ALBERT

Description: Pre-main sequence (PMS) stars evolve into main sequence (MS) phase over a period of time. Interestingly, we found a scarcity of studies in existing literature that examines and attempts to better understand the stars in PMS to MS transition phase. The purpose of the present study is to detect such rare stars, which we named as ‘Transition Phase’ (TP) candidates – stars evolving from the PMS to the MS phase. We identified 98 TP candidates using photometric analysis of a sample of 2167 classical Be (CBe) and 225 Herbig Ae/Be (HAeBe) stars. This identification is done by analyzing the near- and mid-infrared excess and their location in the optical colour-magnitude diagram. The age and mass of 58 of these TP candidates are determined to be between 0.1–5 Myr and 2–10.5 M⊙, respectively. The TP candidates are found to possess rotational velocity and colour excess values in between CBe and HAeBe stars, which is reconfirmed by generating a set of synthetic samples using the machine learning approach.

Description: Recent searches for the hosts of z ∼ 4 damped Lyα absorbers (DLAs) have detected bright galaxies at distances of tens of kpc from the DLA. Using the FIRE-2 cosmological zoom simulations, we argue that these relatively large distances are due to a predominantly cool and neutral inner circumgalactic medium (CGM) surrounding high-redshift galaxies. The inner CGM is cool because of the short cooling time of hot gas in ≲ 1012 M⊙ haloes, which implies that accretion and feedback energy are radiated quickly, while it is neutral due to high volume densities and column densities at high redshift which shield cool gas from photoionization. Our analysis predicts large DLA covering factors ($gtrsim 50{{ m per cent}}$) out to impact parameters ∼0.3((1 + z)/5)3/2Rvir from the central galaxies at z ≳ 1, equivalent to a proper distance of $sim 21, M_{12}^{1/3} left(left(1+z ight)/5 ight)^{1/2}, { m kpc}$ (Rvir and M12 are the halo virial radius and mass in units of 1012 M⊙, respectively). This implies that DLA covering factors at z ∼ 4 may be comparable to unity out to a distance ∼10 times larger than stellar half-mass radii. A predominantly neutral inner CGM in the early universe suggests that its mass and metallicity can be directly constrained by absorption surveys, without resorting to the large ionization corrections as required for ionized CGM.

Description: The Internal Linear Combination (ILC) method has been extensively used to extract the cosmic microwave background (CMB) anisotropy map from foreground contaminated multi-frequency maps. However, the performance of simple ILC is limited and can be significantly improved by heavily constraint equations, dubbed constrained ILC (cILC). The standard ILC and cILC works on spin-0 fields. Recently, a generalised version of ILC has been developed, named Polarization ILC (PILC), in which Q ± iU at multiple frequencies are combined using complex coefficients to estimate Stokes Q and U maps. A statistical moment expansion method has recently been developed for high precision modelling of the Galactic foregrounds. This paper develops a semi-blind component separation method combining the moment approach of foreground modelling with a generalised version of the PILC method for heavily constraint equations. The algorithm is developed in pixel space over a spin-2 field. We demonstrate the performance of the method on three sets of absolutely calibrated simulated maps at WMAP and Planck frequencies with varying foreground models. We apply this component separation technique in simultaneous estimation of Stokes Q and U maps of the thermal dust at 353 GHz and synchrotron at 30 GHz. We also recover both dust and synchrotron maps at 100 and 143 GHz, where separating two components is challenging.

Description: Luminous active galactic nuclei and X-ray binaries often contain geometrically thin, radiatively cooled accretion discs. According to theory, these are – in many cases – initially highly misaligned with the black hole equator. In this work, we present the first general relativistic magnetohydrodynamic simulations of very thin (h/r ∼ 0.015–0.05) accretion discs around rapidly spinning (a ∼ 0.9) black holes and tilted by 45°–65°. We show that the inner regions of the discs with h/r ≲ 0.03 align with the black hole equator, though out to smaller radii than predicted by analytic work. The inner aligned and outer misaligned disc regions are separated by a sharp break in tilt angle accompanied by a sharp drop in density. We find that frame dragging by the spinning black hole overpowers the disc viscosity, which is self-consistently produced by magnetized turbulence, tearing the disc apart and forming a rapidly precessing inner sub-disc surrounded by a slowly precessing outer sub-disc. We find that the system produces a pair of relativistic jets for all initial tilt values. At small distances, the black hole launched jets precess rapidly together with the inner sub-disc, whereas at large distances they partially align with the outer sub-disc and precess more slowly. If the tearing radius can be modeled accurately in future work, emission model independent measurements of black hole spin based on precession-driven quasi-periodic oscillations may become possible.

Description: We present the second part of results of the ongoing project aimed at searching for and studying eXtremely Metal-Poor (XMP) – adopted as those with Zgas ≲ Z⊙/30, or with 12+log (O/H) ≲ 7.21 dex − very gas-rich blue dwarfs in voids. They were first identified in the course of the ‘unbiased’ study of the galaxy population in the nearby Lynx–Cancer void. These very rare and unusual galaxies seem to be the best proxies of so-called Very Young Galaxies (VYGs) defined recently in model simulations by Tweed et al. To date, for 16 pre-selected void XMP candidates, using the Big Telescope Alt-azimuth (BTA), the SAO 6-m telescope, we have obtained spectra suitable for the determination of O/H. For majority of the observed galaxies, the principal line [O iii] λ4363 , used for the direct classical Te method of O/H determination, is undetected. Therefore, to estimate O/H, we use a new ‘strong-lines’ method by Izotov et al. This appears to be the most accurate empirical O/H estimator for the range of 12+log (O/H) ≲ 7.4–7.5. For objects with higher O/H, we use the semi-empirical method by Izotov & Thuan with our modification accounting for variance of the excitation parameter O32. Six of those 16 candidates are found, with confidence, to be XMP dwarfs. In addition, eight studied galaxies are less metal-poor, with 12+log (O/H) = 7.24–7.33, and these can also fall into the category of VYG candidates. Taking into account our recently published work and the previously known (nine prototype galaxies) XMP gas-rich void objects, the new findings increase the number of this type of galaxy known to date to a total of 19.

Description: This paper explores methods for constructing low multipole temperature and polarization likelihoods from maps of the cosmic microwave background anisotropies that have complex noise properties and partial sky coverage. We use Planck 2018 High Frequency Instrument (HFI) and updated SRoll2 temperature and polarization maps to test our methods. We present three likelihood approximations based on quadratic cross spectrum estimators: (i) a variant of the simulation-based likelihood (SimBaL) techniques used in the Planck legacy papers to produce a low multipole EE likelihood; (ii) a semi-analytical likelihood approximation (momento) based on the principle of maximum entropy; (iii) a density-estimation ‘likelihood-free’ scheme (delfi). Approaches (ii) and (iii) can be generalized to produce low multipole joint temperature-polarization (TTTEEE) likelihoods. We present extensive tests of these methods on simulations with realistic correlated noise. We then analyse the Planck data and confirm the robustness of our method and likelihoods on multiple inter- and intra-frequency detector set combinations of SRoll2 maps. The three likelihood techniques give consistent results and support a low value of the optical depth to reoinization, τ, from the HFI. Our best estimate of τ comes from combining the low multipole SRoll2momento (TTTEEE) likelihood with the CamSpec high multipole likelihood and is $au = 0.0627^{+0.0050}_{-0.0058}$. This is consistent with the SRoll2 team’s determination of τ, though slightly higher by ∼0.5σ, mainly because of our joint treatment of temperature and polarization.

Description: X-ray flares in gamma-ray bursts (GRBs) are believed to be generated by the late activities of central engine, and thus provide an useful tool to diagnose the properties of central objects. In this paper, we work on a GRB X-ray flare sample whose bulk Lorentz factors are constrained by two different methods and the jet opening angles are determined by the jet breaks in afterglow light curves. Considering a hyperaccreting stellar-mass black hole (BH) as the central engine of GRBs and the Blandford & Znajek process (BZ) as the jet production mechanism, we constrain the parameters of central engine by using the X-ray flare data. We find that the BZ mechanism is so powerful making it possible to interpret both GRB prompt emissions and bright X-ray flares. The wind parameter (p) and accreted mass (Md) fall into reasonable ranges. Our result is also applied to GRB 170817A. The late X-ray flare in GRB 170817A, if it is true, might not be a BH origin.

Description: In this work, we expand and test the capabilities of our recently developed superresolution (SR) model to generate high-resolution (HR) realizations of the full phase-space matter distribution, including both displacement and velocity, from computationally cheap low-resolution (LR) cosmological N-body simulations. The SR model enhances the simulation resolution by generating 512 times more tracer particles, extending into the deeply nonlinear regime where complex structure formation processes take place. We validate the SR model by deploying the model in 10 test simulations of box size 100 h−1 Mpc, and examine the matter power spectra, bispectra, and two-dimensional power spectra in redshift space. We find the generated SR field matches the true HR result at per cent level down to scales of k ∼ 10 h  Mpc−1. We also identify and inspect dark matter haloes and their substructures. Our SR model generates visually authentic small-scale structures that cannot be resolved by the LR input, and are in good statistical agreement with the real HR results. The SR model performs satisfactorily on the halo occupation distribution, halo correlations in both real and redshift space, and the pairwise velocity distribution, matching the HR results with comparable scatter, thus demonstrating its potential in making mock halo catalogues. The SR technique can be a powerful and promising tool for modelling small-scale galaxy formation physics in large cosmological volumes.

Description: Hydrogen cyanide (HCN) and its isomer hydrogen isocyanide (HNC) play an important role in molecular cloud chemistry and the formation of more complex molecules. We investigate here the impact of protostellar shocks on the HCN and HNC abundances from high-sensitivity IRAM 30 m observations of the prototypical shock region L1157-B1 and the envelope of the associated Class 0 protostar, as a proxy for the pre-shock gas. The isotopologues H12CN, HN12C, H13CN, HN13C, HC15N, H15NC, DCN, and DNC were all detected towards both regions. Abundances and excitation conditions were obtained from radiative transfer analysis of molecular line emission under the assumption of local thermodynamical equilibrium. In the pre-shock gas, the abundances of the HCN and HNC isotopologues are similar to those encountered in dark clouds, with an HCN/HNC abundance ratio ≈1 for all isotopologues. A strong D-enrichment (D/H ≈ 0.06) is measured in the pre-shock gas. There is no evidence of 15N fractionation neither in the quiescent nor in the shocked gas. At the passage of the shock, the HCN and HNC abundances increase in the gas phase in different manners so that the HCN/HNC relative abundance ratio increases by a factor 20. The gas-grain chemical and shock model uclchem allows us to reproduce the observed trends for a C-type shock with pre-shock density n(H) = $10^5hbox{cm$^{-3}$}$ and shock velocity $V_mathrm{ s}= 40hbox{kms$^{-1}$}$. We conclude that the HCN/HNC variations across the shock are mainly caused by the sputtering of the grain mantle material in relation with the history of the grain ices.

Description: We present results from a polarization study of the radio-intermediate quasar, III Zw 2, at a redshift of 0.089, with the upgraded Giant Metrewave Radio Telescope (uGMRT) at 685 MHz and the Karl G. Jansky Very Large Array (VLA) at 5 and 34 GHz. We detect a kpc-scale outflow, exhibiting transverse magnetic (B-) fields. The curved jet terminates in a bow-shock-like radio structure with inferred B-fields aligned with the lobe edges. We suggest that the radio outflow in III Zw 2 is a combination of a collimated jet along with a wind-like component. This ‘wind’ component could be a magnetized accretion disc wind or the outer layers of a broadened jet or a combination of both. The current data cannot differentiate between these possibilities. We also detect kpc-scale lobe emission that is misaligned with the primary lobes in the uGMRT images. The spectral indices and the electron lifetimes in the misaligned lobe are similar to the primary lobe, suggesting that the misaligned lobe is not a relic. We propose that changing spectral states of the accretion disc, and the subsequent intermittent behaviour of the outflow, along with the close interplay between the jet and ‘wind’ could explain the radio-intermediate nature of III Zw 2. Our study shows that radio-intermediate quasars are promising sources for understanding the role of jets and winds in galaxy evolution and demonstrates the power of radio polarization studies towards achieving this.

Description: The peripheral regions of globular clusters (GCs) are extremely challenging to study due to their low surface brightness nature and the dominance of Milky Way contaminant populations along their sightlines. We have developed a probabilistic approach to this problem through utilizing a mixture model in spatial and proper motion space that separately models the cluster, extra-tidal, and contaminant stellar populations. We demonstrate the efficacy of our method through application to Gaia third early data release photometry and astrometry in the direction of NGC 5139 (ω Centauri, hereafter ω Cen), a highly challenging target on account of its Galactic latitude (b ≈ 15○) and low proper motion contrast with the surrounding field. We recover the spectacular tidal extensions, spanning the 10○ on the sky explored here, seen in earlier work and quantify the star count profile and ellipticity of the system out to a cluster-centric radius of 4○. We show that both RR Lyrae and blue horizontal branch stars consistent with belonging to ω Cen are found in the tidal tails, and calculate that these extensions contain at least ≈0.1 per cent of the total stellar mass in the system. Our high-probability members provide prime targets for future spectroscopic studies of ω Cen out to unprecedented radii.

