James Webb Telescope gives UArizona astronomers unprecedented glimpses into stellar nurseries
As part of the largest survey of nearby galaxies, University of Arizona astronomers have obtained never-before-seen details of how young, newly forming stars influence the structure of the gas and dust in their host galaxies. 

By Daniel Stolte, University Communications
Feb. 17, 2023


The spiral arms of nearby galaxy NGC 1433 light up in this image taken by the James Webb Space Telescope, revealing evidence of extremely young stars releasing energy.
Nearby spiral galaxy NGC 1433 takes on a completely new look when observed by the James Webb Telescope's Mid-Infrared Instrument (MIRI). Its spiral arms are littered with evidence of extremely young stars releasing energy and, in some cases, blowing out the gas and dust of the interstellar medium. Areas that appear dark and dim in optical imaging light up under Webb’s infrared eye. Despite lying more than 46 million years away from Earth, the galaxy is considered "nearby" by astronomical standards. Science: NASA, ESA, CSA, Janice Lee (NOIRLab). Image processing: Alyssa Pagan (STScI)

Researchers using NASA's James Webb Space Telescope are getting their first look at star formation, gas and dust in nearby galaxies with unprecedented resolution at infrared wavelengths. The data has led to publication of a collection of 21 research papers that provide new insight into how some of the smallest-scale processes in our universe – the beginnings of star formation – impact the evolution of the largest objects in our cosmos: galaxies.

The largest survey of nearby galaxies in Webb's first year of science operations is being carried out by the Physics at High Angular resolution in Nearby Galaxies, or PHANGS, collaboration, involving more than 100 researchers around the globe. The survey is led by Janice Lee, an associate astronomer at the University of Arizona and Gemini Observatory chief scientist at the National Science Foundation's NOIRLab. The team's initial findings are detailed in the 21 studies, which were recently published in a special issue of The Astrophysical Journal Letters.

Using Webb, astronomers have for the first time observed embedded star clusters in galaxies beyond the Magellanic Clouds, the Milky Way's closest neighboring galaxies, said Jimena Rodriguez, a postdoctoral research associate at the UArizona Steward Observatory who is the lead author on one of the papers and co-authored two others.

"Theoretically, the Hubble Space Telescope has the resolution power needed to observe these star-forming regions in galaxies that are farther away, but it is limited to the visible light spectrum," she said. "These stellar nurseries are occulted by dust, so to observe them, we need infrared instruments that can penetrate the dust."

That's where the James Webb Space Telescope instruments come in. UArizona Regents Professor of Astronomy Marcia Rieke led the development of Webb's primary imager – the Near-Infrared Camera, or NIRCam – and serves as the instrument's principal investigator. Marcia's husband George Rieke, also a Regents Professor of Astronomy, is the science team lead for the telescope's Mid-Infrared Instrument, or MIRI.

Images captured by MIRI reveal the presence of a network of highly structured features within the galaxies included in the survey – glowing cavities of dust and huge cavernous bubbles of gas that line the galaxies' spiral arms. In some regions of the galaxies observed, this web of features appears to be built from both individual and overlapping shells and bubbles where young stars are releasing energy.

"Areas which are completely dark in Hubble imaging light up in exquisite detail in these new infrared images, allowing us to study how the dust in the interstellar medium has absorbed the light from forming stars and emitted it back out in the infrared, illuminating an intricate network of gas and dust," said PHANGS team member Karin Sandstrom of the University of California, San Diego.

The PHANGS team is studying a diverse sample of 19 galaxies, all within about 65 million light-years from Earth and belonging to a category known as main sequence disc galaxies. A common feature of such galaxies is a yet-to-be elucidated mechanism allowing them to attract material from their surroundings and form stars at a fairly steady rate. In Webb's first few months of science operations, observations of five of those galaxies – M74, NGC 7496, IC 5332, NGC 1365 and NGC 1433 – have taken place. The results, which are made available to the public as they are observed and received, are already astounding astronomers.

"The PHANGS team has spent years observing these galaxies at optical, radio and ultraviolet wavelengths using NASA's Hubble Space Telescope, the Atacama Large Millimeter/Submillimeter Array, and the Very Large Telescope's Multi Unit Spectroscopic Explorer," said PHANGS team member Adam Leroy of the Ohio State University. "But the earliest stages of a star's lifecycle have remained out of view because the process is enshrouded within gas and dust clouds."

For example, specific wavelengths observable by MIRI (7.7 and 11.3 microns) and NIRCam (3.3 microns) are sensitive to emission from polycyclic aromatic hydrocarbons. These molecules play a critical role in the formation of stars and planets and were detected by Webb in the first observations by the PHANGS program. Studying these interactions at the finest scale can help provide insights into the larger picture of how galaxies have evolved over time.

Stars begin their lives inside cocoons of dense gas and dust – so-called molecular clouds – and typically not as individual star embryos, according to PHANGS team member Daniel Maschmann, a postdoctoral research associate at Steward Observatory who contributed to three of the published papers. When a giant molecular cloud collapses under its own gravity, it gives rise to local clumps of matter that turn into pockets of star formation.

"In many cases, the intense radiation from the newborn stars and even short-lived stars exploding as supernovae blow away the gas and dust around a young star cluster, which deprives it of material for growth and thereby ends star formation in that region," he said. "JWST gives us a glimpse into star clusters before their surroundings are blown away by those later processes, so it gives us a new piece of the puzzle."

The PHANGS team will work to create and release data sets that align Webb's data to each of the complementary data sets obtained previously from other observatories, to help accelerate discovery by the broader astronomical community. The project's overall goal is to better understand the physics underlying star formation in general, Maschmann said.

"For example, do these galaxies form stars at different rates depending on where their stellar nurseries are located, for example, in the bar structures that we see in some of them, or their central bulges, or further out in the spiral arms?"

"Thanks to the telescope's resolution, for the first time we can conduct a complete census of star formation, and take inventories of the interstellar medium bubble structures in nearby galaxies beyond the Local Group (of galaxies including the Milky Way)," Lee said. "That census will help us understand how star formation and its feedback imprint themselves on the interstellar medium, then give rise to the next generation of stars, or how it actually impedes the next generation of stars from being formed."


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Daniel Stolte

Science Writer, University Communications