Astrophysics and Cosmology
The research of the CMU Astrophysics and Cosmology group covers a wide range of problems in theoretical, computational, and observational cosmology. These problems include the study of the earliest energy emission in the universe -the Cosmic Background Radiation- to the evolution of galaxies and the formation of large-scale structure. We are part of the worldwide scientific effort to put constraints on the basic cosmological parameters that describe the evolution of the universe. Many of these parameters are expected to be tied down over the next decade using data from the current and planned ground-based and space-based observatories. The analysis of these new data sets is very challenging and will require both the development of highly sophisticated numerical simulations and the application of the latest tools in data-mining, statistics, and computer science.
Our group has full institutional membership in the ongoing Sloan Digital Sky Survey IV, including the extended baryon oscillation spectroscopic survey (eBOSS) and the mapping nearby galaxies at APO experiments (MaNGA); and in the Large Synoptic Survey Telescope (LSST) collaboration, focusing primarily on involvement in the scientific activities and leadership of the Dark Energy Science Collaboration (DESC). Together these surveys will provide data for premier cosmological analyses until 2030. Some members of our group also have access to other ongoing or future surveys. In terms of computing infrastructure, the McWilliams Center has a ≈1500 core computer cluster available for use by researchers in cosmology. For more details on access to large sky surveys and computing capabilities, visit the McWilliams Center for Cosmology.
Rupert Croft’s research interests are in computational cosmology, involving both simulations and the analysis of data from large surveys. This includes the physics of the intergalactic medium and its use as a probe of cosmology and of galaxy and quasar formation. He is participating in the SDSS surveys of galaxies and quasar absorption lines which are constraining dark energy, and is making the first "intensity mapping" measurements of structure using optical emission lines. Croft also works on the re-ionization of the Universe, and high redshift galaxies, as well as new cosmological probes of modified gravity, such as gravitational redshifts and other relativistic effects which are just starting to be measured from galaxies and large-scale structure. He makes use of the McWilliams Center’s high performance computing facilities, including the Warp and Coma clusters to analyze SDSS data and perform cosmological hydrodynamic and radiative transfer simulations.
Shirley Ho is a cosmologist whose interest ranges from theory to observations, and whose research involves both simulations and analyses of large scale structure via novel techniques developed in Machine Learning and Statistics. Utilizing large scale structure and the cosmic microwave background, she seeks to understand the beginning of the Universe and its evolution, its dark components (dark energy and dark matter), and the light, elusive neutrinos. Her recent research focuses on the use of a standard ruler called Baryon Acoustic Oscillations via various large scale structure tracers such as the 3D clustering. In this way, she plays leading roles in large scale structure analyses in the SDSS-III, SDSS-IV, and Large Synoptic Sky Telescope collaborations (in particular, within the LSST Dark Energy Science Collaboration). In addition, she is a member of the future Dark Energy Spectroscopic Instrument (DESI) and Euclid surveys.
Sergey Koposov’s research explores large astronomical surveys such as SDSS, Gaia and LSST in order to understand structure, formation and evolution of galaxies as well as properties of dark matter. His current research focus is on studying the Milky Way and its satellite galaxies that orbit around it together with the "stellar streams" – stellar structures formed from tidally disrupted star clusters and dwarf galaxies.
In his research, Dr. Koposov applies advanced statistical, machine learning and Big Data methods to the extremely large datasets produced by massive astronomical surveys.
Jeffrey Peterson's group carries out cosmological observations using the 21 cm emission line of neutral hydrogen. The group pioneered the field of 21-cm Intensity Mapping using existing telescopes to make the first detection ofcosmic structure at redshifts near one. The team now contributes to the design of custom-built 21-cm telescopes in Canada, Mexico and China. Currently, Peterson leads the RF design program for the HIRAX telescope in South Africa, an array of 1024 six-meter dishes slated for the South African Radio Astronomy Reserve. This telescope will map cosmic structure from redshift 0.8 to 2.5 allowing a sharp test of models of Dark Energy. These telescopes can also be used to study the mysterious, rare Fast Radio Bursts. The team recently reported the detection of the first convincingly extra-galactic radio burst.
Hy Trac is a theoretical and computational cosmologist whose scientific interests include cosmic evolution and structure formation. His work includes the development and application of numerical simulations to model and interpret the observable Universe. He is currently developing a novel mesh-free hydrodynamic code. In cosmology, he is 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, he would particularly like to work on star and planet formation and the development of planetary atmospheres. He also collaborates with machine learning experts and statisticians to apply modern approaches to improve multi wavelength data analysis and numerical simulations. He is a member of the Atacama Cosmology Telescope (ACT) and Simons Observatory (SO) Collaborations.
Matthew Walker studies the astrophysical properties of dark matter, thus far via optical imaging, spectroscopy and dynamical modelling of the dwarf galaxies that surround the Milky Way and neighboring Andromeda. The dwarf galaxies include the oldest, smallest and 'darkest' (i.e., composed almost entirely of dark matter) galaxies known, and currently represent the smallest physical scales (sizes of ≈100 light years, speeds of a few kilometers per second, masses of ≈100,000 Suns) that are associated empirically with dark matter. If dark matter is made from some kind of new fundamental particle, then the manner in which dark matter clumps at such small scales can help to decide among various ideas about the properties of that particle. By measuring the spatial distribution of dark matter in dwarf galaxies, Walker aims to help figure out what the dark matter actually is. His research is at the intersection of dynamics, cosmology and particle physics. He uses some of the world's largest optical telescopes, including the 6.5-meter Magellan telescopes at Las Campanas Observatory in Chile, the 6.5-meter MMT at Mt. Hopkins, Arizona, and the 8.2-meter Very Large Telescope at Cerro Paranal in Chile. He is also a member of the SDSS IV collaboration.