Papers for Thursday, Aug 25 2022

No statistical study of COMs toward a large sample of high-mass protostars with ALMA has been carried out so far. We aim to study six N-bearing species: CH$_3$CN, HNCO, NH$_2$CHO, C$_2$H$_5$CN, C$_2$H$_3$CN and CH$_3$NH$_2$ in a large sample of high-mass protostars. From the ALMAGAL survey, 37 of the most line-rich hot molecular cores are selected. Next, we fit their spectra and find column densities and excitation temperatures of the above N-bearing species, in addition to CH$_3$OH. We (tentatively) detect CH$_3$NH$_2$ in $\sim32%$ of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH$_2$CHO; Tex > 250 K), warm (C$_2$H$_3$CN, HN$^{13}$CO and CH$_{3}^{13}$CN; 100 K < Tex < 250 K) and cold species (CH$_3$OH and CH$_3$NH$_2$; Tex < 100 K). This temperature segregation reflects the trend seen in their sublimation temperatures and validates the idea of onion-like structure of COMs around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor $\sim3$ around the mean. The constant column density ratios point to a common formation environment of COMs or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars.

We present a new mechanism for cosmic acceleration consisting of a scalar field coupled to a triplet of classical U(1) gauge fields. The gauge fields are arranged in a homogeneous, isotropic configuration, with both electric- and magnetic-like vacuum expectation values. The gauge fields provide a mass-like term via a Chern-Simons interaction that suspends the scalar away from its potential minimum, thereby enabling potential-dominated evolution. We show this mechanism can drive a brief period of acceleration, such as dark energy, without the need for fine tunings. We obtain simple analytic results for the dark energy equation of state and dependence on model parameters. In this model, the presence of the gauge field generically leads to a suppression of long-wavelength gravitational waves, with implications for the experimental search for cosmic microwave background B-modes and direct detection of a stochastic gravitational wave background.

Hydrodynamical numerical methods that converge with high-order hold particular promise for astrophysical studies, as they can in principle reach prescribed accuracy goals with higher computational efficiency than standard second- or third-order approaches. Here we consider the performance and accuracy benefits of Discontinuous Galerkin (DG) methods, which offer a particularly straightforward approach to reach extremely high order. Also, their computational stencil maps well to modern GPU devices, further raising the attractiveness of this approach. However, a traditional weakness of this method lies in the treatment of physical discontinuities such as shocks. We address this by invoking an artificial viscosity field to supply required dissipation where needed, and which can be augmented, if desired, with physical viscosity and thermal conductivity, yielding a high-order treatment of the Navier-Stokes equations for compressible fluids. We show that our approach results in sub-cell shock capturing ability, unlike traditional limiting schemes that tend to defeat the benefits of going to high order in DG in problems featuring many shocks. We demonstrate exponential convergence of our solver as a function of order when applied to smooth flows, such as the Kelvin-Helmholtz reference problem of arXiv:1509.03630. We also demonstrate excellent scalability of our GPU implementation up to hundreds of GPUs distributed on different compute nodes. In a first application to driven, sub-sonic turbulence, we highlight the accuracy advantages of high-order DG compared to traditional second-order accurate methods, and we stress the importance of physical viscosity for obtaining accurate velocity power spectra.

We use machine learning techniques to classify galaxy merger stages, which can unveil physical processes that drive the star formation and active galactic nucleus (AGN) activities during galaxy interaction. The sample contains 4,690 galaxies from the integral field spectroscopy survey SDSS-IV MaNGA, and can be separated to 1,060 merging galaxies and 3630 non-merging or unclassified galaxies. For the merger sample, there are 468, 125, 293, and 174 galaxies in (1) incoming pair phase, (2) first pericentric passage phase, (3) aproaching or just passing the apocenter, and (4) final coalescence phase or post-mergers. With the information of projected separation, line-of-sight velocity difference, SDSS gri images, and MaNGA Ha velocity map, we are able to classify the mergers and their stages with good precision, which is the most important score to identify interacting galaxies. For the 2-phase classification (binary; non-merger and merger), the performance can be high (precision>0.90) with LGBMClassifier. We find that sample size can be increased by rotation, so the 5-phase classification (non-merger, 1, 2, 3, and 4 merger stages) can be also good (precision>0.85). The most important features come from SDSS gri images. The contribution from MaNGA Ha velocity map, projected separation, and line-of-sight velocity difference can further improve the performance by 0-20%. In other words, the image and the velocity information are sufficient to capture important features of galaxy interactions, and our results can apply to the entire MaNGA data as well as future all-sky surveys.

Relying on the dramatic increase in the number of stars with full 6D phase-space information provided by the Gaia Data Release 3, we discover unambiguous signatures of phase-mixing in the stellar halo around the Sun. We show that for the stars likely belonging to the last massive merger, the (v_r,r) distribution contains a series of long and thin chevron-like overdensities. These phase-space sub-structures are predicted to emerge following the dissolution of a satellite, when its tidal debris is given time to wind up, thin out and fold. Additionally, the observed energy and angular momentum (E, L_z) distribution appears more prograde at high energies, possibly revealing the original orbital angular momentum of the in-falling galaxy. The energy distribution of the debris is strongly asymmetric with a peak at low E -- which, we surmise, may be evidence of the dwarf's rapid sinking -- and riddled with wrinkles and bumps. If these small-scale energy inhomogeneities have been seeded during or immediately after the interaction with the Milky Way, and are not due to the spatial restriction of our study, then making use of the (v_r,r) chevrons to constrain the time of the merger becomes cumbersome. Nonetheless, we demonstrate that similar phase-space and (E,L_z) sub-structures are present in numerical simulations of galaxy interactions, both in bespoke N-body runs and in cosmological hydrodynamical zoom-in suites. The remnant traces of the progenitor's disruption and the signatures of the on-going phase-mixing discovered here will not only help to constrain the properties of our Galaxy's most important interaction, but also can be used as a novel tool to map out the Milky Way's current gravitational potential and its perturbations.

