Papers for Tuesday, May 17 2022

Dissecting the underlying structure of galaxies is of main importance in the framework of galaxy formation and evolution theories. While a classical bulge+disc decomposition of disc galaxies is usually taken as granted, this is only rarely solidly founded upon the full exploitation of the richness of data arising from spectroscopic studies with integral field units. In this work we describe a fully Bayesian estimation method of the global structure of disc galaxies which makes use of the wealth of photometric, kinematic, and mass-to-light ratio data, and that can be seen as a first step towards a machine-learning approach, certainly needed when dealing with larger samples of galaxies. Ours is a novel, hybrid line of action in tackling the problem of galactic parameter estimation, neither purely photometric nor orbit-based. Being rooted on a nested sampler, our code, which is available publicly as an online repository, allows for a statistical assessment of the need for multiple components in the dissecting process. As a first case-study the GPU-optimized code is applied to the S0 galaxy NGC-7683, finding that in this galaxy a pseudo-bulge, possibly the remnant of a bar-like structure, does exist in the center of the system. These results are then tested against the publicly available, orbit-based code DYNAMITE, finding substantial agreement.

Molecular clouds in the central molecular zone (CMZ) have been observed to feature turbulent line widths that are significantly higher, and scale with cloud size more steeply, than in the rest of the Milky Way. In the same Galactic region, the stellar density is also much higher than in the rest of the Milky Way, and the vertical stellar velocity dispersion is large, meaning that even young stars are likely to cross the entire vertical extent of the CMZ within their lifetimes. Here, we investigate whether interactions of CMZ molecular clouds with crossing stars can account for the extraordinary properties of observed turbulence in this part of the Galaxy. We calculated the rate of energy deposition by stars crossing CMZ clouds due to (a) stellar winds and (b) dynamical friction, and compared it to the rate of turbulence decay. We calculated the predicted scaling of turbulence line width with cloud size in each case. We find that energy deposition by stellar winds of crossing massive stars can account for both the level and the scaling of CMZ cloud turbulence with cloud size. We also find that the mechanism stops being effective at a Galactocentric distance comparable to the CMZ extent. On the other hand, we find that dynamical friction by crossing stars does not constitute a significant driver of turbulence for CMZ clouds.

Initial distributions of pulsar periods and magnetic fields are essential components of multiple modern astrophysical models. Not enough work has been done to properly constrain these distributions using direct measurements. Here we aim to fill this gap by rigorously analysing properties of young neutron stars associated to supernova remnants. In order to perform this task, we compile a catalogue of 56 neutron stars uniquely paired to supernova remnants with known age estimate. Further, we analyse this catalogue using multiple statistical techniques. We found that distribution of magnetic fields and periods for radio pulsars are both well described using the log-normal distribution. The mean magnetic field is $\log_{10} [B/\mathrm{G}] = 12.44$ and standard deviation is $\sigma_B = 0.44$. Magnetars and central compact objects do not follow the same distribution. The mean initial period is $\log_{10} P_0 [P / \mathrm{s}] = -1.04_{-0.2}^{+0.15}$ and standard deviation is $\sigma_p = 0.53_{-0.08}^{+0.12}$. We show that the normal distribution does not describe the initial periods of neutron stars sufficiently well. Parameters of the initial period distribution are not sensitive to the exact value of the braking index.

Feedback to the interstellar medium (ISM) from ionising radiation, stellar winds and supernovae is central to regulating star formation in galaxies. Due to their low mass ($M_{*} < 10^{9}$\,M$_\odot$), dwarf galaxies are particularly susceptible to such processes, making them ideal sites to study the detailed physics of feedback. In this perspective, we summarise the latest observational evidences for feedback from star forming regions and how this drives the formation of 'superbubbles' and galaxy-wide winds. We discuss the important role of external ionising radiation -- 'reionisation' -- for the smallest galaxies. And, we discuss the observational evidences that this feedback directly impacts galaxy properties such as their star formation histories, metal content, colours, sizes, morphologies and even their inner dark matter densities. We conclude with a look to the future, summarising the key questions that remain unanswered and listing some of the outstanding challenges for galaxy formation theories.

Constraints on dark matter halo masses from weak gravitational lensing can be improved significantly by using additional information about the morphology of their density distribution, leading to tighter cosmological constraints derived from the halo mass function. This work is the first of two in which we investigate the accuracy of halo morphology and mass measurements in 2D and 3D. To this end, we determine several halo physical properties in the MICE-Grand Challenge dark matter only simulation. We present a public catalogue of these properties that includes density profiles and shape parameters measured in 2D and 3D, the halo centre at the peak of the 3D density distribution as well as the gravitational and kinetic energies and angular momentum vectors. The density profiles are computed using spherical and ellipsoidal radial bins, taking into account the halo shapes. We also provide halo concentrations and masses derived from fits to 2D and 3D density profiles using NFW and Einasto models for halos with more than $1000$ particles ($\gtrsim 3 \times 10^{13} h^{-1} M_{\odot}$). We find that the Einasto model provides better fits compared to NFW, regardless of the halo relaxation state and shape. The mass and concentration parameters of the 3D density profiles derived from fits to the 2D profiles are in general biased. Similar biases are obtained when constraining mass and concentrations using a weak-lensing stacking analysis. We show that these biases depend on the radial range and density profile model adopted in the fitting procedure, but not on the halo shape.

We report on the variability of a multi-component broad absorption line (BAL) system observed in the hyper-luminous quasar J1538+0855 at z=3.6. Observations from SDSS, VLT, LBT and Subaru telescopes taken at five different epochs, spanning 17 yr in the observed frame, are presented. We detect three (A, B, C) CIV variable troughs exhibiting extreme velocities ($\sim$40,000-54,000 km s$^{-1}$) similar to the ultra-fast outflows (UFOs) typically observed in the X-ray spectra. The A component of the BAL UFO ($\rm v_{ufo}$ $\sim$0.17 c) shows strength variations, while B ($\rm v_{ufo}$ $\sim$0.15 c) and C ($\rm v_{ufo}$ $\sim$0.13 c) components show changes both in shape and strength, appearing and disappearing at different epochs. In addition, during the last observation on June 2021 the entire BAL system disappears. The variability trends observed during the first two epochs (1.30 yr rest-frame) in the CIV, SiIV, OVI and NV absorption spectral regions are the same for B and C troughs, while the A component of the BAL varies independently. This suggests a change in the ionization state of the absorbing gas for B and C components and tangential motion for the A component, as causes of this temporal behavior. Accordingly, it is possible to provide an upper limit for distance of the gas responsible for the A component of $R\rm_{out}^{A}$$\le$58 pc, and in turn, a kinetic power of $\dot{E}\rm_{K,ufo}$ $\le$5.2 $\times$ 10$^{44}$ erg s$\rm^{-1}$. We also obtain $R\rm_{out}^{B,C}$ $\le$2.7 kpc for B and C components, which implies an upper limit estimation of $\dot{E}\rm_{K,ufo}$ $\le$2.1$\times$10$^{46}$ erg s$\rm^{-1}$ and $\dot{E}\rm_{K,ufo}$ $\le$1.4$\times$10$^{46}$ erg s$\rm^{-1}$, respectively. Future spectral monitoring with high-resolution instruments is mandatory to accurately constrain physical properties of the BAL UFO discovered in the UV spectrum of J1538+0855.

An observer moving with respect to the cosmic rest frame should observe a concentration and brightening of galaxies in the direction of motion and a spreading and dimming in the opposite direction. The velocity inferred from this dipole should match that of the cosmic microwave background (CMB) temperature dipole if galaxies are on average at rest with respect to the CMB rest frame. However, recent studies have claimed a many-fold enhancement of galaxy counts and flux in the direction of the solar motion compared to the CMB expectation, calling into question the standard cosmology. Here we show that the sky distribution and brightness of extragalactic radio sources are consistent with the CMB dipole in direction and velocity. We use the first epoch of the Very Large Array Sky Survey combined with the Rapid Australian Square Kilometer Array Pathfinder Continuum Survey to estimate the dipole via several different methods, and all show similar results. Typical fits find a $331^{+161}_{-107}$ km s$^{-1}$ velocity dipole with apex $(\ell,b) = (271^{+55}_{-58}, 56^{+13}_{-35})$ in Galactic coordinates from source counts and $399^{+264}_{-199}$ km s$^{-1}$ toward $(\ell,b) = (301^{+30}_{-30}, 43^{+19}_{-17})$ from radio fluxes. These are consistent with the CMB-solar velocity, 370 km s$^{-1}$ toward $(\ell,b) = (264, 48)$, and show that galaxies are on average at rest with respect to the rest frame of the early universe, as predicted by the canonical cosmology.

One of the earliest indicators of the importance of shock acceleration of solar energetic particles (SEPs) was the broad spatial extent of the "gradual" SEP events produced as the shock waves, driven by wide, fast coronal mass ejections (CMEs), expand across the Sun. Contrasting "impulsive" SEP events, with characteristic enhancements of 3He and of heavy elements, are now associated with magnetic reconnection on open field lines in solar jets. However, large shock waves can also traverse pools of residual impulsive suprathermal ions and jets can produce fast CMEs that drive shock waves; in both cases shocks reaccelerate ions with the "impulsive" abundance signatures as well as coronal plasma. These more-complex events produce "excess protons" that identify this process, and recently, differences in the distribution of 4He abundances have also been found to depend upon the combination of seed population and acceleration mode. Extreme differences in the 4He abundances may reflect underlying differences in the abundances of the coronal regions being sampled by solar jets and, surprisingly, SEP events where shock waves sample two seed-particle populations seem to have about twice the 4He/O ratio of those with a single source.

We study the impact of the environment on galaxies as they fall in and orbit in the potential well of a Local Group (LG) analogue, following them with high cadence. The analysis is performed on eight disc satellite galaxies from the CIELO suite of hydrodynamical simulations. All galaxies have stellar masses within the range $[10^{8.1} - 10^{9.56}] M_{\sun} $h$^{-1}$. We measure tidal torques, ram pressure and specific star formation rates (sSFR) as a function of time, and correlate them with the amount of gas lost by satellites along their orbits. Stronger removal episodes occur when the disc plane is oriented perpendicular to the direction of motion. More than one peripassage is required to significantly modify the orientations of the discs with respect to the orbital plane. The gas removed during the interaction with the central galaxies may be also found opposite to the direction of motion, depending on the orbital configuration. Satellites are not totally quenched when the galaxies reach their first peripassage, and continue forming about $10\%$ of the final stellar mass after this event. The fraction of removed gas is found to be the product of the joint action of tidal torque and ram pressure, which can also trigger new star formation activity and subsequent supernova feedback.

The majority of stars have one or more stellar companions. As exoplanets continue to be discovered, it is crucial to examine planetary systems to identify their stellar companions. By observing a change in proper motion, companions can be detected by the acceleration they induce on their host stars. We selected 701 stars from the Hipparcos-Gaia Catalog of Accelerations (HGCA) that have existing adaptive optics imaging data gathered with Gemini/NIRI. Of these, we examined 21 stars known to host planet candidates and reduced their archival NIRI data with Gemini's DRAGONS software. We assessed these systems for companions using the NIRI images as well as Renormalized Unit Weight Error values in Gaia and accelerations in the HGCA. We detected three known visible companions and found two more systems with no visible companions but astrometric measurements indicating likely unresolved companions.

Current and future cosmic microwave background (CMB) experiments fielding kilo-pixel arrays of transition-edge sensor (TES) bolometers require accurate and robust gain calibration methods. We simplify and refactor the standard TES model to directly relate the detector responsivity calibration and optical time constant to the measured TES current $I$ and the applied bias current $I_{\mathrm{b}}$. The calibration method developed for the Cosmology Large Angular Scale Surveyor (CLASS) TES bolometer arrays relies on current versus voltage ($I$-$V$) measurements acquired daily prior to CMB observations. By binning Q-band (40GHz) $I$-$V$ measurements by optical loading, we find that the gain calibration median standard error within a bin is 0.3%. We test the accuracy of this "$I$-$V$ bin" detector calibration method by using the Moon as a photometric standard. The ratio of measured Moon amplitudes between detector pairs sharing the same feedhorn indicates a TES calibration error of 0.5%. We also find that for the CLASS Q-band TES array, calibrating the response of individual detectors based solely on the applied TES bias current accurately corrects TES gain variations across time but introduces a bias in the TES calibration from data counts to power units. Since the TES current bias value is set and recorded before every observation, this calibration method can always be applied to raw TES data and is not subject to $I$-$V$ data quality or processing errors.

