Decoding the Contents of Distant Galaxies with the James Webb Space Telescope

Artist’s conception of JWST (Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez). Far Right: Examples of JWST/NIRSpec averaged spectra of  distant galaxies observed within the first couple of billion years of cosmic time, showing emission lines from hydrogen, oxygen, nitrogen and sulfur. This pattern of emission lines is used to infer many fundamental properties of a galaxy, including the rate at which new stars are being born (Credit: Shapley et al. 2023, ApJ, 954, 157).

Professor Alice Shapley

Understanding the formation and evolution of galaxies remains one of the great challenges of modern cosmology. The launch of the James Webb Space Telescope (JWST) on December 25th, 2021, represented a transformative moment for studies of galaxy formation, astronomy as a whole, and even humanity itself (see Figure, left). Since the summer of 2022, JWST has been beaming back breathtaking data that advance the frontiers of our knowledge.

Building on extensive work with the MOSFIRE instrument at the Keck Observatory, the Shapley Research Group is particularly interested in using the infrared spectroscopic capabilities of JWST to understand how galaxies formed within the first few billion years of cosmic time. The JWST Near Infrared Spectrograph (NIRSpec) opens up an entirely new discovery space for distant galaxies, due to both its lack of sky background from our own atmosphere (because JWST operates approximately a million miles away, in space), and also its extended wavelength coverage. Due to the expansion of the universe, pushing to longer wavelengths means looking further back in time.

Using publicly available JWST data, Shapley and her collaborators presented some of the very first measurements of hydrogen emission lines within the first billion years of cosmic time, in order to infer the rate at which new stars are forming (see Figure, right). They have also measured the dust and oxygen content of these early galaxies, and developed robust methods for constraining both of these quantities that are so essential to the story of galaxy formation. Shapley is looking forward to collecting additional spectacular datasets in several additional approved JWST observing programs that she either leads or plays a key role.

Shapley was honored to give the 132nd UCLA Faculty Research Lecture on May 17th, 2022.