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Using Hydrodynamic Simulations To Understand The Structure And Composition Of The Circumgalactic Medium Of Milky Way Sized Galaxies
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Book Synopsis Using Hydrodynamic Simulations to Understand the Structure and Composition of the Circumgalactic Medium of Milky Way-sized Galaxies by : Munier Salem
Download or read book Using Hydrodynamic Simulations to Understand the Structure and Composition of the Circumgalactic Medium of Milky Way-sized Galaxies written by Munier Salem and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We explore the structure and evolution of baryons within Milky Way-sized halos (M ~ 1012 Msun) via hydrodynamic simulations. First, we employ a two-fluid model to study the dynamics of a relativistic, diffusive cosmic ray proton (CR) fluid interacting with the thermal interstellar medium (ISM). This model was implemented into the eulerian hydrodynamics code enzo, used throughout this dissertation. After testing this model on analytically tractable scenarios in one dimension, it is unleashed upon an idealized disk simulation in a rapidly-star forming setting, where we find evidence for robust, mass-loaded winds driven by the diffusive CR fluid. These winds reduce the galaxy’s star formation rate (SFR) and circulate on order as much mass into winds as into forming stars. We then extend this model to a cosmological setting where the diffuse CR fluid proves capable of redistributing star formation within the forming disk, reducing the overly-peaked rotation curves in non-CR runs and producing thin, extended disks with visible spiral structure.
Book Synopsis Understanding the Circumgalactic Medium Through Hydrodynamic Simulations and Hubble's Cosmic Origins Spectrograph by : Amanda Brady Ford
Download or read book Understanding the Circumgalactic Medium Through Hydrodynamic Simulations and Hubble's Cosmic Origins Spectrograph written by Amanda Brady Ford and published by . This book was released on 2014 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: My dissertation focuses on a relatively new field of study: the region immediately around galaxies known as the circumgalactic medium (CGM). The CGM holds vast quantities of mass and metals, yet its connection to galaxies is not well understood. My work uses cosmological hydrodynamic simulations and comparisons to data from Hubble's Cosmic Origins Spectrograph (COS) to understand the CGM's connection to galaxy evolution, gas accretion, outflows, star formation, and baryon cycling. This includes studies of the CGM's extent and physical conditions; the cause and nature of outflows; gas dynamics, including the first comprehensive study of tracers of inflowing and outflowing gas at low redshift (z=0.25); and direct comparison of theoretical results to observational data. Chapter 1 introduces my research and show its connection to galaxy evolution. Chapter 2 investigates hydrogen and metal line absorption around low-redshift galaxies in cosmological hydrodynamic simulations. This chapter studies different models for stellar outflows, physical conditions, and dependencies on halo mass. Chapter 3 examines the flow of gas into, out of, and around galaxies using a novel particle tracking technique. This chapter examines the baryon cycle in detail for our preferred model of stellar outflows. Chapter 4 compares our model results, including two separate prescriptions for outflows, with data from COS. We contrast these wind models, showing how they cycle baryons differently, and show degeneracies in observational diagnostics. In Chapter 5, I summarize and discuss plans for future research in this field, and how it can be more fully leveraged to understand galaxy evolution.
