Papers for Friday, Feb 18 2022

[Abridged] We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations, and spectral line content and evolution. We identify transient, double-peaked Bowen (N iii), He i, He ii and Halpha emission lines. We model medium resolution optical spectroscopy of the He ii (after careful deblending of the N iii contribution) and Halpha lines during the rise, peak and early decline of the light curve using relativistic, elliptical accretion disk models. We find that the spectral evolution before peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around peak the envelope reaches its maximum extent (approximately 10^15 or 3000-6000 gravitational radii for an inferred black hole mass of 5-10 10^5) and becomes optically thin. The Halpha and He ii emission lines at and after peak can be reproduced with a highly inclined (i=85+-5 degrees), highly elliptical (e=0.97+-0.01) and relatively compact (Rin = several 100 Rg and Rout = several 1000 Rg ) accretion disk. Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary SMBH hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination) - and rule out high black hole spin values (a < 0.8).

Transitional millisecond pulsars (tMSPs) have emerged in the last decade as a unique class of neutron stars at the crossroads between accretion- and rotation-powered phenomena. In their (sub-luminous) accretion disk state, with X-ray luminosities of order $10^{33}-10^{34}$ erg s$^{-1}$, they switch rapidly between two distinct X-ray modes: the disk-high (DH) and disk-low (DL) states. We present a systematic XMM-Newton and Chandra analysis of the aperiodic X-ray variability of all three currently known tMSPs, with a main focus on their disk state and separating DH and DL modes. We report the discovery of flat-topped broadband noise in the DH state of two of them, with break frequencies of 2.8 mHz (PSR J1023+0038) and 0.86 mHz (M28-I). We argue that the lowest frequency variability is similar to that seen in disk-accreting X-ray binaries in the hard state, at typical luminosities at least 2 orders of magnitude higher than tMSPs. We find strong variability in the DH state around 1 Hz, not typical of hard state X-ray binaries, with fractional rms amplitudes close to 30%. We discuss our results and use them to constrain the properties of the accretion disk, assuming that the X-ray variability is produced by fluctuations in mass accretion rate, and that the break frequency corresponds to the viscous timescale at the inner edge of the disk. In this context, we find that the newly found break frequencies are broadly consistent with a disk truncated close to the light cylinder with $\dot{M}\simeq10^{13}-5\times10^{14}$ g s$^{-1}$ and a viscosity parameter $\alpha\gtrsim$0.2.

Axion dark matter (DM) may efficiently convert to photons in the magnetospheres of neutron stars (NSs), producing nearly monochromatic radio emission. This process is resonantly triggered when the plasma frequency induced by the underlying charge distribution approximately matches the axion mass. We search for evidence of this process using archival Green Bank Telescope data collected in a survey of the Galactic Center in the C-Band by the Breakthrough Listen project. While Breakthrough Listen aims to find signatures of extraterrestrial life in the radio band, we show that their high-frequency resolution spectral data of the Galactic Center region is ideal for searching for axion-photon transitions generated by the population of NSs in the inner pc of the Galaxy. We use data-driven models to capture the distributions and properties of NSs in the inner Galaxy and compute the expected radio flux from each NS using state-of-the-art ray tracing simulations. We find no evidence for axion DM and set leading constraints on the axion-photon coupling, excluding values down to the level $g_{a \gamma \gamma} \sim 10^{-11}$ GeV$^{-1}$ for DM axions for masses between 15 and 35 $\mu$eV.

We use deep Herschel observations of the complete 2Jy sample of powerful radio AGNs in the local universe (0.05 < z < 0.7) to probe their cool interstellar medium (ISM) contents and star-forming properties, comparing them against other samples of nearby luminous AGNs and quiescent galaxies. This allows us to investigate triggering and feedback mechanisms. We find that the dust masses of the strong-line radio galaxies (SLRGs) in our sample are similar to those of radio-quiet quasars, and that their median dust mass (Mdust = 2 x 10^7 Msun) is enhanced by a factor ~200 compared to that of non-AGN ellipticals, but lower by a factor ~16 relative to that of local ultra-luminous infrared galaxies (UILRGs). Along with compelling evidence for merger signatures in optical images, the SLRGs in our sample also show relatively high star-formation efficiencies, despite the fact that many of them fall below the main sequence for star forming galaxies. Together, these results suggest that most of our SLRGs have been re-triggered by late-time mergers that are relatively minor in terms of their gas contents. In comparison with the SLRGs, the radio AGNs with weak optical emission lines (WLRGs) and edge-darkened radio jets (FRIs) have both lower cool ISM masses and star-formation rates (by a factor of >30), consistent with being fuelled by a different mechanism (e.g. the direct accretion of hot gas).

We reassess the claimed detection of variability in the atmosphere of the hot Jupiter HAT-P-7 b, reported by Armstrong et al. (2016). Although astronomers expect hot Jupiters to have changing atmospheres, variability is challenging to detect. We looked for time variation in the phase curves of HAT-P-7 b in Kepler data using similar methods to Armstrong et al. (2016), and identified apparently significant variations similar to what they found. Numerous tests show the variations to be mostly robust to different analysis strategies. However, when we injected unchanging phase curve signals into the light curves of other stars and searched for variability, we often saw similar levels of variations as in the HAT-P-7 light curve. Fourier analysis of the HAT-P-7 light curve revealed background red noise from stellar supergranulation on timescales similar to the planet's orbital period. Tests of simulated light curves with the same level of noise as HAT-P-7's supergranulation show that this effect alone can cause the amplitude and phase offset variability we detect for HAT-P-7 b. Therefore, the apparent variations in HAT-P-7 b's atmosphere could instead be caused by non-planetary sources, most likely photometric variability due to supergranulation on the host star.

X-shaped radio galaxies (XRGs) produce misaligned X-shaped jet pairs and make up $\lesssim10\%$ of radio galaxies. XRGs are thought to emerge in galaxies featuring a binary supermassive black hole ($\rm SMBH$), $\rm SMBH$ merger, or large-scale ambient medium asymmetry. We demonstrate that XRG morphology can naturally form without such special, preexisting conditions. Our 3D general-relativistic magnetohydrodynamic (GRMHD) simulation for the first time follows magnetized rotating gas from outside the $\rm SMBH$ sphere of influence of radius $R_{\rm B}$ to the $\rm SMBH$ of gravitational radius $R_{\rm g}$, at the largest scale separation $R_{\rm B}/R_{\rm g} = 10^3$ to date. Initially, our axisymmetric system of constant-density hot gas contains weak vertical magnetic field and rotates in an equatorial plane of a rapidly spinning $\rm SMBH$. We seed the gas with small-scale $2\%$-level pressure perturbations. Infalling gas forms an accretion disk, and the $\rm SMBH$ launches relativistically-magnetized collimated jets reaching well outside $R_{\rm B}$. Under the pressure of the infalling gas, the jets intermittently turn on and off, erratically wobble, and inflate pairs of cavities in different directions, resembling an X-shaped jet morphology. Synthetic X-ray images reveal multiple pairs of jet-powered shocks and cavities. Large-scale magnetic flux accumulates on the $\rm SMBH$, becomes dynamically important, and leads to a magnetically arrested disk state. The $\rm SMBH$ accretes at $2\%$ of the Bondi rate ($\dot{M}\simeq2.4\times10^{-3}M_{\odot}\,{\rm yr}^{-1}$ for M87*), and launches twin jets at $\eta=150\%$ efficiency. These jets are powerful enough ($P_{\rm jets}\simeq2\times10^{44}\,{\rm erg\,s}^{-1}$) to escape along the spin axis and end the short-lived jets state whose transient nature can account for the rarity of XRGs

We present general relativistic magneto-hydrodynamical simulations of equal-mass spinning black hole binary mergers embedded in a magnetized gas cloud. We focus on the effect of the spin orientation relative to the orbital angular momentum on the flow dynamics, mass accretion rate and Poynting luminosity. We find that, across the inspiral, the gas accreting onto the individual black holes concentrates into disk-like overdensities, whose angular momenta are oriented towards the spin axes and which persist until merger. We identify quasi-periodic modulations occurring in the mass accretion rate at the level of 1-20%, evolving in parallel with the gravitational wave chirp. The similarity between the accretion rate time-series and the gravitational strain is a consequence of the interplay between strong, dynamical gravitational fields and magnetic fields in the vicinity of the inspiralling black holes. This result suggests that quasi-periodicity in the pre-merger accretion rate of massive binaries is not exclusive of environments in which the black holes are embedded in a circumbinary accretion disk, and could provide an additional useful signature of electromagnetic emission concurrent to low-frequency gravitational wave detection.

