Collaborative Research: Advancing Measurements of Supermassive Black Holes with Triaxial Stellar-Dynamical Models

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Supermassive black holes (SMBHs) are fundamental components of galaxies. Discovering a SMBH requires both exquisite observational datasets and extensive numerical modeling. Over 30 years of research effort have produced about 100 SMBH masses in nearby galaxies. The local SMBH census, however, is still highly incomplete above a few billion solar masses. Moreover, only a handful of studies have made direct comparisons of SMBH masses obtained using the motions of stars and using the motion of gas or under different modeling assumptions. When this important check was performed, it was common to find disagreements of a factor of two or more. The research team will make major advances modeling stellar motions. They will apply this tool to uncover a new population of massive SMBHs in the Universe and to make direct comparisons of SMBH mass measurements determined using stars and gas. The program will improve the census of local SMBHs and our understanding of how SMBHs and galaxies grow over time. The project further benefits society by giving research opportunities and career mentoring to high school and college students from diverse backgrounds. The students will be immersed in research during the summer. They will work closely with the principal investigators and their teams on projects involving the detailed study of SMBHs and nearby galaxies.The research team will populate and expand the sparse upper-end of the correlations between SMBH and host galaxies, as well as identify and investigate possible discrepancies in SMBH masses resulting from stellar-dynamical modeling assumptions (axisymmetric and triaxial shapes) and from different dynamical tracers (stars and molecular gas). They will exploit the exciting recent opportunities afforded by our newly revised triaxial orbit modeling code, highly sensitive integral-field spectrographs on large telescopes, and ALMA-based gas-dynamical SMBH mass measurements. They will apply our triaxial code and develop a modern parameter search strategy to enable efficient grid-free sampling of high-dimensional parameter space and rapid convergence to best-fit models. They will then apply this technique to two galaxy samples observed with integral field spectrographs on the Keck and Gemini telescopes: giant elliptical galaxies with large, diffuse stellar cores and early-type galaxies with existing molecular gas-dynamical SMBH masses. The program will advance triaxial orbit modeling from a rarity to a standard technique, double the number of known ultra-massive SMBHs in the mass range of ten billion suns, provide critical assessment of the two main dynamical SMBH mass measurement methods, and enable the study of galaxy intrinsic shapes and stellar orbital distributions.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.