Shockwaves driven by supernovae both destroy dust and reprocess the surviving grains, greatly affecting the resulting dust properties of the interstellar medium (ISM). While these processes have been extensively studied theoretically, observational constraints are limited. We use physically-motivated models of dust emission to fit the infrared (IR) spectral energy distributions of seven Galactic supernova remnants, allowing us to determine the distribution of dust mass between diffuse and dense gas phases, and between large and small grain sizes. We find that the dense ($\sim 10^3 \,{\rm cm}^{-3}$), relatively cool ($\sim 10^3 \, {\rm K}$) gas phase contains $>90\%$ of the dust mass, making the warm dust located in the X-ray emitting plasma ($\sim 1 \,{\rm cm}^{-3}$/$10^6 \, {\rm K}$) a negligible fraction of the total, despite dominating the mid-IR emission. The ratio of small ($\lesssim 10 \, {\rm nm}$) to large ($\gtrsim 0.1 \, {\rm \mu m}$) grains in the cold component is consistent with that in the ISM, and possibly even higher, whereas the hot phase is almost entirely devoid of small grains. This suggests that grain shattering, which processes large grains into smaller ones, is ineffective in the low-density gas, contrary to model predictions. Single-phase models of dust destruction in the ISM, which do not account for the existence of the cold swept-up material containing most of the dust mass, are likely to greatly overestimate the rate of dust destruction by supernovae.

Identifying merging galaxies is an important - but difficult - step in galaxy evolution studies. We present random forest classifications of galaxy mergers from simulated JWST images based on various standard morphological parameters. We describe (a) constructing the simulated images from IllustrisTNG and the Santa Cruz SAM, and modifying them to mimic future CEERS observations as well as nearly noiseless observations, (b) measuring morphological parameters from these images, and (c) constructing and training the random forests using the merger history information for the simulated galaxies available from IllustrisTNG. The random forests correctly classify $\sim60\%$ of non-merging and merging galaxies across $0.5 < z < 4.0$. Rest-frame asymmetry parameters appear more important for lower redshift merger classifications, while rest-frame bulge and clump parameters appear more important for higher redshift classifications. Adjusting the classification probability threshold does not improve the performance of the forests. Finally, the shape and slope of the resulting merger fraction and merger rate derived from the random forest classifications match with theoretical Illustris predictions, but are underestimated by a factor of $\sim 0.5$.

We reanalyze the recently released SH0ES data for the determination of $H_0$. We focus on testing the homogeneity of the Cepheid+SnIa sample and the robustness of the results in the presence of new degrees of freedom in the modeling of Cepheids and SnIa. We thus focus on the four modeling parameters of the analysis: the fiducial luminosity of SnIa $M_B$ and Cepheids $M_W$ and the two parameters ($b_W$ and $Z_W$) standardizing Cepheid luminosities with period and metallicity. After reproducing the SH0ES baseline model results, we allow for a transition of the value of any one of these parameters at a given distance $D_c$ or cosmic time $t_c$ thus adding a single degree of freedom in the analysis. When the SnIa absolute magnitude $M_B$ is allowed to have a transition at $D_c\simeq 50Mpc$ (about $160Myrs$ ago), the best fit value of the Hubble parameter drops from $H_{0}=73.04\pm1.04\,km\,s^{-1}\,Mpc^{-1}$ to $H_0=67.32\pm 4.64\, km\,s^{-1}\,Mpc^{-1}$ in full consistency with the Planck value. Also, the best fit SnIa absolute magnitude $M_B^>$ for $D>D_c$ drops to the Planck inverse distance ladder value $M_{B}^>=-19.43\pm 0.15$ while the low distance best fit $M_B^<$ parameter remains close to the original distance ladder calibrated value $M_{B}^<=-19.25\pm 0.03$. Similar hints for a transition behavior is found for the other three main parameters of the analysis ($b_W$, $M_W$ and $Z_W$) at the same critical distance $D_c\simeq 50\,Mpc$ even though in that case the best fit value of $H_0$ is not significantly affected. When the inverse distance ladder constraint on $M_B^>$ is included in the analysis, the uncertainties for $H_0$ reduce dramatically ($H_0= 68.2\pm 0.8\, km\,s^{-1}\,Mpc^{-1}$) and the $M_B$ transition model is strongly preferred over the baseline SH0ES model ($\Delta \chi^2 \simeq -15$, $\Delta AIC \simeq -13$) according to AIC and BIC model selection criteria.

The early lightcurves of Type Ia supernovae (SNe Ia) can be used to test predictions about their progenitor systems. If the progenitor system consists of a single white dwarf in a binary with a Roche-lobe-overflowing non-degenerate stellar companion, then the SN ejecta should collide with that companion soon after the explosion and get shock-heated, leaving an early UV excess in the lightcurve. This excess would only be observable for events with favorable viewing angles, $\sim$10\% of the time. We model the 2018 ZTF sample of 127 SNe Ia using companion shocking models, and recover an observed early excess rate of $12.0\pm3.6\%$, consistent both with several other rates calculated throughout the literature, and with the expectation that SNe Ia predominantly occur in single-degenerate systems. We observe early excesses only in spectroscopically normal SNe Ia, in contradiction to the claim that such excesses occur more frequently in overluminous SNe Ia. We also show that the detection of early excesses can be methodology-dependent. We encourage the observation of large samples of SNe Ia with high-cadence multiwavelength early data in order to test the statistical predictions of SN Ia progenitor models, and we also encourage the refinement of existing models.

