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Author: Andrew Fox
Publisher: Springer
ISBN: 3319525123
Category : Science
Languages : en
Pages : 386
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Book Description
This edited volume presents the current state of gas accretion studies from both observational and theoretical perspectives, and charts our progress towards answering the fundamental yet elusive question of how galaxies get their gas. Understanding how galaxies form and evolve has been a central focus in astronomy for over a century. These studies have accelerated in the new millennium, driven by two key advances: the establishment of a firm concordance cosmological model that provides the backbone on which galaxies form and grow, and the recognition that galaxies grow not in isolation but within a “cosmic ecosystem” that includes the vast reservoir of gas filling intergalactic space. This latter aspect in which galaxies continually exchange matter with the intergalactic medium via inflows and outflows has been dubbed the “baryon cycle”. The topic of this book is directly related to the baryon cycle, in particular its least well constrained aspect, namely gas accretion. Accretion is a rare area of astrophysics in which the basic theoretical predictions are established, but the observations have been as yet unable to verify the expectations. Accretion has long been seen around the Milky Way in so-called High Velocity Clouds, but detecting accretion even around nearby galaxies has proved challenging; its multi-phase nature requires sensitive observations across the electromagnetic spectrum for full characterization. A promising approach involves looking for kinematic signatures, but accretion signatures are often confused with internal motions within galaxies. Accretion studies therefore touch a wide range of astrophysical processes, and hence a wide cross-section of the astronomical community. As observational facilities are finally able to access the wavelength ranges and depths at which accretion processes may be manifest, the time is right to survey these multiple lines of investigation and determine the state of the field in accretion studies of the baryon cycle.
Author: Andrew Fox
Publisher: Springer
ISBN: 3319525123
Category : Science
Languages : en
Pages : 386
Get Book Here
Book Description
This edited volume presents the current state of gas accretion studies from both observational and theoretical perspectives, and charts our progress towards answering the fundamental yet elusive question of how galaxies get their gas. Understanding how galaxies form and evolve has been a central focus in astronomy for over a century. These studies have accelerated in the new millennium, driven by two key advances: the establishment of a firm concordance cosmological model that provides the backbone on which galaxies form and grow, and the recognition that galaxies grow not in isolation but within a “cosmic ecosystem” that includes the vast reservoir of gas filling intergalactic space. This latter aspect in which galaxies continually exchange matter with the intergalactic medium via inflows and outflows has been dubbed the “baryon cycle”. The topic of this book is directly related to the baryon cycle, in particular its least well constrained aspect, namely gas accretion. Accretion is a rare area of astrophysics in which the basic theoretical predictions are established, but the observations have been as yet unable to verify the expectations. Accretion has long been seen around the Milky Way in so-called High Velocity Clouds, but detecting accretion even around nearby galaxies has proved challenging; its multi-phase nature requires sensitive observations across the electromagnetic spectrum for full characterization. A promising approach involves looking for kinematic signatures, but accretion signatures are often confused with internal motions within galaxies. Accretion studies therefore touch a wide range of astrophysical processes, and hence a wide cross-section of the astronomical community. As observational facilities are finally able to access the wavelength ranges and depths at which accretion processes may be manifest, the time is right to survey these multiple lines of investigation and determine the state of the field in accretion studies of the baryon cycle.
Author: Muhammad Latif
Publisher: World Scientific
ISBN: 9813227966
Category : Science
Languages : en
Pages : 376
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Book Description
The formation of the first supermassive black holes is one of the main open questions in our understanding of high-redshift structure formation. In this book, we aim to provide a summary of state-of-the-art modern research on this topic, exploring the formation of massive black holes from a fluid-dynamical, stellar-dynamical and chemical perspective. The book thus presents a solid theoretical foundation, a comparison with current observations and future observational perspectives with upcoming missions such as the Square Kilometre Array, the European Extremely Large Telescope, the Euclid satellite as well as possible detections via gravitational waves.