Description: Many astrophysical hydrodynamics simulations must account for gravity, and evaluating the gravitational field at the positions of all resolution elements can incur significant cost. Typical algorithms update the gravitational field at the position of each resolution element every time the element is updated hydrodynamically, but the actual required update frequencies for hydrodynamics and gravity can be different in general. We show that the gravity calculation in hydrodynamics simulations can be optimized by only updating gravity on a time-scale dictated by the already determined maximum time-step for accurate gravity integration Δtgrav, while staying well within the typical error budget of hydro schemes and gravity solvers. Our implementation in the gizmo code uses the time-scale derived from the tidal tensor $t_{ m tidal} = Vert mathbf {T}Vert ^{-1/2}$ to determine Δtgrav and the force update frequency in turn, and uses the rate of change of acceleration evaluated by the gravity solver to construct a predictor of the acceleration for use between updates. We test the scheme on standard self-gravitating hydrodynamics test problems, finding solutions very close to the standard scheme while evaluating far fewer gravity forces, optimizing the simulations. We also demonstrate a $sim 70{{ m per cent}}$ speed-up in an example simulation of a giant molecular cloud. In general, this scheme introduces a new tunable parameter for obtaining an optimal compromise between accuracy and computational cost, in conjunction with, e.g. time-step tolerance, numerical resolution, and gravity solver tolerance.

Description: The rotation powered pulsar loses angular momentum at a rate of the rotation power divided by the angular velocity Ω*. This means that the length of the lever arm of the angular momentum extracted by the photons, relativistic particles, and wind must be on average c/Ω*, which is known as the light cylinder radius. Therefore, any deposition of the rotation power within the light cylinder causes insufficient loss of angular momentum. In this paper, we investigate two cases of this type of energy release: polar cap acceleration and Ohmic heating in the magnetospheric current inside the star. As for the first case, the outer magnetosphere beyond the light cylinder is found to compensate the insufficient loss of the angular momentum. We argue that the energy flux coming from the sub-rotating magnetic field lines must be larger than the solid-angle average value, and as a result, an enhanced energy flux emanating beyond the light cylinder is observed in different phases in the light curve from those of emission inside the light cylinder. As for the second case, the stellar surface rotates more slowly than the stellar interior. We find that the way the magnetospheric current closes inside the star is linked to how the angular momentum is transferred inside the star. We obtain numerical solutions that shows that the magnetospheric current inside the star spreads over the polar cap magnetic flux embedded in the star in such a way that electromotive force is gained efficiently.

Description: The structure and evolution of protoplanetary discs (PPDs) are largely governed by disc angular momentum transport, mediated by magnetic fields. In the most observable outer disc, ambipolar diffusion is the primary non-ideal magnetohydrodynamic (MHD) effect. In this work, we study the gas dynamics in outer PPDs by conducting a series of global three-dimensional non-ideal MHD simulations with ambipolar diffusion and net poloidal magnetic flux, using the Athena++ MHD code, with resolution comparable to local simulations. Our simulations demonstrate the coexistence of magnetized disc winds and turbulence driven by the magneto-rotational instability (MRI). While MHD winds dominate disc angular momentum transport, the MRI turbulence also contributes significantly. We observe that magnetic flux spontaneously concentrates into axisymmetric flux sheets, leading to radial variations in turbulence levels, stresses, and accretion rates. Annular substructures arise as a natural consequence of magnetic flux concentration. The flux concentration phenomena show diverse properties with different levels of disc magnetization and ambipolar diffusion. The disc generally loses magnetic flux over time, though flux sheets could prevent the leak of magnetic flux in some cases. Our results demonstrate the ubiquity of disc annular substructures in weakly MRI turbulent outer PPDs and imply a stochastic nature of disc evolution.

Description: Motivated by recent theoretical work on tidal disruption events and other peculiar transients, we present moving-mesh radiation-hydrodynamic simulations of radiative luminosity emitted by a central source being reprocessed by a wind-like outflow. We couple the moving-mesh hydrodynamic code jet with our newly developed radiation module based on mixed-frame grey flux-limited diffusion with implicit timestep update. This allows us to study the self-consistent multidimensional radiation-hydrodynamic evolution over more than 10 orders of magnitude in both space and time in a single run. We simulate an optically thick spherical wind with constant or evolving mass-loss rate, which is irradiated by a central isotropic or angularly dependent radiation source. Our spherically symmetric simulations confirm previous analytic results by identifying different stages of radiation reprocessing: radiation trapped in the wind, diffusing out through the wind, and reaching constant maximum attenuation. We find that confining the central radiation source in a cone with moderate opening angles decrease up to one order of magnitude the early flux along sightlines oriented away from the direction of radiation injection but that the reprocessed radiation becomes isotropic roughly after one lateral diffusion time through the ejecta. We discuss further applications and guidelines for the use of our novel radiation-hydrodynamics tool in the context of transient modelling.

Description: Since the detection of X-ray pulses from ultraluminous X-ray sources (ULXs) in 2014, neutron stars have been considered as their central objects. However, it remains unclear how neutron stars can be brighter than the Eddington luminosity, and no unified view exists on the magnetic field of neutron stars and the degree of beaming. Recent observations suggest that some X-ray pulsating ULXs have Be-type donors, and some of them occupy the same region as Be-type high-mass X-ray binaries (Be-HMXBs) on the Corbet diagram, which reveals the relation between spin and orbital periods. This suggests that at least some ULXs are special cases of Be-HMXBs. In this study, we use the framework of mass accretion models for Be-HMXBs to investigate the conditions under which neutron stars achieve mass accretion rates beyond the Eddington limit and become observable as ULXs. We show that a Be-HMXB may become a ULX if the magnetic field of the neutron star and the density of the Be disc meet certain conditions. We also show that, although a stronger magnetic field increases the brightness of a neutron star ULX with a Be donor, its brightness cannot exceed the Eddington limit by a more than a factor of ≈50. Finally, we propose a scenario whereby some normal Be-HMXBs may evolve into ULXs as the donor evolves into a giant.

Description: We present an analysis of the intracluster light (ICL) in the Frontier Field Cluster MACS J1149.5+2223 (z = 0.544), which combines new and archival Hubble WFC3/IR imaging to provide continuous radial coverage out to 2.8 Mpc from the brightest cluster galaxy (BCG). Employing careful treatment of potential systematic biases and using data at the largest radii to determine the background sky level, we reconstruct the surface brightness profile out to a radius of 2 Mpc. This radius is the largest to which the ICL has been measured for an individual cluster. Within this radius, we measure a total luminosity of 1.5 × 1013 L⊙ for the BCG plus ICL. From the profile and its logarithmic slope, we identify the transition from the BCG to ICL at r ∼ 70 kpc. Remarkably, we also detect an apparent inflection in the profile centred in the 1.2–1.7 Mpc (0.37–0.52 r200m) radial bin, a signature of an infall caustic in the stellar distribution. Based upon the shape and strength of the feature, we interpret it as potentially being at the splashback radius, although the radius is smaller than theoretical predictions. If this is the splashback radius, then it is the first such detection in the ICL and the first detection of the splashback radius for an individual cluster. Similar analyses should be possible with the other Frontier Field clusters, and eventually with clusters observed by the Euclid and Roman missions.

Description: Hi intensity mapping will provide maps of the large-scale distribution of neutral hydrogen (Hi) in the universe. These are prime candidates to be used to constrain primordial non-Gaussianity using the Large Scale Structure of the Universe as well as to provide further tests of Einstein’s theory of Gravity (GR). But Hi maps are contaminated by foregrounds, which can be several orders of magnitude above the cosmological signal. Here we quantify how degenerated are the large-scale effects (fNL and GR effects) with the residual foregrounds. We conclude that a joint analysis does not provide a catastrophic degradation of constraints and provides a framework to determine the marginal errors of large scale-effects in the presence of foregrounds. Similarly, we conclude that the macroscopical properties of the foregrounds can be measured with high precision. Notwithstanding, such results are highly dependent on accurate forward modelling of the foregrounds, which incorrectly done catastrophically bias the best fit values of cosmological parameters, foreground parameterisations, and large-scale effects.

Description: The [O iii] 88 μm fine structure emission line has been detected into the Epoch of Reionization (EoR) from star-forming galaxies at redshifts 6 〈 z ≲ 9 with ALMA. These measurements provide valuable information regarding the properties of the interstellar medium (ISM) in the highest redshift galaxies discovered thus far. The [O iii] 88 μm line observations leave, however, a degeneracy between the gas density and metallicity in these systems. Here we quantify the prospects for breaking this degeneracy using future ALMA observations of the [O iii] 52 μm line. Among the current set of ten [O iii] 88 μm emitters at 6 〈 z ≲ 9, we forecast 52 μm detections (at 6-σ) in SXDF-NB1006-2, B14-6566, J0217-0208, and J1211-0118 within on-source observing times of 2-10 hours, provided their gas densities are larger than about nH ≳ 102 − 103 cm−3. Other targets generally require much longer integration times for a 6-σ detection. Either successful detections of the 52 μm line, or reliable upper limits, will lead to significantly tighter constraints on ISM parameters. The forecasted improvements are as large as ∼3 dex in gas density and ∼1 dex in metallicity for some regions of parameter space. We suggest SXDF-NB1006-2 as a promising first target for 52 μm line measurements. We discuss how such measurements will help in understanding the mass metallicity relationship during the EoR.

Description: Misalignments within protoplanetary discs are now commonly observed, and features such as shadows in scattered light images indicate departure from a co-planar geometry. VLT/SPHERE observations of the disc around HD 143006 show a large-scale asymmetry, and two narrow dark lanes which are indicative of shadowing. ALMA observations also reveal the presence of rings and gaps in the disc, along with a bright arc at large radii. We present new hydrodynamic simulations of HD 143006, and show that a configuration with both a strongly inclined binary and an outer planetary companion is the most plausible to explain the observed morphological features. We compute synthetic observations from our simulations, and successfully reproduce both the narrow shadows and the brightness asymmetry seen in IR scattered light. Additionally, we reproduce the large dust observed in the mm continuum, due to a 10 Jupiter mass planet detected in the CO kinematics. Our simulations also show the formation of a circumplanetary disc, which is misaligned with respect to the outer disc. The narrow shadows cast by the inner disc and the planet-induced “kink” in the disc kinematics are both expected to move on a time-scale of ∼5–10 years, presenting a potentially observable test of our model. If confirmed, HD 143006 would be the first known example of a circumbinary planet on a strongly misaligned orbit.

Description: Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magneto-rotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate ($dot{M}$∼10−8 M⊙ yr−1) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the midplane. As a result, both the disc midplane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges onto grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.

Description: Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 Extreme Emission Line Galaxies (EELGs) at a redshift 0 ≲ z ≲ 0.49, selected from the Sloan Digital Sky Survey (SDSS) to be local analogues of high-redshift galaxies, was used to analyse their most prominent emission lines and to derive total oxygen abundances and nitrogen-to-oxygen ratios following the direct method in the ranges 7.7 〈 12+log(O/H) 〈 8.6 and -1.8 〈 log(N/O) 〈 -0.8. They allow us to obtain new empirically calibrated strong-line methods and to evaluate other recipes based on photoionization models that can be later used for a chemical analysis of actively star-forming galaxies in very early stages of galaxy evolution. Our new relations are in agreement with others found for smaller samples of objects at higher redshifts. When compared with other relations calibrated in the local Universe, they differ when the employed strong-line ratio depends on the hardness of the ionizing radiation, such as O32 or Ne3O2, but they do not when the main dependence is on the ionization parameter, such as S23. In the case of strong-line ratios depending on [N ii] lines, the derivation of O/H becomes very uncertain due to the very high N/O values derived in this sample, above all in the low-metallicity regime. Finally, we adapt the bayesian-like code HII-Chi-mistry for the conditions found in this kind of galaxies and we prove that it can be used to derive within errors both O/H and N/O, in consistency with the direct method .