We analyzed the contribution of the intracluster light (ICL) to the total luminosity of two massive galaxy clusters observed by the Hubble Space Telescope within the Frontier Fields program, Abell 370 (z ~ 0.375) and Abell S1063 (z ~ 0.348), in order to correlate it with the dynamical stage of these systems.We applied an algorithm based on the Chebyshev-Fourier functions called CICLE, specially developed to disentangle the ICL from the light of galaxies and measure the ICL fraction. We measured the ICL fraction in three broadband optical filters, F435W, F606W, and F814W, without assuming any prior hypothesis about the ICL physical properties or morphology. The results obtained from the ICL fraction vary between ~7% - 25%, and ~3% - 22% for both A370 and AS1063, respectively, which are consistent with theoretical predictions for the total amount of ICL obtained by ICL formation and evolution simulations.We found enhanced ICL fractions in the intermediate filter F606W for both clusters and we suggest that this is due to the presence of an excess of younger/lower-metallicity stars in the ICL compared to the cluster galaxies. We conclude that both Abell 370 and Abell S1063 are merging systems since they exhibit a similar feature as merging CLASH and Frontier Fields clusters sub-sample previously analyzed. We compare these results to the dynamical indicators obtained through different methods and we reinforce the use of ICL as a new and independent method to determine the dynamical state of clusters of galaxies.

Early Dark Energy (EDE) relies on scalar field dynamics to resolve the Hubble tension, by boosting the pre-recombination length scales and thereby raising the CMB-inferred value of the Hubble constant into agreement with late universe probes. However, the collateral effect of scalar field microphysics on the linear perturbation spectra appears to preclude a fully satisfactory solution. $H_0$ is not raised without the inclusion of a late universe prior, and the "$S_8$-tension", a discrepancy between early- and late-universe measurements of the structure growth parameter, is exacerbated. What if EDE is not a scalar field? Here, we investigate whether different microphysics, encoded in the constitutive relationships between pressure and energy density fluctuations, can relieve these tensions. We show that EDE with an anisotropic sound speed can soften both the $H_0$ and $S_8$ tensions while still providing a quality fit to CMB data. Future observations from the CMB-S4 experiment may be able to distinguish the underlying microphysics at the $4\sigma$ level, and thereby test whether a scalar field or some richer physics is at work.

The vertical structure of debris disks provides clues about their dynamical evolution and the collision rate of the unseen planetesimals. Thanks to the ever-increasing angular resolution of contemporary instruments and facilities, we are beginning to constrain the scale height of a handful of debris disks, either at near-infrared or millimeter wavelengths. Nonetheless, this is often done for individual targets only. We present here the geometric modeling of eight disks close to edge-on, all observed with the same instrument (SPHERE) and using the same mode (dual-beam polarimetric imaging). Motivated by the presence of CO gas in two out of the eight disks, we then investigate the impact that gas can have on the scale height by performing N-body simulations including gas drag and collisions. We show that gas can quickly alter the dynamics of particles (both in the radial and vertical directions), otherwise governed by gravity and radiation pressure. We find that, in the presence of gas, particles smaller than a few tens of microns can efficiently settle toward the midplane at the same time as they migrate outward beyond the birth ring. For second generation gas ($M_\mathrm{gas} \leq 0.1$ $M_\oplus$), the vertical settling should be best observed in scattered light images compared to observations at millimeter wavelengths. But if the gas has a primordial origin ($M_\mathrm{gas} \geq 1$ $M_\oplus$), the disk will appear very flat both at near-infrared and sub-mm wavelengths. Finally, far beyond the birth ring, our results suggest that the surface brightness profile can be as shallow as $\sim -2.25$.

Magnetic fields are a dynamically important component of the turbulent interstellar medium (ISM) of star-forming galaxies. These magnetic fields are due to a dynamo action, which is a process of converting turbulent kinetic energy to magnetic energy. A dynamo that acts at scales less than the turbulent driving scale is known as the turbulent dynamo. The ISM is a multiphase medium and observations suggests that the properties of magnetic fields differ with the phase. Here, we aim to study how the properties of the turbulent dynamo depend on the phase. We simulate the non-isothermal turbulent dynamo in a two-phase medium (most previous work assumes an isothermal gas). We find that the growth rate of magnetic fields in the exponentially growing stage is similar in both the phases, and this is because of a roughly equal amount of vorticity being generated in each phase. We further compute each term responsible for amplification and destruction of vorticity and show that the amplification of vorticity by turbulent motions is a dominant term (similar in both the phases) followed by the baroclinic term (only present in non-isothermal gases, higher in the warm phase) and the term for viscous interactions in the presence of logarithmic density gradients (higher in the cold phase). We find that the final ratio of magnetic to turbulent kinetic energy is lower due to a stronger Lorentz force. We find that the non-isothermal turbulent dynamo is less efficient than its isothermal counterpart.

The eclipsing binary IT Librae is an unusual system of two B-type stars that is situated about 1 kpc above the galactic plane. The binary was probably ejected from its birthplace in the disk, but the implied time-of-flight to its current location exceeds the evolutionary lifetime of the primary star. Here we present a study of new high dispersion spectroscopy and an exquisite light curve from the Kepler K2 mission in order to determine the system properties and resolve the timescale discrepancy. We derive a revised spectroscopic orbit from radial velocity measurements and determine the component effective temperatures through comparison of reconstructed and model spectra ($T_1 = 23.8 \pm 1.8$ kK, $T_2 = 13.7 \pm 2.5$ kK). We use the Eclipsing Light Curve (ELC) code to model the K2 light curve, and from the inclination of the fit, we derive the component masses ($M_1 = 9.6 \pm 0.6 M_\odot$, $M_2 = 4.2 \pm 0.2 M_\odot$) and mean radii ($R_1 = 6.06 \pm 0.16 R_\odot$, $R_2 = 5.38 \pm 0.14 R_\odot$). The secondary star is overluminous for its mass and appears to fill its Roche lobe. This indicates that IT~Librae is a post-mass transfer system in which the current secondary was the mass donor star. The current primary star was rejuvenated by mass accretion, and its evolutionary age corresponds to the time since the mass transfer stage. Consequently, the true age of the binary is larger than the ejection time-of-flight, thus resolving the timescale discrepancy.

Electrons accelerated on Earth by a rich variety of wave scattering or stochastic processes generate hard non-thermal X-ray bremsstrahlung up to >~ 1 MeV and power Earth's various types of aurorae. Although Jupiter's magnetic field is an order of magnitude larger than Earth's, space-based telescopes have previously detected X-rays only up to ~7 keV. On the basis of theoretical models of the Jovian auroral X-ray production, X-ray emission in the ~2-7 keV band has been interpreted as thermal (arising from electrons characterized by a Maxwell-Boltzmann distribution) bremsstrahlung. Here we report the observation of hard X-rays in the 8-20 keV band from the Jovian aurorae, obtained with the NuSTAR X-ray observatory. The X-rays fit to a flat power-law model with slope 0.60+/-0.22 - a spectral signature of non-thermal, hard X-ray bremsstrahlung. We determine the electron flux and spectral shape in the keV to MeV energy range using coeval in situ measurements by the Juno spacecraft's JADE and JEDI instruments. Jovian electron spectra of the form we observe have previously been interpreted to arise in stochastic acceleration, rather than coherent acceleration by electric fields. We reproduce the X-ray spectral shape and approximate flux observed by NuSTAR, and explain the non-detection of hard X-rays by Ulysses, by simulating the non-thermal population of electrons undergoing precipitating electron energy loss, secondary electron generation and bremsstrahlung emission in a model Jovian atmosphere. The results highlight the similarities between the processes generating hard X-ray auroras on Earth and Jupiter, which may be occurring on Saturn, too.

In recent years, ALMA has been able to observe large-scale substructures within protoplanetary disks. Comparison with the predictions from models of planet-disk interaction has indicated that most of these disk substructures can be explained by the presence of planets with the mass of Neptune or larger at orbital radii of $\approx 5 - 100$ au. Better resolution is needed to observe structures closer to the star, where terrestrial planets are expected to form, as well as structures opened by planets with masses lower than Neptune. We investigate the capabilities of a possible extension to ALMA that would double the longest baseline lengths in the array to detect and resolve disk substructures opened by Earth-mass and Super Earth planets at orbital radii of $1-5$ au. By simulating observations of a family of disk models using this extended configuration in ALMA Bands 6 and 7, we show that an upgraded ALMA would detect gaps in disks formed by super-Earths as close as 1 au, as well as Earth-mass planets down to $2-3$ au from the young host stars in nearby star forming regions.

We investigate the role played by dark energy perturbations in the skewness $S_3$ of large-scale matter distribution. We consider a two-fluid universe composed by matter and dark energy, with perturbations in both components, and we estimate numerically the skewness of the matter density field as a function of the dark energy parameters. We characterize today's $S_3$ value for quintessence and phantom dark energy cosmologies as well as its dependence on the matter density parameter $\Omega_{m0}$ and the dark energy sound speed $c^2_s$ with accurate numerical fitting. These fits can be used to test cosmology against future high quality data on large scale structure.

