M.Sc Thesis

M.Sc StudentHilsenrat Marcos
SubjectHighly Photoionized Dusty Gas: Theory and Applications
DepartmentDepartment of Physics
Supervisor PROF. Ari Laor


Active Galactic Nuclei (AGNs) are the strongest persistent sources of ionizing radiation in the Universe and contain large amounts of dust.

The interaction of the ionizing continuum with dust implies that photoionized dusty gas must be prevalent in AGNs. These interactions were explored in dusty gas with low to intermediate ionization parameters. The purpose of this work is to explore the properties of photoionized dusty gas when the ionization parameter is high.

In our research, we developed a code that makes detailed calculations of photon-dust interactions, as follows. We assumed a dust grain shape and composition based on observational data, and then we calculated the pathlength distribution function of photoelectrons formed in a grain. This allowed us to calculate the electron energy deposition in the grain, and thus, their energy distribution at the grain surface, which gave us the outgoing current and the heating rate by the grain. We assumed a continuum source luminosity, a power law radiation field, and a grain size distribution based on observations, and then, assuming a gas and dust number density, we integrated over those distributions to obtain the total outgoing current from the grains. The next step was to calculate the incoming current on grains due to the interaction of grains with the surrounding plasma. This allowed us to calculate the equilibrium current, and therefore, the grain equilibrium charge and electrostatic potential, and to estimate the grain heating and cooling of the gas. Finally, we calculated the survival of grains as a function of their size, ionization parameter, shape of the ionizing continuum and distance from the ionizing continuum.

These calculations are relevant to obtain the gas equilibrium temperature, and to the understanding of the observed low ionization state of the gas in x-ray absorbers.