlinear perturbation theory, generalizing the integrated perturbation theory for scalar fields. In this work, the formalism is extended to include the full-sky and wide-angle effects in evaluating the power spectra and correlation functions of cosmological tensor fields of any ranks. With the newly developed formalism, one can evaluate the nonlinear power spectra and correlation functions to arbitrary higher orders in principle. After describing the general formalism, we explicitly derive and give analytic results of the lowest-order linear theory for an illustrative purpose in this paper. The derived linear formulas with full-sky and wide-angle effects are numerically compared with the previous formulas with flat-sky and distant-observer limits in a simple model of tensor bias.

Heating of charged particles via collisionless shocks, while ubiquitous in the universe, is an intriguing yet puzzling plasma phenomenon. One outstanding question is how electrons and ions approach an equilibrium after they were heated to different immediate-postshock temperatures. In order to fill the significant lack of observational information of the downstream temperature-relaxation process, we observe a thermal-dominant X-ray filament in the northwest of SN~1006 with Chandra. We divide this region into four layers with a thickness of 15$^{\prime\prime}$ or 0.16 pc each, and fit each spectrum by a non-equilibrium ionization collisional plasma model. The electron temperature was found to increase toward downstream from 0.52-0.62 keV to 0.82-0.95 keV on a length scale of 60 arcsec (or 0.64 pc). This electron temperature is lower than thermal relaxation processes via Coulomb scattering, requiring some other effects such as plasma mixture due to turbulence and/or projection effects, etc, which we hope will be resolved with future X-ray calorimeter missions such as XRISM and Athena.

The magnetic field of a molecular cloud core may play a role in the formation of circumstellar disks in the core. We present magnetic field morphologies in protostellar cores of 16 targets in the Atacama Large Millimeter/submillimeter Array large program "Early Planet Formation in Embedded Disks (eDisk)", which resolved their disks with 7 au resolutions. The 0.1-pc scale magnetic field morphologies were inferred from the James Clerk Maxwell Telescope (JCMT) POL-2 observations. The mean orientations and angular dispersions of the magnetic fields in the dense cores are measured and compared with the radii of the 1.3 mm continuum disks and the dynamically determined protostellar masses from the eDisk program. We observe a significant correlation between the disk radii and the stellar masses. We do not find any statistically significant dependence of the disk radii on the projected misalignment angles between the rotational axes of the disks and the magnetic fields in the dense cores, nor on the angular dispersions of the magnetic fields within these cores. However, when considering the projection effect, we cannot rule out a positive correlation between disk radii and misalignment angles in three-dimensional space. Our results suggest that the morphologies of magnetic fields in dense cores do not play a dominant role in the disk formation process. Instead, the sizes of protostellar disks may be more strongly affected by the amount of mass that has been accreted onto star+disk systems, and possibly other parameters, for example, magnetic field strength, core rotation, and magnetic diffusivity.

Recent studies suggested that the ejecta velocity of Type Ia supernova (SN Ia) is a promising indicator in distinguishing the progenitor systems and explosion mechanisms. By classifying the SNe Ia based on their ejecta velocities, studies found SNe Ia with high Si II $\lambda$6355 velocities (HV SNe Ia; v>12000 km/s) tend to be physically different from their normal-velocity counterparts (NV SNe Ia). In this work, we revisit the low-$z$ sample studied in previous work and closely look into the spatially resolved environment local to the site of SN explosion. Our results reveal a possible trend (at $2.4\sigma$ significance) that HV SNe Ia are likely associated with older stellar populations than NV SNe Ia. While the trend is inconclusive, the local host-galaxy sample studied in this work is likely skewed toward massive galaxies, limiting the parameter space that we would like to investigate from the original parent sample. Nevertheless, our results do not rule out the possibility that parameters other than the host-galaxy age (such as metallicity) could be the underlying factors driving the differences between HV and NV SNe Ia due to the limitation of our dataset.

Starting with the density field equation of a self-gravity fluid in a static Universe, using the Schwinger functional differentiation technique, we derive the field equation of the 4-point correlation function (4PCF) of galaxies in the Gaussian approximation, which contains hierarchically 2PCF and 3PCF. By use of the known solutions of 2PCF and 3PCF, the equation of 4PCF becomes an inhomogeneous, Helmholtz equation, and contains only two physical parameters: the mass $m$ of galaxy and the Jeans wavenumber $k_J$, like the equations of the 2PCF and 3PCF. We obtain the analytical solution of 4PCF that consists of four portions, $\eta= \eta^0_{odd} + \eta^0_{even} +\eta^{FP} +\eta^I$, and has a very rich structure. $\eta^0_{odd}$ and $\eta^0_{even}$ form the homogeneous solution and depend on boundary conditions. The parity-odd $\eta^0_{odd}$ is more interesting and qualitatively explains the observed parity-odd data of BOSS CMASS, the parity-even $\eta^0_{even}$ contains the disconnected 4PCF $\eta^{disc}$ (arising from a Gaussian random process), and both $\eta^0_{odd}$ and $\eta^0_{even}$ are prominent at large scales $r\gtrsim 10$Mpc, and exhibit radial oscillations determined by the Jeans wavenumber. $\eta^{FP}$ and $ \eta^I$ are parity-even, and form the inhomogeneous solution. $\eta^{FP}$ is the same as the Fry-Peebles ansatz for 4PCF, and dominates at small scales $r \lesssim 10$Mpc. $\eta^I$ is an integration of the inhomogeneous term, subdominant. We also compare the parity-even 4PCF with the observation data.

In order to help facilitate the future study of ultra-diffuse galaxies (UDGs) we compile a catalogue of their spectroscopic properties. Using it, we investigate some of the biases inherent in the current UDG sample that have been targeted for spectroscopy. In comparison to a larger sample of UDGs studied via their spectral energy distributions (SED), current spectroscopic targets are intrinsically brighter, have higher stellar mass, are larger, more globular cluster-rich, older, and have a wider spread in their metallicities. In particular, many spectroscopically studied UDGs have a significant fraction of their stellar mass contained within their globular cluster (GC) system. We also search for correlations between parameters in the catalogue. Of note is a correlation between alpha element abundance and metallicity as may be expected for a `failed galaxy' scenario. However, the expected correlations of metallicity with age are not found and it is unclear if this is evidence against a `failed galaxy' scenario or simply due to the low number statistics and the presence of outliers. Finally, we attempt to segment our catalogue into different classes using a machine learning K-means method. We find that the clustering is very weak and that it is currently not warranted to split the catalogue into multiple, distinct sub-populations. Our catalogue is available online and we aim to maintain it beyond the publication of this work.

