Дисертації з теми "Galaxies: abundance"
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Hempel, Angela. "Classification and abundance of extremely red galaxies with R-J]= 5." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973946733.
Повний текст джерелаSAMUROVIC, SRDJAN. "DARK MATTER IN EARLY-TYPE GALAXIES WITH X-RAY HALOES. A SPECTROSCOPIC STUDY OF DYNAMICS AND ABUNDANCE INDICES." Doctoral thesis, Università degli studi di Trieste, 2004. http://thesis2.sba.units.it/store/handle/item/12724.
Повний текст джерелаSakr, Ziad. "Cosmology beyond ΛCDM model in the light of cluster abundance tension". Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30346.
Повний текст джерелаThe ΛCDM model has proved successful in describing to a high precision most of nowadays cosmological observations. However, one of its parameters, σ 8, measuring the present matter amplitude fluctuations, constrained from CMB angular power spectrum, the Cls, was found by the Planck mission, in significant tension with value constrained by SZ galaxy cluster counts in the near universe. In the present work we investigate extensions to ΛCDM model as possible origins behind this discrepancy. To test these extensions, we performed a Monte Carlo analysis to compare constraints on σ 8 in ΛCDM with constraints under these extensions, using mainly CMB Cls combined with cluster counts sample. The later were based on different mass observables relations and covered different redshift ranges: X-ray cluster in the local universe, SZ Planck mission clusters from the near universe or photometric richness estimated detected clusters from future high redshift upcoming Euclid alike mission. Because an improper determination of the calibration of cluster mass function could also be behind this discrepancy, our approach was, when combined with CMB, to leave the calibration factor free to vary and be constrained by data. Introducing three degenerate massive neutrinos, we found that they have no significant effect on fixing the discrepancy between CMB and Xray or SZ cluster counts. We then allowed the growth index ƴ to vary. We find a correlation in the confidence space between ƴ and the X-ray mass observable factor not affected by the presence of massive neutrinos, indicating that a modifying gravity is favored over massive neutrinos as a way to alleviate the tension. However, when a SZ cluster sample covering a larger redshift range was used, we found that the correlation between ƴ and the calibration factor, is constrained by the evolution of the growth through redshift and limited to a region where it cannot fix the discrepancy. [...]
Diaz, Beltran A. I. "Chemical abundances in spiral galaxies." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372064.
Повний текст джерелаGuo, Yicheng, David C. Koo, Yu Lu, John C. Forbes, Marc Rafelski, Jonathan R. Trump, Ricardo Amorín, et al. "STELLAR MASS–GAS-PHASE METALLICITY RELATION AT 0.5 ≤ z ≤ 0.7: A POWER LAW WITH INCREASING SCATTER TOWARD THE LOW-MASS REGIME." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621237.
Повний текст джерелаLipman, Keith. "Chemical abundances of primeval galaxies from QSO absorption lines." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363292.
Повний текст джерелаVan, der Swaelmen Mathieu. "Évolution chimique du Grand Nuage de Magellan." Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00833887.
Повний текст джерелаJeon, Myoungwon, Gurtina Besla, and Volker Bromm. "Connecting the First Galaxies with Ultrafaint Dwarfs in the Local Group: Chemical Signatures of Population III Stars." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627108.
Повний текст джерелаSpencer, Meghin E., Mario Mateo, Matthew G. Walker, and Edward W. Olszewski. "A Multi-epoch Kinematic Study of the Remote Dwarf Spheroidal Galaxy Leo II." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623237.
Повний текст джерелаTinker, Jeremy L., Joel R. Brownstein, Hong Guo, Alexie Leauthaud, Claudia Maraston, Karen Masters, Antonio D. Montero-Dorta, et al. "The Correlation between Halo Mass and Stellar Mass for the Most Massive Galaxies in the Universe." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624043.
Повний текст джерелаVidal-García, A., S. Charlot, G. Bruzual, and I. Hubeny. "Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625298.
Повний текст джерелаZahedy, Fakhri S., Hsiao-Wen Chen, Michael Rauch, and Ann Zabludoff. "HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z = 0.4." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625809.
Повний текст джерелаvan, Haaften Lennart M., Thomas J. Maccarone, Paul H. Sell, J. Christopher Mihos, David J. Sand, Arunav Kundu, and Stephen E. Zepf. "An Excess of Low-mass X-Ray Binaries in the Outer Halo of NGC 4472." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626536.
Повний текст джерелаRosales, Ortega Fernando Fabián. "Multi-dimensional analysis of the chemical and physical properties of spiral galaxies." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/224843.
Повний текст джерелаConstantin, Anca. "Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1097611827.
Повний текст джерелаSaro, A., S. Bocquet, J. Mohr, E. Rozo, B. A. Benson, S. Dodelson, E. S. Rykoff, et al. "Optical-SZE scaling relations for DES optically selected clusters within the SPT-SZ Survey." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/624426.
Повний текст джерелаBelfiore, Francesco M. C. "Star formation, quenching and chemical enrichment in local galaxies from integral field spectroscopy." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/266684.
Повний текст джерелаFields, Dale L. "Absorption-line measurements of AGN outflows." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1155913695.
Повний текст джерелаGutkin, Julia. "Constraints on the physical properties and chemical evolution of star-forming gas in primeval galaxies." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066255/document.
Повний текст джерелаI present a new model of nebular emission from star-forming galaxies, which I have developed by combining updated stellar population synthesis models with a standard photoionization code. I detail the main features of this new model, such as the recent advances in the theories of stellar interiors and atmospheres it incorporates to interpret the ionizing radiation from star-forming galaxies, and the careful treatment of individual abundances and depletion onto dust grains, which allows one to properly explore the signatures of non-solar metal abundance ratios, and then the properties of chemically young galaxies out to the reionization epoch. I present the public comprehensive grid of photoionization models I have computed, including full ranges of stellar and interstellar parameters. I describe the ability of the models to account simultaneously for observational trends followed by star-forming galaxies in several ultraviolet and optical diagnostic line-ratio diagrams, and I explore the influence of the various adjustable model parameters on predicted line-luminosity ratios. I also describe how the combination of this model with calculations of narrow-line emitting regions from active galactic nuclei computed using the same photoionization code allows one to define new ultraviolet and optical emission-line diagnostics to discriminate between star formation and nuclear activity in galaxies. Finally, I show how the new model presented in this thesis has already been used successfully to interpret the rest-frame ultraviolet and optical line emission of different types of high-redshift star-forming galaxies, mainly lensed dwarf star-forming galaxies at redshift between 2-7
Ballero, Silvia Kuna. "Evolution of chemical abundances in active and quiescent spiral bulges." Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2560.
