Matching Items (3)
Filtering by
- Creators: Scannapieco, Evan
ContributorsPowell, Devon (Author) / Gardner, Carl (Thesis director) / Scannapieco, Evan (Committee member) / Windhorst, Rogier (Committee member) / Barrett, The Honors College (Contributor)
Created2012-05
Description
Galaxies in the universe are surrounded by a hot medium called the Circum-Galactic Medium (CGM). Present the CGM is gas that forms up clouds which travel within the CGM at speeds that approximately range between 100 km/s and 300 km/s. These gas clouds are very interesting because they play a crucial in the formation of stars within the galaxies and also in the overall evolution of galaxies. The clouds could in fact be thought of as mobile "gas stations" whose sole purpose is facilitate the ionization of elements and ultimately supply gas to galaxies. My thesis project is a follow-up study on CGM gas cloud observations that were made by Borthakur et. al. (2016). Using Cosmic Origins Spectrograph (COS) data from the Hubble Space Telescope (HST), Borthakur et. al. (2016) observed the presence of both Carbon IV (C IV) and Oxygen VI (O IV) but did not observe any Nitrogen V (N V) in the gas cloud when expected to be observable. Therefore, the ultimate goal of my research was to determine whether indeed CGM gas clouds have an actual shortage of the N V ion. My research involves the generation of cosmological simulations of a cold gas cloud that has a radius of 98 parsecs, relative velocity of 200 km/s, density range of 10-3 to -5 and a temperature in the range of ~104 to 5 K, and also a hot CGM that has density in the range of 10-4.5 to -6 particles/cm3 and temperature of approximately 106 K. Traces of N v are observed in my simulations.
ContributorsSaboi, Kezman (Author) / Scannapieco, Evan (Thesis director) / Borthakur, Sanchayeeta (Committee member) / Cottle, JNeil (Committee member) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The interactions that take place in the ionized halo of gas surrounding galaxies, known as the circumgalactic medium (CGM), dictates the host galaxy's evolution throughout cosmic time. These interactions are powered by inflows and outflows that enable the transfer of matter and energy, and are driven by feedback processes such as accretion, galactic winds, star formation and active galactic nuclei. Such feedback and the interactions that ensue leads to the formation of non-equilibrium chemistry in the CGM. This non-equilibrium chemistry is implied by observations that reveal the highly non-uniform distribution of lower ionization state species, such as Mg II and Si II, along with widespread higher ionization state material, such as O VI, that is difficult to match with equilibrium models. Given these observations, the CGM must be viewed as a dynamic, multiphase medium, such as occurs in the presence of turbulence. To better understand this ionized halo, I used the non-equilibrium chemistry package, MAIHEM, to perform hydrodynamic (HD) simulations. I carried out a suite of HD simulations with varying levels of artificially driven, homogeneous turbulence to learn how this influences the non-equilibrium chemistry that develops under certain conditions present in the CGM. I found that a level of turbulence consistent with velocities implied by observations replicated many observed features within the CGM, such as low and high ionization state material existing simultaneously. At higher levels of turbulence, however, simulations lead to a thermal runaway effect. To address this issue, and conduct more realistic simulations of this environment, I modeled a stratified medium in a Milky Way mass Navarro-Frenk-White (NFW) gravitational potential with turbulence that decreased radially. In this setup and with similar levels of turbulence, I alleviated the amount of thermal runaway that occurs, while also matching observed ionization states. I then performed magneto-hydrodynamic (MHD) simulations with the same model setup that additionally included rotation in the inner halo. Magnetic fields facilitate the development of an overall hotter CGM that forms dense structures within where magnetic pressure dominates. Ion ratios in these regions resemble detections and limits gathered from recent observations. Furthermore, magnetic fields allow for the diffusion of angular momentum throughout the extended disk and gas cooling onto the disk, allowing for the maintenance of the disk at late times.
ContributorsBuie II, Edward (Author) / Scannapieco, Evan (Thesis advisor) / Borthakur, Sanchyeeta (Committee member) / Groppi, Christopher (Committee member) / Jacobs, Danny (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2022