Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Manuel A. Bautista, Ph.D.

Second Advisor

Kirk T. Korista, Ph.D.

Third Advisor

Zbigniew Chajecki Ph.D.

Fourth Advisor

Timothy R. Kallman Ph.D.


Active galactic nuclei warm absorber, density diagnostic of absorbing and emitting gases with time dependent calculations, time dependent modeling of warm absorber outflow, time-dependent calculation of photoionized plasma


Warm absorber spectra are bound-bound and bound-free absorption features, seen in the X-ray and UV spectra from many active galactic nuclei (AGN). The widths and centroid energies of these features indicate they occur in outflowing gas moving with hundreds to thousands of km/s. Depending upon the energy and momentum of the outflow, it can affect the gas within the host galaxy. Thus, warm absorbers’ mass and energy budgets are of great interest. Estimates for these properties depend on models that connect the absorption features' observed strengths with the density, composition, and ionization state of the absorbing gas. Such models assume that the ionization and heating of the gas are determined primarily by the strong continuum radiation from near the central black hole. They also assume that the various heating, cooling, ionization, and recombination processes are in a time-steady balance. However, this assumption may not be valid, owing to the intrinsic time-variability of the illuminating continuum or other factors like sudden adiabatic expansion and gas moving with high speed, which changes the cloud environment.

Understanding outflowing gas, including warm absorbers, is crucial for understanding the AGN. We study the properties of such outflow exposed to the highly variable ionizing source using time-dependent calculations, which is different from equilibrium modeling commonly approached in modeling the photoionized gas. To model the outflow, we numerically solved the time-dependent forms of the balance equations for ionization, internal energy, and radiative transfer in a self-consistent manner. A new computer code is deployed to investigate the properties and associated spectrum for various warm absorber models.

This study presents models for warm absorbers which follow the time dependence of the ionization, temperature, and radiation field in gas clouds in response to a changing continuum illumination. We show that the effects of time variability are essential over a range of parameters and that time-dependent models differ from equilibrium models in meaningful ways. Thus time-dependent effects should be included in models that derive properties of warm absorber outflows.

Access Setting

Dissertation-Open Access

Included in

Physics Commons