Discovery Magazine

Reverberation Mapping of the size of the Dusty Tori in Active Galactic Nuclei

Despite its central role in active galactic nuclei unification models and its importance for studies of supermassive black hole demographics, our current understanding of the size and structure of active galactic nuclei tori is weak. We propose to use the unique opportunity provided by the warm phase of Spitzer to determine the sizes of circum-nuclear dust tori in active galactic nuclei.

To accomplish this we will carry out a monitoring campaign, coordinated with ground-based observations, to measure the 'light echo" as the dust emission responds to variations in the AGN optical/UV continuum. We have selected a sample of 12 bright type 1 nuclei in close proximity to the Spitzer Continuous Viewing Zone, which can be observed repeatedly with visibility windows for at least 70% of the ~400 day cycle and generally > 90% (10 objects )of the ~400 day cycle. We will observe each AGN with 3 day sampling on Spitzer for the whole of Cycle 8. We have in place a plan for a supporting ground-based monitoring program using a variety of conventional and robotic telescopes, which will allow "world-wide" coverage, to determine the AGN light-curves in the B band.

These observations will more than double the number of AGN with simultaneous optical and NIR time-series data, providing well-sampled, high signal-to-noise light curves of both S1 and NLS1. Such high fidelity, continuously sampled lR light curves covering hundreds of days cannot be obtained from the ground, and are needed because the expected reverberation time scales are many tens of days (30-150).

We will apply well-developed techniques to determine the reverberation lag and therefore obtain the characteristic size of the torus in this sample, which has diverse properties and samples a range of black hole mass and Eddington ratio. Our team contains many leading experts in reverberation mapping of AGN and in the observational study and theoretical modeling of the physics of the dusty torus. We are requesting a total of 196 hrs in the cycle to perform our observations.