We report on the development and commissioning of a new Q-band receiver for the Nobeyama 45-m telescope, covering 30--50 GHz with a receiver noise temperature of about 15 K. We name it eQ (extended Q-band) receiver. The system noise temperatures for observations are measured to be $\sim$ 30 K at 33 GHz and $\sim$ 75 K at 45 GHz. The Half-Power-Beam-Width (HPBW) is around 38\arcsec at 43 GHz. To enhance the observation capability, we tested the smoothed bandpass calibration technique and demonstrated the observation time can be significantly reduced compared to the standard position switch technique. The wide-bandwidth capability of this receiver provides precise determination of rest frequencies for molecular transitions with an accuracy of a few kHz through simultaneous observations of multiple transitions. Particularly, we determined the rest frequency of SO ($J_N$ = $1_0$--$0_1$) to be 30.001542 GHz, along with the rest frequency of CCS ($J_N$ = $4_3$--$3_2$) being 45.379033 GHz, adopting CCS ($J_N$ = $3_2$--$2_1$) at 33.751370 GHz as a reference line. The SO profile shows a double peak shape at the Cyanopolyyne Peak (CP) position of the Taurus Molecular Cloud-1 (TMC-1). The SO peaks coincide well with the CCS sub-components located near the outer parts of the TMC-1 filament. We interpret that the gravitational infall of TMC-1 generates shocks which enhance the SO abundance. The TMC-1 map shows that carbon-chain molecules are more abundant in the southern part of the filament, whereas SO is more abundant in the northern part. The eQ's excellent sensitivity allowed us to detect faint CO ($J$ = 1--0) spectra from the high-redshift object at a redshift of 2.442. Our receiver is expected to open new avenues for high-sensitivity molecular line observations in the Q-band.

This study employs Bayesian analysis and machine learning techniques to analyze the young open cluster NGC 6383 using data from Gaia DR3 and 2MASS. We identified 254 probable cluster members through HDBSCAN based on proper motions and determined the cluster's core and tidal radius. To perform this analysis, we utilized an extension of Hamiltonian Monte Carlo, the No-U-Turn Sampler, using the Bayesian library PyMC. Our results indicate a mean cluster age of $4 \pm 1$ Myr and a distance of $1.107 \pm 0.035$ kpc. The analysis reveals mass segregation, especially among binary stars, and suggests that NGC 6383 is not fully relaxed. We observed a well-defined main sequence and a population of pre-main sequence stars, with a star formation range from $\sim 1$ to $6$ Myr, indicating recent star formation activity.

We model the currently available $\gamma$-ray data from the Fermi Large Area Telescope on Cyg X-3. Thanks to its very strong $\gamma$-ray activity during 2018--2021, the data quality has significantly improved. We study the strong orbital modulation of the $\gamma$-rays observed during at high $\gamma$-ray fluxes. The modulation, as found earlier, is well modeled by anisotropic Compton scattering of the donor blackbody emission by relativistic electrons in a jet strongly misaligned with respect to the orbital axis. We confirm that this model fits well both the average $\gamma$-ray modulation light curve and the spectrum. However, we find that if the jet is aligned with the spin axis of a rotating black hole, it would undergo geodetic precession with the period of $\sim$50 years. However, its presence is ruled out by both the $\gamma$-ray and radio data. Therefore, we consider an alternative model in which the average jet direction jet is aligned, but it is bent to outside the orbit owing to the thrust of the donor stellar wind, and thus precesses at the orbital period. The $\gamma$-ray modulation appears then owing to the variable Doppler boosting of synchrotron self-Compton jet emission. The model also fits well the data. However, the fitted bending angle is much larger than the theoretical one based on the binary and wind parameters as currently known. Thus, both models disagree with important aspects of our current theoretical understanding of the system. We discuss possible ways to find the correct model.

The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a powerful probe of the mass and spin of the central black hole. The vast majority of existing ``continuum fitting'' models neglect emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however, find non-zero emission sourced from these regions. In this work we extend existing techniques by including the emission sourced from within the plunging region, utilising new analytical models which reproduce the properties of numerical accretion simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component, but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component has been added in by hand in an ad-hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional models which neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820+070 black hole spin which must be low $a_\bullet < 0.5$ to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission component in the MAXI J1820+070 spectrum between $6$ and $10$ keV, highlighting the necessity of including this region. Our continuum fitting model is made publicly available.

We present an updated catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope aboard the Spektrum-Roentgen-Gamma (SRG) observatory during its all-sky survey. It is based on the data of the first four and the partially completed fifth scans of the sky (ARTSS1-5). The catalog comprises 1545 sources detected in the 4-12 keV energy band. The achieved sensitivity ranges between $\sim 4\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ near the ecliptic plane and $\sim 7\times 10^{-13}$ erg s$^{-1}$ cm$^{-2}$ near the ecliptic poles, which is a $\sim$30-50% improvement over the previous version of the catalog based on the first two all-sky scans (ARTSS12). There are $\sim 130$ objects, excluding the expected contribution of spurious detections, that were not known as X-ray sources before the SRG/ART-XC all-sky survey. We provide information, partly based on our ongoing follow-up optical spectroscopy program, on the identification and classification of the majority of the ARTSS1-5 sources (1463), of which 173 are tentative at the moment. The majority of the classified objects (964) are extragalactic, a small fraction (30) are located in the Local Group of galaxies, and 469 are Galactic. The dominant classes of objects in the catalog are active galactic nuclei (911) and cataclysmic variables (192).

The origin of bright X-ray emission lines that appear late in a nova eruption remains largely a puzzle. We present two high-resolution X-ray grating spectra of the classical nova YZ Ret, observed 77 and 115 days post-eruption, using XMM-Newton and Chandra , respectively. Both spectra feature resolved emission lines blueshifted by $v = -1500$ km s$^{-1}$ and broadened by $\sigma_v=500$ km s$^{-1}$. The two spectra are well described by a collisionally ionized plasma of $kT\sim 70$ eV that dimmed by a factor of $\sim40$ between the two exposures. The spectra also show narrow radiative recombination continua (RRCs) of C$^{+4}$, C$^{+5}$, and N$^{+5}$, indicating the interaction of the hot ionized plasma with cold electrons of $kT\sim 2$ eV. The high-$n$ Rydberg series of C$^{+4}$ is anomalously bright, allowing us to measure the electron density through continuum lowering, which is in agreement with the He-like N$^{+5}$ density diagnostic of $n_e=(1.7\pm0.4)\times10^{11}$ cm$^{-3}$. The high population of these high-$n$ levels constitutes the best evidence to date of charge exchange (CX) with neutral H in an astrophysical ionized plasma. The remarkable fact that the velocity and plasma temperature are the same after 38 days, despite the high density and decreasing flux is evidence for ongoing heating. We suggest the heating is due to a reverse shock in the nova ejecta, which forms a thin X-ray shell. The narrow RRCs and CX are attributed to direct mixing with cold gas, which overtakes the hot plasma either from the shock front, or through the contact discontinuity.

