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The formation of the first galaxies in the Universe is the new frontier of both galaxy formation and reionization studies. This creates a fierce new challenge, i.e. to simultaneously understand in a unique and coherent picture the processes of galaxy formation and reionization, and – crucially – their connection. To this end, we present the thesan suite of cosmological radiation-magneto-hydrodynamical simulations. They are unique since they: (i) cover a very broad range of spatial and temporal scales; (ii) include an unprecedentedly-broad range of physical processes for simulations of such scales and resolution; (iii) exploit knowledge accumulated at low redshift to minimize the number of free parameters in the physical model; (iv) use a variance-suppression technique in the production of initial conditions to increase their statistical fidelity. Finally, the thesan suite includes multiple runs of the same initial conditions, exploring current unknowns in the physics of dark matter and ionizing sources.
Self-interacting dark matter (SIDM) is promising to solve or at least mitigate small-scale problems of cold collisionless dark matter. N-body simulations have proven to be a powerful tool to study SIDM within the astrophysical context. However, it turned out to be difficult to simulate dark matter (DM) models that typically scatter about a small angle, for example, light mediator models. We developed a novel numerical scheme for this regime of frequent self-interactions that allows for N-body simulations of systems like galaxy cluster mergers or even cosmological simulations. We have studied equal and unequal mass mergers of galaxies and galaxy clusters and found significant differences between the phenomenology of frequent self-interactions and the commonly studied large-angle scattering (rare self-interactions). For example, frequent self-interactions tend to produce larger offsets between galaxies and DM than rare self-interactions.
The progress of cosmic reionization depends on the presence of over-dense regions that act as photon sinks. Such sinks may slow down ionization fronts as compared to a uniform intergalactic medium (IGM) by increasing the clumping factor. We present simulations of reionization in a clumpy IGM resolving even the smallest sinks. The simulations use a novel, spatially adaptive and efficient radiative transfer implementation in the SWIFT SPH code, based on the two-moment method. We find that photon sinks can increase the clumping factor by a factor of ∼10 during the first ∼100 Myrs after the passage of an ionization front. After this time, the clumping factor decreases as the smaller sinks photoevaporate. Altogether, photon sinks increase the number of photons required to reionize the Universe by a factor of η ∼2, as compared to the homogeneous case. The value of η also depends on the emissivity of the ionizing sources.
We provide analysis of the baryon asymmetry generated in the Scalar Field Condensate (SFC) baryogenesis model obtained in new inflation, chaotic inflation, Starobinsky inflation, MSSM inflation, quintessential inflation, considering both cases of efficient thermalization after inflation and also delayed thermalization. We have found that baryon asymmetry generated in SFC baryogenesis model is considerably bigger than the observed one for the new inflation, new inflation model by Shafi and Vilenkin, MSSM inflation, chaotic inflation with high reheating temperature and the simplest Shafi-Vilenkin chaotic inflationary model. Therefore, strong diluting mechanisms are needed to reduce the baryon excess to its observational value today for these models. We have shown that for the SFC baryogenesis model a successful generation of the observed baryon asymmetry is possible in Modified Starobinsky inflation, chaotic inflation with low reheating temperature, chaotic inflation in SUGRA and quintessential inflationary model.
The late-time effect of primordial non-Gaussianity offers a window into the physics of inflation and the very early Universe. In this work we study the consequences of a particular class of primordial non-Gaussianity that is fully characterized by initial density fluctuations drawn from a non-Gaussian probability density function, rather than by construction of a particular form for the primordial bispectrum. We numerically generate multiple realisations of cosmological structure and use the late-time matter polyspectra to determine the effect of these modified initial conditions. In this non-Gaussianity has only a small imprint on the first polyspectra, when compared to a standard Gaussian cosmology. Furthermore, some of our models present an interesting scale-dependent deviation from the Gaussian case in the bispectrum and trispectrum, although the signal is at most at the percent level.
We present here self-consistent zoom-in simulations of massive galaxies forming in a full cosmological setting. The simulations are run with an updated version of the KETJU code, which is able to resolve the gravitational dynamics of their supermassive black holes, while simultaneously modelling the large-scale astrophysical processes in the surrounding galaxies, such as gas cooling, star formation and stellar and AGN feedback. The KETJU code is able to accurately model the complex behaviour of multiple SMBHs, including dynamical friction, stellar scattering and gravitational wave emission, and also to resolve Lidov–Kozai oscillations that naturally occur in hierarchical triplet SMBH systems. In general most of the SMBH binaries form at moderately high eccentricities, with typical values in the range of , meaning that the circular binary models that are commonly used in the literature are insufficient for capturing the typical binary evolution.