SCALES (Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy) is a 2 to 5 micron high-contrast lenslet-based Integral Field Spectrograph (IFS) designed to characterize exoplanets and their atmospheres. Like other lenslet-based IFSs, SCALES produces a short micro-spectrum of each lenslet's micro-pupil. We have developed an image slicer that sits behind the lenslet array and dissects and rearranges a subset of micro-pupils into a pseudo-slit. The combination lenslet array and slicer (or slenslit) allows SCALES to produce much longer spectra, thereby increasing the spectra resolution by over an order of magnitude and allowing for comparisons to atmospheric modeling at unprecedented resolution. This proceeding describes the design and performance of the slenslit.

NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used two meteor stations. Observations were performed with colour video cameras in the daytime sky. We have developed a special observation technique, for detecting and evaluating UAP characteristics. According to our data, there are two types of UAP, which we conventionally call: (1) Cosmics, and (2) Phantoms. We note that Cosmics are luminous objects, brighter than the background of the sky. Phantoms are dark objects, with contrast from several to about 50 per cent. We observe a significant number of objects whose nature is not clear. Flights of single, group and squadrons of the ships were detected, moving at speeds from 3 to 15 degrees per second. Some bright objects exhibit regular brightness variability in the range of 10 - 20 Hz. We use colourimetry methods to determine of distance to objects and evaluate their colour characteristics. Objects RGB colours of the Adobe colour system had converted to the Johnson BVR astronomical colour system using the colour corrections. Phantom shows the colour characteristics inherent in an object with zero albedos. It is a completely black body that does not emit and absorbs all the radiation falling on it. We see an object because it shields radiation due to Rayleigh scattering. An object contrast makes it possible to estimate the distance using colourimetric methods. Phantoms are observed in the troposphere at distances up to 10 - 12 km. We estimate their size from 3 to 12 meters and speeds up to 15 km/s.

Context. Direct imaging of exoplanets takes advantage of state-of-the-art adaptive optics (AO) systems, coronagraphy, and post-processing techniques. Coronagraphs attenuate starlight to mitigate the unfavorable flux ratio between an exoplanet and its host star. AO systems provide diffraction-limited images of point sources and minimize optical aberrations that would cause starlight to leak through coronagraphs. Post-processing techniques then estimate and remove residual stellar speckles such as noncommon path aberrations (NCPAs) and diffraction from telescope obscurations. Aims. We aim to demonstrate an efficient method to minimize the speckle intensity due to NCPAs during an observing night on VLT/SPHERE. Methods. We implement an iterative dark-hole (DH) algorithm to remove stellar speckles on-sky before a science observation. It uses a pair-wise probing estimator and a controller based on electric field conjugation. This work presents the first such on-sky minimization of speckles with a DH technique on SPHERE. Results. We show the standard deviation of the normalized intensity in the raw images is reduced by a factor of up to 5 in the corrected region with respect to the current calibration strategy under median conditions for VLT. This level of contrast performance obtained with only 1 min of exposure time reaches median performances on SPHERE that use post-processing methods requiring 1h-long sequences of observations. We also present an alternative calibration method that takes advantage of the starlight coherence and improves the post-processed contrast levels rms by a factor of about 3. Conclusions. This on-sky demonstration represents a decisive milestone for the future design, development, and observing strategy of the next generation of ground-based exoplanet imagers for 10m to 40m telescope.

Type IIb supernovae are believed to originate from core-collapse progenitors having kept only a very thin hydrogen envelope. We aim to explore how some physical factors, such as rotation, metallicity, overshooting, and the initial orbital period in binaries, significantly affect the Roche lobe overflow and the formation of type IIb supernovae. It is found that binaries are the main channel that capable of producing type typeIIb supernovae progenitors in the mass range for initial masses below 20 $M_{\odot}$. The formation of type IIb supernova progenitors is extremely sensitive to the initial orbital period. A less massive hydrogen indicates smaller radius and a higher effective temperatures, and vice versa. Binary systems with initial periods between 300 and 720 days produce type IIb progenitors that are a red supergiant. Those with an initial period between 50 and 300 days produce yellow supergiant progenitors and those with initial periods shorter than 50 days, blue supergiant progenitors. Both rapid rotation and larger overshooting can enlarge the carbon-oxygen core mass and lead to higher core temperature and lower central density at the pre-collapse phase. They are also beneficial to surface nitrogen enrichment but restrict the efficiency of the first dredge-up. SN IIb progenitors with low metallicity have smaller hydrogen envelope masses and radii than the high metallicity counterparts. Ultra-stripped binary models have systematically higher core mass fraction $\rm ^{12}C$ left, which has important influence on the compactness of type IIb progenitors.

The modulation of the microwave emission intensity from a flaring loop by a standing linear sausage fast magnetoacoustic wave is considered in terms of a straight plasma slab with the perpendicular Epstein profile of the plasma density, penetrated by a magnetic field. The emission is of the gyrosynchrotron (GS) nature, and is caused by mildly relativistic electrons which occupy a layer in the oscillating slab, i.e., the emitting and oscillating volumes do not coincide. It is shown that the microwave response to the linear sausage wave is highly non-linear. The degree of the non-linearity, defined as a ratio of the Fourier power of the second harmonic to the Fourier power of the principal harmonic, is found to depend on the combination of the width of the GS source and the viewing angle, and is different in the optically thick and optically thin parts of the microwave spectrum. This effect could be considered as a potential tool for diagnostics of the transverse scales of the regions filled in by the accelerated electrons.