Description: Stellar tidal streams are sensitive tracers of the properties of the gravitational potential in which they orbit and detailed observations of their density structure can be used to place stringent constraints on fluctuations in the potential caused by, e.g., the expected populations of dark matter subhalos in the standard cold dark matter paradigm (CDM). Simulations of the evolution of stellar streams in live N-body halos without low-mass dark-matter subhalos, however, indicate that streams exhibit significant perturbations on small scales even in the absence of substructure. Here we demonstrate, using high-resolution N-body simulations combined with sophisticated semi-analytic and simple analytic models, that the mass resolutions of 104–$10^5, m {M}_{odot }$ commonly used to perform such simulations cause spurious stream density variations with a similar magnitude on large scales as those expected from a CDM-like subhalo population and an order of magnitude larger on small, yet observable, scales. We estimate that mass resolutions of $approx 100, m {M}_{odot }$ ($approx 1, m {M}_{odot }$) are necessary for spurious, numerical density variations to be well below the CDM subhalo expectation on large (small) scales. That streams are sensitive to a simulation’s particle mass down to such small masses indicates that streams are sensitive to dark matter clustering down to these low masses if a significant fraction of the dark matter is clustered or concentrated in this way, for example, in MACHO models with masses of 10–$100, m {M}_{odot }$.

Description: We present TES, a new n-body integration code for the accurate and rapid propagation of planetary systems in the presence of close encounters. TES builds upon the classic Encke method and integrates only the perturbations to Keplerian trajectories to reduce both the error and runtime of simulations. Variable step size is used throughout to enable close encounters to be precisely handled. A suite of numerical improvements are presented that together make TES optimal in terms of energy error. Lower runtimes are found in the majority of test problems considered when compared to direct integration using IAS15. TES is freely available.

Description: As deep spectroscopic campaigns extend to higher redshifts and lower stellar masses, the interpretation of galaxy spectra depends increasingly upon models for very young stellar populations. Here we present new HST/COS ultraviolet spectroscopy of seven nearby (

Description: Supernova Ia magnitude surveys measure the dimensionless luminosity distance H0DL. However, from the distances alone one cannot obtain quantities like H(z) or the dark energy equation of state, unless further cosmological assumptions are imposed. Here we show that by measuring the power spectrum of density contrast and of peculiar velocities of supernovae one can estimate also H(z)/H0 regardless of background or linearly perturbed cosmology and of galaxy-matter bias. This method, dubbed Clustering of Standard Candles (CSC) also yields the redshift distortion parameter β(k, z) and the biased matter power spectrum in a model-independent way. We forecast that an optimistic (pessimistic) LSST may be able to constrain H(z)/H0 to 5–13% (9–40%) in redshift bins of Δz = 0.1 up to at least z = 0.6.

Description: We identify 228 periodic variables in the region of young open cluster NGC 281 using time series photometry carried out from 1 m class ARIES telescopes, Nainital. The cluster membership of these identified variables is determined on the basis colour-magnitude, two colour diagrams and kinematic data. Eighty one variable stars are found to be members of the cluster NGC 281. Of 81 variables, 30 and 51 are probable main-sequence and pre-main-sequence members, respectively. Present study classifies main-sequence variable stars into different variability types according to their periods of variability, shape of light curves and location in the Hertzsprung-Russell diagram. These identified main-sequence variables could be β Cep, δ Scuti, slowly pulsating B type and new class variables. Among 51 pre-main-sequence variables, majority of them are weak line T Tauri stars. The remaining 147 variables could belong to the field population. The variability characteristics of the field population indicate that these variables could be RR Lyrae, δ Scuti and binaries type variables.

Description: ΛCDM cosmological models with Early Dark Energy (EDE) have been proposed to resolve tensions between the Hubble constant H0 = 100 h kmṡ−1Ṁpc−1 measured locally, giving h ≈ 0.73, and H0 deduced from Planck cosmic microwave background (CMB) and other early universe measurements plus ΛCDM, giving h ≈ 0.67. EDE models do this by adding a scalar field that temporarily adds dark energy equal to about 10% of the cosmological energy density at the end of the radiation-dominated era at redshift z ∼ 3500. Here we compare linear and nonlinear predictions of a Planck-normalized ΛCDM model including EDE giving h = 0.728 with those of standard Planck-normalized ΛCDM with h = 0.678. We find that nonlinear evolution reduces the differences between power spectra of fluctuations at low redshifts. As a result, at z = 0 the halo mass functions on galactic scales are nearly the same, with differences only 1-2%. However, the differences dramatically increase at high redshifts. The EDE model predicts 50% more massive clusters at z = 1 and twice more galaxy-mass haloes at z = 4. Even greater increases in abundances of galaxy-mass haloes at higher redshifts may make it easier to reionize the universe with EDE. Predicted galaxy abundances and clustering will soon be tested by the James Webb Space Telescope (JWST) observations. Positions of baryonic acoustic oscillations (BAOs) and correlation functions differ by about 2% between the models – an effect that is not washed out by nonlinearities. Both standard ΛCDM and the EDE model studied here agree well with presently available acoustic-scale observations, but the Dark Energy Spectroscopic Instrument (DESI) and Euclid measurements will provide stringent new tests.

Description: The detection of the binary neutron star (BNS) merger GW170817 and the associated electromagnetic (EM) counterpart, the “kilonova” (kN) AT2017gfo, opened a new era in multi-messenger astronomy. However, despite many efforts, it has been proven very difficult to find additional kilonovae, even though LIGO/Virgo has reported at least one BNS event during their latest run, O3. The focus of this work is the exploration of the sensitivity of the adopted optical surveys searching for kNe during O3. We propose ways to optimize the choices of filters and survey depth to boost the detection efficiency for these faint and fast-evolving transients in the future. In particular, we use kN models to explore the dependence on ejecta mass, geometry, viewing angle, wavelength coverage and source distance. We find that the kN detection efficiency has a strong viewing-angle dependency, especially for filters blueward of i-band. This loss of sensitivity can be mitigated by early, deep, observations. Efficient gri counterpart searches for kNe at ∼200 Mpc would require reaching a limiting magnitude mlim = 23 mag, to ensure good sensitivity over a wide range of the model phase-space. We conclude that kN searches during O3 were generally too shallow to detect BNS optical counterparts, even under optimistic assumptions.

Description: Theoretical models are vital for exploring the galaxy merger process, which plays a crucial role in the evolution of galaxies. Recent advances in modelling have placed tight constraints on the buildup of stellar material in galaxies across cosmic time. Despite these successes, extracting the merger rates from observable data remains a challenge. Differences in modelling techniques, combined with limited observational data, drive conflicting conclusions on the merging timescales of close pairs. We employ an empirical model for galaxy formation that links galaxy properties to the growth of simulated dark matter haloes, along with mock lightcone galaxy catalogues, to probe the dependencies of pair merging probabilities and merging timescales. In this work, we demonstrate that the pair merging probabilities are best described by a logistic function and that mean merging timescales can be well approximated by a linear relation in the projected separation and line of sight velocity difference in observed pairs. Together, our fitting formulae can accurately predict merger rates from galaxy pairs to at least z ∼ 4 under a wide variety of pair selection criteria. Additionally, we show that some commonly used pair selection criteria may not represent a suitable sample of galaxies to reproduce underlying merger rates. Finally, we conclude from our analysis that observation timescales are primarily driven by dynamics and are not strongly impacted by the star formation properties of the component galaxies.

Description: At the end of its life, a very massive star is expected to collapse into a black hole. The recent detection of an 85 M⊙ black hole from the gravitational wave event GW 190521 appears to present a fundamental problem as to how such heavy black holes exist above the approximately 50 M⊙ pair-instability limit where stars are expected to be blown to pieces with no remnant left. Using MESA, we show that for stellar models with non-extreme assumptions, 90..100 M⊙ stars at reduced metallicity ($Z/{, m{Z}_{odot }}le 0.1$) can produce blue supergiant progenitors with core masses sufficiently small to remain below the fundamental pair-instability limit, yet at the same time lose an amount of mass via stellar winds that is small enough to end up in the range of an “impossible” 85 M⊙ black hole. The two key points are the proper consideration of core overshooting and stellar wind physics with an improved scaling of mass loss with iron (Fe) contents characteristic for the host galaxy metallicity. Our modelling provides a robust scenario that not only doubles the maximum black hole mass set by pair instability, but also allows us to probe the maximum stellar black hole mass as a function of metallicity and Cosmic time in a physically sound framework.

Description: We perform a joint BAO and RSD analysis using the eBOSS DR16 LRG and ELG samples in the redshift range of z ∈ [0.6, 1.1], and detect a RSD signal from the cross power spectrum at a ∼4σ confidence level, i.e., fσ8 = 0.317 ± 0.080 at zeff = 0.77. Based on the chained power spectrum, which is a new development in this work to mitigate the angular systematics, we measure the BAO distances and growth rate simultaneously at two effective redshifts, namely, DM/rd (z = 0.70) = 17.96 ± 0.51, DH/rd (z = 0.70) = 21.22 ± 1.20, fσ8 (z = 0.70) = 0.43 ± 0.05, and DM/rd (z = 0.845) = 18.90 ± 0.78, DH/rd (z = 0.845) = 20.91 ± 2.86, fσ8 (z = 0.845) = 0.30 ± 0.08. Combined with BAO measurements including those from the eBOSS DR16 QSO and Lyman-α sample, our measurement has raised the significance level of a nonzero ΩΛ to ∼11σ. The data product of this work is publicly available at https://github.com/icosmology/eBOSS_DR16_LRGxELG and https://www.sdss.org/science/final-bao-and-rsd-measurements/

Description: Tidal dissipation due to turbulent viscosity in the convective regions of giant stars plays an important role in shaping the orbits of pre-common envelope systems. Such systems are possible sources of transients and close compact binary systems that will eventually merge and produce detectable gravitational wave signals. Most previous studies of the onset of common envelope episodes have focused on circular orbits and synchronously rotating donor stars under the assumption that tidal dissipation can quickly spin-up the primary and circularize the orbit before the binary reaches Roche lobe overflow (RLO). We test this assumption by coupling numerical models of the post main sequence stellar evolution of massive-stars with the model for tidal dissipation in convective envelopes developed in Vick & Lai (2020) — a tidal model that is accurate even for highly eccentric orbits with small pericentre distances. We find that, in many cases, tidal dissipation does not circularize the orbit before RLO. For a 10 M⊙ (15 M⊙) primary star interacting with a 1.4 M⊙ companion, systems with pericentre distances within 3 AU (6 AU) when the primary leaves the main sequence will retain the initial orbital eccentricity when the primary grows to the Roche radius. Even in systems that tidally circularize before RLO, the donor star may be rotating subsynchronously at the onset of mass transfer. Our results demonstrate that some possible precursors to double neutron star systems are likely eccentric at the Roche radius. The effects of pre-common envelope eccentricity on the resulting compact binary merit further study.

Description: The maximum temperature and radial temperature profile in a protoplanetary disc are important for the condensation of different elements in the disc. We simulate the evolution of a set of protoplanetary discs from the collapse of their progenitor molecular cloud cores as well as the dust decoupling within the discs as they evolve. We show how the initial properties of the cloud cores affect the thermal history of the protoplanetary discs using a simple viscous disc model. Our results show that the maximum midplane temperature in the disc occurs within 0.5 AU. It increases with the initial cloud temperature and decreases with its angular velocity and the viscosity of the disc. From the observed properties of the molecular cloud cores we find the median value of the maximum temperature is around 1250 K, with roughly 90 per cent of them being less than 1500 K – a value that is lower than the 50 per cent condensation temperatures of most refractory elements. Therefore, only cloud cores with high initial temperatures or low angular velocities and/or low viscosities within the planet-forming discs will result in refractory-rich planetesimals. To reproduce the volatile depletion pattern of CM, CO, and CV chondrites and the terrestrial planets in Solar system, one must either have rare properties of the initial molecular cloud cores like high core temperature, or other sources of energy to heat the disc to sufficiently high temperatures. Alternatively, the volatile depletion observed in these chondrites may be inherited from the progenitor molecular cloud.

Description: We present the radio and X-ray monitoring campaign of the 2019/2020 outburst of MAXI J1348–630, a new black hole X-ray binary (XRB) discovered in 2019 January. We observed MAXI J1348–630 for ∼14 months in the radio band with MeerKAT and the Australia Telescope Compact Array (ATCA), and in the X-rays with MAXI and Swift/XRT. Throughout the outburst we detected and tracked the evolution of the compact and transient jets. Following the main outburst, the system underwent at least 4 hard-state-only re-flares, during which compact jets were again detected. For the major outburst, we observed the rise, quenching, and re-activation of the compact jets, as well as two single-sided discrete ejecta, launched ∼2 months apart and travelling away from the black hole. These ejecta displayed the highest proper motion (≳100 mas day−1) ever measured for an accreting black hole binary. From the jet motion, we constrain the ejecta inclination and speed to be ≤46○ and ≥0.69 c, and the opening angle and transverse expansion speed of the first component to be ≤6○ and ≤0.05 c. We also infer that the first ejection happened at the hard-to-soft state transition, before a strong radio flare, while the second ejection was launched during a short excursion from the soft to the intermediate state. After traveling with constant speed, the first component underwent a strong deceleration, which was covered with unprecedented detail and suggested that MAXI J1348–630 could be located inside a low-density cavity in the interstellar medium, as already proposed for XTE J1550–564 and H1743–322.

