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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The structure of galaxies : the division of stellar mass by morphological type and structural component

Kelvin, Lee Steven January 2013 (has links)
The mechanisms which cause galaxies to form and evolve each leave behind distinct structural markers in their wake. Dynamically hot processes (e.g., monolithic collapse, hierarchical merging) give rise to pressure-supported spheroidal structures, including elliptical galaxies and classical bulges. By contrast, dynamically cold processes (e.g., gas accretion, AGN splashback) lead to flattened rotationally-supported disk-like structures, often found on their own or as part of a spiral galaxy. If left in isolation for a sufficient length of time, secular evolutionary processes cause the formation of a bar-like structure within the disk, precipitating the genesis of a rotationally-supported pseudo-bulge. Robustly measuring galaxy structure enables us to ascertain the relative importance of these competing evolutionary mechanisms and; in so doing, help broaden our understanding of how the Universe around us came to be. This thesis explores the relation between galaxy structure, morphology and stellar mass. In the first part I present single-Sérsic two-dimensional model fits to 167,600 galaxies modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey (UKIDSS LAS) imaging data available via the Galaxy and Mass Assembly (GAMA) data base. In order to facilitate this study, we developed Structural Investigation of Galaxies via Model Analysis (SIGMA): an automated wrapper around several contemporary astronomy software packages. We confirm that variations in global structural measurements with wavelength arise due to the effects of dust attenuation and stellar population/metallicity gradients within galaxies. In the second part of this thesis we establish a volume-limited sample of 3,845 galaxies in the local Universe and visually classify these galaxies according to their morphological Hubble type. We find that single-Sérsic photometry accurately reproduces the morphology luminosity functions predicted in the literature. We employ multi-component Sérsic profiling to provide bulge-disk decompositions for this sample, allowing for the luminosity and stellar mass to be divided between the key structural components: spheroids and disks. Grouping the stellar mass in these structures by the evolutionary mechanisms that formed them, we find that hot-mode collapse, merger or otherwise turbulent mechanisms account for ~46% of the total stellar mass budget, cold-mode gas accretion and splashback mechanisms account for ~48% of the total stellar mass budget and secular evolutionary processes for ~6.5% of the total stellar mass budget in the local (z<0.06) Universe.
2

The cosmic web unravelled : a study of filamentary structure in the Galaxy and Mass Assembly survey

Alpaslan, Mehmet January 2014 (has links)
I have investigated the properties of the large scale structure of the nearby Universe using data from the Galaxy and Mass Assembly survey (GAMA). I generated complementary halo mass estimates for all groups in the GAMA Galaxy Group Catalogue (G³C) using a modified caustic mass estimation algorithm. On average, the caustic mass estimates agree with dynamical mass estimates within a factor of 2 in 90% of groups. A volume limited sample of these groups and galaxies are used to generate the large scale structure catalogue. An adapted minimal spanning tree algorithm is used to identify and classify structures, detecting 643 filaments that measure up to 200 Mpc/h, each containing 8 groups on average. A secondary population of smaller coherent structures, dubbed `tendrils,' that link filaments together or penetrate into voids are also detected. On average, tendrils measure around 10 Mpc/h and contain 6 galaxies. The so-called line correlation function is used to prove that tendrils are real structures rather than accidental alignments. A population of isolated void galaxies are also identified. The properties of filaments and tendrils in observed and mock GAMA galaxy catalogues agree well. I go on to show that voids from other surveys that overlap with GAMA regions contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of the galaxies observed by a survey. Finally, I examine the properties of galaxies in different environments, finding that galaxies in filaments tend to be early-type, bright, spheroidal, and red whilst those in voids are typically the opposite: blue, late-type, and more faint. I show that group mass does not correlate with the brightness and morphologies of galaxies and that the primary driver of galaxy evolution is stellar mass.

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