Matching Items (4)
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- All Subjects: Cosmology
- Creators: Scannapieco, Evan
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
The formation of the firsts stars some 100-300 Myr after the Big Bang marked the end of the cosmic darks ages and created the elemental building blocks of not only rocky planets but eventually us. Understanding their formation, lifetimes, and contributions to the evolution of our universe is one of the current frontiers in astronomy and astrophysics.
In this work I present an improved model for following the formation of Pop III stars, their effects on early galaxy evolution, and how we might search for them. I make use of a new subgrid model of turbulent mixing to accurately follow the time scales required to mix supernova (SN) ejecta -- enriched with heavy elements -- into the pristine gas. I implement this model within a large-scale cosmological simulation and follow the fraction of gas with metallicity below a critical value marking the boundary between Pop III and metal enriched Population II (Pop II) star formation. I demonstrate that accounting for subgrid mixing results in a Pop III stars formation rate that is 2-3 times higher than standard models with the same physical resolution.
I also implement and track a new "Primordial metals" (PM) scalar that tracks the metals generated by Pop III SNe. These metals are taken up by second generation stars and likely result in a subclass of carbon-enhanced, metal-poor (CEMP) stars. By tracking both regular metals and PM, I can model, in post-processing, the elemental abundances of simulation stars. I find good agreement between observations of CEMP-no Milky Way halo stars and second generation stars within the simulation when assuming the first stars had a typical mass of 60 M☉, providing clues as to the Pop III initial mass function.
In this work I present an improved model for following the formation of Pop III stars, their effects on early galaxy evolution, and how we might search for them. I make use of a new subgrid model of turbulent mixing to accurately follow the time scales required to mix supernova (SN) ejecta -- enriched with heavy elements -- into the pristine gas. I implement this model within a large-scale cosmological simulation and follow the fraction of gas with metallicity below a critical value marking the boundary between Pop III and metal enriched Population II (Pop II) star formation. I demonstrate that accounting for subgrid mixing results in a Pop III stars formation rate that is 2-3 times higher than standard models with the same physical resolution.
I also implement and track a new "Primordial metals" (PM) scalar that tracks the metals generated by Pop III SNe. These metals are taken up by second generation stars and likely result in a subclass of carbon-enhanced, metal-poor (CEMP) stars. By tracking both regular metals and PM, I can model, in post-processing, the elemental abundances of simulation stars. I find good agreement between observations of CEMP-no Milky Way halo stars and second generation stars within the simulation when assuming the first stars had a typical mass of 60 M☉, providing clues as to the Pop III initial mass function.
ContributorsSarmento, Richard John (Author) / Scannapieco, Evan (Thesis advisor) / Windhorst, Rogier (Committee member) / Young, Patrick (Committee member) / Timmes, Frank (Committee member) / Patience, Jennifer (Committee member) / Arizona State University (Publisher)
Created2018
Description
The Universe transitioned from a state of neutral hydrogen (HI) shortly after recombination to its present day ionized state, but this transition, the Epoch of Reionization (EoR), has been poorly constrained by observational data. Estimates place the EoR between redshifts 6 < z <13 (330-770 Myr).
The interaction of the 21 cm hyperfine ground state emission/absorption-line of HI with the cosmic microwave background (CMB) and the radiation from the first luminous sources in the universe can be used to extract cosmological information about the EoR. Theorists have created global redshifted 21 cm EoR models of this interaction that predict the temperature perturbations to the CMB in the form of a sky-averaged difference temperature, Tb. The difficulty in measuring Tb is that it is
predicted to be on the order of 20 to 100 mK, while the sky foreground is dominated
by synchrotron radiation that is 105 times brighter. The challenge is to subtract the much brighter foreground radiation without subtracting the Tb signal and can only be done when the data has small error levels.
The Experiment to Detect the Global EoR Signature (EDGES) is an effort to measure Tb with a single wide field-of-view well-calibrated antenna. This dissertation focuses on reducing systematic errors by quantifying the impact of the chromatic nature of the antenna’s beam directivity and by measuring the variability of the spectral index of the radio sky foreground. The chromatic beam study quantified the superior qualities of the rectangular blade-shaped antenna and led to its adoption over the previously used fourpoint-shaped antenna and determined that a 5 term polynomial was optimum for removing the foreground. The spectral index, β, of the sky was measured, using 211 nights of data, to be −2.60 > β > −2.62 in lower LST regions, increasing to −2.50 near the Galactic plane. This matched simulated results using the Guzm´an et al. (2011) sky map (∆β < 0.05) and demonstrated the exceptional stability of the EDGES instrument. Lastly, an EoR model by Kaurov & Gnedin (2016) was shown to be inconsistent with measured EDGES data at a significance level of 1.9.
