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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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Chemical evolution of galaxies with an environment-dependent stellar initial mass function
Yan, Zhiqiang ; Kroupa, Pavel (advisor) ; Thomas, Daniel (referee) ; Martín-Navarro, Ignacio (referee)
The presented study gives a comprehensive overview of the theory and the evidence for a systematically varying stellar initial mass function (IMF). Then we focus on the impact of this paradigm change, that is, from the universal invariant IMF to a variable IMF, on galaxy chemical evolution (GCE) studies. For this aim, we developed the first GCE code, GalIMF, that is able to incorporate the empirically calibrated environment-dependent IMF variation theory, the integrated galactic initial mass function (IGIMF) theory. In this theory, the galaxy-wide IMF is calculated by summing all the IMFs in all embedded star clusters which formed throughout the galaxy in 10 Myr time epochs. The GalIMF code recalculates the galaxy-wide IMF at each time step because the integrated galaxy- wide IMF depends on the galactic star formation rate and metallicity. The resulting galaxy-wide IMF and metal abundance evolve with time. Using this code, we examine the chemical evolution of early-type galaxies (ETGs) from dwarf to the most massive. We find that the introduction of the non-canonical IMF affects the best estimation of the galaxy properties such as their mass, star formation history, and star formation efficiency. Moreover, we are able to provide an independent estimation on the stellar formation timescale of galaxies, the...
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The Young Star Clusters in the Galactic Centre
Jakš, Sebastian ; Haas, Jaroslav (advisor) ; Kroupa, Pavel (referee)
In addition to three massive star clusters - Arches, Quintuplet, Nuclear Star Cluster - the Galactic Centre hosts a significant number of isolated stars. It has been proposed that at least some of these stars were formed inside one of the three clusters and, subsequently, ejected out of them during their dynamical evolution. In this work, I investigate the dependence of this complex dynamical process for the Arches cluster upon its unknown line-of-sight distance by means of numerical N-body modelling. It turns out that both the dissipation rate of the Arches and spatial distribution of the ejected stars differs significantly if various values of the line-of-sight distance are considered. In the context of this finding, I critically evaluate the approach of Habibi et al. (2014) who assumed the Arches cluster to be 100 pc in front of the Galactic Centre when modelling its contribution to the observed isolated stars. 1
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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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The perception of crisis communication via social networks by subculture of university students
Kroupa, Pavel ; Opatrný, Martin (advisor) ; Černík, Roman (referee)
The subject of my thesis is perception of crisis communication through social network. The aim of this work is to verify the connection and context between social network, interpretation and risk evaluation. The first theoretical part deals on the research of appropriate literature and defines key words like perception of information, communication, crisis communication, social medias and social networks. It also analyses the structure and communication process, types of communication, theoretical models of crisis communication, instruments of crisis communication and social networks themselves such as Twitter and Facebook. The theoretical part is the basis of the empirical part, which describes the realization of the research among college students. Stated hypotheses lead to the formulation of research questions and build the questionnaire. The questions in the questionnaire are built to verify that the high number of shared posts, sharing a particular user or a large number of controversial comments to that contribution may be related to the interpretation and evaluation of the crisis. It is emerging from the research that the high amount of sharing a post and the concrete person who shares this post has influence on the interpretation and evaluation of the risk. Benefit of this work is the fact that...
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