New COMAP radio survey will peer beneath the ‘tip of the iceberg’ of galaxies to reveal a hidden era of star formation
Sometime around 400 million years after the birth of our universe the first stars began to form. It was the end of the so-called dark age of the universe, and a new age full of light began. Over time, more and more galaxies began to take shape and served as factories for the production of new stars. This process peaked about four billion years after the Big Bang.
Fortunately for astronomers, this bygone era can still be observed. Distant light takes time to reach us, and powerful telescopes can pick up light emitted by galaxies and stars billions of years ago (the age of our universe is 13.8 billion years). But the details of this chapter in the history of our universe are obscure because most of the stars formed then are faint and obscured by dust.
A new Caltech project called COMAP will give us a new look at this era of galaxy formation. It will help answer questions about the real cause of the rapid increase in star formation in the universe.
“Most instruments will perhaps see the tip of the iceberg when looking at galaxies from this period,” says Kieran Cleary, the project’s principal investigator and deputy director of Caltech’s Owens Valley Radio Observatory (OVRO). “But COMAP will see what lies beneath, hidden from view.”
Kieran Cleary. Credit: Kieran Cleary/Caltech
In the current phase of the project, the 10.40 meter diameter Layton radio antenna at OVRO is being used to study the most common types of star-forming galaxies scattered throughout space and time. This includes galaxies that are too difficult to see in other ways because they are too faint or obscured by too much dust. The radio observations detect cold hydrogen gas, the raw material from which stars are formed. It is not easy to detect this gas directly, so instead COMAP measures bright radio signals from carbon monoxide (CO) gas, which is always found together with hydrogen. The COMAP radio camera is the most powerful ever built to detect these radio signals.
The first scientific results from the project have just been published in seven papers in The Astrophysical Journal. Based on observations made at the end of one year in a planned five-year survey, COMAP established upper limits for the amount of cold gas that must be present in galaxies during the period under study, including galaxies that are normally too faint and too dusty to be seen. The project has yet to directly detect a signal of CO, but these initial results show it is on track to do so by the end of the initial five-year survey, ultimately producing the most comprehensive picture yet of the universe’s star formation history.
“Looking to the future of the project, we intend to use this technique to repeatedly look further and further back in time,” says Cleary. “Starting 4 billion years after the big bang, we will continue to move backwards in time until we reach the period of the first stars and galaxies, about two billion years before.”
Anthony Readhead, co-principal investigator and professor emeritus of astronomy, says COMAP will not only see the first ages of stars and galaxies, but also their epic sunsets. “We will observe the formation, rise and fall of stars like the tides of the sea,” he says.
COMAP works by capturing fuzzy radio images of galaxy clusters over cosmic time instead of sharp images of individual galaxies. This blurring allows astronomers to effectively capture all the radio light coming from a larger pool of galaxies, even the faintest and dustiest that have never been seen.
“This way we can find the average properties of typical faint galaxies without having to know very precisely where each individual galaxy is,” explains Cleary. “It’s like finding the temperature of a large amount of water using a thermometer instead of analyzing the movement of the individual water molecules.”
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