Reverberation Mapping of the Dusty Torus in Active Galactic Nuclei
Geisert, Erich Franz
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The Dusty Torus is a structure that is believed to exist in Active Galactic Nuclei. The Torus is physically too small to be spatially resolved, so Reverberation Mapping can be performed in order to replace spatial resolution with temporal resolution, yielding observations that can unravel the mystery of the Dusty Torus. One of the unknowns about the Torus is how the dust is distributed. The two competing theories are that either the dust resides in discrete clouds or that there is a solid wall of dust. This thesis presents the results of a year long observation program, starting in August 2011, that surveyed 12 Active Galactic Nuclei. Their fluxes were measured in two wavelengths: 3.6 and 4.5 µm. These two light curves were cross correlated with each other in a process called Flux Redistribution/Random Subset Selection in order to measure the lag in the signal between them. If there are discrete clouds of dust, the interchannel lag should be much smaller than the lag between the continuum and the 3.6 µm emissions. If there is a solid wall of dust, then the lag should be either as long or longer than the lag behind the continuum. Only one of the Active Galactic Nuclei, NGC 6418, had a measurable time lag, which was 12.3 +2.3 −1.9 days. This result, paired with estimates of the lag between the AGN continuum and the 3.6 µm emissions, is consistent with the discrete clouds theory.