Over the past decade, the BeSSeL Survey and the VERA project have measured trigonometric parallaxes to approximately 250 massive, young stars using VLBI techniques. These sources trace spiral arms over nearly half of the Milky Way. What is now needed are accurate distances to such stars which are well past the Galactic center. Here we analyze the potential for addressing this need by combining line-of-sight velocities and proper motions to yield 3D kinematic distance estimates. For sources within about 10 kpc of the Sun, significant systematic uncertainties can occur, and trigonometric parallaxes are generally superior. However, for sources well past the Galactic center, 3D kinematic distances are robust and more accurate than can usually be achieved by trigonometic parallaxes.

The Saturn System has been studied in detail by the Cassini-Huygens Mission. A major thrust of those investigations has been to understand how Saturn formed and evolved and to place Saturn in the context of other gas giants and planetary systems in general. Two models have been proposed for the formation of the giant planets,the core accretion model and the disk instability model. The heavy element enrichment, core size, and internal structure of Saturn, compared to Jupiter strongly favor the core accretion model as for Jupiter. Two features of the core accretion model that are distinct from the disk instability model are the growth of a core with a mass several times that of the Earth, followed by runaway collapse of gas onto the core once a mass threshold is reached. The heavy element core grows slowly over millions of years through accretion of cm-m sized pebbles, even larger bodies, and moon sized embryos in the gaseous disk. The abundance pattern of heavy elements is thus a key constraint on formation models. C, N, S, and P at Saturn are presently known to varying degree of uncertainty. The He to H ratio in the atmosphere is crucial for understanding heat balance, interior processes, and planetary evolution, but present values at Saturn range from low to high, allowing for a wide range of possibilities. While the very low values are favored to explain excess luminosity, high values might indicate presence of layered convection in the interior, resulting in slow cooling. Additional insight into Saturn's formation comes from the unique data on the rings from Cassini's Grand Finale orbits. While the solar system is the only analog for the extra solar systems, detection of the alkali metals and water in giant exoplanets is useful for understanding the formation and evolution of Saturn, where such data are presently lacking.

The major-axis density profiles of bars are known to be either exponential or 'flat'. We develop an automated non-parametric algorithm to detect flat profiles and apply it to a suite of simulations (with and without gas). We demonstrate that flat profiles are a manifestation of a bar's secular growth, producing a 'shoulder' region (an overdensity above an exponential) in its outskirts. Shoulders are not present when bars form, but develop as the bar grows. If the bar does not grow, shoulders do not form. Shoulders are often accompanied by box/peanut bulges, but develop separately from them and are independent tracers of a bar's growth. They can be observed at a wide range of viewing orientations with only their slope varying significantly with inclination. We present evidence that shoulders are produced by looped x1 orbits. Since the growth rate of the bar moderately correlates with the growth rate of the shoulder strength, these orbits are probably recently trapped. Shoulders therefore are evidence of bar growth. The properties of the shoulders do not, however, establish the age of a bar, because secondary buckling or strong spirals may destroy shoulders, and also because shoulders do not form if the bar does not grow much. In particular, our results show that an exponential profile is not necessarily an indication of a young bar.

Thermal convection is commonly believed to be the energy source of stellar or planetary dynamo. In this short paper we provide another possibility, namely large-scale tidal flow. In close binary stars, say, solar-like stars with orbital period at 2 or 3 days, large-scale tidal flow is comparable to or even stronger than convective flow, and it can induce magnetic dynamo action. Based on dynamo equation and tidal theory we estimate the magnetic energy induced by large-scale tidal flow, which is proportional to the cube of orbital frequency. Our estimation can be tested by the future spectropolarimetric observations and numerical simulations for close binary stars.

Gamma-ray bursts (GRB) are the most intense electromagnetic (EM) sources in the Universe. Long GRB (LGRB) correspond to those events with a typical prompt emission of more than a few seconds. It is generally assumed that they are originated after an implosion of a very massive star within a central compact object engine that can be either a black hole (BH) or a rapidly-spinning highly-magnetized neutron star (NS). Nevertheless, one of the most challenging aspects of defining a unique model is that the progenitor remains initially hidden for direct EM observation. In this work, we investigate the evolution of thermally-produced neutrino properties in both GRB progenitors to provide an alternative solution. We consider the characteristics of both progenitors and the fireball scenario to calculate the oscillation probabilities within a three-flavor admixture regime. Then we obtain the expected neutrino ratio and we also estimate the number of events from these sources that could be detected in the future Hyper-Kamiokande (Hyper-K) detector, considering a sample of previously observed GRB with remarkably signs of being magnetar-produced. Our findings indicate that examining the predicted neutrino rates result in an additional mechanism to determine the type of progenitor associated with these events. This is especially useful when, for instance, we cannot directly observe an electromagnetic counterpart, such as so-called "failed" GRB with hidden jets, or when light curve analysis is inconclusive.

We report on high resolution observations of recurrent fan-like jets by the Goode Solar telescope (GST) in multi-wavelengths inside a sunspot group. The dynamics behaviour of the jets is derived from the Ha line profiles. Quantitative values for one well-identified event have been obtained showing a maximum projected velocity of 42 km s^-1 and a Doppler shift of the order of 20 km s^-1. The footpoints/roots of the jets have a lifted center on the Ha line profile compared to the quiet sun suggesting a long lasting heating at these locations. The magnetic field between the small sunspots in the group shows a very high resolution pattern with parasitic polarities along the inter-granular lanes accompanied by high velocity converging flows (4 km s^-1) in the photosphere. Magnetic cancellations between the opposite polarities are observed in the vicinity of the footpoints of the jets. Along the inter-granular lanes horizontal magnetic field around 1000 Gauss is generated impulsively. Overall, all the kinetic features at the different layers through photosphere and chromosphere favor a convection-driven reconnection scenario for the recurrent fan-like jets, and evidence a site of reconnection between the photosphere and chromosphere corresponding to the inter-granular lanes.

Gravitational waves (GWs) originated from mergers of stellar-mass binary black holes (SBBHs) are considered as dark sirens in cosmology since they usually do not have electromagnetic counterparts. In order to study cosmos with these events, we not only need the luminosity distances extracted from GW signals, but also require the redshift information of sources via, say, matching GW sky localization with galaxy catalogs. Based on such a methodology, we explore how well decihertz GW detectors, DO-Optimal and DECIGO, can constrain cosmological parameters. Using Monte-Carlo simulated dark sirens, we find that DO-Optimal can constrain the Hubble parameter to ${\sigma_{H_0}} / {H_0}\, \lesssim 0.2\%$ when estimating $H_0$ alone, while DECIGO performs better by a factor of 6 with ${\sigma_{H_0}} / {H_0}\lesssim 0.03\%$. Such a good precision of $H_0$ will shed light on the $H_0$ tension. For multiple-parameter estimation, DECIGO can still reach a level of ${\sigma_{H_0}} / {H_0} \lesssim 5\%$. The reason why decihertz detectors perform well is explained by their large numbers of SBBH GW events with good distance and angular resolution.

Spokes in Saturn's rings are radially-extended structures consisting of dust grains. Although spacecraft and space telescope observations have revealed various detailed features of the spokes and their time variation, their formation mechanism is still under debate. Previous models examined charging mechanisms to attempt at explaining dust release from cm-sized ring particles; however, the attempt has been unsuccessful, because the electrostatic force caused by such charging mechanisms is much weaker than the cohesive force acting on dust grains at ordinary conditions in the ring environment. Here we propose a novel model for the formation of the spokes, where the temperature dependence of cohesion plays an essential role. Ring particles with a temperature below 60K adsorb an O2 ring atmosphere, which facilitates release of dust grains from them by a reduction in the cohesive force between the grains and the particles on the morning ansa. Then, intense electrostatic forces sufficient to overcome the cohesive force are generated on the surface of ring particles and the released dust grains form the structure of spokes. Our model explains observational features of the spokes including their longitudinal location, lifetime, radial expansion velocity, and seasonality.

The mismatch between different independent measurements of the expansion rate of the Universe is known as the Hubble constant ($H_0$) tension, and it is a serious and pressing problem in cosmology. We investigate this tension considering the dataset from the Pantheon sample, a collection of 1048 Type Ia Supernovae (SNe Ia) with a redshift range $0<z<2.26$. We perform a binned analysis in redshift to study if the $H_0$ tension also occurs in SNe Ia data. Hence, we build equally populated subsamples in three and four bins, and we estimate $H_{0}$ in each bin considering the $\Lambda$CDM and $w_{0}w_{a}$CDM cosmological models. We perform a statistical analysis via a Markov Chain Monte Carlo (MCMC) method for each bin. We observe that $H_0$ evolves with the redshift, using a fit function $H_{0}(z)=\tilde{H}_{0} (1+z)^{-\alpha}$ with two fitting parameters $\alpha$ and $\tilde{H}_{0}$. Our results show a decreasing behavior of $H_0$ with $\alpha\sim 10^{-2}$ and a consistency with no evolution between 1.2 $\sigma$ and 2.0 $\sigma$. Considering the $H_0$ tension, we extrapolate $H_{0}(z)$ until the redshift of the last scattering surface, $z=1100$, obtaining values of $H_0$ consistent in 1 $\sigma$ with the cosmic microwave background (CMB) measurements by Planck. Finally, we discuss possible $f(R)$ modified gravity models to explain a running Hubble constant with the redshift, and we infer the form of the scalar field potential in the dynamically equivalent Jordan frame.

The identification of a virial broadening estimator in the quasar UV rest frame suitable for black hole mass computation at high redshift has become an important issue. We compare the HI Balmer H-beta line width to the ones of two intermediate ionization lines: the Aliii 1860 doublet and the Ciii] 1909 line, over a wide interval of redshift and luminosity (0 < z < 3.5; 43 < logL < 48.5 [erg a/]), for 48 sources belonging to the quasar population characterized by mid-to-high values of the Eddington ratio (Population A). The present analysis indicates that the line width of Aliii 1860 and H-beta are highly correlated, and can be considered equivalent for most Population A quasars over five orders of magnitude in luminosity; forCiii] 1909, multiplication by a constant correction factor xi ~ 1.25 is sufficient to bring the FWHM of Ciii] in agreement with the one of H-betaa. The statistical concordance between low-ionization and intermediate-ionization lines suggests that they predominantly arise from the same virialized part of the broad line region. However, blueshifts of modest amplitude (few hundred km /s) with respect to the quasar rest frame and an excess (~ 1.1) Aliii broadening with respect to H-beta are found in a fraction of our sample. Scaling laws to estimate M_BH of high redshift quasar using the Aliii and the Ciii] line widths have rms scatter ~ 0.3 dex. The Aliii scaling law takes the form log M_BH ~ 0.58 log L1700,44 + 2 log FWHM + 0.49 [solar masses].

From recently-acquired, high-resolution images obtained by the Cassini spacecraft, we examine the patterns and spatial distributions of rayed craters on Dione. We identify 29 rayed craters with diameters larger than 2km on Dione's surface. The density of rayed craters and theoretical cratering rates indicate that the retention time for rays on Dione can be approximately 1-50 My. Such a short retention time is interpreted to be due to bombardment of plasma and E-ring particles, as well as implantation of dark particles (presumably the same dark material found on Hyperion, Iapetus, and other saturnian satellites). We also find that when the ray system of Creusa crater was formed, it extended over most of the surface of Dione. Later, the ray system deposited on the trailing hemisphere might have been partially erased, mostly due to implantation of dark particles, which may have also removed other bright ray systems in that region. The pattern of Creusa's ray system implies that the implantation of the dark material occurred more recent than both the age of Creusa crater and the typical retention time for rays on Dione.

Current endeavours in exoplanet characterisation rely on atmospheric retrieval to quantify crucial physical properties of remote exoplanets from observations. However, the scalability and efficiency of the technique are under strain with increasing spectroscopic resolution and forward model complexity. The situation becomes more acute with the recent launch of the James Webb Space Telescope and other upcoming missions. Recent advances in Machine Learning provide optimisation-based Variational Inference as an alternative approach to perform approximate Bayesian Posterior Inference. In this investigation we combined Normalising Flow-based neural network with our newly developed differentiable forward model, Diff-Tau, to perform Bayesian Inference in the context of atmospheric retrieval. Using examples from real and simulated spectroscopic data, we demonstrated the superiority of our proposed framework: 1) Training Our neural network only requires a single observation; 2) It produces high-fidelity posterior distributions similar to sampling-based retrieval and; 3) It requires 75% less forward model computation to converge. 4.) We performed, for the first time, Bayesian model selection on our trained neural network. Our proposed framework contribute towards the latest development of a neural-powered atmospheric retrieval. Its flexibility and speed hold the potential to complement sampling-based approaches in large and complex data sets in the future.