Description: We estimate the solar peculiar velocities and Oort constants using a sample of 5,627 A-type stars with $d

Description: In addition to the well-known gas phase mass-metallicity relation (MZR), recent spatially-resolved observations have shown that local galaxies also obey a mass–metallicity gradient relation (MZGR) whereby metallicity gradients can vary systematically with galaxy mass. In this work, we use our recently-developed analytic model for metallicity distributions in galactic discs, which includes a wide range of physical processes – radial advection, metal diffusion, cosmological accretion, and metal-enriched outflows – to simultaneously analyse the MZR and MZGR. We show that the same physical principles govern the shape of both: centrally-peaked metal production favours steeper gradients, and this steepening is diluted by the addition of metal-poor gas, which is supplied by inward advection for low-mass galaxies and by cosmological accretion for massive galaxies. The MZR and the MZGR both bend at galaxy stellar mass $sim 10^{10} - 10^{10.5}, m {M_{odot }}$, and we show that this feature corresponds to the transition of galaxies from the advection-dominated to the accretion-dominated regime. We also find that both the MZR and MZGR strongly suggest that low-mass galaxies preferentially lose metals entrained in their galactic winds. While this metal-enrichment of the galactic outflows is crucial for reproducing both the MZR and the MZGR at the low-mass end, we show that the flattening of gradients in massive galaxies is expected regardless of the nature of their winds.

Description: The success of H i intensity mapping is largely dependent on how well 21cm foreground contamination can be controlled. In order to progress our understanding further, we present a range of simulated foreground data from two different ∼3000 deg2 sky regions, with varying effects from polarisation leakage. Combining these with cosmological H i simulations creates a range of intensity mapping test cases that require different foreground treatments. This allows us to conduct the most generalised study to date into 21cm foregrounds and their cleaning techniques for the post-reionisation era. We first provide a pedagogical review of the most commonly used blind foreground removal techniques (PCA/SVD, FASTICA, GMCA). We also trial a non-blind parametric fitting technique and discuss potential hybridization of methods. We highlight the similarities and differences in these techniques finding that the blind methods produce near equivalent results, and we explain the fundamental reasons for this. Our results demonstrate that polarised foreground residuals should be generally subdominant to H i on small scales (k ≳ 0.1 h Mpc−1). However, on larger scales, results are more case-dependent. In some cases, aggressive cleans severely damp H i power but still leave dominant foreground residuals. We find a changing polarisation fraction has little impact on results within a realistic range (0.5% - 2%), however a higher level of Faraday rotation does require more aggressive cleaning. We also demonstrate the gain from cross-correlations with optical galaxy surveys, where extreme levels of residual foregrounds can be circumvented. However, these residuals still contribute to errors and we discuss the optimal balance between over- and under-cleaning.

Description: We present high signal-to-noise, full polarization pulse profiles for 40 bright, ‘slowly’-rotating (non-recycled) pulsars using the new Ultra-Wideband Low-frequency (UWL; 704–4032 MHz) receiver on the Parkes radio telescope. We obtain updated and accurate interstellar medium parameters towards these pulsars (dispersion measures and Faraday rotation measures), and reveal Faraday dispersion towards PSR J1721–3532 caused by interstellar scattering. We find general trends in the pulse profiles including decreasing fractional linear polarization and increasing degree of circular polarization with increasing frequency, consistent with previous studies, while also revealing new features and frequency evolution. This demonstrates results that can be obtained using UWL monitoring observations of slow pulsars, which are valuable for improving our understanding of pulsar emission and the intervening interstellar medium. The calibrated data products are publicly available.

Description: Dark matter as a Bose-Einstein condensate, such as the axionic scalar field particles of String Theory, can explain the coldness of dark matter on large scales. Pioneering simulations in this context predict a rich wave-like structure, with a ground state soliton core in every galaxy surrounded by a halo of excited states that interfere on the de Broglie scale. This de Broglie scale is largest for low mass galaxies as momentum is lower, providing a simple explanation for the wide cores of dwarf spheroidal galaxies. Here we extend these “wave dark matter” (ψDM) predictions to the newly discovered class of “Ultra Diffuse Galaxies” (UDG) that resemble dwarf spheroidal galaxies but with more extended stellar profiles. Currently the best studied example, DF44, has a uniform velocity dispersion of ≃ 33km/s, extending to at least 3 kpc, that we show is reproduced by our ψDM simulations with a soliton radius of ≃ 0.5 kpc. In the ψDM context, we show the relatively flat dispersion profile of DF44 lies between massive galaxies with compact dense solitons, as may be present in the Milky Way on a scale of 100pc and lower mass galaxies where the velocity dispersion declines centrally within a wide, low density soliton, like Antlia II, of radius 3 kpc.

Description: The vast majority of stars in galaxy groups are contained within their constituent galaxies. Some small fraction of stars is expected, however, to follow the global dark matter potential of the group. In compact groups, interactions between the galaxies should be frequent. This leads to a more intensive material stripping from the group members, which finally forms an intra-group light component (IGL). Therefore, the distribution of the IGL should be related to the distribution of the total mass in the compact group and its dynamical status. In this study we consider the distribution and fraction of the IGL in a sample of 36 Hickson compact groups (HCGs). We use deep observations of these compact groups (down to surface brightness ∼28 mag arcsec−2 in the r band) obtained with the WISE 28-inch telescope. For five HCGs with a bright symmetric IGL component, we carry out multicomponent photometric decomposition to simultaneously fit the galaxy profiles and the IGL. For the remaining groups, we only fit the profiles of their constituent galaxies. We find that the mean surface brightness of the IGL correlates with the mean morphology of the group: it becomes brighter in the groups with a larger fraction of early-type galaxies. On the other hand, the IGL brightness depends on the total luminosity of the group. The IGL profile tends to have a Sérsic index n ∼ 0.5 − 1, which is generally consistent with the mass density profile of dark matter haloes in compact groups obtained from cosmological simulations.

Description: White dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. In this paper, we present a Bayesian model to explain the abundances observed in the atmospheres of 202 DZ white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. The majority (〉60%) of systems are consistent with the accretion of primitive material. We attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. A range in Na abundances in the pollutant material is attributed to a range in formation temperatures from below 1,000 K to higher than 1,400 K, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. We also find that Solar System-like differentiation is common place in exo-planetary systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. In systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. The 13 systems are estimated to have accreted masses ranging from the mass of the Moon to half that of Vesta. Our analysis suggests that accretion continues for 11Myrs on average.

Description: In dense star clusters, such as globular and open clusters, dynamical interactions between stars and black holes (BHs) can be extremely frequent, leading to various astrophysical transients. Close encounters between a star and a stellar mass BH make it possible for the star to be tidally disrupted by the BH. Due to the relative low mass of the BH and the small cross-section of the tidal disruption event (TDE) for cases with high penetration, disruptions caused by close encounters are usually partial disruptions. The existence of the remnant stellar core and its non-negligible mass compared to the stellar mass BH alters the accretion process significantly. We study this problem with SPH simulations using the code Phantom, with the inclusion of radiation pressure, which is important for small mass BHs. Additionally, we develop a new, more general method of computing the fallback rate which does not rely on any approximation. Our study shows that the powerlaw slope of the fallback rate has a strong dependence on the mass of the BH in the stellar mass BH regime. Furthermore, in this regime, self-gravity of the fallback stream and local instabilities become more significant, and cause the disrupted material to collapse into small clumps before returning to the BH. This results in an abrupt increase of the fallback rate, which can significantly deviate from a powerlaw. Our results will help in the identification of TDEs by stellar mass BHs in dense clusters.

Description: Accurate metallicities of RR Lyrae are extremely important in constraining period-luminosity-metallicity relationships (PLZ), particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope (SALT). We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.15 dex. All but one RR Lyrae in this sample has accurate ($sigma _{varpi }lesssim 10\%$) parallax from Gaia. Combining these new high resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ relationships in WISE W1 and W2 magnitudes, and the Wesenheit magnitudes W(W1,V-W1) and W(W2,V-W2).

Description: We perform a cross validation of the cluster catalog selected by the red-sequence Matched-filter Probabilistic Percolation algorithm (redMaPPer) in Dark Energy Survey year 1 (DES-Y1) data by matching it with the Sunyaev-Zel’dovich effect (SZE) selected cluster catalog from the South Pole Telescope SPT-SZ survey. Of the 1005 redMaPPer selected clusters with measured richness $hat{lambda }〉40$ in the joint footprint, 207 are confirmed by SPT-SZ. Using the mass information from the SZE signal, we calibrate the richness–mass relation using a Bayesian cluster population model. We find a mass trend λ∝MB consistent with a linear relation (B ∼ 1), no significant redshift evolution and an intrinsic scatter in richness of σλ = 0.22 ± 0.06. By considering two error models, we explore the impact of projection effects on the richness–mass modelling, confirming that such effects are not detectable at the current level of systematic uncertainties. At low richness SPT-SZ confirms fewer redMaPPer clusters than expected. We interpret this richness dependent deficit in confirmed systems as due to the increased presence at low richness of low mass objects not correctly accounted for by our richness-mass scatter model, which we call contaminants. At a richness $hat{lambda }=40$, this population makes up $〉12\%$ (97.5 percentile) of the total population. Extrapolating this to a measured richness $hat{lambda }=20$ yields $〉22\%$ (97.5 percentile). With these contamination fractions, the predicted redMaPPer number counts in different plausible cosmologies are compatible with the measured abundance. The presence of such a population is also a plausible explanation for the different mass trends (B ∼ 0.75) obtained from mass calibration using purely optically selected clusters. The mean mass from stacked weak lensing (WL) measurements suggests that these low mass contaminants are galaxy groups with masses ∼3- 5 × 1013 M⊙ which are beyond the sensitivity of current SZE and X-ray surveys but a natural target for SPT-3G and eROSITA.

Description: In this paper, we investigate whether overdensity formation via streaming instability is consistent with recent multi-wavelength ALMA observations in the Lupus star forming region. We simulate the local action of streaming instability in 2D using the code Athena, and examine the radiative properties at mm wavelengths of the resulting clumpy dust distribution by focusing on two observable quantities: the optically thick fraction ff (in ALMA band 6) and the spectral index α (in bands 3-7). By comparing the simulated distribution in the ff − α plane before and after the action of streaming instability, we observe that clump formation causes ff to drop, because of the suppression of emission from grains that end up in optically thick clumps. α, instead, can either increase or decline after the action of streaming instability; we use a simple toy model to demonstrate that this behaviour depends on the sizes of the grains whose emission is suppressed by being incorporated in optically thick clumps. In particular, the sign of evolution of α depends on whether grains near the opacity maximum at a few tenths of a mm end up in clumps. By comparing the simulation distributions before/after clump formation to the data distribution, we note that the action of streaming instability drives simulations towards the area of the plane where the data are located. We furthermore demonstrate that this behaviour is replicated in integrated disc models provided that the instability is operative over a region of the disc that contributes significantly to the total mm flux.

Description: V555 Ori is a T Tauri star, whose 1.5 mag brightening was published as a Gaia science alert in 2017. We carried out optical and near-infrared photometric, and optical spectroscopic observations to understand the light variations. The light curves show that V555 Ori was faint before 2017, entered a high state for about a year, and returned to the faint state by mid-2018. In addition to the long-term flux evolution, quasi-periodic brightness oscillations were also evident, with a period of about 5 days. At optical wavelengths both the long-term and short-term variations exhibited colourless changes, while in the near-infrared they were consistent with changing extinction. We explain the brightness variations as the consequence of changing extinction. The object has a low accretion rate whose variation in itself would not be enough to reproduce the optical flux changes. This behaviour makes V555 Ori similar to the pre-main sequence star AA Tau, where the light changes are interpreted as periodic eclipses of the star by a rotating inner disc warp. The brightness maximum of V555 Ori was a moderately obscured (AV=2.3 mag) state, while the extinction in the low state was AV=6.4 mag. We found that while the Gaia alert hinted at an accretion burst, V555 Ori is a standard dipper, similar to the prototype AA Tau. However, unlike in AA Tau, the periodic behaviour was also detectable in the faint phase, implying that the inner disc warp remained stable in both the high and low states of the system.

