ALBERT

Beschreibung: We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), nonactive galaxies, and clusters of galaxies. These mocks are based on up-to-date observational results on the demographic of extragalactic X-ray sources and their extrapolations. They reach fluxes below 10−20 erg cm−2 s−1 in the 0.5–2 keV band, that is, more than an order of magnitude below the predicted limits of future deep fields, and they therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We used our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming ATHENA mission and with the AXIS probe, a subarcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15 Ms, AXIS would detect ∼225 000 AGNs and ∼50 000 nonactive galaxies, reaching a flux limit of f0.5−2 ∼ 5 × 10−19 erg cm−2 s−1 in the 0.5–2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments such as AXIS and ATHENA are expected to detect ∼20 000 z 〉 3 AGNs and ∼250 sources at redshift z 〉 6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe.

Beschreibung: Context. Galaxy clusters in the local universe descend from high-redshift overdense regions known as protoclusters. The large gas reservoirs and high rate of galaxy interaction in protoclusters are expected to enhance star-formation activity and trigger luminous supermassive black-hole accretion in the nuclear regions of the host galaxies. Aims. We investigated the active galactic nucleus (AGN) content of a gas-rich and starbursting protocluster at z = 4.002, known as the Distant Red Core (DRC). In particular, we search for luminous and possibly obscured AGN in 13 identified members of the structure, and compare the results with protoclusters at lower redshifts. We also test whether a hidden AGN can power the Lyα blob (LAB) detected with VLT/MUSE in the DRC. Methods. We observed all of the identified members of the structure with 139 ks of Chandra ACIS-S imaging. Being less affected by absorption than optical and IR bands, even in the presence of large column densities of obscuring material, X-ray observations are the best tools to detect ongoing nuclear activity in the DRC galaxies. Results. We detect obscured X-ray emission from the two most gas-rich members of the DRC, named DRC-1 and DRC-2. Both of them are resolved into multiple interacting clumps in high-resolution Atacama Large Millimeter Array and Hubble Space Telescope observations. In particular, DRC-2 is found to host a luminous (L2−10 keV ≈ 3 × 1045 erg s−1 ) Compton-thick (NH ≳ 1024 cm−2) quasar (QSO) candidate, comparable to the most luminous QSOs known at all cosmic times. The AGN fraction among DRC members is consistent with results found for lower redshift protoclusters. However, X-ray stacking analysis reveals that supermassive black hole (SMBH) accretion is likely also taking place in other DRC galaxies that are not detected individually by Chandra. Conclusions. The luminous AGN detected in the most gas-rich galaxies in the DRC and the widespread SMBH accretion in the other members, which is suggested by stacking analysis, point toward the presence of a strong link between large gas reservoirs, galaxy interactions, and luminous and obscured nuclear activity in protocluster members. The powerful and obscured QSO detected in DRC-2 is likely powering the nearby LAB detected with VLT/MUSE, possibly through photoionization; however, we propose that the diffuse Lyα emission may be due to gas shocked by a massive outflow launched by DRC-2 over a ≈10 kpc scale.

Beschreibung: Various studies have laid claim to finding an alignment of the polarization vectors or radio jets of active galactic nuclei over large distances, but these results have proven controversial and so far, there is no clear explanation for this observed alignment. To investigate this case further, we tested the hypothesis that the position angles of radio galaxies are randomly oriented in the sky by using data from the Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS). A sample of 7555 double-lobed radio galaxies was extracted from the list of 318 520 radio sources in the first data release of LoTSS at 150 MHz. We performed statistical tests for uniformity of the two-dimensional (2D) orientations for the complete 7555 source sample. We also tested the orientation uniformity in three dimensions (3D) for the 4212 source sub-sample with photometric or spectroscopic redshifts. Our sample shows a significant deviation from uniformity (p-value 〈  10−5) in the 2D analysis at angular scales of about four degrees, mainly caused by sources with the largest flux densities. No significant alignment was found in the 3D analysis. Although the 3D analysis has access to fewer sources and suffers from uncertainties in the photometric redshift, the lack of alignment in 3D points towards the cause of the observed effect being unknown systematics or biases that predominantly affect the brightest sources, although this has yet to be demonstrated irrefutably and should be the subject of subsequent studies.

