Papers for Monday, Feb 26 2024

Policy Brief on "Large Projects in Astronomy: An Indian Endeavour", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. Cutting-edge astronomy initiatives often entail substantial investment and require a high level of expertise. Even the most technologically advanced nations recognize the value of establishing international partnerships to secure both financial resources and talent for these ambitious endeavours as they hold immense promise for catalysing transformative scientific discoveries, driving technological innovation, provide training opportunities for the next generation of scientists and engineers, and expanding our understanding of the cosmos that surrounds us. Crucially, large-scale multilateral collaborations serve as powerful agents for promoting unity and peace among the global population. Participants from various nations share a vested interest in the success of these projects and the wealth of knowledge they yield, fostering a sense of common purpose and shared goals. By utilizing astroinformatics capabilities, these initiatives are not merely enhancing our comprehension of the universe but are also actively contributing to the attainment of sustainable development objectives. In this discussion, we delve into the challenges faced, and prospects for substantial astronomical undertakings. Additionally, we present recommendations aimed at guaranteeing their effectiveness and optimizing their influence on both scientific advancement and society. The policy webinar took place during the G20 presidency in India (2023). A summary based on the seven panels can be found here: arxiv:2401.04623.

Policy Brief on "Regional and Global Collaborations in Astronomy", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. Astronomy brings together advanced scientific research, state-of-the-art technology, and educational initiatives, all while captivating and stimulating people of all ages. By doing so, it possesses the potential to serve as a powerful catalyst for sustainable global development and the resolution of global societal issues. It attracts a diverse range of scientists and experts from various fields, fostering collaboration and innovation. By leveraging their resources, influence, and diplomatic initiatives, S20 academies can foster an enabling environment for international collaborations in astronomy, facilitate knowledge exchange, and drive scientific advancements that benefit humanity. This policy brief explores the opportunities and challenges presented by regional and global collaborations in astronomy. The policy webinar took place during the G20 presidency in India (2023). A summary based on the seven panels can be found here: arxiv:2401.04623.

We introduce SigNova, a new semi-supervised framework for detecting anomalies in streamed data. While our initial examples focus on detecting radio-frequency interference (RFI) in digitized signals within the field of radio astronomy, it is important to note that SigNova's applicability extends to any type of streamed data. The framework comprises three primary components. Firstly, we use the signature transform to extract a canonical collection of summary statistics from observational sequences. This allows us to represent variable-length visibility samples as finite-dimensional feature vectors. Secondly, each feature vector is assigned a novelty score, calculated as the Mahalanobis distance to its nearest neighbor in an RFI-free training set. By thresholding these scores we identify observation ranges that deviate from the expected behavior of RFI-free visibility samples without relying on stringent distributional assumptions. Thirdly, we integrate this anomaly detector with Pysegments, a segmentation algorithm, to localize consecutive observations contaminated with RFI, if any. This approach provides a compelling alternative to classical windowing techniques commonly used for RFI detection. Importantly, the complexity of our algorithm depends on the RFI pattern rather than on the size of the observation window. We demonstrate how SigNova improves the detection of various types of RFI (e.g., broadband and narrowband) in time-frequency visibility data. We validate our framework on the Murchison Widefield Array (MWA) telescope and simulated data and the Hydrogen Epoch of Reionization Array (HERA).

This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of $\sim$2000 stars in the Galactic Bulge/bar spatially contained within $|X_{Gal}|<$5 kpc, $|Y_{Gal}|<$3.5 kpc, and $|Z_{Gal}|<$1 kpc, and spanning metallicities between $-$2.0$\lesssim$[Fe/H]$\lesssim$+0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our Bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd]$<$0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of Bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the Bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magneto-rotational supernovae.

Overdensities in the radial phase space $(r,v_r)$ of the Milky Way's halo have previously been associated with the phase-mixed debris of a highly radial merger event, such as Gaia Sausage-Enceladus. We present and test an alternative theory in which the overdense 'chevrons' are instead composed of stars trapped in resonances with the Galactic bar. We develop an analytic model of resonant orbits in the isochrone potential, and complement this with a test particle simulation of a stellar halo in a realistic barred Milky Way potential. These models are used to predict the appearance of action space $(J_\phi,J_r)$ and radial phase space in the Solar neighbourhood. They are able to reproduce almost all salient features of the observed chevrons. In particular, both the analytic model and simulation predict that the chevrons are more prominent at $v_r<0$ when viewed near the Sun, as is observed by Gaia. This is inconsistent with formation by an ancient merger event. We also associate individual chevrons with specific resonances. At a bar pattern speed of $\Omega_\mathrm{b}=35$ km s$^{-1}$kpc$^{-1}$, the two most prominent prograde chevrons align very closely with the corotation and outer Lindblad resonances. The former can be viewed as a highly eccentric extension of the Hercules stream. Finally, our model predicts that the $v_r$ asymmetry changes sign as a function of Galactic radius and azimuth, and we find evidence that this is indeed the case in the Milky Way.

We have discovered the stellar counterpart to the ALFALFA Virgo 7 cloud complex, which has been thought to be optically dark and nearly star-free since its discovery in 2007. This ~190 kpc long chain of enormous atomic gas clouds ($M_\mathrm{HI} \sim 10^9 \; \mathrm{M_\odot}$) is embedded in the hot intracluster medium of the Virgo galaxy cluster but is isolated from any galaxy. Its faint, blue stellar counterpart, BC6, was identified in a visual search of archival optical and UV imaging. Follow-up observations with the Green Bank Telescope, Hobby-Eberly Telescope, and Hubble Space Telescope demonstrate that this faint counterpart is at the same velocity as the atomic gas, is actively forming stars, and is metal-rich ($12 + \mathrm{(O/H)} = 8.58 \pm 0.25$). We estimate its stellar mass to be only $\log ( M_\ast/\mathrm{M_\odot}) \sim 4.4$, making it one of the most gas-rich stellar systems known. Aside from its extraordinary gas content, the properties of BC6 are entirely consistent with those of a recently identified class of young, low-mass, isolated, and star-forming clouds in Virgo, that appear to have formed via extreme ram pressure stripping events. We expand the existing discussion of the origin of this structure and suggest NGC 4522 as a likely candidate, however, the current evidence is not fully consistent with any of our proposed progenitor galaxies. We anticipate that other "dark" gas clouds in Virgo may have similarly faint, star-forming counterparts. We aim to identify these through the help of an ongoing citizen science search of the entire cluster.

Context. Large thermal variations have been observed in neutron stars that typically are not aligned with density gradients. Such terms may activate the Biermann battery effect, leading to thermo-electric interactions and the generation of electromotive force. Aims. We aim to identify the impact a temperature anisotropy on a neutron star's crust can have in the evolution of its magnetic field, through the thermo-electric terms. Methods. We consider a neutron star crust with large temperature gradients, associated with long-lived hot spots, described by a Gaussian-type function localized. We simulate the interplay between the battery term and the Hall and Ohmic evolution numerically, for axisymmetric systems. Results. The results indicate that for crust temperatures of $\sim$$10^9$ K the toroidal field can be amplified up to $\sim$$10^{14}$ - $10^{15}$ G near the points of maximum temperature gradients, and it locally changes the architecture of the poloidal field lines. For internal crustal temperatures around $\sim$$10^8$ K, the temperature gradient generates fields of about two orders of magnitude lower. In such cases, saturation is achieved after some hundred thousand years, after which the battery and Ohmic dissipation balance each other. Conclusions. We conclude that the thermoelectric effect can impact the overall magnetic field evolution, provided that the thermal gradient is maintained for a sufficiently long time. Neutron stars endowned with moderate strength magnetic fields may be affected by the thermoelectric effect if the hotspots survive for timescales of a few kiloyears.

