Auflistung Astronomy and Geoscience nach Erscheinungsdatum
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Rakić, Nemanja (Beograd , 2022)[more][less]
Zusammenfassung: Active Galactic Nuclei (AGN) are galaxy cores in which a supermassive black hole is being surrounded with an accretion disk, which emits powerful continuum emission. This continuum ionizes the surrounding gas which than emits the broad lines, detected in the optical band. The aim of this thesis is to model complex optical spectra of large numbers of type 1 AGNs (AGNs with broad emission lines) and study physical properties of the emitting gas, so-called broad line region. Understanding the physics of the broad line region, as well as the physics of AGN as a whole is important for understanding the galaxy formation and evolution. This thesis investigate a large sample of type 1 AGNs taken from the SDSS spectral database. In total, over 1500 spectra were analyzed, for which a completely new software for modeling of optical AGN spectra (named FANTASY) was developed. Automated simultaneous modeling of all emission components in the optical spectrum enables reliable measurement of spectral parameters, which can have significant application in future investigation of large AGN samples, collected within the upcoming large spectroscopic sky surveys. The physical properties in the broad line region were studied through the analysis of a still unexplained (anti)correlation between the equivalent width of the emission lines and the conti- nuum flux (the so-called Baldwin effect). It has been confirmed that the intrinsic Baldwin effect exists in the Balmer hydrogen lines in type 1 AGNs, and that a potential physical explanati- on for this effect might be presence of an additional non-ionizing optical continuum emission, which originates from the broad line region. Finally, the significant outcome of this thesis is is the new publicly available software package FANTASY, which can be widely used in the future spectral analysis of AGN. URI: http://hdl.handle.net/123456789/5451 Dateien zu dieser Ressource: 1
Doktorska_disertacija_nrakic.pdf ( 5.806Mb ) -
Mitrašinović, Ana (Beograd , 2022)[more][less]
Zusammenfassung: The subject of this dissertation is to study the effects of galaxy flybys on the structural evolution of galaxies. Galaxy flybys are very close interactions that do not result in a merger. With the high frequency in the late Universe, their role in the evolution of galaxies is significant. Earlier studies focused on equal-mass flybys, which are extremely rare. We focus on typical flybys with a lower mass ratio. We aim to explore the structure and evolution of galaxies in greater detail and demonstrate that these flybys are just as important as equal-mass ones. We performed a series of N body simulations of typical flybys with varying impact para- meters. We demonstrated the applicability and importance of isolated N body simulations and developed an efficient method for reliable bar detection in galaxy discs. For the first time, we examined the evolution of the secondary galaxy, focusing on its dark matter mass loss. The results show that the leftover mass follows logarithmic growth law with impact parameter and suggest that flybys contribute to the formation of dark matter-deficient galaxies. The primary galaxy is affected in a similar way as in equal-mass flybys. Bars form in closer flybys, two-armed spirals form during all flybys, and the dark matter halo spins up. Most of the parameters of these structures are correlated or anti-correlated with the impact parameter. We also noticed that a double bar could form as evolving spirals wrap around the early-formed bar. We successfully demonstrated that frequent, typical flybys with lower mass ratios signifi- cantly affect the evolution of galaxies, producing various observed effects. Our results should serve as a warning not to disregard these interactions in future studies. URI: http://hdl.handle.net/123456789/5441 Dateien zu dieser Ressource: 1
mitrasinovic_ana.pdf ( 5.370Mb ) -
Pavlović, Marina (Beograd , 2022)[more][less]
Zusammenfassung: The study of galaxies through high redshifts are key to understanding the evolution of galaxies through cosmic times. As such objects are very difficult to observe directly, they are mainly examined using empirically derived tools such as the numerous correlations between their different parametric characteristics, one of them being the linear relationship between far-infrared and radio emission in star-forming galaxies, named the Far Infrared-Radio (FIR) Correlation.Although the correlation was considered to be stable in terms of linearity, recent works, which include galaxies at high redshifts (0 < z < 6), showed a large deviation from the correlation in these systems. The goal of this doctoral dissertation is an examination of the physical processes that lead to this kind of behavior. As a possible cause of this evolution, we will assume for the first time, and examine interactions between galaxies (collisions and close approaches). Interactions be- tween galaxies lead to the formation of shock waves on large scales that can lead to changes in the relationship between infrared and radio emissions. Our hypoth- esis was tested in several stadiums and the main results are as follows: 1. We developed models of the evolution of the FIR correlation with redshift as functions of the galaxy interaction rate. We tested the models on a sample of galaxies with an already determined morphology separately for disc galaxies and for galaxies that have recently been or are currently interacting - irregular galaxies. 