Beschreibung: The partial ionization of the solar plasma causes several nonideal effects such as the ambipolar diffusion, the Hall effect, and the Biermann battery effect. Here we report on the first three-dimensional realistic simulations of solar local dynamo where all three effects were taken into account. The simulations started with a snapshot of already saturated battery-seeded dynamo, where two new series were developed: one with solely ambipolar diffusion and another one also taking into account the Hall term in the generalized Ohm’s law. The simulations were then run for about 4 h of solar time to reach the stationary regime and improve the statistics. In parallel, a purely MHD dynamo simulation was also run for the same amount of time. The simulations are compared in a statistical way. We consider the average properties of simulation dynamics, the generation and dissipation of compressible and incompressible waves, and the magnetic Poynting flux. The results show that, with the inclusion of the ambipolar diffusion, the amplitudes of the incompressible perturbations related to Alfvén waves are reduced, and the Poynting flux is absorbed, with a frequency dependence. The Hall effect causes the opposite action: significant excess of incompressible perturbations is generated and an excess of the Poynting flux is observed in the chromospheric layers. The model with ambipolar diffusion shows, on average, sharper current sheets and slightly more abundant fast magneto-acoustic shocks in the chromosphere. The model with the Hall effect has higher temperatures at the lower chromosphere and stronger and more vertical magnetic field concentrations all over the chromosphere. The study of high-frequency waves reveals that significant power of incompressible perturbations is associated with areas with intense and more vertical magnetic fields and larger temperatures. This behavior explains the large Poynting fluxes in the simulations with the Hall effect and provides confirmation as to the role of Alfvén waves in chromospheric heating in internetwork regions, under the action of both Hall and ambipolar effects. We find a positive correlation between the magnitude of the ambipolar heating and the temperature increase at the same location after a characteristic time of 102 s.

Beschreibung: Context. The detectability of exoplanets and the determination of their projected mass in radial velocity are affected by stellar magnetic activity and photospheric dynamics. Among those processes, the effect of granulation, and even more so of supergranulation, has been shown to be significant in the solar case. The impact for other spectral types has not yet been characterised. Aims. Our study is aimed at quantifying the impact of these flows for other stars and estimating how such contributions affect their performance. Methods. We analysed a broad array of extended synthetic time series that model these processes to characterise the impact of these flows on exoplanet detection for main sequence stars with spectral types from F6 to K4. We focussed on Earth-mass planets orbiting within the habitable zone around those stars. We estimated the expected detection rates and detection limits, tested the tools that are typically applied to such observations, and performed blind tests. Results. We find that both granulation and supergranulation on these stars significantly affect planet mass characterisation in radial velocity when performing a follow-up of a transit detection: the uncertainties on these masses are sometimes below 20% for a 1 MEarth (for granulation alone or for low-mass stars), but they are much larger in other configurations (supergranulation, high-mass stars). For granulation and low levels of supergranulation, the detection rates are good for K and late G stars (if the number of points is large enough), but poor for more massive stars. The highest level of supergranulation leads to a very poor performance, even for K stars; this is both due to low detection rates and to high levels of false positives, even for a very dense temporal sampling over 10 yr. False positive levels estimated from standard false alarm probabilities sometimes significantly overestimate or underestimate the true level, depending on the number of points: it is, therefore, crucial to take this effect into account when analysing observations. Conclusions. We conclude that granulation and supergranulation significantly affect the performance of exoplanet detectability. Future works will focus on improving the following three aspects: decreasing the number of false positives, increasing detection rates, and improving the false alarm probability estimations from observations.

Beschreibung: Context. The pressure equilibrium between the inner heliosheath and the outer heliosheath (referred to as the local interstellar medium) is an eminent theoretical and practical problem; theoretical, because the relevant pressure carriers have to be identified, and practical, because data must be gathered in order to confirm such a pressure equilibrium. The problem is closely connected with the stability of the heliopause, that is, of the tangential discontinuity between these two counterflowing media, and is of utmost importance for understanding the stability of the whole circumsolar plasma structure. Aims. In this paper we analyze the thermodynamic conditions of the multi-fluid plasma between the solar wind termination shock and the heliopause determining the total heliosheath pressure. We look into this problem from a theoretical standpoint and revisit theoretical descriptions of the solar wind plasma after its passage over the solar wind termination shock, thereafter forming the subsonic heliosheath region. Methods. Hereby we take into account the 3D magnetohydrodynamics shock conditions and the resulting 3D temperature structure of the downstream plasma flow. We use a kind of seismological procedure to probe the heliosheath plasma by inquiring into the propagation conditions of traveling shock wave perturbations in this predetermined 3D heliosheath plasma structure. We discuss the fact that the front geometry of such a traveling shock wave most probably does not remain spherical, if it was to begin with, due to asymmetric shock propagation conditions. In contrast, the wave front is likely to become strongly deformed into an upwind bulge. Results. Concerning the plasma pressure, in addition to solar wind and pick-up proton pressures, we have to take into account the solar wind electron pressure which as a surprise turns out to be of comparable magnitude. As a consequence, the characteristic propagation speed of the traveling shock wave in the weakly magnetized heliosheath plasma is given as a mixed speed expressed by the sound speeds of the protons and the electrons. We describe local low-energy proton density signatures that can be found in Voyager-2 proton data as a consequence of traveling shock wave passages and show that the total local plasma pressure can be directly derived from them.

