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To advance our understanding of the evolution of the interstellar medium (ISM) of our Galaxy, numerical models of Milky Way (MW) type galaxies are widely used. However, most models only vaguely resemble the MW (e.g. in total mass), and often use imposed analytic potentials (which cannot evolve dynamically). This poses a problem in asserting their applicability for the interpretation of observations of our own Galaxy. The goal of this work is to identify a numerical model that is not only an MW-type galaxy, but one that can mimic some of the main observed structures of our Galaxy, using dynamically evolving potentials, so that it can be used as a base model to study the ISM cycle in a galaxy like our own. This paper introduces a suite of 15 MW-type galaxy models developed using the arepo numerical code, that are compared to Galactic observations of |$^{12}$| CO and H  i emission via longitude–velocity plots, from where we extract and compare the skeletons of major galactic features and the terminal gas velocities. We found that our best-fitting model to the overall structure, also reproduces some of the more specific observed features of the MW, including a bar with a pattern speed of |$30.0 \pm 0.2$| km s |$^{-1}$|  kpc |$^{-1}$|⁠ , and a bar half-length of |$3.2 \pm 0.8$|  kpc. Our model shows large streaming motions around spiral arms, and strong radial motions well beyond the inner bar. This model highlights the complex motions of a dynamic MW-type galaxy and has the potential to offer valuable insight into how our Galaxy regulates the ISM and star formation. [ABSTRACT FROM AUTHOR]

We investigate the properties of circumstellar discs (CDs) produced in hydrodynamical simulations of gravoturbulent core collapse considering Kolmogorov and Burger-type turbulence. We report that massive discs are more prevalent in the Kolmogorov regime than for Burger-type turbulence. A significant number of discs are formed with a radius of ∼15 au in both cases. However, the number of extended discs with radii >15 au is significantly larger in case of Kolmogorov turbulence. The two regimes of turbulence, in general, yield disc radii in the ranges of 7−30 au and 13−39 au, respectively. The corresponding ranges of the disc masses are 30.37 M Jup−0.92 M⊙ and 2.09  M Jup−0.13 M⊙, respectively. Moreover, the ratio M disc/ M star is higher in models of Kolmogorov-type turbulence than in models of Burgers-type turbulence. We do not find any correlation between R disc and M disc over the explored range of initial temperatures (8−14 K) and the type of turbulence. Also, for these initial thermal variations, the turbulent CD structures do not exhibit signs of turbulent diffusion. Nonetheless, both sub- and supersonic velocity dispersions cause variations in the specific angular momentum of infalling gas, especially for CDs with radii ∼ 16−21 au. The radial profiles of CDs do not correlate with the initial conditions. [ABSTRACT FROM AUTHOR]

Observations of the 21 cm line of hydrogen are poised to revolutionize our knowledge of reionization and the first galaxies. However, harnessing such information requires robust and comprehensive theoretical modelling. We study the non-linear effects of hydrodynamics and astrophysical feedback processes, including stellar and AGN feedback, on the 21 cm signal by post-processing three existing cosmological hydrodynamical simulations of galaxy formation: Illustris, IllustrisTNG, and Eagle. Despite their different underlying galaxy-formation models, the simulations return similar predictions for the global 21 cm brightness temperature and its power spectrum. At fixed redshift, most differences are attributable to alternative reionization histories, in turn driven by differences in the buildup of stellar sources of radiation. However, several astrophysical processes imprint signatures in the 21 cm power spectrum at two key scales. First, we find significant small-scale (⁠|$k \ge 10\, \rm {Mpc}^{-1}$|⁠) differences between Illustris and IllustrisTNG, where higher velocity winds generated by supernova feedback soften density peaks, leading to lower 21 cm power in TNG. Thus, constraints at these scales could rule out extreme feedback models. Secondly, we find more 21 cm power at intermediate scales (⁠|$k \approx 0.8\, \rm {Mpc}^{-1}$|⁠) in Eagle due to ionization differences driven by highly effective stellar feedback, resulting in lower star formation, older and redder stellar populations, and lower ionizing luminosities for |$M_h \gt 10^9 \, \rm M_\odot$|⁠. Different source models can manifest similarly in the 21 cm power spectrum, leading to often ignored degeneracies. These subtle features could allow future observations of the 21 cm signal, in conjunction with other observables, to constrain theoretical models for galactic feedback at high redshift. [ABSTRACT FROM AUTHOR]