2. In a small sample of 34 galaxies that we took from paper Miettinen et al. (2017), it was shown that there is an indication that the interaction between galaxies can be responsible for the evolution of the correlation with the redshift. 3. The next analysis was performed on a much larger sample of star-forming galaxies taken from COSMOS field, where we did not find any evolution of corre- lation with the redshift. Also, it was shown that the mean value of the correlation parameter is lower in irregular galaxies than in disk galaxies. Although recent observations indicated an evolution of the FIR correlation with redshift, the results of this research failed to reproduce that evolution and showed that the FIR correlation is stable with redshift. However, it was also shown that due to the interaction of galaxies, the evolution of the FIR correlation is possible if the representation of interacting systems in the sample is higher. URI: http://hdl.handle.net/123456789/5460 Dateien zu dieser Ressource: 1
Disertacija_Marina_Pavlovic.pdf ( 8.624Mb ) -
Milošević, Stanislav (Beograd , 2023)[more][less]
Zusammenfassung: In this dissertation, we presented galaxy mergers and the forming of stellar morphological substructures. We assume a large spiral galaxy and dwarf galaxy which is a satellite of the first one. We used N-body simulations to present different scenarios for the merger of two galaxies, and after that, we analyzed the properties of formed structures. The investigation of the formation of these structures and their properties is important for understanding the dynamics and evolution of galaxies. First, we did simulations where we investigated the influence of the properties of dwarf galaxies on the forming structures. We tested: 1. morphology of the dwarf galaxy where we used two models – dwarf with a disk and spheroidal dwarf galaxy; 2. inclination of the orbit in the case of a very radial merger, because in that case, we have the formation of the stellar shells and streams; 3. direction of rotation of the dwarf in the case of a dwarf with a disk. In each case, after the merger, we have stellar shells and streams formed. Morphology, inclination of the orbit, and direction of rotation have their influence on the properties of formed substructures, and on the timescale of disruption of the remnant of the dwarf. In the case of the merger of Andromeda galaxy (M31) and dwarf galaxy, the satellite of M31, we investigate the properties of the Giant Stellar Stream (GSS), as well as the Northeast shell (NE) and West shell (W). The orientation of the GSS, distances, and velocities of the GSS, NE, and W shells from our simulation are in agreement with the observed one. For the first time, we explained the observed metallicity distribution in these substructures. With a linearly decreasing gradient of the initial metallicity in the dwarf galaxy before the merger, using Monte Carlo (MC) simulations, we successfully explained the observed metallicity distribution in these substructures. These results are a contribution to the investigation of metallicity gradients in dwarf galaxies which is important for galaxy evolution in general. URI: http://hdl.handle.net/123456789/5583 Dateien zu dieser Ressource: 1
SM_Doktorat_18_07_2023.pdf ( 18.08Mb ) -
Kostić, Petar (b , 2023)[more][less]
Zusammenfassung: The models of radio synchrotron emission of supernova remnants (SNRs) imply uniform density ahead of shock wave, so the evolution of luminosity is usu- ally studied in such an environment, most often through the surface-brightness-to- diameter dependence, the Σ–D relation. This field aims to better understand the SNR evolution, the emission models, but also the methods for determining their distance. It is not an easy task because of a very large scatter in the Σ–D Milky Way sample. The dissertation puts a different perspective at the Σ–D relation (usually treated as power-law function), assuming that non-uniform environment around the stars considerably affects its shape and slope, that may vary during the SNR expansion. It makes the ambient density structure an important factor whose impact must be investigated. The numerical code for hydrodynamic (HD) simulations and the emission model were developed. The 3D HD simulations were performed in different non-uniform environments, including low-density bubbles and a variety of clumpy models. Based on the simulation results, a semi-analytical 3D spherically-symmetric model of HD and Σ–D evolution of SNRs in clumpy medium was developed, which is used to generate large Σ–D samples. The results show that after entering the clumpy medium the SNR brightness enhances, but afterward the Σ–D slope steepens, shortening the brightness evolu- tion lifetime. Despite the evident increase in slope in clumpy medium, the Galactic sample average slope flattens at ≈ 13–50 pc. After analyzing the generated SNR samples in clumpy medium it is concluded that the significant flattening and scatter in Galactic sample originates in sporadic emission jumps of individual SNRs in a limited diameter interval. The additional analyses of selection effects are needed to investigate these issues. URI: http://hdl.handle.net/123456789/5606 Dateien zu dieser Ressource: 1