We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four of these systems, DW Cnc, V515 And, V1223 Sgr and RX J2133.7+5107, we are able to perform timing analysis in and out of the low states. We find that, for DW Cnc and V515 And, the dominant periodicities in the light curves change as the flux decreases, indicating a change in the sources' accretion properties as they transition to the low state. For V1223 Sgr we find that the variability is almost completely quenched at the lowest flux, but do not find evidence for a changing accretion geometry. For RX J2133.7+5107, the temporal properties do not change in the low state, but we do see a period of enhanced accretion that is coincident with increased variability on the beat frequency, which we do not associate with a change in the accretion mechanisms in the system.

We report a new, plasmoid-fed scenario for the formation of an eruptive prominence (PF$^2$), involving reconnection and condensation. We use grid-adaptive resistive two-and-a-half-dimensional magnetohydrodynamic (MHD) simulations in a chromosphere-to-corona setup to resolve this plasmoid-fed scenario. We study a pre-existing flux rope (FR) in the low corona that suddenly erupts due to catastrophe, which also drives a fast shock above the erupting FR. A current sheet (CS) forms underneath the erupting FR, with chromospheric matter squeezed into it. The plasmoid instability occurs and multiple magnetic islands appear in the CS once the Lundquist number reaches $\sim 3.5\times 10^{4}$. The remnant chromospheric matter in the CS is then transferred to the FR by these newly formed magnetic islands. The dense and cool mass transported by the islands accumulates in the bottom of the FR, thereby forming a prominence during the eruption phase. More coronal plasma continuously condenses into the prominence due to the thermal instability as the FR rises. Due to the fine structure brought in by the PF$^2$ process, the model naturally forms filament threads, aligned above the polarity inversion line. Synthetic views at our resolution of $15 \mathrm{km}$ show many details that may be verified in future high-resolution observations.

We present the United States Naval Observatory (USNO) Bright-Star Astrometric Database (UBAD), a current-epoch high-accuracy astrometric catalog. The catalog consists of 364 bright northern hemisphere stars, including all but five such stars with either $V < 3.5$ or with $I < 3.2$ and $V < 6$, as well as a large fraction of slightly fainter stars; 36 of the brightest catalog stars are not included in Gaia Early Data Release 3 (EDR3). Observations were conducted with the USNO, Flagstaff Station, Kaj Strand 61-inch Astrometric Reflector. Target stars were imaged through a small 12.5-magnitude neutral-density spot, while the remainder of the stars in the field of view were unattenuated. This allowed for unsaturated images of the bright target stars to be calibrated directly against much fainter reference stars from Gaia EDR3. The median position errors are 1.9 mas in both right ascension and declination at the catalog epoch of 2017.0, with 90% of catalog stars having errors less than 2.6 mas; systematic errors are 1 -- 3 mas. Combining UBAD observations with Hipparcos-2 positions yields proper motions with median errors of 0.045 and 0.049 mas year$^{-1}$ in right ascension and declination, respectively, with 90% of stars having errors less than 0.1 mas year$^{-1}$; systematic errors are about 0.1 mas year$^{-1}$. Single-frame accuracy for positions of the target stars is typically 5 -- 6 mas. Gaia EDR3 astrometry for these bright stars, which are heavily saturated in the Gaia observations, is validated over the magnitude range $2 \lesssim G \lesssim 6$.

Titan's stratosphere has been observed in a superrotation state, where the atmosphere rotates many times faster than the surface does. Another characteristics of Titan's atmosphere is the presence of thick haze layer. In this paper, we performed numerical experiments using a General Circulation Model (GCM), to explore the effects of the haze layer on the stratospheric superrotation. We employed a semi-gray radiation model of Titan's atmosphere following McKay et al. (1999), which takes account of the sunlight absorption by haze particles. The phase change of methane or the seasonal changes were not taken into account. Our model with the radiation parameters tuned for Titan yielded the global eastward wind around the equator with larger velocities at higher altitudes except at around 70 km after $10^5$ Earth days. Although the atmosphere is not in an equilibrium state, the zonal wind profiles is approximately consistent with the observed one. Analysis on our experiments suggests that the quasi-stationary stratospheric superrotation is maintained by the balance between the meridional circulation decoupled from the surface, and the eddies that transport angular momentum equatorward. This is different from, but similar to, the so-called Gierasch mechanism, in which momentum is supplied from the surface. This structure may explain the no-wind region at about $80$ km in altitude.

Grid-based modelling is widely used for estimating stellar parameters. However, stellar model grid is sparse because of the computational cost. This paper demonstrates an application of a machine-learning algorithm using the Gaussian Process (GP) Regression that turns a sparse model grid onto a continuous function. We train GP models to map five fundamental inputs (mass, equivalent evolutionary phase, initial metallicity, initial helium fraction, and the mixing-length parameter) to observable outputs (effective temperature, surface gravity, radius, surface metallicity, and stellar age). We test the GP predictions for the five outputs using off-grid stellar models and find no obvious systematic offsets, indicating good accuracy in predictions.As a further validation, we apply these GP models to characterise 1,000 fake stars. Inferred masses and ages determined with GP models well recover true values within one standard deviation. An important consequence of using GP-based interpolation is that stellar ages are more precise than those estimated with the original sparse grid because of the full sampling of fundamental inputs.

We report on the discovery of a UV absorption counterpart of a low-ionization X-ray ultra-fast outflow (UFO) in the Narrow-Line Seyfert-1 galaxy IRAS 17020+4544. This UV signature of the UFO is seen as a narrow and blueshifted Lyman-alpha absorption feature in the far-UV spectrum, taken with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). The Lyman-alpha feature is found to be outflowing with a velocity of -23430 km/s (0.078 c). We carry out high-resolution UV spectroscopy and photoionization modeling to study the UFO that is seen in the HTS/COS spectrum. The results of our modeling show that the UV UFO corresponds to a low-ionization, low-velocity component of the X-ray UFO found previously with XMM-Newton's Reflection Grating Spectrometer (RGS). The other higher-velocity and higher-ionization components of the X-ray UFOs are not significantly detected in the HST/COS spectrum, consistent with predictions of our photoionization calculations. The multiple ionization and velocity components of the UFOs in IRAS 17020+4544 suggest a scenario where a powerful primary UFO entrains and shocks the ambient medium, resulting in formation of weaker secondary UFO components, such as the one found in the UV band.

The global 21 cm HI emission-line profile of a galaxy encodes valuable information on the spatial distribution and kinematics of the neutral atomic gas. Galaxy interactions significantly influence the HI disk and imprint observable features on the integrated HI line profile. In this work, we study the neutral atomic gas properties of galaxy mergers selected from the Great Observatories All-sky LIRG Survey. The HI spectra come from new observations with the Five-hundred-meter Aperture Spherical Telescope and from a collection of archival data. We quantify the HI profile of the mergers with a newly developed method that uses the curve-of-growth of the line profile. Using a control sample of non-merger galaxies carefully selected to match the stellar mass of the merger sample, we show that mergers have a larger proportion of single-peaked HI profiles, as well as a greater tendency for the HI central velocity to deviate from the systemic optical velocity of the galaxy. By contrast, the HI profiles of mergers are not significantly more asymmetric than those of non-mergers.

Untangling the connection between redshift space coordinates, a velocity measurement, and three dimensional real space coordinates, is a cosmological problem that is often modeled through a linear understanding of the velocity-position coupling. This linear information is better preserved in the Lagrangian space picture of the matter density field. Through Lagrangian space measurements, we can extract more information and make more accurate estimates of the linear growth rate of the universe. In this paper, we address the linear modelling of matter particle velocities through transfer functions, and in doing so examine to what degree the decrease in correlation with initial conditions may be contaminated by velocity-based nonlinearities. With a thorough analysis of the monopole-quadrupole ratio, we find the best-fit value for the Eulerian velocity dispersion, $\sigma_p = 378.3$ km/s. The covariance of the cosmological linear growth rate $f$, is estimated in the Eulerian and Lagrangian cases. Comparing Lagrangian and Eulerian, we find that the error in $f$ improves by a factor of 3, without the need for nonlinear velocity dispersion modelling.