Повний текст джерелаIn this thesis I develop a chemical evolution model which takes advantage of the most recent high-quality abundance observations in the Galactic bulge to put constraints on its formation and evolution and to obtain a baseline model for bulges in general. I adopt updated massive star nucleosynthesis and follow the evolution of several alpha-elements and Fe by varying the evolutionary parameters. The [alpha/Fe] ratios in the bulge are correctly predicted to be supersolar for a wide range in [Fe/H], and the stellar metallicity distribution is reproduced assuming a short formation timescale, a high star formation efficiency and an initial mass function flatter than the disk. Metallicity-dependent oxygen yields with stellar mass loss are included in the chemical evolution models for the bulge and the solar neighbourhood. The agreement between predicted and observed [O/Mg] trends above solar metallicity is significantly improved; a normalisation problem probably indicates that the adopted semi-empirical yields need adjustment. The difference between [O/Fe] and the other [alpha/Fe] ratios in the bulge and solar neighbourhood is explained. I test the so-called universal initial mass function, suitable for ellipticals and disks, to see if the bulge stellar metallicity distribution can be reproduced by varying the yields for very massive stars, and included M31 in my analysis. I show that assuming a flatter initial mass function than the universal one is necessary, and that a variation exists in the initial mass function among different environments. Finally, I investigate the evolution of spiral bulges hosting Seyfert nuclei, with detailed calculations of the galactic potential and of the feedback from the central supermassive black hole in an Eddington-limited accretion regime. New spectro-photometrical evolution codes covering a wide range of stellar ages and metallicities allowed to model the photometric features of local bulges. I successfully predict the observed black hole-host bulge mass relation. The observed present-day nuclear bolometric luminosity is achieved only for the most massive bulges, otherwise a rejuvenation is necessary. The observed high star formation rates and metallicities, constancy of chemical abundances with the redshift and bulge present-day colours are reproduced, but a steeper initial mass function is required to match the colour-magnitude relation and the present K-band bulge luminosity.
In questa tesi, ho sviluppato un modello di evoluzione chimica che si avvale di recenti osservazioni ad alta qualità di abbondanze chimiche nel bulbo della Via Lattea, per porre dei vincoli sui suoi meccanismi di formazione ed evoluzione e ottenere un modello generale per i bulbi di spirale. Ho adottato una nucleosintesi aggiornata per le stelle massicce e seguito l'evoluzione di diversi elementi-alpha e del ferro, variando i parametri evolutivi. Si prevede correttamente che i rapporti [alpha/Fe] nel bulbo siano soprasolari per un ampio intervallo in [Fe/H]. La distribuzione in metallicità è riprodotta con un tempo di formazione breve, un'alta efficienza di formazione stellare e una funzione iniziale di massa più piatta che nel disco. Yields di ossigeno con perdita di massa stellare in funzione della metallicità sono stati inclusi nei modelli di evoluzione chimica del bulbo e dei dintorni solari. L'accordo tra gli andamenti di [O/Mg] previsti e osservati per metallicità soprasolari risulta sensibilmente migliorato; si spiega inoltre la differenza tra il rapporto [O/Fe] e gli altri [alpha/Fe] nel bulbo e nei dintorni solari. Un problema di normalizzazione indica che probabilmente gli yields semi-empirici adottati necessitano una revisione. Ho verificato se con la cosiddetta funzione iniziale di massa universale, adeguata per galassie ellittiche e dischi, la distribuzione in metallicità stellare del bulge può essere riprodotta calibrando gli yields delle stelle supermassicce, includendo M31 nell'analisi. Si dimostra che una funzione iniziale di massa più piatta di quella universale è necessaria, e che esiste una variazione nella funzione iniziale di massa tra i diversi ambienti. Infine, ho studiato l'evoluzione di bulbi di spirali che ospitano galassie di Seyfert, mediante calcoli dettagliati del potenziale galattico e del feedback dal buco nero supermassiccio centrale in un regime di accrescimento limitato dal tasso di Eddington. Nuovi codici spettro-fotometrici che coprono un ampio intervallo di età stellari e di metallicità hanno permesso di modellizzare le caratteristiche fotometriche dei bulbi locali. La relazione osservata tra massa del buco nero e del bulbo ospite è prevista con successo. La luminosità bolometrica nucleare misurata al tempo presente si consegue solo per i bulbi più massicci, negli altri casi è necessario un "ringiovanimento". Le osservazioni di alto tasso di formazione stellare, alte metallicità, invarianza di abbondanze chimiche col redshift e colori dei bulbi locali sono riprodotte; una funzione iniziale di massa più ripida è invece richiesta per la relazione colore-magnitudo e la luminosità dei bulbi in banda K al tempo presente.
XX Ciclo
1979
Rémy-Ruyer, Aurélie. "Probing the impact of metallicity on the dust properties in galaxies." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112340/document.
Повний текст джерелаAs galaxies evolve, their Interstellar Medium (ISM) becomes continually enriched with metals, and this metal enrichment influences the subsequent star formation. Low metallicity dwarf galaxies of the local Universe are ideal candidates to study the influence of metal enrichment on the ISM properties of galaxies and gives us insight into the enrichment process and star formation under ISM conditions that may provide clues to conditions in early universe metal-poor systems. Previous studies have shown that the ISM of dwarf galaxies poses a number of interesting puzzles in terms of the abundance of dust grains, the dust composition and even the FIR emission processes. However these studies were limited to the warmer dust emitting at wavelengths shorter than 200 microns and were done only on a small number of dwarf galaxies. Thanks to its increased sensitivity and resolution in FIR and submillimeter (submm) wavelengths, Herschel gives us a new view on the cold dust properties in galaxies and enables us to study the lowest metallicity galaxies in a systematic way. In this work, I carry out a study of the dust properties in dwarf galaxies and compare with more metal rich environments, in order to address the question of the impact of metallicity on the dust properties. The novelty of this work lays in the fact that dwarf galaxies are studied here in a systematic way, enabling us to derive and quantify the general properties that are representative of these systems. This study is conducted over the full IR-to-submm range, using new FIR/submm Herschel observations, Spitzer, WISE, IRAS and 2MASS data. We complete this set of data with longer submm measurements from ground-based facilities such as APEX and JCMT to study the presence and characteristics of the submm excess in my sample of galaxies. I also collect Hi and CO data to access the gas properties of the galaxies and study the evolution of the G/D with metallicity. Our study reveal different dust properties in low-metallicity environments than that observed in more metal-richs systems (e.g., an overall warmer dust component). An excess submm emission is often apparent near and/or beyond 500 microns rendering large uncertainties in the dust properties, even for something as fundamental as dust masses. Some of the smallest excesses can be explained by using another dust composition with more emissive grains. Ideal tracer of the chemical evolutionary stage of a galaxy, the gas-to-dust mass ratios (G/D) is found to be much higher than what is expected by simple chemical evolution models. Interpreted with more sophisticated chemical evolution models, including dust growth in the ISM and/or episodic star formation, the relation of the G/D with metallicity and its scatter can be explained by the wide variety of environments we are considering
Spitoni, Emanuele. "The effects of galactic fountains on the chemical evolution of galaxies." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3435.