Author: Yujin Yang
Publisher:
ISBN:
Category :
Languages : en
Pages : 476
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Book Description
This thesis focuses primarily on how two important processes --- galaxymergers and gas accretion from the surrounding intergalactic medium ---affect the evolution of galaxies. Using post-starburst, or E+A, galaxies as a marker sample that undergoesa rapid transition from gas-rich star-forming galaxies to quiescent, passively-evolving E/S0s, we study what triggers E+A evolution andwhat E+A galaxies will become after the fading of their young stellarpopulation. With high resolution HST WFPC2/ACS imaging, we investigatetheir small and large scale properties, including their detailedmorphologies, bulge fractions, color gradients, scaling relationships, and newly formed star-clusters. 70% of E+A galaxies show disturbancesand tidal features indicating a merger origin and all their propertiesare either consistent with those of E/S0s or, if left to evolve passively, will become like those of early-types. Using cosmological simulations, we study hydrogen and helium gravitationalcooling radiation from gas accretion by young galaxies, finding thatobserving optically thin cooling lines such as HeII 1640 and hydrogenHalpha is critical in understanding the nature of galaxies forming viagas-accretion. To obtain an unbiased sample of Lyman alpha blobs thatwill allow us to follow-up their optically thin Halpha lines in the NIR, we conduct a blind, wide-field, narrow-band imaging survey for Lymanalpha blobs. After searching over 4.82 deg2̂, we discover four blobsthat we spectroscopically confirm to lie at z=2.3. The properties ofthese blobs are diverse: two blobs are X-ray-detected and have broadoptical emission lines (e.g., CIV) characteristic of AGN. The other50\% of blobs are not X-ray or optically-detected as AGN down tosimilar limits. The number density of the four blobs is extremely low,3̃ x 10-̂6 Mpc-̂3, comparable to that of galaxy clusters at similarredshifts. The two X-ray undetected blobs are separated by only70"(550 kpc) and have almost identical redshifts (corresponding to
Author: Hsiang-Hsu Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Author: Juhan Frank
Publisher: Cambridge University Press
ISBN: 9780521629577
Category : Science
Languages : en
Pages : 390
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Book Description
Accretion Power in Astrophysics examines accretion as a source of energy in both binary star systems containing compact objects, and in active galactic nuclei. Assuming a basic knowledge of physics, the authors describe the physical processes at work in accretion discs and other accretion flows. The first three chapters explain why accretion is a source of energy, and then present the gas dynamics and plasma concepts necessary for astrophysical applications. The next three chapters then develop accretion in stellar systems, including accretion onto compact objects. Further chapters give extensive treatment of accretion in active galactic nuclei, and describe thick accretion discs. A new chapter discusses recently discovered accretion flow solutions. The third edition is greatly expanded and thoroughly updated. New material includes a detailed treatment of disc instabilities, irradiated discs, disc warping, and general accretion flows. The treatment is suitable for advanced undergraduates, graduate students and researchers.
Author: Claude R. Canizares
Publisher:
ISBN:
Category :
Languages : en
Pages : 42
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Book Description
Author: Dylan Nelson
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Despite significant advances in the numerical modeling of galaxy formation and evolution, it is clear that a satisfactory theoretical picture of how galaxies acquire their baryons across cosmic time remains elusive. In this thesis we present a computational study which seeks to address the question of how galaxies get their gas. We make use of new, more robust simulation techniques and describe the first investigations of cosmological gas accretion using a moving-mesh approach for solving the equations of continuum hydrodynamics.
Author: Nicolas Cornuault
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
We now understand theoretically that galaxy evolution involves inflows of “cold” gas from the cosmic web. But corresponding models grow galaxies with amounts of baryons larger than observed galaxies. To overcome this issue, theorists focus on making star formation inefficient by massively blowing gas out of star-forming disks. I explore a different road, investigating processes that may moderate gas accretion onto disks. We present a phenomenological scenario where gas accretion flows - if it is shocked - become biphasic and, as a result, turbulent. In this framework, we show that the formation of warm, turbulent clouds, embedded in a hot component, occurs in the important mass range of ∼ 10^11 - 10^13 Msun, where the bulk of stars have formed in galaxies. Gas accreted from intergalactic filaments (IGF) may eventually lose coherence and mix with the ambient halo gas. The direct interaction between galaxy feedback and accretion streams is thus more likely. Moderating the accretion efficiency may help to alleviate a number of significant challenges in theoretical galaxy formation. Using the code Ramses, I performed a zoom-in simulation and extracted the results for a particular accreting IGF into a halo of ∼ 3 10^11 Msun at z ∼ 2. I investigate the gas thermodynamics and structuration, along and across the filament, with respect to dark matter. I study several key quantities as they evolve along the filament and derive a refined paradigm to study filaments, as well as consequences regarding their fate after entering a halo. I finally make use of these results to extrapolate gas processes that the simulation may not have captured accurately.
Author: Hannah V. Bish
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
Author: Ignacio Ferreras
Publisher: UCL Press
ISBN: 1911307614
Category : Science
Languages : en
Pages : 200
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Book Description
Galaxies, along with their underlying dark matter halos, constitute the building blocks of structure in the Universe. Of all fundamental forces, gravity is the dominant one that drives the evolution of structures from small density seeds at early times to the galaxies we see today. The interactions among myriads of stars, or dark matter particles, in a gravitating structure produce a system with fascinating connotations to thermodynamics, with some analogies and some fundamental differences. Ignacio Ferreras presents a concise introduction to extragalactic astrophysics, with emphasis on stellar dynamics, and the growth of density fluctuations in an expanding Universe. Additional chapters are devoted to smaller systems (stellar clusters) and larger ones (galaxy clusters). Fundamentals of Galaxy Dynamics, Formation and Evolution is written for advanced undergraduates and beginning postgraduate students, providing a useful tool to get up to speed in a starting research career. Some of the derivations for the most important results are presented in detail to enable students appreciate the beauty of maths as a tool to understand the workings of galaxies. Each chapter includes a set of problems to help the student advance with the material.