We study the populations of stellar clumps in three high-redshift galaxies, at z=4.92, 4.88 and 4.03, gravitationally lensed by the foreground galaxy clusters MS1358, RCS0224 and MACS0940, respectively. The lensed galaxies consist of multiple counter-images with large magnifications, mostly above $\rm \mu>5$ and in some cases reaching $\rm \mu>20$. We use rest-frame UV observations from the HST to extract and analyse their clump populations, counting 10, 3 and 11 unique sources, respectively. Most of the clumps have derived effective radii in the range $\rm R_{eff}=10-100$ pc, with the smallest one down to 6 pc, i.e. consistent with the sizes of individual stellar clusters. Their UV magnitudes correspond to $\rm SFR_{UV}$ mostly in the range $\rm 0.1-1\ M_\odot yr^{-1}$; the most extreme ones, reaching $\rm SFR_{UV}=5\ M_\odot yr^{-1}$ are among the UV-brightest compact ($\rm R_{eff}<100$ pc) star-forming regions observed at any redshift. Clump masses span a broad range, from $10^6$ to $\rm 10^9\ M_\odot$; stellar mass surface densities are comparable, and in many cases larger, than the ones of local stellar clusters, while being typically 10 times larger in size. By compiling published properties of clump populations at similar spatial resolution between redshift 0 and 5, we find a tentative evolution of $\rm \Sigma_{SFR}$ and $\rm \Sigma_{M_\star}$ with redshift, especially when very compact clumps ($\rm R_{eff}\leqslant20$ pc) are considered. We suggest that these trends with redshift reflect the changes in the host galaxy environments where clumps form. Comparisons with the local universe clumps/star clusters shows that, although rare, conditions for elevated clump $\rm \Sigma_{SFR}$ and $\rm \Sigma_{M_\star}$ can be found.

Fullerenes have been observed in several astronomical objects since the discovery of C$_{60}$ in the mid-infrared (mid-IR) spectrum of the planetary nebula (PN) Tc 1. It has been suggested that the carriers of the broad unidentified infrared (UIR) plateau features, such as the 9$-$13$\mu$m emission feature (12$\mu$m hereafter), may be related to the formation of fullerenes. In particular, their carriers have been suggested to be mixed aromatic or aliphatic hydrocarbons such as hydrogenated amorphous carbon (HAC-like hereafter) grains. For this study, we modeled the mid-IR emission of the C$_{60}$-PN Tc 1 with a photoionization code, including for the first time the laboratory optical constants ($n$ and $k$ indices) of HAC-like dust at 300 K. Interestingly, we find that the broad 12$\mu$m plateau feature in Tc 1 is well reproduced by using a distribution of canonical HAC grains, while at the same time they provide an important fraction of the IR dust continuum emission and are consistent with the other UIR features observed (e.g., the broad 6$-$9$\mu$m plateau feature). This finding suggests that HAC-like grains may be possible carriers of the 12$\mu$m plateau feature, being likely related to the fullerene formation mechanism in PNe. More laboratory experiments, to obtain the optical constants of HAC-like dust with several structures or a composition at different physical conditions, are strongly encouraged -- that is, in order to extend this pilot study to more fullerene PNe, and to unveil the details of fullerene formation and of the potential carriers of the elusive UIR plateau features.

For ongoing studies of the role of rotation in stellar evolution, we require large catalogs of rotation periods for testing and refining gyrochronology. While there is a wealth of data from the Kepler and K2 missions, TESS presents both an opportunity and a challenge: despite its all-sky coverage, rotation periods remain hard to detect. We analyzed individual TESS sectors to detect short-period stellar rotation, using only parameters measured from light curves for a robust and unbiased method of evaluating detections. We used random forest classifiers for vetting, trained on a large corpus of period measurements in KELT data from the Oelkers et al. (2018) catalog and using TESS full-frame image light curves generated by eleanor (Feinstein et al. 2019). Finally, using data from the first 26 sectors of TESS, we analyzed 432,704 2-minute cadence single-sector light curves for FGKM dwarfs. We detected 16,800 periods in individual sector light curves, covering 10,909 distinct targets, and we present a catalog of the median period for each target as measured by a Lomb-Scargle periodogram.

This review highlights the role of the \textit{Gaia} space mission in transforming white dwarf research. These stellar remnants constitute 5-7\% of the local stellar population in volume, yet before \textit{Gaia} the lack of trigonometric parallaxes hindered their identification. The mission's Data Release 2 in 2018 provided the first unbiased colour-absolute magnitude diagram of the local stellar population, identifying 260\,000 white dwarfs, with the number later increasing to over 355\,000 in Data Release 3. Since then, more than 400 white dwarf studies have made critical use of \textit{Gaia} data, establishing it as a fundamental resource for white dwarf identification, fundamental parameter determination and more recently spectral type characterisation. The review underscores the routine reliance on \textit{Gaia} parallaxes and extensive use of its photometry in white dwarf surveys. We also discuss recent discoveries firmly grounded \textit{Gaia} data, including white dwarf mergers, exotic compact binaries and evolved planetary systems.

The Gaia M dwarf gap, also known as the Jao Gap, is a novel feature discovered in the Gaia DR2 G vs. BP-RP color magnitude diagram. This gap represents a 17 percent decrease in stellar density in a thin magnitude band around the convective transition mass ($\sim 0.35 M_{\odot}$) on the main sequence. Previous work has demonstrated a paucity of Hydrogen Alpha emission coincident with the G magnitude of the Jao Gap in the solar neighborhood. The exact mechanism which results in this paucity is as of yet unknown; however, the authors of the originating paper suggest that it may be the result of complex variations to a star's magnetic topology driven by the Jao Gap's characteristic formation and breakdown of stars' radiative transition zones. We present a follow up investigating another widely used magnetic activity metric, Calcium II H\&K emission. Ca II H\&K activity appears to share a similar anomalous behavior as H$\alpha$ does near the Jao Gap magnitude. We observe an increase in star-to-star variation of magnetic activity near the Jao Gap. We present a toy model of a stars magnetic field evolution which demonstrates that this increase may be due to stochastic disruptions to the magnetic field originating from the periodic mixing events characteristic of the convective kissing instabilities which drive the formation of the Jao Gap.

