Nancy Grace Roman Telescope Will do its Own, Wide-Angle Version of the Hubble Deep Field

Remember the Hubble Space Telescope’s Deep Field and Ultra-Deep Field images?

Those images showed everyone that what appears to be a tiny, empty part of the sky contains thousands of galaxies, some dating back to the Universe’s early days. Each of those galaxies can have hundreds of billions of stars. These early galaxies formed only a few hundred million years after the Big Bang. The images inspired awe in the human minds that took the time to understand them. And they’re part of history now.

The upcoming Nancy Grace Roman Space Telescope (NGRST) will capture its own version of those historical images but in wide-angle. To whet our appetites for the NGRST’s image, a group of astrophysicists have created a simulation to show us what it’ll look like.

The NGRST’s previous name was WFIRST. That stands for Wide-Field Infrared Survey Telescope. NGRST will launch in the latter half of 2027 if everything goes according to plan. The Hubble launched in 1990, so there are almost 35 years between the two. Technology has progressed enormously in those intervening years, so the NGRST will be much more powerful and effective than the Hubble in many respects.

The Hubble Deep Field (HDF) and Hubble Ultra Deep Field (HUDF) images were mosaics of individual images. Hubble took 10 days in December 1995 to capture the 342 images comprising the Deep Field. The Ultra Deep Field was made of even more images captured with multiple instruments on the Hubble. Both images required painstaking efforts, with detailed planning and execution. The images took hundreds of hours to capture.

And they were worth it.

This image shows the Hubble Ultra Deep Field in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

The NGRST is different than the Hubble in many ways. The main difference is the Roman’s field of view (FOV.) The NGRST has a FOV 100 times larger than the Hubble’s. That wider FOV is typical of survey telescopes. Survey telescopes image large swathes of the sky at once rather than individual targets. The Hubble has the Wide Field Camera 3 and the Advanced Camera for Surveys, but the Nancy Roman is superior to both of them. While Hubble’s Ultra-Deep Field contains thousands of galaxies—up to 10,000 or more—the NGRST’s deep field image will contain millions of galaxies, possibly up to 10 million.

The Roman’s strength lies in observing large sky areas at once. And when it eventually gets to work later this decade, its Ultra-Deep Field images will be extraordinary. This new simulated image will not only whet our appetites as astronomy “fans,” it’s part of a new study.

The study’s title is “Deep Realistic Extragalactic Model (DREaM) Galaxy Catalogs: Predictions for a Roman Ultra-Deep Field.” The lead author is Nicole Drakos, a postdoctoral scholar at the University of California, Santa Cruz. The Astrophysical Journal will publish the study.

“Roman has the unique ability to image very large areas of the sky, which allows us to see the environments around galaxies in the early universe,” said Drakos in a press release. “Our study helps demonstrate what a Roman ultra-deep field could tell us about the universe while providing a tool for the scientific community to extract the most value from such a program.”

This synthetic image visualizes what a Roman ultra-deep field could look like. The 18 squares at the top of this image outline the area Roman can see in a single observation, known as its footprint. The inset at the lower-right zooms into one of the squares of Roman’s footprint, and the inset at the lower-left zooms in even further. The image, which contains more than 10 million galaxies, was constructed from a simulation that produced a realistic distribution of the galaxies in the universe. Image Credit: Nicole Drakos, Bruno Villasenor, Brant Robertson, Ryan Hausen, Mark Dickinson, Henry Ferguson, Steven Furlanetto, Jenny Greene, Piero Madau, Alice Shapley, Daniel Stark, Risa Wechsler

It’s a mistake to focus on just the size of the images and how many galaxies they contain. It’s not a contest. It’s the information about the Universe that’s the intriguing part.

“The Hubble Ultra Deep Field gave us a glimpse of the universe’s youth, but it was too small to reveal much information about what the cosmos was really like back then as a whole,” said Brant Robertson, an astronomy professor at the University of California Santa Cruz and a co-author of the study. “It’s like looking at a single piece of a 10,000-piece puzzle. Roman could give us 100 connected puzzle pieces, offering a much better picture of what the early universe was like and opening up new scientific opportunities.”

The team behind the simulated image also created a website with a zoomable image to explore.

