The topic of this thesis is the study of the vertical structure of the disk galaxies and their dark matter halos through theoretical modeling and numerical calculations. The basic theoretical model of the galactic disk used involves gravitationally-coupled stars and gas under the force-field of a dark matter halo; the disk is rotationally-supported in the plane and pressure-supported perpendicular to the plane of the galaxy. The first part of the thesis involves evaluating the vertical structure of stars and gas in normal as well as dwarf spiral galaxies. The second part of the thesis deals with probing the dark matter halo density profiles of disk galaxies using both the observed rotation curve and the H i scale height data. Following is the layout of the thesis. Chapter 1 gives a general introduction to the topic of vertical structure of spiral galaxies and their dark matter halos, followed by a broad overview of the theoretical development of the topic and ends with highlighting the motivation and challenges met in this thesis. Chapters 2 & 3 deal with the vertical structure of stars and gas in galaxies, Chapters 4-6 focus on obtaining the dark matter halo density profiles of disk galaxies from the observed rotation curve and the H i scale height data whereas Chapter 7 is devoted to the summary of results and future research plans. Vertical structure of stars and gas in galaxies The vertical thickness of the stars and the gas, namely atomic hydrogen (H i) and molecular hydrogen (H2) in a spiral galaxy, is crucial in regulating the disk dynamics close to the mid-plane, especially in the inner galaxy. However, measuring it observationally is not in general practicable due to the limitations of astronomical observations, and often impossible as in the case of face-on galaxies. Therefore, it is imperative to develop a theoretical model of the galaxy which can predict the thickness of the disk components by using as input parameters the physical quantities, which are more observationally-amenable compared to the disk thickness. The vertical thickness of the disk components is determined by a trade-off between the upward kinetic pressure and the net downward gravitational pull of the galaxy. The fraction of the disk mass due to the stars is an order of magnitude higher than that of the gas in ordinary spiral galaxies, and therefore the gas contribution to the disk gravity is ignored in general. We have developed a multi-component model of gravitationally-coupled stars, HI and H2 subjected to the force-field of an external dark matter halo, and conclusively demonstrated the importance of the inclusion of gas gravity in explaining the steep vertical stellar distribution observed in galaxies. These apart, this model does not implicitly assume a flat rotation curve for the galaxy and therefore is applicable in general to obtain the thickness of stars and gas in dwarfs (with linearly rising rotation curves) as well as in ordinary spirals. In Chapter 2, we investigate the origin of the steep vertical stellar distribution in the Galactic disk. One of the direct fall outs of our above model of the galaxy, which incor¬porates the self-gravity of the gas unlike the earlier theoretical models, lies in explaining the long-standing puzzle of the steep vertical stellar density distribution of the disk galax¬ies near the mid-plane. Over the past two decades, observations revealed that the vertical density distribution of stars in galaxies near the mid-plane is substantially steeper than the sech2 function that is expected for a self-gravitating system of stars under isothermal ap¬proximation. However, the physical origin for this has not been explained so far. We have clearly demonstrated that the inclusion of the self-gravity of the gas in the dynamical model of the Galaxy solves the problem even under the purview of isothermal approximation for the disk components. Being a low dispersion component, the gas resides closer to the mid¬plane compared to the stars, and forms a thin, compact layer near the mid-plane, thereby strongly governing the local disk dynamics. This novel idea, highlighting the significance of gas gravity has produced substantial impact on the field and triggered research activities by other groups in related areas of disk dynamics. The strong effect of the gas gravity on the vertical density profile of the stellar disk indicates that it should also bear its imprint on the Milky way thick disk, as the epoch of its formation 109 years ago is marked by a value of gas fraction, almost an order of magnitude higher than its present day value. Interest-ingly, the findings of the upcoming Gaia mission can be harnessed to verify this theoretical prediction. It may also hold the clue as to the reason behind the absence of thick disk in superthin galaxies. In Chapter 3, we use the same model to theoretically determine the H i vertical scale heights in the dwarf galaxies: DDO 154, Ho II, IC 2574 & NGC 2366 for which most of the necessary input parameters are available from observations. We stress the fact that the observational determination of the gas thickness in these dwarf