We attempt to interpret the cosmic-ray positron excess by injection from the nearby pulsar Geminga, assuming a two-zone diffusion scenario and an injection spectrum with a low energy cutoff. Since the high energy positrons and electrons from Geminga can induce $\gamma$ rays via inverse Compton scattering, we take into account the extended $\gamma$-ray observations around Geminga from HAWC for $\sim 10$ TeV and from Fermi-LAT for $\mathcal{O}(10)$ GeV. According to the extended $\gamma$-ray observation claimed by an analysis of Fermi-LAT data, we find that Geminga could explain the positron excess for a $40\%$ energy conversion efficiency into positrons and electrons. However, based on the constraint on the extended $\gamma$ rays given by another Fermi-LAT analysis, positrons from Geminga would be insufficient to account for the positron excess. A further robust analysis of Fermi-LAT data for the extended $\gamma$ rays would be crucial to determine whether Geminga can explain the positron excess or not.

The trailing hemisphere of Dione is characterized by the Wispy Terrain, where it exhibits a hemispheric-scale network of extensional tectonic faults superposed on the moon's cratered surface. The faults likely reflect past endogenic activity and Dione's interior thermal history. Although fresh exposures of pristine scarps indicate that the timing of the faulting is relatively recent, the absolute age of the faulting remains uncertain. To estimate the timing of the faulting, we investigated stratigraphic relationships between impact craters and faults. Using high-resolution images obtained by ISS cameras onboard the Cassini spacecraft, we investigated craters with diameters exceeding or equal to 10 km that coincide spatially with the faults, and classified the craters as crosscut craters or superposed craters. As a result, at least 82% of the craters were interpreted as clear examples of crosscut craters and 12% of the craters were interpreted to be candidates of superposed craters, although stratigraphic relationships are often ambiguous. The paucity of superposed craters and a predicted cratering rate indicate that the faulting of the Wispy Terrain is 0.30-0.79 Ga. If 12-18% of the craters are assumed to be superposed, the timing of the faulting could be in the range 0.30-0.79 Ga. However, it is possible that the faulting of the Wispy Terrain is still ongoing.

Context. To enable radial velocity (RV) precision on the order of ~0.1 m/s required for the detection of Earth-like exoplanets orbiting solar-type stars, the main obstacle lies in mitigating the impact of stellar activity. Aims. This study investigates the dependence of derived RVs with respect to the formation temperature of spectral line segments. Methods. Using spectral synthesis, we compute for each observed wavelength point of unblended spectral lines the stellar temperature below which 50% of the emergent flux originates. We can then construct RV time series for different temperature ranges, using template matching. Results. With HARPS-N solar data and HARPS $\alpha$ Cen B measurements, we demonstrate on time intervals of prominent stellar activity that the activity-induced RV signal has different amplitude and periodicity depending on the temperature range considered. We compare the solar measurements with simulated contributions from active surface regions seen in simultaneous images, and find that the suppression of convective motion is the dominant effect. Conclusions. From a carefully selected set of spectral lines, we are able to measure the RV impact of stellar activity at various stellar temperatures ranges. We are able to strongly correlate the effect of convective suppression with spectral line segments formed in hotter temperature ranges. At cooler temperatures, the derived RVs exhibit oppositely directed variations compared to the average RV time series and stronger anti-correlations with chromospheric emission.

We present the first branon dark matter (DM) search in the very high-energy gamma-ray band with observations of the dwarf spheroidal galaxy Segue~1 carried out by the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system. Branons are new degrees of freedom that appear in flexible brane-world models corresponding to brane fluctuations. They behave as weakly interacting massive particles, which are natural DM candidates. In the absence of a gamma-ray signal in the Segue~1 data, we place constraints on the branon DM parameter space by using a binned likelihood analysis. Our most constraining limit to the thermally-averaged annihilation cross-section (at $95\%$ confidence level) corresponds to $ \langle \sigma v \rangle \simeq 1.4 \times 10^{-23}~\text{cm}^{3}\text{s}^{-1} $ at a branon DM mass of $ \sim 0.7~\text{TeV}$.

We study the effects of the magnetic fields on the formation of massive, self-gravitationally bound cores (MBCs) in high-speed cloud-cloud collisions (CCCs). Extending our previous work (Sakre et al. 2021), we perform magnetohydrodynamic simulations following the high-speed (20 - 40 km s$^{-1}$) collisions between two magnetized (4 $\mu$G initially), turbulent clouds of different sizes in the range of 7 - 20 pc. We show that a magnetic field effect hinders the core growth, particularly after a short-duration collision during which cores cannot get highly bound. In such a case, a shocked region created by the collision rapidly expands to the ambient medium owing to the enhanced magnetic pressure, resulting in the destruction of the highly unbound cores and suppression of gas accretion to massive cores. This negative effect on the MBC formation is a phenomenon not seen in the past hydrodynamic simulations of similar CCC models. Together with our previous work, we conclude that the magnetic fields provide the two competing effects on the MBC formation in CCC; while they promote the mass accumulation into cores during a collision, they operate to destroy cores or hinder the core growth after the collision. The duration of collision determines which effect prevails, providing the maximum collision speed for the MBC formation with given colliding clouds. Our results agree with the observed trend among CCC samples in the corresponding column density range; clouds with higher relative velocity require higher column density for the formation of massive stars (Enokiya et al. 2021).

We perform a direct search for an isotropic stochastic gravitational-wave background (SGWB) produced by cosmic strings in the Parkes Pulsar Timing Array second data release. We find no evidence for such an SGWB, and therefore place $95\%$ confidence level upper limits on the cosmic string tension, $G\mu$, as a function of the reconnection probability, $p$, which can be less than 1 in the string-theory-inspired models. The upper bound on the cosmic string tension is $G\mu \lesssim 5.1 \times 10^{-10}$ for $p = 1$, which is about five orders of magnitude tighter than the bound derived from the null search of individual gravitational wave burst from cosmic string cusps in the PPTA DR2.

Based on the data of the solar wind (SW) measurements of the OMNI base for the period 1976-2019, the behavior of SW types as well as plasma and interplanetary magnetic field (IMF) parameters for 21-24 solar cycles (SCs) is studied. It is shown that with the beginning of the Era of Solar Grand Minimum (SC 23), the proportion of magnetic storms initiated by CIR increased. In addition, a change in the nature of SW interaction with the magnetosphere could occur due to a decrease in the density, temperature, and IMF of the solar wind.

The copious scientific literature produced after the detection of GW170817 electromagnetic counterpart demonstrated the importance of a prompt and accurate localization of the gravitational wave within the co-moving volume. In this letter, we present FIGARO, a ready to use and publicly available software that relies on Bayesian non-parametrics. FIGARO is designed to run in parallel with parameter estimation algorithms to provide updated three-dimensional volume localization information. Differently from any existing algorithms, the analytical nature of the FIGARO reconstruction allows a ranking of the entries of galaxy catalogues by their probability of being the host of a gravitational wave event, hence providing an additional tool for a prompt electromagnetic follow up of gravitational waves. We illustrate the features of FIGARO on binary black holes as well as on GW170817. Finally, we demonstrate the robustness of FIGARO by producing so-called pp-plots and we present a method based on information entropy to assess when, during the parameter estimation run, it is reasonable to begin releasing skymaps.

A discussion of the history of scientific computing for Radio Astronomy in the Cavendish Laboratory of the University of Cambridge in the decades after the Second World War. This covers the development of the aperture synthesis technique for Radio Astronomy and how that required using the new computing technology developed by the University's Mathematical Laboratory: the EDSAC, EDSAC 2 and TITAN computers. It looks at the scientific advances made by the Radio Astronomy group, particularly the assembling of evidence which contradicted the Steady State Hypothesis. It also examines the software advances that allowed bigger telescopes to be built: the Fast Fourier Transform (FFT) and the degridding algorithm. Throughout, the contribution of women is uncovered, from the diagrams they drew for scientific publications, through programming and operating computers, to writing scientific papers.

The Probabilistic Solar Particle Event foRecasting (PROSPER) model predicts the probability of occurrence and the expected peak flux of Solar Energetic Particle (SEP) events. Predictions are derived for a set of integral proton energies (i.e. E$>$10, $>$30 and $>$100 MeV) from characteristics of solar flares (longitude, magnitude), coronal mass ejections (width, speed) and combinations of both. Herein the PROSPER model methodology for deriving the SEP event forecasts is described and the validation of the model, based on archived data, is presented for a set of case studies. The PROSPER model has been incorporated into the new operational Advanced Solar Particle Event Casting System (ASPECS) tool to provide nowcasting (short term forecasting) of SEP events as part of ESA's future SEP Advanced Warning System (SAWS). ASPECS also provides the capability to interrogate PROSPER for historical cases via a run on demand functionality.

Rocky bodies of the inner solar system display a systematic depletion of the "Moderately Volatile Elements" (MVEs) that correlates with the expected condensation temperature of their likely host materials under protoplanetary nebula conditions. In this paper, we present and test a new hypothesis in which open system loss processes irreversibly remove vaporized MVEs from high nebula altitudes, leaving behind the more refractory solids residing much closer to the midplane. The MVEs irreversibly lost from the nebula through these open system loss processes are then simply unavailable for condensation onto planetesimals forming even much later, after the nebula cooled, overcoming a critical difficulty encountered by previous models of this type. We model open system loss processes operating at high nebula altitudes, such as resulting from disk winds flowing out of the system entirely, or layered accretion directly onto the young sun. We find that mass loss rates higher than found in typical T-Tauri disk winds, lasting short periods of time, are most satisfactory, pointing to multiple intense early outburst stages. Using our global nebula model, incorporating realistic particle growth and inward drift for solids, we constrain how much the MVE depletion signature in the inner region is diluted by the drift of undepleted material from the outer nebula. We also find that a significant irreversible loss of the common rock-forming elements (Fe, Mg, Si) can occur, leading to a new explanation of another longstanding puzzle of the apparent "enhancement" in the relative abundance of highly refractory elements in chondrites.

Compact groups of galaxies are devised as extreme environments where interactions may drive galaxy evolution. In this work, we analysed whether the luminosities of galaxies inhabiting compact groups differ from those of galaxies in loose galaxy groups. We computed the luminosity functions of galaxy populations inhabiting a new sample of 1412 Hickson-like compact groups of galaxies identified in the Sloan Digital Sky Survey Data Release 16. We observed a characteristic absolute magnitude for galaxies in compact groups brighter than that observed in the field or loose galaxy systems. We also observed a deficiency of faint galaxies in compact groups in comparison with loose systems. Our analysis showed that the brightening is mainly due to galaxies inhabiting the more massive compact groups. In contrast to what is observed in loose systems where only the luminosities of Red (and Early) galaxies show a dependency with group mass, luminosities of Red and Blue (also Early and Late) galaxies in compact groups are affected similarly as a function of group virial mass. When using Hubble types, we observed that Elliptical galaxies in compact groups are the brightest galaxy population, and groups dominated by an Elliptical galaxy also display the brightest luminosities in comparison with those dominated by Spiral galaxies. Moreover, we show that the general luminosity trends can be reproduced using a mock catalogue obtained from a semi-analytical model of galaxy formation. These results suggest that the inner extreme environment in compact groups prompts a different evolutionary history for their galaxies.

The ISM is a turbulent, multi-phase, and multi-scale medium following scaling relations. Analytical models of galactic gaseous disks need to take into account the multi-scale and multi-phase nature of the interstellar medium. They can be described as clumpy star-forming accretion disks in vertical hydrostatic equilibrium, with the mid-plane pressure balancing the gravity of the gaseous and stellar disk. ISM turbulence is taken into account by applying Galactic scaling relations to the cold atomic and molecular gas phases. Turbulence is maintained through energy injection by supernovae. With the determination of the gas mass fraction at a given spatial scale, the equilibrium gas temperature between turbulent heating and line cooling, the molecular abundances, and the molecular line emission can be calculated. The resulting model radial profiles of IR, H{\sc i}, CO, HCN, and HCO$^+$ emission are compared to THINGS, HERACLES, EMPIRE, SINGS, and GALEX observations of 17 local spiral galaxies. The Toomre parameter, which measures the stability against star formation (cloud collapse), exceeds unity in the inner disk of a significant number of galaxies. In two galaxies it also exceeds unity in the outer disk. Therefore, in spiral galaxies $Q_{\rm tot}=1$ is not ubiquitous. The model gas velocity dispersion is consistent with the observed H{\sc i} velocity dispersion where available. Within our model HCN and HCO$^+$ is already detectable in relatively low-density gas ($\sim 1000$~cm$^{-3}$). CO and HCN conversion factors and molecular gas depletion time were derived. Both conversion factors are consistent with values found in the literature. Whereas in the massive galaxies the viscous timescale greatly exceeds the star formation timescale, the viscous timescale is smaller than the star formation timescale within $\rm{R}~\sim~2~\rm{R}_{\rm d}$, the disk scale length, in the low-mass galaxies.