During their formation, nascent planetary systems are subject to FU Orionis outbursts that heat a substantial part of the disc. This causes water ice in the affected part of the disc to sublimate as the ice line moves outwards to several to tens of astronomical units. In this paper, we investigate how the subsequent cooling of the disc impacts the particle sizes. We calculate the resulting particle sizes in a disc model with cooling times between 100 and 1,000 years, corresponding to typical FU Orionis outbursts. As the disc cools and the ice line retreats inwards, water vapour forms icy mantles on existing silicate particles. This process is called heterogeneous nucleation. The nucleation rate per surface area of silicate substrate strongly depends on the degree of super-saturation of the water vapour in the gas. Fast cooling results in high super-saturation levels, high nucleation rates, and limited condensation growth because the main ice budget is spent in the nucleation. Slow cooling, on the other hand, leads to rare ice nucleation and efficient growth of ice-nucleated particles by subsequent condensation. We demonstrate that close to the quiescent ice line, pebbles with a size of about centimetres to decimetres form by this process. The largest of these are expected to undergo cracking collisions. However, their Stokes numbers still reach values that are high enough to potentially trigger planetesimal formation by the streaming instability if the background turbulence is weak. Stellar outbursts may thus promote planetesimal formation around the water ice line in protoplanetary discs.

NASA's Juno mission provided exquisite measurements of Jupiter's gravity field that together with the Galileo entry probe atmospheric measurements constrains the interior structure of the giant planet. Inferring its interior structure range remains a challenging inverse problem requiring a computationally intensive search of combinations of various planetary properties, such as the cloud-level temperature, composition, and core features, requiring the computation of ~10^9 interior models. We propose an efficient deep neural network (DNN) model to generate high-precision wide-ranged interior models based on the very accurate but computationally demanding concentric MacLaurin spheroid (CMS) method. We trained a sharing-based DNN with a large set of CMS results for a four-layer interior model of Jupiter, including a dilute core, to accurately predict the gravity moments and mass, given a combination of interior features. We evaluated the performance of the trained DNN (NeuralCMS) to inspect its predictive limitations. NeuralCMS shows very good performance in predicting the gravity moments, with errors comparable with the uncertainty due to differential rotation, and a very accurate mass prediction. This allowed us to perform a broad parameter space search by computing only ~10^4 actual CMS interior models, resulting in a large sample of plausible interior structures, and reducing the computation time by a factor of 10^5. Moreover, we used a DNN explainability algorithm to analyze the impact of the parameters setting the interior model on the predicted observables, providing information on their nonlinear relation.

The QUIJOTE MFI instrument (2012-2018) observed the sky at four frequency bands, namely 11, 13, 17 and 19GHz, at 1 degree angular resolution. Using around 10000 h of observations in the so-called nominal mode, QUIJOTE MFI produced sky maps covering approximately 29000 deg2. Here we use the full database of MFI wide survey observations to characterize the correlation properties of the atmospheric signal in those frequency bands. This information will be useful to improve the current sky models at these frequencies, and could be used in further MFI reanalyses, or for the preparation of future observations at these frequencies (e.g., MFI2 and the Tenerife Microwave Spectrometer).

The sources of galactic charged cosmic rays are so far unknown, because their arrival directions are randomized in the galactic magnetic field. Objects accelerating hadrons are expected to produce high-energy neutrinos. In addition, a diffuse galactic neutrino flux is predicted from interactions of galactic cosmic rays with matter during propagation through the galaxy. The IceCube neutrino observatory at the geographic South Pole instruments a cubic kilometer of ice with optical modules to detect the Cherenkov light of particles produced in neutrino interactions. Operating for more than a decade in its complete detector configuration, IceCube is in a unique position to search for neutrino sources. This contribution discusses the searches for a diffuse flux of neutrinos as wells as for neutrinos from candidate point sources and extended sources in the galactic plane.

We present recent work on the Spectra of IceCube Neutrino (SIN) candidate sources project. We defined a selection of candidate neutrino sources by identifying blazars in the vicinity of IceCube's highest-energy neutrinos. We now want to shed light on these source candidates' nature, starting at their redshift, continuing with their black hole masses, their variability, and, for the first time, a combined photon-neutrino spectral energy distribution. We present their hybrid spectral energy distributions (combining photon and neutrino fluxes), investigate the sources' variability in the near-infrared, optical, X-ray, and $\gamma$-ray bands, and compare the variability with a blazar sample of non-candidate sources. Furthermore, we search for flares at the arrival time of the high-energy neutrinos.

A magma ocean (MO) is thought to be a ubiquitous stage in the early evolution of rocky planets and exoplanets. During the lifetime of the MO, exchanges between the interior and exterior envelopes of the planet are very efficient. In particular, volatile elements that initially are contained in the solid part of the planet can be released and form a secondary outgassed atmosphere. We determine trends in the H-C-N-O-S composition and thickness of these secondary atmospheres for varying planetary sizes and MO extents, and the oxygen fugacity of MOs, which provides the main control for the atmospheric chemistry. We used a model with coupled chemical gas-gas and silicate melt-gas equilibria and mass conservation to predict the composition of an atmosphere at equilibrium with the MO depending on the planet size and the extent and redox state of the MO. We used a self-consistent mass-radius model for the rocky core to inform the structure of the planet, which we combined with an atmosphere model to predict the transit radius of lava worlds. We find that MOs (especially the shallow ones) on small planets are generally more reduced, and are thus dominated by H2-rich atmospheres (whose outgassing is strengthened at low planetary mass), while larger planets and deeper MOs vary from CO to CO2-N2-SO2 atmospheres, with increasing fO2 . In the former case, the low molecular mass of the atmosphere combined with the low gravity of the planets yields a large vertical extension of the atmosphere, while in the latter cases, secondary outgassed atmospheres on super-Earths are likely significantly shrunk. Both N and C are largely outgassed regardless of the conditions, while the S and H outgassing is strongly dependent on the fO2 , as well as on the planetary mass and MO extent for the latter.

ALMA's high-resolution images allow to resolve the filamentary structure of the ISM down to few thousand au at kpc distances. We aim to systematically quantify the impact of the interferometric response and the effects of the short-spacing information during the characterization of the ISM structure using ALMA observations. We create a series of continuum ALMA synthetic observations to test the recovery of the observational properties of dense cores and filaments (i.e. intensity peak, radial profile, and width) at different scales. We compare the results obtained with and without different data combination techniques using different ALMA arrays and SD telescopes in simulated data and real observations. Our analysis illustrates the severity of interferometric filtering effects. ALMA-12m alone observations show significant scale-dependent flux losses systematically corrupting (>30%error) all the physical properties inferred in cores and filaments (i.e. column density, mass, and size) before the maximum recoverable scale of the interferometer. These effects are only partially mitigated by the addition of the ALMA ACA-7m array although degrading the telescope PSF. Our results demonstrate only the addition of the ALMA Total Power information allows to recover the true sky emission down to few times the ALMA beamsize with satisfactory accuracy (<10% error). Additional tests demonstrate the emission recovery at all scales is further improved if the 7mTP data are replaced by maps obtained by a larger SD telescope (e.g., IRAM-30m), even if the latter are noisier than expected. These observational biases particularly affect partially resolved targets, becoming critical especially for studies in nearby regions such as Taurus or Orion. Our results demonstrate the need for the use of data combination techniques to accurately characterize the complex physical structure of the ISM in the ALMA era.

