No description available.

No description available.

I use observational evidence to examine the nature and role in galaxy evolution of a population of dust-obscured galaxies (DOGs) at z ∼ 2. These objects are selected with the Spitzer Space Telescope, are bright in the mid-infrared (mid-IR) but faint in the optical, and contribute a significant fraction of the luminosity density in the universe at z ∼ 2. The first component of my thesis is a morphological study using high spatial resolution imaging with the Hubble Space Telescope of two samples of DOGs. One set of 33 DOGs have mid-IR spectral features typical of an obscured active galactic nucleus (AGN) (called power-law DOGs), while the other set of 20 DOGs have a local maximum in their spectral energy distribution (SED) at rest-frame 1.6μm associated with stellar emission (called bump DOGs). The host galaxy dominates the light profile in all but two of these DOGs. In addition, bump DOGs are larger than power-law DOGs and exhibit more diffuse and irregular morphologies; these trends are consistent with expectations from simulations of major mergers in which bump DOGs evolve into power-law DOGs. The second component of my thesis is a study of the dust properties of DOGs, using sub-mm imaging of 12 power-law DOGs. These power-law DOGs are hyper- luminous (2 × 10¹³ L⊙) and have predominantly warm dust (T(dust) > 35 - 60 K). These results are consistent with an evolutionary sequence in which power-law DOGs represent a brief but important phase when AGN feedback heats the interstellar medium and quenches star-formation. The third component of my thesis is a study of the stellar masses and star- formation histories of DOGs, using stellar population synthesis models and broad- band photometry in the rest-frame ultra-violet, optical, and near-IR. The best-fit quantities indicate bump DOGs are less massive than power-law DOGs. The relatively low stellar masses found from this line of analysis favor a merger-driven origin for ULIRGs at z ∼ 2.

We present Chandra ACIS-S and Australia Telescope Compact Array (ATCA) radio continuum observations of the strongly lensed dusty, star-forming galaxy SPT-S J034640-5204.9 (hereafter SPT0346-52) at z = 5.656. This galaxy has also been observed with ALMA, HST, Spitzer, Herschel, Atacama Pathfinder EXperiment, and the Very Large Telescope. Previous observations indicate that if the infrared (IR) emission is driven by star formation, then the inferred lensing-corrected star formation rate (SFR) (similar to 4500 M-circle dot yr(-1)) and SFR surface density Sigma(SFR) (similar to 2000 M-circle dot yr(-1) kpc(-2)) are both exceptionally high. It remained unclear from the previous data, however, whether a central active galactic nucleus (AGN) contributes appreciably to the IR luminosity. The Chandra upper limit shows that SPT0346-52 is consistent with being star formation dominated in the X-ray, and any AGN contribution to the IR emission is negligible. The ATCA radio continuum upper limits are also consistent with the FIR-to-radio correlation for star-forming galaxies with no indication of an additional AGN contribution. The observed prodigious intrinsic IR luminosity of (3.6 +/- 0.3) x 10(13) L-circle dot originates almost solely from vigorous star formation activity. With an intrinsic source size of 0.61 +/- 0.03 kpc, SPT0346-52 is confirmed to have one of the highest Sigma(SFR) of any known galaxy. This high Sigma(SFR), which approaches the Eddington limit for a radiation pressure supported starburst, may be explained by a combination of very high star formation efficiency and gas fraction.

No description available.

Magíster en Ciencias, Mención Astronomía / Se presenta fotometría óptica en 11 bandas medias a partir de observaciones realizadas con el telescopio de 2.2m en LSO (WFI) sobre un campo de ~30'×30' deg extendido en el Hubble Deep Field-South (EHDF-S), el cual es uno de los campos que contiene información en multibandas como parte del Multiwavelength Survey by Yale-Chile (MUSYC). Este campo tiene una gran cantidad de datos públicos y datos auxiliares en bandas UV, óptico, infrarrojo cercano e infrarrojo lejano. Se determinaron aperturas óptimas para fotometría de alta precisión para diversas fuentes y brillos. Se proporcionan incertezas en magnitud a través de una técnica mejorada que considera correlaciones a mayor y menor escala en el ruido. Se incluyen datos auxiliares en el óptico a partir del catálogo de MUSYC en bandas UBVRIz ' hasta una magnitud total de R=25 (AB), además de datos en infrarrojo cercano JHK de dos campos de 10 '× 10' deg con profundidades de J~22.5, H~21.5 y K~21 (5σ; Vega). Se creó un catálogo fotométrico de ~62.000 galaxias detectadas en la imagen BVR de MUSYC. Se miden redshifts fotométricos mediante el código EAzY y se compara con ~500 fuentes identificadas espectroscópicamente con la finalidad de probar la precisión y desempeño de los filtros en bandas medias. Los redshifts fotométricos resultaron más confiables para R<24 cuando la muestra contiene ~12.000 galaxias, particularmente en 0.1 < z < 1.2, región de sampleo en el óptico de características como el quiebre de Balmer. La precisión de los redshifts fotométricos en Δz/(1+z) es de 0.029, lo cual es comparable a estudios recientes con un mejoramiento del 20%. Estos valores se degradan en calidad para galaxias más débiles o cuando se utilizan menos bandas. Como demostración de la calidad de los resultados, se derivan tipos espectrales de las fuentes, luego se construyen funciones de luminosidad para comparar con trabajos similares, y así confirmar la fuerte dependencia de las SEDs con la densidad numérica de fuentes. Se incorporan datos observacionales en radio en el HDFS del Australia Telescopio Hubble Deep Field-South para estudiar en detalle su población. Este proyecto realizó observaciones en cuatro longitudes de onda, 20, 11, 6 y 3 cm y alcanza una sensibilidad en rms alrededor de 10 μJy para cada longitud de onda. Utilizando una muestra de 227 fuentes en radio seleccionadas, se realiza una clasificación detallada de la población en AGNs (-loud de radio (9%) y -quiet (46%)), galaxias con formación estelar (SFG; 39%), y galaxias normales (6%), usando los redshifts fotométricos, información en multibanda, un template combinado quasares, índices espectrales, las SEDs derivadas y la dependencia redshift luminosidad. Se confirman los resultados recientes sobre la disribución de AGNs y SFGs. Asimismo las LFs muestran consistencia para las fuentes en radio para z~1.0. Los resultados obtenidos siguen la tendencia de los trabajos previos de los últimos 4 a 5 años en la distribución de las fuentes de radio, y sugiere nuevas metodologías en torno a la caracterizacón la población en radio.

