Ph.D. Thesis Defenses
Sunyaev Zel'dovich Effect Observations of X-ray Cavities in Galaxy Clusters
February 8, 2018 | ERC 401 | 10:30 AM | PhD Advisor: John E. Carlstrom | PhD Thesis Defense
Zubair Abdulla

"Zubair has done it all, from building 10 ultra-sensitive receivers, commissioning them on CARMA, developing the data reduction pipeline, to imaging and analyzing the first Sunyaev-Zel'dovich effect imaging of x-ray cavities in galaxy clusters. His thesis places tight constraints on the nature of plasma within the cavities and mechanisms for heating of the inter cluster medium."
- John Carlstrom, Ph.D. advisor

Multiphase Gaseous Halos around Galaxies
June 15, 2018 | ERC 401 | 1:00 PM | PhD Advisor: Andrey V. Kravtsov | PhD Thesis Defense
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Cameron Jia Liang

There is no doubt that our atmosphere is an integral part of the ecosystem of the Earth. Everyday weather and long-term climate of the atmosphere are directly linked to activities on the surface of the Earth and vice versa. Gaseous halos, known as the circumgalactic medium (CGM), are the equivalent atmospheres of galaxies.

In this thesis, I provide a major step towards the empirical constraints and theoretical modeling of the CGM and the co-evolution with their host galaxies. Using background quasars, I statistically map the spatial extent of multiphase gaseous halos in a sample of ~200 galaxies that span nearly five orders of magnitude in stellar mass, from dwarf to L*, and more massive galaxies. With these empirical constraints, I explore the effects of theoretical modeling of star formation and feedback processes using a set of high-resolution cosmological zoom-in simulations of a Milk-Way progenitor. To connect more closely with observations, I develop a synthetic absorption pipeline, as a virtual telescope, to observe the simulated galaxy and their CGM. This series of observational and theoretical studies have led to new insights of the cold gas in galactic winds and halos. I explore a new model, the circumgalactic mist, with a set of magneto-hydrodynamic simulations. I will present the model implications on the spatial distribution of multiphase gas around galaxies.

The Propagation of Flame Fronts Through Inhomogeneously Magnetized Plasma
June 20, 2018 | ERC 576 | 2:00 PM | PhD Advisors: Fausto Cattaneo; Alexei M. Khokhlov | PhD Thesis Defense
Image credit: David A. Hardy
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Ian Remming

Ph.D. Committee members: Fausto Cattaneo (PhD advisor), Doyal "Al" Harper, Arieh Konigl, and Robert Rosner.

Thesis Abstract: The effects of an inhomogeneous magnetic medium on the propagation of magneto-hydrodynamical (MHD) laminar flame fronts are investigated. This investigation is motivated by the occurrence of magnetized thermonuclear combustion in several astrophysical systems. Magnetized thermonuclear burning occurs on the surfaces of neutron stars during Type I X-ray bursts, within the interiors of white dwarfs during Type Ia supernovae, during classical novae, and may be important for certain core collapse supernovae as well. Thermonuclear flames that propagate in these systems travel through inhomogeneous magnetic fields. We present the results of a series of numerical simulations of magnetized flame propagation conducted using the MHD extension to the High-Speed Combustion and Detonation (HSCD) code. A simplified flame model is used with one-step Arrhenius kinetics, a perfect gas equation of state, and constant thermal conductivity coefficients. Although idealized, the model allows for the opportunity to study the physics of the problem without the complexities of the nuclear kinetics of thermonuclear burning. We simulate the propagation of laminar flames through inhomogeneous magnetic media. A changing magnetic medium significantly alters the structure of the flame through the generation of an electric current that propagates out of the plane of the flame front. The electric current rotates the direction of the magnetic field across the flame and produces strong shear flows. Furthermore, for flames that conduct heat anisotropically and that propagate at an angle to the magnetic field, the flame speed increases due to the non-uniform magnetic field. Naturally occurring flames in astrophysical systems may experience similar changes to their structure and speed that would influence the observational properties of these systems.