This document is a correction to a previously published paper titled "Binary black hole mergers from population III stars: uncertainties from star formation and binary star properties." The authors discovered a minor bug in the code used to produce the results shown in various figures. The correction provides the updated figures and lists the changes made to the published version. The authors state that the bug did not significantly affect the results and conclusions of the paper. The main data presented in the paper are publicly available on Zenodo and GitLab. [Extracted from the article]

In this work, we analyse the density profiles of subhaloes with masses M sh ≥ 1.4 × 108 M⊙ in the TNG50 simulation, with the aim of including baryonic effects. We evaluate the performance of frequently used models, such as the standard Navarro–Frenk–White (NFW), the Einasto, and a smoothly truncated version of the NFW profile. We find that these models do not perform well for the majority of subhaloes, with the NFW profile giving the worst fit in most cases. This is primarily due to mismatches in the inner and outer logarithmic slopes, which are significantly steeper for a large number of subhaloes in the presence of baryons. To address this issue, we propose new three-parameter models and show that they significantly improve the goodness of fit independently of the subhalo's specific properties. Our best-performing model is a modified version of the NFW profile with an inner log-slope of −2 and a variable truncation that is sharper and steeper than the slope transition in the standard NFW profile. Additionally, we investigate how both the parameter values of the best density profile model and the average density profiles vary with subhalo mass, V max, distance from the host halo centre, baryon content, and infall time, and we also present explicit scaling relations for the mean parameters of the individual profiles. The newly proposed fit and the scaling relations are useful to predict the properties of realistic subhaloes in the mass range 108 M⊙ ≤ M sh ≤ 1013 M⊙ that can be influenced by the presence of baryons. [ABSTRACT FROM AUTHOR]

The cold neutral medium (CNM) is an important part of the galactic gas cycle and a precondition for the formation of molecular and star-forming gas, yet its distribution is still not fully understood. In this work, we present extremely high resolution simulations of spiral galaxies with time-dependent chemistry such that we can track the formation of the CNM, its distribution within the galaxy, and its correlation with star formation. We find no strong radial dependence between the CNM fraction and total neutral atomic hydrogen (H  i) due to the decreasing interstellar radiation field counterbalancing the decreasing gas column density at larger galactic radii. However, the CNM fraction does increase in spiral arms where the CNM distribution is clumpy, rather than continuous, overlapping more closely with H2. The CNM does not extend out radially as far as H  i , and the vertical scale height is smaller in the outer galaxy compared to H  i with no flaring. The CNM column density scales with total mid-plane pressure and disappears from the gas phase below values of P T/ k B = 1000 K cm−3. We find that the star formation rate density follows a similar scaling law with CNM column density to the total gas Kennicutt–Schmidt law. In the outer galaxy, we produce realistic vertical velocity dispersions in the H  i purely from galactic dynamics, but our models do not predict CNM at the extremely large radii observed in H  i absorption studies of the Milky Way. We suggest that extended spiral arms might produce isolated clumps of CNM at these radii. [ABSTRACT FROM AUTHOR]