Повний текст джерелаIn this thesis we study the effect of galactic fountains, namely gas and flows from the disk of galaxies produced by multiple supernova explosions, on the chemical evolution of galaxies. Sequential supernova explosions create a superbubble, whereas the swept up interstellar medium is concentrated in a supershell which can break out a stratified medium, producing bipolar outflows. The gas of the supershells can fragment into clouds which eventually fall toward the disk producing so-called galactic fountains. Many works in literature have dealt with superbubble expansion in stratified media. However, very few papers in the past have taken into account the chemical evolution of the superbubble and how the supershell get polluted from the metals produced by supernova explosions. With this thesis for the first time the effect of galactic fountains we consider in a detailed chemical evolution model for the Milky Way. In the first part of our work we study the expansion law and chemical enrichment of a supershell powered by the energetic feedback of a typical Galactic OB association at various galactocentric radii. We follow the orbits of the fragments created when the supershell breaks out and we compare their kinetic and chemical properties with the available observations of high - and intermediate - velocity clouds. We use the Kompaneets (1960) approximation for the evolution of the superbubble driven by sequential supernova explosions and we compute the abundances of oxygen and iron residing in the thin cold supershell. Due to Rayleigh-Taylor instabilities we assume that supershells are fragmented and we follow the orbit of the clouds either ballistically or by means of a hybrid model considering viscous interaction between the clouds and the extra-planar gas. We find that if the initial metallicity is solar, the pollution from the dying stars of the OB association has a negligible effect on the chemical composition of the clouds. The maximum height reached by the clouds above the plane seldom exceeds 2 kpc and when averaging over different throwing angles, the landing coordinate differs from the throwing coordinate by only 1 kpc. Therefore, it is unlikely that galactic fountains can affect abundance gradients on large scales. The range of heights and [O/Fe] ratios spanned by our clouds suggest that the high velocity clouds cannot have a Galactic origin, whereas intermediate velocity clouds have kinematic properties similar to our predicted clouds but have observed overabundances of the [O/Fe] ratios that can be reproduced only with initial metallicities which are too low compared to those of the Galaxy disk. Even if it is unlikely that galactic fountains can affect abundance gradients on large scales, they can still affect the chemical enrichment of the interstellar medium (ISM) because of the time-delay due to the non-negligible time taken by fountains to orbit around and fall back into the Galaxy. This implies a delay in the mixing of metals in ISM which conflicts with the instantaneous mixing approximation usually assumed in all models in literature. We test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigate two possible causes for relaxing of the instantaneous mixing: i) the ``galactic fountain time delay effect'' and ii) the ``metal cooling time delay effect''. We find that the effect of galactic fountains is negligible if an average time delay of 0.1 Gyr, as suggested by our model, is assumed. Longer time delays produce differences in the results but they are not realistic. The metal cooling time delays produce strong effects on the evolution of the chemical abundances only if we adopt stellar yields depending on metallicity. If, instead, the yields computed for the solar chemical composition are adopted, negligible effects are produced, as in the case of the galactic fountain delay. The relaxation of the IMA by means of the galactic fountain model, where the delay is considered only for massive stars and only in the disk, does not affect the chemical evolution results. The combination of metal dependent yields and time delay in the chemical enrichment from all stars starting from the halo phase, instead, produces results at variance with observations.
XXII Ciclo
1979
Trevisan, Marina. "Formação e evolução de galáxias: populações estelares na Via Láctea, galáxias elípticas e propriedades de galáxias em grupos." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-18042012-162353/.
Повний текст джерелаUnderstanding the way galaxies form and evolve throughout the cosmic time remains one of the greatest challenges of modern cosmology. Several processes are known to play a role in the formation of galaxies, such as feedback from supernovae and active galactic nuclei, chemical and dynamical evolution and environmental effects. This thesis encompasses these processes, from an observational point of view. The Milky Way plays a pivotal role in understanding the various processes involved in the formation of a galaxy, and we start our understanding program by studying our own Galaxy. Different formation processes leave typical signatures in the velocity and metallicity distribution of stars. For this reason, we were able to trace the origin of old and metal-rich stars by combining their kinematics and chemical abundances. Understanding how and where these stars were formed is closely related to mechanisms driving the evolution of the Galactic disk. Although we cannot observe individual stars in distant galaxies, only the integrated spectra, we are able to infer the mass assembly history of galaxies by combining single stellar population (SSP) models that reproduce the observed spectrum. Using this methodology, we traced the star formation history of elliptical galaxies and, by studying the signatures left in the star formation history, we were able to constrain the feedback mechanisms regulating the star formation within halos. In the LCDM scenario, small scale structures are formed first, and then they merge forming larger and larger structures. Therefore, galaxies grow into more and more massive systems, and processes operating in these high-density environments change their properties. For this reason, galaxy evolution and formation of large-scale structures go hand in hand, as we show in our study of properties of galaxies in groups. We explored the spatial distribution of galaxies within and in the surrounding of groups, and we also used the velocity distribution of galaxies as a probe of the evolutionary stage of the group. We found important correlations between the evolutionary stage of the group and the population of galaxies residing within it.
Rojas-Arriagada, Álvaro. "Étude du bulbe galactique avec le Gaia-ESO survey." Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4056/document.
