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

Scientists have created a giant synthetic study that shows what we can expect from the Nancy Grace Roman Space Telescope’s future observations. Although it represents only a small part of the real future survey, 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 vast amounts of data, and explore what we can learn from tandem observations with other telescopes.

“The amount of data 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 we can use to make sure we get the most out of the mission’s observations.”

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

A paper describing the findings, led by Troxel, has been accepted for publication in the The Monthly Notices of the Royal Astronomical Society.

Cosmic construction

Roman’s High Latitude Wide Area Survey will consist of both imaging – the focus of the new simulation – and spectroscopy across the same vast swath of the universe. Spectroscopy involves measuring the intensity of light from cosmic objects at different wavelengths, while Roman’s imaging 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 spacetime. The greater the mass, the greater the chain. This creates an effect called gravitational lensing, which occurs when light from a distant source is distorted as it travels past intervening objects. When these lensing objects are massive galaxies or galaxy clusters, background sources can be smeared or appear as multiple images.

Less massive objects can create more subtle effects called weak lensing. Roman will be sensitive enough to use weak lensing to see how clumps of dark matter distort the appearance of distant galaxies. By observing these lensing effects, scientists will be able to fill in more of the gaps in our understanding of dark matter.

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

“However, the predictions are statistical in nature, so we test them by observing large areas of the cosmos. With its wide field of view, Roman will be optimized to efficiently survey the sky and complement observatories such as the James Webb Space Telescope, which are designed for deeper study of individual objects.”

Earth and space

The synthetic Roman survey covers 20 square degrees of the sky, roughly equivalent to 95 full moons. The survey itself will be 100 times larger and reveal more than a billion galaxies. Rubin will scan an even larger area — 18,000 square degrees, nearly half the entire sky — but with lower resolution, as it will have to look through Earth’s turbulent atmosphere.

Pairing the Roman and Rubin simulations gives the researchers the first opportunity 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 close sources as separate objects. Sometimes they blur together, affecting weak lens measurements. Now, scientists can determine the difficulties and benefits of “deglazing” such objects in Rubin images by comparing them to Roman ones.

With Roman’s colossal cosmic view, astronomers will be able to achieve far more than the primary goal of the study, which is to study the structure and evolution of the universe, map dark matter and distinguish between the leading theories that try 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 exquisite detail.

“With Roman’s gigantic 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 in Greenbelt, Maryland. . “The mission will help answer critical questions in cosmology while potentially revealing entirely new mysteries for us to solve.”