We introduce the radiative transfer code Sweep for the cosmological simulation suite arepo. Sweep is a discrete ordinates method in which the radiative transfer equation is solved under the infinite speed of light, steady state assumption by a transport sweep across the entire computational grid. Since arepo is based on an adaptive, unstructured grid, the dependency graph induced by the sweep dependencies of the grid cells is non-trivial. In order to solve the topological sorting problem in a distributed manner, we employ a task-based-parallelism approach. The main advantage of the sweep method is that the computational cost scales only with the size of the grid and is independent of the number of sources or the distribution of sources in the computational domain, which is an advantage for radiative transfer in cosmological simulations, where there are large numbers of sparsely distributed sources. We successfully apply the code to a number of physical tests such as the expansion of H  ii regions, the formation of shadows behind dense objects, the scattering of light, and its behaviour in the presence of periodic boundary conditions. In addition, we measure its computational performance with a focus on highly parallel, large-scale simulations. [ABSTRACT FROM AUTHOR]

Collisions between giant molecular clouds (GMCs) are one of the pathways for massive star formation due to the high densities created. However, the enhancement of the star formation rate (SFR) is not well constrained. In this study, we perform a parameter study of cloud–cloud collisions and investigate how the resulting SFR depends on the details of set-up. Our parameter study explores variations in collision speed, magnetic field inclination (with respect to the collisional axis), and resolution, as defined by the number of cells per Jeans length. In all our collision simulations, we find a factor of 2–3 increase in the SFR compared to our no collision simulation, with star formation beginning sooner with (a) high collisional velocities, (b) parallel orientation between the magnetic field and collision axis, (c) and lower resolution. The mean virial parameter of high density (and thus possible star-forming) gas increases with collisional velocity, but has little variation with magnetic field inclination. The alignment of the velocity and magnetic field remains uniform in low-density environments but becomes more perpendicular with increasing density, indicating the compression of the magnetic field by collapsing gas. Comparing the trends in the SFR with other GMC collision studies, we find good agreement with studies that account for the gravitational boundedness of the gas in their star formation algorithm, but not with those that simply form stars above a prescribed density threshold. This suggests that the latter approach should be used with caution when modelling star formation on resolved cloud scales. [ABSTRACT FROM AUTHOR]

A fundamental prediction of the ΛCDM cosmology is the hierarchical build-up of structure and therefore the successive merging of galaxies into more massive ones. As one can only observe galaxies at one specific time in the cosmic history, this merger history remains, in principle, unobservable. By using the TNG100 simulation of the IllustrisTNG project, we show that it is possible to infer the unobservable stellar assembly and merger history of central galaxies from their observable properties by using machine learning techniques. In particular, in this first paper of ERGO-ML (Extracting Reality from Galaxy Observables with Machine Learning), we choose a set of seven observable integral properties of galaxies to infer the stellar ex-situ fraction, the average merger lookback times and mass ratios, and the lookback time and stellar mass of the last major merger. To infer the posterior distribution for these parameters and hence estimate the uncertainties in the predictions, we use a conditional Invertible Neural Network (cINN). We find that the stellar ex-situ fraction and the time of the last major merger are well-determined by the selected set of observables, that the mass-weighted merger mass ratio is unconstrained, and that, beyond stellar mass, stellar morphology and stellar age are the most informative properties. Finally, we show that the cINN recovers the remaining unexplained scatter and secondary cross-correlations. Overall, this is a first step towards a tool that can be applied to large galaxy surveys in order to infer unobservable properties of the galaxies' past, enabling empirical studies of galaxy evolution enriched by cosmological simulations. [ABSTRACT FROM AUTHOR]

