Astrophysics and Cosmology-Dept of Physics - Carnegie Mellon University

Astrophysics and Cosmology


Rupert Croft
Tiziana Di Matteo
Shirley Ho

Tina Kahniashvili
Rachel Mandelbaum
Jeffrey Peterson
Hy Trac

Matthew Walker

McWilliams Center for Cosmology:

Group Overview

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. 

Group members have access to data from a variety of major telescopes and space missions, including the Sloan Digital Sky Survey, the Chandra and XMM X-ray satellites, and the Hubble Space Telescope. CMU is a partner in The National Virtual Observatory. CMU also owns a 2m sub-millimeter telescope, Viper, at the South Pole. Computer resources are vital to the success of any modern astrophysics group. The CMU group owns a state-of-the-art Beowulf cluster and has access to the TeraScale facilities of the Pittsburgh Super Computing center.

Recent results include those in strong lensing; weak lensing; the Sunyaev-Zeldovich effect; the X-ray background; numerical simulations; and ``baryon wiggles''. The group has also made preliminary measurements of many of the fundamental cosmological parameters including Hubble's Constant, Omega Matter, Omega Total and sigma-8. The group has major involvements in some of the most exciting projects in cosmology and extra-Galactic astronomy e.g. SDSS-III AND SDSS-IV, LSST, ACT, HSC, and Euclid and is well placed to be a world leader in the race to the underlying cosmological model.

Member Research Thrusts

Rupert Croft’s main research interests are in computational cosmology, involving both simulations and the analysis of large surveys. He primarily focuses on the physics of the intergalactic medium, its use as a probe of cosmology and of galaxy and quasar formation. He is a member of the SDSS-III survey of galaxies and quasar absorption lines which aims to measure dark energy parameters using large scale baryonic oscillatory features as a standard ruler. Croft also works on the interaction between matter and radiation in the intergalactic medium, on the re-ionization of the Universe, and predictions for future 21cm radio observations of this high redshift cosmological frontier. He makes use of the McWilliams Center’s high performance computing facilities, including Warp, the 700 core cluster to perform cosmological hydrodynamic and radiative transfer simulations.

Tiziana Di Matteo is a theorist with expertise in both high energy astrophysics and cosmology. Her recent interests focus on state-of-the-art cosmological simulations of galaxy formation including detailed modeling of the impact of black hold feedback on structure formation. She has consistently been awarded large allocations of time on the largest national computing facilities and also makes use of the computational facilities of the McWilliams Center for Cosmology.

Shirley Ho is a cosmologist whose interest ranges from theory to observations, and whose research involves both simulations and analysis of large scale structure surveys such as the Sloan Digital Sky Survey III or of the cosmic microwave background data from Planck HFI and LFI.  She primarily works on utilizing the large scale structure and cosmic microwave background to understand the beginning of the universe, the dark components of the universe such as dark energy and dark matter and its lighter but equally elusive contents such as neutrinos and the evaluation of the universe.  Her recent interest focuses on the use of a standard ruler called Baryon Acoustic Oscillations via various large scale structure tracers, such as the 3D clustering tracer of large scale structure.

Tina Kahniashvili's main research areas include investigation of physical processes in the Universe at very early epochs, as well as late times. In particular, she studies (i) fundamental symmetries tests at very high energies (early epochs of the universe expansion) using currently available data of astrophysical, cosmological, and particle physics experiments; (ii) gravitational waves signal from very early universe (inflation, phase transitions); (iii) CMB fluctuations in beyond standard cosmological models. She is interested in alternative scenarios to explain the accelerated expansion of the universe, such as modifications of general relativity (especially massive gravity models).  She also works on cosmological magnetic fields and the origins, evolution, and observable signatures of primordial turbulence.

Rachel Mandelbaum's research interests are predominantly in the areas of observational cosmology and galaxy studies. This work includes the use of weak gravitational lensing and other analysis techniques, with projects that range from development of improved data analysis methods, to actual application of such methods to existing data. Currently, she is focusing on data from the SDSS (including the ongoing SDSS-III), and is working on upcoming surveys including Hyper-SuprimeCam (HSC), LSST, HSC, LSST, and Euclid.

Jeffrey Peterson's group carries out cosmological observations using the 21 cm emission line of neutral hydrogen. The group is involved in projects using existing telescopes to make three dimensional maps of 21 cm emission for redshifts around ten. These maps will be used to study the first stars and their interaction with surrounding gas. The team also designs and builds 21 cm telescopes. In particular, the group is working to build the Cylinder Radio Telescope in Morocco. This 10,000 square meter telescope will map most of the sky at redshifts near one in order to constrain models of Dark Energy.

Hy Trac is a theoretical and computational cosmologist whose scientific interests include cosmic evolution and structure formation. He is actively working on understanding how the first generation of stars and galaxies re-ionize the universe and how the intergalactic medium can be studied using the Lyman alpha forest. As a member of the Atacama Cosmology Telescope (ACT) project, he is studying how galaxy clusters can be discovered through the Sunyaev-Zel'dovich effect. His research also focuses on the development and application of N-body, hydrodynamic, and radiative transfer algorithms.

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 Sloan Digital Sky Survey IV collaboration.