Beschreibung: We present a new catalogue of ∼2400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM–Newton. The sample can be used to investigate the non-linear relation between the ultraviolet (UV) and X-ray luminosity of quasars as well as to build a Hubble diagram up to a redshift of z ∼ 7.5. We selected sources that are neither reddened by dust in the optical and UV nor obscured by gas in the X-rays, and whose X-ray fluxes are free from flux-limit-related biases. After checking for any possible systematics, we confirm, in agreement with our previous works, that the X-ray to UV relation provides distance estimates matching those from supernovae up to z ∼ 1.5, and its slope shows no redshift evolution up to z ∼ 5. We provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat cold dark matter model up to z ∼ 1.5–2, but strong deviations emerge at higher redshifts. Since we have minimised all non-negligible systematic effects and proven the stability of the LX − LUV relation at high redshifts, we conclude that an evolution of the expansion rate of the Universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars.

Beschreibung: We present the results of a programme to search and identify the nature of unusual sources within the All-sky Wide-field Infrared Survey Explorer (WISE) that is based on a machine-learning algorithm for anomaly detection, namely one-class support vector machines (OCSVM). Designed to detect sources deviating from a training set composed of known classes, this algorithm was used to create a model for the expected data based on WISE objects with spectroscopic identifications in the Sloan Digital Sky Survey. Subsequently, it marked as anomalous those sources whose WISE photometry was shown to be inconsistent with this model. We report the results from optical and near-infrared spectroscopy follow-up observations of a subset of 36 bright (gAB 〈  19.5) objects marked as “anomalous” by the OCSVM code to verify its performance. Among the observed objects, we identified three main types of sources: (i) low redshift (z ∼ 0.03 − 0.15) galaxies containing large amounts of hot dust (53%), including three Wolf-Rayet galaxies; (ii) broad-line quasi-stellar objects (QSOs) (33%) including low-ionisation broad absorption line (LoBAL) quasars and a rare QSO with strong and narrow ultraviolet iron emission; (iii) Galactic objects in dusty phases of their evolution (3%). The nature of four of these objects (11%) remains undetermined due to low signal-to-noise or featureless spectra. The current data show that the algorithm works well at detecting rare but not necessarily unknown objects among the brightest candidates. They mostly represent peculiar sub-types of otherwise well-known sources. To search for even more unusual sources, a more complete and balanced training set should be created after including these rare sub-species of otherwise abundant source classes, such as LoBALs. Such an iterative approach will ideally bring us closer to improving the strategy design for the detection of rarer sources contained within the vast data store of the AllWISE survey.

Beschreibung: Context. The progenitor and explosion properties of type II supernovae (SNe II) are fundamental to understanding the evolution of massive stars. Particular attention has been paid to the initial masses of their progenitors, but despite the efforts made, the range of initial masses is still uncertain. Direct imaging of progenitors in pre-explosion archival images suggests an upper initial mass cutoff of ∼18 M⊙. However, this is in tension with previous studies in which progenitor masses inferred by light-curve modelling tend to favour high-mass solutions. Moreover, it has been argued that light-curve modelling alone cannot provide a unique solution for the progenitor and explosion properties of SNe II. Aims. We develop a robust method which helps us to constrain the physical parameters of SNe II by simultaneously fitting their bolometric light curve and the evolution of the photospheric velocity to hydrodynamical models using statistical inference techniques. Methods. We created pre-supernova red supergiant models using the stellar evolution code MESA, varying the initial progenitor mass. We then processed the explosion of these progenitors through hydrodynamical simulations, where we changed the explosion energy and the synthesised nickel mass together with its spatial distribution within the ejecta. We compared the results to observations using Markov chain Monte Carlo methods. Results. We apply this method to a well-studied set of SNe with an observed progenitor in pre-explosion images and compare with results in the literature. Progenitor mass constraints are found to be consistent between our results and those derived by pre-SN imaging and the analysis of late-time spectral modelling. Conclusions. We have developed a robust method to infer progenitor and explosion properties of SN II progenitors which is consistent with other methods in the literature. Our results show that hydrodynamical modelling can be used to accurately constrain the physical properties of SNe II. This study is the starting point for a further analysis of a large sample of hydrogen-rich SNe.