Comet 67P/Churyumov-Gerasimenko (67P) become observable for the first time in 2021 since the Rosetta rendezvous in 2014--16. Here, we present pre-perihelion polarimetric measurements of 67P from 2021 performed with the Very Large Telescope (VLT), as well as post-perihelion polarimetric measurements from 2015--16 obtained with the VLT and the William Herschel Telescope (WHT). This new data covers a phase angle range of ~4-50° and presents polarimetric measurements of unprecedentedly high S/N ratio. Complementing previous measurements, the polarimetric phase curve of 67P resembles that of other Jupiter family comets and high-polarisation, dusty comets. Comparing pre- and post-perihelion data sets, we find only a marginal difference between the polarimetric phase curves. In our imaging maps, we detect various linear structures produced by the dust in the inner coma of the comet. Despite this, we find a homogeneous spread of polarisation around the photocentre throughout the coma and tail, in contrast to previous studies. Finally, we explore the consequences of image misalignments on both polarimetric maps and aperture polarimetric measurements.

Lensed quasars are powerful cosmic laboratories; they are used to simultaneously probe various astrophysical phenomena. Microlensing by stars within distant galaxies acts as strong gravitational lenses of multiply imaged quasars, and provides a unique and direct measurement of the lensed quasar internal structure. Microlensing of the continuum emitting region as well as the broad-line region (BLR) is well characterized by four observable indices, $\mu^{cont}$, $\mu^{BLR}$, $WCI$ (wing-core), and $RBI$ (red-blue), measured directly from the spectra. During the 2004-2007 monitoring period, image A of the quadruply lensed system Q2237+0305 underwent a strong microlensing amplification, while image D remained unaffected. We used 35 epochs of archival spectrophotometric data of Q2237+0305 obtained with the Very Large Telescope of the European Southern Observatory to develop an independent microlensing method for estimating the geometry and size of the BLR. We measured the index time series for the CIV line and the continuum emission at $1450\,\unicode{x212B}$. We built a library of the simulated microlensing index time series that reproduce the observed times series based on three representative BLR models: Keplerian disk (KD), polar wind (PW), and equatorial wind (EW). After sampling the model parameter space, we find that KD is the predominant model, while PW and EW are less likely. We infer that the system is viewed at an intermediate viewing angle $i\sim 35^\circ$, and we estimate the most likely CIV BLR half-light radius $r_\mathrm{1/2}=51\pm 23$ light days. Our results are in good agreement with previous findings in the literature and extend the validity of the index-based approach to a temporal domain.

The detection of high-energy neutrino signals from the nearby Seyfert galaxy NGC 1068 provides us with an opportunity to study nonthermal processes near the center of supermassive black holes. Using the IceCube and latest Fermi-LAT data, we present general multimessenger constraints on the energetics of cosmic rays and the size of neutrino emission regions. In the photohadronic scenario, the required cosmic-ray luminosity should be larger than about 1-10% of the Eddington luminosity and the emission radius should be 15 Schwarzschild radii in low-beta plasma and 3 Schwarzschild radii in high-beta plasma. The leptonic scenario overshoots the NuSTAR or Fermi-LAT data for any emission radii we consider, and the required gamma-ray luminosity is much larger than the Eddington luminosity. The beta decay scenario also violates not only the energetics requirement but also gamma-ray constraints especially when the Bethe-Heitler and photomeson production processes are consistently considered. Our results rule out the leptonic and beta decay scenarios in a nearly model-independent manner, and support hadronic mechanisms in magnetically-powered coronae if NGC 1068 is a source of high-energy neutrinos.

Thanks to the successful performance of the James Webb Space Telescope, our understanding of the epoch of reionization of the Universe has been advanced. The ultraviolet luminosity functions (UV LFs) of galaxies span a wide range of redshift, not only revealing the connection between galaxies and dark matter (DM) halos but also providing the information during reionization. In this work, we develop a model connecting galaxy counts and apparent magnitude based on UV LFs, which incorporates redshift-dependent star formation efficiency (SFE) and corrections for dust attenuation. By synthesizing some observations across the redshift range $4\le z \le 10$ from various galaxy surveys, we discern the evolving SFE with increasing redshift and DM halo mass through model fitting. Subsequent analyses indicate that the Thomson scattering optical depth was $\tau_{\rm e} = 0.052^{+0.003}_{-0.002}$ and the epoch of reionization started (ended) at $z=20.58^{+6.25}_{-6.75}$ ($z=5.38^{+0.65}_{-0.70}$) which is insensitive to the choice of the truncated magnitude of the UV LFs. Incorporating additional dataset and some reasonable constraints, the amplitude of matter perturbation is found to be $\sigma_8=0.79\pm0.05$, which is consistent with the standard $\Lambda$CDM model. Future galaxy surveys and the dynamical simulations of galaxy evolution will break the degeneracy between SFE and cosmological parameters, improving the accuracy and the precision of the UV LF model further.

We present a study of the growth of the quiescent galaxy population between 0.5 < z < 3 by tracing the number density and structural evolution of a sample of 4518 old and 583 young quiescent galaxies with log($M_*$/$M_{\odot}$)>10.4, selected from the COSMOS2020 catalog with complementary HST/F160W imaging from the 3D-DASH survey. Among the quiescent population at z$\sim$2, roughly 50% are recently quenched galaxies; these young quiescent galaxies become increasingly rare towards lower redshift, supporting the idea that the peak epoch of massive galaxy quenching occurred at z>2. Our data show that while the effective half-light radii of quiescent galaxies generally increases with time, young quiescent galaxies are significantly smaller than their older counterparts at the same redshift. In this work we investigate the connection between this size difference and other structural properties, including axis ratios, color gradients, stellar mass, and the intrinsic scatter in effective radii. We demonstrate that the size difference is driven by the most massive sub-population (log($M_*$/$M_{\odot}$)>11) and does not persist when restricting the sample to intermediate mass galaxies (10.4<log($M_*$/$M_{\odot}$)<11). Interestingly, the intrinsic scatter in physical size shows a strong co-evolution over the investigated time period and peaks around z$\sim$2 for both populations, only diverging at z < 1. Taken together, and assuming we are not missing a significant population of lower surface brightness galaxies, while the formation and quenching mechanisms that dominate at higher redshifts yield compact remnants, multiple evolutionary pathways may explain the diverse morphologies of galaxies that quench at z<1.