NASA released this rendering of the Nancy Grace Roman Telescope in May 2020. Image Credit: By NASA (WFIRST Project and Dominic Benford) – Adapted from, Public Domain,

Camera owners know they have to choose between a wide-angle lens that captures wider FOV or a narrower angle lens to focus on individual subjects. A similar thing happens in astronomy. Powerful telescopes can capture deeper, more detailed images, requiring longer exposures. That’s how the Hubble captured its DF and UDF images. That’s not always easy to achieve because observing time at the world’s observatories is a highly-coveted commodity.

But the Roman telescope is different.

Its enormously broad field of view, combined with its infrared capabilities, helps skirt around this problem.

The result of all this power will be an image that contains millions of galaxies of all ages. It’ll show young, small galaxies just starting to form stars. Those galaxies are of great interest to astronomers, as is everything about the early Universe. Astronomers will compare these youngsters to more massive, modern galaxies that hardly form any new stars and learn about galaxy evolution from the comparison.

There are huge blank spots in our knowledge of galactic evolution, and the NGRST’s wide-field power will show galaxies in their environments. Researchers will probe the galaxies and their surroundings to see how they affect galactic evolution and star formation.

One exciting part of this concerns the massive galaxies that no longer have much active star formation. They’re called quiescent galaxies, and they’re hard to find the further back in time astronomers search for them. “We’re not sure whether we haven’t detected very distant quiescent galaxies because they don’t exist or simply because they’re so difficult to find,” Drakos said.

But Drakos and the other authors of the paper think that the Roman Telescope could change that. They’re hopeful that they can find up to 100,000 of these quiescent galaxies and that some of them will be the furthest ever seen.

“It’s amazing to think that no one knew for sure whether other galaxies existed until about a hundred years ago.”

Bruno Villasenor, U of C Santa Cruz, study co-author.

The NGRST should also help astronomers address another burning question in astronomy concerning the Epoch of Reionization (EoR.)

After the Big Bang, the Universe was dense hot plasma, which was opaque to light. Astronomers sometimes refer to this early time in the Universe as the “Cosmic Dark Ages.” As the Universe expanded and cooled, those dark ages ended. The EoR followed between 600 million and 900 million years after the Big Bang. Neutral hydrogen atoms could form now, and galaxies and quasars began to form during the EoR. There was light, and the dark ages ended.

Probing the Universe’s early days is difficult. But astronomers think that ionizing radiation from the early galaxies caused the EoR and brought the dark ages to an end. Here’s where the Roman telescope comes in.

If, like the authors of this paper predict, the NGRST can find up to 10,000 of these early galaxies and study them in their environments, they may be able to determine if early galaxies ionized the Universe and ended the dark ages.

This illustration shows the timeline of the Universe. Credit: NASA, ESA, and A. Feild (STScI)

“The EoR is the final frontier for galaxy surveys,” the authors write in their paper. “Given the difficulty in measuring galaxies at high redshifts, this period in the universe’s history is remarkably unconstrained. High-redshift low-mass galaxies were likely the major source of the ionizing photons in the EoR, and observations indicate that reionization was a “patchy” process. To fully understand the EoR, we need a complete census of galaxies and their ionizing photon contribution.”

The Roman is so powerful that it may address the EoR problem quickly.

“Roman could shine a light on so many cosmic mysteries in just a few hundred hours of observing time,” said Bruno Villasenor, a graduate student at the University of California Santa Cruz and a co-author of the study. “It’s amazing to think that no one knew for sure whether other galaxies existed until about a hundred years ago. Now, Roman offers us the opportunity to observe thousands of the first galaxies that appeared in the very early universe!”

The NGRST won’t be alone in addressing the dark ages and the EoR. The James Webb Space Telescope is on its way to its LaGrange Point, and it looks like the telescope’s sun shields and mirrors have deployed successfully. Its infrared observing power will probe the early Universe and the EoR, so by the time the NGRST is operational, this early period in the Universe’s history might be more tightly constrained.

However it ends up happening, it looks like we’re about to make progress on one of cosmology’s most pressing questions.

But we can also take a step back from all that in-depth science. We can simply enjoy the images from the Roman telescope. Hopefully, they’ll ignite our sense of wonder.

Just like the Hubble did.


Evan Gough

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