The primary conceptual bottleneck in our understanding of the formation of galaxies is feedback: the entropy and thermal energy injected into the protogalactic interstellar medium by stellar winds, supernovae, and accreting supermassive black holes. The first comprehensive survey of X-ray gas morphology in normal elliptical galaxies has shown that the gas is rarely, if ever, in hydrostatic equilibrium, but is being continually pushed about by modest outbursts from comparatively weak active galactic nuclei (AGN). It also revealed three new, fundamental correlations that constrain the thermodynamic state of the gas and its relation to AGN activity. This project will elucidate the hydrodynamic histories of elliptical galaxies, and constrain the physical nature of feedback, using these new correlations, coupled with detailed hydrodynamical simulations. These simulations will progress to increasing complexity, in order to isolate the effects of quiescent AGN feedback, merger-induced AGN feedback, and merger-induced star formation and supernova feedback. The results will contribute to the ability to perform realistic simulations of structure formation on cluster, supercluster, and cosmological scales.
The project supports a new collaboration between Ohio University and Los Alamos National Laboratory, helping to foster close ties between the national centers and academia. The associated graduate student will receive scientific and technical training in current research tools, including parallel computing. The research activities will also enhance the vigorous series of public programs carried on by the PI and his fellow faculty at Ohio University, which serves a traditionally underserved broader community. The results will be used in the PI's astronomy-related radio broadcasts and newspaper column.
The purpose of this project was to better understand how the energetic effects of supermassive black holes in the centers of galaxies affect galaxy evolution, and to use the observed properties of galaxies to improve our understanding of how supermassive black holes produce energy and inject it into interstellar space. The basic plan was to simulate the evolution of isolated elliptical galaxies, interacting elliptical galaxies, and merging spiral galaxies using different models for black hole energetics, predict the observable properties of the galaxies, and use the observed properties to constrain the models. The grant supported completion of a paper (third in a series) on the thermal properties of the hot (10 million degree) interstellar plasma in elliptical galaxies, observed using the Chandra X-Ray Observatory. We demonstrated in this paper that the power of the active (black-hole-powered) nucleus is correlated with the temperature profile of the hot plasma through the entire galaxy. This result strengthened the evidence that the hot plasma is being continually affected, perhaps cyclically, by the central black hole. Primarily, the grant supported the doctoral dissertation work of a graduate student, which concentrated on the gas-dynamical simulations described above. The student's work produced special-purpose software to perform three tasks: (1) create dynamical equilibrium "N-body" configurations of mass particles representative of real elliptical galaxies, to use as the backbone of the gas-dynamics simulations; (2) create initial gas configurations, in gravitational and pressure equilibrium in the "N-body" galaxies, from which gas-dynamical simulations can be started; and (3) add computational modules to the hydrodynamical code (Gadget-2) used in the project to simulate the accretion of gas onto the central black hole and radiative cooling of the hot plasma by emission of X-rays. The supported student had a change of career goals late in the period of support and earned a Master's degree. There were nonetheless notable broader impacts in scientific workforce development; as a result of this support, the student became well versed in parallel scientific computing, and is now working in a science support capacity at a leading national astrophysics research facility.
