Mapping AGN Accretion Through Echo Mapping and Radiation MHD Simulations

Princeton University, Princeton NJ

Investigators

Abstract

Understanding material flowing onto objects is a universal challenge in astrophysics, from the formation of stars and planets to the most extreme explosions like Gamma Ray Bursts. The PIs of this research program use observations of the material flowing onto supermassive black holes (accretion disks) to refine models of accretion. Specifically, we observe changes in the amount of light from accretion disks over time at different wavelengths. Over long timescales, they can effectively watch material moving inward in the accretion disk through this variability, which in turn tells us basic things about the disk, like how thick it is, and how dense. They will then build new models of accretion disks that will help us understand exactly how the signals propagate through the accretion disk. With the upcoming Vera Rubin Telescope Legacy Survey of Space and Time (LSST) poised to observe thousands of accretion disks around black holes, now is the time to get these models and our measurement tools ready. The PIs at Princeton will also be in a strong position to train the next generation of scientists to utilize LSST. In addition to the students and postdocs that the PIs collaborate with, they have built a summer research program for formerly incarcerated students, and short summer projects associated with this project will position these students for STEM careers and future involvement in LSST. Accretion onto supermassive black holes in active galactic nuclei (AGN) is one of the most energetic phenomena in the Universe, and AGN feedback likely plays a central role in galaxy evolution. Yet, despite years of study, we still have basic open questions about the mechanisms of accretion. While we cannot directly spatially resolve accretion disks, echo mapping -- tracing variability signals with wavelength -- can tell us about the temperature profile, size scale, and even aspect ratio of the disk. This last property can be probed by tracing variability signals that originate at large distance in the accretion disk and then move inwards with the flow on a viscous time, the so-called "negative" lags that move from red to blue wavelengths. The PIs of this award have detected such a negative lag in one well-studied AGN, and this project is focused on finding more such negative lags through: (a) archival searches; (b) 3D radiation magnetohydrodynamic simulations that will give us insight into the response function, or the delay distribution of the signal as it moves inward; (c) the creation of mock light curves, informed by (b), to optimize lag recovery and the cadence of next-generation surveys like the Vera Rubin Observatory Legacy Survey of Space and Time. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.