Award Date

May 2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Committee Member

Daniel Proga

Second Committee Member

Zhaohuan Zhu

Third Committee Member

Stephen Lepp

Fourth Committee Member

Monika Neda

Number of Pages

88

Abstract

Accretion onto super massive black holes (SMBH) plays a vital role in explaining our observations of active galactic nuclei (AGN). One key aspect of observations of AGN is the prevalence of massive outflows which transport matter and energy away from the galactic core. These outflows are characterized by highly blueshifted absorption lines as radiation from the accretion disk is absorbed by gas which is moving toward us. Radiation pressure on spectral lines is expected to play a vital role in launching and accelerating these winds. At the other end of the spectrum of black hole masses, accretion disks in X-ray binaries exhibit outflows likely driven by thermal pressure. Despite the difference in magnitude, both of these systems' driving mechanisms share a strong dependence on the radiation field which permeates the gas above the accretion disk.While we have observations of accretion disks of all sizes throughout the universe, from X-ray binaries to AGN, they all share one limitation: accretion disks are far away from us. Especially in the case of AGN, each accretion disk is at such a distance from us that, over any reasonable timescale, we may only observe it from one distance and inclination angle. In contrast, along the outflow's journey from the surface of the disk to the ISM, the radiation it sees from the accretion disk system changes drastically. We cannot use our observations from a great distance as a reliable proxy for the radiation field which is actually launching and accelerating the outflows. Accurately modeling the radiation at any position near the disk requires solving radiative transfer in all directions. This can be done to a fair extent utilizing radiation-hydrodynamic simulations in tandem with photoionization codes, but only at significant computational cost. This thesis works to develop tools which can quickly and accurately compute, as a function of position, properties of the radiation field, in order to alleviate some of the computational load. We motivate our work with an overview of outflows observed in AGN. We then review photoionization, its effect on heating and cooling of the gas, and line driving. Next, we extend prior position dependent theory to frequency dependent calculations, which allows us to compute spectral energy distributions (SEDs), ionizing intensities, mean photon energies, ionization parameters, line-driving force multipliers, and net cooling rates all in a position and direction dependent manner. We show verification of our methods using analytically tractable limits, followed by discussion of results at intermediate locations. Finally, we discuss future steps in the development of tools which will improve our ability to efficiently model radiative processes due to accretion disks.

Disciplines

Astrophysics and Astronomy | Physics

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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