Book Synopsis Hydrodynamic Simulations and Tomographic Reconstructions of the Intergalactic Medium by : Casey William Stark
Download or read book Hydrodynamic Simulations and Tomographic Reconstructions of the Intergalactic Medium written by Casey William Stark and published by . This book was released on 2015 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Intergalactic Medium (IGM) is the dominant reservoir of matter in the Universe from which the cosmic web and galaxies form. The structure and physical state of the IGM provides insight into the cosmological model of the Universe, the origin and timeline of the reionization of the Universe, as well as being an essential ingredient in our understanding of galaxy formation and evolution. Our primary handle on this information is a signal known as the Lyman-alpha forest (or Ly-alpha forest) -- the collection of absorption features in high-redshift sources due to intervening neutral hydrogen, which scatters HI Ly-alpha photons out of the line of sight. The Ly-alpha forest flux traces density fluctuations at high redshift and at moderate overdensities, making it an excellent tool for mapping large-scale structure and constraining cosmological parameters. Although the computational methodology for simulating the Ly-alpha forest has existed for over a decade, we are just now approaching the scale of computing power required to simultaneously capture large cosmological scales and the scales of the smallest absorption systems. My thesis focuses on using simulations at the edge of modern computing to produce precise predictions of the statistics of the Ly-alpha forest and to better understand the structure of the IGM. In the first part of my thesis, I review the state of hydrodynamic simulations of the IGM, including pitfalls of the existing under-resolved simulations. Our group developed a new cosmological hydrodynamics code to tackle the computational challenge, and I developed a distributed analysis framework to compute flux statistics from our simulations. I present flux statistics derived from a suite of our large hydrodynamic simulations and demonstrate convergence to the per cent level. I also compare flux statistics derived from simulations using different discretizations and hydrodynamic schemes (Eulerian finite volume vs. smoothed particle hydrodynamics) and discuss differences in their convergence behavior, their overall agreement, and the implications for cosmological constraints. In the second part of my thesis, I present a tomographic reconstruction method that allows us to make 3D maps of the IGM with Mpc resolution. In order to make reconstructions of large surveys computationally feasible, I developed a new Wiener Filter application with an algorithm specialized to our problem, which significantly reduces the space and time complexity compared to previous implementations. I explore two scientific applications of the maps: finding protoclusters by searching the maps for large, contiguous regions of low flux and finding cosmic voids by searching the maps for regions of high flux. Using a large N-body simulation, I identify and characterize both protoclusters and voids at z = 2.5, in the middle of the redshift range being mapped by ongoing surveys. I provide simple methods for identifying protocluster and void candidates in the tomographic flux maps, and then test them on mock surveys and reconstructions. I present forecasts for sample purity and completeness and other scientific applications of these large, high-redshift objects.
Book Synopsis Unveiling the Circumgalactic Medium Using a Cloud-by-cloud, Multiphase, Bayesian Ionization Modeling Approach by : Sameer
Download or read book Unveiling the Circumgalactic Medium Using a Cloud-by-cloud, Multiphase, Bayesian Ionization Modeling Approach written by Sameer and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis investigates the physicochemical nature of the gaseous structures in the vicinity of galaxies. Intervening absorption systems seen in the spectra of background quasars probe the circumgalactic medium (CGM) around galaxies and can provide insights into the nature of the gas. The CGM is a dynamic and multiphase interface between a galaxy and its surroundings. Unraveling the origin of the multiphase gas in the CGM is important because it potentially allows us to learn about the processes that supply inflowing gas to the galaxy, enrich the surroundings with metal-rich outflows, and send enriched material back to the galaxy as recycled accretion. First, I present a new method aimed at improving the efficiency of component-by-component ionization modeling of intervening quasar absorption line systems. I carry out cloud-by-cloud, multiphase modeling making use of CLOUDY and Bayesian methods to extract physical properties from an ensemble of absorption profiles. As a demonstration of the method, I focus on four weak, low ionization absorbers at low redshift, because they are multi-phase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds and show that the values vary from component to component across the absorption profile. This