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PhD Defense - Malachi Tatum

You're invited to attend Malachi's dissertation defense.

Date: Thursday, November 14, 2013
Time: 9:45 am
Location: PHYS 401

Examining the Role of the Compton-thick, X-ray reprocessor in Type 1 Active Galactic Nuclei

Studies have indicated that black holes and their host galaxies must co-evolve, although the mechanism linking the two is not yet clear. X-ray observations of the actively accreting systems (active galactic nuclei, hereafter AGNs) over a valuable probe of conditions in the inner environs of the supermassive black hole, as X-ray production within these systems comprises a significant fraction (5%-40%) of the bolometric luminosity and originates close to the nucleus. Detailed spectroscopy in this bandpass has established that the inner environs comprise multiple X-ray absorbing zones with column densities extending into the Compton-thick regime (N_H > 10^24 atoms cm^-2). Compton-thick absorbers are known to have outflowing velocities up to 0.3c. The kinetic energy of oufltowing material with velocities > 0.1c may possibly be comparable to the gravitational binding energy of the stellar bulge and serve as a link between the black hole and the host galaxy. In addition, weak outflows may have a signicant effect on star formation in the host galaxy.

In this study, we use X-ray observations of radio-quiet AGN to examine some aspects of the flow of material between the black hole and the host galaxy. First, we model a small sample of unabsorbed Seyfert galaxies, finding their X-ray spectra to be consistent with arising as reflection from tens to hundreds of r_g in a Compton-thick, accretion disk wind of solar abundances seen face-on. Then, we explore properties of the local AGN population in the very hard band, above 10 keV, where there has been scant data available to date. We finnd a high flux for local AGN above 10 keV, and thus a very hard spectral shape over the Suzaku bandpass. Taken together, the spectral hardness and equivalent width of Fe K emission are consistent with reprocessing by an ensemble of Compton-thick clouds that partially cover the continuum source. Simple considerations place the distribution of Compton-thick clouds at or within 10^17 cm.

This work demonstrates not only that a Compton-thick wind can have a profound effect on the observed X-ray spectrum of an AGN, even when the system is not viewed through the flow, but that at least 50% of the continuum in type 1 AGNs is partially-covered by Compton-thick gas, suggesting that type 1 AGNs may not offer a completely direct view of the primary continuum, as once thought.