Building on the recent release of a new \emph{Gaia}-based blue straggler star catalog in Galactic open star clusters (OCs), we explored the properties of these stars in a cluster sample spanning a wide range in fundamental parameters. We employed \emph{Gaia} EDR3 to assess the membership of any individual blue or yellow straggler to their parent cluster. We then made use of the \texttt{ASteCA} code to estimate the fundamental parameters of the selected clusters, in particular, the binary fraction. With all this at hand, we critically revisited the relation of the blue straggler population and the latter. For the first time, we found a correlation between the number of blue stragglers and the host cluster binary fraction and binaries. This supports the hypothesis that binary evolution is the most viable scenario of straggler formation in Galactic star clusters. The distribution of blue stragglers in the Gaia color-magnitude diagram was then compared with a suite of composite evolutionary sequences derived from binary evolutionary models that were run by exploring a range of binary parameters: age, mass ratio, period, and so forth. The excellent comparison between the bulk distribution of blue stragglers and the composite evolutionary sequences loci further supports the binary origin of most stragglers in OCs and paves the way for a detailed study of individual blue stragglers

Multi-wavelength photometry of brown dwarfs and planetary-mass objects provides insight into their atmospheres and cloud layers. We present near-simultaneous $J-$ and $K_s-$band multi-wavelength observations of the highly variable T2.5 planetary-mass object, SIMP J013656.5+093347. We reanalyze observations acquired over a single night in 2015 using a recently developed data reduction pipeline. For the first time, we detect a phase shift between $J-$ and $K_s-$band light curves, which we measure to be $39.9^{\circ +3.6}_{ -1.1}$. Previously, phase shifts between near-infrared and mid-infrared observations of this object were detected and attributed to probing different depths of the atmosphere, and thus different cloud layers. Using the Sonora Bobcat models, we expand on this idea to show that at least two different patchy cloud layers must be present to explain the measured phase shift. Our results are generally consistent with recent atmospheric retrievals of this object and other similar L/T transition objects.

Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. We built a comprehensive census of hot core candidates towards the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission that is a complex species commonly observed towards sites of star formation. We built up a catalog of 76 hot core candidates with masses ranging from about 0.2 to 80 Msun , of which 56 are new detections. A large majority of these objects are compact, rather circular, with deconvolved FWHM sizes of about 2300 au on average. About 30% of our sample of methyl formate sources have core masses above 8 Msun within sizes ranging from about 1000 au to 13400 au, which well correspond to archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores can be explained by a mixture of contribution from shocks, or may correspond to objects in a more evolved state, i.e. beyond the hot core stage. We find that the fraction of hot core candidates increases with the core mass. The large fraction of hot core candidates towards the most massive cores suggests that they rapidly enter the hot core phase and feedback effects from the forming protostar(s) impact their environment on short time-scales.

Specutils is an Astropy affiliated package which provides a consistent interface to astronomical spectra (primarily 1D). As Specutils can be adapted to parse spectra in many different formats, Specutils plays a key role at Data Central, allowing us to handle the diverse formats provided to us by survey teams. In this poster, I will cover what Specutils is, how it works, how Data Central uses it, and why you too should use and contribute to it.

AT2018cow is the most extensively observed and widely studied fast blue optical transient to date; its unique observational properties challenge all existing standard models. In this paper, we model the luminosity evolution of the optical, soft X-ray, and hard X-ray emission, as well as the X-ray spectrum of AT2018cow with a magnetar-centered engine model. We consider a two-zone model with a striped magnetar wind in the interior and an expanding ejecta outside. The soft and hard X-ray emission of AT2018cow can be explained by the leakage of high-energy photons produced by internal gradual magnetic dissipation in the striped magnetar wind, while the luminous thermal UV/optical emission results from the thermalization of the ejecta by the captured photons. The two-component energy spectrum yielded by our model with a quasi-thermal component from the optically thick region of the wind superimposed on an optically thin synchrotron component well reproduces the X-ray spectral shape of AT2018cow. The Markov Chain Monte Carlo fitting results suggest that in order to explain the very short rise time to peak of the thermal optical emission, a low ejecta mass $M_{\rm ej}\approx0.1~M_\odot$ and high ejecta velocity $v_{\rm SN}\approx0.17c$ are required. A millisecond magnetar with $P_0\approx3.7~\rm ms$ and $B_p\approx2.4\times10^{14}~\rm G$ is needed to serve as the central engine of AT2018cow.

We report two phenomena detected in PSR J0344$-$0901 from two observations conducted at frequency centered at 1.25 GHz using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The first phenomenon manifests as shifting in the pulse emission to later longitudinal phases and then gradually returns to its original location. The event lasts for about 216 pulse periods, with an average shift of about $0.7^\circ$ measured at the peak of the integrated profile. Changes in the polarization position angle (PPA) are detected around the trailing edge of the profile, together with an increase in the profile width. The second phenomenon is characterized by the apparent movement of subpulses, which results in different subpulse track patterns across the profile window. For the first time in this pulsar, we identify four emission modes, each with unique subpulse movement, and determine the pattern periods for three of the emission modes. Pulse nulling was not detected. Modeling of the changes in the PPA using the rotating vector model gives an inclination angle of $75.12^\circ \pm 3.80^\circ$ and an impact parameter of $-3.17^\circ \pm 5.32^\circ$ for this pulsar. We speculate that the subpulse movement may be related to the shifting of the pulse emission.

We have mapped the magnetic field ($B$-field) for a region of about 30 pc around the centre of our Galaxy, which encompasses the circumnuclear disk (CND), the mini-spirals, and the 20 km s$^{-1}$ and 50 km s$^{-1}$ molecular clouds, using thermal dust polarization observations obtained from SOFIA/HAWC+ and JCMT/SCUPOL. We decompose the spectra of $^{12}$CO ($J=3\rightarrow2$) transition from this region into individual clustered cloud components and find the polarization observed at different wavelengths might be tracing completely different layers of dust along the line-of-sight (LOS). We use modified Davis-Chandrasekhar-Fermi methods to estimate the $B$-field from the observations. From our analysis we find the mean strength of the plane-of-sky $B$-field ($B_{{}_{\mathrm{POS}}}$) of the CND and the mini-spirals, probed at 53 $\mu$m to be of the order of $\sim2$ mG. The magnetic field is lowest close to the Galactic Centre, in the region of the ionized mini-cavity within the CND with $B_{{}_{\mathrm{POS}}}<1$ mG, and increases outwards. However, the longer wavelength polarization at 216 $\mu$m appears to come from a dust layer that is cooler and behind the CND and has a stronger $B$-field of about 6 mG. The $B$-field has the least strength along the Eastern Arm of the mini-spiral, which is also the only region with $\mathcal{M}_{\mathrm{A}}>1$ and a mass-to-flux ratio of $\lambda\gtrsim1$. The similarity between the $B_{{}_{\mathrm{POS}}}$ estimates of the 53 $\mu$m and 850 $\mu$m observations might indicate them originating from the same depth along the LOS, mostly from the CND and its foreground cloud features, including the negative-longitude extension.

We explore the redshift evolution of the radio luminosity function (RLF) of star-forming galaxies using GALFORM, a semi-analytic model of galaxy formation (SAMGF) and MAGNETIZER, a dynamo model of the magnetic field evolving in a galaxy through its formation history. Assuming energy equipartition between the magnetic field and cosmic rays, we derive the synchrotron luminosity of each sample galaxy. In a model where the turbulent speed is correlated with the star formation rate, the RLF is in fair agreement with observations in the redshift range $0 \leq z \leq 2$. At larger redshifts, the structure of galaxies, their interstellar matter and turbulence appear to be rather different from those at $z\lesssim2$, so that the turbulence and magnetic field models applicable at low redshifts become inadequate. The strong redshift evolution of the RLF at $0 \leq z \leq 2$ can be attributed to an increased number, at high redshift, of galaxies with large disc volumes and strong magnetic fields. On the other hand, in models where the turbulent speed in galaxies is a constant or assumed to be an explicit function of the redshift, the redshift evolution of the RLF is poorly captured. The evolution of the interstellar turbulence and outflow parameters appear to be major (but not the only) drivers of the RLF changes. We find that both the small- and large-scale magnetic fields contribute significantly to the RLF but the small-scale field dominates at high redshifts. Polarisation observations will therefore be important to distinguish these two components and understand better the evolution of galaxies and their nonthermal constituents.