irregulars is not viable. Nevertheless, it is important to estimate it theoretically as it plays a crucial role in calculating the star-formation activities and other related phenomena. However, two vital aspects have to be taken care of while modeling these dwarf galaxies. Firstly, the mass fraction in gas in these galaxies is comparable to that of the stars, and hence the gas gravity cannot be ignored on any account unlike in the case of large spirals. Secondly, dwarf galaxies have a rising rotation curve over most of the disk unlike the flat rotation curves of ordinary spirals. Both these factors have been considered in developing our model of the dwarf galaxies. We find that three out of the four galaxies studied show a flaring of their H i disks with increasing radius, by a factor of a few within several disk scale lengths. The fourth galaxy (Ho II) has a thick H1 disk throughout. A comparison of the size distribution of H1 holes in the four sample galaxies reveals that of the 20 type 3 holes, all have radii that are in agreement with them being still fully contained within the gas layer. Probing the dark matter halo profiles of disk galaxies The next part of the thesis involves the dynamical study of the shapes and density profiles of galactic dark matter halos using observational constraints on our theoretical model of a spiral galaxy. The density distribution of the dark matter halo is generally modeled using the observed rotation curve of the spiral galaxies. The rotational velocity at any radius is determined by the radial component of the net gravitational force of the galaxy, which, however, is weakly dependent on the shape of the dark matter halo. Therefore, one cannot trace the dark matter halo shape by the observed rotation curve alone. The vertical thickness of the stars and gas, on the other hand, is strongly dependent on the flattening of the dark matter halo, and therefore the observed gas thickness can be used as a diagnostic to probe the halo shape. In this thesis, we have used the double constraints of the rotation curve and the H i thickness data to obtain the best-fit values of the core density, core radius and the vertical-to-planar axis ratio (or flattening) of the dark matter halos of our largest nearby galaxy Andromeda (or M31), a low-surface brightness (LSB) superthin galaxy UGC 7321 and to study the dark matter halo shape of our Galaxy. In Chapter 4, we study the dark matter halo of M31 or Andromeda, the largest nearby galaxy to the Milky Way. We find that M31 has a highly flattened isothermal dark matter halo with the vertical-to-horizontal axis ratio equal to 0.4, which interestingly lies at the most oblate end of the halo shapes found in cosmological simulations. This indicates that either M31 is a unusual galaxy, or the simulations need to include additional physics, such as the effect of the baryons, that can affect the shape of the halo. This is quite a remarkable result as it challenges the popular practice of assuming a spherical dark matter halo in the dynamical modeling of the galaxy In Chapter 5, we have applied this technique to the superthin galaxy UGC 7321. Su¬perthins are somewhat the “extreme” objects in the local Universe because of their high gas fraction and absence of a thick disk component. It is interesting to analyze their so-called extreme characteristics in the light of the physical mechanisms which determined them to understand better the properties of ordinary spirals. We find that UGC 7321 has a spher¬ical isothermal halo, with a core radius almost equal to the disk scale length. This reveals that the dark matter dominates the dynamics of this galaxy at all radii, including the inner parts of the galaxy. This is unlike the case for the large spiral galaxies, where the core radius is typically about 3-4 disk scale lengths. Interestingly, the best-fit halo core density and the core radius are consistent, with deviations of a few percent, with the dark matter fundamental plane correlations, which depict the systematic properties of the dark matter halo in late-type and dwarf spheroidal galaxies. This apart, a high value of the gas velocity dispersion is required to get a better fit to the H i scale height data, although the superthin nature of the stellar disk implies a dynamically cold dynamic galactic disk. However, it explains the low star-formation rates in these galaxies since the Toomre Q criterion (Q < 1) for instability is less likely to be satisfied, and hence the disk is liable to be more stable to star formation. In Chapter 6, we investigate the shape of the dark matter halo in the outer Galaxy. We find that the halo is prolate, with the vertical-to-planar axis ratio monotonically increasing to 2.0 at 24 kpc, or 8 radial disk scale lengths. The resulting prolate-shaped halo can explain several long-standing puzzles in galactic dynamics, for example, it permits long-lived warps thus explaining their ubiquitous nature. It also imposes novel constraints on the galaxy formation models. Finally, in Chapter 7, the thesis is concluded with a summary of the main results and a brief discussion of the scope for future work.

