Distant galaxies offer a glimpse of the universe as it was billions of years ago. Understanding how the Milky Way and other galaxies originated provides a unique perspective on the fundamental physics of cosmology, the invisible dark matter, and repulsive force of dark energy. Patrick McCarthy uses the facilities at Carnegie’s Las Campanas Observatory to explore the early formation and evolution of galaxies. He is also director of the Giant Magellan Telescope Organization, an international consortium that is building the next generation giant telescope.
Galaxy formation is driven by the interplay between the large-scale distribution of dark matter—that non-luminous unidentified fundamental particles—and processes at the atomic scale that regulate the cooling of gas into stars. McCarthy wants to understand when the first massive, gravitationally bound stellar systems formed and how the diverse properties of today’s galaxies are linked to their histories.
Using the du Pont telescope and the Wide-field Infrared Camera (WIRC) built by Eric Persson, McCarthy has mapped several areas of the faint sky to identify the most massive stellar systems at each point in time. He surprisingly found many galaxies with masses in excess of 100 billion solar masses when the universe was only 3 billion years old. The data indicate their stars are 2-3 billion years old, implying an early formation.
Also contrary to theory, McCarthy and colleagues find that the largest and most massive galaxies formed earliest in the universe, while the small and dwarf galaxies formed late; many are still forming today. High-resolution images, obtained with the Hubble Space Telescope, indicate that they are structurally similar to today’s elliptical galaxies and the central bulge of the Milky Way. McCarthy also uses the IMACS spectrograph on the Baade telescope to explore the connection between environment, mass, and star formation history in distant galaxies.
McCarthy received his B.S. in physics and astronomy at the University of Arizona and his Ph.D. from the University of California, Berkeley. Before joining the scientific staff in 1993, he was a Carnegie and Hubble fellow at the Observatories. For more information see http://obs.carnegiescience.edu/users/pmc2