We report the cross-correlation function studies of a Neutron star low mass X-ray binary, a Z source GX 5-1 using SXT and LAXPC energy bands onboard AstroSat. For the first time, we report the lag between soft (0.8-2.0 keV, SXT) and hard X-ray energy bands (10-20 keV and 16-40 keV, LAXPC) in GX 5-1 and detected lags of the order of a few tens to hundreds of seconds in the Horizontal branch. We interpreted them as the readjustment time scale of the inner region of the accretion disc. We used various two components and three-component spectral models to unfold the spectra and observed the changes in soft and hard component fluxes which were exhibiting Horizontal Branch Oscillation variations. It was observed that the bbody component assumed to be originating from the boundary layer over the NS, was also found to vary along with the HBO variation where lags were detected. We constrained the size of the Comptonizing region of the order 15-55 km assuming that lags were due to variation in the size of the corona. We noticed a similar size of the Comptonizing region after employing other models and suggest that the overall size of corona must be of the order of a few tens of km to explain the lags, HBO variation, and respective spectral variations. In a case study, it was noted that the BL size increases as GX 5-1 vary from the top of the HB to the upper vertex.

We present the testbench aimed at integrating the GRAVITY+ adaptive optics GPAO. It consists of two independent elements, one reproducing the Coud{\'e} focus of the telescope, including the telescope deformable mirror mount (with its surface facing down), and one reproducing the Coud{\'e} room opto-mechanical environment, including a downwards-propagating beam, and the telescope mechanical interfaces in order to fit in the new GPAO wavefront sensor. We discuss in this paper the design of this bench and the solutions we adopted to keep the cost low, keep the design compact (allowing it to be fully contained in a 20 sqm clean room), and align the bench independently from the adaptive optics. We also discuss the features we have set in this bench.

In this paper we explore the use of spatial clustering algorithms as a new computational approach for modeling the cosmic web. We demonstrate that such algorithms are efficient in terms of computing time needed. We explore three distinct spatial methods which we suitably adjust for (i) detecting the topology of the cosmic web and (ii) categorizing various cosmic structures as voids, walls, clusters and superclusters based on a variety of topological and physical criteria such as the physical distance between objects, their masses and local densities. The methods explored are (1) a new spatial method called Gravity Lattice ; (2) a modified version of another spatial clustering algorithm, the ABACUS; and (3) the well known spatial clustering algorithm HDBSCAN. We utilize HDBSCAN in order to detect cosmic structures and categorize them using their overdensity. We demonstrate that the ABACUS method can be combined with the classic DTFE method to obtain similar results in terms of the achieved accuracy with about an order of magnitude less computation time. To further solidify our claims, we draw insights from the computer science domain and compare the quality of the results with and without the application of our method. Finally, we further extend our experiments and verify their effectiveness by showing their ability to scale well with different cosmic web structures that formed at different redshifts.

Ammonium hydrosulphide has long since been postulated to exist at least in certain layers of the giant planets. Its radiation products may be the reason for the red colour seen on Jupiter. Several ammonium salts, the products of NH3 and an acid, have previously been detected at comet 67P/Churyumov-Gerasimenko. The acid H2S is the fifth most abundant molecule in the coma of 67P followed by NH3. In order to look for the salt NH4+SH-, we analysed in situ measurements from the Rosetta/ROSINA Double Focusing Mass Spectrometer during the Rosetta mission. NH3 and H2S appear to be independent of each other when sublimating directly from the nucleus. However, we observe a strong correlation between the two species during dust impacts, clearly pointing to the salt. We find that NH4+SH- is by far the most abundant salt, more abundant in the dust impacts than even water. We also find all previously detected ammonium salts and for the first time ammonium fluoride. The amount of ammonia and acids balance each other, confirming that ammonia is mostly in the form of salt embedded into dust grains. Allotropes S2 and S3 are strongly enhanced in the impacts, while H2S2 and its fragment HS2 are not detected, which is most probably the result of radiolysis of NH4+SH-. This makes a prestellar origin of the salt likely. Our findings may explain the apparent depletion of nitrogen in comets and maybe help to solve the riddle of the missing sulphur in star forming regions.

Ultra-hot Jupiters (UHJs), rendering the hottest planetary atmospheres, offer great opportunities of detailed characterisation with high-resolution spectroscopy. MASCARA-4 b is a recently discovered close-in gas giant belonging to this category. In order to refine system and planet parameters, we carried out radial velocity measurements and transit photometry with the CORALIE spectrograph and EulerCam at the Swiss 1.2m Euler telescope. We observed two transits of MASCARA-4 b with the high-resolution spectrograph ESPRESSO at ESO's Very Large Telescope. We searched for atomic, ionic, and molecular species via individual absorption lines and cross-correlation techniques. These results are compared to literature studies on UHJs characterised to date. With CORALIE and EulerCam observations, we updated the mass of MASCARA-4 b (1.675 +/- 0.241 Jupiter masses) as well as other system and planet parameters. In the transmission spectrum derived from ESPRESSO observations, we resolve excess absorption by H$\alpha$, H$\beta$, Na D1 & D2, Ca+ H & K, and a few strong individual lines of Mg, Fe and Fe+. We also present the cross-correlation detection of Mg, Ca, Cr, Fe and Fe+. The absorption strength of Fe+ significantly exceeds the prediction from a hydrostatic atmospheric model, as commonly observed in other UHJs. We attribute this to the presence of Fe+ in the exosphere due to hydrodynamic outflows. This is further supported by the positive correlation of absorption strengths of Fe+ with the H$\alpha$ line. Comparing transmission signatures of various species in the UHJ population allows us to disentangle the hydrostatic regime (as traced via the absorption by Mg and Fe) from the exospheres (as probed by H$\alpha$ and Fe+) of the strongly irradiated atmospheres.

