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Shell galaxies
Ebrová, Ivana ; Jungwiert, Bruno (advisor) ; Bomans, Dominik J. (referee) ; Combes, Francoise (referee) ; Šubr, Ladislav (referee)
Title: Shell galaxies Author: Ivana Ebrová Department / Institute: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor of the doctoral thesis: RNDr. Bruno Jungwiert, Ph.D., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies presumably result from radial minor mergers of galaxies. We show that the line-of- sight velocity distribution of the shells has a quadruple-peaked shape. We found simple analytical expressions that connect the positions of the four peaks of the line profile with the mass distribution of the galaxy, namely, the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger, and the potential of the simulated host galaxy was successfully recovered. Shell kinematics can thus become an independent tool to determine the content and distribution of dark matter in shell galaxies up to ~100 kpc from the center of the host galaxy. Moreover we investigate the dynamical friction and gradual disruption of the cannibalized galaxy during the shell formation in the framework of a simulation with test particles. The...
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Slupkové galaxie a modifikovaná Newtonova dynamika
Bílek, Michal ; Jungwiert, Bruno (advisor) ; Růžička, Adam (referee)
Our work has two recherchive parts. The first is devoted to the shell galaxies and we describe the observational facts here, different models of origin and the possibility of determining the gravitational potential with the use of shells. The second part is on the modified Newtonian dynamics (MOND). We explain what it consists in, its implications and its experimental tests. The third part is devoted to our numerical simulations of a shell system evolution both in the classical and modified dynamics. Our mission is to explain the differences in the two simulation theoretically and to verify, whether the result of the modified simulation oppose the observed shells around the galaxy NGC 3923. The conclusion is it doesn't, but our test is not very strong.
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Galaxy interactions: dark matter vs. Modified Newtonian dynamics (MOND)
Bílek, Michal ; Jungwiert, Bruno (advisor) ; Kroupa, Pavel (referee) ; Stuchlík, Zdeněk (referee)
MOND is an observational rule for predicting the acceleration of stars and galaxies from the distribution of the visible matter. It possibly stems from a new law of physics. I list the theoretical aspects of MOND, its achievements and problems. MOND has been tested mainly in disc galaxies so far. Its tests in elliptical galaxies are rare because the MOND effects are small for them in the parts observable by the conventional methods. In the thesis, I explain the methods and ideas I developed for testing MOND in the ellipticals using stellar shells. Moreover, the shells enable us to test MOND for stars in radial orbits for the first time. The shells are results of galactic interactions. I discuss the shell formation mechanisms and summarize the findings from shell observations and simulations.
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Shell galaxies - "sticky particles" hydrodynamical simulations
Zimandl, Martin ; Jungwiert, Bruno (advisor) ; Šolc, Martin (referee)
Shell galaxies are usually ellipticals with concentric faint arc-like stellar structures with sharp outer edges. They originate from galactic collisions (so called mergers). According to observations, some galaxies has also gaseous structures, that can be associated with stellar shells. We carry out a few numerical simulations, in which we recreate gaseous shells throug radial collisions of small and large elliptical galaxies. Then we analyze the differences between stellar and gaseous shells. Our simulations are based on earlier models, which describes gas by using so called "sticky-particles" hydrodynamics. This approach was so far quite succesful in resolving origin of gaseous shells. Our conclusion is, that gas in preset galaxies is not sufficient to make any difference. Higher quantities on the other hand has significant effect. Powered by TCPDF (www.tcpdf.org)
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Shell galaxies: kinematical signature of shells, satellite galaxy disruption and dynamical friction
Ebrová, Ivana ; Jungwiert, Bruno (advisor) ; Šubr, Ladislav (referee) ; Šolc, Martin (referee)
Title: Shell galaxies: kinematical signature of shells, satellite galaxy disruption and dynamical friction Author: Ivana Ebrová Department / Institute: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor of the doctoral thesis: RNDr. Bruno Jungwiert, Ph.D., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies presumably result from radial minor mergers of galaxies. We show that the line-of-sight velocity distribution of the shells has a quadruple-peaked shape. We found simple analytical expressions that connect the positions of the four peaks of the line profile with the mass distribution of the galaxy, namely, the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger, and the potential of the simulated host galaxy was successfully recovered. Shell kinematics can thus become an independent tool to determine the content and distribution of dark matter in shell galaxies up to ~100 kpc from the center of the host galaxy. Moreover we investigate the dynamical friction and gradual disruption of the cannibalized galaxy...
