Toward physically-predictive modeling of massive black hole growth and feedback in galaxy formation

Northwestern University, Evanston IL

Investigators

Abstract

A longstanding problem in astrophysics is to understand how galaxies form and develop throughout their lifetimes. Such understanding is necessary to uncover how our Universe evolved and to gain insight into the origin of our own Milky Way Galaxy. Nearly all galaxies appear to have massive central black holes (BHs)---many with ones much, much larger than our Milky Way's. Observations reveal close connections between galaxies and massive BHs. However, the formation of massive BHs, how they grow, and how they affect the galaxy life cycle via feedback remain poorly understood. Fundamental advances in our understanding of gas transport from galactic scales into galactic nuclei by gravitational torques and in observations of galaxy-scale winds driven by active galactic nuclei (AGN) are transforming our understanding of BH growth and feedback and are enabling definitive progress in answering these questions. This project is a multi-scale simulation program that builds on these breakthroughs and on the investigators' previous analytic modeling. The project will begin with ultra-high resolution simulations (down to about 0.01 pc) of BH growth and feedback in galaxies and galactic nuclei. The group will also produce visualizations from their simulations specifically designed to support their education and outreach efforts. The visualizations, which will include both time-dependent animations and 3-D interactive exploration modules, will be displayed at the Space Visualization Laboratory at the Adler Planetarium in Chicago. The PI, the postdoc funded by this award, and graduate students in the group will volunteer once a month for "astronomy conversations" at Adler, which attract up to 300 visitors per hour of all ages. Through these astronomy conversations, the team will explain the fascinating roles of black holes in galaxy evolution to the public. They will also integrate educational materials into a year long computational astrophysics course for high school students offered through Northwestern's Center for Talent Development. In the course, students learn to code in Python and apply these skills to pursuing an independent research project using a large astronomical data set of their choosing. Videos (which will include explanations of the science behind the simulations and of how they were created) will introduce the students to a new kind of simulated data set that they can work on for their projects. The investigators will also continue to actively involve undergraduate students in their research. The project's simulations will include an explicit model for stellar feedback that self-consistently produces a multiphase interstellar medium and star-formation driven outflows. These simulations will be used to study the physics of BH accretion and the interaction of wide-angle AGN-driven outflows in a representative set of model galaxies, including the effects of AGN on gas and star formation, and to calibrate AGN fueling and feedback models for use in cosmological simulations. BHs will then be implemented in cosmological simulations (about 1 to 100 pc resolution) that will allow the PI to investigate the origin of massive BHs (seed models and the need for super-Eddington accretion), the emergence of galaxy-BH scaling relations, the role of AGN feedback in quenching star formation in massive galaxies, and the effects of AGN outflows on halo gas. A systematic approach, building up from small to larger scales, will enable the PI to resolve the main uncertainties of previous simulations of BHs on galaxy and cosmological scales. To maximize the impact of the simulations, radiative transfer calculations, which will allow a direct test of the results with a wealth of current and future observations, will be tightly incorporated in the project. The goal of this multi-scale BH study is to achieve for BHs a level of predictive power comparable to what has become possible for star formation. The sub-resolution BH models that will be developed will enable substantially more predictive BH modeling in galaxy-scale and cosmological simulations---thus alleviating arguably the largest uncertainty in current galaxy formation theories.