method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise. The measured Doppler parameter, b, of the optimized transition provides a constraint on the Doppler parameter of HI, thus providing leverage in metallicity measurements even when hydrogen lines are saturated. I present several tests of this methodology, demonstrating that I can recover the input parameters from simulated profiles. I also consider how the model results are affected by which radiative transitions are covered by observations (for example how many HI transitions) and by uncertainties in the $b$ parameters of optimized transitions. I discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the CGM. Next, I present an absorption line study of the physical and chemical properties of the Leo HI Ring and the Leo I Group as traced by 11 quasar sightlines spread over a ~ 600 kpc x 800 kpc region. Using HST/COS G130/G160 archival observations as constraints, I couple cloud-by-cloud, multiphase, Bayesian ionization modeling with galaxy property information to determine the plausible origin of the absorbing gas along these sightlines. I find absorption plausibly associated with the Leo Ring towards five sightlines. The absorption along these five sightlines is stronger in metal lines than expected from individual galaxies, indicative of multiple contributions, and of the complex kinematics of the region. Along three other sightlines, I find absorption likely to be associated with individual galaxies, intragroup gas, and/or large-scale filamentary structure. I also identify three sightlines within a 7° x6° field around the Leo Ring, along which I do not find any absorption. I find that the metallicities associated with the Leo Ring are generally high, with values between solar and several times solar. The inferred high metallicities are consistent with the origin of the ring as tidal debris from a major galaxy merger. Next, I analyze archival ultraviolet quasar spectra from HST/COS covering 47 absorption line systems produced by the CGM of galaxies that have galaxy imaging with HST with known impact parameters and orientations. I conducted a large statistical study with this sample to determine if the metallicities of any of the multiple structures depend on orientation. Cloud-by-cloud, multiphase Bayesian modeling was applied to provide constraints on metallicity, density, and temperature of multiple regions along the sightline. I find that the high metallicity clouds span a large range of velocities while the low metallicity clouds are found close to the systemic velocity of the galaxy. I also find that clouds close to the systemic velocity show a full range of metallicities. High-velocity clouds, on the other hand, show a tendency for tracing high metallicities. I do not find metallicity trends with azimuthal angle, inclination, impact parameter, or galaxy type. Despite the lack of a link between azimuthal angle and metallicity, the independent effects of inflows and outflows are seen in absorption systems using cloud-by-cloud modeling. Finally, I employ the same techniques that I have developed with real absorption systems to investigate absorption systems in cosmological simulations in order to assess the efficacy of the methods in extracting true properties from simulations. I find that the assumption of photoionization thermal equilibrium should be relaxed, particularly for the high ionization gas phases, and this assumption only holds in a particular regime of the CGM phase space. For a discrete distribution of clouds, the inferred posterior distributions contain the actual values in the simulations. For a complex and continuous distribution of clouds in simulations, I find that the properties of the best-constrained clouds agree well with the true values. These findings strengthen our confidence in reliably extracting the properties of the CGM from observational datasets.
Book Synopsis Probing Galaxy Evolution Through Numerical Simulations by : Maan H. Hani
Download or read book Probing Galaxy Evolution Through Numerical Simulations written by Maan H. Hani and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Large observational surveys have compiled substantial galaxy samples with an array of different properties across cosmic time. While we have a broad understanding of how galaxies grow and build their observable properties, the details of galaxy growth and evolution pose a fundamental challenge to galaxy evolution theories. Nonetheless, galaxy evolution is ultimately regulated by the properties of the gas reservoir. In this thesis I use numerical simulations to answer key questions related to the galactic gas reservoir, and galaxy mergers: a major transformational process. In Chapter 2 I present an analysis of 28 simulated L* galaxies to understand the physical processes that shape the massive gas reservoir surrounding galaxies (i.e. the circum-galactic medium; CGM). I show that (1) the gas and metal content of the CGM is driven by galaxy growth and the strength/presence of feedback processes, and (2) the ionisation and internal structures of the CGM are shaped by galactic outflows, and active galactic