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The results of a study of the neutral hydrogen (HI) content and distribution within a sample of 18 blue compact dwarf galaxies (BCDs) are presented. An investigation of the behaviour of the gas-to-dust ratio (GDR) as a function of metallicity (Z) is also presented. Observations of these BCDs was performed using the Very Large Array (VLA) in 2009, a year in which the array was undergoing a technological upgrade to the the Karl G. Jansky VLA (JVLA). The observations were reduced and images processed using the Astronomical Image Processing Software (AIPS), and data cubes for each galaxy were produced. The results include detections of eleven HI lines (two new detections) and ten background continuum sources (two new discoveries). All detections are at a higher resolution and/or sensitivity than previous measurements. These detections spanned a large range of line widths and HI masses; some masses comparable to those in normal galaxies. Of particular interest was the discovery of a compact absorption feature in the dwarf galaxy Haro 11. A paper submitted to the Monthly Notices of the Royal Astronomical Society (MNRAS) Letters on this discovery is presented. Another significant result was the discovery of a highly extended and massive HI region in the dwarf galaxy CGCG 297-017. For those galaxies with no detected HI line or radio continuum, an upper limit to the flux density was computed, which was used to derive upper limits to the HI mass or star-formation rate (SFR) respectively. Three HI flux density upper limits are new results, and seven continuum flux density upper limits are also new. The GDR-Z relation at low metallicities shows a potential power law or broken power law relation with a turning point at Z=7.96 or Z=8.05. To within error, these turning points and power law indices of the broken power law fits are consistent with other work. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-30 20:21:20.045

I review theoretical expectations for the probable appearance of galaxies during their formation phase, placing particular emphasis on the uncertainties in these ideas. Recent models suggest that formation may occur relatively recently, but that young galaxies are less spectacular than previously supposed. They may be analogous to recently discovered high red - shift radio galaxies, and indeed they may have been observed directly in faint galaxy counts. I summarise several other lines of evidence which suggest that galaxy formation may have been a recent process. Finally I give preliminary results from a detailed analytic study of the observable properties of young galaxies in a Cold Dark Matter universe. Predictions are given for faint galaxy counts and redshift distributions, and for the galaxy luminosity function.

The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass-halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy's total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined specific frequency of between 0.06 and 0.39 GCs per 10(9)M(circle dot) of total mass, the surviving Milky Way (MW) subhalos with masses smaller than 10(10)M(circle dot) could host as many as 5-31 GCs, broadly consistent with the actual population of outer halo MW GCs, although matching the radial distribution in detail remains a challenge. Using a subhalo mass function from published high-resolution numerical simulations and a Poissonian model for populating those halos with the aforementioned empirically constrained frequency, we find that about 90% of these GCs lie in lower-mass subhalos than that of Eri II. From what we know about the stellar mass-halo mass function, the subhalo mass function, and the mass-normalized GC specific frequency, we conclude that some of the MW's outer halo GCs are likely to be hosted by undetected subhalos with extremely modest stellar populations.

In this work I have examined the spatially resolved properties of the local early- type galaxy population. Using Hubble Space Telescope and ground based pho- tometry I constructed Jeans Anisotropic Multi Gaussian Expansion models of the SAURON sample of early-type galaxies, from which I determined the depth of the local gravitational potential well, quantified by the local escape velocity, Vesc. I found that Vesc correlated tightly with the three Lick indices: Mgb, Fe5015 and Hβ. The Mgb-Vesc relation within individual galaxies is identical to that between different galaxies; the relation is both local and global. The Mgb-Vesc relation is: log Mgb = (0.35 ± 0.01) log Vesc − (0.41 ± 0.03). While the metallicity, [Z/H] is cor- related with Vesc it does not show the same local and global behaviour. Age (t) and alpha enhancement ([α/Fe]) are only weakly correlated with Vesc. A combination of [Z/H] and t is tightly correlated with Vesc, with scatter comparable to the Mgb-Vesc relation, and does show the local and global behaviour. This combination is given by: log Vesc = 0.85[Z/H] + 0.43 log t. Using the volume limited ATLAS3D sample of 260 local ETGs I examined in detail the behaviour of the Mgb-Vesc relation and its dependence on other galaxy properties. I found that systematic deviations from the relation correlate with the local environmental density and molecular gas mass of a galaxy, and with the local [α/Fe] measurement. I found that there is a population of galaxies that do not follow the relation, found only at Vesc < 400 kms−1. These galaxies have negative gradients, high central Hβ indices and young (t < 3 Gyrs) ages. Using stellar population models I demonstrated that these negative gradient galaxies are perturbed from the relation by recent star formation and will return to the relation as they age. I also describe the observation, reduction and analysis of a new sample of ETGs in the core of the Coma cluster, the highest density environment in the local Universe, observed with the SWIFT Integral Field Spectrograph. I determined the fraction of slow rotators in the sample, comparing it to results from the ATLAS3D survey, and found an enhanced slow rotator fraction in the Coma cluster. I also determined the Fundamental Plane of Coma early-type galaxies, given by: log Re = (1.20 ± 0.22) log σe − (0.79 ± 0.09) log⟨Ie⟩.