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The influence of the stellar mass-loss on the dynamics of star clusters
Dinnbier, František ; Jungwiert, Bruno (advisor) ; Šubr, Ladislav (referee)
This work aims at studying the influence of the stellar mass-loss, resulting from the stellar evolution, on the dynamics of massive star clusters. The emphasis has been put on the mass-loss by low-mass and intermediate-mass stars (m < 8 Mo) that form, at the end of their life, a planetary nebula. The expansion speed of gas released by these stars is lower than the escape speed from sufficiently massive star clusters, and the gas can be retained by the cluster. For modelling of the gas hydrodynamics, a simple sticky-particles method was used. To carry out simulations in which gaseous and stellar particles mutually interact through their gravity, substantial modifications had to be realized in the N-body codes Nbody6 and Hermit. For the sake of comparing the influence of stellar mass-loss and relaxation processes, which are happening in the simplified model, two types of simulations were performed: one with the formation of gaseous particles and the other consisting of purely stellar component. The simulations in which the gas component was present showed out a significantly different evolution in the central part of the cluster than those in which the presence of gas was not considered.
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Symmetries and dynamics of star clusters
Haas, Jaroslav ; Šubr, Ladislav (advisor) ; Baumgardt, Holger (referee) ; Jungwiert, Bruno (referee)
We investigate the orbital evolution of an initially thin stellar disc around a supermassive black hole, considering various perturbative sources of gravity. By means of direct numerical N-body modelling, we first focus on the case when the disc is embedded in an extended spherically symmetric star cluster. We find that the gravitational influence of the disc triggers formation of macroscopic non- spherical substructure in the cluster which, subsequently, significantly affects the evolution of the disc itself. In another approximation, when the cluster is emu- lated by an analytic spherically symmetric potential, we further consider pertur- bative gravitational influence of a distant axisymmetric source. Using standard perturbation methods, we derive a simple semi-analytic model for such a config- uration. It turns out that the additional axisymmetric potential leads to mutual gravitational coupling of the individual orbits from the disc. Consequently, the dense parts of the disc can, for some period of time, evolve coherently. Finally, we apply some of our results to the young stellar disc which is observed in the innermost parsec of the Galactic Centre. 1
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Determinating the cosmological omega factors with supernovae Ia
Rieb, Tomáš ; Mészáros, Attila (advisor) ; Jungwiert, Bruno (referee)
My thesis is an attempt to determine cosmological omega factors using the data measured during observations of the supernovae type Ia with cosmological redshift z 0,1. For the determination of omega factors I use the method of fi tting measured data in Hubble s diagram. I evaluate the ts by the 2-tests. The values of omega factors, coming out of the analyses as the most probable ones di ffer from the results which are published in the contemporary scienti c literature. The question which I am posing is, if it is correct to reject the cosmological models with a zero value of the cosmological constant. At the first sight statistical results of 2-test, which issue from my thesis, seem to be su fficient enough to reject these models. But the denial of the zero cosmological constant appears as ambivalent by detailed analysis of the occasions and reasons for it. As the basis for my analyses, I use the data collected by a number of scientifi c teams. I cannot succesfully fi t most of these data, because the dispersions of their positions in Hubble s diagrams are too large. I can conclude that the observations of the supernovae Ia alone are not satisfactory for a reliable determination of the cosmological omega factors.
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Galaxy interactions: dark matter vs. Modified Newtonian dynamics (MOND)
Bílek, Michal ; Jungwiert, Bruno (advisor) ; Kroupa, Pavel (referee) ; Stuchlík, Zdeněk (referee)
MOND is an observational rule for predicting the acceleration of stars and galaxies from the distribution of the visible matter. It possibly stems from a new law of physics. I list the theoretical aspects of MOND, its achievements and problems. MOND has been tested mainly in disc galaxies so far. Its tests in elliptical galaxies are rare because the MOND effects are small for them in the parts observable by the conventional methods. In the thesis, I explain the methods and ideas I developed for testing MOND in the ellipticals using stellar shells. Moreover, the shells enable us to test MOND for stars in radial orbits for the first time. The shells are results of galactic interactions. I discuss the shell formation mechanisms and summarize the findings from shell observations and simulations.
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