We use seven different methods to estimate broad-line and continuum reddenings of NGC 5548. We investigate two possible reddening curves considered for active galactic nuclei (AGNs): the mean AGN reddening curve of Gaskell & Benker (2007) which is relatively flat in the ultraviolet, and a curve that rises strongly into the ultraviolet like a Small Magellanic Cloud (SMC) reddening curve. We also consider a standard Milky Way curve. Regardless of the curve adopted, we find a total reddening ~14 times greater than the small amount of reddening due to dust in the solar neighbourhood. The UV-to-optical ratios rule out a steep SMC-like reddening curve for NGC 5548. The Milky Way and Gaskell & Benker curves give a mean reddening of E(B-V) = 0.25 +/- 0.02. The four non-hydrogen-line reddening indicators imply that the intrinsic hydrogen line ratios are consistent with Baker-Menzel case B values. The unreddened optical-to-UV spectral energy distribution is consistent with the predicted distribution for an externally-illuminated accretion disc. The reddening we derive for NGC 5548 is typical of previous estimates for type-1 AGNs. Neglecting internal extinction leads to an underestimate of the luminosity at 1200 Angstroms by a factor of seven. The size scale of the accretion disc has therefore been underestimated by a factor of ~2.6. This is similar to the accretion disc size discrepancy found in the 2013 AGNSTORM campaign and thus supports the proposal by Gaskell (2017) that the accretion disc size discrepancy is primarily due to the neglect of reddening.

The next generation of galaxy surveys will provide more precise measurements of galaxy clustering than have previously been possible. The 21-cm radio signals that are emitted from neutral atomic hydrogen (HI) gas will be detected by large-area radio surveys such as WALLABY and the SKA, and deliver galaxy positions and velocities that can be used to measure galaxy clustering statistics. But, to harness this information to improve our cosmological understanding, and learn about the physics of dark matter and dark energy, we need to accurately model the manner in which galaxies detected in HI trace the underlying matter distribution of the Universe. For this purpose, we develop a new HI-based Halo Occupation Distribution (HOD) model, which makes predictions for the number of galaxies present in dark matter halos conditional on their HI mass. The parameterised HOD model is fit and validated using the Dark Sage semi-analytic model, where we show that the HOD parameters can be modelled by simple linear and quadratic functions of HI mass. However, we also find that the clustering predicted by the HOD depends sensitively on the radial distributions of the HI galaxies within their host dark matter halos, which does not follow the NFW profile in the Dark Sage simulation. As such, this work enables -- for the first time -- a simple prescription for placing galaxies of different HI mass within dark matter halos in a way that is able to reproduce the HI mass-dependent galaxy clustering and HI mass function simultaneously. Further efforts are required to demonstrate that this model can be used to produce large ensembles of mock galaxy catalogues for upcoming surveys.

The dramatic first images with James Webb Space Telescope (JWST) demonstrated its power to provide unprecedented spatial detail for galaxies in the high-redshift universe. Here, we leverage the resolution and depth of the JWST Cosmic Evolution Early Release Science Survey (CEERS) data in the Extended Groth Strip (EGS) to perform pixel-level morphological classifications of galaxies in JWST F150W imaging using the Morpheus deep learning framework for astronomical image analysis. By cross-referencing with existing photometric redshift catalogs from the Hubble Space Telescope (HST) CANDELS survey, we show that JWST images indicate the emergence of disk morphologies before z~2 and with candidates appearing as early as z~5. By modeling the light profile of each object and accounting for the JWST point-spread function, we find the high-redshift disk candidates have exponential surface brightness profiles with an average Sersic (1968) index n=1.04 and >90% displaying "disky" profiles (n<2). Comparing with prior Morpheus classifications in CANDELS we find that a plurality of JWST disk galaxy candidates were previously classified as compact based on the shallower HST imagery, indicating that the improved optical quality and depth of the JWST helps to reveal disk morphologies that were hiding in the noise. We discuss the implications of these early disk candidates on theories for cosmological disk galaxy formation.

Early observations with JWST have led to the discovery of an unexpected large density (stellar mass density $\rho_*\approx 10^{6}\,M_{\odot}\,Mpc^{-3}$) of massive galaxies (stellar masses $M_*\geq 10^{10.5}M_{\odot}$) at extremely high redshifts $z\approx 10$. We show that - under the most conservative assumptions, and independently of the baryon physics involved in galaxy formation - such abundance is not only in tension with the standard $\Lambda$CDM cosmology, but provides extremely tight constraints on the expansion history of the Universe and on the growth factors corresponding to a wide class of Dark Energy (DE) models. The constraints we derive rule out with high ($>2\sigma$) confidence level a major portion of the parameter space of Dynamical DE models allowed (or even favoured) by existing cosmological probes.

The CZTI (Cadmium Zinc Telluride Imager) onboard AstroSat is a high energy coded mask imager and spectrometer in the energy range of 20 - 100 keV. Above 100 keV, the dominance of Compton scattering cross-section in CZTI results in a significant number of 2-pixel Compton events and these have been successfully utilized for polarization analysis of Crab pulsar and nebula (and transients like Gamma-ray bursts) in 100 - 380 keV. These 2-pixel Compton events can also be used to extend the spectroscopic energy range of CZTI up to 380 keV for bright sources. However, unlike the spectroscopy in primary energy range, where simultaneous background measurement is available from masked pixels, Compton spectroscopy requires blank sky observation for background measurement. Background subtraction, in this case, is non-trivial because of the presence of both short-term and long-term temporal variations in the data, which depend on multiple factors like earth rotation and the effect of South Atlantic Anomaly (SAA) regions etc. We have developed a methodology of background selection and subtraction that takes into account for these effects. Here, we describe these background selection and subtraction techniques and validate them using spectroscopy of Crab in the extended energy range of 30 - 380 keV region, and compare the obtained spectral parameters with the INTEGRAL results. This new capability allows for the extension of the energy range of AstroSat spectroscopy and will also enable the simultaneous spectro-polarimetric study of other bright sources like Cygnus X-1.