With the advent of new spectroscopic surveys from ground and space, observing up to hundreds of millions of galaxies, spectra classification will become overwhelming for standard analysis techniques. To prepare for this challenge, we introduce a family of deep learning tools to classify features in one-dimensional spectra. As the first application of these Galaxy Spectra neural Networks (GaSNets), we focus on tools specialized at identifying emission lines from strongly lensed star-forming galaxies in the eBOSS spectra. We first discuss the training and testing of these networks and define a threshold probability, PL, of 95% for the high quality event detection. Then, using a previous set of spectroscopically selected strong lenses from eBOSS, confirmed with HST, we estimate a completeness of ~80% as the fraction of lenses recovered above the adopted PL. We finally apply the GaSNets to ~1.3M spectra to collect a first list of ~430 new high quality candidates identified with deep learning applied to spectroscopy and visually graded as highly probable real events. A preliminary check against ground-based observations tentatively shows that this sample has a confirmation rate of 38%, in line with previous samples selected with standard (no deep learning) classification tools and follow-up by Hubble Space Telescope. This first test shows that machine learning can be efficiently extended to feature recognition in the wavelength space, which will be crucial for future surveys like 4MOST, DESI, Euclid, and the Chinese Space Station Telescope (CSST).

Warm dark matter particles with masses in the keV range have been linked with the large group representations in gauge theories through a high number of species at decoupling. In this paper, we address WDM fermionic degrees of freedom from such representations. Bridging higher-dimensional particle physics theories with cosmology studies and astrophysical observations, our approach is two-folded, i.e., it includes realistic models from higher-dimensional representations and constraints from simulations tested against observations. Starting with superalgebras in exceptional periodicity theories, we discuss several symmetry reductions and we consider several representations that accommodate a high number of degrees of freedom. We isolate a model that naturally accommodates both the standard model representation and the fermionic dark matter in agreement with both large and small-scale constraints. This model considers an intersection of branes in $D=27+3$ in a manner that provides the degrees of freedom for the standard model on one hand and 2048 fermionic degrees of freedom for dark matter, corresponding to a $\sim$2 keV particle mass, on the other. In this context, we discuss the theoretical implications and the observable predictions.

We report on the systematic analysis of the X-ray observations of the ultra-luminous X-ray source XMMU J122939.7+075333 located in the globular cluster RZ 2109 in the Virgo galaxy NGC 4472. The inclusion of observations and time intervals ignored in previous works and the careful selection of extraction regions and energy bands have allowed us to identify new flaring episodes, in addition to the ones that made it one of the best black hole candidates in globular clusters. Although most observations are too short and sparse to recognize a regular pattern, the spacing of the three most recent X-ray flares is compatible with a ~34 hours recurrence time. If confirmed by future observations, such behavior, together with the soft spectrum of the X-ray flares, would be strikingly similar to the quasi-periodic eruptions recently discovered in galactic nuclei. Following one of the possible interpretations of these systems and of a peculiar class of extra-galactic X-ray transients, we explore the possibility that XMMU J122939.7+075333 might be powered by the partial disruption of a white dwarf by an intermediate mass (M~700 Msun) black hole.

Using a three-component, multi-scale diffusion model, we show that the cosmic-ray (CR) proton and helium spectra and the dipole anisotropy can be explained with reasonable parameters. The model includes a nearby source associated with the supernova remnant (SNR) that gave rise to the Geminga pulsar, a source at the Galactic center, and a component associated with the Galactic disk. The CR flux below TeV is dominated by the disk component. The center source with a continuous injection of CRs starting about 18 Myr ago is needed to explain the anisotropy above 100 TeV. With the assumption of universal CR spectra injected by all SNRs, the nearby source can produce a TeV spectral bump observed at Earth via slow diffusion across the interstellar magnetic field, which needs to have an angle $ \theta \approx 5^{\circ} $ between the field line and the line of sight toward the source, and have weak magnetic turbulence with the Alfv\'{e}n Mach number $ M_{\text{A}}\approx 0.1 $. Considering the modulation of the Galactic-scale anisotropy by this magnetic field, in a quasi-local approach the field may be directed at a right ascension about $ -90^{\circ} $ and a declination about $ -7.4^{\circ} $ in the equatorial coordinate system.

To understand the formation mechanism of large plumes in solar prominences, we investigate the formation process of two such phenomena. We studied the dynamic and thermal properties of two large plumes using observations from New Vacuum Solar Telescope, the Solar Dynamic Observatory, and the Solar Terrestrial Relations Observatory-Ahead. We find that two large plumes observed with high-resolution data are quite different from previously studied small-scale plumes. They are born at the top of a prominence bubble with a large projected area of 10-20 Mm^2 . Before the occurrence of each large plume, the bubble expands and takes on a quasi-semicircular appearance. Meanwhile, the emission intensity of extreme-ultra-violet (EUV) bands increases in the bubble. A small-scale filament is found to erupt in the bubble during the second large plume. At the point at which the height of the bubble is comparable with half the width of the bubble, the bubble becomes unstable and generates the plumes. During the formation of plumes, two side edges of the top of the bubble, which are dominated by opposite Doppler signals, approach each other. The large plume then emerges and keeps rising up with a constant speed of about 13-15 km/s. These two large plumes have temperatures of 1.3 x 10^6 Kelvin and densities of 2.0 x 10^9 cm^-3, two orders hotter and one order less dense than the typical prominence. We also find that the bubble is a hot, low-density volume instead of a void region beneath the cold and dense prominence. Therefore, we conclude that these two large plumes are the result of the breakup of the prominence bubble triggered by an enhancement of thermal pressure; they separate from the bubble, most likely by magnetic reconnection.

Clusters of galaxies are powerful probes with which to study cosmology and astrophysics. However, for many applications an accurate measurement of a cluster's mass is essential. A systematic underestimate of hydrostatic masses from X-ray observations (the so-called hydrostatic bias) may be responsible for tension between the results of different cosmological measurements. We compare X-ray hydrostatic masses with masses estimated using the caustic method (based on galaxy velocities) in order to explore the systematic uncertainties of both methods and place new constraints on the level of hydrostatic bias. Hydrostatic and caustic mass profiles were determined independently for a sample of 44 clusters based on Chandra observations of clusters from the Hectospec Cluster Survey. This is the largest systematic comparison of its kind. Masses were compared at a standardised radius ($R_{500}$) using a model that includes possible bias and scatter in both mass estimates. The systematics affecting both mass determination methods were explored in detail. The hydrostatic masses were found to be systematically higher than caustic masses on average, and we found evidence that the caustic method increasingly underestimates the mass when fewer galaxies are used to measure the caustics. We limit our analysis to the 14 clusters with the best-sampled caustics where this bias is minimised ($\ge210$ galaxies), and find that the average ratio of hydrostatic to caustic mass at $R_{500}$ is $M_X/M_C=1.12^{+0.11}_{-0.10}$. We interpret this result as a constraint on the level of hydrostatic bias, favouring small or zero levels of hydrostatic bias (less than $20\%$ at the $3\sigma$ level). However, we find systematic uncertainties associated with both mass estimation methods remain at the $10-15\%$ level, which would permit significantly larger levels of hydrostatic bias.

We study the properties and the origin of the radio emission in the most luminous early-type galaxies (ETGs) in the nearby Universe (MK<-25, recession velocity < 7,500 km/s) as seen by the 150 MHz Low-Frequency ARray (LOFAR) observations. LOFAR images are available for 188 of these giant ETGs (gETGs) and 146 (78%) of them are detected above a typical luminosity of ~10E21 W/Hz. They show a large spread in power, reaching up to ~10E26 W/Hz. We confirm a positive link between the stellar luminosity of gETGs and their median radio power, the detection rate, and the fraction of extended sources. About two-thirds (91) of the detected gETGs are unresolved, with sizes <4 kpc, confirming the prevalence of compact radio sources in local sources. Forty-six gETGs show extended emission on scales ranging from 4 to 340 kpc, at least 80% of which have a FRI class morphology. Based on the morphology and spectral index of the extended sources, ~30% of them might be remnant or restarted sources but further studies are needed to confirm this. Optical spectroscopy (available for 44 gETGs) indicates that for seven of them the nuclear gas is ionized by young stars suggesting a contribution to their radio emission from star forming regions. Their radio luminosities correspond to a star formation rate (SFR) in the range 0.1-8 Msun/yr and a median specific SFR of 0.8x10E-12 yr-1. The gas flowing toward the center of gETGs can accrete onto the supermassive black hole but also stall at larger radii and form new stars, an indication that feedback does not completely quench star formation. The most luminous gETGs (25 galaxies with MK < -25.8) are all detected at 150 MHz however they are not all currently turned on: at least four of them are remnant sources and at least one is likely powered by star formation.

We revisit the problem of the existence of KAM tori in extrasolar planetary systems. Specifically, we consider the $\upsilon$ Andromed{\ae} system, by modelling it with a three-body problem. This preliminary study allows us to introduce a natural way to evaluate the robustness of the planetary orbits, which can be very easily implemented in numerical explorations. We apply our criterion to the problem of the choice of a suitable orbital configuration which exhibits strong stability properties and is compatible with the observational data that are available for the $\upsilon$ Andromed{\ae} system itself.