Повний текст джерелаThe Galactic bulge, as a massive and old Galactic component, is key to understand the physicalprocesses responsibles for the formation of the Galaxy. The spectroscopic study of long lived low massstars represents an opportunity to characterize the detailed chemical and kinematical patterns of theeventual mix of stellar populations building up the bulge. In this thesis we made use of data comingfrom the Gaia-ESO survey to conduct a detailed analysis of the disk system as well as bulge stellarpopulations. The bulge metallicity distribution function is bimodal. The metal-rich population exhibitsbar-like kinematics, displays the double RC feature and overlaps the metal-rich end of the thin disksequence in the [Mg/Fe] vs. [Fe/H] plane. We associate these stars with the bar X-shape bulge formedas the product of secular evolution of the early thin disk. On the other hand, the metal-poor populationpresents isotropic hot kinematics and does not participate in the X-shaped bulge. When compared to thethick disk, bulge stars seem to mimic their distribution in the [Mg/Fe] vs. [Fe/H] plane. Whencomparing the metallicity position of the so called ``knee'', that of the bulge is found to be at [Fe/H]=-0.37+/-0.09 dex, being 0.6 dex higher than that of the thick disk. A chemical evolution model suitablyfits the whole bulge sequence by assuming a fast (<1 Gyr) intense burst of star formation taking place atearly epochs. The origin of the metal-poor bulge still remains unconstrained, but further research shouldallow to distinguish between violent processes or secular evolution for its origin
Titarenko, Anastasia. "Indicateurs chimiques d’âge stellaire à l’ère de Gaia." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4065/document.
Повний текст джерелаStars record the past in their ages, chemical compositions and kinematics. They can provide unprecedented detailed constraints on the early epochs of galaxy formation, back to redshifts greater than two (a look-back time of around 10 billion years). In particular, stellar ages are crucial to the understanding of the Milky Way history and for comparison with galactic evolution models. The advent of the Gaia space mission has opened the path to stellar age estimations for large samples of stars, in particular, based on isochrone fitting methods. In addition, Gaia precise distances allow to develop indirect age estimations based on the stellar population chemical evolution clock. In fact, the chemical abundance patterns imprinted on stellar atmospheres represent the gas conditions at the time of the stars’ formation back to redshifts greater than two. The chemical evolution products of different nucleosynthetic channels can therefore provide a time proxy. After calibration, it can be used as an age estimator.This thesis is focussed on the use of a particular chemical clock, the [Y/Mg] abundance. To this purpose, the astrometric Gaia mission data from the first data release was combined with high resolution spectroscopic data from the AMBRE-HARPS catalogue. First of all, the object identification of the AMBRE archival data was improved, thanks to a cross match with the 2MASS catalog, and later the Gaia DR1. In total, 6776 different stars have been identified.Secondly, in order to obtain precise estimations of the [Y/Mg] abundance ratio for galactic disc stars, the automated GAUGUIN tool integrated in the Gaia DPAC APSIS chain, has been optimized and tested. In particular, the abundance estimation capabilities of the APSIS GAUGUIN tool have been improved for irregularly distributed synthetic spectra grids, spanning a large range in stellar atmospheric parameters.Thirdly, the [Y/Mg] abundance ratio has been estimated for about 2000 stars from the AMBRE HARPS spectroscopic data. In addition, the internal and external errors of the abundances were carefully analysed. The studied stars belong mainly to the galactic thin and thick disc, in the metallicity range from --1.0 dex to 0.5 dex.Fourth, thanks to the isochrone fitting age estimations of 342 turn-off stars of the sample, the age sensitivity of the [Y/Mg] ratio has been studied. The analysis reveals a clear correlation between [Y/Mg] and age for thin disk stars of different metallicities, in synergy with previous studies of Solar type stars. In addition, no metallicity dependence with stellar age is detected, allowing to use the [Y/Mg] ratio as a reliable age proxy.Finally, the [Y/Mg] vs. age relation presents a discontinuity between thin and thick disk stars around 9–10 Gyrs. For thick disk stars, the correlation has a different zero point and probably a steeper trend with age, reflecting the different chemical evolution histories of the two disk components
Cesetti, Mary. "Observational constraints to the stellar populations in the center of galactic spheroids." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426046.
Повний текст джерелаGli sferoidi galattici rappresentano uno dei punti chiave per comprendere la formazione e l'evoluzione delle galassie, sopratutto per quanto riguarda la formazione stellare. Infatti, conoscere il contenuto stellare delle galassie early-type fornishe importanti indicazioni sulla formazione e l'evoluzione chimica delle loro stelle. Due sono gli argomenti trattati in questa tesi entrambi connessi con lo studio delle popolazione stellari non risolte nel centro delle galassie. Il primo studia dettagliatamente le proprietà fotometriche di tre galassie appartenenti all'ammasso della Vergine che ospitano un disco stellare nel loro nucleo. Il secondo mira ad individuare le righe spettrali fondamentali per lo studio delle popolazioni stellari nel vicino infrarosso (NIR). I nuovi indici spettrali definiti nel NIR hanno dimostrato essere notevolmente efficaci per l'analisi delle popolazioni stellari. Un semplice modello di popolazione stellare semplice (SSP) è stato creato per interpretare la luce integrata nel vicino infrarosso. Lo sviluppo del modello SSP ha messo in evidenza alcuni limiti delle librerie stellari spettrali oggigiorno disponibili. Pertanto è stato studiato lo spettro di alcune stelle supergiganti rosse a bassa metallicità nel NIR.
Boeche, Corrado. "Chemical gradients in the Milky Way from unsupervised chemical abundances measurements of the RAVE spectroscopic data set." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5247/.