We study pinning and unpinning of superfluid vortices in the inner crust of a neutron star using 3-dimensional dynamical simulations. Strong pinning occurs for certain lattice orientations of an idealized, body-centered cubic lattice, and occurs generally in an amorphous or impure nuclear lattice. The pinning force per unit length is $\sim 10^{16}$ dyn cm$^{-1}$ for a vortex-nucleus interaction that is repulsive, and $\sim 10^{17}$ dyn cm$^{-1}$ for an attractive interaction. The pinning force is strong enough to account for observed spin jumps (glitches). Vortices forced through the lattice move with a slip-stick character; for a range of superfluid velocities, the vortex can be in either a cold, pinned state or a hot unpinned state, with strong excitation of Kelvin waves on the vortex. This two-state nature of vortex motion sets the stage for large-scale vortex movement that creates an observable spin glitch. We argue that the vortex array is likely to become tangled as a result of repeated unpinnings and repinnings. We conjecture that during a glitch, the Kelvin-wave excitation spreads rapidly along the direction of the mean superfluid vorticity and slower in the direction perpendicular to it, akin to an anisotropic deflagration.

The relativistic hydrodynamics equations are adapted for the spherically symmetric case and the Lagrangian form. They are used to model the explosive disruption of a minimum-mass neutron star: a key ingredient of the stripping model for short gamma-ray bursts. The shock breakout from the neutron star surface accompanied by the acceleration of matter to ultrarelativistic velocities is studied. A comparison with the results of previously published nonrelativistic calculations is made.

We investigate electromagnetic and gravitational radiation generated during a process of the tidal stripping of a white dwarf star circulating a black hole. We model a white dwarf star by a Bose-Fermi droplet at zero temperature and use the quantum hydrodynamic equations to simulate evolution of a black hole-white dwarf binary system. While going through the periastron, the white dwarf loses a small fraction of its mass. The mass falling onto a black hole is a source of powerful electromagnetic and gravitational radiation. Bursts of ultraluminous radiation are flared at each periastron passage by a white dwarf. This resembles the recurrent flaring of X-ray sources discovered recently by Irwin et al. Gravitational energy bursts occur mainly through emission at very low frequencies. The accretion disc, formed due to the stripping of a white dwarf, starts at some point to contribute continuously to radiation of both electromagnetic and gravitational type.

We show the detectability of interacting and non-interacting cubic Galileon models from the $\Lambda$CDM model through the 21 cm power spectrum. We show that the interferometric observations like the upcoming SKA1-mid can detect both the interacting and the non-interacting cubic Galileon model from the $\Lambda$CDM model depending on the parameter values.

Experiments on crater formation in the strength regime were conducted using projectiles of various shapes with an aspect ratio of ~1, including both solid and hollow interiors. The surface diameter, inner (pit) diameter, and depth of the craters on basalt and porous gypsum targets were measured. Using the bulk density of the projectile, the surface diameter and depth for basalt and the pit diameter and depth for porous gypsum were scaled using the pi-scaling law for crater formation in the strength regime. The numerical code iSALE was used to simulate the impact of projectiles of various shapes and interior structure with similar bulk densities. Results show that the distributions of the maximum (peak) pressure experienced and particle velocity in the targets were similar regardless of projectile shape and interior structure, implying that the dimensions of the final craters were almost identical. This is consistent with the experimental results. Thus, we conclude that the size of the craters formed by the impact of projectiles with different shape and interior structure can be scaled using a conventional scaling law in the strength regime, using bulk density as projectile density.

Recent MeerKAT radio continuum observations of the Galactic center at 20 cm show a large population of nonthermal radio filaments (NRFs) in the inner few hundred pc of the Galaxy. We have selected a sample of 57 radios ources, mainly compact objects, in the MeerKAT mosaic image that appear to be associated with NRFs. The selected sources are about 4 times the number of radio point sources associated with filaments than would be expected by random chance. Furthermore, an apparent correlation between bright IR stars and NRFs is inferred from their similar latitude distributions, suggesting that they both co-exist within the same region. To examine if compact radio sources are related to compact IR sources, we have used archival 2MASS, and {\em Spitzer} data to make spectral energy distribution of individual stellar sources coincident or close to radio sources. We provide a catalogue of radio and IR sources for future detailed observations to investigate a potential 3-way physical association between NRFs, compact radio and IR stellar sources. This association is suggested by models in which NRFs are cometary tails produced by the interaction of a large-scale nuclear outflow with stellar wind bubbles in the Galactic center.

Located in southern Arizona, VERITAS is amongst the most sensitive detectors for astrophysical very high energy (VHE; E>100 GeV) gamma rays and has been operational since April 2007. We highlight some recent results from VERITAS observations. These include the long-term observations of the gamma-ray binaries HESS J0632+057 and LS I +61{\deg} 303, the observations of the Galactic Center region, and of the supernova remnant Cas~A. We discuss the results from a decade of multi-wavelength observations of the blazar 1ES 1215+303, the EHT 2017 campaign on the M87 galaxy, the discovery of 3C 264 in VHE, and the observation of three flaring quasars. Brief highlights of the indirect dark matter searches and targets-of-opportunity (ToO) observations are also discussed. The ToO observations allow for rapid follow-up of multi-messenger alerts and astrophysical transients.

Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules, which are ubiquitous in a variety of astrophysical objects and environments. In this work, we use JWST/MIRI MRS spectroscopy of 3 Seyferts to compare their nuclear PAH emission with that of star-forming regions. This study represents the first of its kind using sub-arcsecond angular resolution data of local luminous Seyferts (Lbol>10^44.89 erg/s) on a wide wavelength coverage (4.9-28.1 micron). We present an analysis of their nuclear PAH properties by comparing the observed ratios with PAH diagnostic model grids, derived from theoretical spectra. Our results show that a suite of PAH features is present in the innermost parts (~0.45 arcsec at 12 micron; in the inner ~142-245 pc) of luminous Seyfert galaxies. We find that the nuclear regions of AGN lie at different positions of the PAH diagnostic diagrams, whereas the SF regions are concentrated around the average values of SF galaxies. In particular, we find that the nuclear PAH emission mainly originates in neutral PAHs. In contrast, PAH emission originating in the SF regions favours ionised PAH grains. The observed PAH ratios in the nuclear region of AGN-dominated galaxy NGC 6552 indicate the presence of larger-sized PAH molecules compared with those of the SF regions. Therefore, our results provide evidence that the AGN have a significant impact on the ionization state (and probably the size) of the PAH grains on scales of ~142-245 pc.

The last 60 years of space exploration have shown that the interplanetary medium is continually perturbed by a myriad of different solar winds and storms that transport solar material across the whole heliosphere. If there is a consensus on the source of the fast solar wind that is known to originate in coronal holes, the question is still largely debated on the origin of the slow solar wind (SSW). The recent observations from the Parker Solar Probe mission provide new insights on the nascent solar wind. And a great challenge remains to explain both the composition and bulk properties of the SSW in a self-consistent manner. For this purpose we exploit and develop models with various degrees of complexity. This context constitutes the backbone of this thesis which is structured as follows: we exploit the first images taken by the Wide-Field Imager for Solar PRobe (WISPR) from inside the solar corona to test our global models at smaller scales, because WISPR offers an unprecedented close-up view of the fine structure of the nascent SSW. This work provides further evidence for the transient release of plasma trapped in coronal loops into the solar wind, that we interpret by exploiting high-resolution magneto-hydrodynamics simulations. Finally we develop and exploit a new multi-specie model of coronal loops called the Irap Solar Atmosphere Model (ISAM) to provide an in-depth analysis of the plasma transport mechanisms at play between the chromosphere and the corona. ISAM solves for the coupled transport of the main constituents of the solar wind with minor ions through a comprehensive treatment of collisions as well as partial ionization and radiative cooling/heating mechanisms near the top of the chromosphere. We use this model to study the different mechanisms that can preferentially extract ions according to their first ionization potential (FIP) from the chromosphere to the corona.

In this paper we estimate the "star formation change parameter", SFR$_{79}$, which characterizes the current SFR relative to the average during the last 800 Myr, for $\sim$ 300'000 galaxies selected from the Sloan Digital Sky Survey (SDSS). The goals are to examine, in a much larger and independent sample, the trends previously reported in a sample of star-forming MaNGA galaxies, and also to search for spectroscopic signatures of ongoing quenching in the so-called "Green Valley", which is generally believed to contain galaxies that are migrating from the star-forming (SF) population to the quenched population of galaxies. Applying SFR$_{79}$ to our large sample of SDSS galaxies, we first confirm the basic results of SF galaxies published by Wang & Lilly. We then discuss in detail the calibration and meaning of SFR$_{79}$ for galaxies that are well below the SFMS and establish what would be the expected signatures of systematic ongoing quenching within the population. We conclude that it is not possible at present to establish unambiguous observational evidence for systematic ongoing quenching processes with the data at hand, due to limitations of noise in the observational data, in particular in the measurements of H$\delta$ absorption, and in the calibration of SFR$_{79}$, as well as biases introduced by the necessity of selecting objects with significant amounts of H$\alpha$ emission. We do however see plausible indications of ongoing quenching, which are quantitatively consistent with expectations from pertinent "growth+quenching" models of galaxy evolution and a typical e-folding timescale for quenching of order $\sim500$ Myr.

We present DESI observations of the inner halo of M31, which reveal the kinematics of a recent merger - a galactic immigration event - in exquisite detail. Of the 11,416 sources studied in 3.75 hours of on-sky exposure time, 7,438 are M31 sources with well measured radial velocities. The observations reveal intricate coherent kinematic structure in the positions and velocities of individual stars: streams, wedges, and chevrons. While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way. We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the NE Shelf and Western Shelf regions. The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1 - 2 Gyr ago. Significant numbers of metal-rich stars are present in all of the detected substructures, suggesting that the immigrating galaxy had an extended star formation history. We also investigate the ability of the shells and Giant Stellar Stream to constrain the gravitational potential of M31, and estimate the mass within a projected radius of 125 kpc to be ${\rm log_{10}}\, M_{\rm NFW}(<125\,{\rm kpc})/M_\odot = 11.78_{-0.10}^{+0.13}$. The results herald a new era in our ability to study stars on a galactic scale and the immigration histories of galaxies.