Les Antennes sont une des fusions de galaxies les plus connues dans l’Univers proche. Sa proximité nous permet d’observer et d’étudier ses gaz à l’échelle de la formation des amas stellaires. C’est une source idéale pour comprendre comment la dynamique dans les fusions de galaxies déclenche la formation d’étoiles. La plupart des étoiles dans les Antennes sont formées dans des amas stellaires compacts et massifs, surnommés super-star clusters (SSC). Les SSC les plus massifs (>106 M⊙) et les plus jeunes (<6 Myr) sont situés dans la région de collision entre les deux galaxies et sont associés aux complexes moléculaires massifs (~108 M⊙) et super-géants (des centaines de pc) (super-giant molecular clouds, SGMCs). La formation de SSC doit impliquer une intéraction complexe entre la dynamique des gaz et une turbulence entraînée par la fusion des galaxies, et la dissipation de l’énergie cinétique des gaz. Dans les SGMC, une hiérarchie de structures doit être produite, incluant des concentrations denses et compactes de gaz moléculaires qui sont suffisamment massifs pour former un SSC, des nuages pre-cluster clouds (PCC). La formation des étoiles se produira si l’énergie mécanique des PCC est émise dans le lointain, permettant à l’auto-gravité de gagner localement les pressions thermique et turbulente du gaz. Des diagnostics spécifiques de dissipation turbulente sont donc des éléments essentiels pour tester la validité de ce scénario.J’étudie la région d’intéraction des Antennes. J’utilise des observations avec le spectro- imageur SINFONI sur le VLT (raies rovibrationnelles de H2) et ALMA (raie CO(3–2) et l’émission du continuum de la poussière). Les données ont des résolutions angulaires pour résoudre les échelles de la formation des SSC et des résolutions spectrales pour résoudre les mouvements à l’intérieur du SGMC. La combinaison des raies CO et H2 est essentielle dans mon travail. J’utilise le CO comme traceur de la distribution et de la cinématique du gaz moléculaire, et H2 comme traceur du taux de dissipation d’énergie mécanique de gaz.Ma thèse se concentre sur des sources traçant des différentes étapes de la formation d’étoiles : le rassemblement des gaz pour former des SGMCs, la formation des PCC dans les SGMCs et la destruction des nuages moléculaires par les SSC. Je montre que la turbulence joue un rôle essentiel à chaque étape. J’ai trouvé que l’énergie cinétique de rencontre des deux galaxies n’est pas thermalisée dans les chocs aux échelles où elle est injectée. Elle entraîne une turbulence dans l’ISM moléculaire à un niveau beaucoup plus élevé que celui observé dans la Voie Lactée. Sauf dans les SSC encore intégrés dans les nuages moléculaires, la raie de H2 est produite par des chocs et trace la dissipation de l’énergie cinétique turbulente du gaz. J’associe l’émission de H2 à la perte d’énergie cinétique nécessaire pour former des nuages gravitationnellement liés. Cette interprétation est étayée par la découverte d’une source lumineuse et compacte en H2, qui n’est associée à aucun SSC connu, située là où les données montrent le plus grand gradient de vitesse. À notre connaissance, c’est la première fois qu’une source extragalactique avec ces caractéristiques est identifiée. Nous observons la formation d’un nuage suffisamment massif pour former un SSC. Les données montrent également la destruction d’un nuage moléculaire par un SSC récemment formé. Sa matière est faiblement liée. Sa gravité serait soutenue par la turbulence, ce qui rend plus facile pour les mécanismes de rétroaction de perturber le nuage parent.Enfin, je présente deux projets. Je propose d’établir d’autres traceurs de dissipation d’énergie observables avec ALMA, proposition du Cycle 1 acceptée en première priorité. Je propose également d’étendre mon travail pour étudier la formation des étoiles entraînées par la turbulence dans différentes sources extragalactiques en combinant les observations dans le proche infrarouge et submillimétrique. / The Antennae (22 Mpc) is one of the most well-known mergers in the nearby Universe. Its distance allow us to observe and study the