nucleus luminosity. Albeit dependent on internal galactic properties and the physical processes that shape them, the CGM remains greatly diverse, thus posing a challenge for observational surveys. As a follow-up to my study of normal L* galaxy gas halos, in Chapter 3 I present a theoretical study of the effect of galaxy mergers on the CGM. I demonstrate that galaxy mergers can leave a strong imprint on the CGM's gas and metal content, metallicity, and size. The merger can increase (1) the CGM's metallicity by 0.2-0.3 dex within 0.5 Gyr post-merge, and (2) the metal covering fractions by factors of 2-3. In spite of the increase in the CGM's metal content, the hard ionising field during the merger can drive a decline in the covering fractions of commonly observed ions. In Chapter 4 I shift focus to star formation, particularly the effects of galaxy mergers on star formation. While the effects of galaxy mergers have been proven observationally, theoretical predictions are limited to small binary merger suites and cosmological zoom-in studies. I present a statistical study of 27,691 post-merger galaxies from IllustrisTNG to quantify the effect of galaxy mergers on galactic star formation. I report a dependence in the merger-induced star formation rate (SFR) on mass ratio, stellar mass, gas fraction, and galaxy SFR. I also track the evolution of the effects of galaxy mergers demonstrating their decay over ~500 Myr. In Chapter 6, I leverage galactic scaling relations to extend my work on the effects of galaxy mergers to resolved scales. However, before using the simulated resolved scaling relations, I first examine their existence and robustness. In Chapter 5, I demonstrate the emergence of the kpc-scale star forming main sequence (rSFMS) in the FIRE-2 simulations. Nonetheless, the slope of the rSFMS is dependent on the (1) star formation tracer's timescale, and (2) observed resolution, which I propose is caused by the clumpiness of star formation. I develop a toy model that quantitatively captures the effects of clumpy star formation. I then illustrate how the model can be used to characterise the mass of star-forming clumps. Having demonstrated the existence and robustness of known scaling relations in numerical simulations, I explore the effects of galaxy mergers on resolved scales in Chapter 6. I generate synthetic observations for 1,927 post-mergers in IllustrisTNG and examine the radially-dependent merger-driven SFR enhancement, and metallicity suppression in post-mergers. Galaxy mergers preferentially boost star formation in the centres and suppress metallicities globally. The effects of the merger depends on galaxy properties such as stellar mass, SFR, mass ratio, and gas fraction.
Book Synopsis Interplay of Galactic Winds and Circumgalactic Media by : Drummond Fielding
Download or read book Interplay of Galactic Winds and Circumgalactic Media written by Drummond Fielding and published by . This book was released on 2018 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: The flow of gas through the circumgalactic medium (CGM) regulates galaxy growth over cosmic time. Observations have recently revealed a complex multi-phase structure in the CGM that has challenged many of the established theories and highlights significant gaps in our understanding of this critical aspect of galaxy formation. The spatial scales relevant to the CGM span a huge range with its structure and evolution determined by small-scale processes—such as the launching of galactic winds by clustered supernovae and thermal instability in the hydrostatic halo—and large-scale processes—such as cosmological accretion. I will describe my efforts to use controlled numerical simulations to understand the details and interplay of these multi-scale processes in order to develop a coherent picture of the CGM that is consistent with observations.
Book Synopsis Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality by : Nickolay Y. Gnedin
Download or read book Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality written by Nickolay Y. Gnedin and published by Springer. This book was released on 2015-09-09 with total page 375 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains the elaborated and updated versions of the 24 lectures given at the 43rd Saas-Fee Advanced Course. Written by four eminent scientists in the field, the book reviews the physical processes related to star formation, starting from cosmological down to galactic scales. It presents a detailed description of the interstellar medium and its link with the star formation. And it describes the main numerical computational techniques designed to solve the equations governing self-gravitating fluids used for modelling of galactic and extra-galactic systems. This book provides a unique framework which is needed to develop and improve the simulation techniques designed for understanding the formation and evolution of galaxies. Presented in an accessible manner it contains the present day state of knowledge of the field. It serves as an entry point and key reference to students and researchers in astronomy, cosmology, and physics.