During primordial star formation, the main cooling channel is provided by H2 and super-molecules, such as H2 or H2, at sufficiently high densities. When the latter form at |$n_{\rm H}\, \ge \, 10^{14}$|  cm−3, collision-induced emission (CIE) provides efficient gas cooling. We investigate how CIE cooling affects the formation of metal-free binaries comparing simulations with and without this process. Irrespective of the cooling mechanism, we find a typical protostellar mass range between 0.01 and 100 M⊙. However, models with only H2 line cooling produce a greater number of low-mass protostars that exhibit stronger variations in their radial velocities than the high-mass protostars. Similarly, in models with both H2 cooling and CIE cooling, significant variations in the radial velocities are found for protostars in the intermediate-mass range. The initial number of fragments N max decreases with increasing strength of turbulence. Cooling via super-molecules lets the most massive protobinaries (MMPBs) efficiently accrete mass. The maximum mass accretion rate |$\dot{M}_{\rm max}$| for the MMPBs is more than an order of magnitude higher in the presence of CIE cooling than for pure H2 line cooling. As a result, compact binaries with a semimajor axis as small as 3.57 au may form through the H2– H2 cooling channel. Our results indicate that, in addition to the MMPBs, most population III (Pop. III) binaries should be in eccentric i.e. non-circular orbits. This provides an important connection to the eccentric binaries reported in previous studies, which were found to exhibit rich temporal accretion signals during their evolution. [ABSTRACT FROM AUTHOR]

We revisit the conditions present in supermassive discs (SMDs) formed by the merger of gas-rich, metal-enriched galaxies at redshift z ∼ 10. We find that SMDs naturally form hydrostatic cores which go through a rapidly accreting supermassive star phase, before directly collapsing into massive black holes via the general relativistic instability. The growth and collapse of the cores occurs within ∼5 × 105 yr from the formation of the SMD, producing bright electromagnetic, neutrino and gravitational wave transients with a typical duration of a few minutes and, respectively, a typical flux and a typical strain amplitude at Earth of ∼10−8 erg s−1 cm−2 and ∼4 × 10−21. We provide a simple fitting formula for the resulting black hole masses, which range from a few 106 to 108 M⊙ depending on the initial SMD configuration. Crucially, our analysis does not require any specific assumption on the thermal properties of the gas, nor on the angular momentum loss mechanisms within the SMD. Led by these findings, we argue that the merger-driven scenario provides a robust pathway for the rapid formation of supermassive black holes at z > 6. It provides an explanation for the origin of the brightest and oldest quasars without the need of a sustained growth phase from a much smaller seed. Its smoking gun signatures can be tested directly via multimessenger observations. [ABSTRACT FROM AUTHOR]

The probability density function (PDF) of the logarithmic density contrast, s  = ln (ρ/ρ0), with gas density ρ and mean density ρ0, for hydrodynamical supersonic turbulence is well known to have significant non-Gaussian (intermittent) features that monotonically increase with the turbulent Mach number, |$\mathcal {M}$|⁠. By studying the mass- and volume-weighted s -PDF for an ensemble of 36 sub-to-trans-Alfv́enic mean-field, supersonic, isothermal turbulence simulations with different modes of driving, relevant to molecular gas in the cool interstellar medium, we show that a more intricate picture emerges for the non-Gaussian nature of s. Using four independent measures of the non-Gaussian components, we find hydrodynamical-like structure in the highly magnetized plasma for |$\mathcal {M} \lesssim 4$|⁠. However, for |$\mathcal {M} \gtrsim 4$|⁠ , the non-Gaussian signatures disappear, leaving approximately Gaussian s -statistics – exactly the opposite of hydrodynamical turbulence in the high- |$\mathcal {M}$| limit. We also find that the non-Gaussian components of the PDF increase monotonically with more compressive driving modes. To understand the |$\mathcal {M} \lesssim 4$| non-Gaussian features, we use one-dimensional pencil beams to explore the dynamics along and across the large-scale magnetic field, |$\mathrm{{\boldsymbol {\mathit {B}}}}_0$|⁠. We discuss kinetic, density, and magnetic field fluctuations from the pencil beams, and identify physical sources of non-Gaussian components to the PDF as single, strong shocks coupled to fast magnetosonic compressions that form along |$\mathrm{{\boldsymbol {\mathit {B}}}}_0$|⁠. We discuss the Gaussianization of the |$\mathcal {M} \gtrsim 4$| s -fields through the lens of two phenomenologies: the self-similarity of the s -field and homogenization of the dynamical time-scales between the over- and underdense regions in the compressible gas. [ABSTRACT FROM AUTHOR]