During star formation, the dense gas undergoes significant chemical evolution leading to the emergence of a rich variety of molecules associated with hot cores and hot corinos. The physical and chemical conditions are poorly constrained; the early phases of emerging hot cores in particular represent an unexplored territory. We provide here a full molecular inventory of a massive protostellar core that is proposed to be a precursor of a hot core. We performed an unbiased spectral survey towards the hot core precursor associated with clump G328.2551-0.5321 between 159GHz and 374GHz. To identify the spectral lines, we used rotational diagrams and radiative transfer modelling assuming LTE. We detected 39 species and 26 isotopologues, and were able to distinguish a warm and compact inner region, a colder more extended envelope, and the kinematic signatures of the accretion shocks that have previously been observed with ALMA. We associate most of the emission of the small molecules with the cold gas, while the molecular emission of the warm gas is enriched by complex organic molecules (COMs). We find a high abundance of S-bearing molecules in the cold gas phase suggesting a low sulphur depletion, with a factor of > 1%. We identify nine COMs in the warm gas, four in the cold gas, and four towards the accretion shocks. The high abundances of S-bearing species originating from the undisturbed gas may suggest a contribution from shocked gas at the outflow cavity walls. The molecular composition of the warm gas is similar to that of both hot cores and hot corinos, but the molecular abundances are closer to the values found towards hot corinos than to values found towards hot cores. Considering the compactness of the warm region and its moderate temperature, we suggest that thermal desorption has not been completed towards this object yet, representing an early phase of the emergence of hot cores.

The heliophysics catalogues published by the Ebro Observatory during 1910--1937 have been converted into a digital format in order to provide the data for computational processing. This has allowed us to study in detail the North-South (N-S) asymmetry of solar activity in that period, focusing on two different structures located at two different layers of the solar atmosphere: sunspots (Photosphere) and solar plages (Chromosphere). The examination of the absolute and normalised N-S asymmetry indices in terms of their monthly sum of occurrences and areas has made possible to find out a cyclic behaviour in the solar activity, in which the preferred hemisphere changes systematically with a global period of 7.9 $\pm$ 0.2 yr. In order to verify and quantify accurately this periodicity and study its prevalence in time, we employed the RGO-USAF/NOAA sunspot data series during 1874--2016. Then, we examined each absolute asymmetry index time series through different techniques as the power spectrum analysis, the Complete Ensemble Empirical Mode Decomposition With Adaptive Noise algorithm, or the Morlet wavelet transform. The combined results reveal a cyclic behaviour at different time scales, consisting in two quite stable periodicities of 1.47 $\pm$ 0.02 yr and 3.83 $\pm$ 0.06 yr, which coexist with another three discontinuous components with more marked time-varying periods with means of 5.4 $\pm$ 0.2 yr, 9.0 $\pm$ 0.2 yr, and 12.7 $\pm$ 0.3 yr. Moreover, during 1910--1937, only two dominant signals with averaged periods of 4.10 $\pm$ 0.04 yr and 7.57 $\pm$ 0.03 yr can be clearly observed. Finally, in both signals, periods are slightly longer for plages in comparison with sunspots.

We propose a triple-star scenario where the merger of two pre-main sequence low mass stars, <0.5Mo, ejects a dusty equatorial outflow that obscures and temporarily cause the disappearance of a massive star, >8 Mo. The merger of the low-mass inner binary powers a fain outburst, i.e., a faint intermediate luminosity optical transient (ILOT), but its main effect that can last for decades is to (almost) disappear the luminous massive star of the triple system. The typical orbital period of the triple system in about a year. The merger process proceeds as the more massive star of the two low-mass pre-main sequence star starts to transfer mass to the least massive star in the triple system and as a result of that expands. This 'type II obscuring ILOT' scenario in a triple star system might account for the fading, re-brightening, and then re-fading of the massive post-main sequence star M101-OC1. Our study strengthens the claim that there are alternative scenarios to account for the (almost) disappearing of massive stars, removing the need for failed supernovae. In these scenarios the disappearing is temporary, months to decades, and therefore at later time the massive star explodes as a core collapse supernova even if it forms a black hole.

Massive Early-Type Galaxies (ETG) in the local Universe are believed to be the most mature stage of galaxy evolution. Their stellar population content reveals the evolutionary history of these galaxies. However, while state-of-the-art Stellar Population Synthesis (SPS) models provide an accurate description of observed galaxy spectra in the optical range, the modelling in the Near-Infrared (NIR) is still in its infancy. Here we focus on NIR CO absorption features to show, in a systematic and comprehensive manner, that for massive ETGs, all CO indices, from H through to K band, are significantly stronger than currently predicted by SPS models. We explore and discuss several possible explanations of this "CO mismatch", including the effect of intermediate-age, AGB-dominated, stellar populations, high metallicity populations, non-solar abundance ratios and the initial mass function. While none of these effects is able to reconcile models and observations, we show that ad-hoc "empirical" corrections, taking into account the effect of CO-strong giant stars in the low-temperature regime, provide model predictions that are closer to the observations. Our analysis points to the effect of carbon abundance as the most likely explanation of NIR CO line-strengths, indicating possible routes for improving the SPS models in the NIR.

Observations of scattering polarization and the Hanle effect in various spectral lines are increasingly used to complement traditional solar magnetic field determination techniques. One of the strongest scattering polarization signals in the photosphere is measured in the Sr I line at 4607.3 {\AA} when observed close to the solar limb. Here, we present the first observational evidence of Hanle rotation in the linearly polarized spectrum of this at several limb distances. We observed with the Zurich IMaging POLarimeter, ZIMPOL, at the IRSOL observatory, with exceptionally good seeing conditions, allowing for long integration times. We combined the fast modulating polarimeter with a slow modulator installed in front of the telescope. This combination allows the measurement of spectropolarimetric data being highly precise and unprecedentedly accurate. Fixing the reference direction for positive Stokes $Q$ parallel to the limb, we detect singly-peaked $U/I$ signals well above the noise level. We can exclude instrumental origin for such $U/I$ signals. These signatures are exclusively found in the Sr I line, but not in the adjoining Fe I line, therefore eliminating the Zeeman effect as the mechanism responsible for their appearance. However, we find a clear spatial correlation between the circular polarization produced by the Zeeman effect and the $U/I$ amplitudes. This suggests that the detected $U/I$ signals are the signatures of Hanle rotation caused by a spatially resolved magnetic field. A novel measurement technique allows for determining the absolute level of polarization with unprecedented precision. Using this technique, high-precision spectropolarimetric observations reveal for the first time unambiguous $U/I$ signals due to Hanle rotation in the Sr I line.

The Gaia-ESO Survey (GES) is a large public spectroscopic survey that has collected, over a period of 6 years, spectra of ~ 10^5 stars. This survey provides not only the reduced spectra, but also the stellar parameters and abundances resulting from the analysis of the spectra. The GES dataflow is organised in 19 working groups. Working group 13 (WG13) is responsible for the spectral analysis of the hottest stars (O, B and A type, with a formal cut-off of Teff > 7000 K) that were observed as part of GES. We present the procedures and techniques that have been applied to the reduced spectra, in order to determine the stellar parameters and abundances of these stars. The procedure used is similar to that of other working groups in GES. A number of groups (called `Nodes') each independently analyse the spectra, using their state-of-the-art techniques and codes. Specific for the analysis in WG13 is the large temperature range that is covered (Teff = 7000 - 50,000 K), requiring the use of different analysis codes. Most Nodes can therefore only handle part of the data. Quality checks are applied to the results of these Nodes by comparing them to benchmark stars, and by comparing them one to another. For each star the Node values are then homogenised into a single result: the recommended parameters and abundances. Eight Nodes each analysed (part of) the data. In total 17,693 spectra of 6462 stars were analysed, most of them in 37 open star clusters. The homogenisation led to stellar parameters for 5584 stars. Abundances were determined for a more limited number of stars. Elements studied are He, C, N, O, Ne, Mg, Al, Si and Sc. Abundances for at least one of those elements were determined for 292 stars. The hot-star data analysed here, as well as the Gaia-ESO Survey data in general, will be of considerable use in future studies of stellar evolution and open clusters.

Degeneracy is a method to accommodate exact, low energy vacuum states in scalar-tensor gravitational models despite the presence of an arbitrarily large vacuum energy. However, this approach requires very particular combinations of scalar field and metric couplings in the Lagrangian. In this work we study departures from the restrictive degeneracy condition -- starting from a fiducial model containing an exact Minkowski space solution, we break the degeneracy condition in numerous simple ways to test if the resulting models maintain certain key features -- specifically the dynamical cancellation of a large vacuum energy by the scalar field and the existence of a low energy vacuum state. We highlight the role the tadpole plays in eliminating the fixed points of the dynamical system, generically rendering both the scalar field and metric time dependent. Our results indicate that when violating the degeneracy condition but preserving shift symmetry, the metric maintains an asymptotic Minkowski state, irrespective of the presence of the cosmological constant. In contrast, when shift symmetry is also broken the asymptotic behaviour can radically alter. Regardless, the non-degenerate models in this work share an attractive quality; harboring low energy, late-time asymptotic states that are independent of the vacuum energy. The tadpole allows for a broader class of non-degenerate, self-tuning models than was previously realized.