gas at the scales of stellar cluster formation. It is an ideal source to understand how the galaxy dynamics in mergers trigger the formation of stars. Most of the stars in the Antennae are formed in compact and massive stellar clusters, dubbed super-star clusters (SSCs). The most massive (>106 M⊙) and youngest (<6 Myr) SSCs are located in the overlap region, where the two galaxies collide, and are associated with massive (several 108 M⊙) and super-giant (few hundred of pc) molecular complexes (SGMCs). The formation of SSCs must involve a complex interplay of merger-driven gas dynamics, turbulence fed by the galaxy interaction, and dissipation of the kinetic energy of the gas. Within SGMCs, a hierarchy of structures must be produced, including dense and compact concentrations of molecular gas massive enough to form SSCs, pre-cluster clouds (PCCs). For star formation to occur, the mechanical energy of PCCs must be radiated away to allow their self-gravity to locally win over their turbulent gas pressure. Specific tracers of turbulent dissipation are therefore key inputs to test the validity of this theoretical scenario. In my thesis, I studied the Antennae overlap region. My work is based on observations with the SINFONI spectro-imager at the VLT, which includes H2 rovibrational and Brγ line emission, and with ALMA, which includes the CO(3-2) line and dust continuum emission. Both data-sets have the needed sub-arcsecond angular resolution to resolve the scales of SSC formation. The spectral resolutions are enough to resolve motions within SGMCs. Combining CO and H2 line emission is key in my PhD work. I use CO as a tracer of the distribution and kinematics of the molecular gas, and H2 as a tracer of the rate at which the gas mechanical energy is dissipated.My thesis focuses on diverse sources in the Antennae overlap region which trace different stages of star formation: the gathering of mass necessary to form SGMCs, the formation of PCCs within SGMCs and the disruption of a parent cloud by a newly formed SSC. I show that at each stage turbulence plays a key role. I found that the kinetic energy of the galaxies is not thermalized in large scale shocks, it drives the turbulence in the molecular ISM at a much higher level than what is observed in the Milky Way. Near-IR spectral diagnostics show that, outside of SSCs embedded in their parent clouds, the H2 line emission is powered by shocks and traces the dissipation of the gas turbulent kinetic energy. I relate the H2 emission to the loss of kinetic energy required to form gravitationally bound clouds. This interpretation is supported by the discovery of a compact, bright H2 source not associated with any known SSC. It has the largest H2/CO emission ratio and is located where the data show the largest velocity gradient in the interaction region. To our knowledge, this is the first time that an extragalactic source with such characteristics is identified. We would be witnessing the formation of a cloud massive enough to form a SSC. The data also allow us to study the disruption of a parent molecular cloud by an embedded SSC. Its matter is loosely bound and its gravity would be supported by turbulence, which makes it easier for feedback to disrupt the parent cloud. I end my manuscript presenting two projects. I propose to establish additional energy dissipation tracers observable with ALMA, which gives us the high spatial and spectral resolution needed to isolate scales at which clusters form. This is a Cycle 1 proposal accepted in first priority. I also plan to expand my work to other nearby extragalactic sources by investigating the turbulence-driven formation of stars in different extragalactic sources by combining near-IR and submillimeter observations.

This thesis is focused on design and implementation of procedural generator of galaxy for games or simulations. Second goal is implementation of demonstration application which is showing possible usage of generator. Generator is able to create galaxy by predefined types or by user created map.

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.

