James Clerk Maxwell Telescope Helps Discover 13 Distant, Dusty Galaxies
Utilizing the James Clerk Maxwell Telescope (JCMT) on Maunakea and the James Webb Space Telescope (JWST), an international team of researchers confirmed the existence of 13 new strongly lensed, distant dusty galaxies. Dusty galaxies are the site of the most active star formation in the universe, and these are nearly an order of magnitude fainter than any we have detected so far.
The research was led by Ting-Kai Yang, an undergraduate student at National Taiwan University, and Chian-Chou Chen, an associate research fellow at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and a visiting scientist at JCMT, who have been published in the September 2025 Astrophysical Journal Letters.
The collaboration between a ground-based telescope and a space-based telescope was essential for this discovery, Chen says. Combining the deep submillimeter array data from the JCMT on Maunakea and the unparalleled imaging capabilities of the JWST in space created a fuller picture of both near and distant galaxies.
Image Credit: JWST/Chian-Chou Chen
Chen, Yang, and their colleagues sought to prove that faint, dusty galaxies can be made visible through strong gravitational lenses. Gravitational lensing is a basic fundamental prediction of Einstein’s theory of relativity that happens when a distant galaxy is closely aligned with a nearer galaxy in our line of sight. Because of this alignment, the light emitted from the farther galaxy is then magnified and distorted by the gravity of the foreground galaxy. “This allows us to see the much fainter, farther galaxies that we weren’t able to see before,” Chen explained. In the images produced, the bright light in the center is the foreground galaxy, while the farther galaxy appears as a ring or arc shape around it.
They also sought to determine the “fraction” of the background faint dusty galaxies that are being strongly lensed, meaning how many of the closer galaxies are aligned with and magnifying background galaxies. This gives us a better understanding of the distribution of matter in the universe and how abundant these dusty, star-forming galaxies are.
Previously, it’s been exceedingly difficult to confirm the location or abundance of dusty galaxies. Even though they’re crucial for understanding galaxy evolution, they are often too faint for images to pick up. That’s where the JCMT comes in.
JCMT is equipped with the SCUBA-2 camera, which can take an ultra-deep survey of space at submillimeter wavelengths. JCMT has a far larger aperture than other similar telescopes, which means the JCMT images are much sharper. “For strongly lensed features, those sharp images are essential,” Chen explained, “in order to see both the foreground galaxies and the arc features of the background galaxies.”
Chen has a personal soft spot for the SCUBA-2 camera, as it was the camera he used during his PhD, which he completed at the University of Hawai‘i Mānoa. After finishing his studies and starting a family, he has returned to Hawai‘i as a visiting scientist at JCMT. “It’s great to be back and to be able to bring my family with me this time,” he said. “Working at JCMT, I get a look into the future of science. This is ground zero, where things are happening.”
The fact that the JCMT and JWST’s data is easily accessible greatly contributed to the success of this project. “JWST is awesome in making the data public because we’re able to use it right away. We're grateful to the people at JWST who work hard to make it available to everyone,” Chen said. The modeling software that Yang, the lead author, used was also publicly accessible, allowing her to complete this project within the span of only a year and a half — in her undergraduate education, no less, which is an amazing accomplishment. “She is a very motivated student. I was amazed when she did it so quickly,” Chen said.
Chen, Yang, and the rest of the team were exploring an area of the COSMOS field, one of the best places to study these galaxies. This is the first systematic search for strongly lensed dusty galaxies in this area. Many other studies map very wide, much shallower areas and can miss these faint galaxies. “We wanted to go deeper, where previous studies haven’t looked,” Chen said. The JCMT’s capabilities allowed them to do just that.
Now, the rest of the universe is open to explore with this technology. “We’ve confirmed that this is a feasible method to find faint dusty galaxies, and it’s likely that we’ll be able to find them anywhere we look,” Chen explained. “Our expectation is that the number of these galaxies will grow by orders of magnitude when we expand our area.”
By detecting these faint galaxies, we also hope to understand more about how stars form. “The idea is that you’ll be able to magnify these galaxies even further, study each one, and look at the details,” Chen said. These galaxies produce stars at a rate of a hundred to a thousand times faster than the Milky Way. He thought, “You see that, and you have to ask why.”
Next up — expand the search. Two new telescopes, the Euclid and the Roman, will create much larger-scale maps and surveys of the universe. The Euclid has already been launched into space, and the Roman will be launched in 2026/2027. Together with the JCMT’s deep space data in the future, scientists can explore elsewhere in the sky — and the next stop might be the north ecliptic pole, Chen said. Satellites orbiting around Earth tend to cross over at the poles, giving us a wealth of data from those viewpoints. Wherever it is, one thing is clear: as Chen said, “This is only the starting point.”
