The aim of this project is to perform detailed modeling of the secondary anisotropies in the Cosmic Microwave Background power spectrum caused by the Sunyaev-Zeldovich (SZ) effect. The work will involve both analytic and numerical techniques to investigate in detail how the information contained in the shape of the thermal SZ power spectrum can be used to shed light on the intra-cluster medium, especially in clusters of galaxies at high redshifts and of low masses. The results of this project will be incorporated into an emulation tool that will aid cosmological parameter estimation from observations of the SZ power spectrum. This tool will be made publicly available.
Broader impacts of the work include training of undergraduate and graduate students, and outreach to museums and planetariums. Products of the simulations will be made public for use in research and classroom settings.
Yale Computational Cosmology group led by the PI (Daisuke Nagai) is broadly focused on understanding how galaxies and clusters of galaxies form in the Universe. Knowledge of how these so-called large-scale structures develop has the potential to enlighten us about the fundamental physics of the cosmos, including mysterious dark energy and dark matter. This requires modeling all important astrophysical processes in simulations of the formation of large-scale structure. Over the past four years, we have made significant progress on this problem with the NSF support. The primary science goal of the NSF-funded project concerns the study of small-scale Cosmic Microwave Background (CMB) fluctuations. This is a new research topic that the PI has developed upon his arrival to Yale. Specifically, our team at Yale has developed a novel model of the so-called Sunyaev-Zeldovich (SZ) signal -- a small distortion in the CMB spectrum imprinted by the interaction of CMB photons with hot electrons in clusters. Notably, we were the first to point out the importance of turbulent gas flows on the SZ signal and incorporate it in the model. Our new model has become a standard model for interpreting ongoing CMB experiments, including the Atacama Cosmology Telescope (ACT), South Pole Telescope (SPT), and Planck space mission, which are designed to study the origin, composition, and the development of structure in the Universe The next major research is currently underway. Over the past few years, our research team has developed a novel approach for modeling the growth of supermassive black holes in our cosmological simulation code. We have successfully implemented and tested the new module. We are currently performing a suite of large cosmological simulations to model the co-evolution of black holes, galaxies, and clusters of galaxies at the Yale's High Performance Computing center. We expect that these simulations will significantly advance our understanding of how black holes affect the formation of galaxies and galaxy clusters and, as a result, improve the predictive power of the current cluster model. We expect that this program will make a broad and lasting impact on the field of cosmology and astrophysics in years to come. A partial list of my other accomplishments include significant work on the outskirts of galaxy clusters, extensive study of non-equilibrium phenomena and plasma physics in galaxy clusters (such as turbulence, non-equilibrium electrons, cosmic rays, and helium sedimentation), and constraints of the nature of dark matter particles using gamma-ray observations of galaxy clusters. Much of this work resulted from my attempts to characterize the limitations of the use of galaxy clusters as precision cosmological probes. Through this work, we devised new approaches - both theoretical and observational - to assess uncertainties associated with poorly understood astrophysical phenomena and made a number of testable predictions for future experiments to address some of the outstanding issues in cluster cosmology. During the NSF support period, the Yale Computational Cosmology group has hosted 17 undergraduate students at all levels (including 9 senior essays), 9 graduate students, and 7 postdoctoral scholars. Many of them have moved onto faculty positions, postdocs, and graduate programs in Physics and/or Astronomy as well as non-academic positions in the computer, stock market, and business industries. Our science results were published in 30 refereed publications (29 published; 1 under review) as well as 43 invited talks (15 conferences and workshops and 28 colloquia and seminars) delivered by the PI. Our NSF-funded project has helped advance the use of complex systems, such as galaxy clusters, as laboratories for addressing the fundamental questions in cosmology. I do so by developing a novel model of the structure formation of the Universe, using emergent computing technologies and algorithms. Our work has provided scientific motivation for a number of next-generation space-based and ground-based multi-wavelength cosmology experiments (including the eROSITA Russian-German X-ray space mission and US led Large Synoptic Survey Telescope) that are specifically designed to test whether the dark energy phenomena is due to Einstein's cosmological constant (i.e., non-zero vacuum energy density) or the modification of Einstein's theory of general relativity on the largest scales. Our science results have helped produce several ground-breaking results in X-ray and microwave astronomy, and it is poised to make a mark in other wavebands in addition in the coming years.