In the standard model of cosmology (ΛCDM) the first stars, star clusters, and galaxies are expected to have formed in short bursts of star formation in low-mass dark matter halos at high redshifts (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%5Csim%20%5C,6-10" data-classname="equation_inline" />). Up to this point, attempts to predict the properties and abundances of these luminous objects have made use of numerically expensive cosmological simulations. On top of being numerically expensive, these simulations often lack the required sub-parsec resolution needed to resolve the formation of compact star clusters and/or neglect possibly dominant stellar feedback processes. Motivated by this, I introduce Anaxagoras, as far as I know the most detailed analytical ab initio model of starbursts in low-mass halos to date. The model incorporates sub-models for gas cooling (including a new determination of the H2-cooling threshold in minihalos), central gas accretion and disk formation (using a new selfsimilarsolution), stellar feedback from radiation pressure (direct stellar radiation, Lyman-<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" data-classname="equation_inline" data-title="" /> scattering in H I, and multiple scattering of IR photons by dust), stellar winds, expanding HII regions, and (crudely) supernovae. The resulting star formation efficiency is used to predict the fraction of stars that remain gravitationally bound in a cluster following gas expulsion, andwhat fraction escape the central region of the halo, yet remain bound by the dark matter halo. I apply Anaxagoras to study star formation at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%3E%20%5C,6" data-classname="equation_inline" /> in satellite halos of the Milky Way using a halo merger tree code, as well as Population III (Pop III) star formation in minihalos. For the Milky Way setup, hundreds of galaxies are predicted to form with luminosities (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?L_%7B%5Crm%20V%7D%20%5C,%3C%5C,%20%5Crm%7Bfew%7D%5C,%20%5Ctimes%20%5C,%2010%5E4%20%5C:%20%5Crm%7BL%7D_%7B%5Codot%7D" data-classname="equation_inline" />), half-mass radii (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim%2010-200%5C:%5Crm%20pc" data-classname="equation_inline" />), mass-to-light ratios (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M/L_%7B%5Crm%20V%7D%20%5Csim%20100%20-%20%5Crm%7Bfew%7D%20%5C,%5Ctimes%5C,%2010%5E3%20%5C:%5Crm%7BM%7D_%7B%5Codot%7D/%5Crm%7BL%7D_%7B%5Codot%7D" data-classname="equation" />), and ages (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?13.18%5E%7B+0.29%7D_%7B-0.31%7D%5C:%5Crm%20Gyrs" data-classname="equation_inline" data-title="" />) in good agreement with the observed local population of Ultra-Faint Dwarfs. This shows that ΛCDM is able to explain the properties ofthe faintest dwarf galaxies without fine-tuning. Furthermore, at least ~ 40 compact (initial half-mass radii <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Csim%200.1-5%5C;%5Crm%7Bpc%7D" data-classname="equation_inline" />), old (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?13.27%5E%7B+0.21%7D_%7B-0.39%7D%5C:%5Crm%20Gyrs" data-classname="equation_inline" />) globular cluster (GC) candidates with initial stellar masses <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?10%5E5%20-%2010%5E6%20%5C:%20%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" />  are predicted to form at the center of low-mass halos, and could survive to the present-day and explain at least a fraction of the observed metal-poor GCs. Their properties are consistent with recent candidates for GCs residing in dark matter halos. Thus, Anaxagoras lends support to the viability of the scenario of GC formation in minihalos. Finally, the formation of Population III (Pop III) stars in minihalos is studied, with the conclusion that if Pop III stars are not overly massive (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?25%5C:%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" />) between ~ 1 − 30 stars could form per minihalo at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%20%3E%20%5C,20" data-classname="equation_inline" />, with the number increasing to ~ 10 − 500 stars per minihalo at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%5C,%3C%5C,15" data-classname="equation_inline" /> as Lyman-Werner feedback delay star formation until halos reach larger masses. In the case where Pop III stars are more massive (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?140%5C:%5Crm%7BM%7D_%7B%5Codot%7D" data-classname="equation_inline" data-title="" />) most minihalos form just a single star. Due to self-shielding of H2 in minihalos, I find that the cosmological Lyman-Werner background is insufficient to produce Pop III galaxies in atomic-cooling halos, with the implication that the number of massive Pop III galaxies/star clusters in the early Universe has been greatly overestimated in the literature that ignores self-shielding.

No description available.

Polarization is a powerful tool for understanding stellar atmospheres and circumstellar environments. Mira and semi-regular variable stars have been observed for decades and some are known to be polarimetrically variable, however, the semi-regular variable V Canes Venatici displays an unusually large, unexplained amount of polarization. We present ten years of optical polarization observations obtained with the HPOL instrument, supplemented by published observations spanning a total interval of about forty years for V CVn. We find that V CVn shows large polarization variations ranging from 1 - 6%. We also find that for the past forty years the position angle measured for V CVn has been virtually constant suggesting a long-term, stable, asymmetric structure about the star. We suggest that this asymmetry is caused by the presence of a stellar wind bow shock and tail, consistent with the star's large space velocity.

We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, δ Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, δ Ori Aa2, has a much lower X-ray luminosity than the brighter primary (δ Ori Aa1), δ Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around δ Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3−0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe XVII and Ne X are inconsistent with model predictions, which may be an effect of resonance scattering.