The brightest steady sources of radiation in the universe, active galactic nuclei (AGN), are powered by gas accretion onto a central supermassive black hole (SMBH). The large sizes and accretion rates implicated in AGN accretion disks are expected to lead to gravitational instability and fragmentation, effectively cutting off mass inflow to the SMBH. Radiative feedback from disk-embedded stars has been invoked to yield marginally stable, steady-state solutions in the outer disks. Here, we examine the consequences of this star formation with a semi-analytical model in which stellar-mass black hole (sBH) remnants in the disk provide an additional source of stabilizing radiative feedback. Assuming star formation seeds the embedded sBH population, we model the time-evolving feedback from both stars and the growing population of accreting sBHs. We find that in the outer disk, the luminosity of the sBHs quickly dominates that of their parent stars. However, because sBHs consume less gas than stars to stabilize the disk, the presence of the sBHs enhances the mass flux to the inner disk. As a result, star formation persists over the lifetime of the AGN, damped in the outer disk, but amplified in a narrow ring in the inner disk. Heating from the embedded sBHs significantly modifies the disk's temperature profile and hardens its spectral energy distribution, and direct emission from the sBHs adds a new hard X ray component, resembling a Compton reflection "hump".

Merging galaxy clusters often host spectacular diffuse radio synchrotron sources. These sources can be explained by a non-thermal pool of relativistic electrons accelerated by shocks and turbulence in the intracluster medium. The origin of the pool and details of the cosmic ray transport and acceleration mechanisms in clusters are still open questions. Due to the often extremely steep spectral indices of diffuse radio emission, it is best studied at low frequencies. However, the lowest frequency window available to ground-based telescopes (10-30 MHz) has remained largely unexplored, as radio frequency interference and calibration problems related to the ionosphere become severe. Here, we present LOFAR observations from 16 to 168 MHz targeting the famous cluster Abell 2256. In the deepest-ever images at decametre wavelengths, we detect and resolve the radio halo, radio shock and various steep spectrum sources. We measure standard single power-law behaviour for the radio halo and radio shock spectra and find significant spectral index and curvature fluctuations across the radio halo, indicating an inhomogeneous emitting volume. In contrast to the straight power-law spectra of the large-scale diffuse sources, the various AGN-related sources often show extreme steepening towards higher frequencies and flattening towards low frequencies. We also discover a new fossil plasma source with a steep spectrum between 23 and 144 MHz, with $\alpha=-1.9\pm 0.1$. Finally, by comparing radio and gamma-ray observations, we rule out purely hadronic models for the radio halo origin in Abell 2256, unless the magnetic field strength in the cluster is exceptionally high, which is unsupportable by energetic arguments and inconsistent with the knowledge of other cluster magnetic fields.

In seven billion years, the Sun will be dead. As stars like the Sun pass from their present state to that of a dead white dwarf star, they undergo two phases of extremely high luminosity and radius -- the red giant branch and the asymptotic giant branch -- during which they will lose half or more of their mass. These changes to the star have a significant impact on orbiting planets, asteroids and comets. The large stellar radius (beyond the current orbit of the Earth) leads to the engulfment of bodies entering the stellar envelope, a process enhanced by strong tidal interactions. The high luminosity affects bodies' orbits and physical properties, while mass loss can later trigger the destabilisation of bodies around white dwarfs. It is necessary to understand these processes to understand both the future of our Solar System, and to interpret growing observations of planetary systems around evolved stars.

We investigate the black hole mass function (BHMF) and the Eddington ratio distribution function (ERDF), focusing on the intermediate-mass black holes (IMBHs) with masses down to $M_{\bullet}\sim10^4 M_\odot$. Based on the AGNs with a detected broad H$\alpha$ emission line, we construct a sample of 14,242 AGNs at redshift $z<0.35$, including 243 IMBHs with $M_{\bullet}<10^6 M_\odot$. By jointly modeling the BHMF and ERDF via the maximum posterior estimation, we find that the BHMF peaks at $\sim$$10^{6} M_\odot$ and exhibits a relatively constant value of $10^{-4}\,\mathrm{Mpc^{-3}\,dex^{-1}}$ at the low-mass end. By comparing the derived BHMF of type 1 AGNs with the galaxy mass function based on the updated black hole mass - host galaxy stellar mass relation, we derive the active fraction. We also determine the active fraction for all AGNs using the upper and lower limit of the type 1 fraction. The active fraction decreases from 15%-40% for massive galaxies ($M_\star>10^{10} M_\odot$) to lower than $\sim$2% for dwarf galaxies with $M_\star\sim10^8 M_\odot$. These results suggest that the black hole occupation fraction is expected to be $\sim$50% for low-mass galaxies ($M_\star\sim10^{8.5} M_\odot$-$10^9 M_\odot$) if the duty cycle is similar between intermediate mass and supermassive black holes.

Cosmological observations allow to measure the abundance of light relics produced in the early Universe. Most studies focus on the thermal freeze-out scenario, yet light relics produced by freeze-in are generic for models in which new light degrees of freedom do not couple strongly enough to the Standard Model (SM) plasma to allow for full thermalization in the early Universe. In ultraviolet (UV) freeze-in scenarios, rates for light relic production associated with non-renormalizable interactions typical of beyond the SM (BSM) models grow with temperature more quickly than the Hubble rate. Thus, relatively small couplings to the SM can be probed by current and next-generation cosmic microwave background (CMB) experiments. We investigate several representative benchmark BSM models, such as axion-like particles from Primakoff production, massless dark photons and light right-handed neutrinos. We calculate contributions to the effective number of neutrino species, $\Delta N_{\rm eff}$, in corners of parameter space not previously considered and discuss the sensitivity of CMB experiments compared to other probes. In contrast to freeze-out scenarios, $\Delta N_{\rm eff}$ from UV freeze-in is more dependent on both the specific BSM physics model and the reheating temperature. Depending on the details of the BSM scenario, we find that the sensitivity of next-generation CMB experiments can complement or surpass the current astrophysical, laboratory or collider constraints on the couplings of the SM to the light relic.

We analyzed the CIV line profile distortions due to microlensing in two quasars, J1339 and J1138. J1339 shows a strong, asymmetric line profile deformation, while J1138 shows a more modest, symmetric deformation. To probe the CIV broad line region (BLR), we compared the observed line profile deformations to simulated ones. The simulations are based on three simple BLR models, a Keplerian disk (KD), an equatorial wind (EW), and a polar wind (PW), of various sizes, inclinations, and emissivities. We find that the line profile deformations can be reproduced with the simple BLR models under consideration, with no need for more complex geometries or kinematics. The models with disk geometries (KD and EW) are preferred, while the PW model is definitely less likely. For J1339, we find the CIV BLR half-light radii to be $r_{1/2} =$ 5.1 $^{+4.6}_{-2.9}$ light-days and $r_{1/2} =$ 6.7 $^{+6.0}_{-3.8}$ light-days from spectra obtained in 2014 and 2017, respectively. They do agree within uncertainties. For J1138, the amplitude of microlensing is smaller and more dependent on the macro-magnification factor. From spectra obtained in 2005 (single epoch), we find $r_{1/2} =$ 4.9 $^{+4.9}_{-2.7}$ light-days and $r_{1/2}= $ 12 $^{+13}_{-8}$ light-days for two extreme values of the macro-magnification factor. Combining these new measurements with those previously obtained for the quasars Q2237$+$0305 and J1004$+$4112, we show that the BLR radii estimated from microlensing do follow the CIV radius--luminosity relation obtained from reverberation mapping, although the microlensing radii seem to be systematically smaller, which could indicate either a selection bias or a real offset (abridged).