Book Synopsis Formation of Disk Galaxies in CDM Using Particle-based Hydrodynamics by : Qirong Zhu
Download or read book Formation of Disk Galaxies in CDM Using Particle-based Hydrodynamics written by Qirong Zhu and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past several decades, the current standard model of cosmology (CDM) has been established. Accurate measurements of cosmological parameters provide us a well defined initial condition where we can connect the tiny fluctuations in the early smooth Universe with the rich structures observed at more recent times using direct numerical simulations. Although the nature of dark matter remains elusive, its dynamic evolution can be well studied since gravity is the only force at play.On large scales, hierarchical structures form in the computer simulations which closely resemble the observed galaxy clustering properties. On small scales, how- ever, various tensions arise when numerical calculations are confronted with the observed galaxies. Nearby dwarf galaxies show significant systematic deviations from the computer calculations of CDM. Thin disk geometries and the lack of luminous classical bulge in many nearby galaxies pose additional challenges to CDM cosmology as well. While disk galaxies in the local Universe are ubiqui- tous, forming realistic disk galaxies in hydrodynamic simulations has proven to be a decade-long challenge.In this dissertation, I present my investigation of a Milky Way-sized galaxy formation using two particle-based methods. A particle-based code is naturally suited in cosmological hydrodynamic simulations because it offers an adaptive and flexible description to gas dynamics. Realistic disk galaxies are formed with both SPH and a new Gizmo code, which combines the strengths of traditional SPH and grid-based method.
Book Synopsis Galaxy Formation and Mergers with Stars and Massive Black Holes by : Chi-hun Kim
Download or read book Galaxy Formation and Mergers with Stars and Massive Black Holes written by Chi-hun Kim and published by Stanford University. This book was released on 2011 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: While mounting observational evidence suggests the coevolution of galaxies and their embedded massive black holes (MBHs), a comprehensive astrophysical understanding which incorporates both galaxies and MBHs has been missing. To tackle the nonlinear processes of galaxy formation, we develop a state-of-the-art numerical framework which self-consistently models the interplay between galactic components: dark matter, gas, stars, and MBHs. Utilizing this physically motivated tool, we present an investigation of a massive star-forming galaxy hosting a slowly growing MBH in a cosmological LCDM simulation. The MBH feedback heats the surrounding gas and locally suppresses star formation in the galactic inner core. In simulations of merging galaxies, the high-resolution adaptive mesh allows us to observe widespread starbursts via shock-induced star formation, and the interplay between the galaxies and their embedding medium. Fast growing MBHs in merging galaxies drive more frequent and powerful jets creating sizable bubbles at the galactic centers. We conclude that the interaction between the interstellar gas, stars and MBHs is critical in understanding the star formation history, black hole accretion history, and cosmological evolution of galaxies. Expanding upon our extensive experience in galactic simulations, we are well poised to apply this tool to other challenging, yet highly rewarding tasks in contemporary astrophysics, such as high-redshift quasar formation.
Book Synopsis Dynamics of the Milky Way by : Jason Sanders
Download or read book Dynamics of the Milky Way written by Jason Sanders and published by Springer. This book was released on 2015-06-15 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents a study of methods useful for modeling and understanding dynamical systems in the Galaxy. A natural coordinate system for the study of dynamical systems is the angle-action coordinate system. New methods for the approximation of the action-angle variables in general potentials are presented and discussed. These new tools are applied to the construction of dynamical models for two of the Galaxy’s components: tidal streams and the Galactic disc. Tidal streams are remnants of tidally stripped satellites in the Milky Way that experience the effects of the large scale structure of the Galactic gravitational potential, while the Galactic disc provides insights into the nature of the Galaxy near the Sun. Appropriate action-based models are presented and discussed for these components, and extended to include further information such as the metallicity of stars.
Book Synopsis Galactic Gas Flows from Halo to Disk by : Hannah V. Bish
Download or read book Galactic Gas Flows from Halo to Disk written by Hannah V. Bish and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The evolution of galaxies is closely linked to the exchange of gas between their disk and the circumgalactic medium (CGM) - the massive, extended, diffuse halo of gas in which galaxies are embedded. Recent advances in high-resolution spectroscopy have enabled observers to firmly establish the key role played by the CGM in the life cycle of galaxies: it is the hiding place of at least half of all galactic baryons, acting as a massive reservoir that replenishes the supply of fuel for star formation via gas accretion onto the disk. However, this nearly-invisible halo gas is challenging to observe, and we are still missing a complete picture of its distribution, kinematics, and multiphase structure. In this thesis, I use the Milky Way as a case study to shed light on the nature of cool and warm CGM gas flows, taking advantage of the abundance of quasar and stellar sightlines which probe the Galactic CGM. In particular, I focus on the behavior of low-velocity gas, which is often overlooked by CGM studies because it is difficult to measure in isolation. I show that local CGM gas is predominantly inflowing, place constraints on the inflowing cloud sizes, and determine that these clouds lie close to the disk. I use a novel spectral differencing technique to correct for foreground absorption along sightlines through the Galactic halo, and present the first unobscured measurements of the Milky Way's extended low-velocity CGM. The results demonstrate that either the warm CGM does not have a spherical morphology, as is often assumed for star-forming galaxies, or that the Milky Way is not a typical star-forming galaxy. Finally, I find that inflow velocities are higher for warmer gas, suggesting a picture in which warm accreting gas slows down and cools as it approaches the disk. The mass accretion rates of these inflows indicate that a significant fraction of star-formation fuel may accrete onto the disk at low velocities.
