Matching Items (7)
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- All Subjects: White Dwarfs
- All Subjects: Galaxy evolution
- Creators: Young, Patrick
- Member of: Theses and Dissertations
Description
3D models of white dwarf collisions are used to assess the likelihood of double-degenerate mergers as progenitors for Type Ia supernovae (henceforth SNIa) and to identify observational signatures of double-degenerate collisions. Observations of individual SNIa, SNIa rates in different galaxy types, and double white dwarf binary systems suggest that mergers or collisions between two white dwarfs play a role in the overall SNIa population. Given the possibility of two progenitor systems (single-degenerate and double-degenerate), the sample of SNIa used in cosmological calcula- tions needs to be carefully examined. To improve calculations of cosmological parameters, the development of calibrated diagnostics for double-degenerate progenitor SNIa is essential. Head-on white dwarf collision simulations are used to provide an upper limit on the Ni-56 production in white dwarf collisions. In chapter II, I explore zero impact parameter collisions of white dwarfs using the Eulerian grid code FLASH. The initial 1D white dwarf profiles are created assuming hydrostatic equilibrium and a uniform composition of 50% C-12 and 50% O-16. The masses range from 0.64 to 0.81 solar masses and have an isothermal temperature of 10^7 K. I map these 1D models onto a 3D grid, where the dimensions of the grid are each eight times the white dwarf radius, and the dwarfs are initially placed four white dwarf radii apart (center to center). To provide insight into a larger range of physical possibilities, I also model non-zero impact parameter white dwarf collisions (Chapter III). Although head-on white dwarf collisions provide an upper limit on Ni-56 production, non-zero impact parameter collisions provide insight into a wider range of physical scenarios. The initial conditions (box size, initial separation, composition, and initial temperature) are identical to those used for the head-on collisions (Chapter II) for the same range of masses. For each mass pair- ing, collision simulations are carried out at impact parameters b=1 and b=2 (grazing). Finally, I will address future work to be performed (Chapter IV).
ContributorsHawley, Wendy Phyllis (Author) / Timmes, Frank (Thesis advisor) / Young, Patrick (Committee member) / Starrfield, Sumner (Committee member) / Fouch, Matt (Committee member) / Patience, Jennifer (Committee member) / Arizona State University (Publisher)
Created2012
Description
I combine, compare, and contrast the results from two different numerical techniques (grid vs. particle methods) studying multi-scale processes in galaxy and structure formation. I produce a method for recreating identical initial conditions for one method from those of the other, and explore methodologies necessary for making these two methods as consistent as possible. With this, I first study the impact of streaming velocities of baryons with respect to dark matter, present at the epoch of reionization, on the ability for small halos to accrete gas at high redshift. With the inclusion of this stream velocity, I find the central density profile of halos is reduced, overall gas condensation is delayed, and infer a delay in the inevitable creation of stars.
I then combine the two numerical methods to study starburst outflows as they interact with satellite halos. This process leads to shocks catalyzing the formation of molecular coolants that lead to bursts in star formation, a process that is better captured in grid methods. The resultant clumps of stars are removed from their initial dark matter halo, resemble precursors to modern-day globular clusters, and their formation may be observable with upcoming telescopes.
Finally, I perform two simulation suites, comparing each numerical method's ability to model the impact of energetic feedback from accreting black holes at the core of giant clusters. With these comparisons I show that black hole feedback can maintain a hot diffuse medium while limiting the amount of gas that can condense into the interstellar medium, reducing the central star formation by up to an order of magnitude.
I then combine the two numerical methods to study starburst outflows as they interact with satellite halos. This process leads to shocks catalyzing the formation of molecular coolants that lead to bursts in star formation, a process that is better captured in grid methods. The resultant clumps of stars are removed from their initial dark matter halo, resemble precursors to modern-day globular clusters, and their formation may be observable with upcoming telescopes.
Finally, I perform two simulation suites, comparing each numerical method's ability to model the impact of energetic feedback from accreting black holes at the core of giant clusters. With these comparisons I show that black hole feedback can maintain a hot diffuse medium while limiting the amount of gas that can condense into the interstellar medium, reducing the central star formation by up to an order of magnitude.
ContributorsRichardson, Mark Lawrence Albert (Author) / Scannapieco, Evan (Thesis advisor) / Rhoads, James (Committee member) / Scowen, Paul (Committee member) / Timmes, Frank (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2014
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
Galaxy formation is a complex process with aspects that are still very uncertain or unknown. A mechanism that has been utilized in simulations to successfully resolve several of these outstanding issues is active galactic nucleus (AGN) feedback. Recent work has shown that a promising method for directly measuring this energy is by looking at small increases in the energy of cosmic microwave background (CMB) photons as they pass through ionized gas, known as the thermal Sunyaev-Zel’dovich (tSZ) effect.
