Author: Andrew Rodger Wetzel Publisher: ISBN: Category : Languages : en Pages : 408
Book Description
Mergers between distinct objects are a natural part of hierarchical structure formation. Mergers are also one of the most critical elements in the evolution of both galaxies and halos. I use high-resolution, cosmological volume simulations to explore galaxy and halo evolution and merging activity in a cosmological context, including environmental dependence, merger rates and dynamics, and how these processes in halos connect with those of galaxies. I first explore halo merging and evolution, focusing on its interplay with large-scale environment. While halo spatial clustering has been thought to depend only on mass, I ex- amine how spatial clustering depends on secondary parameters such as halo formation time, concentration, and recent merger history, a phenomenon known as "assembly bias". Next, I examine the extent to which close spatial pairs of objects can be used to predict mergers, finding limited utility to the pair-merger method arising from a competition between merger efficiency and completeness. I also explore the dependence of merging on environmental density, discovering that merging is less efficient in overdense environments. I then investigate how a massive galaxy/halo population at high redshift connects to a massive population of the same number density today, finding that scatter in mass growth and mergers between massive objects preclude a direct population mapping either forward or backward in time. In the latter part of this work, I explore the dynamics and mergers of galaxies in groups and clusters. I first examine the orbital distributions of satellite halos/galaxies at the time of infall onto a more massive host halo, finding that satellite orbits become more radial and penetrate deeper at higher host halo mass and higher redshift. I then track the evolution of galaxies in groups directly, examining the merger rates of galaxies over time and finding that galaxy mergers do not simply trace halo mergers. I also examine the small-scale environments of galaxy mergers, discovering that recently merged galaxies exhibit enhanced small-scale spatial clustering for a short time after a merger. Finally, by using abundance matching to assign stellar mass to subhalos, I explore the importance of merging vs. disruption processes for satellite galaxy evolution. I rigorously test the connection of galaxies to subhalos by comparing simulations against observed galaxy spatial clustering, satellite fractions, and cluster satellite luminosity functions, finding agreement in all cases.
Author: L. Feretti Publisher: Springer Science & Business Media ISBN: 0306480964 Category : Science Languages : en Pages : 329
Book Description
Mergers are the mechanisms by which galaxy clusters are assembled through the hierarchical growth of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. Many of the observed properties of clusters depend on the physics of the merging process. These include substructure, shock, intra cluster plasma temperature and entropy structure, mixing of heavy elements within the intra cluster medium, acceleration of high-energy particles, formation of radio halos and the effects on the galaxy radio emission. This book reviews our current understanding of cluster merging from an observational and theoretical perspective, and is appropriate for both graduate students and researchers in the field.
Author: Chi-hun Kim Publisher: Stanford University ISBN: Category : Languages : en Pages : 189
Book Description
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.
Author: Kyle Robert Stewart Publisher: ISBN: 9781109501018 Category : Languages : en Pages : 173
Book Description
There is a concern in galaxy formation that mergers are too common in LambdaCDM to explain the prominence of thin disk-dominated galaxies in the local universe. In my dissertation, I analyze merger histories of dark matter halos from high resolution N-body simulations and compare dark halo merger statistics to the observable properties of galaxies, in order to study the implications of cosmologically motivated merger histories. I use empirical relations between a galaxy's dark matter halo mass, stellar mass, and cold gas mass to investigate these merger histories in the context of galaxy evolution, focusing on a dark matter mass regime within an order of magnitude of the Milky Way. The principle results of this dissertation may be summarized as follows. Firstly, 70% of Milky Way-size halos have accreted an object with more than twice the mass of the Milky-Way's disk in the past 10 Gyr. To meet the observed fraction of disk dominated galaxies, mergers of this size must not always destroy galactic disks. Secondly, The merger rate of dark halos increases strongly with redshift. A simple `universal' fitting formula describes these merger rates as a function of halo mass, merger mass ratio, and redshift. Thirdly, the fraction of halos have ever experienced a gas poor major merger roughly matches the observed early-type morphological fractions within the regime M=10^11-13 Msun, providing a possible solution to disk survivability, if gas rich mergers do not destroy disk-dominated morphologies. Fourthly, because the mapping between dark matter halo mass and galaxy stellar mass (or baryonic mass) is a non-trivial function, it is important to distinguish between definitions of a merger "mass ratio'' that use dark matter, stellar, or galaxy baryonic masses as a means of comparison. For example, major dark matter mergers in smaller galaxies (Mvir
Author: Publisher: ISBN: Category : Galaxy mergers Languages : en Pages : 11
Book Description