Around a million quasars have been catalogued in the Universe by probing deeper and using new methods for discovery. However, the hardest ones to find seem to be the rarest and brightest specimen. In this work, we study the properties of the most luminous of all quasars found so far. It has been overlooked until recently, which demonstrates that modern all-sky surveys have much to reveal. The black hole in this quasar accretes around one solar mass per day onto an existing mass of $\sim$17 billion solar masses. In this process its accretion disc alone releases a radiative energy of $2\times 10^{41}$ Watts. If the quasar is not strongly gravitationally lensed, then its broad line region (BLR) is expected to have the largest physical and angular diameter occurring in the Universe, and will allow the Very Large Telescope Interferometer to image its rotation and measure its black hole mass directly. This will be an important test for BLR size-luminosity relations, whose extrapolation has underpinned common black-hole mass estimates at high redshift.

The excesses in the electron and positron spectra observed by many experiments, such as PAMELA and AMS-02, have sparked significant theoretical investigation. It is not easy to distinguish the two primary hypotheses dark matter annihilation/decay and pulsars from the spectral features. Should pulsars be the source of this excess, the expected variability in their distribution may introduce distinct irregularities in the positron energy spectrum. In this study, we use an irregularity estimator to detect these potential features in the positron energy spectrum of AMS-02. Our analysis of the current AMS-02 data reveals these spectral irregularities with a statistical significance of $1.75\sigma$. However, our projection indicates that, with AMS-02 data collected over a period of 20 years, such irregularities could be identified with a confidence level of $3\sigma$ level in 71\% of our simulations.

The kinematics and flux evolution of the superluminal knots in blazar 3C345 were interpreted in the framework of the precessing jet-nozzle scenario with a precessing common helical trajectory-pattern. We show that the jet in 3C345 precesses with a period of 7.3yr and the superluminal knots move consistently along a precessing common helical trajectory-pattern in their inner jet regions, which can extend to core distances of about 1.2mas or traveled distances of about 300pc (for knots C4 and C9). Through model-fitting of the observed kinematic behavior of the superluminal knots, their bulk Lorentz factor and Doppler factor were derived as continuous functions of time, which were used to investigate their flux evolution. We found that the light curves measured at 15, 22 and 43GHz can be well model-fitted in terms of their Doppler boosting profiles associated with their superluminal motion. Flux fluctuations on shorter time scales also exist due to knots' intrinsic variations in flux density and spectral index. The close association of the flux evolution with the Doppler boosting effect is important, firmly vadidating the precessing jet-nozzle scenario being fully appropriate to explain both the kinematics and emission properties of the superluminal knots in 3C345. We have proposed both the precessing jet-nozzle scenarios with a single jet and double jets (this paper and Qian[2022b]) to understand the VLBI phenomena in 3C345. VLBI-observations with higher resolutions deep into the core regions (core distances less than 0.1mas) are required to test them.

Co-orbital exoplanets are a by-product of the models of formation of planetary systems. However, none have been detected in nature thus far. Although challenging, the observation of co-orbital exoplanets would provide valuable information on the formation of planetary systems as well as on the interactions between planets and their host star. After a brief review of the stability and formation issues of co-orbital systems, some observational methods dedicated to their detection are presented.

The use of Gaussian processes (GPs) is a common approach to account for correlated noise in exoplanet time-series, particularly for transmission and emission spectroscopy. This analysis has typically been performed for each wavelength channel separately, with the retrieved uncertainties in the transmission spectrum assumed to be independent. However, the presence of noise correlated in wavelength could cause these uncertainties to be correlated, which could significantly affect the results of atmospheric retrievals. We present a method which uses a GP to model noise correlated in both wavelength and time simultaneously for the full spectroscopic data set while avoiding the use of a 'common-mode' correction. To make this analysis computationally tractable, we introduce a fast and flexible GP method which can analyse 2D data sets when the input points lie on a (potentially non-uniform) 2D grid - in our case a time by wavelength grid - and the kernel function has a Kronecker product structure. This simultaneously fits all light curves and enables the retrieval of the covariance matrix of the transmission spectrum. By testing on synthetic data sets, we demonstrate that our new approach can reliably recover atmospheric features contaminated by noise correlated in time and wavelength. In contrast, fitting each spectroscopic light curve separately performed poorly when wavelength-correlated noise was present. It frequently underestimated the uncertainty of the scattering slope and overestimated the uncertainty in the strength of sharp absorption peaks in transmission spectra. Two archival VLT/FORS2 transit observations of WASP-31b were re-analysed, with our method strongly constraining the presence of wavelength-correlated noise in both data sets and recovering significantly different constraints on atmospheric features such as the scattering slope and strength of sodium and potassium features.

Historically the most popular dark matter candidates have been new elementary particles, such as Weakly Interacting Massive Particles and axions. However Primordial Black Holes (PBHs), black holes formed from overdensities in the early Universe, are another possibility. The discovery of gravitational waves from mergers of tens of Solar mass black hole binaries by LIGO-Virgo has generated a surge in interest in PBH dark matter. We overview the formation of PBHs, observational probes of their abundance, and some of the key open questions in the field.

XL-Calibur is a balloon-borne Compton polarimeter for X-rays in the $\sim$15-80 keV range. Using an X-ray mirror with a 12 m focal length for collecting photons onto a beryllium scattering rod surrounded by CZT detectors, a minimum-detectable polarization as low as $\sim$3% is expected during a 24-hour on-target observation of a 1 Crab source at 45$^{\circ}$ elevation. Systematic effects alter the reconstructed polarization as the mirror focal spot moves across the beryllium scatterer, due to pointing offsets, mechanical misalignment or deformation of the carbon-fiber truss supporting the mirror and the polarimeter. Unaddressed, this can give rise to a spurious polarization signal for an unpolarized flux, or a change in reconstructed polarization fraction and angle for a polarized flux. Using bench-marked Monte-Carlo simulations and an accurate mirror point-spread function characterized at synchrotron beam-lines, systematic effects are quantified, and mitigation strategies discussed. By recalculating the scattering site for a shifted beam, systematic errors can be reduced from several tens of percent to the few-percent level for any shift within the scattering element. The treatment of these systematic effects will be important for any polarimetric instrument where a focused X-ray beam is impinging on a scattering element surrounded by counting detectors.

Generation of science-ready data from processed data products is one of the major challenges in next-generation radio continuum surveys with the Square Kilometre Array (SKA) and its precursors, due to the expected data volume and the need to achieve a high degree of automated processing. Source extraction, characterization, and classification are the major stages involved in this process. In this work we focus on the classification of compact radio sources in the Galactic plane using both radio and infrared images as inputs. To this aim, we produced a curated dataset of ~20,000 images of compact sources of different astronomical classes, obtained from past radio and infrared surveys, and novel radio data from pilot surveys carried out with the Australian SKA Pathfinder (ASKAP). Radio spectral index information was also obtained for a subset of the data. We then trained two different classifiers on the produced dataset. The first model uses gradient-boosted decision trees and is trained on a set of pre-computed features derived from the data, which include radio-infrared colour indices and the radio spectral index. The second model is trained directly on multi-channel images, employing convolutional neural networks. Using a completely supervised procedure, we obtained a high classification accuracy (F1-score>90%) for separating Galactic objects from the extragalactic background. Individual class discrimination performances, ranging from 60% to 75%, increased by 10% when adding far-infrared and spectral index information, with extragalactic objects, PNe and HII regions identified with higher accuracies. The implemented tools and trained models were publicly released, and made available to the radioastronomical community for future application on new radio data.

