Millions of galaxies emerge in new simulated images from NASA’s Nancy Grace Roman Space Telescope

This simulated image of the Roman deep field, containing hundreds of thousands of galaxies, represents only 1.3 percent of the synthetic survey, which is itself only one percent of the planned Roman survey. Galaxies are color coded – redder ones are further away and whiter ones are closer. The simulation shows the power of Roman to perform large, deep surveys and to study the universe statistically in ways not possible with current telescopes. Credit: M. Troxel and Caltech-IPAC/R. Hurt

Scientists have created a giant synthetic survey that shows what we can expect from future observations of the Roman Nancy Grace Space Telescope. Although it represents only a small fraction of the real survey of the future, this simulated version contains a staggering number of galaxies – 33 million of them, along with 200,000 foreground stars in our home galaxy.

The simulation will help scientists plan the best observing strategies, test different ways to mine the mission’s large amounts of data, and explore what we can learn from back-to-back observations with other telescopes.

“The volume of data that Roman will return is unprecedented for a space telescope,” said Michael Troxel, an assistant professor of physics at Duke University in Durham, North Carolina. “Our simulation is a testing ground that we can use to make sure we get the most out of the mission’s observations.”

The team extracted data from a mock universe originally developed to support science planning with the Vera C. Rubin Observatory, which is located in Chile and will begin full operation in 2024. Because the Roman and Rubin simulations use the same source, astronomers can compare and see what they can expect to learn from the pair of telescope observations once they both actively scan the universe.

A paper describing the results, led by Troxel, has been accepted for publication in the Monthly Notices of the Royal Astronomical Society. This video begins by showing the most distant galaxies in the simulated deep-field image in red. As it shrinks, the layers of the nearest galaxies (yellow and white) are added to the frame. By studying different cosmic ages, Roman will be able to trace the history of the universe’s expansion, study how galaxies developed over time, and much more. Credit: Caltech-IPAC/R. Hurt and M. Troxel

Cosmic construction

The Novel High Latitude Large Area Survey will consist of imaging – the focus of the new simulation – and spectroscopy of the same large area of ​​the universe. Spectroscopy involves measuring the intensity of light from cosmic objects at different wavelengths, while Roman’s image will reveal the precise positions and shapes of hundreds of millions of faint galaxies that will be used to map dark matter. Although this mysterious substance is invisible, astronomers can infer its presence by observing its effects on regular matter.

Anything with mass distorts the fabric of space-time. The greater the mass, the greater the deformation. This creates an effect called gravitational lensing, which occurs when light from a distant source is distorted as it travels past intervening objects. When those lensed objects are massive galaxies or galaxy clusters, the background sources can be smeared or appear as multiple images.

Less massive objects can create subtler effects called weak lensing. Roman will be sensitive enough to use weak lensing to see how clumps of dark matter distort the view of distant galaxies. By observing these lensing effects, scientists will be able to fill in more gaps in our understanding of dark matter. This graph compares the relative sizes of the synthetic image (inset, outlined in orange), the entire area simulated by the astronomers (top middle square outlined in green), and the size of the full survey they will perform astronomers in the future (large square in the lower left outlined in blue). The background, from the Digitized Sky Survey, illustrates how much sky area each region covers. The synthetic image covers about as much sky as a full moon, and the upcoming Roman survey will cover much more area than the Big Dipper. While the Hubble Space Telescope or the James Webb Space Telescope would take about a thousand years to image an area as large as the upcoming survey, Roman will do so in just over seven months. Credit: NASA Goddard Space Flight Center and M. Troxel

“Cosmic structure formation theories make predictions about how seed fluctuations in the early universe grow into the distribution of matter that can be seen through gravitational lensing,” said Chris Hirata, a professor of physics at Ohio State University in Columbus and a co-author of the paper.

“But the predictions are statistical in nature, so we test them by observing vast regions of the cosmos. The novel, with its wide field of view, will be optimized to efficiently observe the sky, complementing observatories such as the space telescope James Webb that are designed for deeper investigation of individual objects.”

Earth and space

The Roman synthetic survey covers 20 square degrees of the sky, which is roughly equal to 95 full moons. The current survey will be 100 times larger, revealing more than a billion galaxies. Ruby will scan an even larger area — 18,000 square degrees, nearly half the entire sky — but at lower resolution because it will have to look through Earth’s cloudy atmosphere. This animation shows the kind of science astronomers will be able to do with future Roman field observations. The gravity of intervening galaxy clusters and dark matter can bend light from more distant objects, distorting their appearance as shown in the animation. By studying the distorted light, astronomers can study the elusive dark matter, which can only be measured indirectly through its gravitational effects on visible matter. As a bonus, this lens also makes it easier to see more distant galaxies, whose light they magnify. Credit: Caltech-IPAC/R. Hurt

The pairing of the Roman and Rubin simulations provides the first opportunity for scientists to try to detect the same objects in both sets of images. This is important because ground-based observations are not always sharp enough to distinguish multiple, nearby sources as separate objects. Sometimes they blur together, which results in poor lens measurements. Now, scientists can determine the difficulties and benefits of “blending” such objects into Ruby images by comparing them with Roman ones.

With Roman’s colossal cosmic view, astronomers will be able to accomplish much more than the survey’s primary goals, which are to study the structure and evolution of the universe, map dark matter, and distinguish between the leading theories that attempt to explain why the expansion of the universe is accelerating. Scientists can comb through the new simulated Roman data to get a taste of the bonus science that will come from seeing so much of the universe in such fine detail.

“With Roman’s giant field of view, we anticipate many different scientific possibilities, but we will also have to learn to expect the unexpected,” said Julie McEnery, senior project scientist for the Roman mission at NASA’s Goddard Space Flight Center. -s in Greenbelt, Maryland. . “The mission will help answer critical questions in cosmology, while potentially revealing brand new mysteries for us to solve.”

More information: Michael Troxel et al, A Joint Roman Space Telescope and Rubin Synthetic Wide-Field Imaging Survey, The Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad664. On arXiv:
doi.org/10.48550/arXiv.2209.06829

Journal information: Monthly Notices of the Royal Astronomical Society