ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Astrophysics
- Creators: Windhorst, Rogier A.
Description
Galaxies represent a fundamental catalyst in the ``lifecycle'' of matter in the Universe, and the study of galaxy assembly and evolution provides unique insight into the physical processes governing the transformation of matter from atoms to gas to stars. With the Hubble Space Telescope, the astrophysical community is able to study the formation and evolution of galaxies, at an unrivaled spatial resolution, over more than 90% of cosmic time. Here, I present results from two complementary studies of galaxy evolution in the local and intermediate redshift Universe which used new and archival HST images. First, I use archival broad-band HST WFPC2 optical images of local (d<63 Mpc) Seyfert-type galaxies to test the observed correlation between visually-classified host galaxy dust morphology and AGN class. Using quantitative parameters for classifying galaxy morphology, I do not measure a strong correlation between the galaxy morphology and AGN class. This result could imply that the Unified Model of AGN provides a sufficient model for the observed diversity of AGN, but this result could also indicate the quantitative techniques are insufficient for characterizing the dust morphology of local galaxies. To address the latter, I develop a new automated method using an inverse unsharp masking technique coupled to Source Extractor to detect and measure dust morphology. I measure no strong trends with dust-morphology and AGN class using this method, and conclude that the Unified Model remains sufficient to explain the diversity of AGN. Second, I use new UV-optical-near IR broad-band images obtained with the HST WFC3 in the Early Release Science (ERS) program to study the evolution of massive, early-type galaxies. These galaxies were once considered to be ``red and dead'', as a class uniformly devoid of recent star formation, but observations of these galaxies in the local Universe at UV wavelengths have revealed a significant fraction (30%) of ETGs to have recently formed a small fraction (5-10%) of their stellar mass in young stars. I extend the study of recent star formation in ETGs to intermediate-redshift 0.35<1.5 with the ERS data. Comparing the mass fraction and age of young stellar populations identified in these ETGs from two-component SED analysis with the morphology of the ETG and the frequency of companions, I find that at this redshift many ETGs are likely to have experienced a minor burst of recent star formation. The mechanisms driving this recent star formation are varied, and evidence for both minor merger driven recent star formation as well as the evolution of transitioning ETGs is identified.
ContributorsRutkowski, Michael (Author) / Windhorst, Rogier A. (Thesis advisor) / Bowman, Judd (Committee member) / Butler, Nathaniel (Committee member) / Desch, Steven (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2013
Description
Most stars form in groups, and these clusters are themselves nestled within larger associations and stellar complexes. It is not yet clear, however, whether stars cluster on preferred size scales within galaxies, or if stellar groupings have a continuous size distribution. I have developed two methods to select stellar groupings across a wide range of size-scales in order to assess trends in the size distribution and other basic properties of stellar groupings. The first method uses visual inspection of color-magnitude and color-color diagrams of clustered stars to assess whether the compact sources within the potential association are coeval, and thus likely to be born from the same parentmolecular cloud. This method was developed using the stellar associations in the M51/NGC 5195 interacting galaxy system. This process is highly effective at selecting single-aged stellar associations, but in order to assess properties of stellar clustering in a larger sample of nearby galaxies, an automated method for selecting stellar groupings is needed. I have developed an automated stellar grouping selection method that is sensitive to stellar clustering on all size scales. Using the Source Extractor software package on Gaussian-blurred images of NGC 4214, and the annular surface brightness to determine the characteristic size of each cluster/association, I eliminate much of the size and density biases intrinsic to other methods. This automated method was tested in the nearby dwarf irregular galaxy NGC 4214, and can detect stellar groupings with sizes ranging from compact clusters to stellar complexes. In future work, the automatic selection method developed in this dissertation will be used to identify stellar groupings in a set of nearby galaxies to determine if the size scales for stellar clustering are uniform in the nearby universe or if it is dependent on local galactic environment. Once the stellar clusters and associations have been identified and age-dated, this information can be used to deduce disruption times from the age distribution as a function of the position of the stellar grouping within the galaxy, the size of the cluster or association, and the morphological type of the galaxy. The implications of these results for galaxy formation and evolution are discussed.
ContributorsKaleida, Catherine (Author) / Scowen, Paul A. (Thesis advisor) / Windhorst, Rogier A. (Thesis advisor) / Jansen, Rolf A. (Committee member) / Timmes, Francis X. (Committee member) / Scannapieco, Evan (Committee member) / Arizona State University (Publisher)
Created2011
Description
Reionization is the phase transition of intergalactic atoms from being neutral to
becoming fully ionized. This process began ∼400 Myr after the Big Bang, when the first
stars and black holes began emitting ionizing radiation from stellar photospheres and
accretion disks. Reionization completed when all of the neutral matter between galaxies
became ionized ∼1 Gyr after the Big Bang, and the Universe became transparent as
it is today.
Characteristics of the galaxies that drove reionization are mostly unknown. The
physical mechanisms that create ionizing radiation inside these galaxies, and the
paths for this light to escape are even more unclear. To date, only a small fraction of
the numerous searches for this escaping light have been able to detect a faint signal
from distant galaxies, and no consensus on how Reionization was completed has been
established.
In this dissertation, I discuss the evolution of the atomic matter between galaxies
from its initially ionized state, to its current re-ionized state, potential sources of
re-ionizing energy, and the theoretical and observational status of the characteristics of
these sources. I also present new constraints on what fraction of the ionizing radiation
escapes from galaxies using Hubble Space Telescope UV imaging, theoretical models
of the stellar and accretion disk radiation, and models of the absorption of ionizing
radiation by the intergalactic medium.
becoming fully ionized. This process began ∼400 Myr after the Big Bang, when the first
stars and black holes began emitting ionizing radiation from stellar photospheres and
accretion disks. Reionization completed when all of the neutral matter between galaxies
became ionized ∼1 Gyr after the Big Bang, and the Universe became transparent as
it is today.
Characteristics of the galaxies that drove reionization are mostly unknown. The
physical mechanisms that create ionizing radiation inside these galaxies, and the
paths for this light to escape are even more unclear. To date, only a small fraction of
the numerous searches for this escaping light have been able to detect a faint signal
from distant galaxies, and no consensus on how Reionization was completed has been
established.
In this dissertation, I discuss the evolution of the atomic matter between galaxies
from its initially ionized state, to its current re-ionized state, potential sources of
re-ionizing energy, and the theoretical and observational status of the characteristics of
these sources. I also present new constraints on what fraction of the ionizing radiation
escapes from galaxies using Hubble Space Telescope UV imaging, theoretical models
of the stellar and accretion disk radiation, and models of the absorption of ionizing
radiation by the intergalactic medium.
ContributorsSmith, Brent Matthew (Author) / Windhorst, Rogier A. (Thesis advisor) / Bowman, Judd (Committee member) / Borthakur, Sanchayeeta (Committee member) / Butler, Nathaniel (Committee member) / Mauskopf, Phillip (Committee member) / Arizona State University (Publisher)
Created2019