Description: Most of the dark matter (DM) search over the last few decades has focused on WIMPs, but the viable parameter space is quickly shrinking. Asymmetric Dark Matter (ADM) is a WIMP-like DM candidate with slightly smaller masses and no present day annihilation, meaning that stars can capture and build up large quantities. The captured ADM can transport energy through a significant volume of the star. We investigate the effects of spin-dependent ADM energy transport on stellar structure and evolution in stars with 0.9 ≤ M⋆/M⊙ ≤ 5.0 in varying DM environments. We wrote a MESA module* that calculates the capture of DM and the subsequent energy transport within the star. We fix the DM mass to 5 GeV and the cross-section to 10−37 cm2, and study varying environments by scaling the DM capture rate. For stars with radiative cores (0.9 ≤ M⋆/M⊙ ≲ 1.3 ), the presence of ADM flattens the temperature and burning profiles in the core and increases MS (Xc 〉 10−3) lifetimes by up to $sim 20{{ m per cent}}$. We find that strict requirements on energy conservation are crucial to the simulation of ADM’s effects on these stars. In higher-mass stars, ADM energy transport shuts off core convection, limiting available fuel and shortening MS lifetimes by up to $sim 40{{ m per cent}}$. This may translate to changes in the luminosity and effective temperature of the MS turnoff in population isochrones. The tip of the red giant branch may occur at lower luminosities. The effects are largest in DM environments with high densities and/or low velocity dispersions, making dwarf and early forming galaxies most likely to display the effects.

Description: We consider the dynamical tidal response of a neutron star in an inspiralling binary, focussing on the impact of the star’s elastic crust. Within the context of Newtonian gravity, we add the elastic aspects to the theoretical formulation of the problem and quantify the dynamical excitation of different classes of oscillation modes. The results demonstrate the expectation that the fundamental mode dominates the tidal response and show how the usual tidal deformability (and the Love number) emerge in the static limit. In addition, we consider to what extent the different modes may be excited to a level where the breaking strain of the crust would be exceeded (locally). The results show that the fundamental mode may fracture the crust during the late stages of inspiral. This is also the case for the first gravity mode, which reaches the breaking threshold in strongly stratified stars. In our models with a fluid ocean, interface modes associated with the crust-ocean transition may also induce crust fracture. If this happens it does so earlier in the inspiral, at a lower orbital frequency.

Description: Recent observations have shown that circumbinary discs can be misaligned with respect to the binary orbital plane.The lack of spherical symmetry, together with the non-planar geometry of these systems, causes differential precession which might induce the propagation of warps. While gas dynamics in such environments is well understood, little is known about dusty discs. In this work, we analytically study the problem of dust traps formation in misaligned circumbinary discs. We find that pile-ups may be induced not by pressure maxima, as the usual dust traps, but by a difference in precession rates between the gas and dust. Indeed, this difference makes the radial drift inefficient in two locations, leading to the formation of two dust rings whose position depends on the system parameters. This phenomenon is likely to occur to marginally coupled dust particles (St ≳ 1) as both the effect of gravitational and drag force are considerable. We then perform a suite of three-dimensional SPH numerical simulations to compare the results with our theoretical predictions. We explore the parameter space, varying stellar mass ratio, disc thickness, radial extension, and we find a general agreement with the analytical expectations. Such dust pile-up prevents radial drift, fosters dust growth and may thus promote the planet formation in circumbinary discs.

Description: We study the structural evolution of isolated star-forming galaxies in the Illustris TNG100-1 hydrodynamical simulation, with a focus on investigating the growth of the central core density within 2 kpc (Σ*, 2kpc) in relation to total stellar mass (M*) at z 〈 0.5. First, we show that several observational trends in the Σ*, 2kpc − M* plane are qualitatively reproduced in IllustrisTNG, including the distributions of AGN, star forming galaxies, quiescent galaxies, and radial profiles of stellar age, sSFR, and metallicity. We find that galaxies with dense cores evolve parallel to the Σ*, 2kpc − M* relation, while galaxies with diffuse cores evolve along shallower trajectories. We investigate possible drivers of rapid growth in Σ*, 2kpc compared to M*. Both the current sSFR gradient and the BH accretion rate are indicators of past core growth, but are not predictors of future core growth. Major mergers (although rare in our sample; ∼10 per cent) cause steeper core growth, except for high mass (M* ≳ 1010 M⊙) mergers, which are mostly dry. Disc instabilities, as measured by the fraction of mass with Toomre Q 〈 2, are not predictive of rapid core growth. Instead, rapid core growth results in more stable discs. The cumulative black hole feedback history sets the maximum rate of core growth, preventing rapid growth in high-mass galaxies (≳ 109.5 M⊙). For massive galaxies the total specific angular momentum of accreting gas is the most important predictor of future core growth. Our results suggest that the angular momentum of accreting gas controls the slope, width and zero-point evolution of the Σ*, 2kpc − M* relation.

Description: Observations have indicated that the prestellar core mass function (CMF) is similar to the stellar initial mass function (IMF), except for an offset towards larger masses. This has led to the idea that there is a one-to-one relation between cores and stars, such that the whole stellar mass reservoir is contained in a gravitationally-bound prestellar core, as postulated by the core-collapse model, and assumed in recent theoretical models of the stellar IMF. We test the validity of this assumption by comparing the final mass of stars with the mass of their progenitor cores in a high-resolution star-formation simulation that generates a realistic IMF under physical conditions characteristic of observed molecular clouds. Using a definition of bound cores similar to previous works we obtain a CMF that converges with increasing numerical resolution. We find that the CMF and the IMF are closely related in a statistical sense only; for any individual star there is only a weak correlation between the progenitor core mass and the final stellar mass. In particular, for high mass stars only a small fraction of the final stellar mass comes from the progenitor core, and even for low mass stars the fraction is highly variable, with a median fraction of only about 50%. We conclude that the core-collapse scenario and related models for the origin of the IMF are incomplete. We also show that competitive accretion is not a viable alternative.

Description: We present Hubble Space Telescope imaging of a pre-explosion counterpart to SN 2019yvr obtained 2.6 years before its explosion as a type Ib supernova (SN Ib). Aligning to a post-explosion Gemini-S/GSAOI image, we demonstrate that there is a single source consistent with being the SN 2019yvr progenitor system, the second SN Ib progenitor candidate after iPTF13bvn. We also analyzed pre-explosion Spitzer/IRAC imaging, but we do not detect any counterparts at the SN location. SN 2019yvr was highly reddened, and comparing its spectra and photometry to those of other, less extinguished SNe Ib we derive $E(B-V)=0.51substack{+0.27-0.16}$ mag for SN 2019yvr. Correcting photometry of the pre-explosion source for dust reddening, we determine that this source is consistent with a log (L/L⊙) = 5.3 ± 0.2 and $T_{mathrm{eff}} = 6800substack{+400-200}$ K star. This relatively cool photospheric temperature implies a radius of 320$substack{+30-50}~R_{odot }$, much larger than expectations for SN Ib progenitor stars with trace amounts of hydrogen but in agreement with previously identified SN IIb progenitor systems. The photometry of the system is also consistent with binary star models that undergo common envelope evolution, leading to a primary star hydrogen envelope mass that is mostly depleted but still seemingly in conflict with the SN Ib classification of SN 2019yvr. SN 2019yvr had signatures of strong circumstellar interaction in late-time (〉150 day) spectra and imaging, and so we consider eruptive mass loss and common envelope evolution scenarios that explain the SN Ib spectroscopic class, pre-explosion counterpart, and dense circumstellar material. We also hypothesize that the apparent inflation could be caused by a quasi-photosphere formed in an extended, low-density envelope or circumstellar matter around the primary star.

Description: We present the results of a large multi-wavelength follow-up campaign of the Tidal Disruption Event (TDE) AT 2019dsg, focusing on low to high resolution optical spectroscopy, X-ray, and radio observations. The galaxy hosts a super massive black hole of mass $ m (5.4pm 3.2)imes 10^6, M_odot$ and careful analysis finds no evidence for the presence of an Active Galactic Nucleus, instead the TDE host galaxy shows narrow optical emission lines that likely arise from star formation activity. The transient is luminous in the X-rays, radio, UV and optical. The X-ray emission becomes undetected after ∼100 days, and the radio luminosity density starts to decay at frequencies above 5.4 GHz by ∼160 days. Optical emission line signatures of the TDE are present up to ∼200 days after the light curve peak. The medium to high resolution spectra show traces of absorption lines that we propose originate in the self-gravitating debris streams. At late times, after ∼200 days, narrow Fe lines appear in the spectra. The TDE was previously classified as N-strong, but after careful subtraction of the host galaxy’s stellar contribution, we find no evidence for these N lines in the TDE spectrum, even though O Bowen lines are detected. The observed properties of the X-ray emission are fully consistent with the detection of the inner regions of a cooling accretion disc. The optical and radio properties are consistent with this central engine seen at a low inclination (i.e., seen from the poles).

Description: Accreting supermassive black holes (SMBHs), also known as active galactic nuclei (AGN), are generally surrounded by large amounts of gas and dust. This surrounding material reprocesses the primary X-ray emission produced close to the SMBH and gives rise to several components in the broadband X-ray spectra of AGN, including a power-law possibly associated with Thomson-scattered radiation. In this work, we study the properties of this scattered component for a sample of 386 hard-X-ray-selected, nearby (z ∼ 0.03) obscured AGN from the 70-month Swift/BAT catalog. We investigate how the fraction of Thomson-scattered radiation correlates with different physical properties of AGN, such as line-of-sight column density, X-ray luminosity, black hole mass, and Eddington ratio. We find a significant negative correlation between the scattering fraction and the column density. Based on a large number of spectral simulations, we exclude the possibility that this anti-correlation is due to degeneracies between the parameters. The negative correlation also persists when considering different ranges of luminosity, black hole mass, and Eddington ratio. We discuss how this correlation might be either due to the angle dependence of the Thomson cross-section or to more obscured sources having a higher covering factor of the torus. We also find a positive correlation between the scattering fraction and the ratio of [O iii] λ5007 to X-ray luminosity. This result is consistent with previous studies and suggests that the Thomson-scattered component is associated with the narrow-line region.

Description: Jets launched by active galactic nuclei (AGN) are believed to play a significant role in shaping the properties of galaxies and provide an energetically viable mechanism through which galaxies can become quenched. Here we present a novel AGN feedback model, which we have incorporated into the arepo code, that evolves the black hole mass and spin as the accretion flow proceeds through a thin α-disc which we self-consistently couple to a Blandford-Znajek jet. We apply our model to the central region of a typical radio-loud Seyfert galaxy embedded in a hot circumgalactic medium (CGM). We find that jets launched into high pressure environments thermalise efficiently due to the formation of recollimation shocks and the vigorous instabilities that these shocks excite increase the efficiency of the mixing of CGM and jet material. The beams of more overpressured jets, however, are not as readily disrupted by instabilities so the majority of the momentum flux at the jet base is retained out to the head, where the jet terminates in a reverse shock. All jets entrain a significant amount of cold circumnuclear disc material which, while energetically insignificant, dominates the lobe mass together with the hot, entrained CGM material. The jet power evolves significantly due to effective self-regulation by the black hole, fed by secularly-driven, intermittent mass flows. The direction of jets launched directly into the circumnuclear disc changes considerably due to effective Bardeen-Petterson torquing. Interestingly, these jets obliterate the innermost regions of the disc and drive large-scale, multi-phase, turbulent, bipolar outflows.

Description: Large samples of galaxy clusters provide knowledge of both astrophysics in the most massive virialised environments and the properties of the cosmological model that defines our Universe. However, an important issue that affects the interpretation of galaxy cluster samples is the role played by the selection waveband and the potential for this to introduce a bias in the physical properties of clusters thus selected. We aim to investigate waveband-dependent selection effects in the identification of galaxy clusters by comparing the X-ray Multi-Mirror (XMM) Ultimate Extra-galactic Survey (XXL) and Subaru Hyper Suprime-Cam (HSC) CAMIRA cluster samples identified from a common 22.6 deg2 sky area. We compare 150 XXL and 270 CAMIRA clusters in a common parameter space defined by X-ray aperture brightness and optical richness. We find that 71/150 XXL clusters are matched to the location of a CAMIRA cluster, the majority of which (67/71) display richness values N 〉 15 that exceed the CAMIRA catalogue richness threshold. We find that 67/270 CAMIRA clusters are matched to the location of an XXL cluster (defined within XXL as an extended X-ray source). Of the unmatched CAMIRA clusters, the majority display low X-ray fluxes consistent with the lack of an XXL counterpart. However, a significant fraction (64/107) CAMIRA clusters that display high X-ray fluxes are not asociated with an extended source in the XXL catalogue. We demonstrate that this disparity arises from a variety of effects including the morphological criteria employed to identify X-ray clusters and the properties of the XMM PSF.

Description: Across a large range of scales, accreting sources show remarkably similar patterns of variability, most notably the log-normality of the luminosity distribution and the linear root-mean square (rms)-flux relationship. These results are often explained using the theory of propagating fluctuations in which fluctuations in the viscosity create perturbations in the accretion rate at all radii, propagate inwards and combine multiplicatively. While this idea has been extensively studied analytically in a linear regime, there has been relatively little numerical work investigating the non-linear behaviour. In this paper, we present a suite of stochastically driven 1-d α-disc simulations, exploring the behaviour of these discs. We find that the eponymous propagating fluctuations are present in all simulations across a wide range of model parameters, in contradiction to previous work. Of the model parameters, we find by far the most important to be the timescale on which the viscosity fluctuations occur. Physically, this timescale will depend on the underlying physical mechanism, thought to be the magnetorotational instability (MRI). We find a close relationship between this fluctuation timescale and the break frequency in the power spectral density (PSD) of the luminosity, a fact which could allow observational probes of the behaviour of the MRI dynamo. We report a fitting formula for the break frequency as a function of the fluctuation timescale, the disc thickness and the mass of the central object.

