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One of the most iconic images from the Hubble Space Telescope is the Hubble Ultra Deep Field, which unveiled a myriad of galaxies across the universe, dating back a few hundred million years after the Big Bang. Hubble observed a single patch of seemingly empty sky for hundreds of hours beginning in September 2003, and astronomers unveiled the galaxy tapestry in 2004, with more sightings in subsequent years.
NASA’s future Nancy Grace Roman Space Telescope will be able to photograph an area of the sky at least 100 times larger than Hubble with the same sharpness. Among the many observations that will be made possible by this wide view of the cosmos, astronomers are considering the possibility and the scientific potential of an “ultra-deep field” Roman space telescope. Such an observation could reveal new perspectives on topics ranging from star formation during the youth of the universe to how galaxies cluster in space.
Roman will enable new science in all areas of astrophysics, from the solar system to the edge of the observable universe. Much of Roman’s observation time will be spent surveying large areas of the sky. However, some observation time will also be available for the astronomical community at large to request other projects. An ultra-deep Roman field could greatly benefit the scientific community, say astronomers.
“As a concept of community science, there could be some exciting scientific feedback from Roman’s ultra-deep field observations. We want to engage the astronomical community to think about ways in which they could take advantage of Roman’s capabilities, ”said Anton Koekemoer of the Space Telescope Science Institute in Baltimore, Maryland. Koekemoer presented the Roman idea of the ultra-deep field at the 237th meeting of the American Astronomical Society, on behalf of a group of astronomers spanning more than 30 institutions.
For example, a Roman ultra-deep field might be similar to the Hubble Ultra Deep field – looking in one direction for a few hundred hours to build an extremely detailed image of very faint and distant objects. Yet while Hubble would catch thousands of galaxies this way, Roman would collect millions. As a result, it would allow new science and greatly improve our understanding of the universe.
Structure and history of the universe
Perhaps the most exciting is the opportunity to study the very first universe, which corresponds to the most distant galaxies. These galaxies are also the rarest: for example, only a handful is visible in the Hubble Ultra Deep field.
Using Roman’s wide field of view and near-infrared data of similar quality to Hubble’s, he was able to discover several hundred, if not thousands, of these youngest and most distant galaxies, interspersed with millions of other galaxies. This would allow astronomers to measure how they cluster together in space as well as their age and how their stars were formed.
“Roman would also produce powerful synergies with current and future telescopes on the ground and in space, including NASA’s James Webb Space Telescope and others,” Koekemoer said.
Moving forward in cosmic time, Roman would pick up additional galaxies that existed approximately 800 million to 1 billion years after the Big Bang. At that time, galaxies were just starting to cluster together in clusters under the influence of dark matter. As the researchers simulated this process of large-scale structure formation, an ultra-deep Roman field would provide real-world examples to test these simulations.
Star formation over cosmic time
The early universe also experienced a star formation storm. Stars were born at rates hundreds of times faster than what we see today. In particular, astronomers are eager to study “cosmic dawn” and “cosmic noon,” which together cover a period of 500 million to 3 billion years after the big bang, when most star formations were occurring, as well as when supermassive black holes were most active. .
“Because Roman’s field of vision is so large, he will be a game changer. We would be able to sample not only an environment in a narrow field of view, but rather a variety of environments captured by Roman’s wide-eyed sight. This will give us a better idea of where and when star formation was occurring, ”explained Sangeeta Malhotra of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Malhotra is a co-investigator of the Roman scientific research teams working on the Cosmic Dawn, and has led deep spectroscopy programs with Hubble, to learn more about young distant galaxies.
Astronomers are eager to measure the rates of star formation in this distant time, which could influence a variety of factors such as the amount of heavy elements observed. Star formation rates can depend on whether or not a galaxy is in a large cluster. Roman will be able to take weak spectra that will show distinct “fingerprints” of these elements and give precise distances (called redshifts) from galaxies.
“Population experts might ask what differences are there between people who live in large cities and those in suburbs or rural areas? Likewise, as astronomers we can ask ourselves, do the most active star-forming galaxies live in highly clustered regions, or just at the edges of clusters, or do they live in isolation? Malhotra said.
Big Data and Machine Learning
One of the greatest challenges for the Roman mission will be learning to analyze the abundance of scientific information in the public datasets it produces. In a sense, Roman will create new opportunities not only in terms of sky coverage, but also in data mining.
An ultra-deep Roman field would contain information about millions of galaxies – far too much to be studied by researchers one by one. Machine learning – a form of artificial intelligence – will be needed to process the huge database. While this is a challenge, it also offers an opportunity. “You could explore completely new questions that you couldn’t answer before,” Koekemoer said.
“The potential for discovery enabled by the massive data sets from the Roman mission could lead to breakthroughs in our understanding of the universe, beyond what we might currently envision,” Koekemoer added. “This could be Roman’s lasting legacy for the scientific community: not only by answering scientific questions we think we can address, but also new questions we haven’t thought about yet.
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