Beschreibung: One of the main goals of cosmology is to search for the imprint of primordial gravitational waves in the polarisation filed of the cosmic microwave background to probe inflation theories. One of the obstacles in detecting the primordial signal is that the cosmic microwave background B-mode polarisation must be extracted from among astrophysical contaminations. Most efforts have focus on limiting Galactic foreground residuals, but extragalactic foregrounds cannot be ignored at the large scale (ℓ ≲ 150), where the primordial B-modes are the brightest. We present a complete analysis of extragalactic foreground contamination that is due to polarised emission of radio and dusty star-forming galaxies. We update or use current models that are validated using the most recent measurements of source number counts, shot noise, and cosmic infrared background power spectra. We predict the flux limit (confusion noise) for future cosmic microwave background (CMB) space-based or balloon-borne experiments (IDS, PIPER, SPIDER, LiteBIRD, and PICO), as well as ground-based experiments (C-BASS, NEXT-BASS, QUIJOTE, AdvACTPOL, BICEP3+Keck, BICEPArray, CLASS, Simons Observatory, SPT3G, and S4). The telescope aperture size (and frequency) is the main characteristic that affects the level of confusion noise. Using the flux limits and assuming mean polarisation fractions independent of flux and frequency for radio and dusty galaxies, we computed the B-mode power spectra of the three extragalactic foregrounds (radio source shot noise, dusty galaxy shot noise, and clustering). We discuss their relative levels and compare their amplitudes to that of the primordial tensor modes parametrised by the tensor-to-scalar ratio r. At the reionisation bump (ℓ = 5), contamination by extragalactic foregrounds is negligible. While the contamination is much lower than the targeted sensitivity on r for large-aperture telescopes at the recombination peak (ℓ = 80), it is at a comparable level for some of the medium- (∼1.5 m) and small-aperture telescope (≤0.6 m) experiments. For example, the contamination is at the level of the 68% confidence level uncertainty on the primordial r for the LiteBIRD and PICO space-based experiments. These results were obtained in the absence of multi-frequency component separation (i.e. considering each frequency independently). We stress that extragalactic foreground contaminations have to be included in the input sky models of component separation methods dedicated to the recovery of the CMB primordial B-mode power spectrum. Finally, we also provide some useful unit conversion factors and give some predictions for the SPICA B-BOP experiment, which is dedicated to Galactic and extragalactic polarisation studies. We show that SPICA B-BOP will be limited at 200 and 350 μm by confusion from extragalactic sources for long integrations in polarisation, but very short integrations in intensity.

Beschreibung: Water treatment specialists need more and more to understand how viruses behave in potable water pipes and wastewater setups. This work discusses the late advances in dealing with viruses present in water treatment processes. Activated carbon adsorption (ACA) remains one of the most efficient and credible physicochemical methods. Nanoparticles have been utilized to turn activated carbon into a more efficient sorbent. Membrane filtration could lead to total elimination of viruses and ensure the safety of drinking water plants. As a feasible utilization for disinfecting potable water, solar disinfection (SODIS) remains a green and cost-efficient technology with its optical and thermal pathways and deserves more interest in its large and industrial implementation. Identically, solar distillation remains a viable solution for disinfecting and treating water. The water treatment techniques that are currently utilized for surface water treatment are appropriate for eliminating viruses like influenza A viruses, as proved by the literature. More strict precautions have to be taken to secure viruses' total elimination from water and wastewater as for influenza A and H5N1 in terms of advanced oxidation processes, ACA, and membrane processes application. Before reaching surface water, pathogens have to be removed efficiently from hospital and municipal wastewaters.