Description: Feedback from massive stars plays a key role in molecular cloud evolution. After the onset of star formation, the young stellar population is exposed by photoionization, winds, supernovae, and radiation pressure from massive stars. Recent observations of nearby galaxies have provided the evolutionary timeline between molecular clouds and exposed young stars, but the duration of the embedded phase of massive star formation is still ill-constrained. We measure how long massive stellar populations remain embedded within their natal cloud, by applying a statistical method to six nearby galaxies at $20{-}100 {{ m ~pc}}$ resolution, using CO, Spitzer 24$ m , mu m$, and Hα emission as tracers of molecular clouds, embedded star formation, and exposed star formation, respectively. We find that the embedded phase (with CO and 24$ m , mu m$ emission) lasts for 2 − 7 Myr and constitutes $17{-}47\%$ of the cloud lifetime. During approximately the first half of this phase, the region is invisible in Hα, making it heavily obscured. For the second half of this phase, the region also emits in Hα and is partially exposed. Once the cloud has been dispersed by feedback, 24$ m , mu m$ emission no longer traces ongoing star formation, but remains detectable for another 2 − 9 Myr through the emission from ambient CO-dark gas, tracing star formation that recently ended. The short duration of massive star formation suggests that pre-supernova feedback (photoionization and winds) is important in disrupting molecular clouds. The measured timescales do not show significant correlations with environmental properties (e.g. metallicity). Future JWST observations will enable these measurements routinely across the nearby galaxy population.

Description: We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

Description: The Jovian Trojans are two swarms of small objects that share Jupiter’s orbit, clustered around the leading and trailing Lagrange points, L4 and L5. In this work, we investigate the Jovian Trojan population using the technique of astrocladistics, an adaptation of the ‘tree of life’ approach used in biology. We combine colour data from WISE, SDSS, Gaia DR2 and MOVIS surveys with knowledge of the physical and orbital characteristics of the Trojans, to generate a classification tree composed of clans with distinctive characteristics. We identify 48 clans, indicating groups of objects that possibly share a common origin. Amongst these are several that contain members of the known collisional families, though our work identifies subtleties in that classification that bear future investigation. Our clans are often broken into subclans, and most can be grouped into 10 superclans, reflecting the hierarchical nature of the population. Outcomes from this project include the identification of several high priority objects for additional observations and as well as providing context for the objects to be visited by the forthcoming Lucy mission. Our results demonstrate the ability of astrocladistics to classify multiple large and heterogeneous composite survey datasets into groupings useful for studies of the origins and evolution of our Solar system.

Description: In the context of tomographic cosmic shear surveys, a theoretical model for the one-point statistics of the aperture mass (Map) is developed. This formalism is based on the application of the large deviation principle to the projected matter density field and more specifically to the angular aperture masses. The latter holds the advantage of being an observable that can be directly extracted from the observed shear field and to be, by construction, independent from the long wave modes. Furthermore we show that, with the help of a nulling procedure based on the so-called BNT transform, it is possible to build observables that depend only on a finite range of redshifts making them also independent from the small-scale modes. This procedure makes predictions for the shape of the one-point Probability Distribution Function of such an observable very accurate, comparable to what had been previously obtained for 3D observables. Comparisons with specific simulations reveal however inconsistent results showing that synthetic lensing maps were not accurate enough for such refined observables. It points to the need for more precise dedicated numerical developments whose performances could be benchmarked with such observables. We furthermore review the possible systematics that could affect such a formalism in future weak-lensing surveys like Euclid, notably the impact of shape noise as well as leading corrections coming from lens-lens couplings, geodesic deviation, reduced shear and magnification bias.

Description: We present simulations of the multi-phase interstellar medium (ISM) at solar neighbourhood conditions including thermal and non-thermal ISM processes, star cluster formation, and feedback from massive stars: stellar winds, hydrogen ionising radiation computed with the novel TreeRay radiative transfer method, supernovae (SN), and the injection of cosmic rays (CR). N-body dynamics is computed with a 4th-order Hermite integrator. We systematically investigate the impact of stellar feedback on the self-gravitating ISM with magnetic fields, CR advection and diffusion and non-equilibrium chemical evolution. SN-only feedback results in strongly clustered star formation with very high star cluster masses, a bi-modal distribution of the ambient SN densities, and low volume-filling factors (VFF) of warm gas, typically inconsistent with local conditions. Early radiative feedback prevents an initial starburst, reduces star cluster masses and outflow rates. Furthermore, star formation rate surface densities of $Sigma _{dot{M}_star } = 1.4-5.9 imes 10^{-3}$ M⊙ yr−1 kpc−2, VFFwarm = 60 − 80 per cent as well as thermal, kinetic, magnetic, and cosmic ray energy densities of the model including all feedback mechanisms agree well with observational constraints. On the short, 100 Myr, timescales investigated here, CRs only have a moderate impact on star formation and the multi-phase gas structure and result in cooler outflows, if present. Our models indicate that at low gas surface densities SN-only feedback only captures some characteristics of the star-forming ISM and outflows/inflows relevant for regulating star formation. Instead, star formation is regulated on star cluster scales by radiation and winds from massive stars in clusters, whose peak masses agree with solar neighbourhood estimates.

Description: The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard ΛCDM initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations are a consequence of the missing large scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

Description: Super-Earths and sub-Neptunes are commonly thought to have accreted hydrogen/helium envelopes, consisting of a few to ten percent of their total mass, from the primordial gas disk. Subsequently, hydrodynamic escape driven by core-powered mass-loss and/or photo-evaporation likely stripped much of these primordial envelopes from the lower-mass and closer-in planets to form the super-Earth population. In this work we show that after undergoing core-powered mass-loss, some super-Earths can retain small residual H/He envelopes. This retention is possible because, for significantly depleted atmospheres, the density at the radiative-convective boundary drops sufficiently such that the cooling time-scale becomes shorter than the mass-loss time-scale. The residual envelope is therefore able to contract, terminating further mass loss. Using analytic calculations and numerical simulations, we show that the mass of primordial H/He envelope retained as a fraction of the planet's total mass, fret, increases with increasing planet mass, Mc, and decreases with increasing equilibrium temperature, Teq, scaling as $f_mathrm{ret} propto M_mathrm{c}^{3/2} T_mathrm{eq}^{-1/2} exp {[M_mathrm{c}^{3/4} T_mathrm{eq}^{-1}]}$. fret varies from

Description: We present sub-arcsecond resolution ALMA imaging of the CO(3-2) emission in two z ∼ 2.5 heavily reddened quasars (HRQs) - ULASJ1234+0907 and ULASJ2315+0143 - and their companion galaxies. Dynamical modeling of the resolved velocity fields enables us to constrain the molecular gas morphologies and host galaxy masses. Combining the new data with extensive multi-wavelength observations, we are able to study the relative kinematics of different molecular emission lines, the molecular gas fractions and the locations of the quasars on the MBH-Mgal relation. Despite having similar black hole properties, the two HRQs display markedly different host galaxy properties and local environments. J1234 has a very massive host - Mdyn ∼ 5 × 1011M⊙ and two companion galaxies that are similarly massive located within 200 kpc of the quasar. The molecular gas fraction is low (∼6 per cent). The significant ongoing star formation in the host galaxy is entirely obscured at rest-frame UV and optical wavelengths. J2315 is resolved into a close-separation major-merger (Δr=15 kpc; Δv=170 km/s) with a ∼1:2 mass ratio. The total dynamical mass is estimated to be ≲ 1011M⊙ and the molecular gas fraction is high (〉45 per cent). A new HSC image of the galaxy shows unobscured UV-luminous star-forming regions co-incident with the extended reservoir of cold molecular gas in the merger. We use the outputs from the Illustris simulations to track the growth of such massive black holes from z ∼ 6 to the present day. While J1234 is consistent with the simulated z ∼ 2 relation, J2315 has a black hole that is over-massive relative to its host galaxy.

Description: The evolution of the atmospheres of low and intermediate-mass planets is strongly connected to the physical properties of their host stars. The types and the past activities of planet-hosting stars can, therefore, affect the overall planetary population. In this paper, we perform a comparative study of sub-Neptune-like planets orbiting stars of different masses and different evolutionary histories. We discuss the general patterns of the evolved population as a function of parameters and environments of planets. As a model of the atmospheric evolution, we employ the own framework combining planetary evolution in MESA with the realistic prescription of the escape of hydrogen-dominated atmospheres. We find that the final populations look qualitatively similar in terms of the atmospheres survival around different stars, but qualitatively different, with this difference accentuated for planets orbiting more massive stars. We show that a planet has larger chances of keeping its primordial atmosphere in the habitable zone of a solar mass star compared to M or K dwarfs and if it starts the evolution having a relatively compact envelope. We also address the problem of the uncertain initial temperatures (luminosities) of planets and show that this issue is only of particular importance for planets exposed to extreme atmospheric mass-losses.

Description: τ Sco, a well-studied magnetic B-type star in the Uτer Sco association, has a number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface magnetic field is much more complex than a purely dipolar configuration which is unusual for a magnetic massive star. We employ the cmfgen radiative transfer code to determine the fundamental parameters and surface CNO and helium abundances. Then, we employ mesa and genec stellar evolution models accounting for the effects of surface magnetic fields. To reconcile τ Sco’s properties with single-star models, an increase is necessary in the efficiency of rotational mixing by a factor of 3 to 10 and in the efficiency of magnetic braking by a factor of 10. The spin down could be explained by assuming a magnetic field decay scenario. However, the simultaneous chemical enrichment challenges the single-star scenario. Previous works indeed suggested a stellar merger origin for τ Sco. However, the merger scenario also faces similar challenges as our magnetic single-star models to explain τ Sco’s simultaneous slow rotation and nitrogen excess. In conclusion, the single-star channel seems less likely and versatile to explain these discrepancies, while the merger scenario and other potential binary-evolution channels still require further assessment as to whether they may self-consistently explain the observables of τ Sco.

Description: We constrain the mass distribution in nearby, star-forming galaxies with the Star Formation Reference Survey (SFRS), a galaxy sample constructed to be representative of all known combinations of star formation rate (SFR), dust temperature, and specific star formation rate (sSFR) that exist in the Local Universe. An innovative two-dimensional bulge/disk decomposition of the 2MASS/Ks-band images of the SFRS galaxies yields global luminosity and stellar mass functions, along with separate mass functions for their bulges and disks. These accurate mass functions cover the full range from dwarf galaxies to large spirals, and are representative of star-forming galaxies selected based on their infra-red luminosity, unbiased by AGN content and environment. We measure an integrated luminosity density j = 1.72 ± 0.93 × 109 L⊙  h−1 Mpc−3 and a total stellar mass density ρM = 4.61 ± 2.40 × 108 M⊙  h−1 Mpc−3. While the stellar mass of the average star-forming galaxy is equally distributed between its sub-components, disks globally dominate the mass density budget by a ratio 4:1 with respect to bulges. In particular, our functions suggest that recent star formation happened primarily in massive systems, where they have yielded a disk stellar mass density larger than that of bulges by more than 1 dex. Our results constitute a reference benchmark for models addressing the assembly of stellar mass on the bulges and disks of local (z = 0) star-forming galaxies.

Description: Variability is a general property of accretion discs and their associated jets. We introduce a semi-analytic model for particle acceleration and radio jet/lobe evolution and explore the effect of Myr timescale jet variability on the particles accelerated by an AGN jet. Our work is motivated by the need for local powerful ultrahigh energy cosmic ray (UHECR) sources and evidence for variability in AGN and radio galaxies. Our main results are: i) UHECR and nonthermal radiative luminosities track the jet power but with a response set by the escape and cooling times, respectively; ii) jet variability produces structure in the electron, synchrotron and UHECR spectra that deviates from that produced for a constant jet power – in particular, spectral hardening features may be signatures of variability; iii) the cutoff in the integrated CR spectrum is stretched out due to the variation in jet power (and, consequently, maximum CR energy). The resulting spectrum is the convolution of the jet power distribution and the source term. We derive an approximate form for a log-normal distribution of powers; iv) we introduce the idea of ∼10 GeV ‘proxy electrons’ that are cooling at the same rate that UHECRs of rigidity 10 EV are escaping from the source, and determine the corresponding photon frequencies that probe escaping UHECRs. Our results demonstrate the link between the history of an astrophysical particle accelerator and its particle contents, nonthermal emission and UHECR spectrum, with consequences for observations of radio galaxies and UHECR source models.