One of the primary foci of research in astrophysics is on developing a rigorous understanding of the first galaxies. This entails studying the physical processes such as accretion, cooling and star formation in first galaxies, and also investigating the consequences of these processes in the present day Universe. We investigate the star formation in the early galaxies and its subsequent evolution using the eagle simulation and find that the star formation has a smooth evolutionary behaviour at low redshifts leading to a main sequence of star formation that can be explained by deterministic models using accretion history as an input. In contrast, at high redshift (>6), most of the galaxies are bursty. At high redshift, instead of exhibiting a main sequence in SFR – Mh plane, they bunch-up around a halo mass of ≈ 109 Mȯ and SFR ≈0.1 Mȯ yr−1. As a consequence, the reionization of the Universe is led by low mass haloes hosting brighter galaxies that are undergoing intense bursts. Furthermore, the bursts in the infant galaxies lead to a poorly mixed interstellar medium in which the stars can form from gas enriched predominantly by a single nucleosynthetic channel. The lower mass subset of the stars formed in first galaxies resemble the carbon enhanced metal poor stars in our Galaxy while the higher mass ones reionized the Universe.
During the recombination of the universe, supersonic relative motion between baryons and dark matter (DM) generally existed. In the presence of such streaming motions, gas clumps can collapse outside of virial radii of their closest dark matter halos. Such baryon dominant objects are thought to be self-gravitating and are called supersonically induced gas objects; SIGOs. We perform three-dimensional hydrodynamical simulations by including H2 chemical reactions and stream velocity and follow SIGO’s formation from z = 200 to z = 25. SIGOs can be formed under the influence of stream velocity, and cooling is effective in contracting gas clouds. We follow its further evolution with higher resolution. We find that there are SIGOs which become Jeans unstable outside of the virial radius of the closest DM halos. Those SIGOs are gravitationally unstable and trigger star formation.
We use hydrodynamical simulations to study the evolution of baryonic gas in a cosmologically evolving dark matter halo. We model both the inner and outer regions of the halo using a density profile that transitions from an inner NFW profile to a flat profile far from the halo. Metallicity-dependent radiative cooling and AGN jet feedback are implemented, which lead to heating and cooling cycles in the core. We analyze the evolution of gas and the central supermassive black hole (SMBH) across cosmological time. We find that the properties of the gas and the SMBH are correlated across halo masses and feedback efficiencies.
The Bisous model is a tool that uses stochastic methods to detect the network of galactic filaments. This model is explicitly developed to detect the structure from observational data, using only galaxy positions as input. This paper shows that the Bisous model gives reliable results and including photometric data improves the resulting filamentary network. We used MultiDark-Galaxies catalogue to create a mock with photometric redshifts and samples with different galaxy number densities. We found that the filaments detected with the Bisous model are reliable; 85% of the detected filaments are unchanged compared to results with more complete input data. Adding photometric data improves the fraction of galaxies in filaments. Using the confusion matrix technique, we found the false discovery rate to always be below 5% when using photometric data.
Galactic winds probe how feedback regulates the mass and metallicity of galaxies. Galactic winds have cold gas, which is mainly observable with absorption and emission lines. Theoretically studying how absorption lines are produced requires numerical simulations and realistic starburst UV backgrounds. We use outputs from a suite of 3D PLUTO simulations of wind-cloud interactions to first estimate column densities and temperatures. Then, to create synthetic spectra, we developed a python interface to link our PLUTO simulations to TRIDENT via the YT-package infrastructure. We produce UV backgrounds accounting for the star formation rate of starbursts. For this purpose, we use fluxes generated by STARBURST99, which are then processed through CLOUDY to create customised ion tables. Such tables are subsequently read into TRIDENT to generate absorption spectra. We explain how the various packages and tools communicate with each other to create ion spectra consistent with spectral energy distributions of starburst systems.
Thermal energies deposited by OB stellar clusters in starburst galaxies lead to the formation of galactic superwinds. Multi-wavelength observations of starburst-driven superwinds pointed at complex thermal and ionization structures which cannot adequately be explained by simple adiabatic assumptions. In this study, we perform hydrodynamic simulations of a fluid model coupled to radiative cooling functions, and generate time-dependent non-equilibrium photoionization models to predict physical conditions and ionization structures of superwinds using the maihem atomic and cooling package built on the program flash. Time-dependent ionization states and physical conditions produced by our simulations are used to calculate the emission lines of superwinds for various parameters, which allow us to explore implications of non-equilibrium ionization for starburst regions with potential radiative cooling.
The focus of this work is to comprehensively understand hydro-dynamical back-flows and their role in dynamics and non-thermal spectral signatures particularly during the initial phase of X-shaped radio galaxies. In this regard, we have performed axisymmetric (2D) and three dimensional (3D) simulations of relativistic magneto-hydrodynamic jet propagation from tri-axial galaxies. High-resolution dynamical modelling of axisymmetric jets has demonstrated the effect of magnetic field strengths on lobe and wing formation. Distinct X-shape formation due to back-flow and pressure gradient of ambient is also observed in our 3D dynamical run. Furthermore, the effect of radiative losses and diffusive shock acceleration on the particle spectral evolution is demonstrated, which particularly highlights how crucial their contributions are in the emission signature of these galaxies. This imparts a significant effect on the galaxy’s equipartition condition, indicating that one must be careful in extending its use in estimating other parameters, as the criterion evolves with time.