In this Thesis we describe a semi-analytic model of galaxy formation. We apply the model to the problem of galaxy clustering and show that the dependence of galaxy formation efficiency on halo mass leads to a scale-dependent bias in the distribution of galaxies relative to the distribution of mass. Remarkably, this results in a correlation function in a flat, Ωo = 0.3, CDM model that is close to a power-law over four orders of magnitude in amplitude and which agrees well with the correlation function of galaxies measured in the APM survey. The galaxy velocity dispersion is ~ 40% lower than that of the dark matter. Biases cause the redshift space correlation functions of model galaxies and dark matter to be remarkably similar to each other. A dependence of clustering strength on galaxy luminosity exists for extremely bright galaxies and for galaxies selected either by morphology or by colour. We present predictions for the reionization of the intergalactic medium by stars in high-redshift galaxies, including the effects of absorption by interstellar gas and dust. We combine our model with an N-body simulation to calculate the temperature anisotropies induced in the cosmic microwave background by reionization. Finally, we test key aspects of the model. We use ROSAT PSPC data to search for extended X-ray emission from the halos of three nearby, massive, late-type galaxies. The luminosity lies well below the model prediction. We discuss this discrepancy and consider a number of possible explanations. By comparing the statistical properties of galaxies in our model with those of galaxies formed in cosmological hydrodynamics simulations we show that the two techniques produce broadly consistent predictions. However, individual statistics, such as the galaxy mass function, may differ by factors of 2-4. We identify possible reasons for these discrepancies, thereby highlighting avenues for future work to explore.

We use the 2dF QSO Redshift Survey, to investigate whether QSOs are detectably gravitationally lensed. Lensing could magnify and distort light from QSOs, influencing QSO numbers near galaxies, which trace structure in our Universe. Following Boyle, Fong & Shanks (1988), we find a 3σ anti-correlation between QSOs and galaxy groups of strength W (_gg)(< 10') = -0.049. We limit absorption by dust in groups to A(_B) < 0.04 mag. To explain the anti-correlation by dust would need Ab ≈ 0.2 mag. We demonstrate that if the dearth of QSOs around groups is due to statistical lensing, more mass would be required in groups than Ω(_m) = 0.3 models suggest. We use a mock catalogue to test how many of our "2D" galaxy groups, which are detected using angular information, are associated in redshift-space. We then utilise 2dF Galaxy Redshift Survey groups, which are selected to trace dark matter haloes, to test the hypothesis that there is more mass in groups than Ωr(_m) = 0.3 models suggest, finding we cannot discount a lensing mass of 2dFGRS groups that is consistent with ACDM. We find QSOs and galaxies are also anti-correlated at the 3σ level, with strength w(< 10’) = -0.007 and use stars as a control sample to rule out observational systematics as a cause. By measuring QSO colours as a function of QSO-galaxy separation, we argue that obscuration by dust in galaxies could explain at most 30-40 per cent of the anti correlation. We show that if the anti-correlation is due to lensing, galaxies would be anti-biased [b ~ 0.05) on small scales. We discuss two surveys carried out to count faint QSOs, which newly identify 160 QSOs. We calculate that the faint-end QSO number-counts have a slope of 0.29 ± 0.03. Finally, we use our faint QSO data, to estimate that ~ 85(75) per cent of g < 21.15 (≥ 21.15) candidates targeted by the 2dFSDSS survey will be QSOs.

No description available.

No description available.