Description: Most models of the low frequency quasi periodic oscillations (QPOs) in low-mass X-ray binaries (LMXBs) explain the dynamical properties of those QPOs. On the other hand, in recent years reverberation models that assume a lamp-post geometry have been successfull in explaining the energy-dependent time lags of the broad-band noise component in stellar mass black-holes and active galactic nuclei. We have recently shown that Comptonisation can explain the spectral-timing properties of the kilo-hertz (kHz) QPOs observed in neutron star (NS) LMXBs. It is therefore worth exploring whether the same family of models would be as successful in explaining the low-frequency QPOs. In this work, we use a Comptonisation model to study the frequency dependence of the phase lags of the type-C QPO in the BH LMXB GRS 1915+105. The phase lags of the QPO in GRS 1915+105 make a transition from hard to soft at a QPO frequency of around 1.8 Hz. Our model shows that at high QPO frequencies a large corona of ∼ 100−150 Rg covers most of the accretion disc and makes it $100{{ m per cent}}$ feedback dominated, thus producing soft lags. As the observed QPO frequency decreases, the corona gradually shrinks down to around 3−17Rg, and at 1.8 Hz feedback on to the disc becomes inefficient leading to hard lags. We discuss how changes in the accretion geometry affect the timing properties of the type-C QPO.

Description: We present a new suite of mock galaxy catalogs mimicking the low-redshift Universe, based on an updated halo occupation distribution (HOD) model and a scaling relation between optical properties and the neutral hydrogen (Hi) content of galaxies. Our algorithm is constrained by observations of the luminosity function and luminosity- and colour-dependent clustering of SDSS galaxies, as well as the Hi mass function and Hi-dependent clustering of massive Hi-selected galaxies in the ALFALFA survey. Mock central and satellite galaxies with realistic values of r-band luminosity, g − r and u − r colour, stellar mass and Hi mass are populated in an N-body simulation, inheriting a number of properties of the density and tidal environment of their host halos. The host halo of each central galaxy is also ‘baryonified’ with realistic spatial distributions of stars as well as hot and cold gas, along with the corresponding rotation curve. Our default HOD assumes that galaxy properties are a function of group halo mass alone, and can optionally include effects such as galactic conformity and colour-dependent galaxy assembly bias. The mocks predict the relation between the stellar mass and Hi mass of massive Hi galaxies, as well as the 2-point cross-correlation function of spatially co-located optical and Hi-selected samples. They enable novel null tests for galaxy assembly bias, provide predictions for the Hi velocity width function, and clarify the origin and universality of the radial acceleration relation in the ΛCDM framework.

Description: Subaru Strategic Program with the Hyper-Suprime Cam (HSC-SSP) has proven to be successful with its extremely-wide area coverage in past years. Taking advantages of this feature, we report initial results from exploration and research of expansive over- and under-dense structures at z = 0.3 – 1 based on the second Public Data Release where optical 5-band photometric data for ∼ eight million sources with i 〈 23 mag are available over ∼360 square degrees. We not only confirm known superclusters but also find candidates of titanic over- and under-dense regions out to z = 1. The mock data analysis suggests that the density peaks would involve one or more massive dark matter haloes (〉1014 M⊙) of the redshift, and the density troughs tend to be empty of massive haloes over 〉10 comoving Mpc. Besides, the density peaks and troughs at z ≲ 0.6 are in part identified as positive and negative weak lensing signals respectively, in mean tangential shear profiles, showing a good agreement with those inferred from the full-sky weak lensing simulation. The coming extensive spectroscopic surveys will be able to resolve these colossal structures in three-dimensional space. The number density information over the entire survey field is available as grid-point data on the website of the HSC-SSP data release (https://hsc.mtk.nao.ac.jp/ssp/data-release/).

Description: Asteroseismology using space-based telescopes is vital to our understanding of stellar structure and evolution. CoRoT, Kepler, and TESS space telescopes have detected large numbers of solar-like oscillating evolved stars. Solar-like oscillation frequencies have an important role in the determination of fundamental stellar parameters; in the literature, the relations between the two is established by the so-called scaling relations. In this study, we analyse data obtained from the observation of 15 evolved solar-like oscillating stars using the Kepler and ground-based telescopes. The main purpose of the study is to determine very precisely the fundamental parameters of evolved stars by constructing interior models using asteroseismic parameters. We also fit the reference frequencies of models to the observational reference frequencies caused by the He II ionization zone. The 15 evolved stars are found to have masses and radii within ranges of 0.79-1.47 M⊙ and 1.60-3.15 R⊙, respectively. Their model ages range from 2.19 to 12.75 Gyr. It is revealed that fitting reference frequencies typically increase the accuracy of asteroseismic radius, mass, and age. The typical uncertainties of mass and radius are ∼ 3-6 and ∼ 1-2 per cent, respectively. Accordingly, the differences between the model and literature ages are generally only a few Gyr.

Description: The star Fomalhaut hosts a narrow, eccentric debris disc, plus a highly eccentric companion Fomalhaut b. It is often argued that Fomalhaut b cannot have significant mass, otherwise it would quickly perturb the disc. We show that material in internal mean-motion resonances with a massive, coplanar Fomalhaut b would actually be long-term stable, and occupy orbits similar to the observed debris. Furthermore, millimetre dust released in collisions between resonant bodies could reproduce the width, shape and orientation of the observed disc. We first re-examine the possible orbits of Fomalhaut b, assuming that it moves under gravity alone. If Fomalhaut b orbits close to the disc midplane then its orbit crosses the disc, and the two are apsidally aligned. This alignment may hint at an ongoing dynamical interaction. Using the observationally allowed orbits, we then model the interaction between a massive Fomalhaut b and debris. Whilst most debris is unstable in such an extreme configuration, we identify several resonant populations that remain stable for the stellar lifetime, despite crossing the orbit of Fomalhaut b. This debris occupies low-eccentricity orbits similar to the observed debris ring. These resonant bodies would have a clumpy distribution, but dust released in collisions between them would form a narrow, relatively smooth ring similar to observations. We show that if Fomalhaut b has a mass between those of Earth and Jupiter then, far from removing the observed debris, it could actually be sculpting it through resonant interactions.

Description: Extremely elongated, conducting dust particles (also known as metallic “needles” or “whiskers”) are seen in carbonaceous chondrites and in samples brought back from the Itokawa asteroid. Their formation in protostellar nebulae and subsequent injection into the interstellar medium have been demonstrated, both experimentally and theoretically. Metallic needles have been suggested to explain a wide variety of astrophysical phenomena, ranging from the mid-infrared interstellar extinction at ∼ 3–8 μm to the thermalization of starlight to generate the cosmic microwave background. To validate (or invalidate) these suggestions, an accurate knowledge of the optics (e.g., the amplitude and the wavelength dependence of the absorption cross sections) of metallic needles is crucial. Here we calculate the absorption cross sections of iron needles of various aspect ratios over a wide wavelength range, by exploiting the discrete dipole approximation, the most powerful technique for rigorously calculating the optics of irregular or nonspherical grains. Our calculations support the earlier findings that the antenna theory and the Rayleigh approximation, which are often taken to approximate the optical properties of metallic needles, are indeed inapplicable.

Description: Dust is an essential ingredient of galaxies, determining the physical and chemical conditions in the interstellar medium. Several complementary observational evidences indicate that the cosmic dust mass density significantly drops from redshift z = 1 to z = 0. Clearly, and for the first time during cosmic evolution, dust must be destroyed more rapidly than it is formed. By considering the dust production/destruction processes acting in this cosmic time lapse, we find that the drop can be explained if dust is mainly destroyed by astration (49% contribution in the fiducial case) and supernova shocks within galaxies (42%). Our results further imply that on average each supernova destroys only Md, sn = 0.45 M⊙ of dust, i.e. 5 − 10 times less than usually assumed, with a hard upper limit of Md, sn 〈 3.0M⊙ set by the available metal budget and maximal grain growth. The lower efficiency might be explained by effective shielding of dust against shock processing in pre-supernova wind shells.

Description: We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than 1.3 M⊙ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

Description: Future large-scale structure surveys will measure the locations and shapes of billions of galaxies. The precision of such catalogs will require meticulous treatment of systematic contamination of the observed fields. We compare several existing methods for removing such systematics from galaxy clustering measurements. We show how all the methods, including the popular pseudo-Cℓ Mode Projection and Template Subtraction methods, can be interpreted under a common regression framework and use this to suggest improved estimators. We show how methods designed to mitigate systematics in the power spectrum can be used to produce clean maps, which are necessary for cosmological analyses beyond the power spectrum, and we extend current methods to treat the next-order multiplicative contamination in observed maps and power spectra, which reduced power spectrum errors from $Delta chi ^2_{ m C_ell }simeq 10$ to ≃ 1 in simulated analyses. Two new mitigation methods are proposed, which incorporate desirable features of current state-of-the-art methods while being simpler to implement. Investigating the performance of all the methods on a common set of simulated measurements from Year 5 of the Dark Energy Survey, we test their robustness to various analysis cases. Our proposed methods produce improved maps and power spectra when compared to current methods, while requiring almost no user tuning. We end with recommendations for systematics mitigation in future surveys, and note that the methods presented are generally applicable beyond the galaxy distribution to any field with spatial systematics.

Description: We systematically analyze two GRB samples with radio-loud and radio-quiet afterglows, respectively. It is interestingly found that the radio-selected GRB samples exhibit a clear dichotomy in terms of their distributions of intrinsic durations (Tint), isotropic energies in γ-rays (Eγ, iso), the circum-burst medium density (n), the spectral radio peak luminosity (Lν, p) and flux densities (Fhost) of host galaxies. On average, the values of Tint, Eγ, iso, n, Lν, p and Fhost of radio-quiet GRBs are relatively smaller than those of radio-loud ones. However, the redshifts and host flux densities of both samples are similarly distributed. In addition, a positive power-law correlation of $L_{ u ,p}propto E_{gamma ,iso}^{0.41pm 0.04}$ is found for the radio-loud sample, especially in accord with the supernova-associated GRBs, which is marginally consistent with that of the radio-quiet GRB sample. A negative correlation between Tint and z is confirmed to similarly hold for both radio-loud and radio-quiet GRBs. The dividing line between short and long GRBs in the rest frame is at Tint ≃1 s. Consequently, we propose that the radio-selected GRBs could be originated from distinct progenitors and central engines, together with environments.

Description: Open clusters are unique tracers of the history of our own Galaxy’s disk. According to our membership analysis based on Gaia astrometry, out of the 226 potential clusters falling in the footprint of GALAH or APOGEE, we find that 205 have secure members that were observed by at least one of the survey. Furthermore, members of 134 clusters have high-quality spectroscopic data that we use to determine their chemical composition. We leverage this information to study the chemical distribution throughout the Galactic disk of 21 elements, from C to Eu. The radial metallicity gradient obtained from our analysis is −0.076 ± 0.009 dex kpc−1, which is in agreement with previous works based on smaller samples. Furthermore, the gradient in the [Fe/H] - guiding radius (rguid) plane is −0.073 ± 0.008 dex kpc−1. We show consistently that open clusters trace the distribution of chemical elements throughout the Galactic disk differently than field stars. In particular, at given radius, open clusters show an age-metallicity relation that has less scatter than field stars. As such scatter is often interpreted as an effect of radial migration, we suggest that these differences are due to the physical selection effect imposed by our Galaxy: clusters that would have migrated significantly also had higher chances to get destroyed. Finally, our results reveal trends in the [X/Fe]-rguid-age space, which are important to understand production rates of different elements as a function of space and time.

Description: We use direct N-body simulations to explore some possible scenarios for the future evolution of two massive clusters observed toward the center of NGC 4654, a spiral galaxy with mass similar to that of the Milky Way. Using archival HST data, we obtain the photometric masses of the two clusters, M = 3 × 105 M⊙ and M = 1.7 × 106 M⊙, their half-light radii, Reff ∼ 4 pc and Reff ∼ 6 pc, and their projected distances from the photometric center of the galaxy (both

Description: We present the optical (UBVRI) and ultraviolet (Swift-UVOT) photometry, and optical spectroscopy of Type Ia supernova SN 2017hpa. We study broadband UV+optical light curves and low resolution spectroscopy spanning from −13.8 to +108 d from the maximum light in B-band. The photometric analysis indicates that SN 2017hpa is a normal type Ia with ΔmB(15) = 0.98 ± 0.16 mag and MB = −19.45 ± 0.15 mag at a distance modulus of μ = 34.08 ± 0.09 mag. The (uvw1 − uvv) colour evolution shows that SN 2017hpa falls in the NUV-blue group. The (B − V) colour at maximum is bluer in comparison to normal type Ia supernovae. Spectroscopic analysis shows that the Si ii 6355 absorption feature evolves rapidly with a velocity gradient, $dot{v}=128pm 7$ km s−1 d−1. The pre-maximum phase spectra show prominent C ii 6580 Å absorption feature. The C ii 6580 Å line velocity measured from the observed spectra is lower than the velocity of Si ii 6355 Å, which could be due to a line of sight effect. The synthetic spectral fits to the pre-maximum spectra using syn++ indicate the presence of a high velocity component in the Si ii absorption, in addition to a photospheric component. Fitting the observed spectrum with the spectral synthesis code TARDIS, the mass of unburned C in the ejecta is estimated to be ∼0.019 M⊙. The peak bolometric luminosity is $L^{ m {bol}}_{ m {peak}} = 1.43imes 10^{43}$ erg s−1. The radiation diffusion model fit to the bolometric light curve indicates 0.61 ± 0.02 M⊙ of 56Ni is synthesized in the explosion.