Beschreibung: In the effective action approach the imaginary part of the triple pomeron amplitude is calculated. The found dependence on the longitudinal momentum transfer $$e_{-}$$e- is found to separate as a simple factor $$1/|e_{-}|$$1/|e-|. This result is used to calculate the high-mass diffraction on a hadron and double scattering cross-section off a composite target.

Beschreibung: In this paper, we propose an innovative method for conventional triaxial tests of concrete with a confining cell. The polyvinyl chloride (PVC) pipe is used as a mould to cast concrete and also as a membrane to isolate the concrete specimen from oil under confinements. This method is termed as PMM (i.e., PVC pipe is used as a mould and membrane). However, a heat-shrink sleeve is used as a membrane in the traditional test method (TMM). Specimens were made from mortar without coarse aggregates in the present experiment. Under six confinements (0–70 MPa), the conventional triaxial compression tests were performed on ultrahigh-strength (150 MPa) and high-strength (82 MPa) mortar specimens by PMM and TMM. The results indicate the following: (i) there is a characteristic confinement p0; when the confinement is lower than p0, the strength by PMM is higher than that by TMM; on the contrary, when the confinement is higher than p0, the strengths by both methods are almost identical. In this work, p0 is between 0 and 5 MPa. (ii) When the confinement is 5–70 MPa, the relationship between the peak stress of high-strength mortar and confinement is characterized by a monotonically rising straight line; however, a monotonically rising upward convex curve describes the peak stress of ultrahigh-strength mortar related to the confinement. (iii) The residual strength using PMM is significantly higher than that using TMM at zero confinement or lower confinements, but the residual strengths by these two methods are approximately identical at higher confinements. (iv) The transverse cracks appear in the mortar specimen inside the PVC pipe after enduring a triaxial loading using PMM. However, there is no such phenomenon when TMM is applied.

Beschreibung: Chloride corrosion test was carried out in 4% NaCl solution to study the chloride corrosion resistance of rubber concrete. Rubber concrete was prepared by using 20 mesh, 1∼3 mm, and 3∼6 mm rubber particles instead of sand by 5%, 10%, 15%, and 20% of the cementitious material mass. The P-wave velocity and compressive strength of rubber concrete were measured. The microstructure of rubber concrete corroded by chloride was analyzed by SEM. The micromorphology was compared with the macrofailure characteristics under uniaxial compression. The results show that the rubber concrete was still in the early stage of erosion. With the increase of immersion time at the age of 110 days, the P-wave velocity and compressive strength of concrete were generally on the rise. Furthermore, during the period of erosion, the mechanical properties of rubber concrete increased with the increase of rubber particle size and decreased with the increase of the content. Therefore, when the rubber particle size was 3∼6 mm and the content was 5%, the antierosion performance was the best. This study has a certain guiding significance for the chloride corrosion resistance of rubber concrete.

Beschreibung: In this paper, an intelligent modeling approach is presented to predict the shear strength of the internal reinforced concrete (RC) beam-column joints and used to analyze the sensitivity of the influence factors on the shear strength. The proposed approach is established based on the famous boosting-family ensemble machine learning (ML) algorithms, i.e., gradient boosting regression tree (GBRT), which generates a strong predictive model by integrating several weak predictors, which are obtained by the well-known individual ML algorithms, e.g., DT, ANN, and SVM. The strong model is boosted as each weak predictor has its own weight in the final combination according to the performance. Compared with the conventional mechanical-driven shear strength models, e.g., the well-known modified compression field theory (MCFT), the proposed model can avoid the complicated derivation process of shear mechanism and calibration of the involved empirical parameters; thus, it provides a more convenient, fast, and robust alternative way for predicting the shear strength of the internal RC joints. To train and test the GBRT model, a total of 86 internal RC joint specimens are collected from the literatures, and four traditional ML models and the MCFT model are also employed as comparisons. The results indicate that the GBRT model is superior to both the traditional ML models and MCFT model, as its degree-of-fitting is the highest and the predicting dispersion is the lowest. Finally, the model is used to investigate the influences of different parameters on the shear strength of the internal RC joint, and the sensitivity and importance of the corresponding parameters are obtained.