Feedback from active galactic nuclei (AGN) can strongly impact the host galaxies by driving high-velocity winds that impart substantial energy and momentum to the interstellar medium (ISM). In this work, we study the impact of these winds in isolated galaxies using high-resolution hydrodynamics simulations. Our simulations use the explicit ISM and stellar evolution model called Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE). Additionally, using a super-Lagrangian refinement scheme, we resolve AGN feedback coupling to the ISM at $\sim$10-100 pc scales. We find that AGN feedback efficiently regulates the growth of SMBHs. However, its effect on star formation and outflows depends strongly on the relative strengths of AGN vs local stellar feedback and the geometrical structure of the gas disk. When the energy injected by AGN is subdominant to that of stellar feedback, there are no significant changes in the star formation rates or mass outflow rates of the host galaxy. Conversely, when the energy budget is dominated by the AGN, we see a significant decline in the star formation rates accompanied by an increase in outflows. Galaxies with thin gas disks like the Milky Way allow feedback to escape easily into the polar directions without doing much work on the ISM. In contrast, galaxies with thick and diffuse gas disks confine the initial expansion of the feedback bubble within the disk, resulting in more work done on the ISM. Phase space analysis indicates that outflows primarily comprise hot and diffuse gas, with a lack of cold and dense gas.

A new version of CSSTA catalog of the lower main-sequence stars with solar-type activity was presented. It comprises 314618 objects, and the database that is realized on its basis is a developing project that contains hyperlinks to the original photometric and spectral observations.

Gamma-ray bursts (GRBs) are commonly attributed to the demise of massive stars or the merger of binary compact objects. However, their varied emission characteristics strongly imply the existence of multiple GRB classes based on progenitor types, radiation mechanisms, central engines etc. This study utilizes unsupervised clustering with the Nested Gaussian Mixture Model algorithm to analyze {\it Fermi} and BATSE GRB data, identifying four classes (A, B, C, and D) based on duration, spectral peak, and spectral index, comprising approximately 70\%, 10\%, 3\%, and 17\% of the dataset, respectively. Classes A and B consist of long GRBs, C mainly short GRBs, and class D encompasses both short and long GRBs. Using the spectral index, $\alpha$, for the differentiation of radiation models, it is found that classes B and C align with photospheric emission models, while A and D predominantly show synchrotron radiation characteristics. Short GRBs predominantly exhibit photospheric emission, whereas long GRBs show consistency with synchrotron emission. Overall, 63\% of the total bursts exhibit $\alpha$ profiles indicative of synchrotron emission, with the remaining 37\% associated with photospheric emission. The classes were further examined for their progenitor origins, revealing that classes A and D demonstrate a hybrid nature, while classes B and C are predominantly associated with collapsar and merger origins, respectively. This clustering analysis reveals distinct GRB classes, shedding light on their diversity in radiation, duration and progenitor.

We present a UV to millimeter spectral energy distribution (SED) analysis of 16 hyperluminous, dust-obscured quasars at z $\sim$ 3, selected by the \textit{Wide-field Infrared Survey Explorer}. We aim to investigate the physical properties of these quasars, with a focus on their molecular gas content. We decompose the SEDs into three components: stellar, cold dust, and active galactic nucleus (AGN). By doing so, we are able to derive and analyze the relevant properties of each component. We determine the molecular gas mass from CO line emission based on Atacama Large Millimeter/submillimeter Array (ALMA) observations. By including ALMA observations in the multiwavelength SED analysis, we derive the molecular gas fractions, gas depletion timescales, and star formation efficiencies (SFEs). Their sample median and 16th-84th quartile ranges are $f_{\rm gas}\,\sim\,0.33_{-0.17}^{+0.33}$, $t_{\rm depl}\,\sim$ 39$_{-28}^{+85}$ Myr, SFE $\sim\,$ 297$_{-195}^{+659}$ $\rm K\,\rm km\,\rm s^{-1}\,\rm pc^{-2}$. Compared to main-sequence galaxies, they have a lower molecular gas content and higher SFEs, similar to quasars in the literature. This suggests that the gas in these quasars is rapidly depleted, likely as the result of intense starburst activity and AGN feedback. The observed correlations between these properties and the AGN luminosities further support this scenario. Additionally, we infer the black hole to stellar mass ratio and black hole mass growth rate, which indicate a significant central black hole mass assembly over short timescales. Our results are consistent with the scenario that our sample represents a short transition phase toward unobscured quasars.

The kinematic structure of the Radcliffe Wave (RW) is crucial for understanding its origin and evolution. In this work, we present an accurate measurement of the vertical velocity $V_Z$ by where the radial velocity (RV) measures are taken into consideration. This is achieved in two ways. First, the velocities are measured towards Young Stellar Objects (YSOs), using their RV and proper motion measurements from APOGEE-2 and Gaia DR3. Second, we combine RV measurements toward clouds with proper motion measurements of associated YSOs to determine the vertical velocities of the clouds. The results reveal that the oscillations in $V_Z$ are not synchronous with the vertical coordinate. The difference is caused by a combination of the effect of the radial velocity which we include in this paper, and the difference in models. By supplementing our analysis with additional young star samples, we find a consistent dipole pattern in $V_Z$. The fact that no significant amplitude differences are found among the analyzed samples indicates that there is no apparent age gradient within the dipole. We propose that RW evolves at a relatively slow rate. The fact that it will take a much longer time for RW to complete a full period compared to the cloud lifetimes challenges its classification as a traditional "wave". This age discrepancy should explain the phase difference, and non-synchronous oscillation found in kinematic studies.

We study the X-ray power spectrum of Active Galactic Nuclei (AGN) to investigate whether Seyfert I and II power spectra are similar or not, whether the AGN variability depends on black hole mass and accretion rate, and to compare the AGN power spectra with the Galactic X-ray black hole binaries power-spectra. We used 14-195 keV band light curves from the 157th SWIFT/BAT hard X-ray survey and we computed the mean power spectrum and excess variance of AGN in narrow black-hole mass/luminosity bins. We fitted a power-law model to the AGN power spectra, and we investigated whether the power spectrum parameters and the excess variance depend on black hole mass, luminosity and accretion rate. The Seyfert I and Seyfert II power spectra are identical, in agreement with AGN unification models. The mean AGN X-ray power spectrum has the same, power-law like shape with a slope of -1 in all AGN, irrespective of their luminosity and BH mass. We do not detect any flattening to a slope of zero at frequencies as low as 10e-9 Hz. We detect an anti-correlation between the PSD amplitude and the accretion rate, similar to what has been seen in the past in the 2-10 keV band. This implies that the variability amplitude in AGN decreases with increasing accretion rate. The universal AGN power-spectrum is consistent with the mean, 2-9 keV band Cyg X-1 power spectrum in its soft state. The mean, low frequency AGN X-ray power spectrum is consistent with the extension of the mean, 0.01-25 Hz Cyg X-1 power spectrum to lower frequencies. The agreement between the AGN and the Cyg X-1 power spectrum (either in the soft or the hard state) over many decades in frequency indicates that the X-ray variability process is probably the same in all accreting objects, irrespective of the mass of the compact object. We plan to investigate this issue further in the near future.