We employ a high-resolution LCDM N-body simulation to present merger rate predictions for dark matter halos and investigate how common merger-related observables for galaxies - such as close pair counts, starburst counts, and the morphologically disturbed fraction - likely scale with luminosity, stellar mass, merger mass ratio, and redshift from z = 0 to z = 4. We provide a simple 'universal' fitting formula that describes our derived merger rates for dark matter halos a function of dark halo mass, merger mass ratio, and redshift, and go on to predict galaxy merger rates using number density-matching to associate halos with galaxies. For example, we find that the instantaneous merger rate of m/M> 0.3 mass ratio events into typical L (almost equal to)> fL{sub *} galaxies follows the simple relation dN/dt (asymptotically equal to) 0.03(1+f)Gyr−1 (1+z){sup 2.1}. Despite the rapid increase in merger rate with redshift, only a small fraction of> 0.4L{sub *} high-redshift galaxies ((almost equal to) 3% at z = 2) should have experienced a major merger (m/M> 0.3) in the very recent past (t 100 Myr). This suggests that short-lived, merger-induced bursts of star formation should not contribute significantly to the global star formation rate at early times, in agreement with observational indications. In contrast, a fairly high fraction ((almost equal to) 20%) of those z = 2 galaxies should have experienced a morphologically transformative merger within a virial dynamical time. We compare our results to observational merger rate estimates from both morphological indicators and pair-fraction based determinations between z = 0-2 and show that they are consistent with our predictions. However, we emphasize that great care must be made in these comparisons because the predicted observables depend very sensitively on galaxy luminosity, redshift, overall mass ratio, and uncertain relaxation timescales for merger remnants. We show that the majority of bright galaxies at z = 3 should have undergone a major merger ( 0.3) in the last 700 Myr and conclude that mergers almost certainly play an important role in delivering baryons and influencing the kinematic properties of Lyman Break Galaxies (LBGs).
Author: Lars Lindberg Christensen Publisher: Springer Science & Business Media ISBN: 0387938559 Category : Science Languages : en Pages : 143
Book Description
Like no other telescope ever invented, the NASA/ESA Hubble Space Telescope has given us magnificent high resolution views of the gigantic cosmic collisions between galaxies. Hubble's images are snapshots in time and catch the colliding galaxies in different stages of collision. Thanks to a new and amazing set of 60 Hubble images, for the first time these different stages can be put together to form a still-frame movielike montage showing the incredible processes taking place as galaxies collide and merge. The significance of these cosmic encounters reaches far beyond aesthetics. Galaxy mergers may, in fact, be some of the most important processes that shape our universe. Colliding galaxies very likely, hold some of the most important clues to our cosmic past and to our destiny. It now seems clear that the Milky Way is continuously undergoing merging events, some small scale, others on a gigantic scale. And the importance of this process in the lives of galaxies is much greater than what was previously thought.
Author: James Binney Publisher: Princeton University Press ISBN: 1400828724 Category : Science Languages : en Pages : 902
Book Description
Since it was first published in 1987, Galactic Dynamics has become the most widely used advanced textbook on the structure and dynamics of galaxies and one of the most cited references in astrophysics. Now, in this extensively revised and updated edition, James Binney and Scott Tremaine describe the dramatic recent advances in this subject, making Galactic Dynamics the most authoritative introduction to galactic astrophysics available to advanced undergraduate students, graduate students, and researchers. Every part of the book has been thoroughly overhauled, and many sections have been completely rewritten. Many new topics are covered, including N-body simulation methods, black holes in stellar systems, linear stability and response theory, and galaxy formation in the cosmological context. Binney and Tremaine, two of the world's leading astrophysicists, use the tools of theoretical physics to describe how galaxies and other stellar systems work, succinctly and lucidly explaining theoretical principles and their applications to observational phenomena. They provide readers with an understanding of stellar dynamics at the level needed to reach the frontiers of the subject. This new edition of the classic text is the definitive introduction to the field. ? A complete revision and update of one of the most cited references in astrophysics Provides a comprehensive description of the dynamical structure and evolution of galaxies and other stellar systems Serves as both a graduate textbook and a resource for researchers Includes 20 color illustrations, 205 figures, and more than 200 problems Covers the gravitational N-body problem, hierarchical galaxy formation, galaxy mergers, dark matter, spiral structure, numerical simulations, orbits and chaos, equilibrium and stability of stellar systems, evolution of binary stars and star clusters, and much more Companion volume to Galactic Astronomy, the definitive book on the phenomenology of galaxies and star clusters
Author: Priyamvada Natarajan Publisher: World Scientific ISBN: 9814489395 Category : Science Languages : en Pages : 276
Book Description
This book constitutes the proceedings of a very topical workshop aimed at understanding the shapes of the baryonic and dark matter components of galaxies. Several groups presented their recent results from observations and numerical N-body simulations.
Author: Andrew Rodger Wetzel
Author: L. Feretti
Author: Chi-hun Kim
Author: Kyle Robert Stewart
Author: Michael Robert Boylan-Kolchin
Author: 
Author: Risa H. Wechsler
Author: Lars Lindberg Christensen
Author: James Binney
Author: Priyamvada Natarajan