Book Synopsis Simulations of Galaxy Formation and Large Scale Structure by : Felix Stoehr
Download or read book Simulations of Galaxy Formation and Large Scale Structure written by Felix Stoehr and published by Sudwestdeutscher Verlag Fur Hochschulschriften AG. This book was released on 2009-12 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this work we use the N-body resimulation technique to address aspects of structure formation. In the first chapter we study the influence of the local environment of DM haloes on their properties. In the second chapter we address the so-called "substructure problem" which is one of the major challenges of the CDM model of cosmology. We perform ultra-high resolution simulations of the assembly of a Milky Way type dark matter halo within its full cosmological context and propose a new analytical fitting formula (SWTS) which provides a better fit to the simulated Milky Way halo than the NFW or Moore profiles do. In the third chapter we use our ultra-high resolution simulations to study the possible -ray signal from dark matter annihilation. If such a signal was detected, the nature of the dark matter, the answer to one of the most important questions of modern cosmology, would be known. (urn: nbn: de: bvb:19-16446)"
Book Synopsis Hydrodynamical Simulations of Turbulence in Galactic Centers by : Jesus Mario Salas
Download or read book Hydrodynamical Simulations of Turbulence in Galactic Centers written by Jesus Mario Salas and published by . This book was released on 2021 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence is a prevalent phenomenon in the interstellar medium, and in particular, in the environment at the centers of galaxies. For example, detailed observations of the Milky Way's Central Molecular Zone (CMZ) have revealed that it has a complex and turbulent structure. It is suspected that turbulence is responsible for maintaining the relatively high temperatures in the CMZ, as well as for suppressing star formation. Therefore, turbulence is a key phenomenon for understanding the dynamics and energetics of this region. In galactic-scale simulations, turbulence is often modeled by invoking star formation and supernovae feedback. However, these phenomena do not appear to be sufficient for explaining the high-velocity dispersion observed in the CMZ, indicating that additional gas-stirring processes are likely to be operating. In this thesis, I present a new numerical method to driveturbulence in galactic centers. Instead of relying on a particular physical mechanism, I have adopted a Fourier forcing module, which has the advantage of being independent of the actual sources of turbulence, but which is adjustable to the scales needed to match observations. I have applied this method using a Smoothed Particle Hydrodynamics (SPH) code. This turbulence injection method is capable of balancing the self-gravity of gas in different physical scenarios, which allows the simulations to be run for long timescales, thereby enabling my study of the effects of turbulence on the gas dynamics. First, I introduce this new numerical tool and present simulations of a simplistic model of the CMZ to showcase its performance and numerical convergence. I find that turbulence induces a flocculent spiral pattern similar to that observed in the centers of other galaxies. Furthermore, the driving module induces a turbulent viscosity which enhances mass inflowto the center. To further show the flexibility and applicability of this method, I present larger-scale simulations of galactic nuclear rings. Nuclear rings are a common feature of galaxies which form due to the effects of bar potentials, and the CMZ contains such a ring. I find that turbulence thickens nuclear rings and enhances mass accretion towards the center, both effects causedby turbulent viscosity. This mass inflow could explain the feeding of material from the CMZ to the inner few parsecs of the Galaxy. As a final example of my method's versatility, I performed simulations of the Circumnuclear Disk (CND) at the center of the Milky Way. The transient vs long-lived nature of the CND is widely debated in the literature. Some authors have argued that the observed stream morphology and non-axisymmetric density distribution implies that the CND is a transientstructure. However, the results of my simulations suggest that these arguments are not correct. I find that turbulent perturbation on sufficiently large scales, such as those that would be produced by supernova blast waves, creates a disk with a non-uniform density structure, and promotes the creation of streams that endure for longer than a few dynamical timescales. In conclusion, the work I present in this thesis shows that my injection method is a flexible tool that can be applied to a variety of physical scenarios. Furthermore, this method can be adapted to different hydrodynamical codes based on alternative hydrodynamics techniques.