We introduce our project, AGNSTRONG (Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies). Our research goals encompass investigating the kinematic properties of ionized and molecular gas outflows, understanding the impact of AGN feedback, and exploring the coevolution dynamics between AGN strength activity and star formation activity. We aim to conduct a thorough analysis to determine whether there is an increase or suppression in SFRs among targets with and without powerful relativistic jets. Our sample consists of 35 nearby AGNs with and without powerful relativistic jet detections. Utilizing sub-millimeter (sub-mm) continuum observations at 450 {\mu}m and 850 {\mu}m from SCUBA-2 at the James Clerk Maxwell Telescope, we determine star-formation rates (SFRs) for our sources using spectral energy distribution (SED) fitting models. Additionally, we employ high-quality, spatially resolved spectra from UV-optical to near-infrared bands obtained with the Double Spectrograph and Triple Spectrograph mounted on the 200-inch Hale telescope at Palomar Observatory to study their multiphase gas outflow properties. This paper presents an overview of our sample selection methodology, research strategy, and initial results of our project. We find that the SFRs determined without including the sub-mm data in the SED fitting are overestimated by approximately 0.08 dex compared to those estimated with the inclusion of sub-mm data. Additionally, we compare the estimated SFRs in our work with those traced by the 4000Å break, as provided by the MPA-JHU catalog. We find that our determined SFRs are systematically higher than those traced by the 4000Å break. Finally, we outline our future research plans.

To advance our understanding of the evolution of the interstellar medium (ISM) of our Galaxy, numerical models of Milky Way (MW) type galaxies are widely used. However, most models only vaguely resemble the MW (e.g. in total mass), and often use imposed analytic potentials (which cannot evolve dynamically). This poses a problem in asserting their applicability for the interpretation of observations of our own Galaxy. The goal of this work is to identify a numerical model that is not only a MW-type galaxy, but one that can mimic some of the main observed structures of our Galaxy, using dynamically evolving potentials, so that it can be used as a base model to study the ISM cycle in a galaxy like our own. This paper introduces a suite of 15 MW-type galaxy models developed using the {\sc arepo} numerical code, that are compared to Galactic observations of $^{12}$CO and \ion{H}{I} emission via longitude-velocity plots, from where we extract and compare the skeletons of major galactic features and the terminal gas velocities. We found that our best-fitting model to the overall structure, also reproduces some of the more specific observed features of the MW, including a bar with a pattern speed of $30.0 \pm 0.2$ km\,s$^{-1}$\,kpc$^{-1}$, a bar half-length of $3.2 \pm 0.8$\,kpc. Our model shows large streaming motions around spiral arms, and strong radial motions well beyond the inner bar. This model highlights the complex motions of a dynamic MW-type galaxy and has the potential to offer valuable insight into how our Galaxy regulates the ISM and star formation.

We show that by jointly fitting cosmic microwave background (CMB) and astrophysical data - a compilation of UV luminosity data from the Hubble Frontier Field and neutral hydrogen data from distant sources-, we can infer on the shape of the evolution of the ionized hydrogen fraction with redshift in addition to constraining the average optical depth $\tau$.For this purpose, we introduce here a novel extended model that includes hydrogen ionization histories which are monotonic with redshift, but allow for an asymmetry as indicated from our previous works on a free reconstruction of reionization. By using our baseline data combination, we obtain $\tau=0.0542^{+0.0017}_{-0.0028}$, consistent with our previous works and tighter than the one inferred by Planck 2018 data because of the combination of CMB with astrophysical data. We find that the symmetric hypothesis within our parametrization is disfavoured at 4 $\sigma$.We test our findings by using alternative likelihoods for CMB polarization at low multipoles, i.e. based on the 2020 reprocessing of Planck HFI data or on the joint analysis of WMAP and Planck LFI data, obtaining consistent results that disfavour the symmetric hypothesis of the reionization history at high statistical significant level.These results will be further tested by more precise astrophysical data such as from JWST and Euclid deep fields.

We present a time-domain model for the gravitational waves emitted by equal-mass binary neutron star merger remnants for a fixed equation of state. We construct a large set of numerical relativity simulations for a single equation of state consistent with current constraints, totaling 157 equal-mass binary neutron star merger configurations. The gravitational-wave model is constructed using the supervised learning method of K-nearest neighbor regression. As a first step toward developing a general model with supervised learning methods that accounts for the dependencies on equation of state and the binary masses of the system, we explore the impact of the size of the dataset on the model. We assess the accuracy of the model for a varied dataset size and number density in total binary mass. Specifically, we consider five training sets of $\{ 20,40, 60, 80, 100\}$ simulations uniformly distributed in total binary mass. We evaluate the resulting models in terms of faithfulness using a test set of 30 additional simulations that are not used during training and which are equidistantly spaced in total binary mass. The models achieve faithfulness with maximum values in the range of $0.980$ to $0.995$. We assess our models simulating signals observed by the three-detector network of Advanced LIGO-Virgo. We find that all models with training sets of size equal to or larger than $40$ achieve an unbiased measurement of the main gravitational-wave frequency. We confirm that our results do not depend qualitatively on the choice of the (fixed) equation of state. We conclude that training sets, with a minimum size of $40$ simulations, or a number density of approximately $11$ simulations per $0.1\,M_\odot$ of total binary mass, suffice for the construction of faithful templates for the post-merger signal for a single equation of state and equal-mass binaries (abbreviated).

Fuzzy dark matter wormhole solutions coupled with anisotropic matter distribution are explored in 4D Einstein-Gauss-Bonnet and $f(R)$ gravity, where $R$ is the Ricci scalar. We derive the shape function for fuzzy wormholes and explore their possible stability. We study the embedding diagrams of the active gravitational mass associated with fuzzy dark matter wormholes by taking a certain shape function. Aiming to highlight the role of Einstein-Gauss-Bonnet and $f(R)$ gravity in the modeling of less complex fuzzy wormhole structures, we evaluate the complexity factor, the conservation equation, and null energy conditions. Our study reinforces more importance of uniformly distributed pressure effects throughout the less complex region than to the emergence of energy density homogeneity in the stability of fuzzy wormholes. It is shown that the active gravitational mass of the fuzzy wormhole structures varies inversely with the radial distance thereby suggesting the breaching of energy conditions at some arena of Einasto index. Furthermore, it is revealed that stable fuzzy dark matter wormhole structures exist in nature in the surroundings of cold dark matter halos and galactic bulges. The important physics understood from our analysis is that in both four-dimensional Einstein-Gauss-Bonnet and $f(R)$ gravity, feasible geometries of fuzzy dark matter wormholes exist naturally in the environments of different galactic haloes.

