Award Date

May 2023

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Physics and Astronomy

First Committee Member

Stephen Lepp

Second Committee Member

Tao Pang

Third Committee Member

Bernard Zygelman

Fourth Committee Member

Steen Madsen

Number of Pages



This dissertation develops a model for the response of the transition points in the density profiles from atomic (H0) to molecular (H2) hydrogen in a photodissociation region (PDR) due to a hard X-ray flux (HXR). A model for a steady-state PDR due to the photodissociation of H2 by the far-ultraviolet (FUV) Lyman-Werner radiation band is presented both analytically and computa- tionally. A steady state X-ray dissociation region (XDR) from an HXR in the 1 - 100 keV energy range is also developed both analytically and computationally. An analytic model is then developed by combining these two different steady state models. The inclusion of the hard X-rays gives rise to additional ionization in the PDR from secondary electrons which also leads to the generation of an internal FUV radiation field. Computational results for the density profiles and the response of the transition point of the PDR due to the HXR flux are given. A simple analytic formula based upon the separate PDR and XDR is then given which can provide an approximation to the transition point due to their combination.


Astrophysics and Astronomy

File Format


File Size

2650 KB

Degree Grantor

University of Nevada, Las Vegas




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