Carnegie Mellon University

Department of Physics

Mellon College of Science

Matthew G.  Walker

Asstitant Professor

Astrophysics & Cosmology
Wean Hall 8408


Prof. Matt Walker

Education & Professional Experience

PhD: University of Michigan (2007)

Professional Societies:
American Astronomical Society

Honors and Awards:
Martin and Beate Block Award, Aspen Center for Physics (2013)
Hubble Post-doctoral Fellowship (2010)

Curriculum ViTA

Assistant Professor, Carnegie Mellon University, 2013–
Post-doctoral Research: Harvard University, 2010–13
Post-doctoral Research: University of Cambridge (U.K.), 2007–10

Research Interests

I study 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 can form '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, I aim to help figure out what the dark matter actually is. Thus my research has wandered into the intersection of dynamics, cosmology and particle physics.

For this work I use 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. I am also a member of the Sloan Digital Sky Survey IV collaboration.

Night sky at the Magellan telescopes of Las Campanas Observatory, Chile.
(Photography and video editing by Mike Padilla, @mrpadillaphotography).

Selected Publications

Alex Geringer-Sameth, Matthew G. Walker, Savvas M. Koushiappas, Sergey E. Koposov, Vasily Belokurov, Gabriel Torrealba, N. Wyn Evans, Indication of Gamma-Ray Emission from the Newly Discovered Dwarf Galaxy Reticulum IIPhysical Review Letters 115, 81101 (2015) 

M. G. Walker, E. W. Olszewski, M. Mateo, Bayesian analysis of resolved stellar spectra: application to MMT/Hectochelle observations of the Draco dwarf spheroidalMonthly Notices of the Royal Astronomical Society 448, 2717 (2015) 

Matthew G. Walker, Abraham Loeb, Is the universe simpler than ΛCDM?Contemporary Physics 55, 198 (2014) 

C. F. P. Laporte, M. G. Walker, J. Penarrubia, Measuring the slopes of mass profiles for dwarf spheroidals in triaxial cold dark matter potentialsMonthly Notices of the Royal Astronomical Society: Letters 433, L54 (2013)

J. Zavala, M. Vogelsberger, M. G. Walker, Constraining self-interacting dark matter with the Milky Way's dwarf spheroidalsMonthly Notices of the Royal Astronomical Society: Letters 431, L20 (2013)

Jorge Peñarrubia, Sergey E. Koposov, Matthew G. Walker, A statistical method for measuring the galactic potential and testing gravity with cold tidal streamsThe Astrophysical Journal 760, 2 (2012)

Jorge Peñarrubia, Andrew Pontzen, Matthew G. Walker, Sergey E. Koposov, The coupling between the core/cusp and missing satellite problemsThe Astrophysical Journal 759, L42 (2012)

Matthew G. Walker, Jorge Peñarrubia, A method for measuring (slopes of) the mass profiles of dwarf spheroidal galaxiesThe Astrophysical Journal 742, 20 (2011)

Matthew Walker, Dark Matter in the Galactic Dwarf Spheroidal SatellitesPlanets, Stars and Stellar Systems, Volume 5: Galactic Structure and Stellar Populations , Springer-Verlag, p. 1039 (2013)

M. G. Walker, C. Combet, J. A. Hinton, D. Maurin, M. I. Wilkinson, Dark matter in the classical dwarf spheroidal galaxies: a robust constraint on the astrophysical factor for γ-ray flux calculationsThe Astrophysical Journal 733, L46 (2011)

Matthew G. Walker, Stacy S. McGaugh, Mario Mateo, Edward W. Olszewski, Rachel Kuzio de Naray, Comparing the dark matter halos of spiral, low surface brightness, and dwarf spheroidal galaxiesThe Astrophysical Journal 717, L87 (2010)

Matthew G. Walker, Mario Mateo, Edward W. Olszewski, Jorge Peñarrubia, N. Wyn Evans, Gerard Gilmore, A universal mass profile for dwarf spheroidal galaxies?The Astrophysical Journal 704, 1274 (2009)

Matthew G. Walker, Mario Mateo, Edward W. Olszewski, Stellar velocities in the Carina, Fornax, Sculptor, and Sextans DSPH galaxies: Data from the Magellan/MMFS surveyThe Astronomical Journal 137, 3100 (2009)

Matthew G. Walker, Mario Mateo, Edward W. Olszewski, Systemic Proper Motions of Milky Way Satellites from Stellar Redshifts: The Carina, Fornax, Sculptor, and Sextans Dwarf SpheroidalsThe Astrophysical Journal 688, L75 (2008)

Matthew G. Walker, Mario Mateo, Edward W. Olszewski, Oleg Y. Gnedin, Xiao Wang, Bodhisattva Sen, Michael Woodroofe, Velocity Dispersion Profiles of Seven Dwarf Spheroidal GalaxiesThe Astrophysical Journal 667, L53 (2007)

More Publications:
ORCID  Researcher ID