Line ratios in "fir" triplets of helium-like ions have proven to be a powerful diagnostic of conditions in X-ray emitting gas surrounding massive stars. Recent observations indicate that these ratios can be variable with time. The possible causes of variation in line ratios are limited: changes in the radiation field or changes in density, and changes in mass-loss or geometry. In this paper, we investigate the ability of changes in the radiation field to induce variability in the ratio R=f/i. To isolate the radiative effect, we use a heuristic model of temperature and radius changes in variable stars in the B and O range with low-density, steady-state winds. We model the changes in emissivity of X-ray emitting gas close to the star due to differences in level-pumping from available UV photons at the location of the gas. We find that under these conditions, variability in R is dominated by the stellar temperature. Although the relative amplitude of variability is roughly comparable for most lines at most temperatures, detectable variations are limited to a few lines for each spectral type. We predict that variable values in R due to stellar variability must follow predictable trends found in our simulations. Our model uses radial pulsations as a mode of stellar variability that maximizes the amplitude of variation in R. This model is robust enough to show which ions will provide the best opportunity for observing variability in the f/i ratio at different stellar temperatures, and the correlation of that variability with other observable parameters. In real systems, the effects would be more complex than in our model, with differences in phase and suppressed amplitude in the presence of non-radial pulsations. This suggests that changes in R across many lines concurrently are not likely to be produced by a variable radiation field.

<p> The globular cluster system of a nearby giant elliptical galaxy, NGC 5128 is studied to place constraints on the formation history of the galaxy. In this thesis, we have identified 190 new globular clusters via radial velocity measurements, bringing the total known population of globular clusters to 605 within this galaxy. We have examined the colour and spatial distributions of the globular cluster system and find it is bimodal in colour, with both a red and blue globular cluster population. The blue population is more spatially extended than the red, and both populations fall off in number density with radius as a power-law. There is a clear lack of globular clusters along the isophotal minor axis of the galaxy beyond a galactocentric radius of 15' warranting further search. With this new dataset, we have measured the ages, metallicities, and formation timescales for 72 globular clusters. The spectroscopic metallicity distribution function is bimodal indicating there is a metal-rich and metal-poor globular cluster population that corresponds to the red and blue globular clusters, respectively. We find the majority of both metal-rich (56%) and metal-poor (92%) globular clusters are older than 8 Gyr, comparable to the Milky Way globular cluster system. We do find a smaller fraction, 18% of our sample, are metal-rich globular clusters with ages younger than 5 Gyr, while the remaining globular clusters have intermediate ages between 5 -8 Gyr. The formation times of these globular clusters, estimated by their alpha-to-iron abundance ratios, indicate they formed quickly, on a timescale similar to globular clusters in most spiral galaxies, but on slower timescales than those in some other giant elliptical galaxies. The kinematics of the full globular cluster system is analyzed, as well as for the metal-rich and metal-poor globular clusters separately, as a function of galactocentric radius. We find the metal-poor globular cluster system has a small rotation signature of 17±14 km s-1 around no clearly defined axis and its dynamics are dominated by dispersion. The metal-rich globular cluster system has a mild rotation of 41 ± 15 km s-1 about the galaxy's isophotal major axis, following the rotation of a representative field star population, the planetary nebulae. The motion of the metal-rich globular cluster system is also dominated by random motion. We estimate the mass of the galaxy to be (5.5 ± 1.9) x 1011 with a mass-to-light ratio of 15.35 M0 /L80 using the globular cluster M0 population out to 20'. This estimate places NGC 5128 on a mass scale similar to other giant elliptical galaxies. The evidence collected suggests that NGC 5128 formed in a hierarchical scenario, gradually building up larger structure from smaller protogalaxies at early times in the history of the Universe. The group environment of NGC 5128 may have prolonged star formation within the galaxy as well, enabling a small spread in the old ages of globular clusters and also slowing the formation timescales compared to globular clusters in other giant elliptical galaxies. Results from this thesis also support more recent accretions in the history of NGC 5128, building up the more metal-rich and young globular clusters, which have a different rotation axis than the rest of the population. </p> / Thesis / Doctor of Philosophy (PhD)