Повний текст джерелаDie vorliegende Doktorarbeit wurde im Rahmen des RAdial Velocity Experiment (RAVE) angefertigt. Ihr Ziel ist es, chemische Elementhäufigkeiten an RAVE-Spektren zu messen und zur Untersuchung chemischer Gradienten in der Milchstrassenebene zu benutzen, um verschieden Szenarien der Galaxienentstehung einzugrenzen. RAVE ist eine große spektrokopische Durchmusterung, deren Ziel es ist, bis zum Ende des Jahres 2012 insgesamt 10^6 Sterne zu spektroskopieren, um deren Radialgeschwindigkeiten, sternatmosphärische Parameter und chemische Häufigkeiten zu messen. Das Projekt benutzt das UK Schmidt Teleskop am Australian Astronomical Observatory (AAO) in Siding Spring, Australien, welches mit dem Multiobjekt-Spektrographen 6dF bestückt ist. Bis heute hat RAVE die Spektren von mehr als 450,000 Sternen gesammelt und untersucht. Die Genauigkeit, mit der die Elementhäufigkeiten abgeschätzt werden können, hängt von der Zuverlässigkeit der verwendeten Parameter, (insbesondere der Oszillatorstärken der Absorptionslinien sowie von der effektiven Temperatur, Schwerebeschleunigung und der Metallizität des gemessenen Sterns) ab. Daher identifizierten wir zunächst 604 Absorptionslinien im Wellenlängenbereich von RAVE und verbesserten deren Oszillatorstärken durch eine inverse Spektralanalyse. Dann wurden die stellaren Parameter von RAVE verbessert, indem die RAVE Pipeline und die stellaren Parameter, auf denen sie beruht, modifiziert wurden. Die Änderungen eliminierten einen Teil der systematischen Fehler von stellaren Parametern, die im Laufe dieser Arbeit gefunden wurden. Um Elementhäufigkeiten zu bestimmen, haben wir zwei verschiedene Prozessierungs-Pipelines entwickelt. Beide berechnen die Elementhäufigkeiten unter der Annahme von Sternatmosphären im lokalen thermischen Gleichgewicht (local thermal equilibrium, LTE). Die erste Pipeline berechnete Elemenhäufigkeiten anhand der Äquivalentbreiten von Absorptionslinien. Da diese Methode eine geringe Empfindlichkeit für die Elementhäufigeiten relativ zu Eisen erreichte, wurde sie ersetzt. Die neue Pipeline benutzt chi^2-Fits von Modellspektren an die beobachteten Spektren. Dank Ihrer Präzision wurde diese für die Erstellung des RAVE-Katalogs von Elementhäufigkeiten verwendet. Diese Pipeline liefert Elementhäufigkeiten mit einer Genauigkeit von ~0.2dex, während für Spektren mit 20>S/N>40 immerhin noch ~0.3dex Genauigkeit erreicht werden. Für die vorliegende Arbeit wurden für 217.358 Sterne die Häufigkeiten von sieben chemischen Elementen bestimmt. Mit diesen Daten wurde der radiale chemische Gradient unserer Milchstraße untersucht. Wir finden, dass Sterne mit kleinen vertikalen Geschwindigkeiten |W|, die also nahe der galaktischen Ebene bleiben, einen radialen Gradienten der Eisenhäufigkeit zeigen, der mit früheren Studien übereinstimmt (~-0.07 dex Kpc^-1), während Sterne mit großen |W|, also solche, die größere galaktische Höhen erreichen, einen progressiv flachere Gradienten zeigen. Die Gradienten der anderen Element folgen dem gleichen Trend. Das lässt darauf schließen, dass entweder die Durchmischung der galaktischen dicken Scheibe effizient arbeitet oder aber dass die dicke Scheibe aus interstellarer Materie gebildet wurde, die chemisch recht homogen war. Speziell fanden wir hunderte von Sternen, die zwar kinematisch als zur dicken Scheibe zugehörig klassifiziert werden können, die aber die typische chemische Zusammensetzung der dünnen Scheibe aufweisen. Einige wenige dieser Sterne wurden bereits von anderen Autoren entdeckt, aber ihre Herkunft bleibt immer noch unklar. Eine Möglichkeit ist, dass die Sterne der dünnen Scheibe kinematische geheizt werden, sodass sie effizienter radial gemischt werden, was die chemischen Gradienten verwischt und auch flacher macht. Alternativ dazu könnten diese Sterne einer "Übergangspopulation" angehören, welche hinsichtlich der Scheibenevolution die Verbindung zwischen der dünnen und der dicken Scheibe darstellt. Unsere Untersuchung zeigt, dass sich diese beiden Erklärungen gegenseitig nicht ausschließen. Künftige Nachspektroskopierung mit hoher Auflösung wird die Rolle dieser Sterne in der Entwicklungsgeschichte der galaktischen Scheibe aufklären.
Blanco-Cuaresma, Sergi. "Test de la technique de marquage chimique avec des amas ouverts." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0079/document.
Повний текст джерелаContext. Stars are born together from giant molecular clouds and, if weassume that they were chemically homogeneous and well-mixed, we expect them toshare the same chemical composition.Most of the stellar aggregates are disrupted while orbiting the Galaxy and thedynamic information is lost, thus the only possibility to reconstruct the stellarformation history is to analyze the chemical abundances that we observe today.Aims. The chemical tagging technique aims to recover disrupted stellarclusters based merely on their chemical composition. We evaluate the viability of thistechnique to recover conatal stars that are not gravitationally bound anymore.Methods. We built a high-quality stellar spectra library to facilitate theassessment of spectral analyses. We developed our own spectral analysisframework, named iSpec, capable of homogeneizing stellar spectra and derivingatmospheric parameters/chemical abundances. Finally, we compiled stellar spectrafrom 32 Open Clusters, homogeneously derived atmospheric parameters and 17abundance species, and applied machine learning algorithms to group the starsbased on their chemical composition. This approach allows us to evaluate theviability of the chemical tagging technique.Results. We found that stars in different evolutionary stages havedistinguished chemical patterns may be due to NLTE effects, atomic diffusion, mixingand correlations from atmospheric parameter determinations. When separating starsper evolutionary stage, we observed a high degree of overlapping among OpenCluster’s chemical signatures, making it difficult to recover conatal aggregates byapplying the chemical tagging technique
Thévenin, Frédéric. "Contribution a l'etude des abondances des populations stellaires." Paris 7, 1987. http://www.theses.fr/1987PA077294.
Повний текст джерелаGuiglion, Guillaume. "Étude du disque galactique par marquage chimique de ses populations stellaires." Thesis, Nice, 2015. http://www.theses.fr/2015NICE4114/document.