Next-generation cosmic microwave background (CMB) surveys are expected to provide valuable information about the primordial universe by creating maps of the mass along the line of sight. Traditional tools for creating these lensing convergence maps include the quadratic estimator and the maximum likelihood based iterative estimator. Here, we apply a generative adversarial network (GAN) to reconstruct the lensing convergence field. We compare our results with a previous deep learning approach -- Residual-UNet -- and discuss the pros and cons of each. In the process, we use training sets generated by a variety of power spectra, rather than the one used in testing the methods.

We investigate the effects of non-zero spatial curvature on cosmic inflation in the light of cosmic microwave background (CMB) anisotropy measurements from the Planck 2018 legacy release and from the 2015 observing season of BICEP2 and the Keck Array. Even a small percentage of non-zero curvature today would significantly limit the total number of e-folds of the scale factor during inflation, rendering just-enough inflation scenarios with a kinetically dominated or fast-roll stage prior to slow-roll inflation more likely. Finite inflation leads to oscillations and a cutoff towards large scales in the primordial power spectrum and curvature pushes them into the CMB observable window. Using nested sampling, we carry out Bayesian parameter estimations and model comparisons taking into account constraints from reheating and horizon considerations. We confirm the preference of CMB data for closed universes with Bayesian odds of over $100:1$ and with a posterior on the curvature density parameter of $\Omega_{K,0}=-0.051\pm0.017$ for a curvature extension of LCDM and $\Omega_{K,0}=-0.031\pm0.014$ for Starobinsky inflation. Model comparisons of various inflation models give similar results as for flat universes with the Starobinsky model outperforming most other models.

We report the observation of non-stationary Quasi-Periodic Pulsations (QPPs) in high-energy particles during the impulsive phase of an X4.8 flare on 2002 July 23 (SOL2002-07-23T00:35). The X4.8 flare was simultaneously measured by the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Polarimeters, and Nobeyama Radioheliograph. The quasi-period of about 50 s, determined by the wavelet transform, is detected in the Gamma-ray line emission. Using the same method, a quasi-period of about 90 s is found in Gamma-ray continuum, hard X-ray (HXR) and radio emissions during almost the same time. Our observations suggest that the flare QPPs should be associated with energetic ions and nonthermal electrons that quasi-periodically accelerated by the repetitive magnetic reconnection. The different quasi-periods between Gamma-ray line and continuum/HXR/radio emissions indicate an apparent difference in acceleration or propagation between energetic ions and nonthermal electrons of this solar flare.

We used 13 years of Swift/BAT observations to probe the nature and origin of hard X-ray (14-195 KeV) emission in Centaurus A. Since the beginning of the Swift operation in 2004, significant X-ray variability in the 14-195 KeV band is detected, with mild changes in the source spectrum. Spectral variations became more eminent after 2013, following a softer-when-brighter trend. Using the power spectral density method, we found that the observed hard X-ray photon flux variations are consistent with a red-noise process of slope, $-1.3$ with no evidence for a break in the PSD. We found a significant correlation between hard X-ray and 230 GHz radio flux variations, with no time delay longer than 30 days. The temporal and spectral analysis rules out the ADAF (advection-dominated accretion flow) model, and confirms that the hard X-ray emission is produced in the inner regions of the radio jet.

Monitoring observations of solar microwave fluxes and their polarization began in Japan during the 1950s at Toyokawa and Mitaka. At present (April 2022), monitoring observations continue with the Nobeyama Radio Polarimeters (NoRP) at the Nobeyama campus of the National Astronomical Observatory of Japan (NAOJ). In this paper, we present a brief history of the solar microwave monitoring observations preceding those now carried out by NoRP. We then review the solar microwave obtained at Toyokawa and Nobeyama and their metadata. The datasets are publicly provided by the Solar Data Archive System (SDAS) operated by the Astronomy Data Center of the NAOJ, via http (https://solar.nro.nao.ac.jp/norp/) and FTP (this ftp URL) protocols.

The \textit{Herschel} Astrophysical Terahertz Large Area Survey (H-ATLAS), that has covered about 642 sq. deg. in 5 bands from 100 to 500 $\mu\rm m$, allows a blind flux-limited selection of blazars at sub-mm wavelengths. However, blazars constitute a tiny fraction of H-ATLAS sources and therefore identifying them is not a trivial task. Using the data on known blazars detected by the H-ATLAS we have defined a locus for 500\,$\mu$m selected blazars and exploited it to select blazar candidates in the H-ATLAS fields. Candidates and known blazars in the H-ATLAS equatorial and South Galactic Pole fields were followed up with the Australia Telescope Compact Array (ATCA) or with the Karl G. Jansky Very Large Array (VLA), and matched with existing radio- and mm-catalogues to reconstruct the spectral behaviour over at least 6 orders of magnitude in frequency. We identified a selection approach that, combining the information in the sub-mm and radio domains, efficiently singles out genuine blazars. In this way, we identified a sample of 39 blazars brighter than $S_{500\mu\rm m} = 35\,$mJy in the H-ATLAS fields. Tests made cross-matching the H-ATLAS catalogues with large catalogues of blazar candidates indicate that the sample is complete. The derived counts are compared with model predictions finding good consistency with the C2Ex model and with estimates based on ALMA data.

We carried out a cyanopolyyne line survey towards a large sample of HMSFRs using the Shanghai Tian Ma 65m Radio Telescope (TMRT). Our sample consisted of 123 targets taken from the TMRT C band line survey. It included three kinds of sources, namely those with detection of the 6.7 GHz CH3OH maser alone, with detection of the radio recombination line (RRL) alone, and with detection of both (hereafter referred to as Maser-only, RRL-only, and Maser-RRL sources, respectively). We detected HC3N in 38 sources, HC5N in 11 sources, and HC7N in G24.790+0.084, with the highest detection rate being found for Maser-RRL sources and a very low detection rate found for RRL-only sources. Their column densities were derived using the rotational temperature measured from the NH3 lines. And we constructed and fitted the far-infrared (FIR) spectral energy distributions. Based on these, we derive their dust temperatures, H2 column densities, and abundances of cyanopolyynes relative to H2. The detection rate, the column density, and the relative abundance of HC3N increase from Maser-only to Maser-RRL sources and decrease from Maser-RRL to RRL-only sources. This trend is consistent with the proposed evolutionary trend of HC3N under the assumption that our Maser-only, Maser-RRL, and RRL-only sources correspond to massive young stellar objects, ultra-compact HII regions, and normal classical HII regions, respectively. Furthermore, a statistical analysis of the integrated line intensity and column density of HC3N and shock-tracing molecules (SiO, H2CO) enabled us to find positive correlations between them. This suggests that HC3N may be another tracer of shocks, and should therefore be the subject of further observations and corresponding chemical simulations. Our results indirectly support the idea that the neutral--neutral reaction between C2H2 and CN is the dominant formation pathway of HC3N.

This is the second paper in a series of studies of the Coma cluster using the \textit{SRG}/eROSITA X-ray data obtained in the course of the calibration and performance verification observations. Here we focus on the region adjacent to the radio source 1253+275 (Radio Relic, RR hereafter). We show that the X-ray surface brightness steepest gradient at $\sim 79'$ ($\sim 2.2\,{\rm Mpc}\approx R_{200c}$) is almost co-spatial with the outer edge of RR, with an offset of about $\sim 100-150~\rm{kpc}$ between the derived position of the shock front and the brightest part of RR. As in several other relics, the Mach number of the shock derived from the X-ray surface brightness profile ($M_X\approx 1.9$) appears to be lower than needed to explain the slope of the integrated radio spectrum in the DSA model ($M_R\approx 3.5$) if the magnetic field is uniform and the radiative losses are fast. However, the shock geometry is plausibly much more complicated than a spherical wedge centered on the cluster, given a non-trivial correlation between radio, X-ray, and SZ images. While the complicated shock geometry alone might bias $M_X$ low, we speculate on a few other processes that can affect the $M_X$-$M_R$ relation, including a fine structure of the shock that might be modified by the presence of non-thermal filaments stretching across the shock. We also discuss the "history" of the radio galaxy NGC4789 located ahead of the relic in the context of the Coma-NGC4839 merger scenario.

Recently, many studies seem to reveal the existence of some correlations between dark matter and baryonic matter. In particular, the unexpected tight Radial Acceleration Relation (RAR) discovered in rotating galaxies has caught much attention. The RAR suggests the existence of a universal and fundamental acceleration scale in galaxies, which seems to challenge the $\Lambda$CDM model and favour some modified gravity theories. A large debate about whether RAR is compatible with the $\Lambda$CDM model has arisen. Here, by analysing the high quality velocity dispersion profiles of 13 E0-type elliptical galaxies in the SDSS-IV MaNGA sample and assuming a power-law function of radius $r$ for the 3-dimensional velocity dispersion in each galaxy, we report the RAR for E0-type elliptical galaxies and we show that the resultant RAR has more than $5\sigma$ deviations from the RAR in late-type galaxies. This new RAR provides an independent probe to falsify the existence of any universal acceleration scale in galaxies. Our result significantly challenges those modified gravity theories which suggest the existence of any universal acceleration scale.

We report on the observations, analysis and interpretation of the microlensing event MOA-2019- BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite source effects were observed. Therefore the angular Einstein ring radius cannot be measured from the light curve alone. However, the large event duration, t E about 80 days, allows a precise measurement of the microlensing parallax. In addition to the constraints on the angular radius and the apparent brightness I s of the source, we employ the Besancon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two Galactic models: the companion is likely a resident of the brown dwarf desert with a mass Mp about 30 MJup and the host is a main sequence dwarf star. The lens lies along the line of sight to the Galactic Bulge, at a distance of less then4 kpc. We estimate that in about 10 years, the lens and source will be separated by 55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground or space-based observatories.

Satellite systems around giant planets are immersed in a region of complex resonant configurations. Understanding the role of satellite resonances contributes to comprehending the dynamical processes in planetary formation and posterior evolution. Our main goal is to analyse the resonant structure of small moons around Uranus and propose different scenarios able to describe the current configuration of these satellites. We focus our study on the external members of the regular satellites interior to Miranda, namely Rosalind, Cupid, Belinda, Perdita, Puck, and Mab, respectively. We use N-body integrations to perform dynamical maps to analyse their dynamics and proximity to two-body and three-body mean-motion resonances (MMR). We found a complicated web of low-order resonances amongst them. Employing analytical prescriptions, we analysed the evolution by gas drag and type-I migration in a circumplanetary disc (CPD) to explain different possible histories for these moons. We also model the tidal evolution of these satellites using some crude approximations and found possible paths that could lead to MMRs crossing between pairs of moons. Finally, our simulations show that each mechanism can generate significant satellite radial drift leading to possible resonant capture, depending on the distances and sizes.

The direct imaging of potentially habitable Exoplanets is one prime science case for the next generation of high contrast imaging instruments on ground-based extremely large telescopes. To reach this demanding science goal, the instruments are equipped with eXtreme Adaptive Optics (XAO) systems which will control thousands of actuators at a framerate of kilohertz to several kilohertz. Most of the habitable exoplanets are located at small angular separations from their host stars, where the current XAO systems' control laws leave strong residuals.Current AO control strategies like static matrix-based wavefront reconstruction and integrator control suffer from temporal delay error and are sensitive to mis-registration, i.e., to dynamic variations of the control system geometry. We aim to produce control methods that cope with these limitations, provide a significantly improved AO correction and, therefore, reduce the residual flux in the coronagraphic point spread function. We extend previous work in Reinforcement Learning for AO. The improved method, called PO4AO, learns a dynamics model and optimizes a control neural network, called a policy. We introduce the method and study it through numerical simulations of XAO with Pyramid wavefront sensing for the 8-m and 40-m telescope aperture cases. We further implemented PO4AO and carried out experiments in a laboratory environment using MagAO-X at the Steward laboratory. PO4AO provides the desired performance by improving the coronagraphic contrast in numerical simulations by factors 3-5 within the control region of DM and Pyramid WFS, in simulation and in the laboratory. The presented method is also quick to train, i.e., on timescales of typically 5-10 seconds, and the inference time is sufficiently small (< ms) to be used in real-time control for XAO with currently available hardware even for extremely large telescopes.