Integrated superconducting spectrometers (ISSs) for wideband sub-mm astronomy utilise quasi-optical systems for coupling radiation from the telescope to the instrument. Misalignment in these systems is detrimental to the system performance. The common method of using an optical laser to align the quasi-optical components requires accurate alignment of the laser to the sub-mm beam coming from the instrument, which is not always guaranteed to a sufficient accuracy. We develop an alignment strategy for wideband ISSs directly utilising the sub-mm beam of the wideband ISS. The strategy should be applicable in both telescope and laboratory environments. Moreover, the strategy should deliver similar quality of the alignment across the spectral range of the wideband ISS. We measure misalignment in a quasi-optical system operating at sub-mm wavelengths using a novel phase and amplitude measurement scheme, capable of simultaneously measuring the complex beam patterns of a direct-detecting ISS across a harmonic range of frequencies. The direct detection nature of the MKID detectors in our device-under-test, DESHIMA 2.0, necessitates the use of this measurement scheme. Using geometrical optics, the measured misalignment, a mechanical hexapod, and an optimisation algorithm, we follow a numerical approach to optimise the positioning of corrective optics with respect to a given cost function. Laboratory measurements of the complex beam patterns are taken across a harmonic range between 205 and 391 GHz and simulated through a model of the ASTE telescope in order to assess the performance of the optimisation at the ASTE telescope. Laboratory measurements show that the optimised optical setup corrects for tilts and offsets of the sub-mm beam. Moreover, we find that the simulated telescope aperture efficiency is increased across the frequency range of the ISS after the optimisation.

We present the first detection in space of O-protonated carbonyl sulfide (\ch{HOCS+}), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all $K$$_a$ = 0 transitions ranging from $J$$_{lo}$ = 2 to $J$$_{lo}$ = 13 of \ch{HOCS+} covered by our survey, we derive a column density of $N$ = (9 $\pm$ 2)$\times$10$^{12}$ cm$^{-2}$, translating into a fractional abundance relative to H$_2$ of $\sim$7$\times$10$^{-11}$. Conversely, the S-protonated \ch{HSCO+} isomer remains undetected, and we derive an upper limit to its abundance with respect to H$_2$ of $\leq$3$\times$10$^{-11}$, a factor of $\geq$2.3 less abundant than \ch{HOCS+}. We obtain a \ch{HOCS+}/OCS ratio of $\sim$2.5$\times$10$^{-3}$, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of \ch{HOCS+} is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionisation rates (10$^{-15}$-10$^{-14}$ s$^{-1}$) are needed to reproduce the observed abundance of \ch{HOCS+}. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find a \ch{HOCO+}/\ch{HOCS+} ratio of $\sim$31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value ($\sim$37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.

Filaments are omnipresent features in the solar atmosphere. Their location, properties and time evolution can provide information about changes in solar activity and assist the operational space weather forecast. Therefore, filaments have to be identified in full disk images and their properties extracted from these images. Manual extraction is tedious and takes much time; extraction with morphological image processing tools produces a large number of false-positive detections. Automatic object detection, segmentation, and extraction in a reliable manner allows to process more data in a shorter time. The Chromospheric Telescope (ChroTel), Tenerife, Spain, the Global Oscillation Network Group (GONG), and the Kanzelh\"ohe Observatory (KSO), Austria, provide regular full-disk observations of the Sun in the core of the chromospheric H-alpha absorption line. We present a deep learning method that provides reliable extractions of filaments from H-alpha filtergrams. First, we train the object detection algorithm YOLOv5 with labeled filament data of ChroTel. We use the trained model to obtain bounding-boxes from the full GONG archive. In a second step, we apply a semi-supervised training approach, where we use the bounding boxes of filaments, to learn a pixel-wise classification of filaments with u-net. Here, we make use of the increased data set size to avoid overfitting of spurious artifacts from the generated training masks. Filaments are predicted with an accuracy of 92%. With the resulting filament segmentations, physical parameters such as the area or tilt angle can be easily determined and studied. This we demonstrate in one example, where we determine the rush-to-the pole for Solar Cycle 24 from the segmented GONG images. In a last step, we apply the filament detection to H-alpha observations from KSO which demonstrates the general applicability of our method to H-alpha filtergrams.

We perform real-time hydrodynamical simulations of the growth of bubbles formed during cosmological first-order phase transitions under the assumption of local thermal equilibrium. We confirm that pure hydrodynamic backreaction can lead to steady-state expansion and that bubble-wall velocity in such case agrees very well with the analytical estimates. However, this is not the generic outcome. Instead, it is much more common to observe runaways, as the early-stage dynamics right after the nucleation allow the bubble walls to achieve supersonic velocities before the heated fluid shell in front of the bubble is formed. This effect is not captured by other methods of calculation of the bubble-wall velocity which assume stationary solutions to exist at all times and would have a crucial impact on the possible generation of both baryon asymmetry and gravitational wave signals.

When starting an N-body simulation of an isolated galaxy, it is desirable to select particles from a distribution function to ensure that the model is in equilibrium. Random sampling from a DF is widely used, but results in a set of particles that differs by shot noise from that intended. This paper presents a method to reduce sampling noise that has been developed by the author in a many collaborations over a number of years. The technique has been partly described in past papers, though the ideas have not previously been gathered together, nor have its advantages been clearly demonstrated in past work. Of course, sampling errors can also be reduced by a brute force increase in the number of particles, but methods to achieve the same effect with fewer particles have obvious advantages. Here we not only describe the method, but also present three sets of simulations to illustrate the practical advantages of reducing sampling error. The improvements are not dramatic, but are clearly worth having.

Nuclear regions of luminous and ultraluminous infrared galaxies (U/LIRGs) are powered by starbursts and/or active galactic nuclei (AGNs), often obscured by extremely high columns of gas and dust. Molecular lines in the submillimeter windows have potential to determine physical conditions of these compact obscured nuclei (CONs). We aim to reveal the distributions of HCN and HCO$^+$ emission in local U/LIRGs, and investigate whether and how they are related to galaxy properties. Using ALMA, we have conducted sensitive observations of the HCN J=3--2 and HCO$^+$ J=3--2 lines toward 23 U/LIRGs in the local Universe (z < 0.07) with a spatial resolution of ~0.3" (~50--400 pc). We detected both HCN and HCO$^+$ in 21 galaxies, only HCN in one galaxy, and neither in one galaxy. The global HCN/HCO$^+$ line ratios, averaged over scales of ~0.5--4 kpc, range from 0.4 to 2.3, with an unweighted mean of 1.1. These line ratios appear to have no systematic trend with bolometric AGN luminosity or star formation rate. The line ratio varies with position and velocity within each galaxy, with an average interquartile range of 0.38 on a spaxel-by-spaxel basis. In eight out of ten galaxies known to have outflows and/or inflows, we find spatially and kinematically symmetric structures of high line ratios. These structures appear as a collimated bicone/bipole in two galaxies and as a thin spherical shell in six galaxies. Non-LTE analysis suggests that the high HCN/HCO$^+$ line ratio in outflows is predominatly influenced by the abundance ratio. Chemical model calculations indicate that the enhancement of HCN abundance in outflows is likely due to high temperature chemistry triggered by shock heating. These results imply that the HCN/HCO$^+$ line ratio can aid identifying the outflow geometry when the shock velocity of the outflows is sufficiently high to heat the gas.

