In the American Wild West, midday was a time for duets and showdowns. When it comes to the history of the universe, the cosmic noon shows a different kind of fireworks. About 2 to 3 billion years after the Big Bang, most galaxies grew rapidly, forming stars hundreds of times faster than our own galaxy, the Milky Way, today. When it launches by May 2027, NASA’s Nancy Grace Roman Space Telescope promises to bring new insights into the heyday of star formation.
Cosmic noon is an important time in the history of the universe because it shaped how the galaxies are today. But many questions remain unanswered. Why did star formation peak and then decline? Why did some galaxies suddenly stop making stars while others gradually fade? How important were local influences such as the number of galactic neighbors in shaping this development?
To answer these questions, astronomers need a plentiful sample of galaxies from that time period to study. The power of the Roman would lie in its ability to capture thousands of objects of interest in a single scene. With such a large survey, scientists won’t have to pick and choose their preferred targets in advance, which can lead to unexpected biases.
“With a field 100 times wider than the Hubble Space Telescope, the Romans could change the astronomical landscape,” said Kate Whitaker, assistant professor of astronomy at the University of Massachusetts at Amherst. Whitaker’s research focuses on studying the regulation of star formation and quenching in giant galaxies in the early universe.
Roman’s wide field of view will also enable astronomers to place individual galaxies in context by observing how their growth accelerates, and subsequently slows, the “web” of the universe—the basis of their location within the large-scale structure of the universe. But varies.
“You take an image, and you get everything. We’ll see what and where the interesting objects are,” said Casey Papovich, a professor of astronomy at Texas A&M University in College Station, Texas. Papovich’s research involves the discovery of the growth and assemblage of stellar mass in galaxies in the early universe.
go beyond the imagery
While the images can help astronomers find galaxies of interest, much more information can be obtained by spreading a galaxy’s light across a spectrum. Papovich, along with Vicente (Vince) Estrada-Carpenter of St. Mary’s University in San Antonio, Texas, and his colleagues, have pioneered a technique to extract light from all the stars in a galaxy.
By examining a galaxy’s spectrum, you can learn about the ages of its stars, the history of its star formation, how many heavy chemical elements it contains, and much more. By doing this for a large number of early galaxies, astronomers can learn about the processes that drive and eventually end this period of rapid evolution.
Roman’s power can be further enhanced by observing distant galaxies whose light has been distorted by a phenomenon called gravitational lensing. The gravity of an intervening galaxy cluster can make light from a more distant galaxy appear larger and brighter, allowing astronomers to study the background galaxy in more detail than would otherwise be available.
Whitaker is already using this technique with Hubble to study the cores of young galaxies versus their outskirts. This work attempts to determine whether star formation stops from the outside-in or inside-out—that is, from the outskirts of the galaxy to its center, or vice versa.
“Galaxy quenching — the sudden end of star formation — may be a rapid process on cosmological timescales. As a result, it’s difficult to catch any one in the act because they are so rare,” Whitaker said. “The Romans will help us find those rare examples.”
While Roman’s space-based view will provide excellent sharpness and stability, ground-based observatories will also come in handy in studying the cosmic noon. For example, the Atacama Large Millimeter/submillimeter Array can measure the gas and dust content of distant galaxies. And future 30-meter-class telescopes will be able to measure fine details in galaxy spectra because of their ability to collect lots of light.
“The Roman and ground-based observatories would complement each other. The Romans would single-handedly and efficiently identify and characterize the most interesting galaxies in large fields of view. We can then study them in greater detail with ground-based telescopes.” are,” explained Papovich.
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Provided by NASA’s Goddard Space Flight Center
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