The postmerger gravitational-wave (GW) signal of a binary neutron star (BNS) merger is expected to contain valuable information that could shed light on the equation of state (EOS) of NSs, the properties of the matter produced during the merger, as well as the nature of any potential intermediate merger product such as hypermassive or supramassive NSs. However, the postmerger lies in the high frequency regime ($ \gtrsim 1000 $ Hz) where current LIGO-Virgo detectors are insensitive. While proposed detectors such as NEMO, Cosmic Explorer and Einstein Telescope could potentially detect the postmerger for BNSs within $\mathcal{O}(10~\mathrm{Mpc})$, such events are likely to be rare. In this work, we speculate on the possibility of detecting the postmerger from BNSs coalescing in the vicinity of supermassive black holes (SMBH). The redshift produced by the gravitational field of the SMBH, as well as the BNS's proper motion around the SMBH, could effectively "stretch" the postmerger signal into the band of the detectors. We demonstrate, using a phenomenological model, that such BNS coalescences would enable constraints on the peak of the postmerger signal that would otherwise have not been possible, provided the degree of redshifting due to the SMBH can be independently acquired. We further show how such mergers would improve EOS model selection using the postmerger signal. We discuss the mechanisms that might deliver such events, and the limitations of this work.

Recent 21 cm line observations of the ultra-diffuse galaxy AGC~114905 indicate a rotating disc largely supported against gravity by orbital motion, as usual. Remarkably, this study has revealed that the form and amplitude of the HI rotation curve is completely accounted for by the observed distribution of baryonic matter, stars and neutral gas, implying that no dark halo is required. It is surprising to find a DM-free galaxy for a number of reasons, one being that a bare Newtonian disk having low velocity dispersion would be expected to be unstable to both axi- and non-axisymmetric perturbations that would change the structure of the disc on a dynamical timescale, as has been known for decades. We present $N$-body simulations of the DM-free model, and one having a low-density DM halo, that confirm this expectation: the disc is chronically unstable to just such instabilities. Since it is unlikely that a galaxy that is observed to have a near-regular velocity pattern would be unstable, our finding calls into question the suggestion that the galaxy may lack, or have little, dark matter. We also show that if the inclination of this near face-on system has been substantially overestimated, the consequent increased amplitude of the rotation curve would accommodate a halo massive enough for the galaxy to be stable.

Recent results of ground-based telescopes, giving high-quality measurements of the CMB temperature power spectrum on small scales motivate the need for an accurate model of foregrounds, which dominate the primary signal at these multipoles. In a previous work, we have shown that cosmological information could be retrieved from the power spectrum of the thermal Sunyaev Zel'dovich (SZ) effect. In this work, we introduce a physically-motivated model of the Epoch of Reionisation (EoR) in the cosmological analysis of CMB data, coherent on all scales. In particular, at high multipoles, the power spectrum of the kinetic SZ (kSZ) effect is inferred from a set of cosmological parameters by a machine-learning algorithm. First including an asymmetric parameterisation of the EoR history in the Planck 2018 data analysis, we retrieve a value of the CMB optical depth consistent with previous results but giving a completely different history of the high-redshift Universe, in which the first luminous sources light up as early as $z=15$. Considering the latest small-scale data from the South Pole Telescope (SPT) and letting the cosmology free to vary, we find that including the new cosmology-dependent tSZ and kSZ spectra help tighten the constraints on the amplitudes of these two spectra by breaking the degeneracy between their amplitudes. We report a $5\sigma$ measurement of the kSZ signal at $\ell=3000$ ($\mathcal{D}_{3000}^\mathrm{kSZ} = 3.3 \pm 0.7~\mu\mathrm{K}^2$, $1\sigma$), marginalised over cosmology, as well as an upper limit on the patchy signal $\mathcal{D}_{3000}^\mathrm{pkSZ}<1.58~\mu\mathrm{K}^2$ (95\% C.L.). Additionally, we find that the SPT data favours slightly earlier reionisation scenarios than Planck, leading to $\tau = 0.062 \pm 0.012$ and a reionisation midpoint $z_{\rm re} = 7.9\pm1.1$ ($1\sigma$), in line with constraints from high-redshift quasars and galaxies.

In this Letter, we present a new idea of probing the distribution of dark matter exhibiting elastic and velocity-independent self-interactions. These interactions might be revealed in multiple measurements of strongly lensed gravitational waves, which can be observationally explored to determine the strength of self-scatterings. Specifically, each individual galactic-scale strong-lensing system whose source is a coalescing compact binary emitting gravitational waves will provide a model-independent measurement of the shear viscosity of dark matter along the line of sight. These individual measurements could be a probe of large-scale distribution of dark matter and its properties. Our results indicate that with 10-1000 strongly lensed gravitational waves from ET and DECIGO, robust constraints on the large-scale distribution of self-interacting dark matter might be produced. More stringent limits on the dark matter scattering cross-section per unit mass ($\sigma_{\chi}/m_{\chi}$) relevant to galaxy and cluster scales are also expected, compared with the conservative estimates obtained in the electromagnetic domain. Finally, we discuss the effectiveness of our method in the context of self-interacting dark matter particle physics.

We perform spectral fitting for a set of O-type stars based on self-consistent wind solutions, which provide mass-loss rate and velocity profiles directly derived from the initial stellar parameters. The great advantage of this self-consistent spectral fitting is therefore the reduction of the number of free parameters to be tuned. Self-consistent values for the line-force parameters (k,alpha,delta) and subsequently for the mass-loss rate and terminal velocity are provided by the m-CAK prescription introduced in Paper I, updated in this work with improvements such as a temperature structure for the wind, self-consistently evaluated from the line-acceleration. Synthetic spectra are calculated using the radiative transfer code FASTWIND, replacing the classical beta-law for our new calculated velocity profiles. We found that self-consistent m-CAK solutions provide values for theoretical mass-loss rates on the order of the most recent predictions of other studies. From here, we generate synthetic spectra with self-consistent hydrodynamics to fit and obtain a new set of stellar and wind parameters for our sample of O-type stars whose spectra was taken with the high resolution echelle spectrograph HERMES (R=85000). We find a satisfactory global fit for our observations, with good accuracy for photospheric He I and He II lines and a quite acceptable fit for H lines. Although this self-consistent spectral analysis is currently constrained in the optical wavelength range only, this is an important step towards the determination of stellar and wind parameters without using a beta-law. Given these results, we expect that the values introduced here should be helpful for future studies about the stars constituting this sample, together with the prospective that the m-CAK self-consistent prescription be extended to numerous studies about massive stars in future.

Currently new radio detection techniques are being explored to detect astrophysical neutrinos beyond the PeV scale interacting in polar ice. Due to the long attenuation length of radio waves in a medium, it can be expected that such instruments will also be sensitive to the radio emission of cosmic ray air showers. Furthermore, cosmic ray air showers hitting a high-altitude layer of ice will initiate an in-ice particle cascade, also leading to radio emission. We present the first results of detailed simulations of the in-ice continuation of these cosmic-ray-induced particle cascades, using a combination of the CORSIKA Monte Carlo code and the Geant4 simulation toolkit. We give an overview of the general features of such particle cascades and present a parameterization in terms of Xmax of the longitudinal and lateral particle distributions. We discuss the feasibility of observing the in-ice particle cascades, both through the detection of the Askaryan radio emission as well as by using the RADAR reflection technique. Based on these results we find that the expected signals from the continuation of in-ice cosmic-ray induced particle cascades will be very similar to neutrino signals. This means a thorough understanding of these events is necessary in the search for neutrino candidates, while it also promises an interesting in-situ natural calibration source.

Recently, there has been growing interest in the use of machine-learning methods for predicting solar flares. Initial efforts along these lines employed comparatively simple models, correlating features extracted from observations of sunspot active regions with known instances of flaring. Typically, these models have used physics-inspired features that have been carefully chosen by experts in order to capture the salient features of such magnetic field structures. Over time, the sophistication and complexity of the models involved has grown. However, there has been little evolution in the choice of feature sets, nor any systematic study of whether the additional model complexity is truly useful. Our goal is to address these issues. To that end, we compare the relative prediction performance of machine-learning-based, flare-forecasting models with varying degrees of complexity. We also revisit the feature set design, using topological data analysis to extract shape-based features from magnetic field images of the active regions. Using hyperparameter training for fair comparison of different machine-learning models across different feature sets, we show that simpler models with fewer free parameters \textit{generally perform better than more-complicated models}, ie., powerful machinery does not necessarily guarantee better prediction performance. Secondly, we find that \textit{abstract, shape-based features contain just as much useful information}, for the purposes of flare prediction, as the set of hand-crafted features developed by the solar-physics community over the years. Finally, we study the effects of dimensionality reduction, using principal component analysis, to show that streamlined feature sets, overall, perform just as well as the corresponding full-dimensional versions.

