When a batch of bright cosmic objects first appeared in maps in 2008 made with data from the South Pole Telescope, astronomers at the University of Chicago’s Kavli Institute for Cosmological Physics regarded it only as an unavoidable nuisance.
The light sources interfered with efforts to measure more precisely the cosmic microwave background—the afterglow of the big bang. But the astronomers soon realized that they had made a rare find in South Pole Telescope’s large survey of the sky. The spectra of some of the bright objects, which is the rainbow of light they emit, were inconsistent with what astronomers expected from the well-known population of radio galaxies.
Instead they looked like dust-enshrouded, star-forming galaxies. Such galaxies should be easily identified in infrared sky surveys, but there were no known counterparts for what the South Pole Telescope had found. They had to be extremely distant to avoid infrared detection, and therefore extremely luminous. Intrigued, the astronomers performed detailed follow-up imaging of the sources with the new Atacama Large Millimeter Array (ALMA) in Chile’s Atacama Desert. These observations show the dust-filled galaxies were bursting with stars much earlier in cosmic history than previously thought.
Joaquin Vieira, now a postdoctoral scholar at the California Institute of Technology, leads a team that will report the discovery in the March 13 issue of the journal Nature and in two other papers that will appear in the Astrophysical Journal.
“We have been eagerly waiting for ALMA to be ready so we could conduct these observations,” said Vieira, MS’05, PhD’09, who based his doctoral research at UChicago on the discovery of the extragalactic sources. “The sources we discovered with the South Pole Telescope were so far in the southern sky that no telescopes in the Northern Hemisphere could observe them. We are very privileged to be among the first astronomers to use ALMA.”
Vieira has supported the South Pole Telescope from the beginning, helping to build the telescope and its camera, said John Carlstrom, S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at UChicago. “He’s been involved from the ground up, or the ice up, if you will,” said Carlstrom, who leads the SPT collaboration and is a co-author of the Nature paper.