The new COMAP radio survey will look beneath the ‘tip of the iceberg’ of galaxies to uncover a previously unknown era of star formation. The first stars began to form around 400 million years after the birth of our universe. The so-called dark ages of the universe came to an end, and a new light-filled era began. More and more galaxies formed and served as factories for producing new stars, a process that peaked about 4 billion years after the Big Bang.
Fortunately for astronomers, this bygone era can still be observed. It takes time for distant light to reach us, and our telescopes can detect light emitted by galaxies and stars billions of years ago (our universe is 13.8 billion years old). But the details of this chapter in our universe’s history are murky since most of the stars being formed are faint and hidden by dust.
A new Caltech project, called COMAP (CO Mapping Array Project), will offer us a new glimpse into this epoch of galaxy assembly, helping to answer questions about what really caused the universe’s rapid increase in the production of stars.
Looking to the future of the project, we aim to use this technique to successively look further and further back in time. Starting 4 billion years after the Big Bang, we will keep pushing back in time until we reach the epoch of the first stars and galaxies, a couple of billion years earlier.
Kieran Cleary
“Most instruments might see the tip of an iceberg when looking at galaxies from this period,” says Kieran Cleary, the project’s principal investigator and the associate director of Caltech’s Owens Valley Radio Observatory (OVRO). “But COMAP will see what lies underneath, hidden from view.”
The current phase of the project employs a 10.4-meter “Leighton” radio dish at OVRO to study the most common types of star-forming galaxies spread across space and time, including those that are too faint or obscured by dust to be seen in other ways. Radio observations reveal the raw material that stars are made of: cold hydrogen gas. Because this gas is difficult to detect directly, COMAP measures bright radio signals from carbon monoxide (CO) gas, which is always present alongside hydrogen. The radio camera on COMAP is the most powerful ever built for detecting these radio signals.
The project’s first scientific findings have just been published in seven papers in The Astrophysical Journal. COMAP set upper limits on how much cold gas must be present in galaxies at the epoch being studied, including those that are normally too faint and dusty to see, based on observations taken one year into a planned five-year survey. While the project has yet to directly detect the CO signal, these preliminary findings show that it is on track to do so by the end of the initial five-year survey, and that it will eventually paint the most comprehensive picture of the universe’s history of star formation.
“Looking to the future of the project, we aim to use this technique to successively look further and further back in time,” Cleary says. “Starting 4 billion years after the Big Bang, we will keep pushing back in time until we reach the epoch of the first stars and galaxies, a couple of billion years earlier.”
Anthony Readhead, the co-principal investigator and the Robinson Professor of Astronomy, Emeritus, says that COMAP will see the not only the first epoch of stars and galaxies, but also their epic decline. “We will observe star formation rising and falling like an ocean tide,” he says.
COMAP operates by capturing blurry radio images of clusters of galaxies over cosmic time as opposed to sharp images of individual galaxies. This blurriness allows astronomers to efficiently capture all radio light coming from a larger pool of galaxies, including the faintest and dustiest galaxies never seen before.
“We can find the average properties of typical, faint galaxies in this way without needing to know very precisely where any individual galaxy is located,” Cleary explains. “This is analogous to using a thermometer to determine the temperature of a large volume of water rather than analyzing the motions of individual water molecules.”