Extreme debris discs (EDDs) are bright and warm circumstellar dusty structures around main sequence stars. They may represent the outcome of giant collisions occuring in the terrestrial region between large planetesimals or planetary bodies, and thus provide a rare opportunity to peer into the aftermaths of these events. Here, we report on results of a mini-survey we conducted with the aim to increase the number of known EDDs, investigate the presence of solid-state features around 10{\mu}m in eight EDDs, and classify them into the silica or silicate dominated groups. We identify four new EDDs and derive their fundamental properties. For these, and for four other previously known discs, we study the spectral energy distribution around 10{\mu}m by means of VLT/VISIR photometry in three narrow-band filters and conclude that all eight objects likely exhibit solid-state emission features from sub-micron grains. We find that four discs probably belong to the silicate dominated subgroup. Considering the age distribution of the entire EDD sample, we find that their incidence begins to decrease only after 300 Myr, suggesting that the earlier common picture that these objects are related to the formation of rocky planets may not be exclusive, and that other processes may be involved for older objects (>100 Myr). Because most of the older EDD systems have wide, eccentric companions, we suggest that binarity may play a role in triggering late giant collisions.

The satellite Mimas launches a bending wave -- a warping of the rings that propagates radially through self-gravity -- at the 5:3 inner vertical resonance with Saturn's rings. We present a modification of the linear bending wave theory which includes the effects of satellite self-gravity wakes on the particles in the wave. We show that, when treated as rigid, these wakes generate an extra layer of particles whose number density is proportional to the magnitude of the slope of the warped ring. Using a ray-tracing code we compare our predictions with those of linear bending wave theory and with 60 stellar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and find that the extra layer of particles of our perturbed bending wave model has a considerable explanatory power for the UVIS dataset. Our best model explains the most discrepant and surprising features of the Mimas 5:3 bending wave; the enhancement of the signal for the cases of occultations with high ring opening angle and the bigger-than-expected viscosity, $\nu = 576 \, \mathrm{cm^2/s}$, which is more than double the viscosity computed from density waves. This shows that self-gravity wakes can be effective at transporting angular momentum in a vertically perturbed disk. Relative to neighboring density waves, we find a lower-than-expected value for the surface mass density, $\sigma = 36.7 \, \mathrm{g/cm^2}$, which suggests that the enhanced viscous interactions may be transporting material into the surrounding regions.

In the theory of protoplanetary disk turbulence, a widely adopted \emph{ansatz}, or assumption, is that the turnover frequency of the largest turbulent eddy, $\Omega_L$, is the local Keplerian frequency $\Omega_K$. In terms of the standard dimensionless Shakura-Sunyaev $\alpha$ parameter that quantifies turbulent viscosity or diffusivity, this assumption leads to characteristic length and velocity scales given respectively by $\sqrt{\alpha}H$ and $\sqrt{\alpha}c$, in which $H$ and $c$ are the local gas scale height and sound speed. However, this assumption is not applicable in cases when turbulence is forced numerically or driven by some natural processes such as Vertical Shear Instability. Here we explore the more general case where $\Omega_L\ge\Omega_K$ and show that under these conditions, the characteristic length and velocity scales are respectively $\sqrt{\alpha/R'}H$ and $\sqrt{\alpha R'}c$, where $R'\equiv \Omega_L/\Omega_K$ is twice the Rossby number. It follows that $\alpha=\alphat/R'$, where $\sqrt{\alphat} c$ is the root-mean-square average of the turbulent velocities. Properly allowing for this effect naturally explains the reduced particle scale heights produced in shearing box simulations of particles in forced turbulence, and may help with interpreting recent edge-on disk observations; more general implications for observations are also presented. For $R'>1$ the effective particle Stokes numbers are increased, which has implications for particle collision dynamics and growth, as well as for planetesimal formation.

The chemical evolution of distant galaxies cannot be assessed from observations of individual stars, in contrast to the case of nearby galaxies. On the other hand, the study of the interstellar medium (ISM) offers an alternative way to reveal important properties of the chemical evolution of distant galaxies. The chemical enrichment of the ISM is produced by all the previous generations of stars and it is possible to precisely determine the metal abundances in the neutral ISM in galaxies. The chemical abundance patterns in the neutral ISM are determined by the gas metallicity, presence of dust (the depletion of metals into dust grains), and possible deviations due to specific nucleosynthesis, for example, $\alpha$-element enhancements. We aim to derive the metallicities, dust depletion, and $\alpha$-element enhancements in the neutral ISM of gas-rich mostly-metal-poor distant galaxies (Damped Lyman-$\alpha$ absorbers, DLAs). Furthermore, we aim to constrain the distribution of $\alpha$-element enhancements with metallicity in these galaxies. We have constrained, for the first time, the distribution of the $\alpha$-element enhancement with metallicity in the neutral ISM in distant galaxies. Less massive galaxies show an $\alpha$-element knee at lower metallicities than more massive galaxies. This can be explained by a lower star formation rate in less massive galaxies. If this collective behaviour can be interpreted in the same way as it is for individual systems, this would suggest that more massive and metal-rich systems evolve to higher metallicities before the contribution of SN-Ia to [$\alpha$/Fe] levels out that of core-collapse SNe. This finding may plausibly be supported by different SFRs in galaxies of different masses. Overall, our results offer important clues to the study of chemical evolution in distant galaxies.

The field of cosmology is entering an epoch of unparalleled wealth of observational data thanks to galaxy surveys such as DESI, Euclid, and Roman. Therefore, it is essential to have a firm theoretical basis that allows the effective analysis of the data. With this purpose, we compute the nonlinear, gravitationally-induced connected galaxy 4-point correlation function (4PCF) at the tree level in Standard Perturbation Theory (SPT), including redshift-space distortions (RSD). We begin from the trispectrum and take its inverse Fourier transform into configuration space, exploiting the isotropic basis functions of \cite{Iso_fun}. We ultimately reduce the configuration-space expression to low-dimensional radial integrals of the power spectrum. This model will enable the use of the BAO feature in the connected 4PCF to sharpen our constraints on the expansion history of the Universe. It will also offer an additional avenue for determining the galaxy bias parameters, and thus tighten our cosmological constraints by breaking degeneracies. Survey geometry can be corrected in the 4PCF, and many systematics are localized, which is an advantage over data analysis with the trispectrum. Finally, this work is a first step in using the parity-even 4PCF to calibrate out any possible systematics in the parity-odd 4PCF; comparing our model to the measurement will offer a consistency test that can serve as a "canary in the coal mine" for systematics in the odd sector.