The spectral energy distribution (SED) of galaxies provides fundamental information on the related physical processes. However, the SED is significantly affected by dust in its interstellar medium. Dust is mainly produced by asymptotic giant branch stars and Type II supernovae. In addition, the dust mass increases through the metal accretion, and the grain size changes by the collisions between the grains. The contribution of each process and the extinction depend on the size distribution. Therefore, the SED model should treat the evolution of the dust mass and size distribution. In spite of the importance of dust evolution, many previous SED models have not considered the evolution of the total mass and size distribution in a physically consistent manner. In this work, we constructed a new radiative transfer SED model, based on our dust evolution model consistent with the chemical evolution. To reduce the computational cost, we adopted the mega-grain and the one-dimensional plane parallel galaxy approximation. As a fiducial case, we calculated Milky Way-like galaxy SEDs at various ages under the closed-box model. We found that a galaxy at the age of 100~Myr does not produce small grains such as polycyclic aromatic hydrocarbons. After 1~Gyr, we observed a drastic increase of infrared emission and attenuation caused by a rapid increase of dust mass. This phenomenon can be treated appropriately for the first time by our new model. This model can be used for the SED fitting to a galaxy at any stage of evolution.

We present a large ${\sim 30" \times 30"}$ spectroscopic survey of the Galactic Center using the SINFONI IFU at the VLT. Combining observations of the last two decades we compile spectra of over $2800$ stars. Using the Bracket-$\gamma$ absorption lines we identify $195$ young stars, extending the list of known young stars by $79$. In order to explore the angular momentum distribution of the young stars, we introduce an isotropic cluster prior. This prior reproduces an isotropic cluster in a mathematically exact way, which we test through numerical simulations. We calculate the posterior angular momentum space as function of projected separation from Sgr~A*. We find that the observed young star distribution is substantially different from an isotropic cluster. We identify the previously reported feature of the clockwise disk and find that its angular momentum changes as function of separation from the black hole, and thus confirm a warp of the clockwise disk ($p \sim 99.2\%$). At large separations, we discover three prominent overdensities of angular momentum. One overdensity has been reported previously, the counter-clockwise disk. The other two are new. Determining the likely members of these structures, we find that as many as $75\%$ of stars can be associated with one of these features. Stars belonging to the warped clockwise-disk show a top heavy K-band luminosity function, while stars belonging to the larger separation features do not. Our observations are in good agreement with the predictions of simulations of in-situ star formation, and argue for common formation of these structures.

Massive star binaries are critical laboratories for measuring masses and stellar wind mass-loss rates. A major challenge is inferring viewing inclination and extracting information about the colliding wind interaction (CWI) region. Polarimetric variability from electron scattering in the highly ionized winds provides important diagnostic information about system geometry. We combine for the first time the well-known generalized treatment of \citet{brown_polarisation_1978} for variable polarization from binaries with the semi-analytic solution for the geometry and surface density CWI shock interface between the winds based on Canto et al 1996. Our calculations include some simplifications in the form of inverse square-law wind densities and the assumption of axisymmetry, but in so doing arrive at several robust conclusions. One is that when the winds are nearly equal (e.g., O\,+\,O binaries), the polarization has a relatively mild decline with binary separation. Another is that despite Thomson scattering being a gray opacity, the continuum polarization can show chromatic effects at ultraviolet wavelengths but will be mostly constant at longer wavelengths. Finally, when one wind dominates the other, as for example in WR+OB binaries, the polarization is expected to be larger at wavelengths where the OB component is more luminous, and generally smaller at wavelengths where the WR component is more luminous. This behavior arises because from the perspective of the WR star, the distortion of the scattering envelope from spherical is a minor perturbation situated far from the WR star. By contrast, the polarization contribution from the OB star is dominated by the geometry of the CWI shock.

The Vera C. Rubin Observatory's Legacy Survey of Space and Time is forecast to collect a large sample of Type Ia supernovae (SNe Ia) that could be instrumental in unveiling the nature of Dark Energy. The feat, however, requires measuring the two components of the Hubble diagram - distance modulus and redshift - with a high degree of accuracy. Distance is estimated from SNe Ia parameters extracted from light curve fits, where the average quality of light curves is primarily driven by survey parameters such as the cadence and the number of visits per band. An optimal observing strategy is thus critical for measuring cosmological parameters with high accuracy. We present in this paper a three-stage analysis aiming at quantifying the impact of the Deep Drilling (DD) strategy parameters on three critical aspects of the survey: the redshift completeness (originating from the Malmquist cosmological bias), the number of well-measured SNe Ia, and the cosmological measurements. Analyzing the current LSST survey simulations, we demonstrate that the current DD survey plans are characterized by a low completeness ($z~\sim$ 0.55-0.65), and irregular and low cadences (few days) that dramatically decrease the size of the well-measured SNe Ia sample. We then propose a modus operandi that provides the number of visits (per band) required to reach higher redshifts. The results of this approach are used to design a set of optimized DD surveys for SNe Ia cosmology. We show that most accurate cosmological measurements are achieved with Deep Rolling surveys characterized by a high cadence (one day), a rolling strategy (each field observed at least two seasons), and two sets of fields: ultra-deep ($z \gtrsim 0.8$) and deep ($z \gtrsim 0.6$) fields. We also demonstrate that a deterministic scheduler including a gap recovery mechanism is critical to achieve a high quality DD survey required for SNe Ia cosmology.

By assuming the photosphere located at the outmost edge of the ejecta, Arnett et al. (1980, 1982, 1989) presented the light curves of homologous explosions in supernovae analytically and numerically to include recombination effects. Actually as homologous expansion proceeds, the photosphere recedes deeper into the ejecta. In this situation, the photosphere radius increases at early times and decreases later on which can be described by a simple method proposed by Liu et al. (2018). To study how the photosphere recession effect the luminosity evolution, we impose a boundary condition on the photosphere to determine the spatial and time distribution of the temperature of the ejecta which is clarified to be reasonable. We find that the photosphere recession reduce the luminosity compared with the previous result without the recession, which can be tested with observations of Type-IIP supernovae.

Extreme emission line galaxies (EELGs) are a notable galaxy genus, ultimately being regarded as local prototypes of early galaxies at the cosmic noon. Robust characterisation of their stellar content, however, is hindered by the exceptionally high nebular emission present in their optical spectroscopic data. This study is dedicated into recovering the stellar properties of a sample of 414 EELGs as observed by the SDSS Survey. Such is achieved by means of the spectral synthesis code FADO, which self-consistently considers the stellar and nebular emission in an optical spectrum. Additionally, a comparative analysis was carried on, by further processing the EELGs sample with the purely stellar spectral synthesis code Starlight, and by extending the analysis to a sample of 697 normal star-forming galaxies, expected to be less affected by nebular contribution. We find that, for both galaxy samples, stellar mass and mean age estimates by Starlight are systematically biased towards higher values, and that an adequate determination of the physical and evolutionary properties of EELGs via spectral synthesis is only possible when nebular continuum emission is taken into account. Moreover, the differences between the two population synthesis codes can be ascribed to the degree of star-formation activity through the specific star-formation rate and the sum of the flux of the most prominent emission lines. As expected, on the basis of the theoretical framework, our results emphasise the importance of considering the nebular emission while performing spectral synthesis, even for galaxies hosting typical levels of star-formation activity.

Magnetars, a population of isolated neutron stars with ultra-strong magnetic fields of $\sim 10^{14}-10^{15}$ G, have been increasingly accepted to explain a variety of astrophysical transients. A nascent millisecond-period magnetar can release its spin-down energy and power bright sources such as Gamma-ray Bursts (GRBs) and their subsequent X-ray plateaus, Super Luminous Supernovae (SLSNe), and the fast X-ray transients such as CDF-S XT-2. Magnetars with ages of $10^3-10^4$ years have been observed within the Milky Way Galaxy, which are found to power diverse transients with the expense of their magnetic energy, in the form of giant flares and repeated soft-$\gamma$-ray or hard X-ray bursts and occasionally fast radio bursts (FRBs). Magnetar giant flares were also detected as disguised short GRBs from nearby galaxies . Here we report the identification of a GRB as a hyper flare of magnetar in a nearby galaxy. The magnitude of the hyper flare is about one thousand times brighter than that of a typical magnetar giant flare. A significant $\sim 80$ millisecond period is detected in the decaying light curve. Interpreting this period as the rotation period and given a magnetic field strength typical for a young magnetar, the age of the magnetar is constrained to be only a few weeks. The non-detection of a (superluminous) supernova nor a GRB weeks before the event further constrains that the magnetar is likely born from an off-axis merger event of two neutron stars. Our finding bridges the gap between the hypothetical millisecond magnetars and the observed Galactic magnetars, and points toward a broader channel of magnetar-powered gamma-ray transients.

The existence of a hypothetical Planet 9 lurking in the outer solar system has been proposed as an explanation for the the anomalous clustering in the orbits of some trans-Neptunian objects. Here we propose to use meteors arriving at Earth as messengers with the potential of revealing the presence of a hitherto undiscovered massive object. The peculiar meteor CNEOS 2014-01-08, recenty proposed as the first interstellar meteor, might be one such messenger. Its procedence on the sky matches the predicted band of Planet 9's orbit and it is actually compatible with the highest probability region. The odds of this coincidence being due to chance are of ~0.5%. Furthermore, some statistical anomalies about CNEOS 2014-01-08 are resolved under the hypothesis that it was flung at Earth by Planet 9, as opposed to being the result of an unmediated interstellar encounter with our planet. Based on the available data, we propose the region at coordinates RA:50.0{\pm}4{\deg}, dec:11.8{\pm}1.8{\deg} in the constellation of Aries, as the first candidate location for Planet 9.

Planet formation in protoplanetary discs requires dust grains to coagulate from the sub-micron sizes that are found in the interstellar medium into much larger objects. For the first time, we study the growth of dust grains during the earliest phases of star formation using three-dimensional hydrodynamical simulations. We begin with a typical interstellar dust grain size distribution and study dust growth during the collapse of a molecular cloud core and the evolution of the first hydrostatic core, prior to the formation of the stellar core. We examine how the dust size distribution evolves both spatially and temporarily. We find that the envelope maintains its initial population of small dust grains with little growth during these phases, except that in the inner few hundreds of au the smallest grains are depleted. However, once the first hydrostatic core forms rapid dust growth to sizes in excess of $100~\mu$m occurs within the core (before stellar core formation). Progressively larger grains are produced at smaller distances from the centre of the core. In rapidly-rotating molecular cloud cores, the `first hydrostatic core' that forms is better described as a pre-stellar disc that may be gravitationally unstable. In such cases, grain growth is more rapid in the spiral density waves leading to the larger grains being preferentially found in the spiral waves even though there is no migration of grains relative to the gas. Thus, the grain size distribution can vary substantially in the first core/pre-stellar disc even at these very early times.

Fragmentation is an important decay mechanism for polycyclic aromatic hydrocarbons (PAHs) under harsh interstellar conditions and represents a possible formation pathway for small molecules such as H2, C2H2, C2H4. Our aim is to investigate the dissociation mechanism of superhydrogenated PAHs that undergo energetic processing and the formation pathway of small hydrocarbons. We obtain, experimentally, the mass distribution of protonated tetrahydropyrene (C16H15 , py+5H+) and protonated hexahydropyrene (C16H17+, py+7H+) upon collision induced dissociation (CID). The IR spectra of their main fragments are recorded by infrared multiple-photon dissociation (IRMPD). Extended tight-binding (GFN2-xTB) based molecular dynamics simulations are performed in order to provide the missing structure information in experiment and identify fragmentation pathways. The pathways for fragmentation are further investigated at a hybrid-density functional theory (DFT) and dispersion corrected level. A strong signal for loss of 28 mass units of py+7H+ is observed both in the CID experiment and the MD simulation, while py+5H+ shows negligible signal for the product corresponding to a mass loss of 28. The 28 mass loss from py+7H+ is assigned to the loss of ethylene (C2H4) and a good fit between the calculated and experimental IR spectrum of the resulting fragment species is obtained. Further DFT calculations show favorable kinetic pathways for loss of C2H4 from hydrogenated PAH configurations involving three consecutive CH2 molecular entities. This joint experimental and theoretical investigation proposes a chemical pathway of ethylene formation from fragmentation of superhydrogenated PAHs. This pathway is sensitive to hydrogenated edges (e.g. the degree of hydrogenation and the hydrogenated positions). The inclusion of this pathway in astrochemical models may improve the estimated abundance of ethylene.