Description: Magnitude-limited samples have shown that 20–25 per cent of cataclysmic variables contain white dwarfs with magnetic fields of Mega Gauss strength, in stark contrast to the approximately 5 per cent of single white dwarfs with similar magnetic field strengths. Moreover, the lack of identifiable progenitor systems for magnetic cataclysmic variables leads to considerable challenges when trying to understand how these systems form and evolve. Here, we present a sample of six magnetic white dwarfs in detached binaries with low-mass stellar companions where we have constrained the stellar and binary parameters including, for the first time, reliable mass estimates for these magnetic white dwarfs. We find that they are systematically more massive than non-magnetic white dwarfs in detached binaries. These magnetic white dwarfs generally have cooling ages of more than 1 Gyr and reside in systems that are very close to Roche lobe filling. Our findings are more consistent with these systems being temporarily detached cataclysmic variables, rather than pre-cataclysmic binaries, but we cannot rule out the latter possibility. We find that these systems can display unusual asymmetric light curves that may offer a way to identify them in larger numbers in future. Seven new candidate magnetic white dwarf systems are also presented, three of which have asymmetric light curves. Finally, we note that several newly identified magnetic systems have archival spectra where there is no clear evidence of magnetism, meaning that these binaries have been previously missed. Nevertheless, there remains a clear lack of younger detached magnetic white dwarf systems.

Description: High-redshift star-forming galaxies have very different morphologies compared to nearby ones. Indeed, they are often dominated by bright star-forming structures of masses up to 108–9 M⊙ dubbed ‘giant clumps’. However, recent observations questioned this result by showing only low-mass structures or no structure at all. We use Adaptative Mesh Refinement hydrodynamical simulations of galaxies with parsec-scale resolution to study the formation of structures inside clumpy high-redshift galaxies. We show that in very gas-rich galaxies star formation occurs in small gas clusters with masses below 107–8 M⊙ that are themselves located inside giant complexes with masses up to 108 and sometimes 109 M⊙. Those massive structures are similar in mass and size to the giant clumps observed in imaging surveys, in particular with the Hubble Space Telescope. Using mock observations of simulated galaxies, we show that at very high resolution with instruments like the Atacama Large Millimeter Array or through gravitational lensing, only low-mass structures are likely to be detected, and their gathering into giant complexes might be missed. This leads to the non-detection of the giant clumps and therefore introduces a bias in the detection of these structures. We show that the simulated giant clumps can be gravitationally bound even when undetected in mocks representative for ALMA observations and HST observations of lensed galaxies. We then compare the top-down fragmentation of an initially warm disc and the bottom-up fragmentation of an initially cold disc to show that the process of formation of the clumps does not impact their physical properties.

Description: During the last decade, there has been an explosive growth in survey data and deep learning techniques, both of which have enabled great advances for astronomy. The amount of data from various surveys from multiple epochs with a wide range of wavelengths, albeit with varying brightness and quality, is overwhelming, and leveraging information from overlapping observations from different surveys has limitless potential in understanding galaxy formation and evolution. Synthetic galaxy image generation using physical models has been an important tool for survey data analysis, while deep learning generative models show great promise. In this paper, we present a novel approach for robustly expanding and improving survey data through cross survey feature translation. We trained two types of neural networks to map images from the Sloan Digital Sky Survey (SDSS) to corresponding images from the Dark Energy Survey (DES). This map was used to generate false DES representations of SDSS images, increasing the brightness and S/N while retaining important morphological information. We substantiate the robustness of our method by generating DES representations of SDSS images from outside the overlapping region, showing that the brightness and quality are improved even when the source images are of lower quality than the training images. Finally, we highlight several images in which the reconstruction process appears to have removed large artifacts from SDSS images. While only an initial application, our method shows promise as a method for robustly expanding and improving the quality of optical survey data and provides a potential avenue for cross-band reconstruction.

Description: We evaluate the redshift distribution of binary black hole (BBH), black hole – neutron star binary (BHNS) and binary neutron star (BNS) mergers, exploring the main sources of uncertainty: star formation rate (SFR) density, metallicity evolution, common envelope, mass transfer via Roche lobe overflow, natal kicks, core-collapse supernova model and initial mass function. Among binary evolution processes, uncertainties on common envelope ejection have a major impact: the local merger rate density of BNSs varies from ∼103 to ∼20 Gpc−3 yr−1 if we change the common envelope efficiency parameter from αCE = 7 to 0.5, while the local merger rates of BBHs and BHNSs vary by a factor of ∼2 − 3. The BBH merger rate changes by one order of magnitude, when 1σ uncertainties on metallicity evolution are taken into account. In contrast, the BNS merger rate is almost insensitive to metallicity. Hence, BNSs are the ideal test bed to put constraints on uncertain binary evolution processes, such as common envelope and natal kicks. Only models assuming values of αCE ≳ 2 and moderately low natal kicks (depending on the ejected mass and the SN mechanism), result in a local BNS merger rate density within the 90% credible interval inferred from the second gravitational-wave transient catalogue.

Description: Globular Clusters are among the oldest objects in the Galaxy, thus their researchers are key to understanding the processes of evolution and formation that the galaxy has experienced in early stages. Spectroscopic studies allow us to carry out detailed analyzes on the chemical composition of Globular Clusters. The aim of our research is to perform a detailed analysis of chemical abundances to a sample of stars of the Bulge Globular Cluster NGC 6553, in order to determine chemical patterns that allow us to appreciate the phenomenon of Multiple Population in one of the most metal-rich Globular Clusters in the Galaxy. This analysis is being carried out with data obtained by FLAMES/GIRAFFE spectrograph, VVV Survey and DR2 of Gaia Mission. We analyzed 20 Red Horizontal Branch Stars, being the first extensive spectroscopic abundance analysis for this cluster and measured 8 chemical elements (O, Na, Mg, Si, Ca, Ti, Cr and Ni), deriving a mean iron content of [Fe/H] = −0.10 ± 0.01 and a mean of [α/Fe] = 0.21 ± 0.02, considering Mg, Si, Ca and Ti (errors on the mean). We found a significant spread in the content of Na but a small or negligible in O. We did not find an intrinsic variation in the content of α and iron-peak elements, showing a good agreement with the trend of the Bulge field stars, suggesting a similar origin and evolution.

Description: We study the effects of passages of compact objects such as stars, star clusters and black holes through molecular clouds, and propose that the gravitational interaction between the compact object and the ambient gas can lead to the formation of thin and collimated features made of dense gas, which we call “molecular contrails”. Supercritical contrails can collapse further leading to triggered star formation. The width of a molecular contrail is determined by the mass and velocity of the compact object and the velocity dispersion of the ambient molecular medium. Under typical conditions in the Milky Way, passages of stellar-mass objects lead to the formation of width $dgtrsim 0.01,, m {parsec}$ contrails, and passages of star clusters lead to the formation of $dgtrsim 1,, m {parsec}$ contrails. We present a few molecular contrail candidates from both categories identified from ALMA 1.3mm continuum observations of star-forming regions and the 13CO(1-0) map from the Galactic Ring Survey respectively. The contrails represent an overlooked channel where stars and gas in the Galactic disk interact to form structures. They also present a potential way of detecting dark compact objects in the Milky Way.

Description: We introduce a statistical method for estimating magnetic field fluctuations generated from primordial black hole (PBH) populations. To that end, we consider monochromatic and extended Press-Schechter PBH mass functions, such that each constituent is capable of producing its own magnetic field due to some given physical mechanism. Assuming linear correlation between magnetic field fluctuations and matter over-densities, our estimates depend on the mass function, the physical field generation mechanism by each PBH constituent, and the characteristic PBH separation. After computing the power spectrum of magnetic field fluctuations, we apply our formalism to study the plausibility that two particular field generation mechanisms could have given rise to the expected seed fields according to current observational constraints. The first mechanism is the Biermann battery and the second one is due to the accretion of magnetic monopoles at PBH formation, constituting magnetic PBHs. Our results show that, for monochromatic distributions, it does not seem to be possible to generate sufficiently intense seed fields in any of the two field generation mechanisms. For extended distributions, it is also not possible to generate the required seed field by only assuming a Biermann battery mechanism. In fact, we report an average seed field by this mechanism of about 10−47 G, at z = 20. For the case of magnetic monopoles we instead assume that the seed values from the literature are achieved and calculate the necessary number density of monopoles. In this case we obtain values that are below the upper limits from current constraints.

Description: Accurate shear measurement is a key topic in weak lensing community. Point Spread Function (PSF), which smears the observed galaxy image, plays one of the main roles in the systematic errors in shear measurement and must be treated carefully to avoid bias and errors in cosmological parameters. In this paper, we present new PSF measurement methods, Smooth-PCA (SPCA) and Improved-SPCA (iSPCA), which can reconstruct smooth PSFs with high efficiency. Our methods decompose the star images into smooth principal components by using the Expectation-Maximization-PCA (EMPCA) method, and the smooth principal components are composed by Moffatlets basis functions, which are derived from the Moffat function. We demonstrate our approaches based on simulated Moffat PSFs and PhoSim star images. The constructed smooth principal components show flexible and efficient as the same as EMPCA, and have more stable patterns than EMPCA under noises contamination. We then check the reconstruction accuracy on the shape of PSFs. We find that our methods are able to reconstruct the PSFs at the same precision as the EMPCA method which indicates and iSPCA are promising for weak lensing shear measurement.

Description: The bright blazar OJ 287 is the best-known candidate for hosting a supermassive black hole binary system. It inspirals due to the emission of nanohertz gravitational waves (GWs). Observations of historical and predicted quasi-periodic high-brightness flares in its century-long optical lightcurve, allow us to determine the orbital parameters associated with the binary black hole (BBH) central engine. In contrast, the radio jet of OJ 287 has been covered with Very Long Baseline Interferometry (VLBI) observations for only about 30 years and these observations reveal that the position angle (PA) of the jet exhibits temporal variations at both millimetre and centimetre wavelengths. Here we associate the observed PA variations in OJ 287 with the precession of its radio jet. In our model, the evolution of the jet direction can be associated either with the primary black hole (BH) spin evolution or with the precession of the angular momentum direction of the inner region of the accretion disc. Our Bayesian analysis shows that the BBH central engine model, primarily developed from optical observations, can also broadly explain the observed temporal variations in the radio jet of OJ 287 at frequencies of 86, 43, and 15 GHz. Ongoing Global mm-VLBI Array (GMVA) observations of OJ 287 have the potential to verify our predictions for the evolution of its 86 GHz PA values. Additionally, thanks to the extremely high angular resolution that the Event Horizon Telescope (EHT) can provide, we explore the possibility to test our BBH model through the detection of the jet in the secondary black hole .

Description: We present a new determination of the galaxy stellar mass function (GSMF) over the redshift interval 0.25 ≤ z ≤ 3.75, derived from a combination of ground-based and Hubble Space Telescope (HST) imaging surveys. Based on a near-IR selected galaxy sample selected over a raw survey area of 3 deg2 and spanning ≥4 dex in stellar mass, we fit the GSMF with both single and double Schechter functions, carefully accounting for Eddington bias to derive both observed and intrinsic parameter values. We find that a double Schechter function is a better fit to the GSMF at all redshifts, although the single and double Schechter function fits are statistically indistinguishable by z = 3.25. We find no evidence for significant evolution in M⋆, with the intrinsic value consistent with $log _{10}(M^{star }/{ m , M_{odot }})=10.55pm {0.1}$ over the full redshift range. Overall, our determination of the GSMF is in good agreement with recent simulation results, although differences persist at the highest stellar masses. Splitting our sample according to location on the UVJ plane, we find that the star-forming GSMF can be adequately described by a single Schechter function over the full redshift range, and has not evolved significantly since z ≃ 2.5. In contrast, both the normalization and functional form of the passive GSMF evolves dramatically with redshift, switching from a single to a double Schechter function at z ≤ 1.5. As a result, we find that while passive galaxies dominate the integrated stellar-mass density at z ≤ 0.75, they only contribute ≲ 10% by z ≃ 3. Finally, we provide a simple parameterization that provides an accurate estimate of the GSMF, both observed and intrinsic, at any redshift within the range 0 ≤ z ≤ 4.