A high-altitude nuclear blast can produce an electromagnetic pulse (EMP) capable of disrupting electronics on Earth. The basic phenomenology of the initial (E1) phase of the EMP was initially worked out in the 1960s by Longmire, Karzas, and Latter, and although more accurate and sophisticated EMP models have since been devised, the Karzas-Latter model is particularly simple and amenable to implementation as a numerical code. This paper accompanies the release of a new software implementation of an approximation of the Karzas-Latter model due to Seiler. This is, as far as we are aware, the only such publicly available numerical EMP code. After reviewing the physics and assumptions of the model, the numerical results for EMP simulations under a range of conditions are presented. It is shown how the results from multiple line of sight integrations of the field equations can be assembled to form a map of the EMP intensity across a broad geographic region. The model predictions are at least qualitatively correct and in general agreement with other simulation results, including the characteristic "smile" pattern in the spatial variation of the EMP intensity.

It is well-known that the Einstein-Hilbert action exhibits a projective invariance in metric-affine gravity, generated by a single vector (just like diffeomorphisms). However, this symmetry offers no protection against formulating inconsistent models, e.g., with ghost and strong coupling problems. In this letter, we observe that non-minimal kinetic terms of Dirac spinors point to a new extended projective (EP) symmetry generated by a pair of vectors. We prove that the most general EP-invariant theory (at most quadratic in field strengths) is naturally free from all pathologies. Its spectrum only features the massless graviton and a single additional scalar field arising from the square of the Holst curvature. The scalar potential is suitable for inflation and our model moreover contains effective 4-Fermi interactions capable of producing fermionic dark matter. Finally, we point out an alternative double-vector symmetry that similarly leads to a healthy theory with a propagating vector field.

We analyse the lensing images by dynamically robust rotating (mini-)Proca stars surrounded by thin accretion disks. Due to their peculiar geodesic structure we show that these images exhibit striking similarities with the ones of BHs, for appropriately chosen disk intensity profile, when imposing a GRMHD-motivated emission cut off. Additionally, and unlike the non-rotating case, these similarities prevail even when considering equatorial observations. This example illustrates how a horizonless compact object without light rings, with a plausible formation mechanism and dynamically robust, could mimic detailed features of black hole imagiology.

Gravitational-wave observations provide the unique opportunity of studying black hole formation channels and histories -- but only if we can identify their origin. One such formation mechanism is the dynamical synthesis of black hole binaries in dense stellar systems. Given the expected isotropic distribution of component spins of binary black hole in gas-free dynamical environments, the presence of anti-aligned or in-plane spins with respect to the orbital angular momentum is considered a tell-tale sign of a merger's dynamical origin. Even in the scenario where birth spins of black holes are low, hierarchical mergers attain large component spins due to the orbital angular momentum of the prior merger. However, measuring such spin configurations is difficult. Here, we quantify the efficacy of the spin parameters encoding aligned-spin ($\chieff$) and in-plane spin ($\chip$) at classifying such hierarchical systems. Using Monte Carlo cluster simulations to generate a realistic distribution of hierarchical merger parameters from globular clusters, we can infer mergers' $\chieff$ and $\chip$. The cluster populations are simulated using Advanced LIGO-Virgo sensitivity during the detector network's third observing period and projections for design sensitivity. Using a "likelihood-ratio"-based statistic, we find that $\sim2\%$ of the recovered population by the current gravitational-wave detector network has a statistically significant $\chip$ measurement, whereas no $\chieff$ measurement was capable of confidently determining a system to be anti-aligned with the orbital angular momentum at current detector sensitivities. These results indicate that measuring spin-precession through $\chip$ is a more detectable signature of a hierarchical mergers and dynamical formation than anti-aligned spins.

The Inspiral Merger Ringdown Consistency Test (IMRCT) is one among a battery of tests of general relativity (GR) employed by the LIGO-Virgo-KAGRA (LVK) collaboration. It is used to search for deviations from GR in detected gravitational waves (GWs) from compact binary coalescences (CBCs) in a model-agnostic way. The test compares source parameter estimates extracted independently from the inspiral and post-inspiral portions of the CBC signals and, therefore, crucially relies on the accurate modeling of the waveform. Current implementations of the IMRCT routinely use quasicircular waveforms, under the assumption that the residual eccentricity of the binary when the emitted GWs enter the frequency band of the LVK detector network will be negligible. In this work, we perform a detailed study to investigate the typical magnitudes of this residual eccentricity that could potentially lead to spurious violations of the IMRCT. To that end, we conduct injection campaigns for a range of eccentricities and recover with both quasicircular and eccentric waveforms. We find that an eccentric GW signal from a GW150914-like system with $e_{\text{gw}} \gtrsim$ 0.04 at an orbit averaged frequency $\langle f_{\text{ref}} \rangle=$ 25 Hz breaks the IMRCT if recovered with quasicircular waveforms at $\gtrsim 68\%$ confidence. The violation becomes more severe ($\gtrsim 90\%$ confidence) for $e_{\text{gw}} =$ 0.055 at $\langle f_{\text{ref}} \rangle=$ 25 Hz. On the other hand, when eccentric waveforms are used, the IMRCT remains intact for all eccentricities considered. We also briefly investigate the effect of the magnitude and orientation (aligned/antialigned) of the component spins of the binary on the extent of the spurious violations of the IMRCT. Our work, therefore, demonstrates the need for accurate eccentric waveform models in the context of tests of GR.

We present a minimal framework that realises successful Dirac Leptogenesis through the Affleck-Dine mechanism. A single right-handed neutrino and a neutrinophillic Higgs doublet are introduced to the Standard Model, which couple via a Yukawa interaction. The inflationary setting is induced by a combination of the two Higgs doublets, with their global symmetry violating interactions leading to a net charge generation via the Affleck-Dine mechanism. This simple Standard Model extension exhibits a unique and connected set of phenomenological implications including the resultant baryon asymmetry, inflationary predictions, cosmological implications, relic right-handed neutrinos, and its low energy phenomenology, while also being able to be embedded in various neutrino mass generating mechanisms.

This paper develops novel and robust central discontinuous Galerkin (CDG) schemes of arbitrarily high-order accuracy for special relativistic magnetohydrodynamics (RMHD) with a general equation of state (EOS). These schemes are provably bound-preserving (BP), i.e., consistently preserve the upper bound for subluminal fluid velocity and the positivity of density and pressure, while also (locally) maintaining the divergence-free (DF) constraint for the magnetic field. For 1D RMHD, the standard CDG method is exactly DF, and its BP property is proven under a condition achievable by BP limiter. For 2D RMHD, we design provably BP and locally DF CDG schemes based on the suitable discretization of a modified RMHD system. A key novelty in our schemes is the discretization of additional source terms in the modified RMHD equations, so as to precisely counteract the influence of divergence errors on the BP property across overlapping meshes. We provide rigorous proofs of the BP property for our CDG schemes and first establish the theoretical connection between BP and discrete DF properties on overlapping meshes for RMHD. Owing to the absence of explicit expressions for primitive variables in terms of conserved variables, the constraints of physical bounds are strongly nonlinear, making the BP proofs highly nontrivial. We overcome these challenges through technical estimates within the geometric quasilinearization (GQL) framework, which converts the nonlinear constraints into linear ones. Furthermore, we introduce a new 2D cell average decomposition on overlapping meshes, which relaxes the theoretical BP CFL constraint and reduces the number of internal nodes, thereby enhancing the efficiency of the 2D BP CDG method. We implement the proposed CDG schemes for extensive RMHD problems with various EOSs, demonstrating their robustness and effectiveness in challenging scenarios.