Streamer-blowout coronal mass ejections (SBO-CMEs) are the dominant CME population during solar minimum. Although they are typically slow and lack clear low-coronal signatures, they can cause geomagnetic storms. With the aid of extrapolated coronal fields and remote observations of the off-limb low corona, we study the initiation of an SBO-CME preceded by consecutive CME eruptions consistent with a multi-stage sympathetic breakout scenario. From inner-heliospheric Parker Solar Probe (PSP) observations, it is evident that the SBO-CME is interacting with the heliospheric magnetic field and plasma sheet structures draped about the CME flux rope. We estimate that $18 \, \pm \, 11\%$ of the CME's azimuthal magnetic flux has been eroded through magnetic reconnection and that this erosion began after a heliospheric distance of ${\sim}0.35$ AU from the Sun was reached. This observational study has important implications for understanding the initiation of SBO-CMEs and their interaction with the heliospheric surroundings.

Chromospheric swirls are considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determine their properties. We applied a recently developed automated chromospheric swirl detection method to time-series observations of a quiet region of the solar chromosphere obtained in the H$\alpha$-0.2 \r{A} wavelength of the H$\alpha$ spectral line by the CRISP instrument at the Swedish 1-m Solar Telescope. The algorithm exploits the morphological characteristics of swirling events in high contrast chromospheric observations and results in the detection of these structures in each frame of the time series and their tracking over time. We conducted a statistical analysis to determine their various properties, including a survival analysis for deriving the mean lifetime. A mean number of 146 $\pm$ 9 swirls was detected within the FOV at any given time. The mean surface density is found equal to $\sim$0.08 swirls$ $Mm$^{-2}$ and the occurrence rate is $\sim$10$^{-2}$ swirls$ $Mm$^{-2}$ min$^{-1}$. These values are much higher than those previously reported from chromospheric observations. The radii of the detected swirls range between 0.5 and 2.5 Mm, with a mean value equal to 1.3 $\pm$ 0.3 Mm, which is slightly higher than previous reports. The lifetimes range between 1.5 min and 33.7 min with an arithmetic mean value of $\sim$8.5 min. A survival analysis of the lifetimes, however, using the Kaplan-Meier estimator in combination with a parametric model results in a mean lifetime of 10.3 $\pm$ 0.6 min. An automated method sheds more light on their abundance than visual inspection, while higher cadence, higher resolution observations will most probably result in the detection of a higher number of such features on smaller scales and with shorter lifetimes.

We study the relativistic, inviscid, advective accretion flow around the black holes and investigate a key feature of the accretion flow, namely the shock waves. We observe that the shock-induced accretion solutions are prevalent and such solutions are commonly obtained for a wide range of the flow parameters, such as energy (${\cal E}$) and angular momentum ($\lambda$), around the black holes of spin value $0\le a_{\rm k} < 1$. When the shock is dissipative in nature, a part of the accretion energy is released through the upper and lower surfaces of the disc at the location of the shock transition. We find that the maximum accretion energies that can be extracted at the dissipative shock ($\Delta{\cal E}^{\rm max}$) are $\sim 1\%$ and $\sim 4.4\%$ for Schwarzschild black holes ($a_{\rm k}\rightarrow 0$) and Kerr black holes ($a_{\rm k}\rightarrow 1$), respectively. Using $\Delta{\cal E}^{\rm max}$, we compute the loss of kinetic power (equivalently shock luminosity, $L_{\rm shock}$) that is enabled to comply with the energy budget for generating jets/outflows from the jet base ($i.e.$, post-shock flow). We compare $L_{\rm shock}$ with the observed core radio luminosity ($L_R$) of black hole sources for a wide mass range spanning $10$ orders of magnitude with sub-Eddington accretion rate and perceive that the present formalism seems to be potentially viable to account $L_R$ of $16$ Galactic black hole X-ray binaries (BH-XRBs) and $2176$ active galactic nuclei (AGNs). We further aim to address the core radio luminosity of intermediate-mass black hole (IMBH) sources and indicate that the present model formalism perhaps adequate to explain core radio emission of IMBH sources in the sub-Eddington accretion limit.

We address a phenomenon of a confined circumstellar (CS) dense shell and powerful presupernova emission of SN 2020tlf (type IIP). Modeling the \ha\ line and the circumstellar interaction implies the CS shell radius of $\sim$10$^{15}$ cm and the mass of $\sim0.2M_{\odot}$ lost during $\sim$6 yr prior to the explosion. Spectra and photometry of the supernova after the explosion do not show apparent signature of the material lost by the presupernova during its powerful luminosity. This material presumably resided in the inner zone of the CS shell. We present a hydrodynamic model of the outcome of a flash with the energy of $5\times10^{48}$ erg in the convective nuclear burning zone. The model predicts the ejection of outer layers of the presupernova ($\sim0.1M_{\odot}$) and the luminosity of $10^{40}$ erg s$^{-1}$ during several hundreds days in accord with observations. We propose the Lighthill mechanism of acoustic waves generation by the turbulence of the convective nuclear burning zone to account for the phenomenon of a compact CS shell of supernovae related to the core collapse.

This paper presents multi-filter measurements of the night sky brightness at the South African Astronomical Observatory (SAAO) in Sutherland in the presence of a bright moon. The observations cover a wide range of sky directions, lunar phases and lunar positions. A revised simplified scattering model is developed for estimating the sky brightness due to moonlight that more accurately reflects the atmospheric extinction of the lunar beam compared to models frequently applied in astronomical studies. Contributions to night sky brightness due to sources other than moonlight are quantified and subtracted from the total sky background radiation to determine the spectral intensity and angular distribution of scattered moonlight. The atmospheric scattering phase function is then derived by comparing the sky brightening to the strength of the incoming lunar beam, estimated using a novel approach. The phase function is shown to be an excellent match to the combined theoretical Rayleigh and Mie scattering functions, the latter with a Henyey--Greenstein form instead of the exponential angular relationship often used in previous studies. Where deviations between measured and model sky brightness are evident in some bands these are explained by contributions from multiple scattering or airglow, and are quantified accordingly. The model constitutes an effective tool to predict sky brightness at SAAO in optical photometric bands, especially with a bright moon present. The methodology can also be readily be adapted for use at other astronomical sites. The paper furthermore presents $UBV(RI)_c$ and Str{\"o}mgren photometry for 49 stars, most with no prior such data.

We conduct the first case study towards developing optimal foreground mitigation strategies for neutral hydrogen (HI) intensity mapping using radio interferometers at low redshifts. A pipeline for simulation, foreground mitigation and power spectrum estimation is built, which can be used for ongoing and future surveys using MeerKAT and SKAO. It simulates realistic sky signals to generate visibility data given instrument and observation specifications, which is subsequently used to perform foreground mitigation and power spectrum estimation. A quadratic estimator formalism is developed to estimate the temperature power spectrum in visibility space. Using MeerKAT telescope specifications for observations in the redshift range z~0.25-0.30 corresponding to the MIGHTEE survey, we present a case study where we compare different approaches of foreground mitigation. We find that component separation in visibility space provides a more accurate estimation of HI clustering comparing to foreground avoidance, with the uncertainties being 30% smaller. Power spectrum estimation from image is found to be less robust with larger bias and more information loss when compared to estimation in visibility. We conclude that for z~0.25-0.30, the MIGHTEE survey will be capable of measuring the HI power spectrum from k~0.5 Mpc$^{-1}$ to k~10 Mpc$^{-1}$ with high accuracy. We are the first to show that, at low redshift, component separation in visibility space suppresses foreground contamination at large line-of-sight scales, allowing measurement of HI power spectrum closer to the foreground wedge, crucial for data analysis towards future detections.

We report detailed prompt emission observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor (ASIM) installed on the International Space Station ({\it ISS}) and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift of $z$ = 1.937 we find that GRB 210619B falls within the 10 most luminous bursts observed by Fermi so far. The energy-resolved prompt emission light curve of GRB 210619B exhibits an extremely bright hard emission pulse followed by softer/longer emission pulses. The low-energy photon indices ($\alpha_{\rm pt}$) values obtained using the time-resolved spectral analysis of the burst reveal a transition between the thermal (during harder pulse) to non-thermal (during softer pulse) outflow. We examine the correlation between spectral parameters and find that both peak energy and $\alpha_{\rm pt}$ exhibit the flux tracking pattern. The late time broadband photometric dataset can be explained within the framework of the external forward shock model with $\nu_m$ $< \nu_c$ $< \nu_{x}$ (where $\nu_m$, $\nu_c$, and $\nu_{x}$ are the synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral regime supporting a rarely observed hard electron energy index ($p<$ 2). We find moderate values of host extinction of E(B-V) = 0.14 $\pm$ 0.01 for the Small Magellanic Cloud (SMC) extinction law. In addition, we also report late-time optical observations with the 10.4\,m GTC placing deep upper limits for the host galaxy (located at $z$=1.937), favouring a faint, dwarf host for the burst.

Motivated by the recent discovery of interstellar objects passing through the solar system, and by recent developments in dynamical simulations, this paper reconsiders the likelihood for life bearing rocks to be transferred from one planetary system to another. The astronomical aspects of this lithopanspermia process can now be estimated, including the cross sections for rock capture, the velocity distributions of rocky ejecta, the survival times for captured objects, and the dynamics of the solar system in both its birth cluster and in the field. The remaining uncertainties are primarily biological, i.e., the probability of life developing on a planet, the time required for such an event, and the efficiency with which life becomes seeded in a new environment. Using current estimates for the input quantities, we find that the transfer rates are enhanced in the birth cluster, but the resulting odds for success are too low for panspermia to be a likely occurrence. In contrast, the expected inventory of alien rocks in the solar system is predicted to be substantial (where the vast majority of such bodies are not biologically active and do not interact with Earth).

Young massive clusters (YMCs) are compact ($\lesssim$1 pc), high-mass (>10${}^4$ M${}_{\odot}$) stellar systems of significant scientific interest. Due to their rarity and rapid formation, we have very few examples of YMC progenitor gas clouds before star formation has begun. As a result, the initial conditions required for YMC formation are uncertain. We present high-resolution (0.13$^{\prime\prime}$, $\sim$1000 au) ALMA observations and Mopra single-dish data, showing that Galactic Centre dust ridge `Cloud d' (G0.412$+$0.052, mass$\sim 7.6 \times 10^4$ M$_{\odot}$, radius$\sim 3.2$ pc) has the potential to become an Arches-like YMC (10$^4$ M$_{\odot}$, r$\sim$1 pc), but is not yet forming stars. This would mean it is the youngest known pre-star forming massive cluster and therefore could be an ideal laboratory for studying the initial conditions of YMC formation. We find 96 sources in the dust continuum, with masses $\lesssim$3 M$_{\odot}$ and radii of $\sim$10${}^3$ au. The source masses and separations are more consistent with thermal rather than turbulent fragmentation. It is not possible to unambiguously determine the dynamical state of most of the sources, as the uncertainty on virial parameter estimates is large. We find evidence for large-scale ($\sim$1 pc) converging gas flows, which could cause the cloud to grow rapidly, gaining 10$^4$ M$_{\odot}$ within 10$^5$ yr. The highest density gas is found at the convergent point of the large-scale flows. We expect this cloud to form many high-mass stars, but find no high-mass starless cores. If the sources represent the initial conditions for star formation, the resulting IMF will be bottom-heavy.

The scalar-induced gravitational waves (SIGWs) are attracting growing attention for probing extremely short-scale scalar perturbations via gravitational wave measurements. In this paper, we investigate the SIGWs from statistically anisotropic scalar perturbations, which are motivated in inflationary scenarios in the presence of e.g., a vector field. While the ensemble average of the SIGW energy spectrum is isotropic for the standard statistically isotropic scalar perturbations, the statistical anisotropy in the source introduces the multipole moments of the differential SIGW energy spectrum. We consider quadrupole anisotropy in the scalar power spectrum, and show that the SIGW spectrum has anisotropies up to $\ell=4$. We present generic formulas of the multipole moments and then apply them to the delta function like and log-normal source spectra. We find analytic expressions for the former case and show that the infrared scalings of the multipole moments are the same as the isotropic SIGWs. Interestingly, the monopole has an additional local minimum in the high-$k$ tail, a key feature to distinguish from the isotropic SIGWs. The latter log-normal case is analytic for the narrow-peak source, and we perform the numerical calculation for the broad peak. As one expects, the multipole moments become broader with the increasing source width. Our results are helpful to test isotropy of primordial density perturbations at extremely small scales through SIGWs.