Kp-Index is a very important factor for determining how the Sun's magnetic field is affecting the Earth's magnetic field and help us prepare for the worst (like solar or geomagnetic storms). Currently there are around thirteen observation centers to determine the worldwide Kp index. Huge data is generated from all the observation centers which is then used to determine several factors, but the observatories are concentrated in places like North America and Europe only. To eliminate the data dependency from a very limited geographical periphery we can use a constellation of satellites in LEO which can log in data continuously and provide a real time and accurate Kp index which can help humanity for tackling with the impending issues from our nearest star in a better way. The constellation of the satellites will be deployed in the Low Earth Orbit(LEO) and continuously log the geomagnetic data and provide a constant stream of data, which will be more diverse given the area coverage made by one satellite. This is essentially a boon as more the data we can have better geomagnetic data and the Kp index will be all encompassing which can help in better mapping of any solar-catastrophe.

In April 2023, low-latitude aurora observation by the all-sky camera at Hanle, Ladakh, India ($33^{\circ} {} N $ geographic latitude (GGLat)) was reported, which stimulated a lot of discussion among scientists as well as masses across the globe. The reported observation was intriguing as the solar storm that triggered this aurora was moderate and the first such observation from Indian region in the space-era. In this communication, we investigate such a unique modern-day observation of low-latitude auroral sighting occurring during the passage of sheath-region of Interplanetary-Coronal-Mass-Ejection, utilizing in situ multi-spacecraft particle measurements along with geomagnetic-field observations by ground and satellite-based magnetometers. Auroral observations at Hanle coincided with the intense substorm occurrences. It is unequivocally found that the aurora didnt reach India, rather the equatorward boundary of the aurora was beyond $ 50^{\circ} {}N $ GGLat. The multi-instrumental observations enabled us to estimate the altitude of the red auroral emissions accurately. The increased flux of low-energy electrons ($<$100 eV) precipitating at $\sim 54^{\circ}N$ GGLat causing red-light emissions at higher altitudes ($\sim$700-950 km) can be visible from Hanle. The observed low-latitude red aurora from India resulted from two factors: emissions at higher altitudes in the auroral oval and a slight expansion of the auroral oval towards the equator. The precipitating low-energy particles responsible for red auroral emissions mostly originate from the plasma sheet. These particles precipitate due to wave-particle interactions enhanced by strong compression of the magnetosphere during high solar wind pressure. This study using multi-point observations holds immense importance in providing a better understanding of low-latitude auroras.

In the gravitational-wave analysis of pulsar-timing-array datasets, parameter estimation is usually performed using Markov Chain Monte Carlo methods to explore posterior probability densities. We introduce an alternative procedure that relies instead on stochastic gradient-descent Bayesian variational inference, whereby we obtain the weights of a neural-network approximation of the posterior by minimizing the Kullback-Leibler divergence of the approximation from the exact posterior. This technique is distinct from simulation-based inference with normalizing flows, since we train the network for a single dataset, rather than the population of all possible datasets, and we require the computation of the data likelihood and its gradient. Unlike Markov Chain methods, our technique can transparently exploit highly parallel computing platforms. This makes it extremely fast on modern graphical processing units, where it can analyze the NANOGrav 15-yr dataset in few tens of minutes, depending on the probabilistic model, as opposed to hours or days with the analysis codes used until now. We expect that this speed will unlock new kinds of astrophysical and cosmological studies of pulsar-timing-array datasets. Furthermore, variational inference would be viable in other contexts of gravitational-wave data analysis as long as differentiable and parallelizable likelihoods are available.

We revisit the hybrid inflation model within the framework of the Grand Unified Theory (GUT), focusing on cases where the waterfall phase transition extends over several e-foldings to dilute monopoles. Considering the stochastic effects of quantum fluctuations, we demonstrate that the waterfall fields (i.e., GUT Higgs) maintain a nonzero vacuum expectation value around the waterfall phase transition. By accurately accounting for the number of degrees of freedom of the GUT Higgs field, we establish that these fluctuations can produce observable gravitational waves without leading to an overproduction of primordial black holes. The amplitude of these gravitational waves is inversely proportional to the degrees of freedom of the waterfall fields, thereby providing a unique method to probe the representation of the GUT Higgs.

Many present-day axion searches attempt to probe the mixing of axions and photons, which occurs in the presence of an external magnetic field. While this process is well-understood in a number of simple and idealized contexts, a strongly varying or highly inhomogeneous background can impact the efficiency and evolution of the mixing in a non-trivial manner. In an effort to develop a generalized framework for analyzing axion-photon mixing in arbitrary systems, we focus in this work on directly solving the axion-modified form of Maxwell's equations across a simulation domain with a spatially varying background. We concentrate specifically on understanding resonantly enhanced axion-photon mixing in a highly magnetized plasma, which is a key ingredient for developing precision predictions of radio signals emanating from the magnetospheres of neutron stars. After illustrating the success and accuracy of our approach for simplified limiting cases, we compare our results with a number of analytic solutions recently derived to describe mixing in these systems. We find that our numerical method demonstrates a high level of agreement with one, but only one, of the published results. Interestingly, our method also recovers the mixing between the axion and magnetosonic-t and Alfvén modes; these modes cannot escape from the regions of dense plasma, but could non-trivially alter the dynamics in certain environments. Future work will focus on extending our calculations to study resonant mixing in strongly variable backgrounds, mixing in generalized media (beyond the strong magnetic field limit), and the mixing of photons with other light bosonic fields, such as dark photons.

Horizons and bound photon orbits are defining features of black holes that translate into key features of black hole images. We present a purely geometric proof that spherically symmetric, isolated objects with horizons in gravity theories with null-geodesic propagation of light must display bound photon orbits forming a photon sphere. Identifying the key elements of the proof, we articulate a simpler argument that carries over to more general situations with modified light propagation and implies the existence of equatorial spherical photon orbits in axisymmetric spacetimes with reflection symmetry. We conclude that the \emph{non-}observation of photon rings with very-large-baseline interferometry would be a very strong indication against a horizon, irrespective of whether or not the image shows a central brightness depression.