Kostic_Petar_disertacija.pdf ( 1.947Mb ) -
Simovljević, Jovan (None)[more][less]
URI: http://hdl.handle.net/123456789/152 Dateien zu dieser Ressource: 1
phdJLSimovljevic.pdf ( 928.8Kb ) -
Dimitrijević, Milan (Belgrade)[more][less]
Zusammenfassung: A detailed analysis of the motion of a charged particle under the influence of Coulomb, polarization, and quadrupolar potential has been performed, and analytical expressions for particle path parameters have been obtained. Also, conditions for existence of a critical impact parameter, which separates paths ending in the atom from those going to infinity, have been examined, and methods for its determination have been elaborated. Results of this investigations have been applied to the theory of Stark broadening (broadening of spectral lines under the influence of collisions with charged particles), where a special attention has been paid to the adiabatic limit, and to quasistatic and impact approximations. Modification of Stark broadening functions has been performed and it has been demonstrated that the biggest influence of path curvature on them, is in the vicinity of the critical impact parameter, which separates paths ending in the atom from those going to infinity. The change in the values of the Stark broadening functions will have the largest influence on Stark broadening parameters for lines for which, at the most probable velocity, influence of the contribution of inelastic collisions is dominant and effective polarizability large. The application of semiempirical approximative approach for calculation of Stark broadening parameters for multiply charged emitters, has been analyzed as well, and the modification of semiclassical theory has been performed. The averaged ratio of experimental and theoretical results is 0.75 for semiempirical, 1.47 for semiclassical, and 1.04 for modified semiclassical approach.У раду је извршена детаљна анализа кретања наелектрисане честице под утицајем Кулоновог, поларизационог и квадруполног потенцијала и добијени су аналитички изрази за параметре путање честице. Такође су испитани услови за егзистенцију критичног сударног параметра, који раздваја путање које завршавају у атому од оних које одлазе у бесконачност, и разрађене методе за његово налажење. Резултати овог испитивања су примењени на теорију Штарковог ширења (ширења спектралних линија под утицајем судара са наелектрисаним честицама), при чему је посебна пажња посвећена адијабатској граници и квазистатичкој и сударној апроксимацији. Изведена је модификација функција Штарковог ширења и показано је да је највећи утицај закривљености путање на њих, у близини критичног сударног параметра, који раздваја путање које завршавају у атому од оних које одлазе у бесконачност. Промена у величини функција Штарковог ширења ће највише утицати на параметре Штарковог ширења код линија за које је, при највероватнијој брзини, утицај доприноса нееластичних судара доминантан а ефективна поларизабилност велика. Такође је анализирана примена семиемпиријског апроксимативног прилаза за израчунавање параметара Штарковог ширења за вишеструко наелектрисане емитере, при чему је извршена модификација семикласичне теорије. Усредњени однос експерименталних и теоријских резултата је 0.75 за семиемпиријски, 1.47 за семикласични а 1.04 за модификовани семикласични прилаз. URI: http://hdl.handle.net/123456789/77 Dateien zu dieser Ressource: 1
Dimitrijevic.pdf ( 6.262Mb ) -
Đurović, Dragutin (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/324 Dateien zu dieser Ressource: 1
phdDragutinDjurovic.pdf ( 4.035Mb ) -
Sadžakov, Sofija (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/256 Dateien zu dieser Ressource: 1
phdSofijaSadzakov.PDF ( 8.173Mb ) -
Ševarlić, Branislav (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/141 Dateien zu dieser Ressource: 1
phdBranislavMSevarlic.pdf ( 5.662Mb ) -
Knežević, Zoran (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/135 Dateien zu dieser Ressource: 1
phdZoranKnezevic.pdf ( 42.64Mb ) -
Ćatović, Zlatko (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/134 Dateien zu dieser Ressource: 1
phdZlatkoCatovic.pdf ( 4.531Mb ) -
Ninković, Slobodan (Belgrade)[more][less]
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Oskanjan, Vasilije (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/131 Dateien zu dieser Ressource: 1
phdVasilijeOskanjan.pdf ( 41.32Mb ) -
Nikolić, Silvana (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/130 Dateien zu dieser Ressource: 1
phdSilvanaNikolic.pdf ( 61.73Mb ) -
Atanacković-Vukmanović, Olga (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/129 Dateien zu dieser Ressource: 1
phdOlgaAtanackovic.pdf ( 24.18Mb ) -
Kuzmanoski, Mike (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/128 Dateien zu dieser Ressource: 1
phdMikeKuzmanoski.pdf ( 14.21Mb ) -
Milogradov-Turin, Jelena (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/126 Dateien zu dieser Ressource: 1
phdJelenaMilogradovTurin.pdf ( 115.3Mb ) -
Mitić, Ljubiša (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/127 Dateien zu dieser Ressource: 1
phdLjubisaMitic.pdf ( 38.14Mb ) -
Đurašević, Gojko (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/124 Dateien zu dieser Ressource: 1
phdGojkoDjurasevic.pdf ( 34.72Mb )