Book Synopsis Comparing Simulations and Observations of Galaxy Evolution by : Cameron Bryce Hummels
Download or read book Comparing Simulations and Observations of Galaxy Evolution written by Cameron Bryce Hummels and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: First, we create a method for producing synthetic photometric images of grid-based hydrodynamical models for use in a direct comparison against observations in a variety of filter bands. We apply this method to a simulation of a cluster of galaxies to investigate the nature of the red-sequence/blue-cloud dichotomy in the galaxy color-magnitude diagram. Second, we implement several subgrid models governing the complex behavior of gas and stars on small scales in our galaxy models. Several numerical simulations are conducted with similar initial conditions, where we systematically vary the subgrid models, afterward assessing their efficacy through comparisons of their internal kinematics with observed systems. Third, we generate an additional method to compare observations with simulations, focusing on the tenuous circumgalactic medium. Informed by our previous studies, we investigate the sensitivity of this new mode of comparison to hydrodynamical subgrid prescription. Finally, we synthesize the results of these studies and identify future avenues of research.
Book Synopsis Hydrodynamic Simulations of Cosmological Galaxy Merger Trees by :
Download or read book Hydrodynamic Simulations of Cosmological Galaxy Merger Trees written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis we use cosmological merger trees and semi-analytic models of galaxy formation to provide the initial conditions for multi-merger hydrodynamic simulations. In this way we exploit the advantages of merger simulations (high resolution and detailed treatment of the gas physics) and semi-analytic models (cosmological background and low computational cost), and integrate them to create a novel tool. This approach allows us to study the evolution of various galaxy properties with an improved treatment of the gas components, including, for the first time, the hot gaseous halo from which gas cools and accretes onto the central disc. Using a suite of minor merger simulations we find that disc thickening is reduced relative to the collisionless case through the absorption of kinetic impact energy by the gas. In a following series of major merger simulations, we show that adding the hot gas component is a key ingredient in order to reproduce several observed properties of elliptical galaxies, like the abundance of fast rotators. Moreover, the presence of a gaseous halo reduces the starburst efficiency. We then focus on the effects of multiple concurrent mergers, which we found to be cosmologically more common than sequences of isolated binary mergers. For this, we investigate, whether accreted satellite stars can be distinguished kinematically from stars formed 'in situ' in the central galaxy, and find that this is only possible for a fraction of the disrupted satellites. Our simulations to date indicate that the combination of a detailed treatment of gas physics, high resolution, and a cosmological background, brings numerical simulations in better agreement with observations. Overall, the novel tool developed in this thesis will be very useful for pursuing a number of questions pertaining to the transformation of galaxy internal structure by mergers and accretion.
Book Synopsis Mapping the Circumgalactic Medium by : Matthew C. Wilde
Download or read book Mapping the Circumgalactic Medium written by Matthew C. Wilde and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work presented in this dissertation provides the groundwork for understanding key unresolved questions in the study of galaxy evolution: the circumgalactic medium (CGM) and the role of environment. I present a new survey that has the power to drastically improve our understanding of the CGM and use it to estimate the size of the CGM as a function of galactic mass. In addition, a novel method to reconstruct the cosmic web using Physarum polycephalum slime mold is presented and applied to the SDSS surveys. This cosmic web reconstruction was released publicly with SDSS DR17 and will allow exciting connections between galaxies and their environments to be illuminated, to distances greater than other previous catalogs.