Повний текст джерелаStudying both the chemical composition and kinematics of Milky Way stars is essential to understand how big structures of our Galaxy are formed. Indeed, low-mass stars retain in their photosphere the chemical composition of the interstellar medium is which they were born. Additionally, the kinematics are essential to characterize stellar populations. In this thesis, we focus on the galactic disc, a major component of the Milky Way. In the context of the Gaia mission, we have developed an automatic procedure GAUGUIN, devoted to deriving chemical abundances. We first applied our method to the Gaia-ESO Survey (GES) data to derive alpha and iron-peak chemical abundances for 10000 stars. We then derived lithium abundances for 7300 stars from the AMBRE project. GAUGUIN is well adapted to massive spectroscopic surveys, both in terms of computation time and accuracy. GAUGUIN will be soon integrated into the RVS DPAC analysis pipeline of the Gaia mission. We studied the velocity dispersions in the galactic disc as a function of the [Mg/Fe] ratio, used as an age proxy. Thanks to 6800 GES stars, we detected thick disc stars with cool kinematics and high [Mg/Fe] ratio, so presumably old. In the generally turbulent context of the primitive galactic disc, this thesis places these results in the framework of the different disc formation and evolution scenarios. We also showed that the lithium abundance in the galactic disc increases as a function of the metallicity in the domain -1<[M/H]+0 dex and decreases at super-solar metallicities. Finally, the thin and the thick discs could be characterized by different lithium abundance evolutions
Santos-Peral, Pablo. "Archéologie galactique du disque de la Voie Lactée avec la mission spatiale Gaia." Thesis, Université Côte d'Azur, 2021. http://www.theses.fr/2021COAZ4001.
Повний текст джерелаGalactic archaeology aims at unveiling the history of the Milky Way by analysing different stellar properties: chemical abundances, kinematics, dynamics and ages. In particular, the abundance of α-elements (e.g. O, Mg, Si, S, Ca, Ti) with respect to iron ([α/Fe]) is an important fossil signature to trace the chemical evolution of the Galactic disc’s populations, i.e. the thin and the thick disc. The goal of this thesis is to explore the main issues concerning the determination of high-precision abundances from observed spectral data and, by using the high-quality astrometric data provided by the Gaia space mission, analyse the chemodynamical properties of the Galactic disc (e.g. radial abundance gradients, role of stellar migration, age-abundance relations) in order to infer the formation and evolution of the Milky Way.The implemented algorithm was the automated abundance estimation procedure GAUGUIN, which is integrated into the RVS (Radial Velocity Spectrometer) DPAC analysis pipeline of the Gaia mission. We first applied our method to derive [Mg/Fe] abundances for 2210 solar neighbourhood stars observed by the HARPS ESO spectrograph (high spectral resolution: R ∼ 115000), and parametrised by the AMBRE Project (effective temperature, surface gravity, overall metallicity [M/H], [α/Fe] abundance, and radial velocity). We found that the definition of continuum to normalise the observed spectra is responsible for the largest fraction of the uncertainty in the abundance estimate for the metal-rich stellar spectra. We show a methodology that significantly improve the abundance estimate precision, and allows to observe a decreasing trend in the [Mg/Fe] abundance even at supersolar metallicites ([M/H] > 0), partly solving the apparent discrepancies between the observed flat trend in the literature, and the steeper slope predicted by Galactic chemical evolution models.We used these new [Mg/Fe] abundance measurements to interpret the Galactic disc formation and evolution. To this purpose, we estimated ages and orbital properties for 366 main sequence turn-off (MSTO) stars, using PARSEC isochrones, together with astrometric and photometric values from Gaia DR2. We observe a steeper [Mg/Fe] gradient, compared to literature values, which is a direct result of the improvement of the abundance estimates in the metal-rich regime. Moreover, we find a significant spread of stellar ages at any given [Mg/Fe] value, and observe a clear correlated dispersion of the [Mg/Fe] abundance with the metallicity at a given age. While for [M/H] ≤ -0.2, a clear age-metallicity and age-[Mg/Fe] trends are observed, more metal-rich stars display ages from 3 up to 12 Gyr, describing an almost flat trend in the [M/H]-age and [Mg/Fe]-age relations. In addition, we found a significant fraction of radial migrated stars in the Galactic disc, for a wide range of stellar ages. Finally, we observe the appearance of a second chemical sequence at the outer disc, 10-12 Gyr ago. These stars are more metal-poor with respect to the coexisting stellar population in the inner parts of the disc, and show lower [Mg/Fe] abundances than prior disc stars of the same metallicity, leading to a chemical discontinuity. Our data favour the rapid formation of an early disc that settled in the inner regions, followed by the accretion of metal-poor gas, probably related to a major accretion event from a gas-rich satellite merger, that may have triggered the formation of the thin disc population
Nandakumar, Govind. "L’archéologie galactique et son application au centre galactique." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4064/document.
Повний текст джерелаGalactic archaeology deals with dissecting the Milky Way into its various components with the objective to disentangle processes contributing to the Milky Way formation and evolution. This relies on precise estimation of positions, velocities as well as stellar atmosphere properties of individual stars belonging to different stellar populations that make up each of these components. Thus this field relies on photometric, astrometric and spectroscopic observations to measure the above mentioned stellar properties in detail in addition to accurate models to compare the observed results with. In this thesis, I have carried out a detailed study of selection function effects on metallicity trends using larges scale spectroscopic surveys, followed by high and low resolution spectroscopic observations towards the inner Milky Way to characterise the chemical nature of the inner Galactic bulge and to measure the star formation rate in the central molecular zone (CMZ), respectively. With ongoing and upcoming large Galactic archaeology spectroscopic surveys such as APOGEE, RAVE, LAMOST, GALAH etc, it is essential to know the specific selection function which is related to the targeting strategy of each of them. By using common fields along similar lines of sight between APOGEE, LAMOST, GES and RAVE, and together with stellar population synthesis models, I investigate the selection function effect on the metallicity distribution function (MDF) and the vertical metallicitiy gradients in the solar neighborhood. My results indicate that there is negligible selection function effect on the MDF and the vertical metallicity gradients. These results suggest that different spectroscopic surveys (different resolutions and wavelength range) can be combined for such studies provided their metallicities are put on the same scale. While more and more spectroscopic observations of the outer bulge regions reveal the complex morphological, kinematic and chemical nature of the Milky Way bulge, there is a lack of detailed chemical abundances studies in the inner bulge region (400-500 pc). I will present high resolution K-band spectra of K/M giants in this highly obscured region obtained using the high resolution infrared spectrograph, CRIRES (R-50,000), on VLT. I will discuss the MDF and detailed chemical abundances of our sample in this region as well as the North-South symmetry in MDF along the bulge minor axis. A major challenge in the chemical evolution models is the lack of knowledge about the star formation history and the star formation rate in the Milky Way. The inner 200 pc of the Milky way, the so called central molecular zone, has a large reservoir of molecular gas with the evidence of star formation activity during the last 100,000 years. I used low resolution KMOS spectra (VLT) to identify and analyse massive young stellar objects (YSOs) and estimated the star formation rate in the CMZ using the YSO counting method
Neves, Vasco. "Étude sur les paramétres stellaires des naines M et leur lien à la formation planétaire." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY082/document.