Cosmological hydrodynamic simulations have shown that galaxies are fed by dense, cold gas streams at high redshift. However, the presence of such gas has never been observationally confirmed. Using the Horizon- MareNostrum simulation, I examined whether cold flows are detectable with low-ionisation metal absorption lines, such as C II 1334. It is concluded that due to their low metallicity and density, it is extremely difficult to prove/disprove the presence of cold flows using the metal absorption lines. Revisiting the acquisition of angular momentum in disc galaxies using high resolution simulations, I found that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum which is systematically and significantly higher (at minimum by a factor of 2) than that of the dark matter halo as a whole. Whereas cold streams directly deposit this large amount of angular momentum within a sphere of radius r~0.1 Rvir, dark matter particles easily pass through the central region, depositing their angular momentum over a much more spatially extended region. As a result, in our simulations neither the total specific angular momentum of the baryons nor its radial profile ever follows that of the virialised dark matter halo, contrary to what is typically assumed in the standard theory of disc galaxy formation. In order to better understand the formation of disc galaxies and the missing baryon problem in a LCDM universe, continuous, collective galactic winds are implemented. It is demonstrated that stellar feedback processes are able to suppress star formation by ~30% at z=3, compared to that from the run without feedback sources, but it still produces an unrealistic central peak in the rotation curve. Although inclusion of hypernovae further suppresses star formation, it is unable to quench the formation of low-angular momentum stars enough to remove the peaked rotation curves at high redshift. Finally, feedback from active galactic nuclei turns out to be effective at suppressing star formation in massive galaxies at 1<z<2, reproducing their observed number densities in the redshift range. However, further suppression of residual star formation is required to form quiescent galaxies at z=2.

Tudo que vive por muito tempo está apto a contribuir com boas histórias sobre o passado. Isto não é diferente com as estrelas azuis tardias que são encontradas em todos os ambientes estelares. Essas estrelas velhas mostram-se aparentemente muito jovens, e talvez por isso, nunca tenham sido ouvidas em um contexto maior que suas próprias vidas. Este trabalho interpreta a história que elas contam sobre a natureza do halo galáctico, através de seus parâmetros físicos fundamentais: coordenadas, temperaturas, gravidades superficiais, metalicidades, cores, distâncias e idades. Este trabalho utiliza dados do Sloan Digital Sky Survey para reunir candidatas a estrelas azuis tardias (BSSs) através de critérios espectrofotométricos. Ao todo, 8001 candidatas a BSSs sobreviveram aos diversos métodos de seleção aplicados, constituindo a base de dados deste estudo. Essa amostra permitiu estimar a frequência média de BSSs no halo em relação ao número de estrelas azuis do ramo horizontal (BHBs) em 2.15±0.13 BSS/BHB, valor similar ao encontrado em galáxias anãs próximas (~2.24±0.17). Verificou-se também que as BSSs apresentam um gradiente de cor em função da distância ao centro Galáctico, aparentemente independente da metalicidade. À variação de cor foi atribuída uma variação de idade, que forneceu um gradiente médio de -0.034±0.002 Ganos/kpc no halo. Esse resultado mostra que as regiões mais velhas se concentram preferencialmente no centro da Galáxia, e ficam cada vez mais jovens para distâncias maiores. O gradiente de cor das BSSs possibilitou a construção de mapas de idade do halo galáctico, que foram superpostos às posições centrais de uma coleção de subestruturas encontrada na literatura. Aproximadamente 60% delas tem posições que concordam com as flutuações de cor observadas nos mapas, além de apresentarem propriedades cinemáticas e químicas similares às BSSs nessas regiões (em 2). / Everything that lives long enough is able to contribute with good stories about the past. This statement also applies to the blue straggler stars (BSSs), which can be found in all stellar environments. These old stars appear to be very young and perhaps because of this have never been properly addressed in a context larger than their own lives. This work interprets the story they tell about the nature of the Galactic halo, through their fundamental physical parameters: coordinates, temperatures, surface gravities, metallicities, colors, distances and ages. This work uses the Sloan Digital Sky Survey (SDSS) database to select BSS candidates through photometric and spectroscopic criteria. Altogether, 8001 BSS candidates survived the various selection methods applied and were used as the database for this study. This large sample allowed the determination of the average frequency of BSSs in the halo, compared to the number of blue horizontal branch stars (BHBs). The average frequency of BSS/BHB found in the galactic halo by this work is 2.15±0.13, very similar to this ratio in nearby dwarf galaxies (~2.24±0.17). In addition, this work verified that the BSSs show a color gradient as a function of distance to the galactic center, which appears to be independent from metallicity. To this color variation was assigned an age variation, yielding an average gradient of -0.034±0.002 Gyr/kpc in the halo. This result shows that the older regions preferentially occur in the center of the Galaxy and get younger for larger distances. The BSSs color gradient allowed the construction of galactic halo age maps. These maps were superimposed to the central positions of a collection of substructures found in the literature. Approximately 60% of them have positions that agree with the color fluctuations observed in the maps, as well as having similar kinematic and chemical properties to the BSSs in those regions (within 2).

