Between the era of early galaxy formation and today, galaxies have undergone dramatic transformations in all respects. They have produced successive generations of stars from clouds of molecular gas, continuously building up their stellar populations while enriching the interstellar medium with heavy elements.
It has been discovered by new data from the James Webb Space Telescope (JWST) that galaxies in the early universe had features that were considerably more varied and developed 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 at redshifts of z three through nine, or as they were roughly 11-13 billion years ago.
Scientists conducted a set of visual classifications, with each galaxy in the sample classified by three different individuals. Due to the complexity of galaxy morphologies at these redshifts, the classifications are intentionally not mutually exclusive. Instead, scientists note the presence of disks, spheroidal components, and irregular features in each galaxy, allowing for more than one of these choices to be selected.
Associate Professor Jeyhan Kartaltepe from 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 wide mix of galaxies, including many with mature features such as disks and spheroidal components.”
“There have been previous studies emphasizing that we see a lot of galaxies with disks at high redshift, 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, galaxies were already fairly evolved and had a wide range of structures.”
Out of the 850 galaxies utilized in the study that Hubble had previously detected, 488 had their morphologies reclassified after being seen with JWST in more detail.
Kartaltepe said scientists are just beginning to reap the benefits of JWST’s impressive capabilities and are excited by what forthcoming data will reveal.
“This tells us that we don’t yet know when the earliest galaxy structures formed,” said Kartaltepe. “We’re not yet seeing the very first galaxies with disks. We’ll have to examine a lot more galaxies at even higher redshifts to really quantify at what point in time features like disks were able to form.”
For the study, scientists used an initial data set captured by CEERS when JWST first came online in June, but the survey has since captured a total of 60 observing hours, potentially providing thousands of high redshift galaxies to further explore.
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 began 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