Повний текст джерелаAt the time of writing of this Thesis more than 900 planets have been announced and about 2700 planets from the Kepler space telescope are waiting to be confirmed. The very precise spectra and light curves obtained in Doppler and transit surveys, allows the in-depth study of the parameters of the host stars, and opens the possibility to investigate the star-plant correlations. Also, determining the stellar parameters with precision is critical for more precise determinations of the planetary parameters, namely, mass, radius, and density.In the case of the FGK dwarfs, the determination of stellar parameters is well established and can be used with confidence to study the star-planet relation as well as to obtain precise planetary parameters. However, this is not the case for M dwarfs, the most common stars in the Galaxy. Compared to their hotter cousins, M dwarfs are smaller, colder, and fainter, and therefore harder to study. The biggest challenge regarding M dwarfs is related to the presence of billions of molecular lines that depress the continuum making a classical spectral analysis almost impossible. Finding new and innovative ways to overcome this obstacle in order to obtain precise stellar parameters is the goal of this Thesis.To achieve this goal I focused my research into two main avenues: photometric and spectroscopic methods. My initial work had the objective of establishing a precise photometric metallicity calibration, but I could not reach this goal, as I did not have enough FGK+M binaries with good photometric data. However, it was possible, with the available data, to compare the already established photometric calibrations and slightly improve the best one, as described in Chapter 3.Then, I focused on spectroscopic approaches with the aim of obtaining precise M dwarf parame- ters. To this end I used HARPS high-resolution spectra and developed a method to measure the spectral lines disregarding the continuum completely. Using this method I established a new visible calibration with a precision of 0.08 dex for [Fe/H] and 80 K for Te f f . This work is detailed in Chapter 4.Finally, I also participated in the refinement of the parameters of the star GJ3470 and its planet, where my expertise in stellar parameters of M dwarfs had an important role. The details regarding this investigation are shown in Chapter 5
No momento em que escrevo esta Tese, o número de planetas anunciados já ultrapassou os 900 e os cerca de 2700 candidatos detectados pelo telescópio espacial Kepler esperam por confirmação. Os espectros e as curvas de luz obtidos nos programas de procura de planetas permitem, também, o estudo em profundidade dos parâmetros das estrelas com planetas e abrem a possibilidade de investigar a relação estrela-planeta. Neste contexto, a determinação com precisão dos parâmetros estelares é crítica na determinação precisa dos parâmetros planetários, nomeadamente, a massa, o raio e a densidade.No caso das anãs FGK, os métodos de determinação dos parâmetros estelares estão bem estabelecidos e podem ser usados com confiança no estudo da relação estrela-planeta, assim como na obtenção de parâmetros planetários precisos. No entanto, não é esse o caso para as anãs M, as estrelas mais comuns da nossa Galáxia. Ao contrário das suas primas, as estrelas M são mais pequenas, frias e ténues e, assim sendo, mais difíceis de estudar. O grande entrave no estudo das estrelas M está relacionado com a presença de biliões de linhas moleculares que deprimem o contínuo espectral, fazendo com que uma análise espectral clássica se torne quase impossível. A procura de métodos inovadores que possibilitem ultrapassar este obstáculo, tendo em vista a obtenção de parâmetros precisos, é o objectivo desta Tese.Tendo em conta esse objetivo, foquei os meus esforços em duas linhas principais de pesquisa, baseadas em métodos fotométricos e métodos espectroscópicos. O meu trabalho inicial tinha como objetivo o estabelecimento de uma calibração fotométrica para a metalicidade, mas não me foi possível atingir esse objetivo, pois não tinha sistemas binários FGK+M suficientes com bons dados fotométricos. No entanto, foi possível, com os dados disponíveis, comparar as calibrações fotométricas existentes e refinar ligeiramente a melhor delas, como descrito no Capítulo 3.Após este trabalho passei a concentrar-me em técnicas espectroscópicas de obtenção de parâmetros estelares em estrelas M. Tendo em mente esse objetivo, usei espectros HARPS de alta resolução para desenvolver um novo método de medição de linhas espectrais independente do contínuo espectral. Seguidamente, usei este método no desenvolvimento de uma nova calibração de metalicidade e temperatura efectiva em estrelas M na região do visível, através da qual consegui atingir uma precisão de 0.08 dex para a [Fe/H] e de 80 K para a temperatura. Este trabalho está descrito no Capítulo 4.Ao mesmo tempo colaborei na determinação com precisão dos parâmetros da estrela GJ3470 e do seu planeta, onde a minha proficiência na determinação de parâmetros estelares em anãs M teve um papel importante. Os detalhes relacionados com este trabalho de investigação estão descritos no Capítulo 5
Dias, Bruno Moreira de Souza. "Formation and evolution of globular clusters in the Galaxy and Magellanic Clouds." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-26082014-090039/.
Повний текст джерелаAglomerados globulares são traçadores da formação e evolução de suas galáxias. Cinemática, abundâncias químicas, idades e posições dos aglomerados permitem traçar interações entre Via Láctea e galáxias vizinhas e suas histórias de enriquecimento químico. Nesta tese analisamos espectros de média resolução de mais de 800 estrelas gigantes vermelhas em 51 aglomerados globulares Galácticos. É a primeira vez que [Fe/H] and [Mg/Fe] determinados de modo consistente são publicados para uma amostra desse porte, ~1/3 dos objetos catalogados. Nossas metalicidades são mais precisas que trabalhos anteriores similares. Uma quebra em [Fe/H] ~ -1.0 é encontrada no gráfico [Fe/H] vs. [Mg/Fe] para o bojo e halo, embora bojo parece ter uma quebra em [Fe/H] maior, i.e, bojo tem formaçãao mais eficiente que o halo. Comparando abundâncias com idade, a escala de tempo para SNIa ficar importante é 1Gano. [Fe/H] vs. idade corrobora diferentes eficiências de formação do bojo e halo, mas [Mg/Fe] vs. idade não mostra isso. O halo foi formado em mini halos ou galáxias anãs, e dois aglomerados com dispersão em [Fe/H] tiveram suas origens analisadas. M 22 parece ter sido formado na Via Láctea e NGC 5824 possivelmente foi originado em uma galáxia anã, embora os resultados são inconclusivos para NGC 5824. O bojo parece ter sido formado rapidamente e deve possuir o aglomerado mais velho. De fato, HP 1 tem um ramo horizontal mais azul que o esperado para sua metalicidade e vemos isso como um efeito da idade. Determinamos sua distância usando curvas de luz de RR Lyrae de maneira a restringir futuras determinações de idade via diagrama cor-magnitude. Finalmente, investigamos a interação entre Via Láctea e sua galáxia vizinha SMC. Encontramos aglomerados sendo removidos do corpo central da SMC, consistente com cenário de remoção por força de maré para a interação entre as galáxias, em vez de ``ram pressure\'\' que afeta só gás.