Book Synopsis Models of the Galaxy and the Massive Spectroscopic Stellar Survey RAVE by : Tilmann Piffl
Download or read book Models of the Galaxy and the Massive Spectroscopic Stellar Survey RAVE written by Tilmann Piffl and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Numerical simulations of galaxy formation and observational Galactic Astronomy are two fields of research that study the same objects from different perspectives. Simulations try to understand galaxies like our Milky Way from an evolutionary point of view while observers try to disentangle the current structure and the building blocks of our Galaxy. Due to great advances in computational power as well as in massive stellar surveys we are now able to compare resolved stellar populations in simulations and in observations. In this thesis we use a number of approaches to relate the results of the two fields to each other. The major observational data set we refer to for this work comes from the Radial Velocity Experiment (RAVE), a massive spectroscopic stellar survey that observed almost half a million stars in the Galaxy. In a first study we use three different models of the Galaxy to generate synthetic stellar surveys that can be directly compared to the RAVE data. To do this we evaluate the RAVE selection function to great detail. Among the Galaxy models is the widely used Besancon model that performs well when individual parameter distribution are considered, but fails when we study chemodynamic correlations. The other two models are based on distributions of mass particles instead of analytical distribution functions. This is the first time that such models are converted to the space of observables and are compared to a stellar survey. We show that these models can be competitive and in some aspects superior to analytic models, because of their self-consistent dynamic history. In the case of a full cosmological simulation of disk galaxy formation we can recover features in the synthetic survey that relate to the known issues of the model and hence proof that our technique is sensitive to the global structure of the model. We argue that the next generation of cosmological galaxy formation simulations will deliver valuable models for our Galaxy. Testing these models with our approach will provide a direct connection between stellar Galactic astronomy and physical cosmology. In the second part of the thesis we use a sample of high-velocity halo stars from the RAVE data to estimate the Galactic escape speed and the virial mass of the Milky Way. In the course of this study cosmological simulations of galaxy formation also play a crucial role. Here we use them to calibrate and extensively test our analysis technique. We find the local Galactic escape speed to be 533 (+54/-41) km/s (90% confidence). With this result in combination with a simple mass model of the Galaxy we then construct an estimate of the virial mass of the Galaxy. For the mass profile of the dark matter halo we use two extreme models, a pure Navarro, Frenk & White (NFW) profile and an adiabatically contracted NFW profile. When we use statistics on the concentration parameter of these profile taken from large dissipationless cosmological simulations we obtain an estimate of the virial mass that is almost independent of the choice of the halo profile. For the mass M_340 enclosed within R_340 = 180 kpc we find 1.3 (+0.4/-0.3) x 10^12 M_sun. This value is in very good agreement with a number of other mass estimates in the literature that are based on independent data sets and analysis techniques. In the last part of this thesis we investigate a new possible channel to generate a population of Hypervelocity stars (HVSs) that is observed in the stellar halo. Commonly, it is assumed that the velocities of these stars originate from an interaction with the super-massive black hole in the Galactic center. It was suggested recently that stars stripped-off a disrupted satellite galaxy could reach similar velocities and leave the Galaxy. Here we study in detail the kinematics of tidal debris stars to investigate the probability that the observed sample of HVSs could partly originate from such a galaxy collision. We use a suite of $N$-body simulations following the encounter of a satellite galaxy with its Milky Way-type host galaxy. We quantify the typical pattern in angular and phase space formed by the debris stars and develop a simple model that predicts the kinematics of stripped-off stars. We show that the distribution of orbital energies in the tidal debris has a typical form that can be described quite accurately by a simple function. The main parameters determining the maximum energy kick a tidal debris star can get is the initial mass of the satellite and only to a lower extent its orbit. Main contributors to an unbound stellar population created in this way are massive satellites (M_sat > 10^9 M_sun). The probability that the observed HVS population is significantly contaminated by tidal debris stars appears small in the light of our results