Beschreibung: The fracture development and distribution around the deep soft rock roadway are pivotal to any underground design. In this paper, both field investigation and numerical simulation were taken to study the fracture evolution and rock deformation of a coal mine roadway at Kouzidong mine, Fuyang, Anhui Province, China. Based on the borehole imaging technique, we found an asymmetric distribution of the fracture zone in the surrounding rock of the roadway. By analyzing the C value of the fractures in the borehole images,we found that the fracture interval distribution of the surrounding rock of the tunnel, the number of fractures will fluctuate decrease with the increase of the depth. To effectively study the fracture propagation and distribution of the roadway under longwall retreatment and roadway excavation, the global-local numerical technique was applied via FLAC3D and PFC2D. In the roadway excavation process, fractures were first formed in the shallow section of the roadway and progressively propagated toward the deeper soft rock layer; the main failure mechanism was a tensile failure. During longwall retreatment, fractures continuously developed toward the deeper soft rock layer. However, the failure mechanism transformed to shear failure. From numerical results, it can be seen that the stress concentration at the ribs was released, which led to shear failure at the roof and floor. Due to the extensive tensile cracks in the shallow section, the surrounding rock experienced expansion and fracture. The deep shear failure also induced the formation of the nonadjacent crushing zone and elastic zone, which is in line with the borehole imaging results.

Beschreibung: Silty sand is highly permeable and has a large internal friction angle. To ensure the stable and efficient construction of the Earth pressure balance (EPB) shield in silt stratum, it is necessary to reduce the disturbance to the stratum during tunneling and reduce the risk of spewing and blocking during soil discharge. Thus, a new type of dense slurry-EPB shield construction technology is proposed. Using a custom-made test device, the consolidation tests were conducted on sand after mixing it with different amounts of slurry to study the change in the pore pressure in the mixed soil and sand stratum and analyze the stress transmission rule. In addition, slump tests were conducted on the mixed soil to study the change in the fluidity. Based on the laboratory test results, a field investigation was carried out to study the effects of the amount of slurry addition on the pore pressure in the stratum, the driving parameters, and the sand’s flowability during shield tunneling. The results show that when the amount of slurry reaches a certain value, the filter cake effect occurs. The greater the amount of slurry added during the shield tunneling, the smaller the rate of change of the pore pressure in the stratum. When the amount of BC2 slurry added reached 8 m3 per ring, the rate of change was reduced by 57%, and the slump value improved by 93%. The type of filter cake of the DS-EPB shield was only internal filter cake during tunneling, which reduced the disturbance of the excavation face and improved the flowability of the sand. These results are of great significance to the application and promotion of DS-EPB shields in sandy cobble strata.

Beschreibung: An assessment of uncertainty in flood hydrograph features, e.g., peak discharge and flood volume due to variability in the rainfall-runoff model (HEC-HMS) parameters and rainfall characteristics, e.g., depth and duration, is conducted. Flood hydrographs are generated using a rain pattern generator (RPG) and HEC-HMS models through Monte Carlo simulation considering uncertainty in stochastic variables. The uncertainties in HEC-HMS parameters (e.g., loss, base flow, and unit hydrograph) are estimated using their probability distribution functions. The flood events are obtained by simulating runoff for rainfall events using the generated model parameters. The uncertainties due to rainfall and model parameters on generated flood hydrographs are evaluated using the relative coefficient of variation (RCV). The results reveal a higher RCV index for flood volume (RCV = 153) than peak discharge (RCV = 116) for a 12-hr rainfall duration. The average relative RCV (ARRCV) index computed for hydrological component (e.g., base flow, loss, or unit hydrograph) indicates the highest impact of rainfall depth on flood volume and peak. The results indicate that rainfall depth is the main source of uncertainty of flood peak and volume.

Beschreibung: The origin of the population of very massive stars observed within ∼0.4 pc of the supermassive black hole in the Galactic Centre is a mystery. Tidal forces from the black hole would likely inhibit in situ star formation whilst the youth of the massive stars would seem to exclude formation elsewhere followed by transportation (somehow) into the Galactic Centre. Here, we consider a third way to produce these massive stars from the lower mass stars contained in the nuclear stellar cluster which surrounds the supermassive black hole. A passing gas cloud can be tidally shredded by the supermassive black hole forming an accretion disc around the black hole. Stars embedded within this accretion disc will accrete gas from the disc via Bondi–Hoyle accretion, where the accretion rate on to a star, $dot{M}_star propto M_star ^2$. This super-exponential growth of accretion can lead to a steep increase in stellar masses, reaching the required 40–50 M⊙ in some cases. The mass growth rate depends sensitively on the stellar orbital eccentricities and their inclinations. The evolution of the orbital inclinations and/or their eccentricities as stars are trapped by the disc, and their orbits are circularized, will increase the number of massive stars produced. Thus accretion on to low-mass stars can lead to a top heavy stellar mass function in the Galactic Centre and other galactic nuclei. The massive stars produced will pollute the environment via supernova explosions and potentially produce compact binaries whose mergers may be detectable by the LIGO–VIRGO gravitational waves observatories.

