RESEARCH


I am a theoretical and computational cosmologist and astrophysicist. My research is generally centered on the development and application of N-body, hydrodynamic, and radiative transfer simulations to model and interpret the observable Universe. In cosmology, I am especially interested in complex problems involving the gas, stars, galaxies, quasars, and clusters of galaxies that provide information about the underlying dark matter and dark energy. In astrophysics, I would particularly like to work on star and planet formation and the development of planetary atmospheres. I also collaborate with machine learning experts and statisticians to apply modern approaches to improve multi-wavelength data analysis and numerical simulations.

SUPERCOMPUTING


Computational astrophysics and cosmology has advanced considerably in four decades, starting with simulations having only a few thousand particles or cells with just gravitational or hydrody- namic interactions to state-of-the-art simulations with hundreds of billions to trillions of resolution elements having several different types of interactions. To simulate the Universe with supercom- puters, we solve the nonlinear physics of gravity, fluid dynamics, and radiative transfer to model the evolution of dark matter, gas, and radiation. Physically-motivated models for the formation of stars, blackholes, and galaxies as well as supernova, active galactic nuclei, and radiative feedback also have to be included. I am currently developing and applying a meshfree finite-volume particle method (FVPM) hydro code for astrophysical and cosmological simulations.

GALAXY CLUSTERS


Galaxy clusters situated in massive dark matter halos are the largest gravitationally bound systems in the Universe. The largest known system contains up to a thousand galaxies and has a mass over  1015 times the mass of our Sun and over 1000 times the mass of our Galaxy. They make excellent laboratories for studying cosmology and astrophysics. For decades, astronomers have tried to count the number of clusters as a function of mass and redshift, for their abundance can reveal how much dark matter and dark energy exist, and what is the expansion rate of the accelerating Universe. This is one of the most important cosmological probe as recognized by the Astronomy and Astrophysics 2010 Decadal Survey, but it is also challenging because approximately 85% of the matter is in the form of invisible dark matter. I work on galaxy clusters as a member of the Atacama Cosmology Telescope Collaboration and Co-I on DOE grant “Machine Learning Algorithms for Matching Theories, Simulations, and Observations in Cosmology”.

COSMIC REIONIZATION


Cosmic reionization is a milestone event in cosmic history marked by the emergence of the first luminous sources: stars, galaxies, and quasars in the first billion years. The Epoch of Reionization (EoR) is perhaps the only time that luminous sources directly and drastically alter the state of the entire Universe, converting the cold and neutral intergalactic medium (IGM) into a warm and highly ionized one. Current observations suggest that reionization was already in significant progress by z~9 and must have ended by z~6. Current theory suggest that large-scale, overdense regions near radiation sources are generally reionized earlier than large-scale, underdense regions far from sources. Studying the EoR will reveal how the first generation of stars, black holes, galaxies, and quasars formed and evolved. It can also provide complementary constraints on cosmological parameters similar to studies of the cosmic microwave background. As PI on NASA grant “The Imprint of Reionization on the Cosmic Microwave Background”, I am working on the project “Simulations and Construction of the Reionization of Cosmic Hydrogen” (SCORCH) to provide theoretical tools to facilitate more accurate comparisons with observations.

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