In this work, I present stacked CMB measurements of a large number of elliptical galaxies never before measured using this method. I split the galaxies into two redshift groups, "low-z" for z=0.5-1.0 and “high-z” for z=1.0-1.5. I make two independent sets of CMB measurements using data from the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT), respectively, and I use data from the Planck telescope to account for contamination from dust emission. With SPT I find average thermal energies of 7.6(+3.0/−2.3) × 10^60 erg for 937 low-z galaxies, and 6.0(+7.7/−6.3) × 10^60 erg for 240 high-z galaxies. With ACT I find average thermal energies of 5.6(+5.9/−5.6) × 10^60 erg for 227 low-z galaxies, and 7.0(+4.7/−4.4) × 10^60 erg for 529 high-z galaxies.
I then attempt to further interpret the physical meaning of my observational results by incorporating two large-scale cosmological hydrodynamical simulations, one with (Horizon-AGN) and one without (Horizon-NoAGN) AGN feedback. I extract simulated tSZ measurements around a population of galaxies equivalent to those used in my observational work, with matching mass distributions, and compare the results. I find that the SPT measurements are consistent with Horizon-AGN, falling within 0.4σ at low-z and 0.5σ at high-z, while the ACT measurements are very different from Horizon-AGN, off by 6.9σ at low-z and 14.6σ at high-z. Additionally, the SPT measurements are loosely inconsistent with Horizon-NoAGN, off by 1.8σ at low-z but within 0.6σ at high-z, while the ACT measurements are loosely consistent with Horizon-NoAGN (at least much more so than with Horizon-AGN), falling within 0.8σ at low-z but off by 1.9σ at high-z.
In this work, I present stacked CMB measurements of a large number of elliptical galaxies never before measured using this method. I split the galaxies into two redshift groups, "low-z" for z=0.5-1.0 and “high-z” for z=1.0-1.5. I make two independent sets of CMB measurements using data from the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT), respectively, and I use data from the Planck telescope to account for contamination from dust emission. With SPT I find average thermal energies of 7.6(+3.0/−2.3) × 10^60 erg for 937 low-z galaxies, and 6.0(+7.7/−6.3) × 10^60 erg for 240 high-z galaxies. With ACT I find average thermal energies of 5.6(+5.9/−5.6) × 10^60 erg for 227 low-z galaxies, and 7.0(+4.7/−4.4) × 10^60 erg for 529 high-z galaxies.
I then attempt to further interpret the physical meaning of my observational results by incorporating two large-scale cosmological hydrodynamical simulations, one with (Horizon-AGN) and one without (Horizon-NoAGN) AGN feedback. I extract simulated tSZ measurements around a population of galaxies equivalent to those used in my observational work, with matching mass distributions, and compare the results. I find that the SPT measurements are consistent with Horizon-AGN, falling within 0.4σ at low-z and 0.5σ at high-z, while the ACT measurements are very different from Horizon-AGN, off by 6.9σ at low-z and 14.6σ at high-z. Additionally, the SPT measurements are loosely inconsistent with Horizon-NoAGN, off by 1.8σ at low-z but within 0.6σ at high-z, while the ACT measurements are loosely consistent with Horizon-NoAGN (at least much more so than with Horizon-AGN), falling within 0.8σ at low-z but off by 1.9σ at high-z.
ContributorsSpacek, Alexander Edward (Author) / Scannapieco, Evan (Thesis advisor) / Bowman, Judd (Committee member) / Butler, Nat (Committee member) / Groppi, Chris (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2017
Description
White Dwarf stars are the stellar remnants of low mass stars which have completed their evolution. Nearly all stars will become white dwarfs. The interior of a white dwarf encapsulates its evolution history: unraveling a white dwarf’s internal structure constrains the physical events which occurred to construct its composition. Variable, or pulsating, white dwarfs emit pulsations which are sensitive to their internal stratification. Just as seismology reveals Earth’s interior, asteroseismology can reveal stellar interiors. The standard approach to construe an observed white dwarf’s chemical makeup is to match observed pulsation properties to theoretical stellar models. Observed white dwarf pulsation data has reached 6-7 significant digits of precision. As such, it is important for computational modeling to consider systematic offsets from initial conditions and theoretical uncertainties that are within the detectable threshold. By analyzing the magnitude of pulsation differences among various uncertainties from white dwarf models, one can place constraints on important theoretical uncertainties. In this thesis, I explore impacts on white dwarf pulsations that result from accounting for various uncertainties in computational models. I start by showing the importance of 22Ne, and its impact on the pulsations in Helium atmosphere white dwarfs. Next, I discuss how certain trapped modes of white dwarfs may yield a signal for the 12C(α,γ)16O reaction rate probability distribution function. This reaction occurs during the Helium core burning phase in stellar evolution, and chiefly determines the Carbon and Oxygen abundance of white dwarfs. Following this work, I show how overshooting impacts the pulsation signatures of the 12C(α, γ)16O reaction rate. I then touch on the analytical work I’ve done regarding educational research in the HabWorlds course offered at Arizona State University (ASU). I then summarize my conclusions from these efforts.