Beschreibung: We present a 3D semi-analytical model of self-gravitating discs, and include a prescription for dust trapping in the disc spiral arms. Using Monte Carlo radiative transfer, we produce synthetic ALMA (Atacama Large Millimeter/submillimeter Array) observations of these discs. In doing so, we demonstrate that our model is capable of producing observational predictions, and able to model real image data of potentially self-gravitating discs. For a disc to generate spiral structure that would be observable with ALMA requires that the disc’s dust mass budget is dominated by millimetre- and centimetre-sized grains. Discs in which grains have grown to the grain fragmentation threshold may satisfy this criterion; thus, we predict that signatures of gravitational instability may be detectable in discs of lower mass than has previously been suggested. For example, we find that discs with disc-to-star mass ratios as low as 0.10 are capable of driving observable spiral arms. Substructure becomes challenging to detect in discs where no grain growth has occurred or in which grain growth has proceeded well beyond the grain fragmentation threshold. We demonstrate how we can use our model to retrieve information about dust trapping and grain growth through multiwavelength observations of discs, and using estimates of the opacity spectral index. Applying our disc model to the Elias 27, WaOph 6, and IM Lup systems, we find gravitational instability to be a plausible explanation for the observed substructure in all three discs, if sufficient grain growth has indeed occurred.

Beschreibung: The star formation in molecular clouds is inefficient. The ionizing extreme-ultraviolet radiation (hν ≥ 13.6 eV) from young clusters has been considered as a primary feedback effect to limit the star formation efficiency (SFE). Here, we focus on the effects of stellar far-ultraviolet (FUV) radiation (6 eV ≤ hν ≤ 13.6 eV) during the cloud disruption stage. The FUV radiation may further reduce the SFE via photoelectric heating, and it also affects the chemical states of the gas that is not converted to stars (‘cloud remnants’) via photodissociation of molecules. We have developed a one-dimensional semi-analytical model that follows the evolution of both the thermal and chemical structure of a photodissociation region (PDR) during the dynamical expansion of an H ii region. We investigate how the FUV feedback limits the SFE, supposing that the star formation is quenched in the PDR where the temperature is above a threshold value (e.g. 100 K). Our model predicts that the FUV feedback contributes to reduce the SFEs for massive (Mcl ≳ 105 M⊙) clouds with low surface densities ($Sigma _{ m cl}lesssim 100~{ m M}_odot , { m pc}^{-2}$). Moreover, we show that a large part of the H2 molecular gas contained in the cloud remnants should be ‘CO-dark’ under the FUV feedback for a wide range of cloud properties. Therefore, the dispersed molecular clouds are potential factories of CO-dark gas, which returns into the cycle of the interstellar medium.

Beschreibung: The Pan-STARRS1 (PS1) 3π survey is a comprehensive optical imaging survey of three quarters of the sky in the grizy broad-band photometric filters. We present the methodology used in assembling the source classification and photometric redshift (photo-z) catalogue for PS1 3π Data Release 1, titled Pan-STARRS1 Source Types and Redshifts with Machine learning (PS1-STRM). For both main data products, we use neural network architectures, trained on a compilation of public spectroscopic measurements that has been cross-matched with PS1 sources. We quantify the parameter space coverage of our training data set, and flag extrapolation using self-organizing maps. We perform a Monte-Carlo sampling of the photometry to estimate photo-z uncertainty. The final catalogue contains 2,902,054,648 objects. On our validation data set, for non-extrapolated sources, we achieve an overall classification accuracy of $98.1\%$ for galaxies, $97.8\%$ for stars, and $96.6\%$ for quasars. Regarding the galaxy photo-z estimation, we attain an overall bias of =0.0005, a standard deviation of σ(Δznorm) = 0.0322, a median absolute deviation of MAD(Δznorm) = 0.0161, and an outlier fraction of $Pleft(|Delta z_{mathrm{norm}}|〉0.15 ight)=1.89\%$. The catalogue will be made available as a high-level science product via the Mikulski Archive for Space Telescopes.