ResearchJames Webb Space Telescope Reveals Secrets of Nearby Galaxies

22 February 2023

As part of a worldwide collaboration, Heidelberg research groups are studying the impact of young stars on galaxy formation

Astronomical observations with the James Webb Space Telescope have revealed a complex network of structures in nearby galaxies. The infrared images offer a detailed view of stars, gas, and dust and therefore of star formation and galaxy development. Two research groups from the Centre for Astronomy of Heidelberg University are crucially involved in analysing the data. With their work they are part of a worldwide network comprising more than 100 researchers. The latest observations of this so-called PHANGS collaboration form the basis for 21 new research papers that have now been published in “The Astrophysical Journal Letters”. Among other things, the research points to new answers to the question of how young stars impact the development of galaxies.

Galaxy: spiral arms of NGC 7496

The Heidelberg research groups are part of the “Physics at High Angular resolution in Nearby Galaxies” (PHANGS) collaboration. Using NASA’s Hubble Space Telescope, the Atacama Large Millimeter/Submillimeter Array, and the Very Large Telescope of the European Southern Observatory, the PHANGS team has been studying 19 spiral galaxies for several years to learn more about the dynamic processes of star formation. But the earliest stages of a star’s lifecycle have remained out of view because the process is enshrouded within gas and dust clouds. The James Webb Space Telescope (JWST) and its infrared capabilities have changed all that. Infrared radiation penetrates dust and gas, opening up new views into the earliest phases of star formation.

Thus far, the PHANGS team has observed five of the 19 galaxies with the Webb telescope. The researchers discovered a complex network of structures. Glowing cavities of dust and huge cavernous bubbles of gas line the spiral arms. In some regions this web of features appears built from both individual and overlapping shells and bubbles where young stars are releasing energy. The JWST was also able to detect polycyclic aromatic hydrocarbons (PAHs), which play a critical role in the formation of stars and planets, explains Dr Oleg Egorov. He is a member of the research group of Dr Kathryn Kreckel, a junior research group leader at the Institute for Astronomical Computing, which is part of the Centre for Astronomy of Heidelberg University (ZAH).

Within the PHANGS collaboration, Dr Kreckel leads the science working group that studies the connection between gas ionisation and star formation. There Dr Egorov uses the Webb telescope to study the properties of polycyclic aromatic hydrocarbons, something that would have been impossible using ground-based telescopes alone. PAH emissions are an indicator of physical and chemical processes in the interstellar medium in which these molecules are ubiquitous. Earlier studies had already shown that PAHs are less abundant in regions with ionised hydrogen gas than in neutral zones. But why that is remained unclear. “Our measurements suggest that the abundance of PAHs strongly depends on the intensity of the ionising ultraviolet radiation,” states Dr Egorov.

Dr Elizabeth Watkins studied a single galaxy 30 million light years away. Together with her colleagues, she discovered about 1,700 bubbles or pockets of hot expanding gas using the Webb telescope. The bubbles drive thin shells of colder gas and dust, which appear as holes in the astronomical images. The smallest examples have a diameter of approximately 40 light years, although some reach up to 3,000 light years. They were generated by aggregates of young stars. “That tells us something about the conditions needed to form stars in the first place,” states the early-career researcher, who is also a member of Dr Kreckel’s team.

The research group of Dr Mélanie Chevance likewise uses the JWST data to study star formation processes in galaxies. For the first time, Jaeyeon Kim, a doctoral candidate in Dr Chevance’s group, was able to study star formation deeply embedded in a distant galaxy. She identified key environmental factors that are responsible for regulating especially the early phase of star formation. “The radiation of newly formed stars is absorbed by the surrounding interstellar dust and is thus invisible to us,” explains Jaeyeon Kim. The only way to detect this early phase is to study the infrared radiation of the dust, which the Webb telescope now makes possible. Dr Chevance’s research group is located at the Institute of Theoretical Astrophysics, which is also part of the Centre for Astronomy of Heidelberg University.

Original publications

O. V. Egorov et al.: PHANGS-JWST First Results: Destruction of the PAH Molecules in H II Regions Probed by JWST and MUSE. The Astrophysical Journal Letters, Volume 944, Number 2 (16 February 2023).

J. Kim et al.: PHANGS-JWST First Results: Duration of the Early Phase of Massive Star Formation in NGC 628. The Astrophysical Journal Letters, Volume 944, Number 2 (16 February 2023).

E. J. Watkins et al.: PHANGS-JWST First Results: A Statistical View on Bubble Evolution in NGC 628. The Astrophysical Journal Letters, Volume 944, Number 2 (16 February 2023).