Observations of the cosmic evolution of different gas phases across time indicate a marked increase in the molecular gas mass density towards $z\sim 2-3$. Such a transformation implies an accompanied change in the global distribution of molecular hydrogen column densities ($N_{\rm{H_2}}$). Using observations by PHANGS-ALMA/SDSS and simulations by GRIFFIN/IllustrisTNG we explore the evolution of this H$_2$ column density distribution function [$f(N_{\rm{H}_2})$]. The H$_2$ (and HI) column density maps for TNG50 and TNG100 are derived in post-processing and are made available through the IllustrisTNG online API. The shape and normalization of $f(N_{\rm{H}_2})$ of individual main-sequence star-forming galaxies are correlated with the star formation rate (SFR), stellar mass (${M_*}$), and H$_2$ mass ($M_{\rm{H}_2}$) in both observations and simulations. TNG100, combined with H$_2$ post-processing models, broadly reproduces observations, albeit with differences in slope and normalization. Also, an analytically modelled $f(N)$, based on exponential gas disks, matches well with the simulations. The GRIFFIN simulation gives first indications that the slope of $f(N_{\rm{H}_2})$ might not majorly differ when including non-equilibrium chemistry in simulations. The $f(N_{\rm{H}_2})$ by TNG100 implies that higher molecular gas column densities are reached at $z=3$ than at $z=0$. Further, denser regions contribute more to the molecular mass density at $z=3$. Finally, H$_2$ starts dominating compared to HI only at column densities above log($N_{\rm{H}_2} / \rm{cm}^{-2}) \sim 21.8-22$ at both redshifts. These results imply that neutral atomic gas is an important contributor to the overall cold gas mass found in the ISM of galaxies including at densities typical for molecular clouds at $z=0$ and $z=3$.

We present Variable Eddington Tensor-closed Transport on Adaptive Meshes (\texttt{VETTAM}), a new algorithm to solve the equations of radiation hydrodynamics (RHD) with support for adaptive mesh refinement (AMR) in a frequency-integrated, two-moment formulation. The method is based on a non-local Variable Eddington Tensor (VET) closure computed with a hybrid characteristics scheme for ray tracing. We use a Godunov method for the hyperbolic transport of radiation with an implicit backwards-Euler temporal update to avoid the explicit timestep constraint imposed by the light-crossing time, and a fixed-point Picard iteration scheme to handle the nonlinear gas-radiation exchange term, with the two implicit update stages jointly iterated to convergence. We also develop a modified wave-speed correction method for AMR, which we find to be crucial for obtaining accurate results in the diffusion regime. We demonstrate the robustness of our scheme with a suite of pure radiation and RHD tests, and show that it successfully captures the streaming, static diffusion, and dynamic diffusion regimes and the spatial transitions between them, casts sharp shadows, and yields accurate results for rates of momentum and energy exchange between radiation and gas. A comparison between different closures for the radiation moment equations, with the Eddington approximation (0th-moment closure) and the $M_1$ approximation (1st-moment closure), demonstrates the advantages of the VET method (2nd-moment closure) over the simpler closure schemes. \texttt{VETTAM} has been coupled to the AMR \texttt{FLASH} (magneto-)hydrodynamics code and we summarize by reporting performance features and bottlenecks of our implementation.

The emission of very-high-energy photons (VHE, E>100 GeV$) in blazars is closely connected to the production of ultra-relativistic particles and the role of these gamma-ray sources as cosmic particle accelerators. This work focuses on a selection of 22 gamma-ray objects from the 2BIGB catalog of high-synchrotron-peaked sources, which are classified as blazar candidates of uncertain type in the 4FGL-DR2 catalog. We study these sources by means of a re-analysis of the first 10 years of gamma-ray data taken with the Fermi Large Area Telescope, including the attenuation by the extragalactic background light. Their broadband spectral energy distributions are also evaluated, using multi-wavelength archival data in the radio, optical, and X-ray bands, in terms of one-zone synchrotron-self-Compton models, adding an external Compton component when needed. Out of this analysis, we identify 17 new extreme high-synchrotron-peaked (EHSP) candidates and compare their physical parameters with those of prototypical EHSP blazars. Finally, the resulting models are used to assess their detectability by the present and future generation of ground-based imaging atmospheric Cherenkov telescopes. We find two VHE candidates within the reach of the current and next generation of Cherenkov telescopes: J0847.0-2336 and J1714.0-2029.

Features in the primordial power spectrum represent the imprinted signal in the density perturbations of the physics and evolution of the early Universe. A measurement of such signals will represents the need to go beyond the minimal assumption made for the initial conditions of the cosmological perturbations. For the first time, we study different templates with undamped oscillations or a bump from the two-point correlation function measured from BOSS DR12 galaxies constraining the amplitude of the features to be at most a few percent. Constraints are competitive to the ones obtained with {\em Planck} DR3.

Numerical general relativistic radiative magnetohydrodynamic simulations of accretion disks around a stellar mass black hole with a luminosity above 0.5 of the Eddington value reveal their stratified, elevated vertical structure. We refer to these thermally stable numerical solutions as puffy disks. Above a dense and geometrically thin core of dimensionless thickness $h/r \sim 0.1$, crudely resembling a classic thin accretion disk, a puffed-up, geometrically thick layer of lower density and $h/r \sim 1.0$ is formed. We discuss the observational properties of puffy disks, in particular the geometrical obscuration of the inner disk by the elevated puffy region at higher observing inclinations, and collimation of the radiation along the accretion disk spin axis, which may explain the apparent super-Eddington luminosity of some X-ray objects. We also present synthetic spectra of puffy disks, and show that they are qualitatively similar to those of a Comptonized thin disk. We demonstrate that the existing xspec spectral fitting models provide good fits to synthetic observations of puffy disks, but cannot correctly recover the input black hole spin. The puffy region remains optically thick to scattering; in its spectral properties the puffy disk roughly resembles that of a warm corona sandwiching the disk core. We suggest that puffy disks may correspond to X-ray binary systems of luminosities above 0.3 of the Eddington luminosity in the intermediate spectral states.

Transit observations in the helium triplet around 10830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionisation and recombination of helium in the exoplanetary atmosphere. This ionisation is caused by stellar photons at extreme ultra-violet (EUV) wavelengths; however, no currently active telescopes can observe this part of the stellar spectrum. The relevant part of the stellar EUV spectrum consists of individual emission lines, many of them being formed by iron at coronal temperatures. The stellar iron abundance in the corona is often observed to be depleted for high-activity low-mass stars due to the first ionisation potential (FIP) effect. I show that stars with high versus low coronal iron abundances follow different scaling laws that tie together their X-ray emission and the narrow-band EUV flux that causes helium ionisation. I also show that the stellar iron to oxygen abundance ratio in the corona can be measured reasonably well from X-ray CCD spectra, yielding similar results to high-resolution X-ray observations. Taking coronal iron abundance into account, the currently observed large scatter in the relationship of EUV irradiation with exoplanetary helium transit depths can be reduced, improving the target selection criteria for exoplanet transmission spectroscopy. In particular, previously puzzling non-detections of helium for Neptunic exoplanets are now in line with expectations from the revised scaling laws.

We derived the second post-Newtonian solution for the quasi-Keplerian motion of a charged test particle in the Reissner-Nordstr\"om spacetime under the harmonic coordinates. The solution is formulated in terms of the test particle's orbital energy and angular momentum, both of which are constants at the second post-Newtonian order. The charge effects on the test particle's motion including the orbital period and perihelion precession are displayed explicitly. Our results can be applied to the cases in which the test particle has small charge-to-mass ratio, or the test particle has arbitrary charge-to-mass ratio but the multiplication of the test particle and the gravitational source's charge-to-mass-ratios is much smaller than 1.