We present the results of global three-dimensional radiation magnetohydrodynamic simulations of the formation of soft X-ray emitting regions in active galactic nuclei by applying a radiation magnetohydrodynamic code based on the M1-closure scheme. The effect of Compton cooling is taken into account. When the surface density of the accretion flow exceeds the upper limit of the radiatively inefficient accretion flow (RIAF), the optically thin, hot accretion flow near the black hole co-exists with the soft X-ray emitting, warm (T = 106 – 107 K) Comptonized region around r = 20 – 40rs, where rs is the Schwarzschild radius. Numerical results indicate that when the accretion rate approaches the Eddington accretion rate, the warm Comptonized region stays in optically thin for effective optical depth, Thomson thick, and radiation pressure dominant state. This region is found to oscillate between a geometrically thin, cool state and a geometrically thick state inflated by radiation pressure. The time variability of the accretion flow is consistent with that of the narrow-line Seyfert 1 galaxies.
Multiphase outflows driven by active galactic nuclei (AGN) have a profound impact on the evolution of their host galaxies. The effects of AGN feedback are especially prominent in the brightest cluster galaxies (BCGs) of cool-core clusters, where there is a concentration of gas in all phases, ranging from cold molecular gas to hot, >107 K ionized plasma. In this proceeding I describe recent simulation efforts to understand the formation and evolution of the 10-kpc-scale Hα-emitting filaments driven by AGN activities. Combined with observed star formation regions co-spatial with the filaments, this feedback mechanism can directly contribute to the growth of the central galaxy, albeit delayed by the characteristic radiative cooling timescale, ∼10 Myr, of the outflowing plasma.
To study the dynamics of relativistic flows in astrophysical objects such as radio jets, we have developed a new special relativistic hydrodynamic (RHD) code based on the weighted essentially non-oscillatory (WENO) scheme, a high-order finite difference scheme. The code includes different WENO versions, and high-order time integration methods such as the 4th-order accurate Runge-Kutta (RK4) and strong stability preserving RK (SSPRK), as well as the equations of state (EOSs) that closely approximate the EOS of the single-component perfect gas in relativistic regime. Additionally, it is optimized for the reproduction of complex structures in multi-dimensional flows, and implements a modification of eigenvalues for the acoustic modes to effectively control carbuncle instability. As the first application of the code, we have simulated ultra-relativistic jets of FR II radio galaxies, and studied the nonlinear flow structures, such as shocks, velocity shear, and turbulence, through large-scale.
There are indications that the magnetic field evolution in galaxies might be massively shaped by tidal interactions and mergers between galaxies. The details of the connection between the evolution of magnetic fields and that of their host galaxies is still a field of research.
We use a combined approach of magnetohydrodynamics for the baryons and an N-body scheme for the dark matter to investigate magnetic field amplification and evolution in interacting galaxies.
We find that, for two colliding equal-mass galaxies and for varying initial relative spatial orientations, magnetic fields are amplified during interactions, yet cannot be sustained. Furthermore, we find clues for an active mean-field dynamo.
The physical properties of AGN such as accretion rate, column density, temperature of hot corona and other characteristics can be found from X-ray spectral data. We present the results of spatial and spectral analysis for Sy2 type galaxy NGC 3081 obtained with different mathematical tools of the Chandra Interactive Analysis of Observations software. We found evidence of extended emission in 0.5-3.0 keV as well as derived parameters for model A: photon index , column density , warm component and hot component . We detected the presence of a component of the reflection spectrum, Fe Kα emission line with and .
We present Ekster, a new method for simulating the formation and dynamics of individual stars in a relatively low-resolution gas background. Here, we use Ekster to simulate star cluster formation in two different regions from each of two galaxy models with different spiral potentials. We simulate these regions for 3 Myr to study where and how star clusters form. We find that massive GMC regions form more massive clusters than sections of spiral arms. Additionally we find that clusters form both by accreting gas and by merging with other proto-clusters, the latter happening more frequently in the denser GMC regions.
Multidimensional mathematical analysis, like Machine Learning techniques, determines the different features of objects, which is difficult for the human mind. We create a machine learning model to predict galaxies’ detailed morphology (∼ 300000 SDSS-galaxies with z < 0.1) and train it on a labeled dataset defined within the Galaxy Zoo 2 (GZ2). We use convolutional neural networks (CNNs) to classify the galaxies into five visual types (completely rounded, rounded in-between, smooth cigar-shaped, edge-on, and spiral) and 34 morphological classes attaining >94% of accuracy for five-class morphology prediction except for the cigar-shaped (∼ 87%) galaxies.