We report measurements of the angular scale of cosmic homogeneity ($\theta_{h}$) using the recently released luminous red galaxy sample of the sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV LRG DR16). This consists on a model-independent method, as we only use the celestial coordinates of these objects to carry out such an analysis. The observational data is divided in thin redshift bins, namely $0.67<z<0.68$, $0.70<z<0.71$, and $0.73<z<0.74$, in order to avoid projection biases, and we estimate our uncertainties through a bootstrap method and a suite of mock catalogues. We find that the LRGs exhibit an angular scale of homogeneity which is consistent with the predictions of the standard cosmology.

When interpreted within the standard framework of Newtonian gravity and dynamics, the kinematics of stars and gas in dwarf galaxies reveals that most of these systems are completely dominated by their dark matter halos. These dwarf galaxies are thus among the best astrophysical laboratories to study the structure of dark halos and the nature of dark matter. We review the properties of the dwarf galaxies of the Local Group from the point of view of stellar dynamics. After describing the observed kinematics of their stellar components and providing an overview of the dynamical modelling techniques, we look into the dark matter content and distribution of these galaxies, as inferred from the combination of observed data and dynamical models. We also briefly touch upon the prospects of using nearby dwarf galaxies as targets for indirect detection of dark matter via annihilation or decay emission.

This article presents the history of the Visual Survey Group (VSG) - a Professional-Amateur (Pro-Am) collaboration within the field of astronomy working on data from several space missions (Kepler, K2 and TESS). This paper covers the formation of the VSG, its survey-methods including the most common tools used and its discoveries made over the past decade. So far, the group has visually surveyed nearly 10 million light curves and authored 69 peer-reviewed papers which mainly focus on exoplanets and discoveries involving multistellar systems found using the transit method. The preferred manual search-method carried out by the VSG has revealed its strength by detecting numerous sub-stellar objects which were overlooked or discarded by automated search programs, uncovering some of the most rare stars in our galaxy, and leading to several serendipitous discoveries of unprecedented astrophysical phenomena. The main purpose of the VSG is to assist in the exploration of our local Universe, and we therefore advocate continued crowd-sourced examination of time-domain data sets, and invite other research teams to reach out in order to establish collaborating projects.

The atmospheres of ultra-hot Jupiters have been characterized in detail through recent phase curve and low- and high-resolution emission and transmission spectroscopic observations. Previous numerical studies have analyzed the effect of the localized recombination of hydrogen on the atmospheric dynamics and heat transport of ultra-hot Jupiters, finding that hydrogen dissociation and recombination lead to a reduction in the day-to-night contrasts of ultra-hot Jupiters relative to previous expectations. In this work, we add to previous efforts by also considering the localized condensation of clouds in the atmospheres of ultra-hot Jupiters, their resulting transport by the atmospheric circulation, and the radiative feedback of clouds on the atmospheric dynamics. To do so, we include radiatively active cloud tracers into the existing MITgcm framework for simulating the atmospheric dynamics of ultra-hot Jupiters. We take cloud condensate properties appropriate for the high-temperature condensate corundum from CARMA cloud microphysics models. We conduct a suite of GCM simulations with varying cloud microphysical and radiative properties, and we find that partial cloud coverage is a ubiquitous outcome of our simulations. This patchy cloud distribution is inherently set by atmospheric dynamics in addition to equilibrium cloud condensation, and causes a cloud greenhouse effect that warms the atmosphere below the cloud deck. Nightside clouds are further sequestered at depth due to a dynamically induced high-altitude thermal inversion. We post-process our GCMs with the Monte Carlo radiative transfer code gCMCRT and find that the patchy clouds on ultra-hot Jupiters do not significantly impact transmission spectra but can affect their phase-dependent emission spectra.

We explore the assumption, widely used in many astrophysical calculations, that the stellar initial mass function (IMF) is universal across all galaxies. By considering both a canonical Salpeter-like IMF and a non-universal IMF, we are able to compare the effect of different IMFs on multiple observables and derived quantities in astrophysics. Specifically, we consider a non-universal IMF which varies as a function of the local star formation rate, and explore the effects on the star formation rate density (SFRD), the extragalactic background light, the supernova (both core-collapse and thermonuclear) rates, and the diffuse supernova neutrino background. Our most interesting result is that our adopted varying IMF leads to much greater uncertainty on the SFRD at $z \approx 2-4$ than is usually assumed. Indeed, we find a SFRD (inferred using observed galaxy luminosity distributions) that is a factor of $\gtrsim 3$ lower than canonical results obtained using a universal Salpeter-like IMF. Secondly, the non-universal IMF we explore implies a reduction in the supernova core-collapse rate of a factor of $\sim2$, compared against a universal IMF. The other potential tracers are only slightly affected by changes to the properties of the IMF. We find that currently available data do not provide a clear preference for universal or non-universal IMF. However, improvements to measurements of the star formation rate and core-collapse supernova rate at redshifts $z \gtrsim 2$ may offer the best prospects for discernment.

We revisit the joint constraints in the mixed hot dark matter scenario in which both thermally produced QCD axions and relic neutrinos are present. Upon recomputing the cosmological axion abundance via recent advances in the literature, we improve the state-of-the-art analyses and provide updated bounds on axion and neutrino masses. By avoiding approximate methods, such as the instantaneous decoupling approximation, and limitations due to the limited validity of the perturbative approach in QCD that forced to artificially divide the constraints from the axion-pion and the axion-gluon production channels, we find robust and self-consistent limits. We investigate the two most popular axion frameworks: KSVZ and DFSZ. From Big Bang Nucleosynthesis (BBN) light element abundances data we find for the KSVZ axion $\Delta N_{\rm eff}<0.31$ and an axion mass bound $m_a < 0.53 $ eV (i.e., a bound on the axion decay constant $f_a > 1.07 \times 10^7$ GeV) both at $95\%$ CL. These BBN bounds are improved to $\Delta N_{\rm eff}<0.14$ and $m_a< 0.16$ eV ($f_a > 3.56 \times 10^7$ GeV) if a prior on the baryon energy density from Cosmic Microwave Background (CMB) data is assumed. When instead considering cosmological observations from the CMB temperature, polarization and lensing from the Planck satellite combined with large scale structure data we find $\Delta N_{\rm eff}<0.23$, $m_a< 0.28$ eV ($f_a > 2.02 \times 10^7$ GeV) and $\sum m_\nu < 0.16$ eV at $95\%$ CL. This corresponds approximately to a factor of $5$ improvement in the axion mass bound with respect to the existing limits. Very similar results are obtained for the DFSZ axion. We also forecast upcoming observations from future CMB and galaxy surveys, showing that they could reach percent level errors for $m_a\sim 1$ eV.

Pulsar Timing Arrays (PTAs) are exceptionally sensitive detectors in the frequency band $\text{nHz} \lesssim f \lesssim \mu\text{Hz}$. Ultralight dark matter (ULDM), with mass in the range $10^{-23}\,\text{eV} \lesssim m_\phi \lesssim 10^{-20}\,\text{eV}$, is one class of DM models known to generate signals in this frequency window. While purely gravitational signatures of ULDM have been studied previously, in this work we consider two signals in PTAs which arise in presence of direct couplings between ULDM and ordinary matter. These couplings induce variations in fundamental constants, i.e., particle masses and couplings. These variations can alter the moment of inertia of pulsars, inducing pulsar spin fluctuations via conservation of angular momentum, or induce apparent timing residuals due to reference clock shifts. By using mock data mimicking current PTA datasets, we show that PTA experiments outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons. In the case of coupling to quarks or photons, we find that PTAs and atomic clocks set similar constraints. Additionally, we discuss how future PTAs can further improve these constraints, and detail the unique properties of these signals relative to the previously studied effects of ULDM on PTAs.

If ultralight $(\ll$ eV), bosonic dark matter couples to right handed neutrinos, active neutrino masses and mixing angles depend on the ambient dark matter density. When the neutrino Majorana mass, induced by the dark matter background, is small compared to the Dirac mass, neutrinos are "pseudo-Dirac" fermions that undergo oscillations between nearly degenerate active and sterile states. We present a complete cosmological history for such a scenario and find severe limits from a variety of terrestrial and cosmological observables. For scalar masses in the "fuzzy" dark matter regime ($\sim 10^{-20}$ eV), these limits exclude couplings of order $10^{-30}$, corresponding to Yukawa interactions comparable to the gravitational force between neutrinos and surpassing equivalent limits on time variation in scalar-induced electron and proton couplings.

The physics of axions and axion-like particles (ALPs) is enjoying an incredibly productive period, with many new experimental proposals, theoretical idea, and original astrophysical and cosmological arguments which help the search effort. The large number of experimental proposals is likely to lead to fundamental advances (perhaps, a discovery?) in the coming years. The aim of this article is to provide a very brief overview of some of the recent developments in axions and ALP phenomenology, and to discuss some relevant aspects in this important field. A particular attention is given to the definition of motivated regions in the axion parameters space, which should be the targets of experimental searches.

Large-scale magnetic fields thread through the electrically conducting matter of the interplanetary and interstellar medium, stellar interiors, and other astrophysical plasmas, producing anisotropic flows with regions of high-Reynolds-number turbulence. It is common to encounter turbulent flows structured by a magnetic field with a strength approximately equal to the root-mean-square magnetic fluctuations. In this work, direct numerical simulations of anisotropic magnetohydrodynamic (MHD) turbulence influenced by such a magnetic field are conducted for a series of cases that have identical resolution, and increasing grid sizes up to $2048^3$. The result is a series of closely comparable simulations at Reynolds numbers ranging from 1,400 up to 21,000. We investigate the influence of the Reynolds number from the Lagrangian viewpoint by tracking fluid particles and calculating single-particle and two-particle statistics. The influence of Alfv\'enic fluctuations and the fundamental anisotropy on the MHD turbulence in these statistics is discussed. Single-particle diffusion curves exhibit mildly superdiffusive behaviors that differ in the direction aligned with the magnetic field and the direction perpendicular to it. Competing alignment processes affect the dispersion of particle pairs, in particular at the beginning of the inertial subrange of time scales. Scalings for relative dispersion, which become clearer in the inertial subrange for larger Reynolds number, can be observed that are steeper than indicated by the Richardson prediction.

The recently released images of the supermassive black holes in the M87 galaxy and the galaxy of our own make probing black hole spacetimes and testing general relativity (GR) possible. The violation of equatorial reflection symmetry of black hole spacetimes is clearly a smoking gun of physics beyond GR. In this paper, we place constraints on the violation of black hole reflection symmetry using the bounds on the ring size of the Sgr A* black hole images, which are consistent with the critical curve radius predicted in GR within $\sim10\%$. Adopting a theory-agnostic framework, we consider a Kerr-like metric in which the violation of reflection symmetry is parametrized by a single parameter, without altering the multipoles of the black hole. The critical curves are always vertically symmetric due to the existence of hidden symmetry associated with the Killing tensor, even though the spacetime is reflection asymmetric. We find that the size of critical curves is sensitive to the amount of reflection symmetry being violated, and place the first constraints on the parameter space of the model using the Sgr A* images.

The Asymptotic safe gravity program suggests a specific form of the running Newtonian coupling constant which depends on two free parameters, usually denoted with $\om$ and $\gamma$. New metrics can be inferred from a "running" gravitational constant, and in particular new black hole spacetimes. Of course, the minimum requirement satisfied by the new metrics should be the matching with a Schwarzschild field at large radial coordinate. By further imposing the simple request of matching the new metric with the Donoghue quantum corrected potential, we find a negative value of the $\om$ parameter, and hence a not yet explored black hole metric, which naturally turns out to describe the so called Planck stars.

We study first-order electroweak phase transitions nonperturbatively, assuming any particles beyond the Standard Model are sufficiently heavy to be integrated out at the phase transition. Utilising high temperature dimensional reduction, we perform lattice Monte-Carlo simulations to calculate the main quantities characterising the transition: the critical temperature, the latent heat, the surface tension and the bubble nucleation rate, updating and extending previous lattice studies. We focus on the region where the theory gives first-order phase transitions due to an effective reduction in the Higgs self-coupling and give a detailed comparison with perturbation theory.

A `bouncing' cosmological model is proposed in the context of a Weyl-invariant scalar-tensor (WIST) theory of gravity. In addition to being Weyl-invariant the theory is U(1)-symmetric and has a conserved global charge. The entire cosmic background evolution is accounted for by a complex scalar field that evolves in the static `comoving' frame. Its (dimensional) modulus $\chi$ regulates the dynamics of masses and the apparent space expansion. Cosmological redshift is essentially due to the cosmic evolution of the Rydberg constant in the comoving frame. The temporal evolution of $\chi$ is analogous to that of a point particle in the presence of a central potential $V(\chi)$. The scalar field sources the spacetime curvature; as such it can account for the (cosmological) Dark Sector. An interplay between the energy density of radiation and that of the kinetic energy associated with the phase $\alpha$ of the scalar field (which are of opposite signs) results in a classical non-singular stable and nearly-symmetric bouncing dynamics deep in the radiation-dominated era. This encompasses the observed redshifting era which preceded by a `bounce' that follows a blushifting era. The model is essentially free of the horizon or flatness problems. Big Bang nucleosynthesis sets a lower 1-10 MeV bound on the typical energy scale at the `bounce'.

