Using the Sunyaev-Zel'dovich Effect to Measure AGN Feedback

Project: Research project

Project Details


Using the Sunyaev-Zel'dovich Effect to Measure AGN Feedback For the past 10 billion years, the characteristic stellar mass of star-forming galaxies has been decreasing, in direct conflict with the expectations of the long-standing coolingregulated model of structure formation. In this picture, gas falls into dark matter potential wells, is shock-heated and must radiate this energy away before forming stars The larger the structure, the longer it takes to cool, and thus bigger galaxies form later. On the other hand, the observed antihierarchical history of massive galaxy formation has been beautifully reproduced in models that include outflows from active galactic nuclei (AGN). In this picture, AGN outflows deposit enough heat into the surrounding intergalactic medium (IGM) to prevent further generations of stars from forming. This feedback requires large, powerful AGN to be effective in the dense, highredshift IGM, whereas less powerful AGN can quench star formation in the more tenuous, low-redshift IGM, reproducing the observed trend. However, despite the spectacular success of such theoretical models, direct measurements of outflows from AGNs are notoriously difficult and uncertain. In short, a process that has come to play a central role in the theoretical models of galaxy formation is largely based on speculation. Intellectual Merit: It is with this key issue in mind that we propose a comprehensive program to measure AGN feedback using observations of the Sunyaev-Zel'dovich (SZ) effect. The SZ effect occurs when inverse Compton scattering increases the energy of cosmic microwave background (CMB) photons passing through hot, dense gas. Along any sightline, the magnitude of this effect is directly proportional to the integral of the IGM gas pressure. Thus by computing the average distortion in an area of sky around a galaxy, one can measure the volume integral of the pressure of the gas, which is directly proportional to the total thermal energy deposited to the surrounding medium. Thus the SZ effect acts as a calorimeter, telling us exactly how much of energy was added to the IGM and when. Our program will contain both observational and theoretical components, and will make up the thesis work of two graduate students. One student will initially combine public data from the Vista Hemisphere Survey and Blanco Cosmology Survey to find the galaxies with the largest expected signal, and use public data from the South Pole Telescope to make the first SZ measurements of AGN feedback. These measurements will then be improved by making new, targeted observations and by analysing additional public data. A second student will work with existing particle-based simulations to generate simulated images and provide initial interpretations of the SZ measurement. These simulations would then improve as we incorporate adaptive mesh refinement simulations and a variety of detailed AGN feedback models. Together these efforts would shed new light on the history of massive galaxy formation throughout cosmic time. Broader Impact: In addition, the projects broader impact will be enhanced by an emphasis on graduate training, the presentation of public lectures, the development of an interdisciplinary undergraduate course, and the release of simulation packages. The research will be graduate student driven, providing an excellent springboard for future postdoctoral work. In addition we will develop an applied numerical methods course to prepare undergraduates to take full advantage of the trans-disciplinary numerical efforts going on within the PIs home department. The history of galaxy formation is a topic that captures the public imagination. Through writing, teaching and public lectures, we will broadly disseminate our results, enhancing technical understanding and communicating the excitement of astronomy to the public. Finally, we will publicly release the software packages we develop as soon as they are complete, maximizing the impact of the proposal.
Effective start/end date8/15/147/31/18


  • National Science Foundation (NSF): $498,199.00

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