The interaction of the 21 cm hyperfine ground state emission/absorption-line of HI with the cosmic microwave background (CMB) and the radiation from the first luminous sources in the universe can be used to extract cosmological information about the EoR. Theorists have created global redshifted 21 cm EoR models of this interaction that predict the temperature perturbations to the CMB in the form of a sky-averaged difference temperature, Tb. The difficulty in measuring Tb is that it is
predicted to be on the order of 20 to 100 mK, while the sky foreground is dominated
by synchrotron radiation that is 105 times brighter. The challenge is to subtract the much brighter foreground radiation without subtracting the Tb signal and can only be done when the data has small error levels.
The Experiment to Detect the Global EoR Signature (EDGES) is an effort to measure Tb with a single wide field-of-view well-calibrated antenna. This dissertation focuses on reducing systematic errors by quantifying the impact of the chromatic nature of the antenna’s beam directivity and by measuring the variability of the spectral index of the radio sky foreground. The chromatic beam study quantified the superior qualities of the rectangular blade-shaped antenna and led to its adoption over the previously used fourpoint-shaped antenna and determined that a 5 term polynomial was optimum for removing the foreground. The spectral index, β, of the sky was measured, using 211 nights of data, to be −2.60 > β > −2.62 in lower LST regions, increasing to −2.50 near the Galactic plane. This matched simulated results using the Guzm´an et al. (2011) sky map (∆β < 0.05) and demonstrated the exceptional stability of the EDGES instrument. Lastly, an EoR model by Kaurov & Gnedin (2016) was shown to be inconsistent with measured EDGES data at a significance level of 1.9.
ContributorsMozdzen, Thomas J (Author) / Bowman, Judd D (Thesis advisor) / Scowen, Paul A (Committee member) / Groppi, Christopher E (Committee member) / Scannapieco, Evan (Committee member) / Windhorst, Rogier A (Committee member) / Arizona State University (Publisher)
Created2017
Description
Millimeter astronomy unlocks a window to the earliest produced light in the universe, called the Cosmic Microwave Background (CMB). Through analysis of the CMB, overarching features about the universe's evolution and structure can be better understood. Modern millimeter-wave instruments are constantly seeking improvements to sensitivity in the effort to further constrain small CMB anisotropies in both temperature and polarization. As a result, detailed investigations into lesser-known processes of the universe are now becoming possible.
Here I present work on the millimeter-wavelength analysis of z ≈ 1 quiescent galaxy samples, whose conspicuous quenching of star formation is likely the result of active galactic nuclei (AGN) accretion onto supermassive black holes. Such AGN feedback would heat up a galaxy's surrounding circumgalactic medium (CGM). Obscured by signal from cold dust, I isolate the thermal Sunyaev-Zel'dovich effect, a CMB temperature anisotropy produced by hot ionized gas, to measure the CGM's average thermal energy and differentiate between AGN accretion models. I find a median thermal energy that best corresponds with moderate to high levels of AGN feedback. In addition, the radial profile of cold dust associated with the galaxy samples appears to be consistent with large-scale clustering of the universe.
In the endeavor of increasingly efficient millimeter-wave detectors, I also describe the design process for novel multichroic dual-polarization antennas. Paired with extended hemispherical lenslets, simulations of these superconducting antennas show the potential to match or exceed performance compared to similar designs already in use. A prototype detector array, with dual-bowtie and hybrid trapezoidal antennas coupled to microwave kinetic inductance detectors (MKIDs) has been made and is under preparation to be tested in the near future.
Finally, I also present my contributions to the cryogenic readout design of the Ali CMB Polarization Telescope (AliCPT), a large-scale CMB telescope geared towards searching the Northern Hemisphere sky for a unique `B-mode' polarization expected to be produced by primordial gravitational waves. Cryogenic readout is responsible for successful interfacing between room temperature electronics and sensitive detectors operating on AliCPT's sub-Kelvin temperature focal plane. The development of millimeter-wave instruments and future endeavors show great potential for the overall scientific community.
ContributorsMeinke, Jeremy (Author) / Mauskopf, Philip (Thesis advisor) / Alarcon, Ricardo (Committee member) / Scannapieco, Evan (Committee member) / Trichopoulos, Georgios (Committee member) / Arizona State University (Publisher)
Created2023