Author ORCID Identifier

Date Available


Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Arts and Sciences


Physics and Astronomy

First Advisor

Dr. Gary J. Ferland

Second Advisor

Dr. Marios Chatzikos


Over 90% of baryonic matter in the universe exists as astrophysical plasmas. The gas
is often far from thermodynamic equilibrium, so numerical non-equilibrium spectral
synthesis simulations are used to understand observations. cloudy simulates vari-
ous physical conditions, providing spectra predictions. This thesis aims to meet the
challenge of new observatories like the JWST (James Webb Space Telescope) and
XRISM (X-Ray Imaging Spectroscopy Mission). These simulations are no better
than the underlying atomic and molecular database and the fourth chapter details
a long-needed update to an evolving database. The predicted spectra are strongly
affected by the composition of the gas, which is determined in part by the condensa-
tion of certain elements into solid particles called “dust grains”. I showed the effects
of self-consistently depleting abundances within H ii regions, using the Orion Nebula
to demonstrate changes to the spectrum as the degree of dust depletion is altered.
Next, an analysis of emergent strong spectral-line intensities is obtained by calcu-
lating the abundances into cloudy models of a family of extragalactic H ii regions.
These predictions are then compared with Sloan observations to constrain the de-
pletion strength for a large sample of extragalactic H ii regions. These two projects
impact the interpretation of JWST observations. Finally, I improved the treatment
of one-electron doublets, allowing us to simulate observations from the new genera-
tion of X-ray microcalorimeters. These advances impact projects using NASA’s most
recent orbital observatories, JWST and XRISM.

Digital Object Identifier (DOI)