Spontaneous CP violation, such as the Nelson-Barr (NB) mechanism, is an attractive scenario for addressing the strong CP problem while realizing the observed phase of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. However, not only the CKM phase but also the baryon asymmetric Universe requires sources of CP violation. In this study, we show that a supersymmetric NB mechanism can naturally accommodate the Affleck-Dine (AD) baryogenesis within a CP-invariant Lagrangian. The model provides flat directions associated with new heavy quarks. Focusing on one of the directions, we find that the correct baryon asymmetry is obtained with a sufficiently low reheating temperature which does not cause the gravitino problem. Some parameter space is consistent with the gravitino dark matter. We assess radiative corrections to the strong CP phase induced by gauge-mediated supersymmetry breaking and CP-violating heavy fields and show that the strong CP problem is solved in a viable parameter space where the visible sector supersymmetric particles must be lighter than O(100) TeV. Even in the case that they are heavier than the TeV scale, our model predicts the neutron electric dipole moment within the reach of the near future experiments. Our model addresses the electroweak naturalness problem, strong CP problem, baryon asymmetric Universe, and dark matter. Then, the model may give a new compelling paradigm of physics beyond the Standard Model.

The search for nanohertz-frequency gravitational waves (GWs) with pulsar-timing arrays requires a continual expansion of datasets and monitored pulsars. Whereas detection of the stochastic GW background is predicated on measuring a distinctive pattern of inter-pulsar correlations, characterizing the background's spectrum is driven by information encoded in the power spectra of the individual pulsars' time series. We propose a new technique for rapid Bayesian characterization of the stochastic GW background that is fully parallelized over pulsar datasets. This Factorized Likelihood (FL) technique empowers a modular approach to parameter estimation of the GW background, multi-stage model selection of a spectrally-common stochastic process and quadrupolar inter-pulsar correlations, and statistical cross-validation of measured signals between independent pulsar sub-arrays. We demonstrate the equivalence of this technique's efficacy with the full pulsar-timing array likelihood, yet at a fraction of the required time. Our technique is fast, easily implemented, and trivially allows for new data and pulsars to be combined with legacy datasets without re-analysis of the latter.

The future space-borne gravitational wave (GW) detectors would provide a promising probe for the new physics beyond the standard model that admits the first-order phase transitions. The predictions for the GW background vary sensitively among different concrete particle physics models but also share a large degeneracy in the model buildings, which motivates an effective model description on the phase transition based on different patterns of the electroweak symmetry breaking (EWSB). In this paper, using the scalar $N$-plet model as a demonstration, we propose an effective classification for three different patterns of EWSB: (1) radiative symmetry breaking with classical scale invariance, (2) Higgs mechanism in generic scalar extension, and (3) higher dimensional operators. We conclude that a strong first-order phase transition could be realized for (1) and (2) with a small quartic coupling and a small isospin of an additional $N$-plet field for the light scalar field model with and without the classical scale invariance, and (3) with a large mixing coupling between scalar fields and a large isospin of the $N$-plet field for the heavy scalar field model.

We present a summary of the main results within the Scale Invariant Vacuum (SIV) paradigm as related to the Weyl Integrable Geometry. After a brief review of the mathematical framework, we will highlight the main results related to inflation within the SIV [9], the growth of the density fluctuations [8], and the application of the SIV to scale-invariant dynamics of Galaxies, MOND, Dark Matter, and the Dwarf Spheroidals [7]. The connection of the weak-field SIV results to the un-proper time parametrization within the re-parametrization paradigm is also discussed [14].

We investigate the parameter estimation of gravitational waves emitted by the eccentric compact binaries in the mid-frequency (0.1--10 Hz) band. Based on the configuration of one cluster of DECIGO (B-DECIGO), we simulate five types of typical compact binaries in GWTC-3 with component mass ranging from $\mathcal{O}(1\sim100)~M_{\odot}$. For each type of binaries, we assign discrete eccentricities from 0 to 0.4 at 0.1 Hz in $10^3$ random orientations. The multiple harmonics induced by eccentricity can break the degeneracy between parameters. We find that with eccentricity $e_0=0.4$, these typical binaries can achieve $\mathcal{O}(10^2-10^4)$ improvement for the distance inference in the near face-on orientations, compared to the circular case. More importantly, a nonvanishing eccentricity ($0.01\sim0.4$) can significantly improve the source localization of the typical binaries with component mass greater than $30~M_{\odot}$, most by a factor of $1.5\sim{3.5}$ orders of magnitude. Our result shows the remarkable significance of eccentricity for dark sirens in the mid-band as precise probes of the Universe.

We introduce a stochastic multi-photon dynamics on reciprocal space. Assuming isotropy, we derive the diffusion limit for a tagged photon to be a nonlinear Markov process on frequency. The nonlinearity stems from the stimulated emission. In the case of Compton scattering with thermal electrons, the limiting process describes the dynamical fluctuations around the Kompaneets equation. More generally, we construct a photon frequency diffusion process which enables to include nonequilibrium effects. Modifications of the Planck Law may thus be explored, where we focus on the low-frequency regime.

Blip glitches, a type of short-duration noise transient in the LIGO--Virgo data, are a nuisance for the binary black hole (BBH) searches. They affect the BBH search sensitivity significantly because their time-domain morphologies are very similar, and that creates difficulty in vetoing them. In this work, we construct a deep-learning neural network to efficiently distinguish BBH signals from blip glitches. We introduce sine-Gaussian projection (SGP) maps, which are projections of GW frequency-domain data snippets on a basis of sine-Gaussians defined by the quality factor and central frequency. We feed the SGP maps to our deep-learning neural network, which classifies the BBH signals and blips. Whereas the BBH signals are simulated, the blips used are taken from real data throughout our analysis. We show that our network significantly improves the identification of the BBH signals in comparison to the results obtained using traditional-$\chi^2$ and sine-Gaussian $\chi^2$. For example, our network improves the sensitivity by 75% at a false-positive rate of $10^{-2}$ for BBHs with total mass in the range $[80,140]~M_{\odot}$ and SNR in the range $[3,8]$. Also, it correctly identifies 95% of the real GW events in GWTC-3. The computation time for classification is a few minutes for thousands of SGP maps on a single core. With further optimisation in the next version of our algorithm, we expect a further reduction in the computational cost. Our proposed method can potentially improve the veto process in the LIGO--Virgo GW data analysis and conceivably support identifying GW signals in low-latency pipelines.

Based on the accurately calibrated interaction FSUGold, we show that including isovector scalar $\delta$ meson and its coupling to isoscalar scalar $\sigma$ meson in the relativistic mean field (RMF) model can soften the symmetry energy $E_{\rm{sym}}(n)$ at intermediate density while stiffen the $E_{\rm{sym}}(n)$ at high densities. We find this new RMF model can be simultaneously compatible with (1) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (2) the neutron skin thickness of $^{208}$Pb from the PREX-II experiment, (3) the largest mass of neutron star (NS) reported so far from PSR J0740+6620, (4) the limit of $\Lambda_{1.4}\leq580$ for the dimensionless tidal deformability of the canonical 1.4$M_{\odot}$ NS from the gravitational wave signal GW170817, (5) the mass-radius of PSR J0030+0451 and PSR J0740+6620 measured by NICER, and thus remove the tension between PREX-II and GW170817 observed in the conventional RMF model.

The preference for the axial dipole in planetary dynamos is investigated through the analysis of wave motions in spherical dynamo models. Our study focuses on the role of slow magnetostrophic waves, which are generated from localized balances between the Lorentz, Coriolis and buoyancy (MAC) forces. Since the slow waves are known to intensify with increasing field strength, simulations in which the field grows from a small seed towards saturation are useful in understanding the role of these waves in dynamo action. Axial group velocity measurements in the energy-containing scales show that fast inertial waves slightly modified by the magnetic field and buoyancy are dominant under weak fields. However, the dominance of the slow waves is evident for strong fields satisfying $|\omega_M/\omega_C| \sim $ 0.1, where $\omega_M$ and $\omega_C$ are the frequencies of the Alfv\'en and inertial waves respectively. A MAC wave window of azimuthal wavenumbers is identified wherein helicity generation by the slow waves strongly correlates with dipole generation. Analysis of the magnetic induction equation suggests a poloidal--poloidal field conversion in the formation of the dipole. Finally, the attenuation of slow waves may result in polarity reversals in a strongly driven Earth's core.

Numerical relativity simulations are the only way to calculate exact gravitational waveforms from binary neutron star mergers and to design templates for gravitational-wave astronomy. The accuracy of these numerical calculations is critical in quantifying tidal effects near merger that are currently one of the main sources of uncertainty in merger waveforms. In this work, we explore the use of an entropy-based flux-limiting scheme for high-order, convergent simulations of neutron star spacetimes. The scheme effectively tracks the stellar surface and physical shocks using the residual of the entropy equation thus allowing the use of unlimited central flux schemes in regions of smooth flow. We perform the first neutron star merger simulations with such a method and demonstrate up to fourth-order convergence in the gravitational waveform phase. The scheme reduces the phase error up to a factor five when compared to state-of-the-art high-order characteristic schemes and can be employed for producing faithful tidal waveforms for gravitational-wave modelling.