Between the era of early galaxy formation and today, galaxies have undergone dramatic transformations in all respects. They spawned successive generations of stars from clouds of molecular gas, continuously building up their stellar populations while enriching the interstellar medium with heavy elements.
New data from the James Webb Space Telescope (JWST) has discovered that galaxies in the early Universe had features that were significantly more varied and evolved than previously thought. For the Cosmic Evolution Early Release Science (CEERS) Survey, researchers compared JWST images of hundreds of galaxies with equivalent Hubble Space Telescope images.
The study examined 850 galaxies with redshifts from z three to nine, or as they were about 11-13 billion years ago.
Scientists performed a series of visual classifications, classifying each galaxy in the sample by three different individuals. Due to the complexity of galaxy morphology at these redshifts, the classifications are intentionally non-exclusive. Instead, scientists note the presence of disks, globular components, and irregular features in each galaxy, allowing more than one of these choices to be selected.
Associate Professor Jeyhan Kartaltepe of the Rochester Institute of Technology’s School of Physics and Astronomy said: “that JWST’s ability to see faint, high redshift galaxies in sharper detail than Hubble allowed us to resolve more features and see a broad mix of galaxies, including many with mature features such as discs and globular components.”
“There have been previous studies that highlighted that we see a lot of galaxies with high redshift disks, which is true, but in this study we also see a lot of galaxies with other structures, such as spheroids and irregular shapes, as we do at lower redshifts. This means that even at these high redshifts, the galaxies were already quite evolved and had a wide variety of structures.”
Of the 850 galaxies used in the study that Hubble had previously detected, the morphology of 488 was reclassified after looking at them in more detail with JWST.
Kartaltepe said scientists are just beginning to reap the benefits of JWST’s impressive capabilities and are excited about what the upcoming data will reveal.
“This tells us that we don’t yet know when the earliest structures of galaxies formed,” Kartaltepe said. “We are not yet seeing the very first galaxies with disks. We will need to explore many more galaxies with even higher redshifts to really quantify when features like disks could form.”
For the study, scientists used an initial dataset captured by CEERS when JWST first came online in June, but the survey has since captured a total of 60 hours of observation, potentially leaving thousands of high redshift galaxies to explore further.
Kartaltepe said COSMOS-Web, the largest General Observer program selected for JWST’s first year, will provide an even larger sample through 255 hours of observing time with the telescope. COSMOS-Web started its observing campaign this month.
J. Kartaltepe et al. CEERS Key Paper IV: The diversity of galaxy structure and morphology at z = 3−9 with JWST. arXiv:2210.14713v1; DOI: 10.48550/arXiv.2210.14713