Surveying the Universe

Spectroscopy is the key to understanding our universe. Because atoms, ions, and molecules emit and absorb light at specific wavelengths, we can infer the composition and physical conditions of celestial objects from their spectra. I will review the key scientific results from past optical spectroscopic sky surveys and the expected returns from current and planned future surveys. We are inferring the buildup of our own Milky Way galaxy by studying how stars of different chemical compositions are distributed within it. We are tracing the evolution of the structure and chemical composition of galaxies over cosmic time by comparing matched samples of galaxies at different lookback times. We are using luminous objects such as supernovae and galaxies as tracers of our expanding universe and the gravitational flows within it; the motions of these tracers constrain the properties of dark energy and dark matter and test general relativity on large scales. To obtain the vast number of spectra needed for these studies, astrophysicists have conducted ever larger surveys of the heavens over the past three decades. Canada played an early leading role in these surveys in the 1990s, using the 3.6-meter-diameter Canada-France-Hawaii Telescope. A proposed renovation of the CFHT would convert it into an 11.25-meter-diameter dedicated facility known as the Maunakea Spectroscopic Explorer. MSE would obtain spectra of over 4000 objects simultaneously, yielding spectra of millions of objects per year and again placing Canada in the forefront of optical astrophysical sky surveys.

Patrick Hall is a Professor in the Department of Physics and Astronomy at York University in Toronto. His main research interest is the study of quasars, which are supermassive black holes surrounded by glowing accretion disks at the centers of large galaxies. Born in California to Canadian parents, he double-majored in Physics and Astronomy at the University of California, Berkeley. He obtained a doctorate in astronomy at U. Arizona (though it took him seven and a half years). He participated in the historic Canadian Network for Observational Cosmology galaxy survey with the Canada-France-Hawaii Telescope as a postdoctoral fellow at U. Toronto. He has been continually involved with the Sloan Digital Sky Survey since 2000, starting as a joint postdoctoral fellow at Princeton University and the Universidad Catolica de Chile before joining the faculty at York in 2004. He has used the SDSS to study a wide range of objects including: quasars with outflowing gas spanning a huge range of physical properties including velocities up to 20% of the speed of light; a gravitationally lensed quasar with six images; a previously overlooked, fast-moving, relatively nearby white dwarf; and a population of quasars which appear to exhibit gas falling toward the black