We search for stochastic gravitational wave background emitted from cosmic strings using the Parkes Pulsar Timing Array data over 15 years. While we find that the common power-law excess revealed by several pulsar timing array experiments might be accounted for by the gravitational wave background from cosmic strings, the lack of the characteristic Hellings-Downs correlation cannot establish its physical origin yet. The constraints on the cosmic string model parameters are thus derived with conservative assumption that the common power-law excess is due to unknown background. Two representative cosmic string models with different loop distribution functions are considered. We obtain constraints on the dimensionless string tension parameter $G\mu<10^{-11}\sim10^{-10}$, which is more stringent by two orders of magnitude than that obtained by the high-frequency LIGO-Virgo experiment for one model, and less stringent for the other. The results provide the chance to test the Grand unified theories, with the spontaneous symmetry breaking scale of $U(1)$ being two-to-three orders of magnitude below $10^{16}$ GeV. The pulsar timing array experiments are thus quite complementary to the LIGO-Virgo experiment in probing the cosmic strings and the underlying beyond standard model physics in the early Universe.

In this paper we shall consider an axionic Chern-Simons corrected $f(R)$ gravity theoretical framework, and we shall study the chirality of the generated primordial gravitational waves. Particularly, we shall consider two main axion models, the canonical misalignment axion model and the kinetic axion model, both of which provide an interesting particle phenomenology, in the presence of $R^2$ terms in the inflationary Lagrangian. The axion does not affect significantly the background evolution during the inflationary era, which is solely controlled by $R^2$ gravity. However, the due to the presence of the Chern-Simons term, the tensor perturbations are directly affected, and our aim is to reveal the extent of effects of the Chern-Simons term on the gravitational waves modes, for both the axion models. We aim to produce analytical descriptions of the primordial tensor modes behavior, and thus we solve analytically the evolution equations of the tensor modes, for a nearly de Sitter primordial evolution controlled by the $R^2$ gravity. We focus the analytical study on superhorizon and subhorizon modes. For the misalignment model, we were able to produce analytic solutions for both the subhorizon and superhorizon modes, in which case we found the behavior of the circular polarization function. Our results indicate that the produced tensor spectrum is strongly chiral. For the kinetic axion model though, analytic solutions are obtained only for the superhorizon modes. In order to have a grasp of the behavior of the chirality of the tensor modes, we studied the chirality of the superhorizon modes, however a more complete study is needed, which is impossible to do analytically though.

An analysis of a tower of hidden sectors coupled to each other, with one of these hidden sectors coupled to the visible sector, is given and the implications of such couplings on physics in the visible sector are investigated. Thus the analysis considers $n$ number of hidden sectors where the visible sector couples only to hidden sector 1, while the latter couples also to hidden sector 2, and the hidden sector 2 couples to hidden sector 3 and so on. A set of successively feeble couplings of the hidden sectors to the visible sector are generated in such a set up. In general each of these sectors live in a different heat bath. We develop a closed form set of coupled Boltzmann equations for the correlated evolution of the temperatures and number densities of each of the heat baths. We then apply the formalism to a simplified model with scalar portals between the different sectors. Predictions related to dark matter direct detection experiments and future CMB probes of dark radiation are made.

The light neutrino masses are at present most stringently constraint via cosmological probes. In particular the Planck collaboration reports $ \sum m_\nu \leq 0.12\,\mathrm{eV}$ at $95\%$ CL within the standard cosmological model. This is more than one order of magnitude stronger than the one arising from laboratory searches. The cosmological bound taken at face value excludes a plethora of neutrino flavour models which can successfully explain the neutrino oscillation data. The indirect nature of the cosmological bound, however, allows to relax the bound to up to $ \sum m_\nu \sim 1\,\mathrm{eV}$ if neutrinos decay on timescales shorter than the age of the Universe, $\tau_\nu \leq t_U$. We present how a decay of the type $\nu_i\to\nu_4\phi$ can be realized within general models of the minimal extended seesaw framework. The idea is then explicitly realized within the context of a $U(1)_{\mu-\tau}$ flavour model.

This study focuses on the X-ray emission of low-mass black hole binaries in massive Brans-Dicke gravity. First, we compute the accretion disk adopting the well-known Shakura-Sunyaev model for an optically thick, cool, and geometrically thin disk. Moreover, we assume that the gravitational field generated by the stellar-mass black hole is an analogue of the Schwarzschild space-time of Einstein's theory in massive Brans-Dicke gravity. We compute the most relevant quantities of interest, i.e., i) the radial velocity, ii) the energy and surface density, and iii) the pressure as a function entirely of the radial coordinate. We also compute the soft spectral component of the X-ray emission produced by the disk. Furthermore, we investigate in detail how the mass of the scalar field modifies the properties of the binary as described by the more standard Schwarzschild solution.

Recently it has been suggested that thermal bremsstrahlung emission, when it decouples prior to recombination, creates an excess over the Planck cosmic microwave background spectrum at sub-GHz frequencies. Remarkable by itself, this would also explain a long-standing unexplained deficit in the predictions of the extragalactic radio background. In this brief note we reiterate that no such non-thermal component can arise by itself when matter and radiation remain kinetically coupled.

We develop the framework required to model the dynamical tidal response of a spinning neutron star in an inspiralling binary system, in the context of Newtonian gravity. The tidal perturbation is decomposed in terms of the normal oscillation modes, used to derive an expression for the effective Love number which is valid for any rotation rate. Our analysis highlights subtle issues relating to the orthogonality condition required for the mode-sum representation of the dynamical tide and shows how the prograde and retrograde modes combine to provide the overall tidal response. Utilising a slow-rotation expansion, we show that the dynamical tide (effective Love number) is corrected at first order in rotation, whereas in the case of the static tide (static Love number) the rotational corrections do not enter until second order.

We use observational data from the S2 star orbiting around the Galactic Center to constrain a black hole solution of extended teleparallel gravity models. Subsequently, we construct the shadow images of Sgr A$^{\star}$ black hole. In particular, we constrain the parameter $\alpha=1/\lambda$ which appears in the Born-Infeld $f(T)$ model. In the strong gravity regime we find that the shadow radius increases with the increase of the parameter $\alpha$. Specifically, from the S2 star observations, we find within 1$\sigma$ that the parameter must lie between $0 \leq \alpha/M^2 \leq 6 \times 10^{-4}$. Consequently, we used the best fit parameters to model the shadow images of Sgr A$^{\star}$ black hole and then using the Gauss-Bonnet theorem we analysed the deflection angle for leading order expansions of the parameter $\alpha$. It is found that within the parameter range, these observables are very close to the Schwarzschild case. Furthermore, using the best fit parameters for the Born-Infeld $f(T)$ model we show the angular diameter is consistent with recent observations for the Sgr A$^{\star}$ black hole angular diameter $(51.8 \pm 2.3) \mu$arcsec and difficult to be distinguished from the GR. For the deflection angle of light, in leading order terms, we find that the deflection angle expressed in the ADM mass coincides with the GR, but the ADM mass in the Born-Infeld $f(T)$ gravity increases with the increase of $\alpha$ and the overall deflection angle is expected to me greater in $f(T)$ gravity. As a consequence of this fact, we have shown that the electromagnetic intensity observed in shadow images is smaller compared to GR.

Heavy long-lived particles are abundant in BSM physics and will, under generic circumstances, get to dominate the energy density of the universe. The resulting matter dominated era has to end before the onset of Big Bang Nucleosynthesis through the decay of the heavy matter component of mass $M$ into a thermal bath of temperature $T$. The process of thermalization primarily involves near-collinear splittings of energetic particles into two particles with lower energy. The correct treatment of these processes requires the inclusion of coherence effects which suppress the splitting rate. We write down and numerically solve the resulting coupled Boltzmann equations including all gauge bosons and fermions of the Standard Model (SM). We then comment on the dependence of the nonthermal spectra on the ratio $M/T$, as well as on the matter decay rate and branching ratios into various SM particles.

The study of the primordial black hole (PBH) gravitational collapse process requires the determination of a critical energy density perturbation threshold $\delta_\mathrm{c}$, which depends on the equation of state of the universe at the time of PBH formation. Up to now, the majority of analytical and numerical techniques calculate $\delta_\mathrm{c}$ by assuming a constant equation-of-state (EoS) parameter $w$ at the time of PBH formation. In this work, after generalizing the constant $w$ prescription of [1] for the computation of $\delta_\mathrm{c}$ and commenting its limitations we give a first estimate for the PBH threshold in the case of a time-dependent $w$ background. In particular, we apply our formalism in the case of the QCD phase transition, where the EoS parameter varies significantly with time and one expects an enhanced PBH production due to the abrupt softening of $w$. At the end, we compare our results with analytic and numerical approaches for the determination of $\delta_\mathrm{c}$ assuming a constant EoS parameter.

Interplanetary coronal mass ejections (ICMEs) contain magnetic field and velocity fluctuations across a wide range of scales. These fluctuations may be interpreted as Alfv\'enic wave packets propagating parallel or anti-parallel to the background magnetic field, with the difference in power between counter-propagating fluxes quantified by the cross helicity. We have determined the cross helicity of inertial range fluctuations at $10^{-3}-10^{-2}$ Hz in 226 ICME flux ropes and 176 ICME sheaths observed by the Wind spacecraft at 1 au during 1995-2015. The flux ropes and sheaths had mean, normalised cross helicities of 0.18 and 0.24, respectively, with positive values here indicating net anti-sunward fluxes. While still tipped towards the anti-sunward direction on average, fluxes in ICMEs tend to be more balanced than in the solar wind at 1 au, where the mean cross helicity is larger. Superposed epoch profiles show cross helicity falling sharply in the sheath and reaching a minimum inside the flux rope near the leading edge. More imbalanced, solar wind-like cross helicity was found towards the trailing edge and laterally further from the rope axis. The dependence of cross helicity on flux rope orientation and the presence of an upstream shock are considered. Potential origins of the low cross helicity in ICMEs at 1 au include balanced driving of the closed-loop flux rope at the Sun and ICME-solar wind interactions in interplanetary space. We propose that low cross helicity of fluctuations is added to the standard list of ICME signatures.

Horizon-scale images of black holes (BHs) and their shadows have opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime, allowing us to test whether the Kerr metric provides a good description of the space-time in the vicinity of the event horizons of supermassive BHs. We consider a wide range of well-motivated deviations from classical General Relativity solutions, and constrain them using the Event Horizon Telescope (EHT) observations of Sagittarius A$^*$ (SgrA$^*$), connecting the size of the bright ring of emission to that of the underlying BH shadow and exploiting high-precision measurements of SgrA$^*$'s mass-to-distance ratio. The scenarios we consider, and whose fundamental parameters we constrain, include various regular BH models, string- and non-linear electrodynamics-inspired space-times, scalar field-driven violations of the no-hair theorem, alternative theories of gravity, new ingredients such as the generalized uncertainty principle and Barrow entropy, and BH mimickers including examples of wormholes and naked singularities. We demonstrate that SgrA$^*$'s image places particularly stringent constraints on models predicting a shadow size which is larger than that of a Schwarzschild BH of a given mass: for instance, in the case of Barrow entropy we derive constraints which are significantly tighter than the cosmological ones. Our results are among the first tests of fundamental physics from the shadow of SgrA$^*$ and, while the latter appears to be in excellent agreement with the predictions of General Relativity, we have shown that various well-motivated alternative scenarios (including BH mimickers) are far from being ruled out at present.

We reanalyze the GW150914 post-merger data searching for quasinormal modes beyond the fundamental, quadrupolar mode. There is currently an ongoing disagreement in the literature about whether, and to what extent, the data contains evidence for a quasinormal mode overtone. We use a frequency-domain approach to ringdown data analysis that was recently proposed by the authors. Our analysis has several advantages compared to other analyses performed mainly in the time domain; in particular, the source sky position and the ringdown start time are marginalized over (as opposed to simply being fixed) as part of a Bayesian ringdown analysis. We find tentative evidence for an overtone in GW150914, but at a lower significance than reported elsewhere. Our preferred analysis, marginalizing over the uncertainty in the time of peak strain amplitude, gives a posterior on the overtone amplitude peaked away from zero at $\sim 1.8\sigma$.