Evans, Ian Nigel. "Calibration of the H II region abundance sequence and abundances in Seyfert galaxies." Phd thesis, 1986. http://hdl.handle.net/1885/138350.
Повний текст джерелаHempel, Angela [Verfasser]. "Classification and abundance of extremely red galaxies with R-J ≥ 5 / presented by Angela Hempel." 2004. http://d-nb.info/973946733/34.
Повний текст джерелаGrossauer, Jonathan. "Abundance Matching with the Galaxies of the Virgo Cluster and the Stellar-to-Halo Mass Relation." Thesis, 2012. http://hdl.handle.net/10012/7062.
Повний текст джерела"Green Pea Galaxies: Physical Properties of Low-redshift Analogs of High-redshift Lyman-alpha Emitters." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.50582.
Повний текст джерелаDissertation/Thesis
Doctoral Dissertation Astrophysics 2018
Günthardt, Guillermo Iván. "Espectroscopía y fotometría de galaxias peculiares /." Doctoral thesis, 2008. http://hdl.handle.net/11086/120.
Повний текст джерелаSe realizó una selección de 70 sistemas interactuantes de tipo M51 y se hizo un estudio fotométrico en el infrarrojo cercano, donde se compararon los colores 2MASS de este tipo de sistemas con los de galaxias aisladas. También se obtuvo información espectrofotométrica en el óptico para 13 objetos de este tipo de categoría de interacción y se construyó un catálogo de 20 sistemas, a partir del cual se estudió la cinemática de las distintas componentes.
Guillermo I. Günthardt, director Rubén J. Díaz.
Άκρας, Σταύρος. "Ανίχνευση και μελέτη φαινομένων μεσοαστρική ύλης". Thesis, 2010. http://nemertes.lis.upatras.gr/jspui/handle/10889/3289.
Повний текст джерелаThe aim of this PhD thesis was the study of two very important interstellar medium phenomena like the Planetary Nebulae (PNe) and the stellar bar in spiral galaxies. In particular, we studied 44 PNe in the Galactic bulge region and we determined their physical parameters, like the effective temperature and luminosity of the central star, the electron temperature and density, the abundance of He, N, O, S etc., using the photo-ionization model “Cloudy” (Akras et al. 2010a). It was also pursued to study the stellar bar component using the 3D radiative transfer model CRETE, in order to investigate the effects of a stellar bar component to the morphology of the galaxy and its dust content. In addition, the parameters of the bar component such as the length, the height, the inclination angle and the position angle were determined for four spiral galaxies (NGC 4013, UGC 2048, IC 2531 and our Galaxy). In the first part of the thesis, the PNe were separated according to their morphology (spherical, elliptical and bipolar shape) and we found that the He and N abundances are greater in bipolar PNe. Moreover, by using the statistical tool PCA, it was found that the circular and the elliptical PNe are different from the bipolar, since the log(O/N) takes negative values in the first two and positive or negative values in the bipolar PNe. The critical value was found at -0.18 dex, which corresponds to a stellar mass of 2.6 (Akras & Boumis 2007). In the second part, we managed to accurately describe the morphology of the bar component by using the function of hyperbolic ellipse. For different inclination angles of the observed galaxies, it was found that the “X-shape" feature can be seen only in the case where the inclination angle is greater than 60 degrees. In the case of Milky Way, it was found that the position angle of the bar is approximately 25 degrees and the length equals to 3.75 kpc (Akras et al. 2010b). Considering that the mean length of the bar component is equal to 3.0-4.0 kpc, it was determined that the position angle of a) NGC 4013 takes values between 5 and 10 degrees, b) UGC 2048 takes values between 40 and 50 degrees, c) IC 2531 takes values between 35 and 45 degrees, and our Galaxy takes values between 20 and 30 degrees (Akras et al. 2010b).
Nicholls, David Conway. "Nebular metallicities in isolated dwarf irregular galaxies." Phd thesis, 2014. http://hdl.handle.net/1885/11923.
Повний текст джерелаSakari, Charli. "Chemical Abundances of Local Group Globular Clusters." Thesis, 2014. http://hdl.handle.net/1828/5621.
Повний текст джерелаGraduate
Ratsimbazafy, Ando Lalaina. "Luminous red galaxies in simulations." Thesis, 2010. http://hdl.handle.net/11394/3483.
Повний текст джерелаThere have been a number of attempts to measure the expansion rate of the Universe using age-dating of Luminous Red Galaxies (LRGs).Assuming stars in LRGs form at the same time, age-dating of two populations of LRGs at different redshifts can provide an estimate of the time difference associated with the corresponding redshift interval (dt/dz). This gives a direct estimate of the Hubble parameter at the average redshift of the two populations. In this thesis, we explore the validity of the assumptions in this method using LRGs identified in the Millenium Simulation.We study the properties of LRGs simulated using two semi-analytical models for galaxy evolution and discuss LRG selection criteria. We use stellar population modelling and spectral synthesis to estimate the errors on ages that can be expected and discuss optimization of an age-dating experiment.We find that H(z) using simulated galaxies from MS can be recovered with high accuracy. Using Single Stellar Populations (SSPs) to age -date LRGs is not sufficient for this experiment but if the star formation histories of galaxies are used, accurate ages are obtainable. We discuss an observing program to carry out this experiment using SALT (Southern African Large Telescope).
CURTI, MIRKO. "Assessing the chemical evolution of galaxies with large spectral surveys and spatially resolved observations." Doctoral thesis, 2018. http://hdl.handle.net/2158/1119026.
Повний текст джерелаBerg, Trystyn Andrew Munro. "Metal Strong Damped Lyman Alpha Systems And Their Context With The Local Group." Thesis, 2014. http://hdl.handle.net/1828/5308.
Повний текст джерелаGraduate
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