ContributorsChidester, Morgan Taylor (Author) / Timmes, Francis X (Thesis advisor) / Young, Patrick (Committee member) / Li, Mingming (Committee member) / Borthakur, Sanchayeeta (Committee member) / Line, Michael (Committee member) / Arizona State University (Publisher)
Created2023
Description
Learning how properties of galaxies such as star formation, galaxy interactions, chemical composition, and others evolve to produce the modern universe has long been a goal of extragalactic astronomy. In recent years, grism spectroscopy from the Hubble Space Telescope (HST) has provided a means to study these properties with spectroscopy while avoiding the limitations of ground-based observation. In this dissertation, I present several studies wherein I used HST G102 grism spectroscopy from the Faint Infrared Grism Survey (FIGS) to investigate these fundamental properties of galaxies and how they interact and evolve. In the first study, I combined the grism spectra with broadband photometry to produce a catalog of redshifts with improved accuracy, reducing the median redshift error from 3\% to 2\%. With this redshift catalog, I conducted a systematic search for galaxy overdensities in the FIGS fields, producing a list of 24 significant candidates. In the second study, I developed a method for identifying emission line galaxy (ELG) candidates from continuum-subtracted 1D spectra, and identified 71 ELGs in one FIGS field. In matching MUSE/VLT spectra, I measured the [OIII]$\lambda$4363 emission line for 14 FIGS ELGs, and used this to measure their $T_e$-based gas-phase metallicities. These ELGs show a low-metallicity offset on the Mass-Metallicity Relation, and I demonstrated that this offset can be explained by recent star formation. In the third study, I expanded the ELG search to all four FIGS fields, identifying 208 H$\alpha$, [OIII]$\lambda\lambda$4959,5007, and [OII]$\lambda\lambda$3727,3729 line emitters. I compiled a catalog of line fluxes, redshifts, and equivalent widths. I combined this catalog with the overdensity study to investigate a possible relationship between line luminosity, star formation, and an ELG's environment. In the fourth study, I usde 15 FIGS H$\alpha$ emitters and 49 ``green pea'' line emitters to compare H$\alpha$ and the far-UV continuum as tracers of star formation. I explored a correlation between the H$\alpha$-FUV ratio and the ratio of [OIII]$\lambda\lambda$4959,5007 to [OII]$\lambda\lambda$3727,3729 and its implications for star formation history.
ContributorsPharo, John (Author) / Malhotra, Sangeeta (Thesis advisor) / Young, Patrick (Thesis advisor) / Rhoads, James (Committee member) / Scannapieco, Evan (Committee member) / Borthakur, Sanchayeeta (Committee member) / Arizona State University (Publisher)
Created2019
Description
I examine the effects of metallicity on solar mass stellar evolution, trying to replicate a previous result in Windhorst et.al., 2018, in which a zer metallicity solar mass star did not reach the AGB, and thus may turn into a helium white dwarf. In trying to replicate this result, I used the M.E.S.A. stellar evolution code and was unable to reproduce this result. While M.E.S.A has undergone several updates since the previous result was obtained, more current evidence suggests that this may have been a one-time occurrence, as no helium white dwarfs were produced for low-metallicity models. Nonetheless, interesting results were obtained, including a lowest metallicity value for which CNO burning does not significantly contribute during the main sequence, 1 −10 Z , which produces noticeable effects on post main sequence evolution. All models are run with no rotation, one solar mass, and a series of MESA parameters kept constant, with the only exception being metallicity. Any metallicity value listed as Nd −10 is an absolute mass fraction, and Z is relative to solar metallicity, 2d*10 −2 .
ContributorsTompkins, Scott Andrew (Author) / Windhorst, Rogier (Thesis director) / Young, Patrick (Committee member) / School of Earth and Space Exploration (Contributor) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2019-12