In this work, which is the first of a series to prepare a cosmological parameter analysis with third-order cosmic shear statistics, we model both the shear three-point correlation functions $\Gamma^{(i)}$ and the third-order aperture statistics $\langle\mathcal{M}_\mathrm{ap}^3\rangle$ from the BiHalofit bispectrum model and validate these statistics with a series of N-body simulations. We then investigate how to bin the shear three-point correlation functions to achieve an unbiased estimate for third-order aperture statistics in real data. Finally, we perform a cosmological parameter analysis on KiDS1000-like mock data with second- and third-order statistics. We recover all cosmological parameters with very little bias. Furthermore, we find that a joint analysis almost doubles the constraining power on $S_8$ and increases the figure-of-merit in the $\Omega_\mathrm{m}$-$\sigma_8$ plane by a factor of 5.9 with respect to an analysis with only second-order shear statistics. Our modelling pipeline is publicly available at https://github.com/sheydenreich/threepoint/releases/.

In this work, a search for nuclearites of strange quark matter by using nine years of ANTARES data taken in the period 2009-2017 is presented. The passage through matter of these particles is simulated %according to the model of de R\'{u}jula and Glashow taking into account a detailed description of the detector response to nuclearites and of the data acquisition conditions. A down-going flux of cosmic nuclearites with Galactic velocities ($\beta = 10^{-3}$) was considered for this study. The mass threshold for detecting these particles at the detector level is \mbox{ $4 \times 10^{13}$ GeV/c$^{2}$}. Upper limits on the nuclearite flux for masses up to $10^{17}$ GeV/c$^{2}$ at the level of $\sim 5 \times 10^{-17}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$ are obtained. These are the first upper limits on nuclearites established with a neutrino telescope and the most stringent ever set for Galactic velocities.

We estimate the gravitational wave spectra generated in strongly supercooled phase transitions by bubble collisions and fluid motion. We derive analytically in the thin-wall approximation the efficiency factor that determines the share of the energy released in the transition between the scalar field and the fluid. We perform numerical simulations including the efficiency factor as a function of bubble radius separately for all points on the bubble surfaces to take into account their different collision times. We find that the efficiency factor does not significantly change the gravitational wave spectra and show that the result can be approximated by multiplying the spectrum obtained without the efficiency factor by its value at the radius $R_{\rm eff} \simeq 5/\beta$, where $\beta$ is the approximate inverse duration of the transition. We also provide updated fits for the gravitational wave spectra produced in strongly supercooled transitions from both bubble collisions and fluid motion depending on the behaviour of the sources after the collision.

We consider reheating for a charged inflaton which is minimally coupled to electromagnetism. The evolution of such an inflaton induces a time-dependent mass for the photon. We show how the massive photon propagator can be expressed as a spatial Fourier mode sum involving three different sorts of mode functions, just like the constant mass case. We develop accurate analytic approximations for these mode functions, and use them to approximate the effective force exerted on the inflaton $0$-mode. This effective force allows one to simply compute the evolution of the inflaton $0$-mode and to follow the progress of reheating.

Observations indicate that intergalactic magnetic fields have amplitudes of the order of $\sim 10^{-6}$ G and are uniform on scales of $\sim 10$ kpc. Despite their wide presence in the Universe, their origin remains an open issue. Even by invoking a dynamo mechanism or a compression effect for magnetic field amplification, the existence of seed fields before galaxy formation is still problematic. General Relativity predicts an adiabatic decrease of the magnetic field evolving as $|\mathbf{B}|\propto 1/a^{2}$, where $a$ is the scale factor of the Universe. It results in very small primordial fields, unless the conformal symmetry of the electromagnetic sector is broken. In this paper, we study the possibility that a natural mechanism for the amplification of primordial magnetic field can be related to extended teleparallel gravity $f(T, B)$ models, where $T$ is the torsion scalar, and $B$ the boundary term. In particular, we consider a non-minimal coupling with gravity in view to break conformal symmetry in a teleparallel background, investigating, in particular, the role of boundary term $B$, which can be consider as a further scalar field. We find that, after solving exactly the $f(T,B)$ field equations both in inflation and reheating eras, a non-adiabatic behavior of the magnetic field is always possible, and a strong amplification appears in the reheating epoch. We also compute the ratio $r=\rho_{B}/ \rho_{\gamma}$ between the magnetic energy density and the cosmic microwave energy density during inflation, in order to explain the present value $r\simeq 1$, showing that, in the slow-roll approximation, power-law teleparallel theories with $B^{n}$ have effects indistinguishable from metric theories $R^{n}$ where $R$ is the Ricci curvature scalar..

We study the possibility of generating baryon asymmetry of the universe from dark matter (DM) annihilations during non-standard cosmological epochs. Considering the DM to be of weakly interacting massive particle (WIMP) type, the generation of baryon asymmetry via leptogenesis route is studied where WIMP DM annihilation produces a non-zero lepton asymmetry. Adopting a minimal particle physics model to realise this along with non-zero light neutrino masses, we consider three different types of non-standard cosmic history namely, (i) fast expanding universe, (ii) early matter domination and (iii) scalar-tensor theory of gravity. By solving the appropriate Boltzmann equations incorporating such non-standard history, we find that the allowed parameter space consistent with DM relic and observed baryon asymmetry gets enlarged with the possibility of lower DM mass in some scenarios. While such lighter DM can face further scrutiny at direct search experiments, the non-standard epochs offer complementary probes on their own.

Flash-X is a highly composable multiphysics software system that can be used to simulate physical phenomena in several scientific domains. It derives some of its solvers from FLASH, which was first released in 2000. Flash-X has a new framework that relies on abstractions and asynchronous communications for performance portability across a range of increasingly heterogeneous hardware platforms. Flash-X is meant primarily for solving Eulerian formulations of applications with compressible and/or incompressible reactive flows. It also has a built-in, versatile Lagrangian framework that can be used in many different ways, including implementing tracers, particle-in-cell simulations, and immersed boundary methods.