We present a model of dark matter as a superconducting fluid of Cooper pairs of right handed neutrinos or of vector-like quarks. The superconducting dark matter is induced by attractive channels in the Standard Model Higgs and color sectors of the Standard Model, respectively. We show that, for each case, the solution to the gap equation provides viable dark matter candidates for suitable chemical potential values. The mechanism yields an ultra-light neutrino condensate with a mass of $m_{\rm DM} \sim 10^{-19} \text{eV}$ or a vector-like quark condensate with wide range of possible masses. Both cosmological and particle physics constraints on the model lead to a connection between the number of effective relativistic species $N_{\rm eff}$, and the chemical potential and CMB temperature at the time of fermion creation. We also find a relation between the superconducting fermion and baryon densities, with implications for the coincidence between the dark matter and baryon densities in standard cosmology. Given the natural $\text{eV}$ scale of neutrinos, this mechanism may have implications for the Hubble tension.

We apply deep learning techniques to the late-time turbulent regime in a post-inflationary model where a real scalar inflaton field and the standard model Higgs doublet interact with renormalizable couplings between them. After inflation, the inflaton decays into the Higgs through a trilinear coupling and the Higgs field subsequently thermalizes with gauge bosons via its $SU(2)\times U(1)$ gauge interaction. Depending on the strength of the trilinear interaction and the Higgs self-coupling, the effective mass squared of Higgs can become negative, leading to the tachyonic production of Higgs particles. These produced Higgs particles would then share their energy with gauge bosons, potentially indicating thermalization. Since the model entails different non-perturbative effects, it is necessary to resort to numerical and semi-classical techniques. However, simulations require significant costs in terms of time and computational resources depending on the model used. Particularly, when $SU(2)$ gauge interactions are introduced, this becomes evident as the gauge field redistributes particle energies through rescattering processes, leading to an abundance of UV modes that disrupt simulation stability. This necessitates very small lattice spacings, resulting in exceedingly long simulation runtimes. Furthermore, the late-time behavior of preheating dynamics exhibits a universal form by wave kinetic theory. Therefore, we analyze patterns in the flow of particle numbers and predict future behavior using CNN-LSTM (Convolutional Neural Network combined with Long Short-Term Memory) time series analysis. In this way, we can reduce our dependence on simulations by orders of magnitude in terms of time and computational resources.

We consider inflation with a constant rate of rolling in which a complex scalar field plays the role of inflaton during the inflationary epoch. We implement the inflationary analysis for an accredited angular speed $\dot{\theta}$ which satisfies our dynamical equations. Scalar and tensorial perturbations generated in the framework of constant roll inflation with a complex field are studied. In this respect, we find analytically solutions to the gauge invariant fluctuations, with which an expression for the scalar power spectrum together with its scalar index spectral in this scenario were found. By comparing the obtained results with the observations coming from the cosmic microwave background anisotropies, the constraints on the parameters space of the model and also its predictions are analyzed and discussed.

Macroscopic dark matter like nontopological solitons can form either via the fusion and accumulation of free particles or during cosmological phase transitions. Both mechanisms can create dark matter with large masses ranging from TeV to solar mass. This can lead to interesting targets in direct detection, astrophysical, and cosmological searches.

We explore the possibility that our universe's current accelerated expansion is explained by a quintessence model with an exponential scalar potential, $V =V_0\, e^{-\lambda\, \phi}$, keeping an eye towards $\lambda \geq \sqrt{2}$ and an open universe, favorable to a string theory realisation and with no cosmological horizon. We work out the full cosmology of the model, including matter, radiation, and optionally negative spatial curvature, for all $\lambda>0$, performing an extensive analysis of the dynamical system and its phase space. The minimal physical requirements of a past epoch of radiation domination and an accelerated expansion today lead to an upper bound $\lambda \lesssim \sqrt{3}$, which is driven slightly up in the presence of observationally allowed spatial curvature. Cosmological solutions start universally in a kination epoch, go through radiation and matter dominated phases and enter an epoch of acceleration, which is only transient for $\lambda>\sqrt{2}$. Field distances traversed between BBN and today are sub-Planckian. We discuss possible string theory origins and phenomenological challenges, such as time variation of fundamental constants. We provide theoretical predictions for the model parameters to be fitted to data, most notably the varying dark energy equation of state parameter, in light of recent results from DES-Y5 and DESI.

We simulated spin-spin interactions of $N$-bodies in linearized General Relativity (GR) and linearized Massive Gravity of the Fierz-Pauli type (mGR). It was noted earlier that there is a discrete difference between the spin-spin interaction potential in GR and mGR for a $2$-body system, akin to the van Dam-Veltman-Zakharov discontinuity in the static Newton's potential. Specifically, at large distances, GR favors anti-parallel spin orientation with total spin pointing along the interaction axis, while mGR favors parallel spin orientation with total spin perpendicular to the axis between the sources. For an $N$-body system, a simulation in mGR hitherto has not been done and one would like to know the total spin of the system in both theories. Here we remedy this. In the simulations of GR, we observed that the total spin tends to decrease from a random initial configuration, while for mGR with a large distance, the total spin increases.

Gravitational waves in the postmerger phase of binary neutron star mergers may become detectable with planned upgrades of existing gravitational-wave detectors or with more sensitive next-generation detectors. The construction of template banks for the postmerger phase can facilitate signal detection and parameter estimation. Here, we investigate the performance of an artificial neural network in predicting simulation-based waveforms in the frequency domain (restricted to the magnitude of the frequency spectrum and to equal-mass models) that depend on three parameters that can be inferred through observations, neutron star mass, tidal deformability, and the gradient of radius versus mass. Compared to a baseline study using multiple linear regression, we find that the artificial neural network can predict waveforms with higher accuracy and more consistent performance in a cross-validation study. We also demonstrate, through a recalibration procedure, that future reduction of uncertainties in empirical relations that are used in our hierarchical scheme will result in more accurate predicted postmerger spectra.

We explore an idea put forward many years ago by Zeldovich and Novikov concerning the existence of compact objects endowed with arbitrarily small mass. The energy-density of such objects, which we call ``Ghost stars'', is negative in some regions of the fluid distribution, producing a vanishing total mass. Thus, the interior is matched on the boundary surface to Minkowski space-time. Some exact analytical solutions are exhibited and their properties are analyzed. Observational data that could confirm or dismiss the existence of this kind of stellar object is commented.

We present a formulation of special relativistic, dissipative hydrodynamics (SRDHD) derived from the well-established Müller- Israel-Stewart (MIS) formalism using an expansion in deviations from ideal behaviour. By re-summing the non-ideal terms, our approach extends the Euler equations of motion for an ideal fluid through a series of additional source terms that capture the effects of bulk viscosity, shear viscosity and heat flux. For efficiency these additional terms are built from purely spatial derivatives of the primitive fluid variables. The series expansion is parametrized by the dissipation strength and timescale coefficients, and is therefore rapidly convergent near the ideal limit. We show, using numerical simulations, that our model reproduces the dissipative fluid behaviour of other formulations. As our formulation is designed to avoid the numerical stiffness issues that arise in the traditional MIS formalism for fast relaxation timescales, it is roughly an order of magnitude faster than standard methods near the ideal limit.