Tudo que vive por muito tempo está apto a contribuir com boas histórias sobre o passado. Isto não é diferente com as estrelas azuis tardias que são encontradas em todos os ambientes estelares. Essas estrelas velhas mostram-se aparentemente muito jovens, e talvez por isso, nunca tenham sido ouvidas em um contexto maior que suas próprias vidas. Este trabalho interpreta a história que elas contam sobre a natureza do halo galáctico, através de seus parâmetros físicos fundamentais: coordenadas, temperaturas, gravidades superficiais, metalicidades, cores, distâncias e idades. Este trabalho utiliza dados do Sloan Digital Sky Survey para reunir candidatas a estrelas azuis tardias (BSSs) através de critérios espectrofotométricos. Ao todo, 8001 candidatas a BSSs sobreviveram aos diversos métodos de seleção aplicados, constituindo a base de dados deste estudo. Essa amostra permitiu estimar a frequência média de BSSs no halo em relação ao número de estrelas azuis do ramo horizontal (BHBs) em 2.15±0.13 BSS/BHB, valor similar ao encontrado em galáxias anãs próximas (~2.24±0.17). Verificou-se também que as BSSs apresentam um gradiente de cor em função da distância ao centro Galáctico, aparentemente independente da metalicidade. À variação de cor foi atribuída uma variação de idade, que forneceu um gradiente médio de -0.034±0.002 Ganos/kpc no halo. Esse resultado mostra que as regiões mais velhas se concentram preferencialmente no centro da Galáxia, e ficam cada vez mais jovens para distâncias maiores. O gradiente de cor das BSSs possibilitou a construção de mapas de idade do halo galáctico, que foram superpostos às posições centrais de uma coleção de subestruturas encontrada na literatura. Aproximadamente 60% delas tem posições que concordam com as flutuações de cor observadas nos mapas, além de apresentarem propriedades cinemáticas e químicas similares às BSSs nessas regiões (em 2). / Everything that lives long enough is able to contribute with good stories about the past. This statement also applies to the blue straggler stars (BSSs), which can be found in all stellar environments. These old stars appear to be very young and perhaps because of this have never been properly addressed in a context larger than their own lives. This work interprets the story they tell about the nature of the Galactic halo, through their fundamental physical parameters: coordinates, temperatures, surface gravities, metallicities, colors, distances and ages. This work uses the Sloan Digital Sky Survey (SDSS) database to select BSS candidates through photometric and spectroscopic criteria. Altogether, 8001 BSS candidates survived the various selection methods applied and were used as the database for this study. This large sample allowed the determination of the average frequency of BSSs in the halo, compared to the number of blue horizontal branch stars (BHBs). The average frequency of BSS/BHB found in the galactic halo by this work is 2.15±0.13, very similar to this ratio in nearby dwarf galaxies (~2.24±0.17). In addition, this work verified that the BSSs show a color gradient as a function of distance to the galactic center, which appears to be independent from metallicity. To this color variation was assigned an age variation, yielding an average gradient of -0.034±0.002 Gyr/kpc in the halo. This result shows that the older regions preferentially occur in the center of the Galaxy and get younger for larger distances. The BSSs color gradient allowed the construction of galactic halo age maps. These maps were superimposed to the central positions of a collection of substructures found in the literature. Approximately 60% of them have positions that agree with the color fluctuations observed in the maps, as well as having similar kinematic and chemical properties to the BSSs in those regions (within 2).